separation of coseismic and postseismic gravity changes for the 2004 sumatra andaman earthquake from 4 6 yr of grace observations and modelling of the coseismic change by normal modes summation eodspatiale grgs for comparison the release 04 solutions of the center for space research csr are also inves tigated after a spectral windowing or a gaussian spatial smoothing results are shown both in terms of geoid height changes and gravity variations coseismic and postseismic gravitational changes estimated from the different gravity solutions are globally similar although their spa tial extent and amplitude depend on the type of filter used in the processing of grace fields the highest signal to noise ratio is found with the grgs solutions the postseismic signature has a spectral content closer to the grace bandwidth than the coseismic signature and is therefore better detected by grace the coseismic signature consists mainly of a strong gravity decrease east of the sunda trench in the andaman sea a gravity increase is also detected at a smaller scale west of the trench the model for the coseismic gravity changes agrees well with the coseismic signature estimated from grace regarding the overall shape and orientation location with respect to the trench and order of magnitude coseismic gravity changes are followed by a postseismic relaxation that are well fitted by an increasing expo nential function with a mean relaxation time of 0 7 yr the total postseismic gravity change consists of a large scale positive anomaly centred above the trench and extending over 15 of latitude along the subduction after 26 months the coseismic gravity decrease has been partly compensated by the postseismic relaxation but a negative anomaly still remains south of phuket a dominant gravity increase extends over 15 of latitude west of the trench being maximal south of the epicentre area by investigating analyses of two global hydrology models and one ocean general circulation model we show that our grace estimates of the coseismic and postseismic gravitational changes are almost not biased by interannual variations originat ing from continental hydrology and ocean circulation in the subduction area and in the central part of the andaman sea while they are biased by several gal in the malay peninsula

rupture area and displacement of past cascadia great earthquakes from coastal coseismic subsidence coastal marshes record a 6500 yr history of coseismic displacements in great earthquakes at the cascadia subduction zone we compiled estimates of coseismic displacement for past megathrust events based on correlations with megathrust triggered turbidites and estimated megathrust slip based on comparisons of marsh displacements with dislocation model predictions age correlated marsh data are compatible with event rupture extents defi ned by the published turbidite record and a 6500 yr mean recurrence interval that increases northward from 230 to 480 yr within the constraints of the marsh data the width of the coseismic rupture zone generally agrees with the downdip width of the interseismic locked zone inferred from geodetic and thermal data in southernmost cascadia where the model does not include the complex deformation near the mendocino triple junction the coastal data may be better fi t by a model with an 25 narrower rupture than that inferred from regional geophysical data at each coastal marsh site coseismic displacements are roughly similar from event to event independent of the time since the previous event slip in the a d 1700 earthquake was consistent with the preceding interval of strain accumulation 200 yr only at the northern and southern ends of the margin but it was apparently much higher in southern washington and northern oregon possibly indicating postseismic contamination and or catch up coseismic slip to make up for a defi cit in the preceding event overall agreement between the dislocation models and the marsh data for most of the margin implies that such models can be usefully applied to rupture and ground shaking predictions

investigation on afterslip and steady state and transient rheology based on postseismic deformation and geoid change caused by the sumatra 2004 earthquake the commonly used rheological model for the earth s mantle when considering geological time scales mantle convection is the viscoelastic maxwell model which assumes a steady state creep process however application of this model to phenomena on shorter time scales such as postglacial rebound or postseismic relaxation leads to difficulties in finding a consistent interpretation of obtained viscosities using standard maxwell viscosity of 1e19 pa s to analyze postseismic near field gps time series from the 2004 sumatra andaman earthquake requires large time dependent afterslip with a relaxation time of about 1 year we show that using linear biviscous burgers rheology for the asthenosphere together with a refined coseismic slip model we can drastically reduce the amount of apparent afterslip comparison of predicted geoid change to observations by the grace satellite mission shows that a univiscous maxwell model with afterslip is not compatible with observations since even large afterslip has a more localized effect than transient relaxation due to the main earthquake which in turn is in agreement with observations thus a combination of ground and space based geodetic observations is very useful in differentiating between rheological models an additional independent discrimination between afterslip and biviscous relaxation could be obtained by installing ocean bottom pressure gauges close to the trench

resonant slow fault slip in subduction zones forced by climatic load stress global positioning system gps measurements at subduction plate boundaries often record fault movements similar to earthquakes but much slower occurring over timescales of 1 week to 1 year these slow slip events have been observed in japan1 2 cascadia3 4 5 6 7 mexico8 9 alaska10 and new zealand11 the phenomenon is poorly understood but several observations hint at the processes underlying slow slip although slip itself is silent seismic instruments often record coincident low amplitude tremor in a narrow 1 5 cycles per second frequency range12 also modelling of gps data3 7 9 and estimates of tremor location13 indicate that slip focuses near the transition from unstable stick slip to stable friction at the deep limit of the earthquake producing seismogenic zone perhaps most intriguingly slow slip is periodic at several locations with recurrence varying from 6 to 18 months depending on which subduction zone or even segment is examined4 5 6 9 here i show that such periodic slow fault slip may be a resonant response to climate driven stress perturbations fault slip resonance helps to explain why slip events are periodic why periods differ from place to place and why slip focuses near the base of the seismogenic zone resonant slip should initiate within the rupture zone of future great earthquakes suggesting that slow slip may illuminate fault properties that control earthquake slip

microwave dielectric structural and salinity properties of simulated sea ice the crystalline structure salinity characteristics and microwave dielectric properties of artificially grown saline ice are presented the ice was grown in an outdoor pool containing salt water of 23 25 0 salinity the structure and salinity profiles of this ice sheet closely simulated those found in arctic first year sea ice the complex relative dielectric permittivity of slabs removed from the ice sheet was measured at 4 75 ghz as a function of temperature the slabs were placed between open end waveguide radiators and dielectic properties were calculated from the forward scattering coefficient the results show both the real r and imaginary r parts to vary almost in direct proportion to the brine volume with values for r showing more variation and are compared with the previous work of others on actual sea ice samples

gravity changes due to the sumatra andaman and nias earthquakes as detected by the grace satellites a reexamination summary in this paper we study the geoid changes caused by the sumatra andaman earthquake 2004 december 26 and the nias earthquake 2005 march 28 using data from the gravity recovery and climate experiment grace satellites new is that we explore the possibility to separate the effects of the sumatra andaman and nias earthquakes based on correlation analysis we investigate the separability of the sumatra andaman and nias signals and the feasibility of separating the non seismic linear trend from the time dependent post seismic relaxation effect as input data we use 76 months of global geopotential coefficients from the gfz release 4 rl04 of grace data to suppress unphysical artefacts in grace data striping the grace coefficients are smoothed with an anisotropic decorrelation filter model parameters are estimated through a bayesian approach we compare our results with geophysical models of both earthquakes calculated based on the viscoelastic gravitational dislocation theory the slip models used are inverted from gps measurements our findings indicate that the inversion of grace data for the sumatra andaman effect will contain significant signal from the nias earthquake and will benefit from removing the modelled nias effect from the data comparing grace measurements to geophysical models reveals significant differences we suggest how the gps calibrated models may be improved to better fit the grace data in the first months after the earthquake we also find evidence for a fast process in the andaman sea possibly due to aseismic slip similar phenomena were observed in previous studies

india and sunda plates motion and deformation along their boundary in myanmar determined by gps using a regional gps data set including 190 stations in asia from nepal to eastern indonesia and spanning 11 years we update the present day relative motion between the indian and sundaland plates and discuss the deformation taking place between them in myanmar revisiting measurements acquired on the main boundary thrust in nepal it appears that points in southern nepal exhibit negligible deformation with respect to mainland india including these points using a longer time span than previous studies and making an accurate geodetic mapping in the newest reference frame allows us to refine the present day indian motion our results confirm that the current motion of india is slower than predicted by the nuvel 1a model and in addition our india eurasia motion is significantly 5 mm yr slower than previous geodetic determinations this new indian motion combined with a refined determination of the sundaland motion gives way to a relative india sunda angular velocity of 20 2 n 26 1 e 0 370 myr in itrf2000 predicting a relative motion of 35 mm yr oriented n10 at the latitude of myanmar there the sagaing fault accommodates only 18 mm yr of right lateral strike slip only half of the shear component of motion we present two models addressing how and where the remaining deformation may occur a first model of distributed deformation implies convergence on the arakan subduction the northern continuation of the now famous sumatra andaman trench and wrench faulting in the arakan wedge the second model uses localized deformation where deformation observed west of the sagaing fault is entirely due to elastic loading on a faster and oblique arakan subduction 23 mm yr this latter model predicts that a major earthquake of mw 8 5 may occur every century on this segment of the subduction

5 9 mw 18th june 2010 earthquake and fault segment linkage at andaman a study based on macroseismic survey gps geodesy and coulomb stress changes abstract 18th june 2010 5 9 mw earthquake at north andaman triggered along nw se pre existing fault with reverse fault mechanism macroseismic survey and gps geodesy reveal maximum damages following ne sw trend due to normal fault mechanism coulomb stress modeling for post and inter seismic earthquakes after the 2004 mega earthquake show different stages of fault segment linkage at north andaman the present earthquake has been explained as co shock due to asiesmic soft linkage of fault propagation

a viscoelastic and afterslip postseismic deformation model for the 1964 alaska earthquake 1 we developed a 3 d viscoelastic model in concert with an afterslip model to describe the postseismic deformation following the 1964 alaska earthquake our model incorporates a realistic geometry including an elastic slab with very low dip angle these geometric factors are important and require a reanalysis of the 1964 coseismic model our coseismic model differs from previous models in that the montague island splay fault extends farther along the kenai peninsula coast and as a result slip on the megathrust in that region is smaller we computed postseismic deformation models using a range of mantle viscosities with maxwell relaxation time of 1 to 50 years with a best estimate of 20 years the viscoelastic model explains most of the trenchward motion observed in the present velocity field but has little impact on cumulative 1965 to present uplifts after removing the viscoelastic response the largest residual cumulative uplifts were located downdip from areas of largest coseismic slip area and we explain them using an afterslip model constrained in space by the observed cumulative postseismic uplifts and in time by tide gauge records no single mechanism can explain both the 30 years of cumulative uplift and the present velocities but a combination of viscoelastic relaxation afterslip interseismic elastic deformation and motion of southern alaska relative to north america explains the first order features of the observations forty years after the earthquake the present day velocities contain a significant component of postseismic deformation so very long lived postseismic deformation plays an important role in the subduction zone earthquake cycle for great earthquakes

the margin between senja and spitsbergen fracture zones implications from plate tectonics abstract analysis of multichannel seismic data from the continental margin off svalbard between the senja and spitsbergen fracture zones suggests that the transition between continental and oceanic crust is located at or close to the hornsund fault zone in the late paleocene early eoeene 57 m y the region between svalbard and northeast greenland was subjected to regional shear movements associated with a transform system between the young lofoten greenland basin and the arctic ocean approximately 50 m y ago the spreading axis migrated to the northeast creating a deep basin north of the greenland senja fracture zone forming the passive margin between bear island and 76 5 n north of 76 5 n the regional transform was maintained at the time of the main reorganization of relative plate motion 36 m y the northern margin evolved a continental fragment was possibly cut off from the svalbard margin forming a small microcontinent the microcontinent appears as the submarine ridge which has been associated with the hovgaard fracture zone it is suggested that the sediments west of the hornsund fault zone are not older than eocene in the south and mid oligocene in the north the position of the spreading axis has greatly influenced the margin sedimentation

viscoelastic relaxation in a heterogeneous earth following the 2004 sumatra andaman earthquake abstract consideration of the three dimensional heterogeneity of mantle rheology allows models of viscoelastic relaxation following the 2004 sumatra andaman earthquake to simultaneously fit both the observed far field and near field postseismic deformation we use horizontal and vertical campaign and continuous gps observations from the andaman nicobar and sumatran forearc islands mainland sumatra thailand the malay peninsula the indian ocean and southern india spanning the first five years of postseismic deformation the postseismic relaxation models consider contributions from the 2004 mw 9 2 sumatra andaman the 2005 mw 8 7 nias and 2007 mw 8 4 bengkulu earthquakes far field motions to the east of the ruptures are equally well fit by homogeneous or laterally variable earth models however only models with contrasting rheology across the subducting slab a ten times higher mantle viscosity under the indian ocean lithosphere than the backarc mantle can also produce the observed enduring postseismic uplift along the forearc and lack of far field transient displacements in southern india while postseismic uplift of forearc stations can also be produced by rapid and enduring down dip afterslip the inferred rheology structure is consistent with the distribution of mantle temperature inferred from seismic tomography

indian national gnss programme crustal deformation measurements in the indian sub continent abstract the indian national gnss programme was launched about one and half decades ago with a view to provide a boost to crustal deformation measurements for constraining the movement of indian plate identifying the regions of strain accumulation and to estimate the convergence rates across some identified faults boundaries under this programme a network of 50 permanent gps receivers has been established which is fully functional for the last about 8 yrs the network has generated very important data sets which in turn have helped in the estimation of indian plate motion regions and rate of strain accumulation rate of convergence across some identified faults etc the measurements have also been utilized in monitoring co seismic and postseismic deformation related to recent earthquakes that occurred in india and adjoining regions such as the 2001 bhuj 2004 sumatra andaman and 2005 kashmir earthquake this article presents some salient results obtained for specific corridors in the himalaya indo burmese arc region andaman nicobar island region and indian plate interior region

lessons learned from the 2004 sumatra andaman megathrust rupture the 2004 sumatra andaman earthquake has been extensively studied because of its great size and devastating consequences large amounts of highquality seismic geodetic and geologic data have led to a number of proposed models for its length duration fault geometry rupture velocity and slip history the latest of these models vary in their details but now largely agree in their large scale features which include significant coseismic slip along the entire 1300 to 1500 km rupture the bulk of which occurred fast enough to radiate seismic waves the earthquake s enormous size has challenged conventional processing approaches and stimulated the development of new analysis and inversion methods including multiple source inversions highfrequency body wave imaging and satellite observations of tsunami heights and gravity changes the sumatra megathrust earthquake was the largest in 40 years and is by far the best documented but it does not seem fundamentally different in its properties from other large subduction zone earthquakes

transtension to transpression a study of strain evolution in andaman islands based on gps measurements following great sumatra andaman earthquake 2004 we use campaign mode and continuous gps data from 2005 to 2008 to examine the evolving strain pattern in andaman islands after the great sumatra andaman earthquake two and half years after the earthquake the post seismic period changes to inter seismic period at port blair post seismic displacement rate reduced to about 95 with clockwise rotation of azimuths and towards north andaman velocity vector gradually rotates towards north with drop in magnitude the inter seismic displacement was dominated by trench parallel movement strain calculations on inclined transpession model shows deformations at andaman were highly heterogeneous both in post and inter seismic periods with dominant strike slip and dip slip shearing along with layer parallel shortening and extension post seismic and inter seismic periods had suffered simultaneous subduction perpendicular extension and contraction leading to transtension and transpression deformational environments respectively occurrence of earthquakes during post and inter seismic periods were results of interplay between simple shear and pure shear components of the strain matrix

the motion and active deformation of india measurements of surface displacements using gps constrain the motion and deformation of india and india eurasia plate boundary deformation along the himalaya the gps velocities of plate interior sites constrain the pole of the angular velocity vector of india with respect to eurasia to lie at 25 6 1 0 n 11 1 9 0 e approximately 6 west of the nuvel 1a pole of 3 ma plate motion the angular rotation rate of 0 44 0 03 myr 1 is 14 slower than the long term rate of 0 51 myr 1 insignificant velocities between plate interior sites indicate that the exposed indian plate is stable to within 7 10 9 yr 1 the observed contraction vector across the himalaya 20 mm yr veers from n20 e in the northwest himalaya to n25 w in east nepal consistent with east west extension of southern tibet

early cenozoic crust at the norwegian continental margin and the conjugate jan mayen ridge multichannel seismic profiles at the voring plateau margin off norway and the northern jan mayen ridge have provided a framework for the early tertiary evolutionary history of these areas which were adjacent prior to the opening of the norwegian sea we propose that their paleogene evolution is quite similar and that the two acoustic basement reflectors ee and jo were formed in the early eocene by extrusion of flow basalts from the time of opening to about anomaly 23 time oceanic seafloor was generated by icelandic type spreading during that time the central jan mayen fracture was the main transform the seaward dipping reflector sequences are flow basalts generated by the icelandic spreading the existence of less well developed dipping sequences seaward of the primary ones probably reflects that these regions submerged later because of higher initial elevation during the early eocene subaerial spreading episode which is related to the north atlantic volcanic province basalt flows also covered the adjacent thinned and heavily intruded continental crust it is proposed that the continent ocean boundary is located just landward of anomaly 24b a short distance seaward of the voring plateau escarpment reflector k is only recognized landward of this boundary in a region of transitional crust the escarpment experienced syndepositional faulting and the most elevated parts of the voring marginal high did not subside below shallow water depths before oligocene miocene time we suggest that the voring margin and the jan mayen ridge represent volcanic passive margins the evolution of this margin type may relate to initial uplift due to rifting in previously thinned crust

a comprehensive model of postseismic deformation of the 2004 sumatra andaman earthquake deduced from gps observations in northern sumatra abstract we investigate the postseismic deformation of the 2004 sumatra andaman earthquake sae using 5 years of global positioning system gps data located in northern sumatra continuous gps data from northern sumatra suggest that the relaxation time in the vertical displacement is longer than horizontal displacements this implies that there are multiple physical mechanisms that control the postseismic deformation which refer to afterslip and viscoelastic relaxation in this study we introduce an analysis strategy of postseismic deformation to simultaneously calculate multiple mechanisms of afterslip and viscoelastic relaxation the afterslip inversion results indicate that the distribution of the afterslip and the coseismic slip are compensatory of each other also afterslip has a limited contribution to vertical deformation in northern sumatra in our rheology model we use a gravitational maxwell viscoelastic response and the result indicates that the elastic layer thickness is 65 5 km and the maxwell viscosity is 8 0 1 0 1018 pa s we find that afterslip plus maxwell viscoelastic relaxation are appropriate to explain the deformation in northern sumatra we also find that our rheology model reproduces the long term features of the gps time series in thailand applying our rheology model to the data in andaman islands our afterslip estimation is located at the down dip part of the plate boundary finally we showed that our rheology model is applicable to the gps datasets of postseismic deformation of the 2004 sae located in northern sumatra thailand and andaman nicobar respectively

spatial and temporal distribution of deformation at the front of the andean orogenic wedge in southern bolivia new observations from an active orogenic wedge help link the seismotectonic behavior of individual faults to wedge deformation rates and patterns over multiple timescales we provide the first detailed constraints on the distribution and timing of deformation at the front of the andean orogenic wedge in southern bolivia where a recent study suggests that great mw 8 earthquakes could rupture the master fault underlying the wedge we use stratigraphic relationships across fault related folds and elastic dislocation modeling of seismic reflection horizons to obtain probabilistic estimates of wedge front fault ages and slip rates our analyses reveal that at least half of the previously determined gps based wedge loading and quaternary whole wedge shortening rates are absorbed across a 20 40 km wide wedge front zone consisting of 1 4 en echelon and partially to fully overlapping faults and folds associated with blind thrust faults the difference between our slip rates and the geodetic geologic observations combined with evidence for activity across internal wedge structures supports the notion that nonsteady state mass balance conditions coupled with elevated erosional efficiency result in distributed wedge deformation the orogenic wedge in southern bolivia behaves in a similar fashion to the taiwanese and himalayan ranges slip accumulates at downdip locations along the master fault and is released incrementally by earthquakes that rupture the wedge front fault zone the faults and folds comprising this zone pose a major source of seismic hazard accumulating slip is also released in the wedge interior and older internal wedge faults must be considered in any future assessment of regional earthquake risk

implications of deformation following the 2002 denali alaska earthquake for postseismic relaxation processes and lithospheric rheology 1 during the first 2 years following the 2002 mw 7 9 denali alaska strike slip earthquake a large array of global positioning system gps receivers recorded rapid postseismic surface motions extending at least 300 km from the rupture and at rates of more than 100 mm yr in the near field here we use three dimensional 3 d viscoelastic finite element models to infer the mechanisms responsible for these postseismic observations we consider afterslip both from an inversion of gps displacements and from stress driven forward models poroelastic rebound and viscoelastic flow in the lower crust and upper mantle several conclusions can be drawn 1 no single mechanism can explain the postseismic observations 2 significant postseismic flow below a depth of 60 km is required to explain observed far field motions best explained by a weak upper mantle with a depth dependent effective viscosity that ranges from 1019 pa s at the moho 50 km depth to 3 4 1018 pa s at 100 km depth 3 shallow afterslip within the upper crust occurs adjacent to and beneath the regions of largest coseismic slip 4 there is a contribution from deformation in the middle and lower crust from either lower crustal flow or stress driven slip afterslip is preferred over broad viscoelastic flow owing to the existence of seismic velocity discontinuities across the fault at depth though our modeling does not favor either mechanism if the process is viscoelastic relaxation the viscosity is a factor of 3 greater than the inferred mantle viscosity 5 poroelastic rebound probably contributed to the observed postseismic deformation in the immediate vicinity of the denali totschunda junction these conclusions lead us to infer an alaskan mechanical lithosphere that is about 60 km thick overlying a weak asthenosphere and a denali fault that cuts through the entire lithosphere with shear accommodated by faulting in the top 20 km and time dependent aseismic shear below

geodetic imaging of coseismic slip and postseismic afterslip sparsity promoting methods applied to the great tohoku earthquake 1 geodetic observations of surface displacements during and following earthquakes such as the march 11 2011 great tohoku earthquake can be used to constrain the spatial extent of coseismic slip and postseismic afterslip and characterize the spectrum of earthquake cycle behaviors slip models are often regularized by assuming that slip on the fault varies smoothly in space which may result in the artificial smearing of fault slip beyond physical boundaries alternatively it may be desirable to estimate a slip distribution that is spatially compact and varies sharply here we show that sparsity promoting state vector regularization methods can be used to recover slip distributions with sharp boundaries representing an alternative end member result to very smooth slip distributions using onshore gps observations at 298 stations during and in the 2 weeks following the tohoku earthquake we estimate a band of coseismic slip between 30 and 50 km depth extending 500 km along strike with a maximum slip of 64 m corresponding to a minimum magnitude estimate of mw 8 8 our estimate of afterslip is located almost exclusively down dip of the coseismic rupture with a transition between 40 and 50 km depth and an equivalent moment magnitude mw 8 2 this depth may be interpreted as coincident with the transition from velocity strengthening to velocity weakening frictional behavior consistent with the upper limit of cold subduction estimates of the thermal structure of the japan trench

the mechanism of postseismic deformation triggered by the 2006 2007 great kuril earthquakes received 21 january 2011 accepted 15 february 2011 published 24 march 2011 1 in 2006 2007 a doublet of great earthquakes mw 8 struck in the center of the kuril subduction zone a thrust event followed by an extensional event our observations of the kuril gps array in 2006 2009 outline a broad zone of postseismic deformation with initial horizontal velocities to 90 mm a and postseismic uplift we show that most of the postseismic signal after the great kuril doublet is caused by the viscoelastic relaxation of shear stresses in the weak asthenosphere with the best fitting maxwell viscosity in the range of 5 10 10 17 pa s an order of magnitude smaller than was estimated for several subduction zones we predict that the postseismic deformation will die out in about a decade after the earthquake doublet our results suggest large variations among subduction zones in the asthenospheric viscosity one of the most important rheological parameters citation kogan m g n f vasilenko d i frolov j t freymueller g m steblov b w levin and a s prytkov 2011 the mechanism of postseismic deformation triggered by the 2006 2007 great kuril earthquakes geophys res lett 38 l06304 doi 10 1029 2011gl046855

seismicity and seismotectonics of norway and nearby continental shelf areas the earthquake activity of norway and nearby offshore areas is low to intermediate with few events above magnitude 5 recent significant improvements in instrumental coverage in parallel with a better utilization of older including historical data have shown that the seismicity in the south is predominantly confined to the coastal areas and to the viking graben while from the northern north sea to svalbard the earthquakes in a broad sense follow the continental margin fifty one focal mechanism solutions from these areas about half of them new reveal stress directions that clearly indicate a connection to the plate tectonic ridge push force at least for the areas at a minimum distance from the continental margin along the margin stress directions also indicate a possible connection to postglacial uplift as well as to lithospheric loading effects a dominance of normal faulting on the landward side and reverse faulting on the oceanic side agrees with this interpretation on a regional level the seismicity in these areas correlate quite well with geologic features such as grabens fault zones fault complexes fracture zones and the margin itself indicating that these structures act in a general sense as weakness zones in the presence of a regionally more stable stress field in the northern north sea however an area with quite anomalous stress orientations with strike slip faulting is found in a region transitional between normal and reverse faulting most of the earthquake foci are confined to the presumably brittle parts of the crust but many events are also located quite close to and on both sides of the moho discontinuity

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

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

gps measurements of postseismic deformation in the andaman nicobar region following the giant 2004 sumatra andaman earthquake 1 we report gps measurements of postseismic deformation from 22 campaign mode and one continuous gps sites in the andaman nicobar region following the great sumatra andaman earthquake of 26 december 2004 large horizontal displacements toward west to southwest varying in magnitude from 10 to 40 cm and with uplift reaching 16 cm occurred in the region in the first year after the earthquake the observed motion decreased logarithmically in the subsequent year we suggest that in the andaman region frictional afterslip occurred farther downdip of the coseismic rupture while in the little andaman and nicobar regions the coseismic rupture and afterslip patch partly overlapped the afterslip was mostly aseismic and did not contribute to the aftershocks the aftershocks and postseismic displacements appear to follow a similar relationship although with different decay times the temporal dependence of the two differs only by a term linear in time thus the temporal evolution of the afterslip seems to be consistent with a mechanism governed by frictional afterslip available rates of interseismic and postseismic deformation and coseismic static offsets allow us to approximately estimate a return period of about 400 years for great earthquakes in the andaman region

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

dc resistivity measurements of model saline ice sheets the dc resistivity structure of an artificially grown saline ice sheet at various stages of growth thermal modification and desalination has been determined by finding layered models to best fit schlumberger array sounding data values between 2 and 90 were obtained for model layers varying from 2 to 200 o brine volume after a strong warming and cooling cycle following 32 cm growth the average resistivity had decreased by a factor of about 2 despite the brine volume having also decreased by nearly a factor of 2 this change with age plus the variability in the resistivity values implies that no simple correlation exists between brine volume and resistivity because permeability which is related to age and temperature is also a strong factor the low resistivity values measured show that resistivity will strongly affect microwave radiometric emissions from young or warm sea ice

postseismic deformation of the andaman islands following the 26 december 2004 great sumatra andaman earthquake 1 two years after the great sumatra andaman earthquake the 3 1 m wsw coseismic displacement at port blair andaman islands had increased by 32 cm postseismic uplift initially exceeded 1 cm per week and decreased to 1 mm week by 2007 points near port blair had risen more than 20 cm a 24 reversal of coseismic subsidence uplift at eight gps sites suggests a gradual eastward shift of the coseismic neutral axis separating subsidence from uplift simulations of the gps postseismic displacements as viscoelastic relaxation of coseismic stress change and as slip on the plate interface indicate that slip down dip of the seismic rupture dominates near field deformation during the first two years postseismic slip beneath the andaman islands released moment equivalent to a magnitude mw 7 5 earthquake and the distribution suggests deep slip in the stable frictional regime accelerated to catch up to the coseismic rupture

slow slip acceleration beneath andaman islands triggered by the 11 april 2012 indian ocean earthquakes the m w 8 6 and 8 2 strike slip earthquakes that struck the northeast indian ocean on 11 april 2012 resulted in coseismic deformation both at near and distant sites the slip distribution deduced using seismic wave analysis for the orthogonal faults that ruptured during these earthquakes is sufficient to predict the coseismic displacements at the global positioning system gps sites such as ntus palk and cusv but fall short at four continuous sites in the andaman islands region slip modeling for times prior to the events suggests that the lower portion of the thrust fault beneath the andaman islands has been slipping at least at the rate of 40 cm yr in response to the 2004 sumatra andaman coseismic stress change modeling of gps displacements suggests that the en echelon and orthogonal fault ruptures of the 2012 intraplate oceanic earthquakes could have possibly accelerated the ongoing slow slip along the lower portion of the thrust fault beneath the islands with a month long slip of 4 10 cm the misfit to the coseismic gps displacements along the andaman islands could be improved with a better source model assuming that no local process contributed to this anomaly

viscoelastic behavior of the crust around the longmenshan thrust belt inferred from post seismic deformation of the 2013 lushan earthquake china abstract seven continuous gps stations are located on the hanging wall of the longmenshan thrust belt and post seismic deformation data of the 2013 lushan earthquake have been recorded for nearly four years following the earthquake we transform the data from a global reference frame to the south china block reference frame and then the secular motion and post seismic deformation of the wenchuan earthquake are excluded using an exponential fit model based on our results the viscosities of the low velocity zone at a depth of 25 km and of the middle and lower crust around the longmenshan thrust belt are obtained as 2 75 10 17 p a s and 2 56 10 18 p a s respectively the post seismic rebound which was observed near the lushan epicenter may represent the occurrence of overslip during the earthquake the more complex structural style may have produced weaker fault activity along the southern segment of the longmenshan thrust belt than along its middle and northern segments

postseismic grace and gps observations indicate a rheology contrast above and below the sumatra slab more than 7 years of observations of postseismic relaxation after the 2004 sumatra andaman earthquake provide an improving view on the deformation in the wide vicinity of the 2004 rupture we include both gravity recovery and climate experiment grace gravity field data that show a large postseismic signal over the rupture area and gps observations in the back arc region with increasing time gps and grace show contrasting relaxation styles that were not easily discernible on shorter time series we investigate whether mantle creep can simultaneously explain the far field surface displacements and the long wavelength gravity changes we interpret contrasts in the temporal behavior of the gps grace observations in terms of lateral variations in rheological properties of the asthenosphere below and above the slab based on 1 d viscoelastic models our results support an almost order of magnitude contrast between oceanic lithosphere viscosity and continental viscosity which likely means that the low viscosities frequently found from postseismic deformation after subduction earthquakes are valid only for the mantle wedge next to mantle creep we also consider afterslip as an alternative mechanism for postseismic deformation we investigate how the combination of grace and gps data can better discriminate between different mechanisms of postseismic relaxation distributed deformation mantle creep versus localized deformation afterslip we conclude that the grace observed gravity changes rule out afterslip as the dominant mechanism explaining long wavelength deformation even over the first year after the event

rupture and variable coupling behavior of the mentawai segment of the sunda megathrust during the supercycle culmination of 1797 to 1833 we refer to periods of subduction strain accumulation beneath the mentawai islands sumatra as supercycles because each culminates in a series of partial ruptures of the megathrust in its final decades the finale of the previous supercycle comprised two giant earthquakes in 1797 and 1833 and whatever happened in between this behavior between two great ruptures has implications for how the megathrust will behave between its more recent partial failure during the m w 8 4 earthquake of 2007 and subsequent large ruptures we synthesize previously published coral microatoll records and a large new coral data set to constrain not only these two giant ruptures but also the intervening interseismic megathrust behavior we present detailed maps of coseismic uplift during the two earthquakes and of interseismic deformation during the periods 1755 1833 and 1950 2000 as well as models of the corresponding slip and coupling on the underlying megathrust the large magnitudes we derive m w 8 6 8 8 for 1797 and m w 8 8 8 9 for 1833 confirm that the 2007 earthquakes released only a fraction of the moment released during the previous rupture sequence whereas megathrust behavior leading up to the 1797 and 2007 earthquakes was similar and comparatively simple behavior between 1797 and 1833 was markedly different and more complex several patches of the megathrust became weakly coupled following the 1797 earthquake we conclude that while major earthquakes generally do not involve rupture of the entire mentawai segment they may significantly change the state of coupling on the megathrust for decades to follow influencing the progression of subsequent ruptures

poroelastic rebound along the landers 1992 earthquake surface rupture maps of surface displacement following the 1992 landers california earthquake generated by interferometric processing of ers 1 synthetic aperture radar sar images reveal effects of various postseismic deformation processes along the 1992 surface rupture the large scale pattern of the postseismic displacement field includes large lobes mostly visible on the west side of the fault comparable in shape with the lobes observed in the coseismic displacement field this pattern and the steep displacement gradient observed near the emerson camp rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture models show that horizontal slip occurring on a buried dislocation in a poisson s material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10 20 km from the fault yet this pattern is not observed in the postseismic interferograms as previously proposed to explain local strain in the fault step overs peltzer et al 1996b we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault compensating the vertical ground shift produced by fault afterslip such a rebound is explained by the gradual change of the crustal rocks poisson s ratio value from undrained coseismic to drained postseismic conditions as pore pressure gradients produced by the earthquake dissipate using the poisson s ratio values of 0 27 and 0 31 for the drained and undrained crustal rocks respectively elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the sar data and the horizontal displacement measured at global positioning system gps sites along a 60 km long transect across the emerson fault savage and svarc 1997 using a detailed surface slip distribution on the homestead valley kickapoo and johnson valley faults we modeled the poroelastic rebound in the homestead valley pull apart a poisson s ratio value of 0 35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3 5 years following the earthquake this large value implies a seismic velocity ratio vp vs of 2 1 consistent with the observed low vs values of fault zone guided waves at shallow depth li et al 1997 the sar data also reveal postseismic creep along shallow patches of the eureka peak and burnt mountain faults with a characteristic decay time of 0 8 years coseismic dilatant hardening locking process followed by post seismic pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault

a unified gps based earthquake catalog for the sumatran plate boundary between 2002 and 2013 we have compiled the first self consistent gps based earthquake catalog for the sumatran plate boundary using continuous daily position time series from the sumatran gps array sugar we document 30 earthquakes which occurred within or outside the sugar network from august 2002 through the end of 2013 and we provide estimates of both vertical and horizontal coseismic offsets associated with 1 m9 2 3 m8 6 m7 19 m6 and 1 m5 9 earthquakes as well as postseismic decay amplitudes and times associated with 9 m 7 earthquakes and 1 m6 7 earthquake for most of the previously studied earthquakes our geodetic catalog provides more complete coseismic displacements than those published showing consistent patterns of motion across a large range of distances for many of the moderate to large earthquakes we publish their coseismic displacements for the first time providing new constraints on their locations and slip distributions for the postseismic time series we have tackled the challenge of separating the signals for individual events from the overlapping effects of many other earthquakes as a result we have obtained either new or much longer time series than previously published based on our long time series we find logarithmic decay times ranging from several days to more than 20 years and sometimes a second decay time is needed suggesting that when studying large to great sumatran earthquakes we need to consider multiple postseismic mechanisms our geodetic catalog provides rich spatial and temporal sumatran earthquake cycle information for future studies of the physics and dynamics of the sumatran plate boundary

2008 little andaman aftershock genetic linkages with the subducting 90 e ridge and 2004 sumatra andaman earthquake we analyse the june 27 2008 little andaman aftershock mw 6 6 of december 26 2004 sumatra andaman earthquake mw 9 2 that occurred near the trench in the subducting india plate beneath the sunda plate unlike majority of the other aftershocks in the frontal arc the little andaman aftershock and its own aftershocks occurred through normal slip on the north south oriented steep planes we use the coseismic and ongoing postseismic deformation due to the 2004 sumatra andaman earthquake at a gps site nearest to the little andaman aftershock and compute changes in the coulomb stresses due to the coseismic slip and postseismic afterslip the coulomb stress on the little andaman aftershock fault plane progressively increased since the 2004 sumatra andaman earthquake which probably led to the occurrence of the little andaman aftershock on the pre existing n s oriented strike slip steep planes of the subducting 90 e ridge that were reactivated through normal slip

andaman postseismic deformation observations still slipping after all these years more than six years after the great m w 9 2 sumatra andaman earthquake postevent processes responsible for relaxation of the coseismic stress change remain controversial modeling of andaman islands global positioning system gps displacements indicated early near field motions were dominated by slip down dip of the rupture but various researchers ascribe elements of relaxation to dominantly poroelastic dominantly viscoelastic and dominantly fault slip processes depending primarily on their measurement sampling and modeling tools used after subtracting a pre 2004 interseismic velocity significant transient motion during the 2008 5 2010 5 epoch confirms that postseismic relaxation processes continue in andaman modeling three component velocities as viscoelastic flow yields a weighted root mean square wrms misfit that always exceeds the wrms of the measured signal 26 3 mm yr the best fitting models are those that yield negligible deformation indicating the model parameters have no real physical meaning gps velocities are well fit wrms 4 0 mm yr by combining a viscoelastic flow model that best fits the horizontal velocities with 50 cm yr thrust slip down dip of the coseismic rupture both deep slip and flow respond to stress changes and each can significantly change stress in the realm of the other it therefore is reasonable to expect that both transient deep slip and viscoelastic flow will influence surface deformation long after a great earthquake

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

short term pre 2004 seismic subsidence near south andaman is this a precursor slow slip prior to a megathrust earthquake abstract we report here on the campaign gps data from the andaman islands just previous to the great 2004 sumatra andaman earthquake the campaign mode acquisitions at port blair showed that the site started to subside between 2003 and 2004 in addition during this period the horizontal displacement of port blair with respect to indian plate deduced from 1996 to 2000 gps data changed its orientation to that obtained during the 26th dec 2004 co seismic this short term subsidence can be modeled as slip in the up dip portion of the fault a slip that is equivalent to an earthquake with moment magnitude of 6 3 previously slow slip was thought to appear at intermediate depths roughly 35 55 km but simple models of the deformation at this single site suggest slow slip at much shallower depth than this this observation of subsidence obtained by gps methods is in rough agreement with subsidence observed from tide gauge data campaign mode gps data between 1996 and 2000 suggest uplift for port blair during the inter seismic period and so does the reported field observations of interseismic micro atoll emergence lack of exposed land with gps stations along the southern part of the thrust fault deprive of arriving at any indication of this preseismic subsidence in those areas although gps data is lacking the geological indices reported from some sites on the alaskan coast for example imply short term subsidence just previous to the great 1964 earthquake the pre earthquake subsidence recorded in port blair therefore may have global implications as a precursor signal of great earthquakes at least along some of the subduction zones

stress and seismicity changes on the sunda megathrust preceding the 2007 mw 8 4 earthquake abstract the bengkulu m w 8 4 earthquake on 12 september 2007 close in time and space to the 2004 m w 9 2 sumatra andaman and 2005 m w 8 7 nias megathrust events suggests that it could be a triggered earthquake it was located in the southern portion of the historic 1833 m w 8 9 rupture however it appears perplexing that the portion of the sunda subduction zone between the nias and bengkulu rupture patches which last ruptured in a 1797 m w 8 7 event did not recur first coulomb failure stress cff modeling of the 2004 and 2005 megathrust earthquakes and subsequent postseismic relaxation processes fails to explain why the 2007 patch ruptured before the northern 1797 segment surprisingly the much smaller 2000 m w 8 0 enggano earthquake produced a much larger positive cff change at the 2007 hypocenter and may help to explain the southern location of the 2007 earthquake investigation of changes in seismicity rates in the region following the 2004 2005 events shows that the megathrust earthquakes may have dynamically triggered slip near the northern end of the 2007 rupture zone a large increase in seismicity levels following the 2000 earthquake may also have influenced the eventual initiation point of the 2007 earthquake regrettably the section of the sunda megathrust near siberut that last ruptured in 1797 still poses a great seismic hazard to the region as the only segment not to have ruptured in the sequence of twenty first century megathrust earthquakes

crustal motion in the zone of the 1960 chile earthquake detangling earthquake cycle deformation and forearc sliver translation temporary deformation in great earthquake cycles and permanent shear deformation associated with oblique plate convergence both provide critical clues for understanding geodynamics and earthquake hazard at subduction zones in the region affected by the mw 9 5 great chile earthquake of 1960 we have obtained gps observations that provide information on both types of deformation our velocity solutions for the first time span the entire latitudinal range of the 1960 earthquake the new observations revealed a pattern of opposing roughly arc normal motion of coastal and inland sites consistent with what was reported earlier for the northern part of this region this finding supports the model of prolonged postseismic deformation as a result of viscoelastic stress relaxation in the mantle the new observations also provide the first geodetic evidence for the dextral motion of an intravolcanic arc fault system and the consequent northward translation of a forearc sliver the sliver motion can be modeled using a rate of 6 5 mm a accommodating about 75 of the margin parallel component of nazca south america relative plate motion with the rate diminishing to the north furthermore the new gps observations show a southward decrease in margin normal velocities of the coastal area we prefer explaining the southward decrease in terms of changes in the width or frictional properties of the megathrust seismogenic zone because of the much younger age of the subducting plate and warmer thermal regime in the south the currently locked portion of the plate interface may be narrower using a three dimensional viscoelastic finite element model of postseismic and interseismic deformation following the 1960 earthquake we demonstrate that this explanation although not unique is consistent with the gps observations to the first order

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

a bayesian source model for the 2004 great sumatra andaman earthquake the 2004 m w 9 1 9 3 sumatra andaman earthquake is one of the largest earthquakes of the modern instrumental era despite considerable efforts to analyze this event the different available observations have proven difficult to reconcile in a single finite fault slip model in particular the critical near field geodetic records contain variable and significant postseismic signal between 2 weeks and 2 months worth while the satellite altimetry records of the associated tsunami are affected by various sources of uncertainties e g source rupture velocity and mesoscale oceanic currents in this study we investigate the quasi static slip distribution of the sumatra andaman earthquake by carefully accounting for the different sources of uncertainties in the joint inversion of available geodetic and tsunami data to this end we use nondiagonal covariance matrices reflecting both observational and modeling uncertainties in a fully bayesian inversion framework modeling errors can be particularly large for great earthquakes here we consider a layered spherical earth for the static displacement field nonhydrostatic equations for the tsunami and a 3 d megathrust interface geometry to alleviate some of the potential epistemic uncertainties the bayesian framework then enables us to derive families of possible models compatible with the unevenly distributed and sometimes ambiguous measurements we infer two regions of high fault slip at 3 n 4 n and 7 n 8 n with amplitudes that likely reach values as large as 40 m and possibly larger these values are a factor of 2 larger than typically found in previous studies potentially an outcome of commonly assumed forms of regularization finally we find that fault rupture very likely involved shallow slip within the resolution provided by the existing data we cannot rule out the possibility that fault rupture reached the trench

microfossils from coastal environments as indicators of paleo earthquakes tsunamis and storms abstract coastal risk assessment and hazard mitigation require datasets on centennial and millennial temporal scales to capture natural variability and multiple occurrences of the largest but least frequent events coastal sediments from low energy depositional environments archive geologic evidence of paleo earthquakes tsunamis and storms many of the best reconstructions of these events are derived from changes in microfossil diatoms foraminifera and pollen assemblages in this review we explain how microfossils are used to reconstruct records of paleoearthquakes by quantifying the amount of coseismic and interseismic vertical land movements along tectonically active coastlines examples from the united states alaska and the pacific northwest japan and chile show that microfossil based transfer functions may provide continuous records of vertical land movement during earthquake deformation cycles we discuss how microfossil habitat preferences and taphonomic character are used to constrain sediment provenance e g beach nearshore or offshore sources and identify overwash deposits and how this information can be used to reconstruct the recurrence of tsunamis and storms analysis of overwash deposits from thailand and malaysia indicates the ability of microfossils to resolve individual waves within tsunami sediments and an example from the sendai coastal plain in japan uses foraminifera to ascribe a beach to nearshore provenance for the 2011 tohoku tsunami deposit finally we present recent examples from the gulf of mexico on the use of foraminifera to estimate the volume and distance of transport of storm overwash from hurricanes

upper mantle rheology from grace and gps postseismic deformation after the 2004 sumatra andaman earthquake 1 mantle rheology is one of the essential yet least understood material properties of our planet controlling the dynamic processes inside the earth s mantle and the earth s response to various forces with the advent of grace satellite gravity measurements of mass displacements associated with many processes are now available in the case of mass displacements related to postseismic deformation these data may provide new constraints on the mantle rheology we consider the postseismic deformation due to the m w 9 2 sumatra 26 december 2004 and m w 8 7 nias 28 march 2005 earthquakes applying wavelet analyses to enhance those local signals in the grace time varying geoids up to september 2007 we detect a clear postseismic gravity signal we supplement these gravity variations with gps measurements of postseismic crustal displacements to constrain postseismic relaxation processes throughout the upper mantle the observed gps displacements and gravity variations are well explained by a model of visco elastic relaxation plus a small amount of afterslip at the downdip extension of the coseismically ruptured fault planes our model uses a 60 km thick elastic layer above a viscoelastic asthenosphere with burgers body rheology the mantle below depth 220 km has a maxwell rheology assuming a low transient viscosity in the 60 220 km depth range the grace data are best explained by a constant steady state viscosity throughout the ductile portion of the upper mantle e g 60 660 km this suggests that the localization of relatively low viscosity in the asthenosphere is chiefly in the transient viscosity rather than the steady state viscosity we find a 8 10 18 pa s mantle viscosity in the 220 660 km depth range this may indicate a transient response of the upper mantle to the high amount of stress released by the earthquakes to fit the remaining misfit to the grace data larger at the smaller spatial scales cumulative afterslip of about 75 cm at depth should be added over the period spanned by the grace models it produces only small crustal displacements our results confirm that satellite gravity data are an essential complement to ground geodetic and geophysical networks in order to understand the seismic cycle and the earth s inner structure

concentrated earthquake zones in svalbard abstract data from a network of seven telemetered and three portable seismic stations operating in the summer of 1979 delineate two concentrated east west trending zones of seismicity in the svalbard archipelago one zone in heer land spitsbergen which has been described previously shows left lateral strike slip movements along a vertical wnw ese striking fault another zone in nordaustlandet reported here for the first time has similar strike direction and dimensions as the heer land zone but differs significantly with regard to its recurrence pattern zones of concentrated intraplate earthquakes appear to be prevalent on the landward side of continental margins in arctic regions the seismicity in these zones can be explained as the interaction of a regional stress field of plate tectonic origin with local zones of weakness

suppression of earthquakes by large continental ice sheets the interior regions of antarctica and greenland are aseismic no earthquake larger than body wave magnitude 4 5 5 0 is known for either except along coastal zones or continental shelves here i advance an explanation for this lack of seismic activity in terms of pressure effects produced by the continental ice sheets that mantle both continents

spectral finite element approach to post seismic relaxation in a spherical compressible earth application to gravity changes due to the 2004 sumatra andaman earthquake

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

poroelastic stress triggering of the 2005 m8 7 nias earthquake by the 2004 m9 2 sumatra andaman earthquake abstract the m9 2 sumatra andaman earthquake sae occurred three months prior to the m8 7 nias earthquake ne we propose that the ne was mechanically triggered by the sae and that poroelastic effects were a major component of this triggering this study uses 3d finite element models fems of the sumatra andaman subduction zone sasz to predict the deformation stress and pore pressure fields of the sae the coseismic slip distribution for the sae is calibrated to near field gps data using fem generated green s functions and linear inverse methods the calibrated fem is then used to predict the postseismic poroelastic contribution to stress triggering along the rupture surface of the ne which is adjacent to the southern margin of the sae the coseismic deformation of the sae combined with the rheologic configuration of the sasz produces two transient fluid flow regimes having separate time constants sae coseismic pore pressures in the relatively shallow forearc and volcanic arc regions within a few km depth dissipate within one month after the sae however pore pressures in the oceanic crust of the down going slab persist several months after the sae predictions suggest that the sae initially induced mpa scale negative pore pressure near the hypocenter of the ne this pore pressure slowly recovered increased during the three month interval separating the sae and ne due to lateral migration of pore fluids driven by coseismic pressure gradients within the subducting oceanic crust because pore pressure is a fundamental component of coulomb stress the mpa scale increase in pore pressure significantly decreased stability of the ne fault during the three month interval after the sae and prior to rupture of the ne a complete analysis of stress triggering due to the sae must include a poroelastic component failure to include poroelastic mechanics will lead to an incomplete model that cannot account for the time interval between the sae and ne our transient poroelastic model explains both the spatial and temporal characteristics of triggering of the ne by the sae