Coseismic & Post Seismic Changes_Andaman is._revised Jan 2009

8/8/2019 Coseismic & Post Seismic Changes_Andaman is._revised Jan 2009

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26 December 2004 Sumatra- AndamanEarthquake :

Vertical Ground Movement in AndamanIslands

Based on the work of Based on the work of

Geological Survey of IndiaGeological Survey of India

Sujit DasguptaSujit Dasgupta


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26 December 2004 Sumatra26 December 2004 Sumatra- -Andaman Earthquake & TsunamiAndaman Earthquake & Tsunami


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T ectonic map and Locations of study area


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B ay of B engal

Morphotectonic elements in North Andaman


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R uptureR upture plainplain of of 2626 DecemberDecember20042004 earthquakeearthquake defineddefined bybyaftershocksaftershocks thatthat occurredoccurred

duringduring thethe firstfirst 2424 HoursHoursSequential northward

propagating aftershocks


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B ackground..B ackground..

Modification of coastline because of submergence/emergence of land was reported inmedia/recorded in a visit to the South Andamanand B aratang Islands in Jan 05

Land emergence and submergence mappedusing pre- and post-earthquake satelliteimageries of high resolution

For assessment of co-seismic/ post-seismicvertical movement, field investigation taken upin May 05, followed by additional fieldexamination in Jan 06.


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Seismologists characterised the mega-earthquake due to thrustfault movement along the 1200 km long rupture

Andaman and Nicobar Islands situated on the hanging wall of themega thrust

In strike-slip or thrust faults, or in oblique slip faults withcombinations of thrust and strike-slip components, no point in thehanging wall can move below its pre-faulting level. Differentialuplift, because of along-strike slip variation, may tilt the hangingwall block, but cannot cause subsidence

Nature and amount of uplift/ subsidence was investigated inground. T his study is based on imagery study and field observationsonly, independent of seismological and geodetic survey data and

interpretations

B ackground of ground investigationB ackground of ground investigation


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Assumptions:

1) Faulting occurred primarily on the megathrust, so the entireAndaman- Nicobar islands locate on the hanging wall

2) T hough there might have been changes in the absolute sea level

immediately after the earthquake and tsunami, it has stabilised to itspre- earthquake level (a global rise in sea level of the order of 1cmwas postulated) after six months

Estimated and mapped co-seismic vertical movement in the

Andaman Group of Islands (north of 11o

N latitude) based on thetenets that sea level has remained unchanged and provides thereference datum for detection of earthquake-related ground levelchanges

B ackground of ground investigationB ackground of ground investigation


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North Andaman

Middle Andaman

South Andaman

Havelock Island

Andaman IslandsAndaman Islands

R amnagarR amnagar

KalighatKishorinagar

Shyamnagar/R adhanagar

Aamkunj

R angat

Uttara

NilamburPort B lairWandoor

Corbyns cove

KarmatangMayabandar

Aerial B a

Interview Is. South Reef Is.

Paschimsagar

Temple Sound

Temple Sound

Casuarina B ay

Anderson Is .

1

2

3

4

5

6

7Interview Is.8

89

10

11

12

13

14

2


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Ground uplift inLandfall & East Island,North Andaman


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Post seismic ground emergence, Northern tip of North Andaman Island


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T emple Sound, south of Duncan B ay in the west coast of NorthAndaman

Fall of HWL to the tune of 1.5mwith consequent newly risenmarine terrace, resulting newlyaccreted beach of width 25 m.

JAN 2006


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O ld Marine T errace

New MarineT

errace

Consecutive marine terraces at different levels, lastuplift 1.5m


JAN 2006


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Emergence and uplift of the coast resultexposure of underlying old mud flats


JAN 2006


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R etreat of sea and uplift of coral banks, exposedwidth ~400m, net uplift ~1.3-1.4m JAN 2006


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O yster barnacles are commonboth over rock outcrops andon coral banks JAN 2006


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Coral bank35cm thick

Oyster bank75cm thick

Chert

JAN 2006


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R owe Island, West Coast,North Andaman

Newly emerged enlargedoutline as a consequence of

great earthquake

JAN 2006


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Elevated,dried up tidal creeks, North AndamanElevated,dried up tidal creeks, North Andaman

Shyamnagar creek Shyamnagar creek

High tide level 1.0m belowpre-earthquake H T L

High tide 1.0 m (in place of May 05 estimate 1.2m) belowthe level before earthquake.

High tide level 1.0m belowpre-earthquake H T L

Direct spin off of theearthquake: completely dried

up tidal creeks, erstwhilenavigableregularly used byfishermen, porters

Vertical uplift of 1.0mVertical uplift of 1.0m

R adhanagar creek

Kishorinagar creek Kishorinagar creek


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Uplift of mangrove colony above tidal lifeline,erosion of banks, complete exposure of mangrove roots, growth of land plants inerstwhile mangrove forest R adhanagarcreek, West Coast, North Andaman JAN 2006


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Near debauchmentmouth of R adhanagarcreek, West Coast,North Andaman

Sub-aerial exposure of newly emergedbeach of approximately 3 sq km area

JAN 2006


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Dried, mud cracked mangrove forest,Dried, mud cracked mangrove forest,Kishorinagar, North AndamanKishorinagar, North Andaman

Pre earthquakespring (new & fullmoon) tide level

Lateral spread atthe bank of a creek

Exposure of once submergedmangrove forest

Uplift of land to thetune of 1.0m (inplace of May 05estimate 1.2m)

INDEX


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Marked fallin HWL allalong the

creek

Kishorinagar creek

Dried up

mangrove forest


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1. Sub aerially exposed mangrovecolony during present high tide,Gudi (Kishorinagar)creek

2. High water 1.1m (in place of previous estimate 1.2m) belowthe pre-earthquake high tide line,Paschimsagar

3. Newly emerged expanse of beach, Paschimsagar[3]

[1]

Gudi creek & Paschimsagar, North AndamanGudi creek & Paschimsagar, North Andaman

[2]Presenthigh tide

Pre-quakehigh tide

Present high tide

[1]


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South of Casuarina bay(Paschimsagar)

Emergence of beach to the tune of 1.1m

JAN 2006


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Coral B anks of differentstages of uplift at differenttimes of tectonic movement,Paschim Sagar, NorthAndaman

JAN 2006


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Exposed coral, (?) old uplift,west coast, Paschimsagar,North Andaman

JAN 2006


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Land EmergenceKalighat, North AndamanLand EmergenceKalighat, North AndamanLand EmergenceKalighat, North Andaman

green arrow-- pre-earthquake HWL red arrow -- post earthquake HWL

Coseismic vertical uplift of about 90cm was estimated inKalighat area in May 2005, however, it was estimated 50cmduring Jan 2006 as a result of post-seismic readjustment.(Ferry service along the creek from Kalighat to Mayabandar withdrawn)


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Post seismic elevated river bed, R amnagar, North AndamanPost seismic elevated river bed, R amnagar, North Andaman

A perennial river dried upas a sequel to uplift

Pre-quake flow direction

Hanging tidal inlet,R amnagar beachHWL is40cm lower than that of thepre-earthquake level


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R amnagar beach, East coast, North AndamanElevated terrace axis

Uplift:40cm (nochange between May

05 and Jan 06) JAN 2006


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R amnagar beach, East Coast, NorthAndaman

AncientT errace

JAN 2006


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East coast of Interview Island linearbanks of coral as well as mangrove colonyraised above tidal lifeline

Interview Passage

West of MiddleAndaman

JAN 2006


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S tabilization ofcoral bank due touplift of coast

InterviewIsland, west of MiddleAndaman JAN 2006


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Nancy Pointsouthernmost point of InterviewIsland rimmed by raised coral bank

JAN 2006


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Stabilization of shoals;rise of underwater

rainforest..InterviewIsland

JAN 2006


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General estimate from coral uplift


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Exposure of extensive coral bankraised aboveS pring tides.. colossal loss of coral colonyInterview Island

JAN 2006


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Aerially Exposed CoralMicroatolls, Interview

Island

JAN 2006


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P ost Eq HTLP re Eq HTL

Raised marine terracelowering of HWL to thetune of 1.4-1.5m

W estern bank of Interview Island

JAN 2006


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S outh Reef Island

Exposed beach withcoral substrate

JAN 2006


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Raised marine terrace of 60cm;

Coral banks remain exposed even in spring tides;

Total uplift 1.3m

S outh ReefIsland

JAN 2006


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Exposed coral banks,North of A nderson Island

JAN 2006


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R ise of an exclusive coral island (? stabilizedshoal) without any land connection

JAN 2006


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Karmatang beach, East Coast,

Middle Andaman

AncientT

errace

JAN 2006


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R ampur beach, Middle Andaman

Ancient Coral B ank JAN 2006


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East coast, Middle AndamanEast coast, Middle Andaman

R ock R ock outcropsoutcrops (near(near thethe coast),coast),earlierearlier exposed,exposed, nownow submergedsubmergedbeneathbeneath 1010cmcm (previous(previous 2020cm)cm) of of duringduring highhigh tidetide

First record of subsidence

Karmatang beach ::HWLHWL showsshows aafallfall of of aboutabout 1010cmcm (earlier(earlierestimateestimate 1515cm)cm) indicatingindicating coco--seismicseismic upliftuplift followedfollowed bybyreadjustmentreadjustment in in thethe areaarea. . Panchabati, Aamkunj,

Sivapuram beaches

T here is no change of tidalwater level or configuration of the beach in the pre and postearthquake scenario.

Neutral line

Nimbutala/ R angat jetty


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Strait between Middle Andaman & B aratang IslandStrait between Middle Andaman & B aratang Island

Uttara jetty: 20cm risein water level both inhigh tide and low tide

Nilambur jetty : amaximum of 50cm of rise of spring tide wasreported


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Submergence around Port Blair, South AndamanSubmergence around Port Blair, South Andaman


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Post- earthquakeInundationaround Port Blair

S b d l i S h A dS b d l i S h A d


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9 Jan 200510 May 2005

Sippighat area during high tide in Jan 05, May 05, Jan 06 and Jan 09


24 Jan 2006 10 Jan 2009

S b d P Bl i S h A dS b d P Bl i S h A d


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O urO ur estimateestimate waswas aboutabout 11 metermeter groundground subsidencesubsidence inin thetheSippighatSippighat areaarea andand aboutabout 7070cmcm (previously(previously inin MayMay 20052005,,8080 cm)cm) inin thethe O grabrajO grabraj areaarea. .

AA riserise of of 8080cmcm of of HWLHWL inin thethe MithakariMithakari JettyJetty ..

AA riserise of of 11..11 (in(in placeplace of of 11..22cm)cm) of of HWLHWL inin thethe ChathamChathamJettyJetty ..

AboutAbout 1010 cmcm (in(in placeplace of of 3030cm)cm) verticalvertical subsidencesubsidence inin thetheWandoorWandoor jetty jetty areaarea waswas estimatedestimated. .

TECTONIC FLOODING! TECTONIC FLOODING!


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Note retaining wall with stepsin the backshore

Change in Ground Elevation :Corbyns coveChange in Ground Elevation :Corbyns cove

November 2004

PostPost--earthquake Ingress of earthquake Ingress of spring tidespring tide

May 2005

R etaining wall filled up withrecently deposited sand


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Post seismic Ground Elevation :Corbyns covePost seismic Ground Elevation :Corbyns cove

About 1.0m rise in high tide level indicating subsidence in that order


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Corbyns cove, oppositemuseum, prior toearthquake. O utcrops of Andaman flysch exposedduring low tide

R ock outcrops remainssubmerged afterearthquake.

Ground submergence in Corbyns coveGround submergence in Corbyns cove


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Havelock Island, R itchies Archipelago,Havelock Island, R itchies Archipelago,

LandLandsubsidencesubsidenceof aboutof about20cm in the20cm in thewesternwesternpart of thepart of theHavelock Havelock IslandIsland waswasestimatedestimated

PrePost


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LocationIndex

Location Longitude Latitude Uplift/Subsidence (m)in 2005

Uplift/Subsidence (m)in2006*

Change

1 Landfall Island* 93.01 13.64 - +0.6 -

2 East of Temple Sound 92.88 13.43 - +1.50.2 -

3 Radhanagar 92.92 13.38 +10.2 +1 -

4 Paschimsagar near Casuariana bay

92.85 13.26 +1.20.2 +1.10.2 0.10.4

5 Aerial bay 93.02 13.27 +0.20.05 +0.86.1 0.66.15

6 Kalipur 93.04 13.2 +0.300.05 +0.400.05 0.10.1

7 Kishorinagar 92.88 13.18 +1.20.05 +1.05 0.2.10

8 Kalighat Jetty 92.96 13.12 +0.900.10 +0.50.1 0.40.20

9 Ramnagar 93.02 13.06 +0.400.05 +0.40.05 -10 North Reef Island* 92.71 13.09 - +1.3 -

11 Forest Check Post,Interview Island

92.71 12.89 - +0.95 -

12 Bennette Island 92.71 12.83 - +0.9 -

13 Interview Island 92.65 12.83 - +1.42 -

14 South Reef Island 92.66 12.75 - 1.3 -

Uplift (+) and subsidence (-) in the Andaman Islands measured in 2005 and 2006

17 Mayabandar 92.89 12.88 +0.100.05 +0.50.05 0.40.10


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y

18 Karmatang 92.93 12.83 +0.150.05 +0.050.05 0.100.10

19 Rampur 92.94 12.79 +0.150.05 +0.050.05 0.100.10

20 Nimbudera, South of Cuthbert Bay

92.95 12.64 0 0 -

21 Panchawati 92.96 12.56 0 0 -

22 Nimbutala (Rangat)Jetty

92.95 12.49 -0.20.10 -0.10.10 0.10.20

23 Bakultala 92.83 12.49 -0.050.05 -0.050.05 -

24 Uttara Jetty 92.78 12.33 -0.20.10 -0.20.10 -

25 Nilambur Jetty 92.75 12.17 -0.50.10 -0.50.10 -26 Radhanagar (Havelock

Island)92.95 11.97 -0.2 - -

27 Ograbraj 92.66 11.66 -0.80.20 -0.70.10 0.10.30

28 Chatham 92.71 11.67 -1.20.10 -1.1.05 0.10.15

29 Corbyns cove 92.73 11.62 -1.00.05 -1.00.05 -

30 Chidiyatapu 92.7 11.52 -0.750.05 -0.700.02 0.050.07

31 Wandoor -0.300.05 -0.100.05 0.200.10

32 Aram Point, RutlandIsland

92.59 11.49 - -0.80.10 -

33 North Sentinel Island* 92.19 11.57 - +1.5 -


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Emergence/Emergence/UpliftUplift

C hange in C oastal C onfigurationC hange in C oastal C onfigurationas detected by comparison ofas detected by comparison ofSatellite ImagesSatellite Images

Submergence/SubsidenceSubmergence/Subsidence


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North Sentinel IslandNorth Sentinel Island

NR SAESA

Newly emerged coastlineNewly emerged coastline

E g i N th S ti l I l d


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Emergence in North Sentinel Island


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Submergence in Katchall & T rincat Islands, NicobarSubmergence in Katchall & T rincat Islands, Nicobar

KatchallKatchallT rincatT rincat


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Submergence in Katchall & T rincat Islands, NicobarSubmergence in Katchall & T rincat Islands, Nicobar


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R esultsR esults

Contours, of +1.5, +1.0,

+0.5( green ), 0, -0.5, and -1.0(blue ) meter vertical movementdrawn; zero contour ( red )indicates no verticalmovement, the neutral line

All the contours are sub-parallel, with a general NNE-SSW trend.

T hose, in turn are parallel tothe trench axis of subducting

Indian plate below theB urmese plate


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R esults R esults

Ground to the west of the neutral line

has been upliftedUplift increases from the neutral line to

the west. T his pattern of spatial variationof vertical uplift indicates that thecausative fault has a significant thrust

componentWesterly increase of uplift indicates that

the trace of the thrust fault lies further tothe west of the Andaman Islands.

T his westerly increase in uplift is likelyto continue up to the trace of the fault,where it would be maximum

B y extending the gradient up to thetrench axis (Inset) along R amnagar-Paschimsagar line, max 6.3 m verticaluplift on the fault estimated

0


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. R esults.. R esults.Ground to the east of the neutral line

has been affected by tectonic subsidence,which increases from the neutral linetowards east

Estimated maximum subsidence in thestudy area around Port B lair recorded

T o the east of Port B lair, only oneobservation in the Havelock Island,

where subsidence is of the order of 20cm

We may infer that towards east of theneutral line the subsidence increases upto a certain distance and then decreases

to neutral

0


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Cartoons of static slip dislocation (upper part)) in

North Andaman (AA) and South Andaman ( BB ) withcorresponding depth section and geometry of B enioff zone.

Squares: Events from 1964 to pre-mega-earthquake

Triangles: Events from 26.12.2004 to 31.12.2005


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Projected zero contour inProjected zero contour inNicobar Group IslandsNicobar Group Islands

00

R esidential area near Malacca jetty,Car Nicobar, gets inundated duringhigh tide (24.03.2005)

Car Nicobar


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ExplanationExplanation

In thrust faults, the vertical component of dip-slip is maximum inthe hanging wall at the fault interface. As we move away from theinterface, the component gradually decreases and ultimatelybecomes nil at the neutral line.

B eyond the neutral line, in the dip direction of the fault, all pointsin the hanging wall should remain at their pre-thrusting level

E l iE l i


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Crustal shortening during the longinterseismic period , resulted inantiformal arch with increase inaccumulated elastic strain. B ecause of this uparching of the crust (red lines),the islands rise at higher elevations,

and grow in area because of landemergence above the waves.

R elease of elastic strain by reversefault earthquake

Coseismic slip associated with downbuckling or elastic unfolding of theantiform, resulted in subsidence. Areasclose to the fault shows tectonic uplift,max at the fault interface, graduallydecreases towards the neutral line

ExplanationExplanation


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Chidiyatapu, Southern tip of South Andaman

before earthquake

24 Jan 2006

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Coseismic & Post Seismic Changes_Andaman is._revised Jan 2009

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