the 2005 and 2010 earthquakes on the sumatra andaman trench evidence for post 2004 megathrust intraplate rejuvenation great earthquakes on oblique subduction zones accommodate slip on strike slip faults on the overriding and subducting plates leading to increased intraplate seismicity after the 2004 sumatra earthquake there was an increase in activity in the wharton basin wb which is considered to be part of a diffuse plate boundary here the intraplate deformation occurs in response to northwest southeast directed compression as opposed to the north northeast south southwest directed plate motion along the sumatra andaman subduction zone earthquakes here mostly occur by left lateral strike slip on north south n s trending fossil fractures although ruptures on east west planes are not uncommon here we discuss the 24 july 2005 m w 7 2 and the 12 june 2010 m w 7 5 earthquakes both of which were left lateral strike slip events sourced in the northern wb our source models for these events based on teleseismic waveform inversion favor slip on the n s fossil fracture systems consistent with previous studies in the wb although the former sourced at similar to 16 km depth was not tsunamigenic the latter similar to 34 km triggered a small tsunami possibly due to its oblique slip at similar to 5 km depth we use conceptual models of plate deformation to suggest that both these events have resulted from post 2004 redistribution of stresses and rejuvenation of intraslab fracture systems within the wb an actively deforming oceanic intraplate region

reassessment of the 1907 sumatra tsunami earthquake based on macroseismic seismological and tsunami observations and modeling on 4 january 1907 an earthquake occurred off the west coast of sumatra indonesia with an instrumental surface wave magnitude ms in the range of 7 5 8 0 at periods of 40 s the tsunami it generated was destructive on the islands of nias and simeulue where it killed hundreds and gave rise to the legend of the s mong this tsunami was also observed in other parts of the indian ocean basin relative to its instrumented magnitude the size of the tsunami was anomalous qualifying the event as a tsunami earthquake however unusually for a tsunami earthquake the shaking on nias was severe 7 ems we revisit the 1907 earthquake with a multidisciplinary approach by extracting evidence describing shaking effects or the tsunami from written documents and by acquiring new seismograms combining these we discriminate two large earthquakes within an hour of each other with clear differences in seismological character the first we interpret to be a tsunami earthquake with characteristic low levels of shaking an estimated average seismic moment m0 of 2 5 1028 dyn cm mw 8 2 in the frequency band 6 8 mhz and an epicentral location close to the front of the sunda megathrust the seismograms we analyzed also document a regular growth of moment with period approaching mw 8 4 at the longest resolvable period 170 s for the second earthquake that caused damage on nias we estimate ms 7 based on seismograms and phase data we also identify two ms 6 aftershocks within 24 h of the mainshock additionally we present a dataset of 88 locations within the indian ocean basin where the tsunami was observed using a subset of these we forward modeled the tsunami to propose a seismic rupture model extending along the sunda megathrust for about 220 km 94 7 e to 97 e with a maximum modeled slip of 21 m our new rupture model provides an acceptable fit to our new dataset of tsunami runup and inundation values from 88 local and far field locations in the indian ocean basin we also urge caution against an over reliance on the s mong legend for tsunami evacuation as its premise that a tsunami will only follow an earthquake with very severe ground motions is rendered ineffective for tsunami earthquakes

broad band deconvolution of gdsn data summary advances in the theory of wave propagation and source mechanism have coincided with the recent deployment of a global network of digitally recording seismographs the gdsn global digital seismograph network we demonstrate that broad band records of body wave ground displacement and velocity with spectral information from several hertz to tens of seconds can be obtained by the simultaneous deconvolution of the long and short period components of the gdsn seismographs frequency dependent effects in body waves that may arise from source complexity or from propagation through the earth are much more apparent and measurable in the broad band records than in the original seismograms

temporal variation of large intraplate earthquakes in coupled subduction zones the focal mechanisms of intraplate earthquakes within subducting lithosphere are frequently used to infer large scale stress regimes induced by slab pull bending or unbending and lateral segmentation and undulations of the slab numerous studies have further postulated that the intraplate activity is influenced by transitory regional stress regimes such as those associated with interplate thrust events temporal variations of the latter type may potentially play an important role in assessing regions of uncertain seismic potential and possibly even in earthquake forecasting a systematic analysis of 1130 focal mechanisms for intraplate earthquakes with m b 5 0 in the depth range 0 300 km is conducted for nine circum pacific subduction zones all of which are known to have large interplate thrust events the spatial and temporal relationships of the earthquakes within the subducting slab to the large thrust events in each region are appraised the earthquake catalog assembled contains all published focal mechanisms and is probably complete for m b 6 5 for the years 1963 1986 for many of the localized regions considered in detail the catalog is complete to lower thresholds of m b 6 0 or m b 5 5 this analysis provides compelling evidence for a temporal link between large interplate thrust activity and intraplate seismicity for the seismically coupled regions considered here outer rise compressional events have occurred prior to several large thrust events or are associated with seismic gaps while outer rise tensional events generally only follow interplate ruptures in the intermediate depth range large down dip tensional events generally precede interplate thrusts and are often concentrated at the down dip edge of the coupled zone a transition to down dip compressional stress or diminished tensional activity at intermediate depth is observed after several large thrust events e g 1960 chile 1974 peru 1957 aleutian 1971 new britain these examples support the notion that the intraplate stress environment responds viscoelastically to the temporally varying interplate stress regime assuming that this concept is correct the seismic potential of several seismic gaps is considered on the basis of both outer rise and intermediate depth earthquake activity

petrophysical inversion of borehole array induction logs part i numerical examples we have developed a new methodology for the quantitative petrophysical evaluation of borehole array induction measurements the methodology is based on the time evolution of the spatial distributions of fluid saturation and salt concentration attributed to mud filtrate invasion we use a rigorous formulation to account for the physics of fluid displacement in porous media resulting from water base mud filtrate invading hydrocarbon bearing rock formations borehole array induction measurements are simulated in a coupled mode with the physics of fluid flow we use inversion to estimate parametric 1d distributions of permeability and porosity that honor the measured array induction logs as a byproduct the inversion yields 2d axial symmetric spatial distributions of aqueous phase saturation salt concentration and electrical resistivity we conduct numerical inversion experiments using noisy synthetic wireline logs the inversion requires a priori knowledge of several mud petrophys ical and fluid param

an approximate 3d inversion method for inversion of single well induction logging responses electromagnetic logging is a technique used to probe differences in electric conductivity around a measurement device electromagnetic logging while drilling can contribute to proactive geosteering to improve well placement in reservoirs because such measurements can serve as an indication for the structure of the surrounding geology we have developed a novel way of predicting the 3d conductivity distribution around a drilling tool based on the contrast source inversion method in which we have replaced the full integral equation approach by the single spherical scatterer sss approximation the approximation took into account the dominant features of the diffusive electromagnetic field this allowed for a substantial gain in computational speed and storage of the inversion method for reconstruction of the conductivity distribution in view of the limited range of the electromagnetic probing the overall reconstruction can be segmented in several local windows this reduced the computational speed requirements and the storage requirements dramatically while safeguarding the overall 3d character of reconstruction we have synthesized 3d electromagnetic logging data using synthetic models and conductivity maps from a hydrocarbon north sea reservoir model reconstructions were made for multiple source frequencies and the results were compared with the results obtained from the born approximation we have observed that reconstruction based on the sss approximation was superior to the one based on the born approximation our algorithm helped us determine the feasibility of producing reconstructions of reservoir sections in a short time frame which allows for real time decision making during drilling operations

spatial aftershock distribution of the 26 december 2004 great sumatra andaman earthquake in the northern sumatra area 1 in july 2005 about 6 months after the 2004 great sumatra andaman earthquake 20 ocean bottom seismometers were deployed in the northern sumatra area more than 1000 events were identified during the 12 day recording period after relocation the seismicity shows different patterns on each side of the lower splay fault east of this feature and beneath the aceh basin and fore arc the deep earthquakes outline the subduction megathrust fault west of it the aftershocks distribution is strongly influenced by the active n s oceanic fracture zones of the subducted plate two n s trending clusters of 10 to 50 km deep earthquakes observed below the lower wedge are interpreted as reactivated oceanic fracture zones the postseismic activity suggests a significant influence of the n s active fracture zones of the oceanic plate on the toe of the wedge explaining the dextral wrenching of wedge thrusts in the morphology the megathrust fault does not extend to the trench but outcrops east of these active oceanic fractures and seems to merge upward along the lower splay fault where shallow earthquakes are observed

problems of seepage to empty ditch and drain analytical solutions for the maximum area of the cross section of a drain ditch and a mole drain are obtained in the case of seepage to a ditch from an underflooded soil surface the extreme curve is represented by a semicircle with a constant value of flow velocity along the curve seepage to a system of empty horizontal drains is studied for one of three possible patterns of water tables at low values of infiltration to a phreatic surface the drain of a maximum area is nearly circular

new insights into regional tectonics of the sunda banda arcs region from integrated magnetic and gravity modelling abstract the lombok island indonesia situated along the sunda banda arcs transition region lies between zones characterized by very large intensity magnetic anomalies these anomalies have been noted as being part of the eight most important ones seen on the 1st edition of the world digital magnetic anomaly map unfortunately only marine magnetic data of surroundings are available and no regional high resolution magnetic surveys of this island had been done since 2004 we have carried out several geomagnetic ground surveys in this region here we present modelling results for a new geological and tectonic interpretation of the magnetic anomalies the new results confirm the general pattern of contiguous negative positive anomalies revealing two active quaternary normal faults and a magmatic arc related to a subduction region this outcome agrees with earlier results in surrounding areas obtained by satellite aeromagnetic and marine platforms and provides a more detailed picture of strong anomalies on this island considering both magnetic anomalies and gravity models it is possible to suggest an extension of the flores thrust zone reaching the northwest off the lombok island the flores thrust zone may be considered as a mature subduction in the back arc region showing a tendency of progressive subduction during last decades

a very broad band inversion method for the recovery of earthquake source parameters abstract waveform studies of the earthquake source have traditionally been performed in narrow bands of the seismic spectrum waveform matching of p and sh waves emphasizes frequencies near and above the corner frequency normal mode and surface wave analyses on the other hand are performed on data which contain information only below the corner frequency a new method is presented which formally includes the result of a long period centroid moment tensor analysis in an inversion of broad band body wave phases a parametrized source model is used which allows for the recovery of a detailed source time function as well as the direction and magnitude of rupture propagation the technical details and the performance of the method are demonstrated in an analysis of the october 28 1983 borah peak idaho earthquake in particular it is shown how the combination of the long period and broad band data sets in the inversion improves the resolution of both the focal mechanism and the scalar moment the very broad band method is applied in an analysis of the september 19 1985 michoacan m w 8 0 earthquake two concentrations of moment release are identified in the source time function separated by 25 30 s in time the spatial distribution of moment is well explained both by a model of unilateral rupture towards the east with a propagation velocity of 2 4 km s 1 and by two point sources separated by 95 km it is shown that the p wave data are largely insensitive to the scalar moment and that source time functions obtained without consideration of the total moment release exaggerate the heterogeneity of slip on the fault plane source time functions which do contain the total moment show that a large fraction of the moment was released smoothly over the whole duration 80 s of the event the results suggest that the fault plane was characterized by two regions of high stress drop but that a large portion of slip occurred on surrounding weak portions of the plane

a two dimensional transient analytical solution for a ponded ditch drainage system under the influence of source sink abstract an analytical solution is developed for predicting two dimensional transient seepage into ditch drainage network receiving water from a non uniform steady ponding field from the surface of the soil under the influence of source sink in the flow domain the flow domain is assumed to be saturated homogeneous and anisotropic in nature and have finite extends in horizontal and vertical directions the drains are assumed to be standing vertical and penetrating up to impervious layer the water levels in the drains are unequal and invariant with time the flow field is also assumed to be under the continuous influence of time space dependent arbitrary source sink term the correctness of the proposed model is checked by developing a numerical code and also with the existing analytical solution for the simplified case the study highlights the significance of source sink influence in the subsurface flow with the imposition of the source and sink term in the flow domain the pathline and travel time of water particles started deviating from their original position and above that the side and top discharge to the drains were also observed to have a strong influence of the source sink terms the travel time and pathline of water particles are also observed to have a dependency on the height of water in the ditches and on the location of source sink activation area

neotectonics and the 2004 and 2005 earthquake sequences at sumatra coseismic and interseismic deformation of the outer arc islands of nias and simeulue associated with the great indonesian earthquakes of 2004 12 26 and 2005 3 28 is generally ascribed to elastic stress storage and release on the interface between the indian and eurasian plates at the java trench however the nature of the associated shallow seismicity and the pattern of holocene deformation of the islands suggest that there has also been substantial activity on imbricate faults within the sediment prism behind the trench the distinction between the two kinds of seismicity is of practical as well as theoretical significance because in contrast with the megathrust outer arc faulting is not subject to appreciable postseismic relaxation and is moreover well placed to generate tsunami

structural geology and the seismotectonics of the 2004 great sumatran earthquake y the authors acknowledge funding support from the australian research council discovery project dp120103554 a unified model for the closure dynamics of ancient tethys constrained by geodesy structural geology argon geochronology and tectonic reconstruction and linkage project lp130100134 where to find giant porphyry and epithermal gold and copper deposits the research was also supported by the satellites seismometers and mass spectrometers initiative within the research school of earth sciences at anu bob engdahl is thanked for his support during earlier versions and for providing data

groundwater flow to a horizontal or slanted well in an unconfined aquifer 1 new semianalytical solutions for evaluation of the drawdown near horizontal and slanted wells with finite length screens in unconfined aquifers are presented these fully three dimensional solutions consider instantaneous drainage or delayed yield and aquifer anisotropy as a basis solution for the drawdown created by a point source in a uniform anisotropic unconfined aquifer is derived in laplace domain using superposition the point source solution is extended to the cases of the horizontal and slanted wells the previous solutions for vertical wells can be described as a special case of the new solutions numerical laplace inversion allows effective evaluation of the drawdown in real time examples illustrate the effects of well geometry and the aquifer parameters on drawdown results can be used to generate type curves from observations in piezometers and partially or fully penetrating observation wells the proposed solutions and software are useful for the parameter identification design of remediation systems drainage and mine dewatering

seismology energy radiation from the sumatra earthquake we determined the duration of high frequency energy radiation from indonesia s great sumatra andaman earthquake 26 december 2004 to be about 500 seconds this duration can be translated into a rupture length of about 1 200 km which is more than twice as long as that inferred from body wave analyses performed soon after the event our analysis was able rapidly to define the extent of rupture thereby aiding the assessment of seismic hazard in the immediate future

aceh andaman earthquake what happened and what s next the huge earthquake of 26 december 2004 and ensuing tsunami were caused by a submarine rupture running from offshore aceh indonesia to the andaman islands a clearer picture of events is starting to emerge

strain partitioning during oblique plate convergence in northern sumatra geodetic and seismologic constraints and numerical modeling global positioning system gps measurements along the subduction zone of northern sumatra 2 s to 3 n reveal that the strain associated with the oblique convergence of the australian plate with eurasia is almost fully partitioned between trench normal contraction within the forearc and trench parallel shear strain within a few tens of kilometers of the sumatran fault kinematic analyses of interplate earthquake slip vectors provide slip rates on the sumatran fault within a few millimeters per year of gps and geologic rates giving us more confidence in the use of slip vectors for inferring slip partitioning elsewhere the inferred slip rate on the sumatran fault is 1 3 less than the full margin parallel component of plate motion an across forearc rotation in the slip vectors suggests that the missing arc parallel shear occurs seaward of the geodetic network between the forearc islands and the trench simple finite element models are used to explore the conditions under which the change in the principal strain rate directions between the forearc and the arc region can occur modeling suggests that neither a preexisting strike slip fault nor a zone of thermally induced lithospheric weakness in the overriding plate is needed for strain partitioning to occur in general forearc slivers form over the region of interplate coupling and are driven along strike by the basal shear a volcanic arc can help the partitioning process by localizing the margin parallel shear strain in the upper plate if its crust and mantle are weaker than its surroundings interplate slip vectors and geodetic results from sumatra together suggest that the highest coupling on the plate boundary occurs beneath and seaward of the forearc islands consistent with inferences about the rupture zones of great nineteenth century earthquakes there the sumatra example suggests that geodetic measurements of interseismic margin parallel shear strain at oblique convergent margins can be used to map the landward extent of the relatively high basal stress beneath the overriding plate if one can correct for strain localization caused by weak upper plate strike slip faults

outer rise earthquakes and seismic coupling outer rise earthquakes can be separated into two basic categories based on focal mechanism compressional and tensional events reflecting compressional and tensional outer rise stress regimes we propose a model that connects the stress regime in the outer rise to the behavior of large subduction earthquakes and explains the focal mechanisms and both the temporal and spatial occurrence of outer rise earthquakes we find that compressional outer rise events tend to occur oceanward of seismic gaps in seismically coupled subduction zones or equivalently just prior to large subduction zone earthquakes the compressional stress regime is probably caused by slip in adjacent subduction zone segments there are two modes of occurrence for tensional outer rise earthquakes depending on whether they occur in coupled or uncoupled subduction zones in coupled subduction zones tensional events tend to occur after large subduction events as tensional stress from slab pull is temporarily transmitted to the outer rise in subduction zones that are inherently uncoupled tensional events can occur at any time therefore in uncoupled subduction zones the outer rise is always in tension and only tensional outer rise events occur there while in coupled subduction zones the outer rise is in a compressional state prior to large subduction earthquakes and a tensional state afterwards due to the large displacements

a dynamic model for the permian panhandle and hugoton fields western anadarko basin panhandle hugoton the largest north american gas field has long been controversial because of extreme subnormal pressures variable gas composition and tilted fluid contacts commonly attributed to hydrodynamic flow despite the absence of an effective updip aquifer these anomalies are addressed in terms of a basin scale petroleum system history largely independent of the geographically underlying pre permian system hydrocarbons were already being generated in the deep anadarko basin during the early permian with efficient southward migration from all potential source rocks via bounding faults and pennsylvanian permian alluvial fans giant amarillo uplift drape structures trapped hydrocarbons immediately following permian evaporite deposition the pre laramide panhandle field at maximum burial depth and pressure contained most of the oil and gas now found in mid continent permian reservoirs the early tertiary laramide orogeny redistributed panhandle field fluid columns possibly spilling gas into the hugoton embayment subsequent erosion of permian reservoir facies in eastern kansas allowed water discharge to outcrops at elevations below the regional hydraulic head as regional pressure dropped in response the panhandle field gas cap expanded rapidly forcing a late tertiary quaternary mass movement of gas northward to fill hugoton and associated fields panhandle hugoton pressures upon discovery were subnormal relative to drilling depth but normal relative to reservoir outcrop elevations in eastern kansas indicating that pressures are controlled by aquifer communication with the surface instead of burial depth variations in fluid contacts pressure and gas composition suggest that reservoir fluids are still moving driven by decompression and the rapid volumetric expansion of a supergiant gas accumulation

epicentre accuracy based on seismic network criteria summary we establish reliable and conservative estimates for epicentre location accuracy using data that are readily available in published seismic bulletins a large variety of seismic studies rely on catalogues of event locations making proper assessment of location uncertainty critical event location and uncertainty parameters in most global regional and national earthquake catalogues are obtained from traditional linearized inversion methods using a 1 d earth model to predict traveltimes reported catalogue uncertainties are based on the assumption that error processes are gaussian zero mean and uncorrelated unfortunately these assumptions are commonly violated leading to the underestimation of true location uncertainty especially at high confidence levels we find that catalogue location accuracy is most reliably estimated by station geometry we make use of two explosions with exactly known epicentres to develop local network location 0 2 5 accuracy criteria using monte carlo simulations of network geometry we find that local network locations are accurate to within 5 km with a 95 per cent confidence level when the network meets the following criteria 1 there are 10 or more stations all within 250 km 2 an azimuthal gap of less than 110 3 a secondary azimuthal gap of less than 160 and 4 at least one station within 30 km to derive location accuracy criteria for near regional 2 5 10 regional 2 5 20 and teleseismic 28 91 networks we use a large data set of exceptionally well located earthquakes and nuclear explosions beyond local distances we find that the secondary azimuthal gap is sufficient to constrain epicentre accuracy and location error increases when the secondary azimuthal gap exceeds 120 when station coverage meets the criterion of a secondary azimuth gap of less than 120 near regional networks provide 20 km accuracy at the 90 per cent confidence level while regional and teleseismic networks provide 25 km accuracy at the 90 per cent confidence level

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

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

multiple cmt source analysis of the 2004 sumatra earthquake while it is agreed that the great sumatra earthquake of december 26 2004 was among the largest earthquakes of the past century there has been disagreement on how large it was which part of the fault ruptured and how the rupture took place we present a centroid moment tensor cmt analysis of the earthquake in which multiple point sources are used in the inversion to mimic a propagating slip pulse the final model consists of five point sources with the southernmost sources accounting for the majority of the moment release the presumed fault planes of the southern sources strike northwest while those in the north strike northeast consistent with the geometry of the subduction trench slip on the fault is found to be more oblique in the north than in the south the inversion with five sources leads to a moment magnitude for the sumatra earthquake of m w 9 3 consistent with estimates from long period normal mode amplitudes

the role of acids in electrical conduction through ice 1 electrical conduction through meteoric polar ice is controlled by soluble impurities that originate mostly from sea salt biomass burning and volcanic eruptions the strongest conductivity response is to acids yet the mechanism causing this response has been unclear here we elucidate conduction mechanisms in ice using broadband dielectric spectroscopy of meteoric polar ice cores we find that conduction through polycrystalline polar ice is consistent with jaccard theory for migration of charged protonic point defects through single ice crystals except that bulk dc conduction is impeded by grain boundaries neither our observations nor modeling using archie s law support the hypothesis that grain boundary networks of unfrozen acids cause significant electrolytic conduction common electrical logs of ice cores by electrical conductivity measurement ecm or dielectric profiling dep and the attenuation of radio waves in ice sheets thus respond to protonic point defects only this response implies that joint interpretation of electrical and chemical logs can determine impurity partitioning between the lattice and grain boundaries or inclusions for example in the greenland ice core project grip ice core from central greenland on average more than half of the available lattice soluble impurities h cl nh4 create defects understanding this partitioning could help further resolve the nature of past changes in atmospheric chemistry

step wise relocation of isc earthquake hypocenters for linearized tomographic imaging of slab structure a vast volume of seismic phase data computed from routinely determined hypocenter locations is presently available for seismic imaging techniques such as tomographic inversion and residual sphere analysis routinely reported earthquake hypocenters however can be in error by several tens of kilometers these biases in hypocenter location can result in the misidentification of seismic phases and the loss of structural signal in the seismic phase data thus the value of these data in constraining seismic images is significantly reduced furthermore hypocenter mislocations degrade the linearization of the tomographic problem and map into the images produced by tomographic inversion to obtain adequate reference hypocenters for linearized inversion we used iasp91 software and reported arrival times to reprocess isc hypocenters and phase data for northwest pacific earthquakes subsequently we inverted p and pp wave residuals for earth structure and source mis location we describe this step wise relocation of isc hypocenters which underlies the linearization of the tomographic inversion and compare the relocation vectors before and after inversion the hypocenter relocations determined prior to inversion are of the order of 10 km which is significant with regard to both the estimated standard errors and the effect on travel time residuals and systematic with regard to earthquake position in the subducted slab in contrast the spatial components of the relocation vectors determined upon inversion of p and pp residuals are up to an order of magnitude smaller do not reveal a correlation with location in the seismic zone and do not generally exceed the noise level the incorporation of pp data in the relocation was essential to remove the depth bias prior to inversion to retrieve slab signal that might have been absorbed in mislocation and to constrain the focal depth upon seismic inversion non linear inversion schemes will not be efficient in removing the depth bias or in retrieving lost slab signal unless seismic phases that contain additional information about the depth bias like the depth phase pp are used

aftershock seismicity of the 27 february 2010 mw 8 8 maule earthquake rupture zone on 27 february 2010 the mw 8 8 maule earthquake in central chile ruptured a seismic gap where significant strain had accumulated since 1835 shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity here we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines by processing the seismic data between 15 march and 30 september 2010 from stations from iris ipgp gfz and university of liverpool we determined 20 205 hypocentres with magnitudes mw between 1 and 5 5 seismic activity occurs in six groups 1 normal faulting outer rise events 2 a shallow group of plate interface seismicity apparent at 25 35 km depth and 50 120 km distance to the trench with some variations between profiles along strike the aftershocks occur largely within the zone of coseismic slip but extend 50 km further north and with predominantly shallowly dipping thrust mechanisms along dip the events are either within the zone of coseismic slip or downdip from it depending on the coseismic slip model used 3 a third band of seismicity is observed further downdip at 40 50 km depth and further inland at 150 160 km trench perpendicular distance with mostly shallow dipping 28 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture and presumably above the intersection of the continental moho with the plate interface 4 a deep group of intermediate depth events between 80 and 120 km depth is present north of 36 s within the maule segment a large portion of events during the inter seismic phase originated from this depth range 5 the magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mw 8 8 maule 2010 earthquake 6 pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of pichilemu 34 5 s these crustal events occur in a 30 km wide region with sharp inclined boundaries and oriented oblique to the trench the best located events describe a plane dipping to the southwest consistent with one of the focal planes of the large normal faulting aftershock mw 6 9 on 11 march 2010

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

recent plumbing system of the krakatau volcano revealed by teleseismic earthquake distribution spatial and temporal analysis of global seismological data 1964 2005 reveals a distinct teleseismic earthquake activity producing a columnar like formation in the continental wedge between the krakatau volcano at the surface and the subducting slab of the indo australian plate these earthquakes occur continuously in time are in the body wave mb magnitude range 4 5 5 3 and in the depth range 1 100 km the krakatau earthquake cluster is vertical and elongated in the azimuth n30 e suggesting existence of a deep rooted fault zone cutting the sunda strait in the ssw nne direction possible continuation of the fault zone in the sw direction was activated by an intensive 2002 2003 aftershock sequence elongated in the azimuth of n55 e beneath the krakatau earthquake cluster an aseismic gap exists in the wadati benioff zone of the subducting plate at the depths 100 120 km we interpret this aseismic gap as a consequence of partial melting inhibiting stress concentration necessary to generate stronger earthquakes whereas the numerous earthquakes observed in the overlying lithospheric wedge beneath the volcano probably reflect magma ascent in the recent plumbing system of the krakatau volcano focal depth of the deepest events 100 km of the krakatau cluster constrains the location of the primary magma generation to greater depths the ascending magmatic fluids stress fault segments within the sunda strait fault zone and change their friction parameters inducing the observed tectonic earthquakes beneath krakatau

teleseismic double difference relocation of earthquakes along the sumatra andaman subduction zone using a 3 d model 1 we have extended the double difference seismic tomography method to teleseismic distances with 3 d ray tracing conducted through nested regional global velocity models and applied the method to relocate seismicity from the sumatra andaman region before and after the great earthquakes of 2004 and 2005 we tested the algorithm s accuracy using both independent local data and an alternate relocation method and found good agreement between the results the use of depth phases differential times and a realistic 3 d velocity model improves the accuracy and precision of epicenters and focal depths systematically shifting them perpendicular to the trench and shallower respectively the relocations refine the location of the megathrust and other faults the patterns of aftershocks and their relation to slip during the two great earthquakes in addition the relocations reveal several discrete features not readily discernible in the scatter of teleseismic catalogs including an arcuate narrow band of earthquakes presumed to define the updip rupture limit in the 2005 event and a lineation at depth tracing the subduction of the investigator fracture zone when viewed in conjunction with tomography results the geometry and structural features of the subduction zone are revealed in unprecedented detail

petrophysical inversion of borehole array induction logs part ii field data examples we describe the application of alpak et al s 2006 petrophysical inversion algorithm to the interpretation of borehole array induction logs acquired in an active north american gas field layer by layer values of porosity and permeability were estimated in two closely spaced vertical wells that penetrated the same horizontal rock formation the wells were drilled with different muds and overbalance pressures and the corresponding electromagnetic induction logs were acquired with different tools rock core laboratory measurements available in one of the two wells were used to constrain the efficiency of gas displacement by water based mud during the process of invasion estimated values of porosity and permeability agree well with measurements performed on rock core samples in addition to estimating porosity and permeability the petrophysical inversion algorithm provided accurate spatial distributions of gas saturation in the invaded rock formations that were not possible to obtain with conventional procedures based solely on the use of density and resistivity logs

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

tsunami earthquakes possibly widespread manifestations of frictional conditional stability 1 tsunami earthquakes shallow events that produce larger tsunamis than expected given their surface wave magnitudes ms typically have long durations and a source spectrum depleted in short period energy seven cases of underthrusting tsunami earthquakes provide information on the rupture processes but little constraint on geographic distribution or frequency we compare their rupture characteristics with smaller magnitude earthquakes on circum pacific interplate thrust faults comparable moment release time histories are found for large tsunami earthquakes and for many smaller shallow subduction zone earthquakes with significantly longer durations and additional source complexity than for events deeper than 15 km thus very shallow interplate earthquake ruptures are scale invariant with variable frictional properties on the plate interface controlling the depth dependent rupture process widespread occurrence of small shallow interplate earthquakes with long durations suggests that many subduction faults have frictional properties that may enable large tsunami generating earthquakes to occur fortunately large shallow ruptures are infrequent

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

lateral variation in slab orientation beneath toba caldera northern sumatra the investigator fracture zone ifz subducts beneath toba caldera the earth s largest quaternary caldera in northern sumatra suggesting a possible relationship between them locations of sub crustal earthquakes based on arrival times of p and s waves at a seismograph network surrounding toba reveal the geometry of the subducted slab and the ifz beneath toba a vertical tear of less than 20 km in the slab across the ifz as previously suggested cannot be ruled out but the large scale geometry of the slab is dominated by a broad bend of slab contours parallel to the concaveseaward indentation of the trench the slab shape is probably a response to the trench curvature can explain the change in trend of the volcanic arc near toba and may cause shallowing of the forearc basin near nias island the decrease in radius of curvature of the slab contours is not accompanied by an observable decrease in dip angle possibly resulting in lateral compressive stress in the slab the high rate of seismicity along the subducted investigator fracture zone that intersects the slab obliquely to its plunge direction is uncommon at subducted fracture zones and is likely caused by such lateral stress in the slab

elastic thickness structure of the andaman subduction zone implications for convergence of the ninetyeast ridge abstract we use the bouguer coherence morlet isostatic response function technique to compute the spatial variation of effective elastic thickness te of the andaman subduction zone the recovered te map resolves regional scale features that correlate well with known surface structures of the subducting indian plate and the overriding burma plate the major structure on the india plate the ninetyeast ridge ner exhibits a weak mechanical strength which is consistent with the expected signature of an oceanic ridge of hotspot origin however a markedly low strength 0

earth s free oscillations excited by the 26 december 2004 sumatra andaman earthquake at periods greater than 1000 seconds earth s seismic free oscillations have anomalously large amplitude when referenced to the harvard centroid moment tensor fault mechanism which is estimated from 300 to 500 second surface waves by using more realistic rupture models on a steeper fault derived from seismic body and surface waves we approximated free oscillation amplitudes with a seismic moment 6 5 10 22 newton meters that corresponds to a moment magnitude of 9 15 with a rupture duration of 600 seconds the fault rupture models represent seismic observations adequately but underpredict geodetic displacements that argue for slow fault motion beneath the nicobar and andaman islands

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

rupture process of an extended earthquake sequence teleseismic analysis of the chilean earthquake of march 3 1985 broadband displacement and velocity records of p waves recorded at teleseismic distances are analyzed to determine the static and dynamic source parameters of the chilean earthquake of march 3 1985 ms 7 8 and seven large mb 5 6 aftershocks besides the usual parameters of depth moment and focal mechanism the analysis provides estimates of radiated energy associated stresses and source dimension for seven of the eight modeled earthquakes to insure that the parameters are describing the same physical aspect of the rupture process the parameters for each shock are computed from the time window in which most of the seismic energy is radiated the hypocenters of an additional 149 small foreshocks and aftershocks of 4 5 mb 5 6 are computed with the method of joint hypocenter determination the spatial and temporal variation of source parameters and earthquake locations are used to infer a description of the rupture process before during and after the main shock the main shock and modeled aftershocks occurred as thrust faulting on the interface between the nazca and south american plates a cluster of foreshocks in the 10 days preceding the main shock also involved thrust faulting on the plate interface the main shock itself was a complex rupture consisting of three events the first two events denoted as ms1 and ms2 released minor amounts of energy and they occurred on the periphery of the small zone defined by the foreshocks the major release of energy occurred with the third event denoted by ms which nucleated downdip of ms1 and ms2 within the time window of major energy release rupture extended approximately 90 km to the south from the point at which ms nucleated the size of the early aftershock zone which far exceeds our inferred dimensions for the major shock and the strong frequency dependence of scalar moment imply that substantial slow slip occurred on the plate interface that was not associated with major energy release the dip of the seismically active interface increases landward from about 15 at 20 km depth to about 35 at 40 km depth where the seismogenic interface reaches its maximum observed depth the vast majority of small and moderate aftershocks occurred in the shallower part of the interface as did the foreshocks ms1 and ms2 it appears however that the asperities that control the rupture of the largest earthquakes are the asperities on the deeper interface ms and the largest 1985 aftershock that of april 9 ms 7 2 occurred on the deeper interface the chilean earthquake of july 9 1971 ms 7 5 which occurred just north of the 1985 earthquake also involved main shock rupture on the deeper interface and was followed by aftershocks on the shallower interface asperities on the deeper interface appear on average to be stronger larger and more uniform in size than asperities on the shallow interface a greater average strength for deeper asperities is suggested by the observation that stress drops and apparent stresses of the main shock and the after shock of april 9 ms 7 2 are higher than those of the large shallow aftershocks and is consistent with arguments that the maximum friction on a fault zone should be near the base of the seismogenic zone one deep interface aftershock with low stress drop and apparent stress may have been situated below the point of maximum friction on the interface the inferred larger and more uniform sizes of the deeper asperities are suggested by the higher proportion of large to small shocks on the deeper interface the downdip change in the asperity size distribution may reflect increased friction on the plate interace or the coalescence of small asperities into large asperities with increased subduction the radiated energies of the main shock and large aftershocks that are computed directly from the broad bandwidth data are smaller than those predicted by standard empirical formulas by factors ranging from 4 to 20

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

seismic evidence of bending and unbending of subducting oceanic crust and the presence of mantle megathrust in the 2004 great sumatra earthquake rupture zone abstract in subduction zones the plate interface megathrust is typically poorly imaged at depths 12 km however its precise geometry and nature as well as the positions of updip and downdip limits of the seismogenic zone are important elements to understand the generation of megathrust earthquakes using deep marine seismic reflection and refraction data we observed discontinuous reflections off the top of the subducting oceanic crust down to 60 km depth in the 2004 great sumatra andaman earthquake rupture zone we find that the top of the downgoing plate does not dip gently into the subduction zone but instead displays a staircase geometry with three successive 5 15 km vertical steps spaced 50 km apart micro earthquake data indicate that most of the seismicity lies below this interface suggesting that the oceanic plate is deforming actively along part of the profile we also image a second reflector located 8 10 km below the top of the oceanic crust the forward modelling of the gravity data along the profile supports the presence of a high density material above this reflector the presence of a staircase shape for the top of the oceanic crust together with constraints from gravity data and earthquake data require that the megathrust goes through this second reflector this leads us to conclude that the megathrust is at least partly located in the oceanic mantle and that underplating of oceanic crust beneath the wedge and underplating of upper mantle beneath the forearc basin are taking place in this region

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

the relationship of the seismic source and subduction zone structure for the 2004 december 26 sumatra andaman earthquake abstract studies of the 2004 december 26 sumatra andaman earthquake indicate that the rupture and subsequent down dip slip of the mw 9 3 event propagated with variable speed as it progressed northwards the transitions between different behaviour for the source correspond to changes in the physical properties of the subducted slab along the sumatra andaman arc revealed by multi wavespeed seismic tomography the transition from rapid slip to dominantly slower slip near 6 5 n and the end of the main zone of tsunamigenic source at 10 n lies in each case just to the south of localised features where changes in the physical properties of the slab are indicated from the ratio of shear wavespeed to bulk sound speed these features are associated mainly with bulk modulus variations the changing morphology of the subduction zone is associated with changes in physical properties that are manifested in the tomographic images and have modified the character of the slip along the 1500 km long arc segment that ruptured during this great earthquake

estimating petrophysical parameters and average mud filtrate invasion rates using joint inversion of induction logging and pressure transient data we introduce an inversion approach for determining the water based mud filtrate invasion profile as well as the formation porosity and horizontal permeability from the induction logging data the inversion is constrained by a multiphase fluid flow simulator that simulates the mud filtrate invasion process to obtain the spatial distributions of the water saturation and the salt concentration which are in turn transformed into the formation resistivity using a resistivity saturation formula by ignoring the diffusion effect we assume that the mud filtrate invasion process is mainly convective so that it can be equivalently simulated by providing an average invasion rate and the duration of invasion the average invasion rate can be directly inverted from the fluid flow constrained inversion of induction logging data we also obtain the mud filtrate invasion profile which is consistent with the fluid flow physics the reconstructed mud filtrate invasion profile benefits the interpretation of the formation test when the pressure transient data are available this approach can be also used to jointly invert both induction logging data and pressure transient data to obtain the mud filtrate invasion profile as well as a parametric distribution of the ti anisotropic formation permeability and porosity assuming a vertical well penetrating horizontal formations the fluid flow problem is solved using an implicit black oil finite difference simulator with brine tracking option based on a cylindrical axially symmetric grid whereas the response of the induction logging tool is simulated using a frequency domain finite difference solver based on a cartesian grid a gauss newton inversion scheme using the multiplicative regularization technique is used for either the fluid flow constrained inversion or the joint inversion the reliability of the inversion results depends on the accuracy of a priori knowledge of the reservoir which needs to be confirmed via sensitivity analysis

application of an improved algorithm to high precision relocation of isc test events abstract new location features for possible implementation by the international seismological centre in its standard location procedures are tested using a set of 156 well located and geographically well distributed earthquakes and explosions the tests are performed using the engdahl et al engdahl e r van der hilst r d buland r p 1998 global teleseismic earthquake relocation with improved travel times and procedures for depth determination bull seism soc am 88 3295 3314 ehb location algorithm with the 1 d reference earth model ak135 kennett b l n engdahl e r buland r 1995 constraints on seismic velocities in the earth from travel times geophys j int 122 108 124 weighting by phase variance as a function of distance improves location accuracy by 7 use of later phase arrival times does not result in a significant improvement in location or depth for events with observing stations well distributed in azimuth however with application of an improved phase identification technique depth phases provide significantly better estimates of focal depth

extremely thin crust in the indian ocean possibly resulting from plume ridge interaction the thickness of the crust created at ocean spreading centres depends on the spreading rate and melt production in the mantle it is 5 8 km for a crust formed at slow and fast spreading centres and 2 4 km at ultra slow spreading centres away from hotspots and mantle anomalies the crust is generally thin at the fracture zones and thick beneath hotspots and large igneous provinces here we present results for the crust generated at the fast wharton spreading centre 55 58 ma ago using seismic reflection and refraction data we find that the crust over a 200 km segment of the wharton basin is only 3 5 4 5 km thick the thinnest crust ever observed in a fast spreading environment a thin crust could be produced by the presence of depleted and or cold mantle numerical simulations and recent laboratory experiments studying the impact of a hot plume under a lithosphere show that a curtain of weak cold downwellings of depleted mantle material is likely to develop around the edges of the hot plume pond because of a strongly temperature dependent viscosity of lithospheric material the hotter therefore less viscous bottom of the lithosphere can be mobilized by an impinging plume if sampled by a spreading centre the locally cold and depleted mantle should result in low production of melt we suggest that the observed thin crust in the wharton basin is likely to have been formed by the interaction between the kerguelen mantle plume and the wharton spreading centre 55 ma ago

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

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

a comparative study of the sumatran subduction zone earthquakes of 1935 and 1984 a m s 7 7 earthquake struck the western equatorial coast of sumatra in december 1935 it was the largest event in the region since the two devastating giant earthquakes of 1833 and 1861 historical seismograms of this event from several observatories around the world provide precious information that constrains the source parameters of the earthquake to more precisely quantify the location geometry and mechanism of the 1935 event and to estimate the coseismic deformation we analyze the best of the available teleseismic historical seismograms by comparing systematically the records of the 1935 earthquake with those of a smaller event that occurred in the same region in 1984 first we constrain the source parameters of the 1984 event using teleseismic records then we compare the records of the 1935 event with those of 1984 from the same sites and instruments to do this we choose several time windows in the corresponding seismograms that contain clearly identifiable phases and deconvolve the modern event from the older one the deconvolutions result in very narrow pulses with similar sizes thus confirming similar locations and mechanisms for the events the initiation of the 1984 event was on the subduction interface at a depth of 27 2 km its m 0 is 6 5 x 10 19 n m m w is 7 2 the sense of slip was nearly pure thrust on a plane dipping 12 the 1935 event also involved rupture of the shallow subduction interface but was about five times larger m 0 3 3 x 10 20 n m m w 7 7 and initiated a few kilometers to the southeast along strike the 1935 rupture propagated unilaterally toward the southeast the along strike rupture length was about 65 km from these source parameters we calculate the surface deformations assuming an elastic multilayered medium these deformations compare favorably with those actually recovered from paleoseismic data in the form of coral microatolls

loci and maximum size of thrust earthquakes and the mechanics of the shallow region of subduction zones earthquakes do not extend updip along the plate interface at most subduction zones all of the way to the plate boundary at the trench axis or deformation front rather the shallowest part of that interface moves mainly through stable aseismic slip that part of the plate boundary referred to here as the aseismic zone occurs along the base of an accreted wedge of young sediments the probable primary cause for the existence of this aseismic zone is the stable slip properties of the unconsolidated and semiconsolidated sediments in that zone subducted sediment is progressively dewatered and underplated to the base of the overriding plate through this process more consolidated rocks eventually come into contact at depth across both sides of the plate boundary from the point where sufficiently hard rock is found across the plate interface that interface will change its slip behavior to unstable stick slip sliding which is characteristic of consolidated material under most conditions this type of motion is accommodated seismically as episodic slip in large earthquakes the location of this transition to seismic behavior referred to as the seismic front marks the deep end of the aseismic zone and the top of the seismogenic zone i e that part of the plate interface that moves primarily in thrust earthquakes several convergent plate margins are discussed to illustrate the seismic front and the aseismic zone we find that the seismic front defined by smaller earthquakes that occur during the interval between large events is nearly the same as that for large events as inferred from the locations of their aftershocks the location of the seismic front is important for making estimates of the maximum possible size of thrust earthquakes along the plate boundary because it delimits the trenchward limit of the potential rupture area of these events the size of large thrust earthquakes is proportional to rupture area and to at least the cube of the downdip width w of that area thus by defining the location of the seismic front for convergent margins it is possible to make better estimates of w and hence to deduce the maximum size of future interplate earthquakes the average repeat time of such events is also related to w and so better estimates of average repeat time are possible from improved knowledge of w the hypothesis that the location of the seismic front is related to the maximum depth of subduction of unconsolidated sediment has implications for forearc mechanics we use a mechanical analysis laboratory modeling and multichannel seismic information to develop a simple model explaining the growth of forearcs the outer arc high or trench slope break that occurs arcward of most accretionary wedges represents an abrupt change in the critical taper of the accretionary wedge we argue that that change is caused by a large arcward increase in the strength of the material within the overriding plate that stronger material is called the backstop our laboratory modeling experiments indicate that a backstop with a trenchward dipping upper surface results in the development of an overlying structure that includes all of the primary morphologic features observed in modern forearcs in our modeling an accretionary wedge develops trenchward of the backstop an outer arc high develops above the trenchward toe of the backstop and farther arcward a passive forearc basin forms above the stronger material of the backstop this model is consistent with the observation that earthquakes do not extend updip along the plate interface all the way to the trench axis we hypothesize that plate motion is accommodated seismically along the base of the consolidated backstop and mostly or entirely aseismically trenchward of the toe of the backstop along the base of the accretionary wedge at several margins the seismic front is approximately coincident with the outer arc high supporting this interpretation

temporal velocity changes in the crust associated with the great sumatra earthquakes abstract co and postseismic slip of the great earthquakes can give rise to temporal changes in the medium either due to strong ground motion damaging near surface sediment layer or stress perturbations modulating crack density and or fluid movement at depth such time varying crustal properties can result in fractional change in seismic velocity that can be probed from cross correlating waveforms and measuring their time lags within a repeating earthquake sequence this study analyzes lag times of high frequency 0 5 2 0 hz p and s coda waves as well as long period 0 03 0 1 hz surface waves from repeating aftershock sequences of the great 2004 sumatra andaman and 2005 nias simeulue earthquakes the observed lag times reveal several major characteristics 1 lag time series t of s coda for the 2004 sequences fluctuate around zero and are sometimes negative as a function of lapse time whereas t of s coda for the 2005 sequences exhibit a monotonic increase as a function of lapse time 2 average velocity reduction of s coda v s is about two times larger than that of p coda v p average velocity reduction of rayleigh waves v lr is 3 4 times larger than that of love waves v lq and 3 v s and v lr display temporal velocity recovery with calendar time especially for the 2005 sequences the form of temporal velocity recovery of v s of the 2005 sequences is similar to available displacement time series of the nearby geodetic station whereas we discuss potential artifacts such as source separation temporal changes of the noise field and instrument response observations collectively point to nonuniform temporal velocity reduction in the crust modulated by co or and postseismic slip of the 2004 2005 great earthquakes online material table of source parameters and figure showing tests on lag time measurements of long period rayleigh waves

analytical solutions for two dimensional groundwater flow with subsurface drainage tiles summary the tile drainage problem in an unconfined aquifer was investigated a mathematical model was established that describes two dimensional groundwater flow in an unconfined aquifer near a river with a linearized boussinesq equation time dependent sources and a sloped tile analytical solutions for groundwater level and discharge were derived and used to compare hydrologic conditions in a system with and without tile natural drainage we found that the spatial and temporal variations of groundwater level and discharge were significantly altered by the presence of drainage tile in an aquifer with tile drainage the groundwater level was lower and total groundwater discharge to the river increased compared to an aquifer with no tile application of the solutions to a synthetic case demonstrates that the analytical solutions derived can be used to quantify effect of tiles on nitrate loads in the baseflow of a river and assess the effectiveness of various conservation practices

stress change and effective friction coefficient along the sumatra andaman sagaing fault system after the 26 december 2004 m w 9 2 and the 28 march 2005 m w 8 7 earthquakes the 2004 aceh and 2005 nias events are the two greatest earthquakes of the past 40 years with a total rupture of 1700 km long and a coseismic slip reaching up to 25 m these two earthquakes have caused large stress perturbations which significantly altered seismic activity in the sumatra andaman region using both detailed mapping of failure planes and various slip distributions we calculate this stress change along the sumatra andaman sagaing fault system from central sumatra to southern myanmar the static coulomb stress change delta cff and the observed seismic activity are in very good agreement with a coulomb index similar to 20 greater than the one obtained for random events compared to previous studies this high coulomb index confirms two important issues on the use of static stress change criterion unsuited to study near field aftershocks and only relevant for aftershocks analysis on large and mature faults at a time scale of several months the calculated delta cff distribution suggests that the 2004 and 2005 earthquakes inhibit failure on the north andaman rift and on the sagaing fault while failure is encouraged along the transform andaman zone the central andaman rift the west andaman fault the sumatra fault system and the offshore thrust faults west of sumatra island the maximum value of similar to 15 20 bar 1 5 2 mpa for delta cff is reached in the northern part of the sumatra fault system this high value together with the lack of major earthquake in the last 170 years result in a high seismic hazard for this region our results are also consistent with temporal evolution of both earthquakes location and focal mechanism prior to and after the events in particular we explain the occurrence and the mechanism of seismic swarms observed in the central andaman rift and along the west andaman fault finally our calculations reveal that the seismicity in the andaman rift zone can only be explained if mu 0 5 this result leads to two end member models one with a constant and high fault friction and one with spatial variations for which friction may depend on either the nature of the lithosphere oceanic versus continental or the fault type

seismicity associated with the sumatra andaman islands earthquake of 26 december 2004 the u s geological survey national earthquake information center usgs neic had computed origins for 5000 earthquakes in the sumatra andaman islands region in the first 36 weeks after the sumatra andaman islands mainshock of 26 december 2004 the cataloging of earthquakes of m b usgs 5 1 and larger is essentially complete for the time period except for the first half day following the 26 december mainshock a period of about two hours following the nias earthquake of 28 march 2005 and occasionally during the andaman sea swarm of 26 30 january 2005 moderate and larger m b 5 5 aftershocks are absent from most of the deep interplate thrust faults of the segments of the sumatra andaman islands subduction zone on which the 26 december mainshock occurred which probably reflects nearly complete release of elastic strain on the seismogenic interplate thrust during the mainshock an exceptional thrust fault source offshore of banda aceh may represent a segment of the interplate thrust that was bypassed during the mainshock the 26 december mainshock triggered a high level of aftershock activity near the axis of the sunda trench and the leading edge of the overthrust burma plate much near trench activity is intraplate activity within the subducting plate but some shallow focus near trench reverse fault earthquakes may represent an unusual seismogenic release of interplate compressional stress near the tip of the overriding plate the interplate thrust nias earthquake of 28 march 2005 in contrast to the 26 december aftershock sequence was followed by many interplate thrust aftershocks along the length of its inferred rupture zone

seepage to ditches from a ponded surface abstract the seepage from an infinite ponded horizontal surface through a uniform soil to a ditch is analysed by the method of conformal transformations for a ditch maintained empty the discharge rate per unit length of ditch for the case of an infinitely deep soil is simply the hydraulic conductivity multiplied by the depth to the ditch base for the case of an impermeable barrier at the level of the ditch base it is reduced to 0 742 of this value when there is water standing to some height in the ditch the seepage rate for the latter situation is shown both by the conformal transformation method and by a simpler analysis of the flow problem initially to decrease slowly with the rise in water level being reduced to only half of its maximum rate when the ditch is 0 8 full and then to decrease rapidly to zero when the ditch is full the results of the analyses show that in all cases the flux through the surface decreases rapidly with the distance from the ditch the results are discussed in the context of the management of areas liable to flooding and also of desalinisation methods used in maintaining lands under irrigation

complex slab subduction beneath northern sumatra 1 new data provided by the 2004 2005 sumatra andaman great earthquake sequences allow us to image with improved detail the p wave velocity structure beneath sumatra and adjacent regions below northern sumatra we find that the slab is folded at depth exhibiting geometry similar to that of the volcanic arc and the trench at the surface we speculate that this fold plays a major role in the segmentation of the sumatra megathrust and may impede rupture propagation in the region north of sumatra significant slab material in the mantle transition zone is imaged for the first time and we infer the presence of a major tear between the upper mantle and transition zone there

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

earthquake clustering in the tectonic pattern and volcanism of the andaman sea region abstract seismicity pattern in the andaman sea region has been analysed to interpret recent dynamics of regional submarine volcanic provinces hypocentral determinations and focal mechanisms of available global seismological data have been used frequent occurrence of earthquake swarms proved to be an important characteristic of seismicity pattern in the investigated region epicenters of the earthquake swarms are situated almost exclusively along a narrow belt forming the easternmost limit of the epicentral area of the andaman sea region the southern zone of the belt between 6 and 10 5 n is trench parallel and coincides with the northward prolongation of the sumatra volcanic arc the northern zone of the belt between 10 5 and 13 n is deflected by about 45 northeast and precisely follows the complicated zigzag pattern of the rift system in the middle of the andaman basin earthquake occurrence in these two zones the northern and the southern differs by several aspects by shape of the epicentral zones of individual swarms by focal mechanisms and by response to the 2004 sumatra andaman great earthquake these differences together with available information on composition of magmas found at the seafloor lead us to the conclusion that the swarms of the southern zone are induced by intrusions of subduction generated calc alkaline magmas whereas the swarms in the northern zone by intrusions of basaltic magmas associated with the seafloor spreading earthquake swarm occurrence defines a brittle seismogenic layer at depths between 9 and 35 km excludes the existence of large magma reservoirs in respective depth interval and puts their hypothetical location to a greater depth episodes of magma ascent from deeper reservoir to shallow magma chamber depth

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

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

seismic history and seismotectonics of the sunda arc historic records of the last 300 years reveal two great interplate earthquakes 1833 mw 8 1861 mw 8 8 which ruptured major segments of the sumatra fore arc in western indonesia a significant percentage of interplate slip along this portion of the plate boundary appears to occur seismically the ends of these rupture zones are coincident with clusters of large ms 7 and moderate 6 ms 7 shocks and with heterogeneities in the plate interface as inferred from geologic and geophysical data the northern extent of the 1833 rupture zone is coincident with a group of moderate and large earthquakes a structural arch in the fore arc and a fracture zone on the subducted plate the southern portion is coincident with a very prominent cluster and the along strike extension of a sediment filled trough on the subducted plate prior to this study sumatra was characterized as relatively aseismic as inferred from the lack of great earthquakes in the instrumental record of this century java and the lesser sunda islands had major ms 6 earthquakes in the historic record but none are of the same magnitude as the great events near sumatra there is no clear evidence that shocks in the java fore arc were interplate events yet geophysical data indicate recent uplift of the trench slope break and a change in strike of the trench axis where the northernmost flank of the roo rise a prominent bathymetrie high appears to be interacting with the fore arc this feature was formed at a ridge crest and is more buoyant and thus more difficult to subduct than the surrounding seafloor there is no increase in seismicity associated with this tectonism however that may indicate a lack of contact between the crystalline portions of the plates at this time we infer that a majority of slip on the plate interface near java occurs aseismically the variation in occurrence of great interplate earthquakes along the sunda arc may be interpreted in terms of a model that attributes variation in interplate coupling to the age of the subducted lithosphere great interplate earthquakes occur near sumatra where the age of the youngest crust is 46 ma the characteristics of the sunda arc and analogies with pacific arcs imply that the entire length of sumatra has the potential to produce great thrust earthquakes its seismic potential should be considered high as there has been no recurrence of the great events of 1833 and 1861 in contrast no such events have been reported off java and the lesser sunda islands where the oldest crust is 152 ma the plate interface near java and the lesser sunda islands should be considered to have low seismic potential

seismic imaging of forearc backthrusts at northern sumatra subduction zone forearc tectonics at accretionary convergent margins has variously been studied using analogue and numerical modelling techniques numerous geophysical investigations have targeted the subsurface structure of active forearc settings at convergent margins however several critical details of the structure mode of tectonic evolution and the role forearcs play in the subduction seismic cycle remain to be further understood especially for large accretionary margins in this study we present a high resolution deep seismic reflection image of the northern sumatran subduction forearc near the 2004 december 26 sumatra earthquake epicentral region the profile clearly demarcates the backthrust branches at the seaward edge of the aceh forearc basin along which the inner forearc continues to evolve sharp bathymetric features at the seafloor suggest that the imaged backthrusts are active coincident wide angle seismic tomographic image of the sumatra forearc allows us to image the geometry of the seaward dipping backstop buttress with which the imaged backthrust branches are associated the presence of forearc backthrusting confirms model predictions for the development of backthrusting over seaward dipping backstops the west andaman fault at the seaward edge of aceh basin appears to be a shallow tributary of the backthrust and sheds light on the complex deformation of the forearc uplifting along the backthrust branches may explain the presence of forearc islands observed all along sumatran margin and help further constrain the tectonic models for their evolution moreover if these backthrusts slip coseismically they would contribute to tsunamigenesis and seismic risk in the region

estimating seepage and hydraulic potentials near incised ditches in a homogeneous isotropic aquifer soil erosion on upland areas is a highly complex phenomenon involving many component processes one of the least explored processes is the role of subsurface flow rain or irrigation water entering the soil profile either accrues to groundwater or exits at some point downslope as seepage in the latter case the positive water pressure may lead to detachment of soil particles aggregates or bulk soil that often is a prelude to incipient rilling or gullying this article concerns the analysis of seepage to ditches with a water level lower than the adjacent field water table and the hydraulic pressures near the ditches in order to assess their contributing role in gully development the approach taken is to analyze the subsurface flow regime under steady state conditions using the theory of conformal transformations first seepage to a fully filled circular drain in a homogeneous isotropic layer overlaying an impermeable layer was analyzed subsequently the case of drainage to a ditch partially filled with water and the effect of a buffer strip adjacent to the ditch on seepage reduction were studied using the same methodology two approaches were considered to approximate the water level in the buffer strip 1 a confined boundary represented by a straight line between the ditch water level and the field surface water level and 2 a free boundary in which the groundwater level was approximated by the pressure potential relationship for flow from a ponded surface area to a sink placed at the surface at a distance equal to the width of the buffer strip the latter analysis yielded explicit expressions of seepage and the groundwater hydraulic and stream potential functions in terms of the spatial coordinates this relationship should facilitate the analysis of the role of the subsurface water regime on seepage soil erosion and gully development published in 2009 by john wiley sons ltd

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 tectonics of the eastern sunda and banda arcs the tectonics of the eastern sunda and banda arcs of eastern indonesia are inferred from the centroid depths seismic moments and fault plane solutions of 63 large earthquakes that occurred between 1962 and 1984 source parameters are estimated by inverting long period teleseismic p and sh waves earthquakes show that the collision of the australian continent with the banda arc shortens the upper plate beneath the forearc and back arc basin over the broad area between the timor and seram troughs along the eastern end of the sunda arc and along the southern banda arc earthquakes reveal that the arc and forearc respond to collision by shortening in the direction of convergence by elongating in the direction perpendicular to convergence and by thrusting over the back arc basin shallow thrust and strike slip earthquakes beneath the banda basin the back arc basin demonstrate that deformation within the back arc accommodates some of the northward motion of the australian continent the rate of north south shortening of the entire upper plate at the longitude of timor calculated from the seismic moments of the earthquakes over the 22 year period is roughly 20 of the predicted convergence rate between australia and southeast asia strike slip faulting within the banda basin results also in eastward motion of the banda arc with respect to western indonesia and australia eastward extrusion of the banda arc results in thrusting at the aru trough earthquakes due to thrusting of the back arc basin beneath the volcanic arc are too shallow to corroborate that the arc s polarity has reversed although the wetar back arc thrust zone at present has a high seismic slip rate earthquakes and their mechanisms provide evidence that the lithosphere of the weber basin a 7500 m deep forearc basin rests on the subducting lithosphere without intervening asthenosphere so that the weber basin subsides in response to sinking of the subducting lithosphere closure of the banda basin is geometrically incompatible with the australian plate subducting simultaneously beneath both the timor and seram troughs instead the bird s head which subducts beneath seram is decoupled from the australian plate in western new guinea and probably moves west or southwest with respect to australia in the eastern indonesian example strike slip faulting plays a major role in the evolution of the collision zone and clearly demonstrates the complexity in three dimensions of continental accretion and mountain building by arc continent collision

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

crustal motion in indonesia from global positioning system measurements terrestrial reference frame 2000 we compute poles of rotation for the australia eurasia and pacific plates based on our analysis of the global gps data we find that regional tectonics is dominated by the interaction of four discrete rotating blocks spanning significant areas of the sunda shelf the south banda arc the bird s head region of new guinea and east sulawesi the largest the sunda shelf block ssh is estimated to be moving 6 3 mm yr se relative to eurasia the south banda block sbb rotates clockwise relative to both the ssh and australia plate resulting in 15 8 mm yr of motion across the timor trough and 60 3 mm yr of shortening across the flores sea southern new guinea forms part of the australia plate from which the bird s head block bhb moves rapidly wsw subducting beneath the seram trough the east sulawesi block rotates clockwise about a nearby axis with respect to the sunda shelf thereby transferring east west shortening between the pacific and eurasia plates into north south shortening across the north sulawesi trench except for the sunda shelf the crustal blocks are all experiencing significant internal deformation in this respect crustal motion in those regions does not fit the microplate tectonics model index terms 1206 geodesy and gravity crustal movements interplate 8155 1243 geodesy and gravity space geodetic surveys 8150 tectonophysics plate boundary general 3040 8158 tectonophysics plate motions present and recent 3040 9320 information related to geographic region asia keywords crustal motion indonesia tectonics gps current plate motions southeast asia

estimating reservoir permeability with borehole radar in oil drilling mud filtrate penetrates into porous formations and alters the compositions and properties of the pore fluids this disturbs the logging signals and brings errors to reservoir evaluation drilling and logging engineers therefore deem mud invasion as undesired and attempt to eliminate its adverse effects however the mud contaminated formation carries valuable information notably with regard to its hydraulic properties typically the invasion depth critically depends on the formation porosity and permeability therefore if adequately characterized mud invasion effects could be used for reservoir evaluation to pursue this objective we have applied borehole radar to measure mud invasion depth considering its high radial spatial resolution compared with conventional logging tools which then allows us to estimate the reservoir permeability based on the acquired invasion depth we investigate the feasibility of this strategy numerically through coupled electromagnetic and fluid modeling in an oil bearing layer drilled using freshwater based mud time lapse logging is simulated to extract the signals reflected from the invasion front and a dual offset downhole antenna mode enables time to depth conversion to determine the invasion depth based on drilling coring and logging data a quantitative interpretation chart is established mapping the porosity permeability and initial water saturation into the invasion depth the estimated permeability is in a good agreement with the actual formation permeability our results therefore suggest that borehole radar has significant potential to estimate permeability through mud invasion effects

earthquake in a maze compressional rupture branching during the 2012 mw 8 6 sumatra earthquake seismological observations of the 2012 moment magnitude 8 6 sumatra earthquake reveal unprecedented complexity of dynamic rupture the surprisingly large magnitude results from the combination of deep extent high stress drop and rupture of multiple faults back projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system with relatively slow rupture speed the east southeast west northwest ruptures add a new dimension to the seismotectonics of the wharton basin which was previously thought to be controlled by north south strike slip faulting the rupture turned twice into the compressive quadrant against the preferred branching direction predicted by dynamic coulomb stress calculations orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure insensitive strength of the deep oceanic lithosphere

global cmt analysis of moderate earthquakes mw 4 5 using intermediate period surface waves a new method for calculating centroid moment tensor cmt solutions for moderate sized earthquakes is presented and tested in the new algorithm which is a modification to the standard harvard cmt method intermediate period surface waves are included in the inversion for source parameters the dispersion of teleseismic surface waves in the period range 40 to 150 sec is predicted by interpolation of recent global phase velocity maps the method is tested on a set of 20 moderate and large 5 2 mw 7 2 earthquakes with known mechanisms the retrieved mechanisms are similar to the previous results even when noise is added to the seismograms to simulate earthquakes of a smaller magnitude mw 4 5 the inversion algorithm is applied to the 1993 klamath falls mainshock and aftershock sequence and the results compare well with earlier results a catalog of mw 4 5 focal mechanisms for greece and surrounding areas for the first six months of 1995 is derived using the new method of analysis

seismic evidence for broken oceanic crust in the 2004 sumatra earthquake epicentral region the 2004 sumatra earthquake was one of the largest events to occur in a subduction zone in the past 50 years seismic reflection data for this subduction zone reveal thrust faults cutting across the entire oceanic crust this observation coupled with the hypocentres of aftershocks suggests that the megathrust the interface between the indo australian plate and the sunda plate currently lies in the oceanic mantle

back arc extension in the andaman sea tectonic and magmatic processes imaged by high precision teleseismic double difference earthquake relocation 1 the geometry kinematics and mode of back arc extension along the andaman sea plate boundary are refined using a new set of significantly improved hypocenters global centroid moment tensor cmt solutions and high resolution bathymetry by applying cross correlation and double difference dd algorithms to regional and teleseismic waveforms and arrival times from international seismological centre and national earthquake information center bulletins 1964 2009 we resolve the fine scale structure and spatiotemporal behavior of active faults in the andaman sea the new data reveal that back arc extension is primarily accommodated at the andaman back arc spreading center absc at 10 which hosted three major earthquake swarms in 1984 2006 and 2009 short term spreading rates estimated from extensional moment tensors account for less than 10 of the long term 3 0 3 8 cm yr spreading rate indicating that spreading by intrusion and the formation of new crust make up for the difference a spatiotemporal analysis of the swarms and coulomb stress modeling show that dike intrusions are the primary driver for brittle failure in the absc while spreading direction is close to ridge normal it is oblique to the adjacent transforms the resulting component of e w extension across the transforms is expressed by deep basins on either side of the rift and a change to extensional faulting along the west andaman fault system after the mw 9 2 sumatra andaman earthquake of 2004 a possible skew in slip vectors of earthquakes in the eastern part of the absc indicates an en echelon arrangement of extensional structures suggesting that the present segment geometry is not in equilibrium with current plate motion demands and thus the ridge experiences ongoing re adjustment

source area and rupture parameters of the 31 december 1881 mw 7 9 car nicobar earthquake estimated from tsunamis recorded in the bay of bengal 1 on the morning of 31 december 1881 a submarine earthquake beneath the andaman islands generated a tsunami with a maximum crest height of 0 8 m that was recorded by eight tide gauges surrounding the bay of bengal since the earthquake occurred 8 years before the construction of the world s first teleseismic recording seismometer little has been known about its rupture parameters or location waveform and amplitude modeling of the tsunami indicate that it was generated by a mw 7 9 0 1 rupture on the india andaman plate boundary resulting in 10 60 cm of uplift of the island of car nicobar the rupture consisted of two segments the northern 40 km long segment is separated from the southern 150 km long segment by a 100 km region corresponding to the westward projection of the west andaman spreading center the main rupture occurred between 8 5 n and 10 n with a total area of 150 km 60 km dipping 20 e with a mean slip of 2 7 m the recurrence time for 1881 type events is estimated to be 114 200 years on the basis of inferred gps convergence rates and inferred plate closure vectors although slip partitioning in the region may extend this estimate by as much as 30

aftershock investigation in the andaman nicobar islands of india and its seismotectonic implications six three component short period digital seismograph four reftek and two kinemetrics stations were established in different parts of the andaman nicobar islands following the 26 december 2004 devastating sumatra andaman mainshock m w 9 3 here we analyze about 18 000 aftershocks m 3 0 recorded from 6 january to 16 march 2005 to better understand the seismotectonics of the region a sudden burst of aftershock activity with irregular trend in the month of january 2005 was observed at almost all seismograph stations the estimate of p value 0 9532 from aftershocks m 4 5 is near to normal value of 1 0 which suggests a slow decay sequence of aftershock with complex and nonuniform stress change in a fault system creep effects and history dependent stress changes the frequency magnitude relation of the aftershocks followed the power law with average b value of 0 7723 and it varies from 0 49 to 1 03 indicating the compressive stress state of the region and its heterogeneous structure with possible variations in frictional conditions along the fault the distribution of the located aftershocks by a multistation method shows a north south trending aftershock cluster in an area of about 800 300 km 2 which reflects an approximate rupture dimension of the mainshock beneath the andaman nicobar islands most of aftershocks occurred in a depth range of 5 65 km the determination of composite fault plane solutions of the best located aftershock clusters at three different depth ranges 0 15 16 30 and 31 km in the ten blocks of the region suggests that the mainshock rupture propagated through normal reverse and strike slip earthquakes the areas in the vicinity of barren and narcondum volcanic zones show a dominantly normal fault mechanism due to predominant tensional forces suggesting the facilitation of brittle failure in the weakened crust by the process of underheating the zone near baratang mud volcano is associated predominantly with thrust fault at depth of 0 30 km suggesting a high compressive force beneath the baratang that ejected a huge amount of mud and slurry materials to the surface after the 26 december 2004 sumatra andaman earthquake m w 9 3 here we propose that the relocation of our large aftershock dataset using converted sp depth phase technique for precise depth control is needed and its sharing with global earthquake data can render more information on the subduction dynamics and geodynamical processes of the region

historical tsunamis and present tsunami hazard in eastern indonesia and the southern philippines 1 eastern indonesia and the southern philippines comprise a huge and seismically highly active region that has received less than the deserved attention in tsunami research compared with the surrounding areas exposed to the major subduction zones in an effort to redress the balance the tsunami hazard in this region is studied by establishing a tsunami event database which in combination with seismological and tectonic information from the region has allowed us to define and justify a number of credible worst case tsunami scenarios these scenarios have been used in numerical simulations of tsunami generation and propagation to study maximum water level along potentially affected shorelines the scenarios have in turn been combined to provide regional tsunami hazard maps in many cases the simulations indicate that the maximum water level may exceed 10 m locally and even reach above 20 m in the vicinity of the source which is of the same order as what is forecasted along the sumatra and java trenches for comparable return periods for sections of coastlines close to a source a tsunami may strike only a few minutes after it is generated providing little time for warning moreover several of the affected areas are highly populated and are therefore also high risk areas the combination of high maximum water levels short warning times dense populations and relatively short return periods suggests strongly that the tsunami hazard and risk in these regions are alarmingly high

repeating aftershocks of the great 2004 sumatra and 2005 nias earthquakes abstract we investigate repeating aftershocks associated with the great 2004 sumatra andaman mw 9 2 and 2005 nias simeulue mw 8 6 earthquakes by cross correlating waveforms recorded by the regional seismographic station psi and teleseismic stations we identify 10 and 18 correlated aftershock sequences associated with the great 2004 sumatra and 2005 nias earthquakes respectively the majority of the correlated aftershock sequences are located near the down dip end of a large afterslip patch we determine the precise relative locations of event pairs among these sequences and estimate the source rupture areas the correlated event pairs identified are appropriately referred to as repeating aftershocks in that the source rupture areas are comparable and significantly overlap within a sequence we use the repeating aftershocks to estimate afterslip based on the slip seismic moment scaling relationship and to infer the temporal decay rate of the recurrence interval the estimated afterslip resembles that measured from the near field geodetic data to the first order the decay rate of repeating aftershocks as a function of lapse time t follows a power law decay 1 t p with the exponent p in the range 0 8 1 1 both types of observations indicate that repeating aftershocks are governed by post seismic afterslip