Expected peak ground acceleration in Uttarakhand Himalaya, India region from a deterministic hazard...

transcript

ORI GIN AL PA PER

Expected peak ground acceleration in UttarakhandHimalaya, India region from a deterministic hazardmodel

A. Joshi Æ K. Mohan

Received: 10 January 2008 / Accepted: 25 February 2009 / Published online: 18 March 2009� Springer Science+Business Media B.V. 2009

Abstract A method of seismic zonation based on the deterministic modeling of rupture

planes is presented. Finite rupture planes along identified lineaments are modeled in the

Uttarakhand Himalaya based on the semi empirical technique of Midorikawa (Tectono-

physics 218:287–295, 1993). The expected peak ground acceleration thus estimated from

this technique is divided into different zones similar to zones proposed by the Bureau of

Indian standard, BIS (Indian standards code of practice for earthquake-resistant design of

structures, 2002). The proposed technique has been applied to Kumaon Himalaya area and

the surrounding region for earthquakes of magnitude M [ 6.0. Approximately 56000 km2

study area is classified into the highest hazard zone V with peak accelerations of more than

400 cm/s2. This zone V includes the cities of the Dharchula, Almora, Nainital, Haridwar,

Okhimath, Uttarkashi, Pithorahargh, Lohaghat, Munsiari, Rudraprayag, and Karnprayag.

The Sobla and Gopeshwar regions belong to zone IV, where peak ground accelerations of

the order from 250 to 400 cm/s2 can be expected. The prepared map shows that epicenters

of many past earthquakes in this region lie in zone V, and hence indicating the utility of

developed map in defining various seismic zones.

Keywords Deterministic modeling � Semi empirical technique �Expected peak ground acceleration

1 Introduction

Uttarakhand Himalaya in India lies in the seismic gap region identified by Khattri and

Tyagi (1983). Most of the area in the Uttarakhand state has been classified as zones V and

IV of the seismic zoning map published by the Bureau of Indian standard (BIS), Gov-

ernment of India, BIS (2002). Two major earthquakes occurred in this region in the last

A. JoshiDepartment of Earth Sciences, Indian Institute of Technology (IIT), Roorkee, Uttarakhand, India

K. Mohan (&)Institute of Seismological Research (ISR), Raisan, Gandhinagar 382009, Gujarat, Indiae-mail: kapil_geo@yahoo.co.in

Nat Hazards (2010) 52:299–317DOI 10.1007/s11069-009-9373-4

decade. According to the census of India 2001, 91.5% houses in the Uttarakhand state are

made up of mud and adobe, brunt brick and stones, and do not show any earthquake-

resistant design. The population of the Uttarakhand state alone counts 8479562 inhabitants

and the decadal growth rate (1991–2001) in the population is 19.20%. This shows that

there is a great need of detailed seismic hazard studies in this area.

Seismic hazard in an area can be estimated by two approaches: (1) probabilistic seismic

hazard assessment approach (PSHA) and (2) deterministic seismic hazard assessment

approach (DSHA) (Reiter 1990). Both approaches use the same datasets, which include

earthquake sources, occurrence frequencies, and ground motion–attenuation relationships.

Due to the discontinuous recording of seismic activity in parts of the Himalaya, there are

no reliable catalogues for the study area which is a major drawback for any hazard study no

matter whether it is a PSHA or DSHA technique. Recently, Joshi and Patel (1997) have

formulated a method of seismic zonation, which is based on the strong motion simulation

technique of Midorikawa (1993) and had been applied to the Doon valley, India (Joshi and

Patel 1997) and the Assam valley (Joshi et al. 2007). This article presents the application of

the same concept of seismic zonation to the Uttarakhand Himalaya region using the

expected peak ground acceleration.

The peak ground acceleration is an important and frequently used parameter for safe

engineering design. There are several techniques to forecast peak ground acceleration for

future earthquakes in the study area. Peak ground acceleration can be estimated from

simulated accelerograms using various techniques including composite source modeling

technique (Zeng et al. 1994; Yu 1994; Yu et al. 1995; Saikia and Hermann 1985 and Saikia

1993), stochastic simulation technique (Boore 1983; Boore and Atkinson 1987 and Lai

1982), empirical Greens function technique (Hartzell 1978; 1982; Kanamori 1979; Hadley

and Helmberger 1980; Mikumo et al. 1981; Irikura and Muramatu 1982, Irikura 1983,

1986; Kamae and Irikura 1998; Munguia and Brune 1984 and Hutchings 1985), and semi-

empirical technique (Midorikawa 1993; Joshi and Patel 1997; Joshi 1997, 2001, 2004). The

outline of various methods used for simulating strong ground motion is listed in Table 1.

Each of these techniques has their advantages and disadvantages. Among these techniques,

the semi-empirical approach is most suitable for the region of the Higher Himalaya

because (i) it is based on simple empirical formulas and parameters and (ii) it does not

require records of aftershock or foreshock events, as required like in the empirical Greens

Table 1 Various methods for strong ground motion simulation

Method Requirement Disadvantage Ref.

1. EGF Aftershock of target eventat that station at whichsimulation is required

Requirement of aftershockrecord at desired pointis always a problem

Hartzell (1978, 1982);Irukara (1983);Hutchings (1985)

2. Stochasticsimulationtechnique

A white Guassian noise withzero expected mean andvariance choosen to giveunit spectrum amplitude onan average and parameterof required event.

It lacks representationof rupture plane.

Housner and Jennings(1964) Boore (1983);Boore and Joyner(1991)

3. CompositefaultModelingtechnique

All parameters of rupturemodel and velocity for anyfuture earthquake createchance of error in theestimation of correctparameters.

Parameters like detailedvelocity structure and Qmodel is difficult priorrequirement in any region.

Zeng et al. (1994);Yu (1994, 1995)

300 Nat Hazards (2010) 52:299–317

function approach. The suitability of this technique in Himalaya has been verified by

simulating and comparing the records of many past events recorded on strong motion

network by Joshi (2001, 2004).

2 Methodology

In this article, we have used the semi-empirical method of simulation of strong ground

motion. This method has been introduced by Midorikawa (1993). In this method, the

envelope of accelerogram is used instead of records of aftershocks of the event used in the

empirical Green function (EGF) technique. The envelope of accelerogram is defined by a

mathematical function. The semi-empirical approach is consistent with omega square

source model. In order to simulate the entire time series, Joshi and Midorikawa (2004)

have modified this technique by incorporating layered earth media, transmission of energy

in each layer, and slip duration of large and small events.

For the preparation of map of expected peak acceleration due to selected ruptures for the

studied area, we make use the tectonic map in which active lineaments have been iden-

tified. In this map, we mark the rupture along the lineament. The length (L) of the rupture

plane is calculated from this map. Using the following rupture length and magnitude

relation given by Araya and Kiureghian (1988) we can calculate the magnitude of earth-

quake by a rupture of length L

Log L ¼ �2:77þ 0:619Ms: ð1ÞThe models obtained using this relationship has been tested by Joshi (2004) for its

application for the Himalayan region. In this study, the rupture plane along the identified

lineament is considered as rectangular in shape (Fig. 1), and the area of the rupture plane

has been calculated using the following empirical relationship proposed by Kanamori and

Anderson (1975)

Log Að Þ ¼ Ms � 4; ð2Þ

Here, A is the area of the rupture plane and Ms is the surface wave magnitude. The

downward extension (D) of the rupture plane has been calculated by simple mathematics

Surface of the earth

Fig. 1 The rectangular ruptureplane is divided into smallequidimensional elements. Thedimension of one such element‘‘a’’ is also shown

Nat Hazards (2010) 52:299–317 301

i.e. D = A/L. In this study, we have considered those ruptures along lineaments, which are

large enough to give magnitude M C 6 earthquake.

The rectangular rupture plane is divided into small elements. Each small element

corresponds to a small earthquake. The total number of such earthquakes within the rupture

plane is ‘‘n2’’. Parameter ‘‘n’’ is calculated using the following self-similarity relationship

given by Kanamori and Anderson (1975):

n ¼ Mo=M0o� �1=3

: ð3Þ

This relation has been modified to the following form by using the relationship of

magnitude and seismic moment (Sato 1989) by Midorikawa (1993)

n ¼ 100:5 M�mð Þ; ð4Þ

where ‘‘M’’ and ‘‘m’’ are the magnitude of the large and small element earthquakes,

respectively. The lower range of magnitude of the elementary earthquake depends upon the

scaling laws used in the studied region. The length (Le) and downward extension (De) of

the small element earthquake is calculated by dividing the length L and downward

extension D of the large earthquake with ‘‘n’’.

In this technique, one point inside the rupture plane is considered as the starting point or

nucleation point of rupture. The rupture initiated from this point. As the rupture propagates

within the rupture plane, it follows propagation geometry. In this work, the simplest radial

rupture geometry has been considered. Rupture releases energy in the form of acceleration

envelope function. The energy reaches to the observation point at the surface of earth with

different time lags. The total travel time is the sum of the time taken by the rupture to reach

from the nucleation point to the center of an element with rupture velocity (Vr) and the time

taken by the envelop from the center of element to the observation point with the velocity

of the medium. In this current study, the following acceleration envelope function pro-

posed by Kameda and Sugito (1978) has been considered

eij tð Þ ¼ aijt

dijexp 1� t

� �; ð5Þ

where aij is the peak horizontal ground acceleration and dij is the duration parameter.

Kameda and Sugito (1978) have proposed the shape of acceleration envelope (Eq. 5)

considering earth as a homogeneous medium. In the case of layered earth, the partitioning

of seismic energy occurs at layer boundaries. Extensive mathematics has been given by

Lay and Wallace (1995) to calculate the post interaction amplitude over the incident

amplitude, which is identified as transmission coefficient. The transmission coefficient of

incident S waves in a solid layer is given by the following formula (after Lay and Wallace

1995, pp. 97–104), and has been used by Joshi et al. (2001) for modeling the effect of

transmission of energy in layered earth.

TSS ¼2l2gb2

l1gb1 þ l2gb2

where the source is in the second layer,

l1 and l2 = Modulus of rigidity in the top and bottom layers, respectively,

b1 and b2 = Shear wave velocity in the top and bottom layers, respectively,

i = angle of incidence,

302 Nat Hazards (2010) 52:299–317

gb1 ¼ 1� p2b21

� �1=2=b1;

gb2 ¼ 1� p2b22

� �1=2=b2;

p ¼ sin ið Þ=b2:

As the energy propagates through various layers, transmission of energy takes place at

the boundary. The resultant transmission factor at the surface is given as

TSS ¼ TSS1TSS2TSS3............TSSn�1:

In this expression, TSS1, TSS2, TSS3,…… TSS n-1 are the transmission coefficients at 1st,

2nd, 3rd….n-1th boundaries of an n layer earth model, respectively. If A0 is the amplitude

of the energy released at the source, then we can express the amplitude at the observation

point ‘A’ as

A ¼ A0TSS:

In the layered earth medium, the transmission of energy takes place at the layer

boundaries. This will change the envelope function arriving at the surface of the earth,

traveling through different layers. This assumption leads to the following modified

expression for the envelope function given by Joshi et al. (2001);

eij tð Þ ¼ Tss

� �exp 1� t

� �; ð6Þ

where Tss is the transmission coefficient.

The waveform envelopes of different peak acceleration and duration arrive at the

observation points at different time lags Tij. The resultant envelope E(t) of the modeled

earthquake is computed from the envelopes eij(t) released by the different elements as

(Midorikawa 1993)

E tð Þ ¼ Re2ij t � Tij

� �h i1=2

: ð7Þ

The peak ground acceleration is the maximum value of the amplitude of the envelope

function and is given as:

Pa ¼ Max E tð Þf g: ð8ÞIn this study, the study region is covered by a rectangular grid. The corner points in the

grid are assumed as observation points for which peak ground acceleration (PGA) is

computed from the simulated envelope of strong motion records. For ‘‘n’’ number of

ruptures along lineaments ‘‘n’’ values of peak accelerations, i.e., PGAa1, PGAa2,……,

PGAan are obtained at a single observation point. Joshi and Patel (1997) have introduced a

new parameter named as expected peak ground acceleration EPGA, which is given by

EPGA ¼ Max PGAa1; PGAa2; . . .. . .; PGAanf g:In order to prepare the seismic hazard map, this process is repeated at all observation

points, and the expected peak acceleration (EPGA) at each point is computed. The contours

of the EPGA have been used to define the five zones. The flow diagram of the computer

code ‘EQZONE’ is given in Fig. 2 (Joshi et al. 2007).

Nat Hazards (2010) 52:299–317 303

3 Scaling laws for the study region

The present methodology of estimation of expected peak ground acceleration is based on

various regression relations. Before using these regression relations, their applicability

needs to be checked. This was done in the previous study by Joshi (2004) for Uttarkashi

and Chamoli earthquakes. The minimum root mean square error (RMSE) was found in the

case of the ground motion model by Abrahamson and Litehiser (1989). As the region of

Uttarakhand covers the source zones of Uttarkashi and Chamoli earthquakes, we have used

the same attenuation relation in this study.

Selection of active Lineaments(Number 1,….n)

Division of region in to a grid Consisting of 'm' points

Selection of parameters for zonation i.e. Peak ground acceleration

Go for all lineaments

Select for max. value of parameters at point 'A'Epga= Max ( P1,P2,P3….)

Go for other points

Store value at each pointi.e. Epga1, Epga2…. Epgam

Prepare a zonation map

P1,P2 ,P3 Pn

modelling of 1stlineament at a point 'A'

H a idw ar

Ut ta rk a sh i

M a n a

G ar t ok

M u n sia ri S o bl aT h a l

D ha rc h u la

P i th or ag a rh

L oh a g h at

D id iha tA lmo ra

18089787

N a in i tal

B ag e sh w a r

R u dr ap ra y ag K a rn p ra y agG op es h w a r

18089787

Fig. 2 The flowchart of the technique developed for seismic hazard estimation

304 Nat Hazards (2010) 52:299–317

Another parameter used in the envelope function is the duration parameter. The duration

parameter defined by Midorikawa (1993) represents the arrival time of the peak in the

acceleration envelope and in this study the relation modified by Joshi (2004) was tested for

its applicability for the Himalayan earthquake

dij ¼ :0015100:2Ms þ :16R0:6; ð9Þ

where Ms in this formula is the surface wave magnitude, R is the hypocentral distance in

km, and dij is the duration parameter in seconds. One of the most important properties of

strong motion is the presence of directivity effect. The directivity effect has been verified

in the semi-empirical modeling technique by Joshi and Midorikawa (2005) and has been

presented in detail by Joshi and Patel (1997). The entire simulation follows x2 source

scaling laws.

4 Geological and tectonic setting of the region

The 2500-km long and 300-km wide Himalayan arc represents the southern margin of the

Indian–Eurasian collision zone and the Tibetan plateau. This is the most active origin of

the world. The area of study include part of NW Himalayas of India, which lies between

latitude 29� to 33� N and longitude 79� to 81� E.

In the Garhwal and Kumaon Himalaya, two major thrusts, the Main Boundary Thrust

(MBT) and the Main Central Thrust (MCT), separate three geologically distinct zones

(Fig. 3). These are the Outer Himalaya (south of MBT), the Lesser Himalaya (between the

MBT and the MCT), and the Higher Himalayan Crystalline (HHC) (north of the MCT).

North of the HHC, to the south of the Indus–Tsangpo Suture Zone (ITSZ), lies the Tethyan

Sedimentary Zone (TSZ).

The outer Himalaya form the foothills bordering the Indo-Gangetic plains and consists

of Tertiary rocks (Karunakaran and Ranga Rao 1979). Rocks of the Lesser Himalaya of

Kumaon and Garhwal are largely Precambrian sedimentary units with a few outcrops of

the Cambrian formation, Subathu formation, and rare upper Paleozoic and upper

Mesozoic strata. There are significant lithologic variations between the northern and

southern parts of the Lesser Himalaya of Kumaon-Garhwal, and thus, the region is

geologically divided into a northern and a southern sedimentary zone. The sedimentary

formations of the Lesser Himalaya are tectonically overlain by several klippen consisting

of largely amphibolite grade metasedimentary rocks and intrusive and basement granites

belonging to the Almora Group. The klippen may be the remnants of an one more

extensive thrust sheet of the HHC. The Almora group is bounded by South Almora

Thrust (SAT) in the south and North Almora Thrust (NAT) in the north. In the south of

the Almora Group, Ramgarh Group is separated from the Lesser Himalayan metasedi-

mentary zone by the Ramgarh Thrust.

The Kumaon sector manifests strong deformation and reactivation of some of the faults

and thrusts during Quaternary times. This is amply evident by the recurrent seismicity

patterns, geomorphic developments, and by geodetic surveys (Valdiya 1999). The MCT is

believed to have developed since Mid-Tertiary time, and there are some geological indi-

cations of major recent movements along MCT (Valdiya 1980). Seeber et al. (1981)

proposed the existence of a detachment surface, representing the upper surface of the

subducting Indian plate, underlying the entire Himalaya. The MCT merges with this

surface at depth.

Nat Hazards (2010) 52:299–317 305

Older cover sequence folded during Himalayan fold- thrust movementCover rocks of frontal belt affected by fold- thrust movement during terminal phase of Himalayan orogeny

Alluvial fill in Superposed basin

Thrust

Location of station of present array

Minor Lineament

Ophiolite/ Melange

Crystalline complex overprinted by Himalayan fold- thrust movement

Older folded cover sequence overprinted by Himalayan fold- thrust movement

LEGEND

Pre to syntectonic granitoid

Basic Volcanics

Accretionary Complex

Almora

Dharchula

Lohaghat

Pithoragarh

Munsiari

Didihat

Indus suture

Alaknanda Fault

Gartok

Haridwar

Dehradun

Uttarkashi

Karakoram

Nainital

330780

0 50 km

Fig. 3 The Geological map of the NW Himalaya (Modified after GSI 2000). The terms MCT stands forMain Central Thrust, SAT for South Almora Thrust, NAT for North Almora Thrust, and MBT stands forMain Boundary Thrust

306 Nat Hazards (2010) 52:299–317

Fig. 4 Tectonic map of the Uttarakhand Himalaya showing various lineaments (Modified after GSI 2000).The lineaments are marked by numbers for modeling purpose. Epicenters (shown as circles) of the recentearthquakes (May 1999–April 2004) are taken from Pant and Paul 2007

Nat Hazards (2010) 52:299–317 307

The HHC is divided into two lithostratigraphic units defined by Munsiari and Vaikrita

group formation. These comprise greenschist to amphibolite facies metamorphic ortho-

genesis mylonites, schists, and paragenesis. These metamorphic assemblages were intruded

by Miocene age leucogranite. The Munsiari formation is bound by the Munsiari thrust/

MCT in the south and Vaikirta thrust in the north. The Vaikrita Group present in the north

of the Munsiari formation is bound by the Vaikirta thrust in the south and the South-

Tibetan Detachment System in the north.

The recent studies in this region suggests that the major thrusts in the region show

southward younging and shallowing depths, indicating southward migration of the main

deformation front (Pant and Paul 2007). The recent seismic activities also show high

seismicity in the region between SAT and MCT (Fig. 4). The previous studies in Garhwal

and Kumaon Himalaya also show that the areas located to the south of the MCT are

relatively more active (Verma et al. 1995; Paul et al. 2005).

5 Case study: zonation map for the point of Uttarakhand

Preparation of expected peak ground acceleration map using the approach given by Joshi

and Patel (1997) and Joshi et al. (2007) requires prior knowledge of active lineaments.

Based on the study of satellite imageries, tectonic features, and geological formations, GSI

(2000) has published a detailed seismotectonic map of the entire Indian subcontinent.

Using this map, ruptures along 67 lineaments, which could give rise to M C 6.0 earthquake

have been selected. These are marked by numbers and shown in Fig. 4. Parameters of these

ruptures are given in Table 2. The average depth of the detachment plane in this region is

12 km and the study of the source models of the Uttarkashi and the Chamoli earthquakes

has shown that the rupture causing these earthquakes has originated at the detachment

plane. Therefore, the rupture causing earthquakes in this region was assumed at a depth of

12 km, which coincides with the plane of detachment. Strike of rupture is measured from

the tectonic map, whereas the dip of the modeled rupture plane is assumed to be 15� as it

follows the dip of the plane of detachment. Assuming the magnitude of an elementary

earthquake as 4.8, the values of other required parameters like length and downward

extension (L and D) of the target earthquake rupture plane and length and downward

extension of elementary earthquake rupture plane (Le and De) are computed from various

empirical relations.

Rupture velocity in this study is assumed as 2.6 km/s and this is 80% of the S-wave

velocity (Mendoza and Hartzell 1988). Method of modeling rupture plane used in this

study requires a reliable velocity structure on which rupture of target event is located. The

velocity structure by Yu et al. (1995) for modeling the strong ground motion of the

Uttarkashi earthquake has been used in this study. This is given in Table 3.

A grid of 63 square cells of 50-km length is assumed with the grid points serving as

virtual observation points. Expected peak ground acceleration (EPGA) is calculated at all

the observation points by modeling rupture along each of the 67 lineaments one by one.

The value of Epga at each observation point is used for the preparation of the contour map

shown in Fig. 5.

The Bureau of Indian Standard (BIS), Government of India has divided the entire Indian

subcontinent into four zones on the basis of expected peak ground acceleration (BIS 2002).

We have followed the same range of peak ground acceleration to divide the entire study

region into five different zones. The proposed zonation map is shown in Fig. 5. In this

zonation map, the Dharchula, Pithoragarh, Lohaghat, Nainital, Almora, Haridwar,

308 Nat Hazards (2010) 52:299–317

Table 2 The lineaments and corresponding rupture parameters computed from various empirical relations

LineamentNo.

Length(km)

Downwardextension(w) (km)

Magnitude(MS)

n Rupture area(sq. km)

Le(km)

We(km)

1 99 50 7.7 28 4999.49 3.52 1.79

2 70 41 7.5 21 2855.83 3.29 1.92

3 46 32 7.2 15 1449.30 3.04 2.08

4 54 35 7.3 17 1877.83 3.13 2.02

5 62 38 7.4 19 2347.38 3.21 1.96

6 74 42 7.5 22 3124.07 3.33 1.90

7 71 41 7.5 22 2922.02 3.30 1.91

8 65 39 7.4 20 2533.60 3.24 1.95

9 52 34 7.2 17 1766.76 3.11 2.03

10 66 39 7.4 20 2596.86 3.25 1.94

11 28 23 6.8 10 649.91 2.76 2.29

12 20 19 6.6 8 377.39 2.59 2.44

13 114 55 7.8 32 6279.25 3.61 1.75

14 20 19 6.6 8 377.39 2.59 2.44

15 75 43 7.5 22 3192.55 3.33 1.89

16 137 62 7.9 37 8449.88 3.74 1.69

17 37 28 7.0 13 1019.54 2.91 2.17

18 16 16 6.4 6 263.16 2.48 2.55

19 25 22 6.7 9 541.18 2.70 2.34

20 101 51 7.7 29 5163.67 3.53 1.79

21 77 43 7.5 23 3331.21 3.35 1.88

22 112 54 7.8 31 6102.24 3.60 1.75

23 78 44 7.5 23 3401.38 3.36 1.88

24 90 48 7.6 26 4286.04 3.45 1.83

25 25 22 6.7 9 541.18 2.70 2.34

26 61 37 7.4 19 2286.52 3.20 1.97

27 74 42 7.5 22 3124.07 3.33 1.90

28 94 49 7.7 27 4597.96 3.48 1.81

29 130 60 7.9 35 7763.43 3.71 1.70

30 68 40 7.4 21 2725.17 3.27 1.93

31 87 47 7.6 25 4057.61 3.43 1.84

32 120 57 7.8 33 6821.74 3.65 1.73

33 95 49 7.7 27 4677.24 3.49 1.81

34 130 60 7.9 35 7763.43 3.71 1.70

35 100 51 7.7 28 5081.33 3.52 1.79

36 85 46 7.6 25 3907.99 3.42 1.85

37 140 63 7.9 37 8750.82 3.76 1.68

38 67 40 7.4 21 2660.72 3.26 1.93

39 62 38 7.4 19 2347.38 3.21 1.96

40 93 49 7.7 27 4519.20 3.47 1.82

41 91 48 7.6 26 4363.23 3.46 1.82

42 88 47 7.6 26 4133.22 3.44 1.84

Nat Hazards (2010) 52:299–317 309

Okhimath, Uttarkashi, and Karnprayag fall into zone V, where the peak ground acceler-

ation of more than 400 cm/s2 can be expected. The Sobla and Gopeshwar regions belong to

zone IV, where peak ground accelerations in the order of 250–400 cm/s2 can be expected.

A rock fill dam on Douliganga River is located at the Sobla Town. This present study

shows that this town is located in zone IV and might experience peak ground acceleration

of the order of 250–400 cm/s2 due to M C 6.0 earthquakes. The map prepared in this study

shows all four zones (zone II to V) in the Uttarakhand Himalaya. However, according to

the Bureau of Indian Standard (BIS 2002), Government of India, the Uttarakhand Hima-

laya falls in zones IV and V. It may be because of the reason that we are preparing the

Table 3 Velocity model usedfor the present study (After Yuet al. 1995)

Depth to the top of the layer (km) Velocity Vs (km/s)

0.4 2.0

1.0 2.86

15.0 2.97

Table 2 continued

LineamentNo.

Length(km)

Downwardextension(w) (km)

Magnitude(MS)

n Rupture area(sq. km)

Le(km)

We(km)

43 35 27 7.0 12 932.00 2.88 2.19

44 28 23 6.8 10 649.91 2.76 2.29

45 70 41 7.5 21 2855.83 3.29 1.92

46 56 36 7.3 18 1991.47 3.15 2.00

47 35 27 7.0 12 932.00 2.88 2.19

48 56 36 7.3 18 1991.47 3.15 2.00

49 21 19 6.6 8 408.34 2.61 2.42

50 47 32 7.2 15 1500.54 3.05 2.07

51 70 41 7.5 21 2855.83 3.29 1.92

52 65 39 7.4 20 2533.60 3.24 1.95

53 70 41 7.5 21 2855.83 3.29 1.92

54 27 23 6.8 10 612.83 2.74 2.30

55 28 23 6.8 10 649.91 2.76 2.29

56 38 28 7.0 13 1064.42 2.93 2.16

57 28 23 6.8 10 649.91 2.76 2.29

58 43 30 7.1 14 1299.70 3.00 2.11

59 42 30 7.1 14 1251.22 2.98 2.12

60 32 25 6.9 11 806.39 2.83 2.23

61 74 42 7.5 22 3124.07 3.33 1.90

62 60 37 7.3 19 2226.27 3.19 1.98

63 45 31 7.1 15 1398.75 3.02 2.09

64 66 39 7.4 20 2596.86 3.25 1.94

65 80 44 7.5 24 3543.39 3.38 1.87

66 17 17 6.5 7 290.24 2.51 2.52

67 84 46 7.6 25 3833.98 3.41 1.85

310 Nat Hazards (2010) 52:299–317

seismic zonation map considering only the moderate earthquakes. The studied area also

falls in source zone 36 and 40 of the Global Seismic Hazard Assessment Program

(GSHAP) source zones and these zones have been assigned magnitudes of 7.5 and 7.5,

respectively (Bhatia et al. 1999). The acceleration shown in these zones in the GSHAP

zoning map varies from 100 to 350 cm/s2 equivalent to Zone II to IV of the Bureau of

Indian Standard.

In order to check the validity of the prepared zonation map, the epicenters of past

earthquakes taken from USGS are superimposed on the zonation map (Fig. 5). It is seen

that the epicenters of most of the earthquakes of magnitude M [ 6 fall in zone V and zone

IV of the proposed seismic zonation map. The strong motion data of Uttarkashi and

Chamoli earthquakes shows that maximum peak ground acceleration of 304 and 353 cm/s2

has been recorded during Uttarkashi and Chamoli earthquakes, respectively (Chandr-

asekaran and Das 1992). Keeping in view the extent of damage during these two events,

the obtained zonation map proves its utility for hazard planners in the region.

The strong ground motion acceleration time history is a vital tool for the evaluation of

the dynamic response of existing structures and also for building an earthquake-resistant

design in an area. Such strong ground motion records are usually obtained by placing

accelerometers in the epicentral area of the earthquake. Scarcity of accelerometers in some

of the most seismically active areas has motivated engineers to use simulated acceleration

78 79 80 81

0 110 km

6-7.55-6

ZONE IV

ZONE III

ZONE II

ZONE V

ZONE IV

ZONE V

ZONEII

GopeshwarRudraprayag Karnprayag

Munsiari Sobla

Dharchula

Pithoragarh

DidihatThal

Bageshwar

Almora

Uttarkashi

Haridwar

LohaghatNainital

Gartok

200250

400 200

500500

250200

° ° ° °

°°°°

Fig. 5 Seismic zonation map of Uttarakhand Himalaya. In this map, zone IV stands for 250 B Epga \400 cm/s2,zone III consist of 200 B Epga \250 cm/s2, and zone II has 100 B Epga \200 cm/s2. Epicenters of earthquakesare taken from USGS

Nat Hazards (2010) 52:299–317 311

time histories for earthquake-resistant design of new buildings in those areas. On the basis

of the space–time patterns of seismicity of the region, Khattri and Tyagi (1983) and Khattri

(1987) have identified the existence of three seismic gaps in the Himalaya plate boundary.

These gaps are (i) Kashmir gap (section west of 1905 Kangra earthquake), (ii) Central gap

(section between the 1905 Kangra and the 1934 Bihar Nepal earthquake and (iii) Assam

gap (section between the 1897 and 1950 Assam earthquakes). Although these seismic gaps

are ruptured in the past, yet these have not been ruptured since the last 100 years. Bilham

et al. (2001) divided the central Himalaya into 10 regions; with lengths roughly corre-

sponding to great Himalayan ruptures (approximately 220 km). With a convergence rate of

20 mm/year along the arc, six of these regions currently have a slip potential of at least

4 m, which is equivalent to the slip inferred for the 1934 Bihar Nepal earthquake of

magnitude Ms 8.3 (Abe 1981). This implies that each of these regions now stores the strain

energy necessary for such an earthquake. Moreover, there is no historic record of great

Ramgarh Thrust

1.04g 2.4g

0.2g 0.1g

Haridwar

Bijnor

AlmoraPithoragarh

Dharchula

Nainital

Uttarkashi

mk 05010Scale

Didihat

MunsiariSobla

- ive y-axis

0.01 0.1 1 10

Munsiari

0.01 0.1 1 10

Pithoragarh

0.01 0.1 1 10

0.0010.010.1

1001000

0.01 0.1 1 10

Dharchula

Didihat

(a) (b)

(d)(c)(a)

)b()a(

(c) (d)

(d)Moradabad Fault

Fig. 6 a NS (b) EW component of acceleration record. The response spectra prepared from (c) NS and (d)EW component of acceleration record for the Sobla, Dharchula, Didihat, Pithoragarh, and Munsiari stationsin Uttarakhand Himalaya. The terms MCT stands for Main Central Thrust, SAT for South Almora Thrust,NAT for North Almora Thrust, and MBT stands for Main Boundary Thrust

312 Nat Hazards (2010) 52:299–317

earthquakes throughout most of the Himalaya since 1700, suggesting that the slip potential

may exceed 6 m in some places (Bilham et al. 2001). Pant and Paul (2007) in their study

on recent seismicity trends in the Uttarakhand region have suggested a low seismic energy

release and a possibility of great earthquake in the region. Seeber and Armbruster (1981)

have also suggested a possibility of great earthquake in the region near Uttarkashi earth-

quake. The study area selected in this study lies in the central seismic gap region of the

Himalaya. Therefore, in order to have some preliminary idea of strong ground motion due

Fig. 7 The H/V ratio curves at five different stations in Uttarakhand Himalaya on which the strong motionparameters have been simulated

Nat Hazards (2010) 52:299–317 313

to a great earthquake in this region, we have simulated the accelerograms of possible great

earthquake in the central seismic gap region using the semi-empirical approach given by

Joshi and Mohan (2008). The magnitude of future earthquake is selected as 8.0 and using

empirical relations of Araya and Kiureghian (1988), the rupture length corresponding to

this earthquake is 160 km. The downward extension of this rupture plane is computed as

66 km using Kanamori and Anderson (1975) relation. Following the idea of a shallow

dipping fault plane of recent major events in this region, we have selected the dip of

probable rupture to be 15� and its depth coinciding with the depth of the plane of

detachment in this area. The velocity model is similar to that assumed by Yu et al. (1995)

to model the Uttarkashi earthquake and rupture velocity is assumed as 2.6 km/s. The

complete method of simulation of the entire time series is explained in detail by Joshi and

Mohan (2008). This method requires site effects in terms of H/V ratio for componentwise

simulation of strong ground motion. Under a major Department of science and technology

(DST), India sponsored project, NGRI, Hyderabad and IIT Roorkee have installed a net-

work of eight strong motion recorders in the Kumaon Himalaya. Using data of local survey

in this region, site amplification at various stations have been estimated using Nakamura

(1989) technique. Figure 7 shows the site amplification curve at various stations. Using

these site amplifications and following the technique of Joshi and Mohan (2008), we have

simulated accelerograms for M = 8 earthquake in this region. The simulated NS and EW

components of strong ground motion and the corresponding response spectra at 5%

damping at stations Sobla, Dharchula, Didihat, Pithoragarh, and Munsiari are shown in

Fig. 6. The peak ground acceleration for NS and EW component at these five stations is

given in Table 4. The Sobla station is the only station of the network that lies in the

downdip direction of assumed rupture plane. Other stations are far away from the projected

area of the rupture plane and lies in the opposite direction of the dipping rupture plane. It

has been shown from the previous study that the strong ground motion is higher in the

down dip direction as compared to the up dip direction and therefore, the value of the peak

ground acceleration is higher at Sobla as compared to the other stations. The peak ground

acceleration calculated from the scenario earthquake of Magnitude M = 8 at a depth of

12 km along the MCT at these five stations varies from 0.2 to 1 g and if it coincides with

nature’s response in future, then it is enough to give alarm which might lead to alarmingly

large devastations in the area.

6 Conclusions

A technique of the preparation of zonation map based on expected peak ground accele-

ration using deterministic modeling of rupture plane is presented in this article and applied

to the Uttarakhand Himalaya, India. The seismic zonation map for Uttarakhand Himalaya

and the surrounding regions shows that 56,000 km2 of the study area fall in zone V. This

Table 4 The peak groundacceleration simulated at fivedifferent stations in UttarakhandHimalaya

Station NS (in g) EW (in g)

Sobla 1.04 2.4

Dharchula 0.58 0.38

Didihat 0.44 0.22

Pithoragarh 0.20 0.10

Munsiari 0.26 0.29

314 Nat Hazards (2010) 52:299–317

indicates that Uttarakhand Himalaya and the surrounding regions are affected by high

seismic hazard. The Dharchula, Pithoragarh, Almora, Haridwar, Okhimath, Uttarkashi, and

Karnprayag regions might experience peak ground accelerations more than 400 cm/s2. The

other important locations in this region like Sobla and Gopeshwar fall in zone IV with peak

ground acceleration of the order of 250–400 cm/s2. This study explains the utility of the

proposed scheme for seismic zonation based on expected peak ground acceleration in any

seismically active regions, where the scarcity of digital seismic data poses hindrance to any

seismic hazard studies.

Acknowledgments The authors are thankful to the Department of Science and Technology, New Delhi forproviding necessary infrastructure to carry out this study and to Dr. B.K. Rastogi, Director General, Instituteof Seismological Research (ISR), Gandhinagar for his constant encouragement and useful scientificdiscussions.

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