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
T emple Sound, south of Duncan B ay in the west coast of NorthAndaman
JAN 2006
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Emergence and uplift of the coast resultexposure of underlying old mud flats
T emple Sound, south of Duncan B ay in the west coast of NorthAndaman
JAN 2006
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T emple Sound, south of Duncan B ay in the west coast of NorthAndaman
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
Submergence around Port Blair, South AndamanSubmergence around Port Blair, South Andaman
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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Submergence around Port Blair, South AndamanSubmergence around Port Blair, South Andaman
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