Vol36.pdf

Volume 36 November 2007 Special Issue

ABSTRACTSFifth Nepal Geological Congress

on Geology, Environment, and Natural Hazards Mitigation:Key to National Development

2627 November 2007Kathmandu, Nepal

JOURNAL

OF

NEPAL GEOLOGICAL SOCIETY

EDITORIAL BOARD

Chief Editor

Dr. Rajendra Bahadur ShresthaDepartment of Mines and Geology

Lainchaur, Kathmandu, NepalTel.: 977-1-4437874

Email:[email protected]

Dr. Dinesh PathakDepartment of Geology,

Tri-Chandra Campus, Tribhuvan UniversityGhantaghar, Kathmandu, Nepal

Tel.: 0977-1-4268034Email: [email protected]

The views and interpretations in this paper are those of the author(s). They are not attributable to the Nepal Geological Society (NGS) anddo not imply the expression of any opinion concerning the legal status of any country, territory, city or area of its authorities, or concerningthe delimitation of its frontiers or boundaries.

Editors

Dr. Ananta Prasad GajurelDepartment of Geology,

Tri-Chandra Campus, Tribhuvan UniversityGhantaghar, Kathmandu, Nepal


Nepal Geological Society

Dr. Naresh Kaji TamrakarCentral Department of Geology

Tribhuvan UniversityKirtipur, Kathmandu, Nepal


Mr. Ghan Bahadur ShresthaMountain Risk Engineering Unit,

Tribhuvan University,Kathmandu, Nepal


Fifth Nepal Geological Congress onGeology, Environment, and Natural Hazards Mitigation: Key to National Development

2627 November 2007Organised by

Nepal Geological Society

Organising Committee

Convener: Dr. M. R. Dhital

Members

Mr. L. N. RimalVice-President, NGS, NepalDr. Danda Pani AdhikariGeneral Secretary, NGS, NepalMr. Sudhir RajaureMember, NGS, NepalMr. Dharma Raj KhadkaTreasurer, NGS, NepalMr. A. N. BhandaryEx-President, NGS, NepalMr. A. M. DixitEx-President, NGS, NepalMr. K. P. KaphleEx-President, NGS, NepalProfessor Dr. B. N. UpretiEx-President, NGS, NepalMr. P. S. TaterEx-President, NGS, NepalDr. R. M. TuladharEx-President, NGS, NepalDr. Toran SharmaManaging Director, NESSDr. V. DangolTribhuvan University, NepalDr. D. R. KansakarDepartment of IrrigationMr. G. S. PokhrelNEA, NepalMr. S. P. MahatoDMG, NepalMr. B. M. JnawaliPEPP, DMG, NepalMr. B. R. Aryal,DMG, NepalMr. J. N. ShresthaMinistry of Industries and Commerce and SupplyMr. J. L. ShresthaDepartment of IrrigationMr. Keshav KunwarSCAEF NepalMr. Shiva Kumar SharmaHimal Hydro

Mr. Hare Ram ShresthaSCAEF NepalMr. J. R. GhimireDMGMr. Soma Nath SapkotaDMGMr. Khagendra Nath KafleNEAMr. Subas Chandra SunuwarBPCMr. Durga Prasad OstiBaneshwor, Kathmandu

Advisory CommitteeProfessor Dr. M. P. SharmaVice-Chancellor, Tribhuvan UniversityDirector General, DMGDirector General, DoIDirector General, DWIDPDirector General, DoRDirector General, DoLIDARManaging Director, NEADirector General, ICIMODMr. M. R. Pandey, Hon. Member, NGSMr. B. M. Pradhan, Hon. Member, NGSMr. J. M. Tater, Ex-President, NGSMr. G. S. Thapa, Ex-President, NGSMr. N. D. Maskey, Ex-President, NGSMr. N. B. Kayastha, Ex-President, NGSMr. V. S. Chhetri, Ex-President, NGSDr. P. C. AdhikaryCDG, Tribhuvan UniversityMr. D. B. Thapa, Ex-DC, NEAMr. P. R. Joshi, Ex-DDG, DMG

Congress SecretariatMr. Rajesh DhunganaCDG, TUMr. A. M. S. PradhanCDG, TUMr. U. K. RaghubanshiCDG, TU,Mr. B. R. PantCDG, TU

Acknowledgements

The Nepal Geological Society is going to organise the Fifth Nepal Geological Congress on the theme Geology, Environment,and Natural Hazards Mitigation: Key to National Development from 26 to 27 November 2007 in Kathmandu, Nepal. Weexpress our hearty felicitations to all the participants and guests of the Congress. The Nepal Geological Society is indebted tothe individuals and organisations that generously supported and co-operated to make this Congress a success. We areconfident that this Congress will be an impressive gathering of geoscientists from all over the world.

The Nepal Geological Society expresses its sincere gratitude to the following organisations for providing the generousfinancial support:

Butwal Power Company Ltd.; Cairn Energy PLC 50, Lothian Road, Edinburgh EH3 9BY, United Kingdom; Dhanvi Cement Pvt. Ltd.; Hetauda Cement Industries Pvt. Ltd.; Himal Hydro and General Construction Company Ltd.; Nepal Electricity Authority (NEA); Project Managers, DDC-JV, Udipur, Lamjung; Nepal Environmental & Scientific Services (NESS) (P) Ltd., and SILT Consultants (P.) Ltd.

Similarly, the Nepal Geological Society also sincerely acknowledges the following institutions and organisations forfinancial support and kind co-operation:

Bhote Kosi Hydropower Project; Butwal Cement Mills (Pvt.) Ltd.; Central Department of Geology, Tribhuvan University; Department of Geology, Tri-Chandra Campus, Tribhuvan University; Department of Irrigation, Government of Nepal; Department of Mines and Geology, Government of Nepal; Department of Water Induced Disaster Prevention, Government of Nepal; DIP Consultancy (P.) Ltd.; East Consult; GEOCE Consultants (P.) Ltd.; Godavari Marble Industries (P.) Ltd.; Himalayan Sherpa Coal Uddyog; Himali Gems Industry (Pvt.) Ltd.; ICIMOD, Lalitpur, Nepal; ITECO Nepal (P.) Ltd.; ITECO-CEMAT Geotech Services (P.) Ltd.; Jagadamba Press; MACCAFERRI (NEPAL) Pvt. Ltd.; Manokamana Coal Industries (Pvt.) Ltd.; Maruti Coal Uddyog; METCON Consultants; NAST, Lalitpur, Nepal; National Society for Earthquake Technololgy-Nepal (NSET-Nepal); Nepal Metal Company Limited; Nippon Koei Prvt. Ltd; NISSAKU Co. (Nepal) Pvt. Ltd.; Petroleum Exploration Promotion Project, DMG, Government of Nepal; Prem Coal Uddyog; Udaypur Cement Industries Limited; and Vivek Coal Uddyog (P.) Ltd.

R. B. Shrestha, D. Pathak, A. P. Gajurel, N. K. Tamrakar, and G. B. Shrestha

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Journal of Nepal Geological Society, 2007, Vol. 36 (Sp. Issue)

Contents

General Geology, Tectonics, and SeismicityWhy geological maps?J. Stcklin ............................................................................................................................................................................... 1

The growth and rise of Tibet: hidden plate tectonics, 4D evolution of the mantle, and topographic evolutionP. Tapponnier .......................................................................................................................................................................... 1

Spatial distribution of frontal faults in Nepal HimalayaM. R. Dhital ............................................................................................................................................................................ 2

Similar earthquake swarms in the trace of southern Tibetan grabens reveal a subtle strain transient eventalong the Main Himalayan ThrustL. Bollinger, S. Rajaure, and S. N. Sapkota ........................................................................................................................... 3

Seismo-tectonics of the Shillong Plateau - a geodynamic perspective through remote sensingB. P. Duarah and S. Phukan ................................................................................................................................................... 3

An investigation on the temporal variation of seismicity in Indo-Burma border regionN. C. Barman and S. Kalita .................................................................................................................................................... 4

Dry climatic evidence in central Himalaya around 40 ka from lacustrine sediments of Kathmandu Basin, NepalA. P. Gajurel, C. France-Lanord, P. Huyghe,J. L. Mugnier, T. Sakai, H. Sakai, and B. N. Upreti ......................................... 4

Contemporary tectonic stress field in the Himalaya-Tibet orogen: a view from 2D finite element modelingD. Chamlagain and D. Hayashi ............................................................................................................................................. 5

Geology and tectonic setting of the volcaniclastic succession ofthe Upper Cretaceous,western Sulaiman fold belt, PakistanT. Khan ................................................................................................................................................................................... 6

Depositional environmental change of the Kathmandu Valley sediments inferred from the stratigraphy,sedimentological and mineralogical studyM. R. Paudel and H. Sakai ..................................................................................................................................................... 6

Petrology of granulites of the Shillong Plateau from west Garo Hills district, Meghalaya, IndiaB. Bhagabaty and A. C. Mazumdar ........................................................................................................................................ 7

Lithostratigraphy of Baitadi area, far western NepalA. S. Mahara ........................................................................................................................................................................... 8

Late Pleistocene plant macrofossils from the Gokarna Formation of the Kathmandu valley, central NepalS.. Bhandari, K. N. Paudayal, and A. Momohara .................................................................................................................. 8

Mineralogy, petrochemistry and genesis of scheelite-bearing skarns and related acid magmatismat Sargipali, Eastern IndiaS. Chowdhury ......................................................................................................................................................................... 9

Major and trace element geochemistry of granitic augen gneisses from Tamakoshi-Likhu Khola area, east NepalK. R. Regmi ............................................................................................................................................................................. 9

Thermal evolution of the Lesser Himalaya, central Nepal: Insights from white mica compositions and K-Ar agesL. P. Paudel, T. Itaya, and K. Arita ....................................................................................................................................... 10

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Fifth Nepal Geological Congress

Geology of the Lesser Himalayan and Higher Himalayan Crystalline sequences of the Everest areaalong the Dudh Koshi valley, eastern Nepal HimalayaS. M. Rai, M. Yoshida, B. N. Upreti, and P. D. Ulak ............................................................................................................. 11

Evidence for seismicity in the lower crust and upper mantle in the Nepal Himalaya, implicationfor the rheology of the lithosphereS. Rajaure, S. N. Sapkota, J. P. Avouac, and L. Bollinger .................................................................................................... 13

An investigation on the seismicity and seismic gaps in the Indo-Myanmar border regionS. Kalita and N.C. Barman ................................................................................................................................................... 14

Engineering Geology and GeophysicsHigh carbon dioxide flux associated with radon-222 gas exhalation and dipolar self-potentialanomaly at the Syabru-Bensi hot springs in central NepalF. Perrier, S. Rajaure, P. Richon, S. R. Pant, C. France-Lanord, A. Revil, S. Byrdina1, S. Contraires, U. Gautam, B. Koirala, P. Shrestha, D. R. Tiwari, L. Bollinger, L. P. Paudel, and S. N. Sapkota ........................................ 15

Rock squeezing problem in tunnels of Nepal and its predictionS. C. Sunuwar ....................................................................................................................................................................... 16

Cross-borehole GPR survey for the study of the groutingS. R. Pant .............................................................................................................................................................................. 16

Quality assessment, reserve estimation and economic analysis of roofing slate in the west central Lesser HimalayaN. R. Neupane and L. P. Paudel ........................................................................................................................................... 17

Deformation analysis of foundation: a case study from the Bir Hospital Trauma Centre, Kathmandu, NepalA. R. Adhikari and A. M. S. Pradhan ................................................................................................................................... 18

Engineering, hydrological, and sedimentation studies of the Kankai River, eastern NepalU. K. Raghubanshi ............................................................................................................................................................... 18

Slope stability analysis using GIS on a regional scaleP. Kayastha ........................................................................................................................................................................... 19

Natural Hazards and Environmental GeologySeismic hazard assessment of NW Himalayan fold-and-thrust belt, Pakistan using deterministic approachMonaLisa, Azam A. Khwaja, and M. Q. Jan ......................................................................................................................... 21

Disaster vulnerability prediction modeling using GIS in the Agra Khola watershed, central NepalP. B. Thapa ............................................................................................................................................................................ 22

Kamikate landslide: a case study of rainfall triggered landslide in far western NepalS. K. Dwivedi, G. Ojha, M. P. Koirala, and S. Dwivedi ......................................................................................................... 22

Some notable disasters in Nepal and their mitigationG. R. Chitrakar, B. Piya, D. Nepali, and S. P. Manandhar ................................................................................................... 23

Geohazards and environmental degradation in some of the urban areas of NepalK. P. Kaphle, L. N. Rimal, A. K. Duvadi, B. Piya, and D. Nepali .......................................................................................... 23

GIS-based landslide hazard mapping in Jhimruk River basin, west NepalD. Pathak, A. P. Gajurel, and G. B. Shrestha ........................................................................................................................ 25

Landslide and debris flow hazards in the Mugling-Narayangarh Highway section, central NepalD. P. Adhikari and S. R. Joshi .............................................................................................................................................. 25

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Flood hazard mitigation in Barpeta district, Assam, north-east IndiaN. K. Talukdar and S. Kalita ................................................................................................................................................ 26

Preliminary investigation of Laprak landslide of Gorkha district, west NepalR. P. Khanal .......................................................................................................................................................................... 27

The Devastating Ramche Landslide (Rasuwa) and the Future of Polchet ResidentsT. Ghimire, L. P. Paudel, and B. Pant ................................................................................................................................... 27

Study of river shifting of Kodku Khola in Kathmandu Valley using remotely sensed dataD. Pathak, A. P. Gajurel, and G. B. Shrestha ........................................................................................................................ 28

Geomorphological observations surrounding Lukla, eastern Nepal HimalayaS. M. Rai, M. Yoshida, and B. N. Upreti ............................................................................................................................... 29

Sea level changes due to climate change facts and fictionS. K. Saha and Md. Hussain Monsur ................................................................................................................................... 30

Author Index ......................................................................................................................................................................... 31

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General Geology, Tectonics, and Seismicity

1Journal of Nepal Geological Society, 2007, Vol. 36 (Sp. Issue)

Why geological maps?

J. StcklinErdbuehlstrasse 4 CH-8472 Seuzach, Switzerland

(Email:[email protected])

The geological map was and remains the fundamentaldocument in classical geological exploration. In Nepal,geological information up to the middle of the 20th centurywas sporadic and geological maps were inexistent. With theopening of the country in 1950, a sharp rise of geologicalactivity set in, and a wealth of factual informationaccumulated. Particularly in the 1970s, some excellent mapsof selected parts of the High Himalaya were published byindividual explorers, while maps of the geologically lessspectacular but economically more important Lesser Himalayawere, even if not published, yet produced for public use bythe Department of Mines and Geology, Goverment of Nepal.Observational facts had priority, interpretation and theorywere of secondary importance.

A change came about with the advent of plate tectonics.It brought important new insights into the interior of theEarth, turned the attention to the oceans, to crustaldifferentiations, to processes in the deeper layers of the Globe,and in general caused a shift of interest from the surface tothe interior of our planet. With it went also a shift of balancefrom data to theory, from observation to speculation, fromfacts to fiction. Models largely replaced the maps.

There remains, however, an unchanged responsibility ofthe geologist towards the community. He is expected to giveanswers to urgent geological problems facing peopleconcerned with natural environment and hazards, with mineralresources and exploration, with hydropower, irrigation, soilconservation, with planning roads and dams, in short, withproblems related to the rocks that form the immediate groundon which we live. The geological map remains the fundamentaldocument giving the answers to many of these questions, beit a map showing the general geology or a map focusing on aspecific geological aspect.

The choice of the principal subjects of this Congress(Regional Geology and Tectonics on the one hand, NaturalEnvironment, Resources and Hazards on the other) and themaps and reports published in the last years by theDepartment of Mines and Geology and by the GeologicalSociety of Nepal show that the responsible Institutions inthis country follow a course that tries to keep a reasonablebalance between theoretical and applied geology.

The growth and rise of Tibet: hidden plate tectonics, 4D evolutionof the mantle, and topographic evolution

P. Tapponnier Institut de Physique du Globe, 4 Place Jussieu, 75252 Paris Cedex 05, France

Results of ongoing studies of Cenozoic deformation andmagmatism, coupled with evidence from seismic tomographyexperiments and the kinematic picture emerging fromHolocene slip-rate measurements support a growth model ofthe 2.5x106 km2 wide and 5000 m high Tibet plateau thatreconciles the two most prominent facets of Cenozoic Asiantectonics: relief building and strike-slip extrusion.

The rise of the plateau, at the expense of Asian lithosphere,likely occurred in three main stages since India collided withAsia 55Ma ago. It probably involved the successive,northeastward growth and uplift of 3-500 km-wide crustalthrust-wedges, with sediment infill of dammed intermontane

basins, in the foreland of mantle megathrusts. The crust thusthickened while the mantle, decoupled beneath gently-dipping decollements, did not. The existence of distinctmagmatic belts younging northwards implies that slabs ofAsian lithospheric mantle subducted one after another underranges north of the Gangdese. Reactivation of deeplithospheric cuts corresponding to Mesozoic sutures of theTibetan collage probably controlled diachronous initiationof subduction from South to North. Oblique subduction ofmantle slabs was coupled with extrusion along sinistral faultsslicing Tibets East side, a slip-partitionning process thataccounts for the striking asymmetry of faulting and mountaingrowth towards the Northeast.

2Fifth Nepal Geological Congress

Ever since the onset of collision, the Indian plate appearsto have overridden its own sinking mantle. Such Indian mantledoes not underthrust Tibet much north of the Zangbo suture,which argues against models of plateau build-up involvingIndian lithosphere. Tomograms below India confirm thatAsian deformation has absorbed at least H1500 km ofconvergence since collision began. Beneath NW-Tibet,teleseismic tomography implies that the Tarim lithosphericmantle plunges 45southwards, down to ~300 km.

The thickening crust in Asia appears to hide motions oflithospheric mantle blocks that are similar to those seen atoblique convergent margins. Even in the heart of the collisionzone, the continental lithospheric mantle retained enoughstrength to behave plate-like, with deep deformation

ocalizing along inherited weak zones. In short, processesoperating beneath the largest plateau on Earth may be littlemore than hidden Plate Tectonics.

In the mosaic of basins that makes the bulk of the plateau,the evolution of river systems and drainage efficiency,coupled with tectonic uplift provides a robust mechanism toexplain systematic regional differences in Tibetan landscape.They also provide a unifying mechanism for the formation ofthe low-relief interior, and for the origin of the high-elevationlow-relief relict surface in SE Tibet. Consequently, they castdoubt on the fashionable contention that a continuous, pre-uplift, low-relief surface formed at low elevation, all the wayto the South China Sea shore, before being warped upwardsin the Late Miocene-Pliocene by lower crustal channel flow.

Spatial distribution of frontal faults in Nepal Himalaya

M. R. DhitalCentral Department of Geology

Tribhuvan University, Kirtipur, Kathmandu, Nepal

Conventionally it has been believed that the Main FrontalThurst (MFT) and Main Boundary Thrust (MBT) continuethroughout the Nepal Himalaya as two continues and sub-parallel faults. However, detailed field studies, the study ofavailable geological maps, and the analysis of satellite imagesas well as SRTM data clearly indicate that the situation ismore complex.

The imbricate frontal faults in the Nepal Himalaya aregenerally sub-parallel; they trend from NW to SE and extendfor tens of kilometres. Each of the faults in this fault swarmterminates in either a fold or another fault. In the latter case,frequently the fault towards the foreland terminates in thefault extending from the hinterland.

The Lesser Himalayan and Siwalik rocks constituteimbricate slices and duplexes. Consequently, there are outliersof the Lesser Himalayan rocks in the Siwaliks of east Nepal in

the vicinity of Katari, Bagpati, and Kampughat. Hence, thedefinition that the MBT separates the Lesser Himalayan andSiwalik rocks becomes invalid. A closer look at the Siwaliksreveals that there are a number of independent anddiscontinues faults at the foreland front. They too cannot beclassified as a single fault. Generally, about 20 to 30 km longtight folds extend from the fault tips and there are extensiveareas where the Siwalik rocks are overturned. There are alsoa number of backthrusts in the Siwaliks as well as in theLesser Himalaya.

A normal fault runs very close to the MBT between theMahakali River and Budar as well as in the area betweenSurkhet and Dang. Steeply inclined Recent gravel beds areobserved in the Siwaliks of the Mahakali area in far-westNepal and at Barphalyang in the Ilam district of east Nepal.Such features clearly indicate that the entire Himalayan frontalfault system is tectonically active.


Similar earthquake swarms in the trace of southern Tibetan grabensreveal a subtle strain transient event along the Main Himalayan Thrust

L. Bollinger1, S. Rajaure2, and S. N. Sapkota21Dpartement Analyse Surveillance Environnement, France

2Department of Mines and Geology, Kathmandu, Nepal

From December 1996 to February 1997 the NepalSeismological Centre (NSC) recorded a simultaneous dramaticincrease in midcrustal seismicity rates in 3 distinct regions,hundred of kilometers from each other, along the MainHimalayan Thrust (MHT). Although the rate of seismicevents and their magnitudes differ between clusters, the 3swarms normalized time structures appear very similar,including a pre-swarm decrease in event rate. Furthermore,two swarms appear weeks before their main shock events.Strikingly, the three regions affected are located in the traceof Southern Tibetan grabens inclined, a few months later, tolarge seismic crisis. The likelihood of three swarms occurring

simultaneously, and depicting the same time structure, bychance alone, is tested. Its probability, determined usingdifferent approaches, is small. The events may be related to asingle process. A subtle transient slip event along the deeperpart of the seismogenic zone of the Main Himalayan Thrustis therefore suspected. However, the seismicity rate changebetween the clusters appears insignificant. We describe thestress pattern along the high Himalayan range in Nepal, andshow that the 3 regions affected by the swarms appear moresensitive than others to small stress changes. ContinuousEverest DORIS station as well as sparse campaign GPS dataallow put an upper bound to this subtle strain transient event.

Seismo-tectonics of the Shillong Plateau - a geodynamicperspective through remote sensing

*B. P. Duarah and S. PhukanDepartment of Geological Sciences

Gauhati University, Guwahati-781 014, Assam, India(*Email: [email protected])

The Shillong Plateau of Northeastern part of India istectonically and geologically interesting entity in thesubducted front of Indian Plate below the Burmese Plate tothe southeast and Tibetan Plate to the north, due to thenortheastern journey of the Indian Plate. Structural features,like horse-tail geometry in the Dafala Hills, east of the JiaBhareli river, associated with south-convex foothill ranges inthe eastern Himalaya and exactly similar structural geometryin the eastern part of Shillong Plateau in Meghalaya seems todevelop due to high resistance received by the ShillongPlateau in its eastward journey, which is possiblyaccompanied by clockwise rotation of the plateau. The wideseparation of the Karbi Anglong Plateau and the ShillongPlateau to the southeast as compared to the northwesternpart seems to represent the shape of the Kopili Graben. Lowseismic activity in the southeastern part of the ShillongPlateau might be related to the stress released field generatedby its clockwise rotation. In conformity with this fact, highconcentration of epicenters is observed in the northwesternpart of the Kopili graben, in the central Brahmaputra valley,

as a result of stress development. The structural interpretationof Landsat ETM+ and SRTM data shows that the central partof the Shillong Plateau possesses young topography withstrong structural fabrics along with relatively hightopography aligning NE-SW following the Kolkota-Pabna-Mymansingh High and if extended passes through Bomdilain the Himalayas. This alignment has been observed in thePrecambrian Gneissic Complex west of the Proterozoicintracratonic Shillong Basin. The epicentral plots from 1918to June 2007 show their high concentration within the ShillongPlateau aligning along this trend. The active geodynamics ofShillong Plateau is reflected in its seismic activity. It isobserved that the Brahmaputra river in the plateau front-between Palasbari (91o30' 39"E: 26o06'58"N) and Goalpara(90o37'47"E: 26o11'01"N) has been shifted by more than 5 kmto the north during the period from 1911-2002, which otherwisea south migrating river. This is also supported by shrinkingpattern of Sandubi (Chandubi) Lake in the Kulsi rivercatchment, a north-flowing tributary of the Brahmaputra inthe north-central part of the plateau.


An investigation on the temporal variation of seismicityin Indo-Burma border region

N. C. Barman and *S. KalitaDepartment of Environmental Science, Gauhati University, India

(*Email: [email protected])

The Indo-Burma border region within 20o28oN latitudesand 93o98oE longitudes shows heterogeneous distributionof earthquakes and on this basis, the region can be dividedinto three tectonic blocks - Block-I (20o22.5oN), Block-II(22.5o25oN) and Block-III (25o28oN). Temporal variation ofearthquakes (M 4mb) in these blocks shows that there issome similarity in the variation patterns of Block-I and Block-III (r = 0.77), which indicates that these two blocks behavesalmost similarly in the process of strain accumulation andrelease. In all the three blocks, there can be identified a lowseismic activity period (1998-2003). For the belt as a whole,monthwise distribution of earthquakes (M 5mb) shows some

clustering of earthquakes in the time domain during the highseismicity phases, which have no regular pattern.

Magnitude-frequency relationship of earthquakes showsthat the values of the constants a and b vary within theranges 6.45-7.47 and 0.97-1.18 respectively. Return periodanalysis of earthquakes indicates that the method of Leastsquares gives better results than that of Maximumlikelihood method. In the region as a whole, the estimatedreturn periods of earthquakes having magnitudes 6mb and7mb are found to be 3.8 years and 56 years respectively.

Dry climatic evidence in central Himalaya around 40 kafrom lacustrine sediments of Kathmandu Basin, Nepal

A. P. Gajurel1, C. France-Lanord2, P. Huyghe3,J. L. Mugnier4, T. Sakai5, H. Sakai6, and B. N. Upreti7

1Department of Geology, Tri-Chandra College, Tribhuvan University, Kathmandu, Nepal2CRPG-CNRS, BP 20, 54501 Vandoeuvre-ls-Nancy, France

3 LGCA-CNRS, Universit Joseph Fourier, 38041 Grenoble, France4 LGCA-CNRS, Universit de Savoie, 73376 Chambry, France

5Department of Geoscience, Shimane University, Matsue 690-8504, Japan6Department of Geology and Mineralogy, Kyoto University, Kyoto 606-01, Japan

7Dean Office, Institute of Science and Technology, Tribhuvan University, Kathmandu, Nepal

The study area of the research work lies in the KathmanduBasin. In the northern part of the Kathmandu Basin, deltaformed topographic surfaces are exposed. One of theprominent and widely distributed sediments below the surfacebelongs to the 34 to 50 ka sediments. The sediments arecomposed of alternating layers of mud, massive to paralleland large-scale cross stratified sands and occasional gravellayers. These sediments can be subdivided into crossstratified sand beds of delta front facies, black sandy silt ofpro-delta facies and parallel or trough cross-stratified gravellysand of fluvial channel facies. Thickness of the sedimentreaches around 40 m. Within the 40 m thick stratigraphy, twowidely traceable marker beds in the northern part of the

Kathmandu Basin are composed of very thick silt beds anddiatomite layer appeared at around 1325 and 1345 m altitudes.The five meters thick marker bed of mud with around onemeter thick diatomite layer at an altitude of 1325 m is rich inoperculum, gastropods, bivalve and plant fossils. The markermud with diatomite layer represents the deposit of decantationprocess in lacustrine environment. Highly enriched C and Oisotopes bearing opercula and mollusk shells particularly inthe thick diatomaceous beds correspond to around 40 kacarbon-14 age. The 13C and 18O isotopic values of operculumvary, respectively, from -4 to 8 and -2 to 8 in PDB. Theintra-shell 13C and 18O values of a gastropod sampled inthe diatomaceous layer range from 5 to 8 and 4 to 8 in


PDB, respectively. In contrast 13C and 18O values of moderngastropod shells sampled from artificial pond, paddy fieldand natural pond in the Kathmandu Valley range,respectively, from -12 to 2 and -8 to 2 . The rain watersamples collected during 2001 to 2002 near the Tribhuvan

International airport in Kathmandu show the 18O values from-16 to 7 in SMOW. The highly enriched isotopic signaturesof around 40 ka sediments in the Kathmandu Basin can beexplained by the dry climatic regime in the central Himalaya.

Contemporary tectonic stress field in the Himalaya-Tibet orogen:a view from 2D finite element modeling

*D. Chamlagain1 and D. Hayashi21GPO Box 5467, Kathmandu, Nepal

2Simulation Tectonics Laboratory, University of the Ryukyus, Okinawa 903-0213, Japan(*Email: [email protected])

The Himalaya-Tibet orogen and surrounding regionsdemonstrate complex contemporary tectonic stress field thatreflects present-day geodynamics of the region. Because ofunderthrusting of the Indian plate below the Eurasian platethrust faults are propagating to the foreland side of theHimalaya indicating southernmost front as a most active zone.This is also shown by focal mechanism solution of a moderateto large earthquakes that are mainly thrust type events.However, there are some events along the transverse faultindicating strike-slip motion. On the other hand, the entireTibetan Plateau is characterized by extensional tectonicsevidenced by normal and strike-slip events. Using differenttypes of tectonic stress indicator (earthquake focalmechanisms, well bore breakouts and drilling-inducedfractures, in-situ stress measurements; e.g., overcoring,hydraulic fracturing, borehole slotter; young geologic datae.g., fault-slip analysis and volcanic vent alignments), WorldStress Map (WSM) project has presented an extensive dataset on stress field in the Himalayan-Tibet region. These datasuggest that the direction of maximum horizontal compressivestress (SHmax) is almost parallel to the direction of plate motion.SHmax trajectories radiate laterally from the Tibetan Plateau tothe northern, eastern, and southeastern part of the Chinesemainland. However, the minimum horizontal compressivestress (SHmin) direction is arc convex outward from the TibetanPlateau. For the Himalaya, SHmax are oriented in the NEdirection in NW Himalaya, NS in central Himalaya and NWdirection in eastern Himalaya. However, eastern syntaxisshows sharp bending of stress trajectories towards southeastdirection. In general, SHmax shows fan shaped stress field.

In this study, taking observed SHmax as a proxy, it is aimedto study stress sources, neotectonics and plate kinematicsin the Himalayan-Tibet orogen using two-dimensional elasticfinite element method under plane stress condition.Furthermore, comparison of recent stress observations withresults of stress modeling is made to refine our understandingof geodynamics acting in this region. This study mainlyconcludes that the convergence normal to the orogen isessential to reproduce observed SHmax, which in turn controlsthe magnitude and orientation of SHmax. The kinematicsequivalent to east-west tectonic escape did not simulate theobserved stress field. Therefore, it is understood that thepresent day stress field is mainly governed by thesoutheastward tectonic escape of the Tibetan crust ratherthan eastward extrusion, and is also supported by GPS data.There is, however, significant increase in SHmax magnitudewith higher crustal depth because of stress amplification.Incorporation of suture zones in the models did not changethe orientation of SHmax significantly. Considering these facts,continuum tectonic model is more preferable than the blocktectonic model for the active deformation of the TibetanPlateau. While the models from this study provide areasonable interpretation of the stress orientation andseismicity observed in the India-Eurasia collision zone, somepart of the model lacks good fit with the observed data. Thiscould be due to perturbation in the stress field associatedwith either local or regional structures and their presentmovement or far field plate kinematics of the Southeast Asia.


Geology and tectonic setting of the volcaniclastic succession ofthe Upper Cretaceous, western Sulaiman fold belt, Pakistan

T. Khan(Email: [email protected])

The volcaniclastic rocks of the Upper Cretaceous BibaiFormation are exposed through out the Ziarat district nearMuslimbagh ophiolite, within the western part of the SulaimanThrust-Fold Belt east of the Quetta Syntaxes. These volcanicrocks generally comprises basic volcanic rocks, volcanicconglomerate and breccias, sandstone, mudstone and ashbeds, deposited by various processes of sediment gravityflows on the western margin of the Indian Plate and indicatedeposition by turbidity currents in over bank (-levee) complexbetween channels. The mudstone, possessing occasionalthin sandstone and siltstone beds in lower part and profusionof shallow marine fauna in upper part, indicate deposition inlower fan / basin plane conditions and also an overallswallowing-up trend of the succession. Limestone,interbedded with volcaniclastic facies in lower part of theformation, is very finely crystalline (bio-micritic) possessingforaminifera of the Globotruncana family suggest depositionduring calm periods when gravity flows had been suspendedintermittently. Paleo-current pattern indicate a south-southwest paleo-flow direction and a source area to the north-northeast of Bibai Peak. Based on characters of various rocksassociations, their vertical and lateral organization, paleo-current pattern and composition of detritus. The BibaiFormation developed on the slope of a series of seamounts(hotspot volcanoes).

Seamounts developed on sea floor of the northwesternmargin of the Indo-Pakistan Plate. Within the Bibai Formation,it is dominantly composed of volcaniclastic sediments andrarely lava flows, as the in-situ volcanic rocks. Detailedpetrography and geochemical analyses of clasts of thevolcanic conglomerate and sandstone were carried out todetermine the origin and provenance of volcaniclasticsediments of the Bibai Formation. Volcanic conglomeratecontains clasts of alkali basalt, picrite, trachy basalt, tepherite/phonolite, trachy andesite, dolerite, diorite and granodiorite,which are varieties of the alkaline magma suite. Sandstonesare also dominantly composed of the basaltic rock fragmentsand pyroxene. XRF data of both major and trace elementswere plotted in various discrimination diagrams of the volcanicand associated intrusive rocks indicate that the analyzedsamples fall in the field of within-plate alkali basalt or close toit suggests that the volcaniclastic sediments of the BibaiFormation were derived from a volcanic terrain composed ofalkali basalts originated by hotspot volcanism. Trace elementspresented in various spider diagrams suggest that the parentmagma was enriched in mantle source and confirm that thefragments of the volcanic conglomerate of the BibaiFormation were derived from a hotspot related (within-platesetting) volcanic terrene. The paleocurrent data confirms thatthese sediments were derived from the volcanic to the north-northeast of the study area.

Depositional environmental change of the Kathmandu Valley sedimentsinferred from the stratigraphy, sedimentological and mineralogical study

*M. R. Paudel1 and H. Sakai21Department of Geology, Tri-chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu, Nepal

2Department of Earth Sciences, Kyushu University, Ropponmatsu 4-2-1, Fukuoka, 810-8560 Japan(*Email: [email protected])

Thick sandy and gravelly sequences were recognisedbetween the central and southern part of the KathmanduBasin, which is named as Sunakothi Formation (Fm). Wedesignated the type locality of the formation at Sunakothi,3.0 km to the south of Patan (Paudel and Sakai 2005). Thisformation is extensively distributed in the Nakkhu, Kodku

and Godawari Khola ranging in altitude from 1420 m in thesouthern margin (at Jorkhu) to 1300 m in the central part. Theaverage thickness of this formation is 45 m. The sedimentarystrata are gently inclined toward the north. On the basis ofgeological mapping this formation is located between muddypart of the Kalimati Formation of the ancient Kathmandu Lake,


and covered by terrace gravel deposits, and divided into thefollowing four stratigraphic units: (1) muddy rhythmic basalpart, (2) sandy lower part, (3) muddy, sandy and gravellymiddle part, and (4) laminated silty upper part. Basal partshows transitional from lacustrine to fluvial environment inthe south and prodeltaic toward the basin center. Lower partshows sandy fluvial to lacustrine delta front, middle partshows sand bar, muddy floodplain and gravelly channelfilldeposits. Upper part of this formation is restricted only in thesouthern part of the basin, and shows marginal shallowlacustrine environments.

In order to clarify the causes of change from openlacustrine facies of the Kalimati to Sunakothi Formation,whether this change has tectonic or climatic origin, weexamined sedimentary facies change and mineralogical studyof this Fm, overlying and underlying Formation. Bothsedimentological and mineralogical study of this formationsindicate that sediments of the Sunakothi Formation which

have hidden history of the draining of the Paleo-Kathmandulake, indicates that sediments of this formation were depositedat the time of lake level rise and fell. The causes of this changeare due to the late Pleistocene climatic change (seasonal andprolonged dry climate indicated by smectite, and precipitationof calcite mineral at the basal part of the Sunakothi Formation)of the Katmandu Valley and triggering of the basin margintectonics. Thick gravel sequence in the southern margin isthe alluvial fan before the origin of the ancient lake, whilethick gravelly facies located above the Sunakothi Formationdeposited during the Late Pleistocene age.

REFERENCE

Paudel, M. and Sakai, H., 2005, Depositional environments andstratigraphic position of the Sunakothi Formation in thesouthern part of the Kathmandu Valley, Central Nepal, Abstract,the 112th Annual Meeting of the Geol. Soc. Japan, pp. 339.

Petrology of granulites of the Shillong Plateau fromwest Garo Hills district, Meghalaya, India

*B. Bhagabaty and A. C. MazumdarDepartment of Geological Sciences, Gauhati University, Guwahati-781014, Assam, India


Intercalated and cofolded bands of Mg-poor and Mg-rich Cordierite + Sillimanite + Garnet + Orthopyroxene bearingmetapelites and Orthopyroxene + Clinopyroxene Hornblende bearing basic granulites constitute locally thegarnuite facies terrain in the West Garo Hills district inMeghalaya, India. These rocks show the evidences of polymetamorphism indicating the peak events, the pre-S2 granulitefacies metamorphism (M2) which was followed by subsequentM3, syn-S2, the dominant solid-state fabric-forming episodein the area. The last metamorphic phase is M4 eventspostdated S2. The earliest metamorphic fabrics so farrecognized are as inclusion phases (M1, syn- to post-S1) inM2 porphyroblasts representing another high-grademetamorphic events, which erased out due to the subsequentmetamorphic episodes. Petrographic evidences indicate thatmetapelites preserve prograde P-T path and high temperatureanatexis of the rocks before attaining granulite faciescondition (M2) while textural features in basic granulitesclearly indicate a prograde path in terms of hornblendebreakdown reaction. The geothermobarometric data on corecomposition pre- S2 (M2) mineral assemblages in combinationwith a comparison of relevant experimental data indicate thatthe peak metamorphic average temperature 730C and 750C

in metapelites and basic granulites, respectively and pressurearound 5.3 5.9 kbar. This P-T estimates of the present studyis relatively lower than the true peak P-T condition of pre-S2, (M2), assemblages, which may have been modified bychemical reequilibration during subsequent M3 and M4stages. The retrograde P-T history is well documented in therocks of the area. The retrograde P-T path as revealed by themineral assemblages forming corona on granulite faciesminerals (Garnet corona on Pyroxene + Plagioclase in basicgranulites) or restabilisation of Fe +Mn- rich Garnet onpreexisting Garnet or post- S2 fabric defined by Sillimanite +Biotite + Quartz in metapelites. The thermobarometric studieson coronitic Garnet in basic granulites quantify an isobariccooling (IBC) through 140C during M4 stage with minimaldecrease in pressure about 0.5 kbar; while metapelites indicatethe IBC- path by a decrease of temperature of ~180C for adecrease of 1.0 kbar. Thus, the present study indicates ananticlockwise P-T path followed by M1- M2 prograde pathand retrograde M3 and M4 as reflected from thermobarometricresults and critical textures and thereby implying that thegranulite facies netamorphism was caused due to magmaticunderplating beneath the continental crust.


Lithostratigraphy of Baitadi area, far western Nepal

A. S. MaharaNepal Electricity Authority,

Middle Marsyangdi Hydro electricity Project,Lamjung, Nepal

Geological mapping of Baitadi and its surrounding areawas carried out focusing on geological mapping andstartigraphic correlation. The metasedimentary rocks of theBaitadi area are classified into the Patan Group, Baitadi Group,and Tosh Group. The Baitadi Group contains carbonate rockswhile the Patan Group is devoid of the carbonate rocks. TheTosh Group is basically a sedimentary rock sequence. ThePatan and Baitadi groups are also distinct with each other bythe characteristic features of coal bands, hematite beds, andpebbly sandstone of fluvial depositional environment.

The Patan Group includes the Arubata, Bhandali, andThum Formations, respectively from bottom to top. Similarly,the Baitadi Group is divided into the five formations namely:the Bhumeshor, Satbaj, and Dehimandu, Gadhi, and JulaghatFormations. The Tosh Group is divided into the AnarkholiFormation and Katal Formation. The Katal Formation andAnarkholi Formation are the younger rock units of the ToshGroup. The stratigraphic units of the area are correlated withthe stratigraphic sequences of central and western Nepal.

Late Pleistocene plant macrofossils from the Gokarna Formationof the Kathmandu valley, central Nepal

*S. Bhandari1, K. N. Paudayal1, 2 and A. Momohara3Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal

Senckenberg Research Institute and Natural History Museum, Senckenberganlage 25, Frankfurt, GermanyFaculty of Horticulture, Chiba University, Matsudo 648, Chiba 271-8510, Japan


The Gokarna Formation, constituting the middle part ofthe sedimentary sequence of the Kathmandu valley comprisesalternating layers of carbonaceous clay, silt, fine- to coarse-grained sand and gravel that were deposited at fluvio-deltaicand lacustrine environment. The organic rich layers of clay,silt, silty-sand and micaceous fine sand consists of abundantplant macro-fossils (fruits, seeds and leaves). Plant macro-fossil assemblage from the Gokarna Formation (thickness 28.5m, Dhapasi section) in the northern part of the valley consistsof 48 taxa. Depending upon the available plant assemblages,six fossil zones, DS-I to DS-VI in ascending order, wereestablished. The dominant fossil fruits and seeds from these

horizons mainly consists of the herbaceous plants such asBoehmeria (>20%), Polygonum (>5%), Carex (>17%),shrubby plants such as Eurya (48%), Rubus (>25%),Euphorbia (10%) and Zizyphus (>2.5%). The tree plants suchas Ficus (>10%), Pyracanta (>18%) and Carpinus (14%) arealso present abundantly. The lower horizons (DS-I and DS-II) were dominated by the herbs and shrubs whereas theupper horizons were dominated by shrubs and trees. Theshifting of vegetation from herbs to shrubs and treesindicates a fluctuation of climatic system. This minorfluctuation might have been due to shifting of cold climate towarm climate during the deposition of the Gokarna Formation.


Mineralogy, petrochemistry and genesis of scheelite-bearing skarnsand related acid magmatism at Sargipali, Eastern India

S. ChowdhuryDepartment of Geology,University of Calcutta, Kolkata 700 019, India

(Email: [email protected])

In Sargipali of Eastern India scheelite-bearing calc-silicateskarn rocks are reported in the so-called Gangpur Group, ametasedimentary geologic unit now in greenschist toamphibolite facies. The skarn rocks, both calcic exoskarn(garnet-pyroxene) and endoskarn (pyroxene-epidote) occurat the contacts of dolomites and granitoids in closeassociation with the mica schist hosted Proterozoic Pb-Cu-Ag sulfide deposits. The skarn rock itself is barren of sulfidemineralization. The main constituents of the scheelite-bearingrocks are clino-pyroxene, garnet, calcic amphiboles (K-richferropargasite and hastingsite, ferrohornblende,magnesiohornblende, tschermakite and actinolite),wollastonite, plagioclase, potash feldspar, epidote, sphene,quartz and magnetite. The granitic complex corresponds toreduced, highly evolved and metallogenically specialized S-type leucogranites, comparable to those commonly associatedwith Mo-poor W-F skarns.

Three distinct and two poorly developed calc-silicatezones are observed between dolomite and granitic intrusiveat Sargipali. The zones are characterized by pyroxene-clinozoisite, garnet, epidote and amphibole-plagioclase. Theobserved zonal sequence is close to that predicted by a simplemodel of cation diffusion metasomatism The calc-silicateskarns are notably enriched in Al, Mg and Fe, and garnets

are grossularite-almandine with 1 to 10 mole percentspessartine while pyroxenes are hedenbergitic to diopssidicin composition. Average Fe/Mn ratio (and mole percenthedenbergite) in pyroxene decreases with distance fromgarnet zones and correlates with an increase in Mg,suggesting a progressive depletion of Fe in solution due toprecipitation of Fe-rich garnet, and a progressive enrichmentin Mg in the fluid as it approached equilibrium with dolomiticwall rocks.

The skarns formed initially at about 5000- 7000 C and of5-6 kbar pressure in a mildly reducing environment duringthe amphibolite-facies regional metamorphism and werealtered subsequently at lower temperatures (< 5000 C).

The paper documented herein comprises a detailed studyof the deposit geology, providing the basis for calc-silicatemineral chemistry and geochemical investigations of skarnand granitoids. This paper also summarises the salientfeatures of the Sargipali granitoid to compare with other world-class tin-tungsten skarns. This comparison suggests a directrelationship between magmatic fluid and Sn-W mineralisation,and the similarity of the geochemical characteristics of theSargipali granitoids to averages for W- and Sn- skarngranitoids.

Major and trace element geochemistry of granitic augen gneissesfrom Tamakoshi-Likhu Khola area, east Nepal

K. R. RegmiCentral Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal

(Email: [email protected])

The Himalaya, originating from the collision of India andEurasia, is characterised by a widespread occurrence ofperaluminous granitic rocks of different ages at differentstructural and tectonic levels. In the Tamakoshi-Likhu Kholaarea, east Nepal granitic augen gneisses are exposed in theHigher Himalayan (HH) crystallines, footwall of the MainCentral Thrust (MCT) and core of Lesser Himalayan (LH)

dome. Major and trace element whole rock geochemistry, andmineral chemistry of selected minerals, particularly K-feldspar(Kfs), plagioclase (Pl), garnet (Grt), biotite (Bt), muscovite(Ms), and tourmaline (Tur) were investigated in these augengneisses. The gneisses show high mol. A/CNK values (i.e.,1.62-2.04 in HH, 1.6-2.7 in MCT footwall and 1.68-2.14 in LHdome gneisses) indicating their peraluminous nature. The

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HH gneisses show lowest average SiO2, and highest TiO2,total FeO, CaO and Na2O contents. K2O/Na2O in thesegneisses is variable (0.27-2.23, 0.42-3.62 and 0.21-2.21respectively in the HH, MCT footwall and LH dome gneisses).The gneisses are characterised by high Rb (78-378 ppm inthe HH, 118- 716 ppm in the MCT footwall and 164-510 ppmin the LH dome gneisses) and low Sr (50-308 ppm in the HH,8-97 ppm in the MCT footwall and 11-104 ppm in the LHdome gneisses) contents. Ba content varies from 222 to 640ppm in the HH, 5 to 642 ppm in the MCT footwall and 208 to542 ppm in the LH dome gneisses. The gneisses underconsideration have a low Nb/Th ratio (0.38-1.2 in the HH,0.28-2.23 in the MCT footwall and 0.5-1.78 in the LH domegneisses), which is characteristics of crustal material. Otherchemical characteristics i.e., high SiO2, low CaO and MgO

contents, and peraluminous nature of the gneisses suggestthat they are products of crustal melting. The Pl from the HHgneisses contains the highest concentration of anorthitecomponent if compared with the Pl from the MCT footwalland the LH dome. The Mg# of Bt from the gneisses of the HHcrystalline zone, MCT footwall, and LH dome varies from0.35 to 0.5, 0.24 to 0.49, and 0.14 to 0.23, respectively. The Btcompositions of augen gneisses from all three zones plot inthe field of Bt of peraluminous (including S-type) granite.The compositions of Ms from the MCT footwall plot in thefield of secondary Ms of granitic rocks, while the Ms fromthe gneisses of the LH dome plot in the field of primary Ms inthe Millers diagram. The Grt from the HH gneisses shows aretrograde zoning pattern, but that from the MCT footwallshows a prograde growth zoning pattern.

Thermal evolution of the Lesser Himalaya, central Nepal: Insights fromwhite mica compositions and K-Ar ages

L. P. Paudel1, T. Itaya2, and K. Arita31Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal

2Research Institute of Natural Sciences, Okayama University of Science, 1-1 Ridai-cho, Okayama 700-0005, Japan.3Hokkaido University Museum, Kita 10, Nishi 8, Sapporo 060-0810, Japan

The Lesser Himalayan low- to medium-grade metamorphicrocks in central Nepal are rich in K-white micas occurring asporphyroblasts and matrix defining S1 and S2. Porphyroclastsare usually zoned with celadonite-poor cores and celadonite-rich rims. The cores are the relics of igneous or high-grademetamorphic muscovites, and the rims were re-equilibratedor overgrown under lower T metamorphic conditions. Thematrix K-white micas defining S1, pre-dating the MCT activity,are generally celadonite-rich. They show heterogeneouscompositional zoning with celadonite rich cores andceladonite-poor rims. They were recrystallized at lower Tcondition prior to the MCT activity. The matrix K-white micasalong S2, synchronous to the MCT activity, are relativelyceladonite poor and were recrystallized under relatively higherT-condition. Average compositions of recrystallized whitemicas show northward increase in metamorphic gradeconforming inverted metamorphism throughout the LesserHimalaya.

K-Ar dating was performed on different-sized fractions(0.5-1, 1-2, 2-4, 4-6 m and #80-100) of nine metapelites samples.The Tansen Group sample is less recrystallized and yieldsextremely old ages (850-1045 Ma) representing the ages ofdetrital materials. The Nawakot Complex yields the agesranging from 458 to 9.5 Ma. Relatively less-sheared and lower-grade (anchizone) samples containing only S1 white micasgive the ages of 280-458 Ma, representing the timing of M0(Pre-Himalayan metamorphism). The youngest age (9.5 Ma)was obtained from the upper part of the MCT zone whichexperienced intense ductile shearing resulting in S2 andrecrystallization (M2) at the temperature of 500-650oC duringthe MCT activity. Intermediate ages were observed in theepizone to the lower part of the garnet zone where the rockshave two types of white micas defining S1 and S2. Thenorthward younging of white mica ages may have beenresulted from the decrease of M0/M2 mica ratio towards thenorth close to the MCT.

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Geology of the Lesser Himalayan and Higher Himalayan Crystallinesequences of the Everest area along the Dudh Koshi valley,

eastern Nepal Himalaya

*S. M. Rai1, M. Yoshida2, B. N. Upreti1,3, and P. D. Ulak11Department of Geology, Tribhuvan University,

Tri-Chandra Campus, Ghantaghar, Kathmandu, Nepal2Gondwana Institute for Geology and Environment,

Hashimoto, Japan3Institute of Science and Technology, Tribhuvan University, Kirtipur, Kathmandu, Nepal


The 40 km sector from Kharikhola to Gorakshep along theDudh Koshi valley is occupied by the Lesser HimalayanMetasedimentary Sequence (LHS) in the south and the HigherHimalayan Crystalline Sequence (HHCS) in the north, withthe Main Central Thrust (MCT) between the above twosequences running at about 2.5 km north from Kharikhola.

All rock units of the LHS below the MCT dip towardsNNE while the rocks of the HHCS immediately above theMCT dip northwards; further north in the middle section,they dip generally ENE to ESE and megascopic synclinal andanticlinal folds.

The main rock types in the LHS are green-schist andlower amphibolite grade metamorphic rocks. They includefine-grained garnet-chlorite-muscovite phyllite,metasandstone and coarse-grained Proterozoic granitic augengneiss in the structural lower section (southern part). In theupper section (northern part), the rocks are medium grainedgarnet schist, garnet-muscovite-biotite-graphite schist, andquartzite. Immediate below the MCT, the rocks are found tobe highly sheared and seem to be gneiss. S-C structures areprominent showing the south sense of shearing.

The rocks of the HHCS are well foliated, amphibolite grademetamorphic rocks which are intruded by Palaeozoic andTertiary granitoids. The metamorphic rocks are garnet gneiss,garnet-kyanite gneiss, garnet-sillimanite-biotite gneiss,quartzite, schist, amphibolite and marble. Granite, pegmatiteand deformed pegmatite are the igneous rocks. In the uppersection, south of Gokyo-Ri, very coarse grained; highlysheared augen gneisses of about 300 m thick are exposed.These rocks are pinkish in color due to abundant pinkfeldspars. This gneiss could be the Cambro-ordoviciangranite. The middle section surrounding Namche Bazar isdominated by migmatite with migmatitic biotite gneiss, augengneiss, granitic gneiss, all carrying more or less sillimanite.The amount of migmatitic granite decreases southward. Thelower section of the HHCS south of Jorsalle is mostly coveredby biotite gneiss with or without garnet and sillimanite.Tourmaline-bearing biotite-muscovite granite is commonthroughout the middle and lower sections, cross cutting thegneisses and migmatite.

The host rocks are folded with the development of majorfoliation during the syn-MCT deformation prior to theintrusion of the granitic pegmatite. Sometimes, pegmatitecarries cleavage, which could be due to late deformation.Some foliated pegmatite is considered to be partially re-meltedfoliated granite of earlier generation.

The early granitic pegmatite is also folded with host rocks.The relationship of folded pegmatite with host rocks, thedevelopment of cleavage in pegmatite and porphyroblastsdeveloped along the foliation plane of gneiss show that themajor foliation was first intruded by two mica-tourmalinepegmatite (Mu-rich) and then both of them were foldedtogether, resulting in the development of the cleavage aswell as flattening of the porphyroblasts. This deformationcould be of the post-MCT.

Pegmatite locally shows contact effect along withshearing; e. g., coarsening of biotite clot is observed in somebiotite schist near the contact with a pegmatite intrusion.This phenomenon is considered to reflect the late stageactivity of the MCT associated with the pegmatite intrusion.In some places coarse-grained biotite schist occurs intrudedby tourmaline-biotite pegmatite dyke, while in other places,fine grained biotite schist is seen apart from the intrusion.

There are a variety of occurrences of folding, foliation,schistosity and cleavage, in relation to augen structure,migmatitic pegmatite and tourmaline granite. Relatedobservations of their relationships will enrich our knowledgeon the tectono-metamorphic evolution of the HHCS.

The gneisses of the HHCS carry dominant foliation andshow a variety of mesoscopic folds. Earliest isoclinal reclinedfolds, earlier tight plunging folds, and later open and kinkupright folds are identified. Some of these structures areconsidered to be pre-MCT, and some others are found to besyn-MCT deformations. The SSW and SSE plunging minerallineation marked by mica and sillimanite is developed,possibly related to the movement of the MCT. The Tertiarytourmaline granite cutting across gneisses suffers uprightfolding and carries cleavage structure parallel to the axialsurface of the fold. In some outcrops, interesting relationships

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among mesoscopic structures, pegmatite intrusion andpotash-feldspar porphyroblasts are observed.

The highly foliated ductile area shows the differentmetamorphic episodes. The grade of metamorphism in thisarea increases towards the upper section of the zone of theHHCS from the MCT . The P-T conditions below the MCT inthis region show the inverse metamorphism in the rocks ofthe LHS. The development of the MCT, the inverse

metamorphism and Miocene granitic intrusion in the highersection are genetically related. From the field observation ofthe middle section of the HHCS, garnet crystals aretransformed to chlorite, indicating the effect of retrogrademetamorphism. It could be related either or both to the late-stage activity of the MCT and/or to the normal faulting (SouthTibetan Detachment Fault) event between the HHCS andTibetan-Tethys Sedimentary Sequence.

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Evidence for seismicity in the lower crust and upper mantle in the NepalHimalaya, implication for the rheology of the lithosphere

S. Rajaure1, S. N. Sapkota1, J. P. Avouac2, and L. Bollinger31Department of Mines and Geology, Nepal

2California Institute of Technology (Caltech), USA3Departement Analyse Surveillance Environnement (DASE), France

It has recently been argued that the strength of thecontinental lithosphere lies in the crust with the upper mantlebeing extremely weak. Pivotal to this argument is theobservation that most of the seismicity occurs in the crustand that the elastic thickness of continental plates is generallycomparable to the depth range of the seismicity. Thishypothesis contradicts the earlier view that seismicity isbimodal with earthquakes occurring either in the shallow crustor in the upper mantle, a view that was first promoted basedon the seismicity in the Himalaya and Tibet, and on model ofthe lithosphere rheology derived from experimental rockmechanics. Here we test whether this hypothesis applies inthe Nepal Himalaya in view of recent progress on the Mohogeometry using the seismicity recorded by the NationalSeismological Centre of Department of Mines and Geology, Nepal.

The seismicity of Nepal Himalaya is characterized by alinear and continuous belt of micro-seismic activity whichruns due NW-SE. Majority of the earthquakes have indeedshallow depths and the depth ranges between 10 and 25 km.However a number of earthquakes are relatively deeper(23

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An investigation on the seismicity and seismic gapsin the Indo-Myanmar border region

*S. Kalita and N.C. Barman Department of Environmental Science, Gauhati University,

Guwahati 781 014, India(*Email: [email protected])

The Indo-Myanmar border region is a complexgeotectonic setting due to the interaction between the activenorth-south convergence along the Himalayas and the east-west convergence and folding within the Indo-Burman rangeswith very high seismicity. It belongs to the north-south tradingIndo-Myanmar Orogenic Belt. The elongated region within20o-28oN latitudes and 93o-98oE longitudes shows that theregion is seismically active and maximum number ofearthquakes falls on and around the Eastern Boundary Thrust(EBT) that is parallel to Indo-Burma plate boundary and ShanBoundary Fault (SHF) towards the southern portion of thebelt. On the other hand, less number of earthquakes fall inand around schuppen belt towards northwest of the studyregion. The epicentral map of the region shows an elongatednarrow zone of concentration of epicenters with significantvariation of seismic activity in its different sections, whichmight be due to the local differential geology (rock properties)along the arc and differences in the generation of stress indifferent section of the arc. On the basis of this variation

pattern of epicentral density, the belt can be divided intothree tectonic blocks - Block-I (20o22.5oN), Block-II (22.5o25oN) and Block-III (25o28oN). The concentration ofearthquakes is found more in the central portion of theelongated belt, which may indicate accelerated convergenceprocess. Moreover, the geographical and the depthdistributions of earthquakes clearly reflect the tectonicbehaviour of the region.

Epicentral plots of the earthquakes (Me5 mb) in thelatitude-time (year) domain for the period 1964-2005 showsome elliptical gaps of different sizes at different locationsand time span. However, no definite pattern can be visualizedand therefore, it is very difficult to explain the occurrencesand the seismic potential of these gaps. As per presentsituation the gap region is prominent around latitude 22O Nin which there is a possibility of occurrence of a majorearthquake in near future.

Engineering Geology and Geophysics

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High carbon dioxide flux associated with radon-222 gas exhalationand dipolar self-potential anomaly at the Syabru-Bensi

hot springs in central Nepal

*F. Perrier1, S. Rajaure2, P. Richon3,1, S. R. Pant4,C. France-Lanord5, A. Revil6, S. Byrdina1, S. Contraires1,

U. Gautam2, B. Koirala2, P. Shrestha2, D. R. Tiwari2, L. Bollinger3,L. P. Paudel4, and S. N. Sapkota2

1Institut de Physique du Globe de Paris, UMR 7154, 4, Place Jussieu, 75005 Paris, France2National Seismic Centre, Department of Mines and Geology, Lainchaur, Kathmandu, Nepal

3Dpartement Analyse Surveillance Environnement,Commissariat lnergie atomique, 91680 Bruyres-le-Chtel, France4Central Department of Geology, Tribhuvan University, Kirtipur, Nepal

5Centre de Recherches Ptrographiques et Gochimiques/CNRS, BP20 54501,Vandoeuvre-les-Nancy, France

6Colorado School of Mines, Golden, USA(*Email:[email protected])

Gas discharges have been identified at the Syabru-Bensihot springs, located at the Main Central Thrust zone in CentralNepal and characterized by a water temperature reaching61C, high salinity and high alkalinity. The gas is mainly drycarbon dioxide, marked by a 13C isotopic anomaly of -0.8.The diffuse carbon dioxide exhalation flux, mapped by theaccumulation chamber method, reaches 19 000 gm-2day-1,comparable with values measured on active volcanoes. Radonexhalation flux at the soil surface has been measured at morethan sixty points in the vicinity of the main gas discharge.Extreme values, larger than 2 Bqm-2s-1, similar to peak valuesmeasured in volcanic areas or above uranium waste piles, areobserved in association with the larger values of the carbondioxide exhalation flux. This high radon exhalation thus resultsfrom emanation at depth, producing a radon concentration inthe pore space varying from 25 000 to more than 50 000 Bqm-3,transported to the surface by the flow of carbon dioxide. Thehigh radon-222 content of the carbon dioxide offers aninteresting tracing method and an additional practical toolfor long term monitoring, for example to study transientchanges preceding large earthquakes. An extended dipolar

self-potential anomaly has also been found, with a negativepole reaching -180 mV at the main gas discharge, and a widepositive lobe on the terrace above. This dipolar anomaly, thelargest reported so far, is interpreted in a hydroelectricalnumerical model assuming a primary upward fluid flowassociated with the gas, coupled with a secondary flowtowards the springs, taking into account the resistivitystructure obtained from profiles of electrical resistivitytomography. Thus, the Syabru-Bensi hot springs provide aunique opportunity to study the generation of electricalcurrents associated with biphasic fluid flow in ageodynamically active area. A pilot multidisciplinary teamhas now undertaken a multidisciplinary study of thegeological, geophysical and geochemical properties of theSyabru-Bensi geothermal system. Studying the spatial andtemporal variations of the gas discharges and the associatedproperties of the hot springs may lead to important clues onthe presence and displacements of crustal fluids in relationwith the nucleation of large earthquakes in the NepalHimalayas.

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Rock squeezing problem in tunnels of Nepal and its prediction

S. C. SunuwarButwal Power Company Limited, Kathmandu, Nepal

Rock squeezing is a common problem in the NepalHimalayas while tunnelling through low strength rock, faultand shear/weak zone. It reduces the cross-section of a tunnelcaused by the in situ stresses, which exceed the rock massstrength. Time of deformation and degree of squeezinggenerally depends on overburden pressure and non-swellingclay content. Higher the overburden pressure and clay contenthigher the degree of squeezing.

Rock squeezing problems such as inward movement,invert heaving and buckling of walls/crown has beenexperienced during tunnelling through low strength rock(phyllite, schist, shale, mudstone etc.), shear zones and faultscontaining considerable amount of non-swelling clay. Basedon the squeezing experienced from the different projects ofNepal, larger convergence was recorded in the section wheretunnel axis is parallel to the foliation with gently dipping andcontaining considerable amount of seepage and non-swellingclay. In the Nepal Himalayas, maximum convergence of 30%of the tunnel size is recorded from the Modi KholaHydroelectric Project while tunneling (Sharma, 2000).

Squeezing may stop or continue for a long time. In worsecase tunnel can be collapsed. Therefore reshaping and re-supporting of the tunnel is time consuming and expensive.Rock squeezing problem delays construction schedule duringunderground excavation and this led to cost overruns paidby the owner or severe financial strains on the contractors.So it is important to recognise the conditions that are likelyto result in rock squeezing. In general all prediction theoriesare based on overburden depth and rock mass strength/orrock mass characterisation to predict the phenomena. It isfound that squeezing ground conditions are greatly influencedby strength, stress condition (overburden), orientation ofdiscontinuity, pore water pressure, excavation methods andstiffness of support but contributions are not the same degreewhich has been experienced during the construction of thedifferent hydropower project in Nepal. Therefore none ofthem give accurate results but provide a good indication ofpotential occurrence of squeezing.

In this paper rock squeezing problem in different tunnelsof hydropower projects and its prediction are presented.

Cross-borehole GPR survey for the study of the grouting

S. R. PantCentral Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal

To check the effectiveness of the grouting in the FlipBucket Area, Spill Way, Damsite of Middle MarsyangdiHydroelectric Project cross-borehole ground penetratingradar (GPR) tomography survey was carried out. The testwas carried out in two pairs of boreholes. The first pair wasBH-1 and BH-2 and the second pair was BH-3 and BH-4.Second pair of boreholes was taken as model site.

In the first pair of boreholes BH-1 and BH-2 cross boreholeGPR tomography survey was conducted before grouting andafter grouting. Before grouting measurement was carried outon June 11, 2006 and after grouting measurement was carriedout on June 28-30, 2006 and September 25-26, 2006. Themeasurement in the pair of model boreholes BH-3 and BH-4was carried out in June 29-30, 2006. The data acquisition

method adapted was Zero Offset Profiling (ZOP) and MultipleOffset Gathering (MOG). The Observation interval was 25cm. The antenna centre frequency used was 200 MHz. Thedistance between the pair of boreholes BH-1 and BH-2, BH-3 and BH-4 was 6 m. In cross-borehole GPR tomographymeasurement of the arrival time of waves are carried out withhigh accuracy. Propagation of the GPR waves linearlydepends on the porosity (water filled) and the chemistry(electrical conductivity) of the water: higher the porosityslower the velocity and higher the electrical conductivitygreater the attenuation of the GPR waves. So, GPR tomogramscan be used to quantify the subsurface.

The results of the investigation were useful to know thesubsurface before and after the grout injection. Before

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grouting the porosity of the fractured rocks between the pairof boreholes BH-1 and BH-2 was between 15% to 20%. Thisvalue is low in comparison with porosity of granular material.In principle GPR monitoring of grout study should be muchmore effective for high porosity formation. Between the pairof boreholes BH-1 and BH-2 grouting is effective below thedepth of around 7.5 m. The September monitoring indicatesthat the GPR wave velocity has been increased in the mostpart of the subsurface from 0.10 m/ns to 0.11 m/ns at depth

greater than 7.5 m. In this zone porosity has also been reduced.There is no clear evidence of the change in the physicalparameters (velocity, porosity and electrical conductivity) atdepth less than 7.5 m and between 18 m and 20 m. This maybe due to the high velocity of the groundwater flow in thesezones. The velocity between the pair of model boreholes BH-3 and BH-4 is greater than 0.11 m/ns. In this model site porosityis less than 12% and the predominant value of porosity isaround 10%.

Quality assessment, reserve estimation and economic analysis of roofingslate in the west central Lesser Himalaya

N. R. Neupane and L. P. PaudelCentral Department of Geology, Tribhuvan University, Kathmandu, Nepal

Quality assessment, reserve estimation and economicanalysis of roofing slate can be carried out at Tharpu ofTanahun District which lies in the Nawakot complex of theLesser Himalaya. It represents a part of northern limb of theMahabharat Synclonorium. Petrological study (pressure andtemperature of metamorphism from mineral assemblage in thinsection) and physio-chemical test (flexure testing, waterabsorption, weathering resistance, abration resistance,sulphuric acid immersion test, wetting and drying test) havebeen done in the laboratory for quality assessment.Geological mapping and preparation of columnar sectionshave been done in the field for Reserve Calculation. The totalreserve of an area is determined by dividing the tonnage withits tonnage factor. The volume is calculated by multiplyingthe total cross-section area by the perpendicular distancebetween each cross-section. Cost Benefit Analysis wasapplied for cost and benefit of slate mining to evaluate theviability of the slate business.

The major slate deposits of the study belong to theBenighat Slate and Nourpul Formation of the Lesser Himalaya.The pressure and temperature of the metamorphism on thebasis of b0-spacing and IC methods are 4.23 kbar and 380Cfor Benighat Slate and 5.10 kbar and 375C for NourpulFormation roofing slate.

Flexure strength of the slate along grain ranges from26. 26 to 50.57 MPa with average 36.24 MPa and standarddeviation (SD) of 9.28 MPa. While, the same property across

grain ranges from 36.37 to 59.78 MPa with average value 43.1MPa and SD of 9.59 MPa. Similalry, the elasticity of the testedsample of slate ranges from 1055.4 to 2974 MPa having meanvalue of 1774 MPa and SD of 740 MPa. Water absorption byweight is 0.789 to 1.473 having mean value 1.02 and SD 0.3.While, the weather resistance of the slate lies within 0.31 mmto 0.55 mm with average value of 0.41 mm and SD is 0.1.Abrasion by weight has a range from 14.3 to 20.4 with averagevalue 16.22 and SD 2.73. The permeability, sulphuric acidimmersion, and wetting and drying tests give excellent resultsto the slate.

It was observed that from the field study, there is fine-grained with a fairly perfect natural cleavage, readily splitableinto thin and smooth sheets of slate at Seratar (3000 mnorthwest from Tharpu Bazaar) and Otandi (1000 m west fromTharpu Bazaar). Due to this thin splitting properties, mostslate are used for roofing purpose. On the basis of physio-chemical testing and Petrological study, the slate of NourpulFormation at Seratar and Benighat slate at Otandi are best forroofing as well as construction purpose even though inferiorto the ASTM standard.

The total probable reserve of the slate calculated by thecross-sectional method is to be 52.9 million m3 at Otandi.Mining method appropriate for the slate deposit is open pitmining. As cost benefit analysis show that B/Q = 1.23, themining of slate is profitable. For profitable business, thebenefits and cost ratio should always be greater than one.

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Engineering, hydrological, and sedimentation studiesof the Kankai River, eastern Nepal

U. K. RaghubanshiCentral Department of Geology, Tribhuvan University,

Kirtipur, Kathmandu, Nepal

With the development of human civilization and rapidlygrowing population the demand and uses of water resourcesis growing abruptly. Water resources have been used fordomestic water supply, industrial use, irrigation andhydropower. For the country like Nepal where there is thespatial and temporal variations of water availability and thedemand for various uses, there are the great challenge inwater resources management and managing the conflicts inthe allocation of water among the different water sectors aswell as among different regions.

Similarly, the sediment related issues of the watershedhave to be addressed as well. Every year million of tons ofsediment get transported by drainage networks in Nepal. Theeffect of temporal and spatial variation of hydrologicalconditions in diversified geographic condition creates

variation in sediment transportations. The efficiency andworkability of different water resource projects like Irrigation,Hydropower and Domestic water supply projects are badlyaffected by the sediment problems.

If proper condition and relations between hydrologicalsystem and sediment problems are well known, the conflictsand the risks in water resources management can be minimizedand proper planning and development of future waterresources project can be done effectively and efficiently.

The Kankai River is one of the class IIb type rainfedperennial river of eastern Nepal. The study area has warmtemperate rainy climates with mild winter. Upper part of basinbasically consists of granitic gneiss of Cambro-Ordovicianage lower part consists of Quaternary rocks. The present

Deformation analysis of foundation: a case study fromthe Bir Hospital Trauma Centre, Kathmandu, Nepal

*A. R. Adhikari and A. M. S. Pradhan(*Email: [email protected])

The rapid increase in population of Kathmandu valley inlast two decades has demanded the construction ofmultistoried buildings. Statistical analysis shows that thedeformation after the construction of structures are rarelyconsidered during the design phase of the structure whichcan be vulnerable to the structure itself. The excessivesettlement of the foundation causes the failure of thefoundation and ultimately the building causing the hugeamount of lives and property loss. The failure process ismore pronounced when the foundation is placed in soft fluvio-lacustrine sediments of Kathmandu valley. Therefore, thispaper aims in estimating the settlements and deformationafter construction of structure by manual and Finite ElementMethods. The subsurface stratification, their geotechnicalproperties; size and shape of foundation and that of buildingwere considered for deformation analysis of foundation. The

geotechnical properties are found in the laboratory and feware estimated by graphical methods.

The deformation analysis of the foundation should beconsidered in two aspects i.e. bearing capacity failure andsettlement. Settlement calculated by conventional testmethods i.e.oedometre test, compressibility index are purelyone-dimensional and doesnt represent the actual value wherelateral influences are possible. The settlement byconventional methods is 41.6 mm for stratification below 4 mdepth and 24 mm for stratification below 8 m depth. Whereas,using finite element method, it is 42 mm for stratification below8m depth using same parameters valid for the site andconsidering the horizontal displacement. The stressdistribution and depth of foundation favors the foundation.

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study is basically focused on two parts. One is thehydrological analysis, which includes rainfall, discharge andclimatic factor analysis; prediction of the flood, estimation ofevapotranspiration, runoff, and also includes the openchannel hydraulics and study of some hydraulic structures.Similarly second part includes some parts of sedimentationengineering which includes sediment properties, sedimentsampling techniques, sediment yields, hydraulics of sedimenttransport and sediment routing.

Rainfall Intensity in the study area is moderate to heavy.Potential Evapotranspiration (PET) obtained by Penmansmethod show maximum PET during the month of May andminimum during January. Among different major crops, PETof rice is high (107.21 cm in total cropping period) and that ofwheat is low with PET=38.90 cm. Annual runoff coefficient ofthe Kankai river basin is 0.65. For the different Hydraulic

Structures and natural river channel with different structuralgeometry and variable slope values, the flow varies from Sub-critical, Critical to Super-critical condition.The Kankai Riveris gravelly river with more than 60% gravel of gneiss andremaining other are of different metamorphic and sedimentaryrocks. There is a seasonal, temporal and spatial variability ofsediment yield in the watershed of the Kankai River. Byapplying the Regional Regression Relationship method, thesediment yield of Kankai River is estimated to be 0.148 millionton/year. Critical Bed Shear Stress varies from 0.589N/m2 forsand to 19.625 N/m2 for gravel. The shield parameter(dimensionless shear stress) varies from 0.7 to 0.021 for gravel.

Mobility No. related to weight concentration of bedmaterial load is calculated to be 0.2161.Sediment accumulationand transportation is influnced by hydrological activities andgeological condition of watershed.

Slope stability analysis using GIS on a regional scale

P. Kayastha(Email: [email protected])

Stability of land is indispensable for the safety of humanlife and development of infrastructure. Landslides are themost common natural hazards in Nepal, where about 83% ofthe area are in the mountainous and hilly regions. In thisstudy, a slope stability analysis on a regional scale ispresented for a area of 347 km2 of Dhading district, Nepal.A physically based slope stability model coupled to asimplified groundwater flow model is used to estimate soilwetness index, and factor of safety maps are produced forthree steady state scenarios (completely dry, half-saturated,and completely saturated soils) and one quasi-dynamicscenario (soil wetness resulting from extreme daily rainfallevents with return periods of 25 years) with both methodsbased on infiltration and contributing area. One model isdeveloped from these three steady state scenarios. Thesemodels help the engineers and planners to apply landslidehazard models on a regional scale to the regions that generallylack advanced information systems with the presentedmethodology and basic GIS tools.

The quantitative relation ships between stability andfactors affecting stability are established by the CertaintyFactor (CF) model. The affecting factors such as land usepattern, soil types and steepness (slope type) are recognized.From CF value, the most significant factors are selected.Based on the model developed on the basis of three steadystate scenarios, 27.71 of the research area is unconditionallystable and 0.59 of the research area is unconditionallyunstable. According to the results of three steady states andone quasi-dynamic state model, there is a decrease in stabilityfrom completely dry condition to completely saturatedcondition. In all scenarios, very steep slope area (slopeangle more than 300) contributes to areas prone to failure. Inaddition, areas having poorly graded gravel and clayeygravel have more effect in instability of slope than thoseareas having other types of soils.

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Natural Hazards and Environmental Geology

21


Seismic hazard assessment of NW Himalayan fold-and-thrust belt,Pakistan using deterministic approach

*MonaLisa1, Azam A. Khwaja2, and M. Q. Jan11Department of Earth Sciences, Quaid-i-Azam University (QAU), Islamabad (45320), Pakistan

2Higher Education Commission, Islamabad, Pakistan

Seismic Hazard Assessment (SHA) of the entireseismically active NW Himalayan Fold and Thrust Belt thatincorporates deterministic approach has been carried out forthe first time. Additional information in the form of earthquakecatalogue, delineation of 40 active faults in a structural map,their relationship to the seismicity, focal mechanism studiesof 45 events, establishment of seismotectonic zones has alsobeen undertaken.

Distribution of 813 events within study area indicatesthat seismicity (4.0 Mw) appears to be associated with boththe surface and blind faults. At the same time, clustering ofevents in specific parts along the surface faults shows thatsome fault segments, especially in the hinterland zone aremore active. In parts of the active deformational front likeSalt Range, southern Potwar and Bannu, lesser seismicactivity (4.0 Mw) could be due to the damping effect of thethick Precambrian salt.

Majority of the earthquakes (86%) range in magnitudefrom 4.0 to 4.9 Mw followed by 107 events (13%) havingmagnitude ranging from 5.0 to 5.9 Mw. The remaining 1%range from 6.0 to 6.7 Mw. There is a predominance of shallowseismicity (

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Disaster vulnerability prediction modeling using GISin the Agra Khola watershed, central Nepal

P. B. ThapaDepartment of Geology, Tri-Chandra Campus,

Tribhuvan University, Kathmandu, Nepal(Email: [email protected])

Disaster vulnerability analysis is an important concern inthe mountainous terrains of Nepal Himalaya. The mountainhill-slope of Agra Khola watershed, central Nepal had sufferedfrom a large

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