the lefkada barrier and beachrock system nw greece controls on coastal evolution and the significance of extreme wave events abstract the lefkada preveza coastal zone nw greece is characterised by an active barrier system and related extensive beachrock sequences besides the gradual coastal processes of longshore drift and spit evolution the presence of active tectonics and the occurrence of tsunamis have been documented in previous studies and are part of the coastal geomorphological system in this paper we present the results of detailed multi proxy sedimentological and geomorphological investigations carried out along the northern part of the barrier system and in back beach positions our findings suggest that extreme wave events contributed to coastal and environmental changes and involved temporary breakdown of the barrier system sedimentary findings suggest that one generation of event deposits may be related to the 365 ad crete earthquake and associated tsunami according to our results the lefkada coastal system formed by the interaction of both long term gradual and sudden impulsive littoral geomorphodynamics extreme wave events are assumed to have played a significant role in the evolution of the present coastline acting as recurrent impulsive disturbances of the coastal system subsequently the onset of long term gradual coastal processes such as longshore drift re established a state of natural coastal balance by re arranging the coastal sediments

modelling the interseismic deformation of a thrust system seismogenic potential of the southern alps this article focuses on the montello thrust system in the eastern southern alps as a potential seismogenic source this system is of particular interest because of its lack of historical seismicity nevertheless the system is undergoing active deformation we developed a finite element model using visco elasto plastic rheology the free parameters of the model essentially the locking status of the three thrusts included in the study were constrained by matching the observed horizontal gps and vertical levelling data we show that the amount of interseismic fault locking and thus the seismic potential is not necessarily associated with the fastest slipping faults more specifically the locked bassano thrust has a greater seismic potential than the freely slipping montello thrust the findings suggest that faults with subtle evidence of quaternary activity should be carefully considered when creating seismic hazard maps

the trace fossil thalassinoides bacae in the cambrian zhangxia formation miaolingian series of north china abstract branched complex burrows with thick linings assigned to thalassinoides bacae are abundant in the cambrian zhangxia formation miaolingian series in southern north china these burrows occur in thinly layered micritic limestones which were formed in a restricted marine environment surrounded by oolitic shoals the macromorphological characteristics of the burrows observed in outcrop combined with microscopic burrow characteristics assessed using light microscopy and scanning electron microscopy were used to analyze the ethology of t bacae the complex geometric characters of horizontal branching tubes and subvertical shafts reflect t bacae is an agrichnical burrow system the horizontal tubes were used to cultivate microbes for food while the subvertical shafts provided openings to the sea floor organic material iron minerals and pyrite framboids just present in the margin of the fill indicate a special micro environment in the burrow system with a reducing environment and a high organic content and they may provide evidence for microbial garden the functions of the thick micrite lining may have included maintenancce of environmental conditions within the burrow and provision of suitable conditions for growing microbes dark colored irregular areas around the lining are identified as diagenetic halos the burrowers of t bacae built complex burrows system and thick lining for cultivating microbes to survive in a restricted marine environment that was oxygen poor and with low food availability reflecting adaptive behavioral evolution of the metazoan in the middle cambrian

penultimate predecessors of the 2004 indian ocean tsunami in aceh sumatra stratigraphic archeological and historical evidence we present stratigraphic archeological and historical evidence for two closely timed predecessors of the giant 2004 tsunami on the northern coast of aceh northern sumatra this is the first direct evidence that a tsunami played a role in a fifteenth century cultural hiatus along the northern sumatran portion of the maritime silk route one seacliff exposure on the eastern side of the lambaro headlands reveals two beds of tsunamigenic coral rubble within a small alluvial fan radiocarbon and uranium thorium disequilibrium dates indicate emplacement of the coral rubble after 1344 3 c e another seacliff exposure on the western side of the peninsula contains evidence of nearly continuous settlement from 1240 c e to soon after 1366 3 c e terminated by tsunami destruction at both sites the tsunamis are likely coincident with sudden uplift of coral reefs above the sunda megathrust 1394 2 c e evidence for which has been published previously the tsunami or tsunami pair appears to have destroyed a vibrant port community and led to the temporary recentering of marine trade dominance to more protected locations farther east the reestablishment of vibrant communities along the devastated coast by about 1500 ce set the stage for the 2004 disaster

short term morphological responses and developments of banda aceh coast sumatra island indonesia after the tsunami on 26 december 2004 the destructive earthquake and tsunami waves have caused sudden and immense changes in the morphology of the low lying coast of banda aceh sumatra island indonesia on 26 december 2004 data from different sources and different instants in time used in this study to investigate the morphological responses and developments of two coasts that were affected by the tsunami near banda aceh i e ulee lheue on the northwest coast and lampu uk on the west coast the objective was to quantify the morphological changes of the two coasts that were affected by the tsunami and tectonic land subsidence and their subsequent short term developments interestingly the foreshore zone of the two coasts after six months showed a contrasting development relative to their pre tsunami s morphological state ulee lheue on the northwest coast experienced ongoing erosion of about 15 of the total sediment loss due to the tsunami and land subsidence the erosion effect from the land subsidence is not pre dominant in this coast compared to the erosion that was caused by the tsunami waves keeping in mind that the coast is a sand poor environment the coastal process under normal condition could not keep pace with not only the sudden loss of sediment due to land subsidence but also to a greater extent due to lack of sediment availability in the coastal system to replace the amount of sediment loss due to the tsunami waves on the other hand the amount of sediment regain in lampu uk was 60 out of the total sediment loss due to the tsunami and land subsidence it compensated to a great extent the sudden loss of sediments due to land subsidence which was greater than the one on the northwest coast the wide and shallow inner shelf and higher wave energy in this coastal region can be the controlling factor of this temporary sediment storage and the rapid accretion

defining the source region of the indian ocean tsunami from gps altimeters tide gauges and tsunami models abstract to understand the role of the co seismic moment magnitude mw 9 1 9 3 sumatra andaman earthquake rupture mechanism on the severity of the indian ocean tsunami we used permanent global positioning system gps data and carried out an analysis of co seismic displacement and tsunami models tsunami modelling validated against independent jason 1 altimetry data and tsunami arrival time data as determined from tide gauges was used to analyse the results of five co seismic slip inversions using gps seismicity and or uplift data in this way we determined the most likely slip distribution characterized by slip maxima of 20 m in the south and 20 m in the north we used both the distribution and temporal evolution of the co seismic slip as derived from the gps data we show that the 9 min propagation time of the rupture led to constructive interference of waves radiating first from the south and minutes later from the north strengthening the tsunami in southern india sri lanka and thailand we conclude that the incorporation of permanent real time gps stations would represent a valuable component of future tsunami warning systems

rupture across arc segment and plate boundaries in the 1 april 2007 solomons earthquake the largest earthquakes are generated in subduction zones and the earthquake rupture typically extends for hundreds of kilometres along a single subducting plate these ruptures often begin or end at structural boundaries on the overriding plate that are associated with the subduction of prominent bathymetric features of the downgoing plate here we determine uplift and subsidence along shorelines for the 1 april 2007 moment magnitude m w 8 1 earthquake in the western solomon islands using coral microatolls which provide precise measurements of vertical motions in locations where instrumental data are unavailable we demonstrate that the 2007 earthquake ruptured across the subducting simbo ridge transform and thus broke through a triple junction where the australian and woodlark plates subduct beneath the overriding pacific plate previously no known major megathrust rupture has involved two subducting plates we conclude that this event illustrates the uncertainties of predicting the segmentation of subduction zone rupture on the basis of structural discontinuities

grace detects coseismic and postseismic deformation from the sumatra andaman earthquake 1 we show that spherical harmonic sh solutions of the gravity recovery and climate experiment grace are now of sufficient quality to observe effects of co seismic and post seismic deformation due to the rupture from the mw 9 3 sumatra andaman earthquake on december 26 2004 and its companion nias earthquake mw 8 7 on march 28 2005 the improved ggm 03 sh level 2 solutions and improved filtering methods provide estimates with spatial resolution comparable to earlier estimates from range rate level 1 grace data the gravityfield disturbance extends over 1800 km along andaman and sunda subduction zones and changes with time following events gravity changes may be due to afterslip viscoelastic relaxation or other processes associated with dilatation satellite gravity measurements from grace provide a unique new measure of deformation and post seismic processes associated with major earthquakes especially in areas which are primarily oceanic citation chen j l c r wilson b d tapley and s grand 2007 grace detects coseismic and postseismic deformation from the sumatraandaman earthquake geophys res lett 34 l13302

low frequency acoustic gravity waves from coseismic vertical deformation associated with the 2004 sumatra andaman earthquake mw 9 2 1 atmospheric pressure perturbations from the 2004 sumatra andaman earthquake mw 9 2 were observed by sensitive microbarographs at several global stations among these observations very low frequency acoustic gravity waves 1 4 2 8 mhz with a group velocity around 300 314 m s and amplitudes ranging between 1 and 12 pa can be clearly identified through data processing at four stations on the japanese islands and also at four international monitoring system ims stations around the indian ocean assuming several seismic source parameters for this great thrust earthquake we produce synthetic barograms using a realistic thermal structure in the atmosphere up to an altitude of 220 km for this modeling we incorporate the source dimensions in different zones the expanding velocity of the source region the vertical displacements of uplift and subsidence and their time constants combinations of these source parameters provide synthetic waveforms consistent with the general features of the observed low frequency records the results clearly indicate that the recorded waves may have been generated by large scale coseismic uplift and subsidence of the sea bottom and associated swelling and depression of the sea surface over the source region extending for 1500 km the uplift in the south central zone of the andaman nicobar regions may be substantially larger than in the other zones the time constant of the coseimic vertical deformation is found to be in the range of 1 0 1 5 min which may correspond to the time elapsed shortly before the generation of tsunami waves

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

constraining the boundary between the sunda and andaman subduction systems evidence from the 2002 mw 7 3 northern sumatra earthquake and aftershock relocations of the 2004 and 2005 great earthquakes the 2004 m w 9 0 sumatra andaman earthquake initiated along the andaman subduction zone north of the last great sumatra earthquake along the sunda trench in 1861 during the 2005 m w 8 7 banyak islands earthquake a portion of the 1861 rupture subsequently failed the boundary between the 2004 and 2005 ruptures broadly coincides with local trench rotation and the southern edge of the andaman microplate which suggests structural control on fault segmentation aftershock relocations of the 2004 and 2005 earthquakes show little overlap and the sharp boundary between the series locates near the 2002 m w 7 3 northern sumatra earthquake we posit that these features represent the southern extent of the stable andaman microplate 50 100 km northwest of what was previously reported broadband analyses of the 2002 earthquake yield a bilateral rupture pattern that is used to model coulomb stress changes near the 2004 hypocenter to assess stress interactions along adjacent fault segments

no evidence of unusually large postseismic deformation in andaman region immediately after 2004 sumatra andaman earthquake 1 static offsets due to the 26 december 2004 sumatra andaman earthquake have been reported from the campaign mode gps measurements in the andaman nicobar region however these measurements contain contributions from postseismic deformation that must have occurred in the 16 25 days period between the earthquake and the measurements we analyse these and tide gauge measurements of coseismic deformation a longer time series of postseismic deformation from gps measurements at port blair in the south andaman and aftershocks to suggest that postseismic displacement not larger than 7 cm occurred in the 16 25 days following the earthquake in the south andaman and probably elsewhere in the andaman nicobar region earlier this contribution was estimated to be as large as 1 m in the andaman region which implied that the magnitude of the earthquake based on these campaign mode measurements should be decreased we suggest an mw for this earthquake as 9 23

nloadf a program for computing ocean tide loading the loading of the earth by the ocean tides produces several kinds of signals which can be measured by geodetic technique in order to compute these most accurately a combination of global and local models of the ocean tides may be needed the program nloadf convolves the green functions for loading with ocean tide models using a station centered grid with fixed dimensions making it easy to combine different ocean models without overlap in the convolution the program computes all the quantities of interest gravity displacement tilt and strain and includes the case where measurements are made beneath the surface of the ocean

paleogeodetic records of seismic and aseismic subduction from central sumatran microatolls indonesia we utilize coral microatolls in western sumatra to document vertical deformation associated with subduction microatolls are very sensitive to fluctuations in sea level and thus act as natural tide gauges they record not only the magnitude of vertical deformation associated with earthquakes paleoseismic data but also continuously track the long term aseismic deformation that occurs during the intervals between earthquakes paleogeodetic data this paper focuses on the twentieth century paleogeodetic history of the equatorial region our coral paleogeodetic record of the 1935 event reveals a classical example of deformations produced by seismic rupture of a shallow subduction interface the site closest to the trench rose 90 cm whereas sites further east sank by as much as 35 cm our model reproduces these paleogeodetic data with a 2 3 m slip event on the interface 88 to 125 km from the trench axis our coral paleogeodetic data reveal slow submergence during the decades before and after the event in the areas of coseismic emergence likewise interseismic emergence occurred before and after the 1935 event in areas of coseismic submergence among the interesting phenomenon we have discovered in the coral record is evidence of a large aseismic slip or silent event in 1962 27 years after the 1935 event paleogeodetic deformation rates in the decades before after and between the 1935 and 1962 events have varied both temporally and spatially during the 25 years following the 1935 event submergence rates were dramatically greater than in prior decades during the past four decades however rates have been lower than in the preceding decades but are still higher than they were prior to 1935 these paleogeodetic records enable us to model the kinematics of the subduction interface throughout the twentieth century

upper plate splay fault earthquakes along the arakan subduction belt recorded by uplifted coral microatolls on northern ramree island western myanmar burma abstract upper plate structures that splay out from the megathrusts are common features along major convergent plate boundaries however their earthquake and tsunami hazard potentials have not yet received significant attention in this study we identified at least one earthquake event that may have been produced by an upper plate splay fault offshore western myanmar based on u th ages of uplifted coral microatolls this event is likely an earthquake that was documented historically in c e 1848 with an estimated magnitude between 6 8 and 7 2 based on regional structural characteristics such magnitude is consistent with the observed co seismic uplift amount of 0 5 m although these events are smaller in magnitude than events produced by megathrusts they may produce higher earthquake and tsunami hazards for local coastal communities due to their proximity our results also indicate that earthquake events with co seismic uplift along the coast may not necessarily produce a flight of marine terraces therefore using only records of uplifted marine terraces as megathrust earthquake proxies may overlook the importance of upper plate splay fault ruptures and underestimate the overall earthquake frequency for future seismic and tsunami hazards along major subduction zones of the world

role of the brittle ductile transition on fault activation abstract we model a fault cross cutting the brittle upper crust and the ductile lower crust in the brittle layer the fault is assumed to have stick slip behaviour whereas the lower ductile crust is inferred to deform in a steady state shear therefore the brittle ductile transition bdt separates two layers with different strain rates and structural styles this contrasting behaviour determines a stress gradient at the bdt that is eventually dissipated during the earthquake during the interseismic period along a normal fault it should form a dilated hinge at and above the bdt conversely an over compressed volume should rather develop above a thrust plane at the bdt on a normal fault the earthquake is associated with the coseismic closure of the dilated fractures generated in the stretched hangingwall during the interseismic period in addition to the shear stress overcoming the friction of the fault the brittle fault moves when the weight of the hangingwall exceeds the strength of the dilated band above the bdt on a thrust fault the seismic event is instead associated with the sudden dilation of the previously over compressed volume in the hangingwall above the bdt a mechanism requiring much more energy because it acts against gravity in both cases the deeper the bdt the larger the involved volume and the bigger the related magnitude we tested two scenarios with two examples from l aquila 2009 italy and chi chi 1999 taiwan events gps data energy dissipation and strain rate analysis support these contrasting evolutions our model also predicts consistently with data that the interseismic strain rate is lower along the fault segment more prone to seismic activation

subduction system variability across the segment boundary of the 2004 2005 sumatra megathrust earthquakes subduction zone earthquakes are known to create segmented patches of co seismic rupture along strike of a margin offshore sumatra repeated rupture occurred within segments bounded by permanent barriers whose origin however is still not fully understood in this study we image the structural variations across the rupture segment boundary between the mw 9 1 december 26 2004 and the mw 8 6 march 28 2005 sumatra earthquakes a set of collocated reflection and wide angle seismic profiles are available on both sides of the segment boundary located offshore simeulue island we present the results of the seismic tomography modeling of wide angle ocean bottom data enhanced with mcs data and gravity modeling for the southern 2005 segment of the margin and compare it to the published model for the 2004 northern segment our study reveals principal differences in the structure of the subduction system north and south of the segment boundary attributed to the subduction of 96 e fracture zone the key differences include a change in the crustal thickness of the oceanic plate a decrease in the amount of sediment in the trench as well as variations in the morphology and volume of the accretionary prism these differences suggest that the 96 e fracture zone acts as an efficient barrier in the trench parallel sediment transport as well as a divider between oceanic crustal blocks of different structure the variability of seismic behavior is caused by the distinct changes in the morphology of the subduction complex across the boundary related to the difference in the sediment supply

probabilistic imaging of tsunamigenic seafloor deformation during the 2011 tohoku oki earthquake diverse observations from the 2011 m w 9 0 tohoku oki earthquake pointed to large coseismic fault slip proximal to the japan trench this seismic failure prompted a reevaluation of the conventional view that the outer forearc is generally aseismic however the nature of near trench fault slip during this event remains debated without consensus on whether slip peaked at the trench or at greater depths here we develop a probabilistic approach to image the spatiotemporal evolution of coseismic seafloor displacement from near field tsunami observations in a bayesian framework we sample ensembles of nonlinear source models parameterized to focus on near trench features incorporating the uncertainty in modeling dispersive tsunami waves in addition to nominal observational errors our models indicate that seafloor in the region of the earthquake was broadly uplifted and tilted seaward approaching the deep ocean trench over length scales of 40 km seafloor uplift peaks at 5 0 6 m near the inner outer forearc transition and decreases to 2 m at the trench axis over a distance of 50 km corresponding to a seafloor tilt of 0 06 0 02 m km over length scales of 20 km peak uplift reaches 7 2 m at the similar location but uplift at the trench is less constrained elastic modeling that reproduces the observed tilt requires a coseismic slip deficit at the trench such a deficit is effectively consistent with a metastable frictional model for the shallowest megathrust while large shallow earthquakes in the region cannot be completely ruled out aseismic deformation is the most likely mode for satisfying the long term slip budget

tectonics and history of the andaman sea region abstract the andaman sea is an active backarc basin lying above and behind the sunda subduction zone where convergence between the overriding southeast asian plate and the subducting australian plate is highly oblique the effect of the oblique convergence has been formation of a sliver plate between the subduction zone and a complex right lateral fault system the late paleocene collision of greater india and asia with approximately normal convergence started clockwise rotation and bending of the northern and western sunda arc the initial sliver fault which probably started in the eocene extended through the outer arc ridge offshore from sumatra through the present region of the andaman sea into the sagaing fault with more oblique convergence due to the rotation the rate of strike slip motion increased and a series of extensional basins opened obliquely by the combination of backarc extension and the strike slip motion these basins in sequence are the mergui basin starting at 32 ma the conjoined alcock and sewell rises starting at 23 ma east basin separating the rises from the foot of the continental slope starting at 15 ma and finally at 4 ma the present plate edge was formed alcock and sewell rises were separated by formation of the central andaman basin and the faulting moved onshore from the mentawai fault to the sumatra fault system bisecting sumatra

sibling earthquakes generated within a persistent rupture barrier on the sunda megathrust under simeulue island a section of the sunda megathrust underneath simeulue is known to persistently halt rupture propagation of great earthquakes including those in 2004 mw 9 2 and 2005 mw 8 6 yet the same section generated large earthquakes in 2002 mw 7 3 and 2008 mw 7 4 to date few studies have investigated the 2002 and 2008 events and none have satisfactorily located or explained them using near field insar gps and coral geodetic data we find that the slip distributions of the two events are not identical but do show a close resemblance and largely overlap we thus consider these earthquakes siblings that were generated by an anomalous parent feature of the megathrust we suggest that this parent feature is a locked asperity surrounded by the otherwise partially creeping simeulue section perhaps structurally controlled by a broad morphological high on the megathrust

new insights into holocene marine terrace development caused by seismic and aseismic faulting in the coastal range eastern taiwan abstract the coastal range in eastern taiwan which has resulted from arc continent collisions involves well developed holocene uplifted marine terraces along a 140 km long stretch of the coast this is the first study that unraveled the aseismic generation of marine terraces associated with coseismic uplift along the creeping fault we organized dems lidar mapping and field surveys to obtain detailed and systematic measurements of the inner and outer edges and wave cut platform elevations along thirty three stream profile transects allowing us to locate the bedrock profile spatial and temporal variations in the 14c age are characterized by an offlapping built feature of significant seaward younging trend of ages across the marine terrace caused by aseismic and coseismic uplift thus heights of the bedrock riser and platform are caused by coseismic large earthquake and aseismic plus moderate coseismic vertical deformations during a large earthquake cycle respectively this indicates that each terrace duration and paleoshoreline ages can be used to infer the recurrence interval and the timing of large earthquake events respectively results of the age of the paleoshoreline indicate six paleoseismic events at 8500 6300 4800 3400 1700 and 700 yr bp this implies that the chihshang creeping fault could be capable of producing large earthquakes greater than m7 at millennial time scales associated with larger coseismic deformations the creep faulting associated with seismic and aseismic uplift is a dominant process constraining the holocene marine terrace evolution

plate boundary deformation associated with the great sumatra andaman earthquake the sumatra andaman earthquake of 26 december 2004 is the first giant earthquake moment magnitude m w 9 0 to have occurred since the advent of modern space based geodesy and broadband seismology it therefore provides an unprecedented opportunity to investigate the characteristics of one of these enormous and rare events here we report estimates of the ground displacement associated with this event using near field global positioning system gps surveys in northwestern sumatra combined with in situ and remote observations of the vertical motion of coral reefs these data show that the earthquake was generated by rupture of the sunda subduction megathrust over a distance of 1 500 kilometres and a width of 150 kilometres megathrust slip exceeded 20 metres offshore northern sumatra mostly at depths shallower than 30 kilometres comparison of the geodetically and seismically inferred slip distribution indicates that 30 per cent additional fault slip accrued in the 1 5 months following the 500 second long seismic rupture both seismic and aseismic slip before our re occupation of gps sites occurred on the shallow portion of the megathrust where the large aceh tsunami originated slip tapers off abruptly along strike beneath simeulue island at the southeastern edge of the rupture where the earthquake nucleated and where an m w 7 2 earthquake occurred in late 2002 this edge also abuts the northern limit of slip in the 28 march 2005 m w 8 7 nias simeulue earthquake

coseismic vs climatic factors in the record of relative sea level changes an example from the last interglacials in se spain abstract trying to decipher how paleoseismic activity has influenced the altitudinal disposition of interglacial deposits is one of the main challenges to be confronted before quantifying relative sea level changes between consecutive highstands at the same time identifying paleoseismic features in an area with low instrumental seismic activity can complement the seismic record thereby contributing to better seismic hazard knowledge in this regard cope basin se spain meets all the requirements necessary for these kinds of analysis firstly on account of its excellent outcrop conditions and secondly because its sea level record is undoubtedly conditioned by both factors climatically driven changes and local and regional seismotectonics the morpho sedimentary sequence presented in this paper provides evidence from three different highstands two littoral sedimentary units separated by terrestrial deposits and affected by liquefaction paleoseismic activity and a younger paleo cliff and its associated wave cut platform carved into those sedimentary units this wave cut platform now tilted and folded reaches heights ranging from 0 to 8 m which has been interpreted as a consequence of cosesimic effect the age of this wave cut platform last interglacial or holocene supports uplift rate estimations of from 0 016 to 0 15 mm yr since the last interglacial holocene active deformation observed on pleistocene holocene sea level geomarkers can not only furnish useful information about seismic activity within the major structure of the aguilas arc but also offer new insight into the cope basin s geodynamic model

shocks in a box an analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution 1 we introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones the quasi two dimensional analogue model features rate and state dependent elastic frictional plastic and viscoelastic material properties and is scaled for gravity inertia elasticity friction and viscosity the experiments are monitored with a high resolution strain analysis tool based on digital image correlation particle imaging velocimetry piv providing deformation time series comparable to seismologic geodetic and geologic observations in order to separate elastic and nonelastic effects inherent the experimental deformation patterns we integrate elastic dislocation modeling edm into a hybrid approach we use the analogue earthquake slip and interseismic locking distribution as edm dislocation input and forward model the coseismic and interseismic elastic response the residual which remains when the edm prediction is subtracted from the experimental deformation pattern highlights the accumulation of permanent deformation in the model the setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations by applying the model to an accretionary type plate margin we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc including a tectonically stable shelf and coastal high 20 plate convergence accommodated by internal shortening overlying the area of large megathrust earthquake slip fifty to 75 of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench the inner forearc region remains undeformed and represents a basin

two hundred thirty years of relative sea level changes due to climate and megathrust tectonics recorded in coral microatolls of martinique french west indies we sampled six coral microatolls that recorded the relative sea level changes over the last 230 years east of martinique on fringing reefs in protected bays the microatolls are cup shaped which is characteristic of corals that have been experiencing submergence x ray analysis of coral slices and reconstructions of the highest level of survival hls curves show that they have submerged at rates of a few millimeters per year their morphology reveals changes in submergence rate around 1829 11 1895 and 1950 tide gauges available in the region indicate a regional sea level rise at a constant mean rate of 1 1 0 8 mm yr which contrasts with our coral record implying additional tectonic subsidence comparing our coral morphology with that of synthetic corals generated with matlab by using the key west tide gauge record florida we show that their growth was controlled by tectonics and that a sudden relative sea level increase drowned them around 1950 simple elastic models show that this sudden submergence probably occurred during the 21 may 1946 earthquake which ruptured the plate interface in front of martinique in the mantle wedge in an area of sustained seismic activity the 1839 m8 earthquake probably occurred in the same area long term subsidence of microatolls indicates that this deep portion of the megathrust is probably locked down to 60 km depth during the interseismic period our oldest coral recorded a long lasting period 50 years of stable relative sea level after the 1839 earthquake indicating that transient interseismic strain rate variations may occur in the lesser antilles

constraints on 2004 sumatra andaman earthquake rupture from gps measurements in andaman nicobar islands the 26 december 2004 sumatra andaman earthquake mw 9 0 9 3 is the greatest earthquake of the modern seismological era the rupture characteristics of the earthquake particularly in the andaman nicobar region are not well resolved from seismological or far field geodetic data here in this article we present campaign mode global positioning system gps measurements of coseismic displacements at 13 sites in the andaman nicobar islands before and after the 2004 sumatra andaman earthquake these measurements provide improved estimates of rupture characteristics in the region coseismic horizontal ground displacement of 1 5 6 5 m towards the southwest and coseismic vertical displacement mostly subsidence of 0 5 2 8 m occurred along the andaman nicobar islands with maximum displacements in the nicobar islands we estimate coseismic slip under the andaman and nicobar islands as 3 8 7 9 m and 11 15 m respectively the length of the rupture is estimated to be about 1500 km with a width varying from 120 km under middle andaman island to 160 km under great nicobar island gps measurements during january 11 22 2005 from port blair suggest rapid afterslip in the postseismic period limited gps data available from 1995 measurements at two sites in andaman provide evidence of strain accumulation that varied significantly in the 10 yr preceding the earthquake d 2005 elsevier b v all rights reserved

holocene sea levels along the andaman sea coast of thailand for the malay thai peninsula several sea level curves for the younger holocene based on field evidence as well as on hydro isostatic modelling of a far field site have been published the general assumption is a rapid rise to a mid holocene maximum up to 5 m above present sea level followed by a constant or oscillating regression however from the andaman sea coast of thailand which was affected by the 2004 tsunami only isolated observations are available regarding holocene sea levels thus the timing and magnitude of the holocene highstand as well as the course of the regression remain to be defined as several palaeotsunamis could be detected in the meantime it is important to know the related sea levels as exactly as possible to judge the energy inundation width and potential wave height of these events therefore fixed biological indicators from the rocky coasts of the phang nga bay and phuket as well as morphological indicators from beach ridge and swale sequences along the exposed west coast ko phra thong were studied to gain information about the holocene sea level development in this region while oyster and coral data from the phang nga bay and phuket document a holocene maximum of 2 6 m at 5700 cal bp the ridge crests and swale bases in the northwest of the study area point to maximum heights of 1 5 2 0 m above the present level around 5300 years ago during the last 3000 years to when the largest part of the holocene palaeotsunami deposits from thailand was dated relative sea levels rsl in both areas did not exceed 1 5 m

modern vertical deformation above the sumatran subduction zone paleogeodetic insights from coral microatolls coral microatolls from the coast and outer arc islands of western sumatra retain a stratigraphic and morphologic record of relative sea level change which is due in large part to vertical tectonic deformation above the sumatran subduction zone low water levels whose fluctuations produce measurable changes in coral morphology limit the upward growth of the microatolls annual rings derived from seasonal variations in coral density serve as an internal chronometer of coral growth the microatolls act as natural long term tide gauges recording sea level variations on time scales of decades field observations and stratigraphic analysis of seven microatolls five from the outer arc islands and two from the mainland coast indicate that the mentawai islands have been submerging at rates of 4 10 mm yr over the last four or five decades while the mainland has remained relatively stable the presence of fossil microatolls up to several thousand years old in the intertidal zone indicates that little permanent vertical deformation has occurred over that time thus most of the strain accumulated in the past few decades represents interseismic deformation that is recovered during earthquakes elastic dislocation models using these submergence data suggest that elastic strain is being accumulated in the interseismic period and that the subduction zone in this region is fully coupled

hydroxyl in clinopyroxene from the deep subducted crust evidence for h2o transport into the mantle clinopyroxenes in eclogites from the deep subducted crust in the kokchetav kazakhstan ultrahigh pressure metamorphic terrane were found by infrared spectroscopy to contain up to 3020 ppm oh these rocks were recrystallized at pressures over 60 kbar and temperatures over 1000 c where no hydrous minerals are stable infrared spectra of the clinopyroxenes show three hydroxyl absorption bands in the regions 3440 3460 cm 1 3500 3530 cm 1 and 3600 3625 cm 1 the hydroxyl absorbance increases with recrystallization pressure of the eclogites and with vacancy concentration in the pyroxene structure ca eskola component clinopyroxenes represent about 40 50 vol of eclogites such that the bulk eclogites contain approximately 1300 ppm hydroxyl at depths greater than 150 km thus subducted oceanic crust can transport trace amounts of h2o into the upper mantle even in the absence of nominally hydrous minerals

analysis of partially emerged corals and reef terraces in the central vanuatu arc comparison of contemporary coseismic and nonseismic with quaternary vertical movements in the central vanuatu arc living and recently deceased reef corals act as natural tide gauges which have allowed us to map vertical tectonic deformation patterns as corals grow the density of the aragonite coral skeletons varies on an annual cycle producing annual growth bands similar to tree rings using coral growth bands we can determine the year coral surfaces died due to emergence we interpret four major coral emergence events as coseismic uplifts that occurred near the epicenters and times of large shallow earthquakes on january 5 1946 ms 7 3 august 11 1965 ms 7 5 october 27 1971 ms 7 1 and december 29 1973 ms 7 5 the 1965 and 1973 events caused maximum uplifts of 120 and 60 cm respectively in the frontal arc also related to these events are uplifts of 10 cm and 6 cm in the back arc on pentecost and maewo islands which lie east of the volcanic chain and the primary forearc zones of uplift and subsidence similar secondary zones of uplift occurred with the great 1960 chile and 1964 alaska earthquakes the amplitude of these secondary uplifts is significantly larger than that predicted by models having a single fault in an elastic half space however the amount of secondary uplift is comparable to that predicted if the fault occurs in a plate of constant thickness overlying a viscoelastic half space at various places in 1957 1969 1970 1977 and 1978 1981 there was about 5 10 cm of emergence not associated with major earthquakes which may indicate nonseismic tectonic uplift however oceanographically lowered sea levels as in el ninos may have determined the times when corals died and recorded these events nevertheless the accumulation of emergence its persistence the limited geographic extent of each event and occurrence in areas of rapid holocene uplift suggest that the causes of the uplifts are tectonic these events suggest that in some areas a third or more of the total accumulated uplift in central vanuatu takes place as aseismic motion however in some areas we find only coseismic emergence in central vanuatu contemporary coseismic vertical deformation holocene uplift and topography have remarkably similar patterns this suggests that the mechanisms and processes causing vertical deformation have varied little over the last 106years apparently the topography structure and seismotectonics are controlled by the subduction of the d entrecasteaux ridge a major bathymetric feature underthrusting this part of the arc the influence of this ridge may have been especially extensive because it migrates very slowly along the arc trend and thus it interacts for a long time with a single portion of the arc system our previous studies of reef terraces indicated the existence of at least four seismotectonic arc segments or blocks along the santo malekula interval of the arc and our present results further support this conclusion each block has uplifted at different times by different amounts at different rates and tilted in a different direction boundaries between the north santo and the south santo segment and between the north malekula and the south malekula segment correlate with the north and south flanks of the d entrecasteaux ridge as does the absence of a physiographic trench west of santo

uplift and subsidence associated with the great aceh andaman earthquake of 2004 rupture of the sunda megathrust on 26 december 2004 produced broad regions of uplift and subsidence we define the pivot line separating these regions as a first step in defining the lateral extent and the downdip limit of rupture during that great m w 9 2 earthquake in the region of the andaman and nicobar islands we rely exclusively on the interpretation of satellite imagery and a tidal model at the southern limit of the great rupture we rely principally on field measurements of emerged coral microatolls uplift extends from the middle of simeulue island sumatra at 2 5 n to preparis island myanmar burma at 14 9 n thus the rupture is 1600 km long the distance from the pivot line to the trench varies appreciably the northern and western andaman islands rose whereas the southern and eastern portion of the islands subsided the nicobar islands and the west coast of aceh province sumatra subsided tilt at the southern end of the rupture is steep the distance from 1 5 m of uplift to the pivot line is just 60 km our method of using satellite imagery to recognize changes in elevation relative to sea surface height and of using a tidal model to place quantitative bounds on coseismic uplift or subsidence is a novel approach that can be adapted to other forms of remote sensing and can be applied to other subduction zones in tropical regions

insight into the 2004 sumatra andaman earthquake from gps measurements in southeast asia data collected at 60 global positioning system gps sites in southeast asia show the crustal deformation caused by the 26 december 2004 sumatra andaman earthquake at an unprecedented large scale small but significant co seismic jumps are clearly detected more than 3 000 km from the earthquake epicentre the nearest sites still more than 400 km away show displacements of 10 cm or more here we show that the rupture plane for this earthquake must have been at least 1 000 km long and that non homogeneous slip is required to fit the large displacement gradients revealed by the gps measurements our kinematic analysis of the gps recordings indicates that the centroid of released deformation is located at least 200 km north of the seismological epicentre it also provides evidence that the rupture propagated northward sufficiently fast for stations in northern thailand to have reached their final positions less than 10 min after the earthquake hence ruling out the hypothesis of a silent slow aseismic rupture data culled from gps stations in indonesia malaysia singapore thailand india and china have answered more questions relating to the 26 december sumatra andaman megathrust earthquake permanent displacements were seen 3 000 km away final displacements occurred within 10 minutes of the earthquake ruling out slow aseismic slip on the fault

the 2004 sumatra earthquake and tsunami lessons learned in subduction zone science and emergency management for the cascadia subduction zone the 26 december 2004 mw 9 3 sumatra earthquake and tsunami was a pivotal turning point in our awareness of the dangers posed by subduction zone earthquakes and tsunamis this earthquake was the world s largest in 40 years and it produced the world s deadliest tsunami this earthquake ruptured a subduction zone that has many similarities to the cascadia subduction zone in this article i summarize lessons learned from this tragedy and make comparisons with potential rupture characteristics slip distribution deformation patterns and aftershock patterns for cascadia using theoretical modeling and interseismic observations both subduction zones are approximately 1 100 1 300 km in length both have similar convergence rates and represent oblique subduction slip along the subduction fault during the 26 december earthquake is estimated at 15 25 m similar to values estimated for cascadia the width of the rupture 80 150 km estimated from modeling seismic and geodetic data is similar to the width of the locked and transition zone estimated for cascadia coseismic subsidence of up to 2 m along the sumatra coast is also similar to that predicted for parts of northern cascadia based on paleoseismic evidence in addition to scientific lessons learned the 2004 tsunami provided many critical lessons for emergency management and preparedness as a result of that tragedy a number of preparedness initiatives are now underway to promote awareness of earthquake and tsunami hazards along the west coast of north america and plans are underway to develop prototype tsunami and earthquake warning systems along cascadia lessons learned from the great sumatra earthquake and tsunami tragedy both through scientific studies and through public education initiatives will help to reduce losses during future earthquakes in cascadia and other subduction zones of the world

age estimates of coastal terraces in the andaman and nicobar islands and their tectonic implications the great indian ocean earthquake of december 26 2004 caused significant vertical changes in its rupture zone about 800 km of the rupture is along the andaman and nicobar islands which forms the outer arc ridge of the subduction zone coseismic deformation along the exposed land could be observed as uplift subsidence here we analyze the morphological features along the coast of the andaman and nicobar islands in an effort to reconstruct the past tectonics taking cues from the coseismic effects we obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates which vary from 1 33 mm yr 1 in the little andaman to 2 80 mm yr 1 in south andaman and 2 45 mm yr 1 in the north andaman our radiocarbon dates converge on sim 600 yr and sim 1000 yr old coastal uplifts which we attribute to the level changes due to two major previous subduction earthquakes in the region

reconstruction of tsunami inland propagation on december 26 2004 in banda aceh indonesia through field investigations this paper presents the results from an extensive field data collection effort following the december 26 2004 earthquake and tsunami in banda aceh sumatra the data were collected under the auspices of tsunarisque a joint french indonesian program dedicated to tsunami research and hazard mitigation which has been active since before the 2004 event in total data from three months of field investigations are presented which detail important aspects of the tsunami inundation dynamics in banda aceh these include measurements of runup tsunami wave heights flow depths flow directions event chronology and building damage patterns the result is a series of detailed inundation maps of the northern and western coasts of sumatra including banda aceh and lhok nga

teleseismic relocation and assessment of seismicity 1918 2005 in the region of the 2004 mw 9 0 sumatra andaman and 2005 mw 8 6 nias island great earthquakes the m w 9 0 2004 sumatra andaman islands and m w 8 6 nias island great earthquake sequences have generated over 5000 catalog reported earthquakes along 1700 km of the sumatra andaman and western sunda regions studies of prior regional seismicity have been limited to global catalog locations that often have poorly constrained epicenters and depths approximately 3650 teleseismically well recorded earthquakes occurring in this region during the period 1918 2005 are relocated with special attention to focal depth reduced uncertainties of epicenters and depths in the region on the order of 15 and 10 km respectively foster interpretation of focal mechanism data and provide additional details about the subducting indian and australian plates the revised earthquake dataset reveals a sharp delineation between aftershocks of the 2004 and 2005 earthquakes near simeulue island and a steepening in slab dip from south to north the downdip width of the aftershock zone of the 2004 m w 9 0 earthquake varies from 200 km at its northern end to 275 km at its southern end and events located between 35 and 70 km focal depth occur more frequently in the southernmost section of this aftershock zone outer rise and near trench normal and strike slip faulting earthquakes also increase in frequency following the 2004 and 2005 earthquakes earthquake swarms triggered along the andaman backarc spreading center both north of sumatra and near siberut island 100 km south of the nias island aftershock sequence illustrate the complex and variable nature of seismicity following these great earthquakes

active crustal faults in the forearc region guerrero sector of the mexican subduction zone this work explores the characteristics and the seismogenic potential of crustal faults on the overriding plate in an area of high seismic hazard associated with the occurrence of subduction earthquakes and shallow earthquakes of the overriding plate we present the results of geomorphic structural and fault kinematic analyses conducted on the convergent margin between the cocos plate and the forearc region of the overriding north american plate within the guerrero sector of the mexican subduction zone we aim to determine the active tectonic processes in the forearc region of the subduction zone using the river network pattern topography and structural data we suggest that in the studied forearc region both strike slip and normal crustal faults sub parallel to the subduction zone show evidence of activity the left lateral offsets of the main stream courses of the largest river basins gps measurements and obliquity of plate convergence along the cocos subduction zone in the guerrero sector suggest the activity of sub latitudinal left lateral strike slip faults notably the regional left lateral strike slip fault that offsets the papagayo river near the town of la venta named la venta fault shows evidence of recent activity corroborated also by gps measurements 4 5 mm year of sinistral motion assuming that during a probable earthquake the whole mapped length of this fault would rupture it would produce an event of maximum moment magnitude mw 7 7 even though only a few focal mechanism solutions indicate a stress regime relevant for reactivation of these strike slip structures we hypothesize that these faults are active and suggest two probable explanations 1 these faults are characterized by long recurrence period i e beyond the instrumental record or 2 they experience slow slip events and or associated fault creep the analysis of focal mechanism solutions of small magnitude earthquakes in the upper plate for the period between 1995 and 2008 revealed that frequent normal faults sub parallel to the trench could be reactivated in the current stress field related to the cocos subduction moreover these features could also be reactivated by subduction megathrust earthquakes

spherical earth finite element model of short term postseismic deformation following the 2004 sumatra earthquake 1 decadal scale postseismic deformation of subduction earthquakes has been widely modeled using a maxwell viscoelastic earth with a mantle wedge viscosity of about 1019 pa s short term postseismic deformation within a few years after the earthquake remains a more challenging problem because of the predominance of afterslip of the megathrust and the potentially more complex mantle rheology questions include the necessity of invoking the transient rheology and the relative importance of contributions from afterslip and viscoelastic relaxation in this work we address these questions by developing a spherical earth viscoelastic finite element model for the short term postseismic deformation following the magnitude 9 2 sumatra earthquake of 2004 the model consists of elastic overriding and subducting plates and a viscoelastic mantle of bi viscous burgers rheology with the continental mantle mantle wedge being less viscous than the oceanic mantle by a factor of ten primary observational constraints for the short term postseismic deformation include 1 year net displacements of nine near field gps sites and 3 year time series from three far field sites several hundred kilometers from the 2004 rupture zone model results indicate that the afterslip of the fault must be at work within the first few years after the earthquake the observed deformation is best explained with a model that includes both the afterslip and transient rheology in the preferred model the transient and steady state viscosities of the mantle wedge are 5 1017 pa s and 1019 pa s respectively