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

slip distribution from the 1 april 2007 solomon islands earthquake a unique image of near trench rupture 1 we estimate the slip distribution from the mw 8 1 solomon islands earthquake in 2007 from two post seismic surveys measuring uplifted coral and submerged coastal features the occurrence of islands extremely proximal to the trench and nucleation of rupture allowed for the collection of unprecedented coseismic deformation dataset along a large megathrust earthquake using data from the two surveys along the southeastern half of the slip zone within five weeks of the event we model the elastic dislocation to identify the optimal 29 and alternate 20 dip and distribution of thrust along the southern rupture the vertical deformation which includes both coseismic and early postseismic deformation has highly variable and large slip within 25 km of the trench and straddling ranongga island the shallow focus of slip in the near trench area may explain the locally high tsunami run up on portions of simbo island however the aseismic contribution of afterslip remains unknown

active deformation near the nicoya peninsula northwestern costa rica between 1996 and 2010 interseismic megathrust coupling 1 we use campaign and continuous gps measurements at 49 sites between 1996 and 2010 to describe the long term active deformation in and near the nicoya peninsula northwestern costa rica the observed deformation reveals partial partitioning of the cocos caribbean oblique convergence into trench parallel forearc sliver motion and less oblique thrusting on the subduction interface the northern costa rican forearc translates northwestward as a whole ridge block at 11 1 mm yr relative to the stable caribbean the transition from the forearc to the stable caribbean occurs in a narrow deforming zone of 16 km wide subduction thrust earthquakes take 2 3 of the trench parallel component of the plate convergence however surface deformation caused by interseismic megathrust coupling is primarily trench normal two fully coupled patches one located offshore nicoya centered at 15 km depth and the other located inland centered at 24 km depth are identified in nicoya with the potential to generate an mw 7 8 1950 type earthquake another fully coupled patch se of nicoya coincides with the rupture region of the 1990 nicoya gulf earthquake interface microearthquakes non volcanic tremor low frequency earthquakes and transient slow slip events generally occur in the intermediately to weakly coupled regions

rupture kinematics of the 2005 mw 8 6 nias simeulue earthquake from the joint inversion of seismic and geodetic data the 2005 mw 8 6 nias simeulue earthquake was caused by rupture of a portion of the sunda megathrust offshore northern sumatra this event occurred within an array of continuous global positioning system gps stations and produced measurable vertical displacement of the fringing coral reefs above the fault rupture thus this earthquake provides a unique opportunity to assess the source character istics of a megathrust event from the joint analysis of seismic data and near field static co seismic displacements based on the excitation of the normal mode data and geodetic data we put relatively tight constraints on the seismic moment and the fault dip where the dip is determined to be 8 to 10 with corresponding moments of 1 24 10 22 to 1 00 10 22 n m respectively the geodetic constraints on slip distribution help to eliminate the trade off between rupture velocity and slip kine matics source models obtained from the inversion of various combinations of the teleseismic body waves and geodetic data are evaluated by comparing predicted and observed long period seismic waveforms 100 500 sec our results indicate a rela tively slow average rupture velocity of 1 5 to 2 5 km sec and long average rise time of up to 20 sec the earthquake nucleated between two separate slip patches one beneath nias and the other beneath simeulue island the gap between the two patches and the hypocentral location appears to be coincident with a local geological disrup tion of the forearc coseismic slip clearly tapers to zero before it reaches the trench probably because the rupture propagation was inhibited when it reached the accre tionary prism using the models from joint inversions we estimate the peak ground velocity on nias island to be about 30 cm sec an order of magnitude slower than for thrust events in continental areas this study emphasizes the importance of util izing multiple datasets in imaging seismic ruptures

coseismic and postseismic slip of the 2005 m w 8 6 nias simeulue earthquake spatial overlap and localized viscoelastic flow

effects of subducted seamounts on megathrust earthquake nucleation and rupture propagation 1 subducted seamounts have been linked to interplate earthquakes but their specific effects on earthquake mechanism remain controversial a key question is under what conditions a subducted seamount will generate or stop megathrust earthquakes here we show results from numerical experiments in the framework of rate and state dependent friction law in which a seamount is characterized as a patch of elevated effective normal stress on the thrust interface we find that whether subducted seamounts generate or impede megathrust earthquakes depends critically on their relative locations to the earthquake nucleation zone defined by depth variable friction parameters a seamount may act as a rupture barrier and such barrier effect is most prominent when the seamount sits at an intermediate range of the seamount to trench distances 20 100 of the nucleation zone to trench distance moreover we observe that seamount induced barriers can turn into asperities on which megathrust earthquakes can nucleate at shallow depths and rupture the entire seismogenic zone these results suggest that a strong barrier patch may not necessarily reduce the maximum size of earthquakes instead the barrier could experience large coseismic slip when it is ruptured

a 15 year slow slip event on the sunda megathrust offshore sumatra in the banyak islands of sumatra coral microatoll records reveal a 15 year long reversal of interseismic vertical displacement from subsidence to uplift between 1966 and 1981 to explain these coral observations we test four hypotheses including regional sea level changes and various tectonic mechanisms our results show that the coral observations likely reflect a 15 year long slow slip event sse on the sunda megathrust this long duration sse exceeds the duration of previously reported sses and demonstrates the importance of multidecade geodetic records in illuminating the full spectrum of megathrust slip behavior at subduction zones

global seasonal and local time variations of ion density structure at the low latitude ionosphere and their relationship to the postsunset equatorial irregularity occurrences 1 seasonal and longitudinal s l variations of ion density structure near 600 km altitude in the low latitude ionosphere observed by rocsat 1 for two similar high solar activity years of 2000 and 2002 are examined in five different local time lt sectors the gross features in the s l variations of density structure during the daytime are very similar to each other in these 2 years a reproducibility of the daytime density structure can thus be assumed including the shape of equatorial ionization anomaly eia for similar solar flux input the nighttime structure during the solstice shows a shape preserving decay in the latitudinal variation and maintains similar density level for these 2 years in contrast the nighttime structure in the equinox indicates noticeable differences in the 2 years a strong global transport effect that exists in the solstice can be identified as the cause of such difference in density structure between the solstice and the equinox the model results from both the 2006 international reference ionosphere model and the thermosphere ionosphere electrodynamics general circulation model cannot reproduce the global seasonal and local time lt variations of the low latitude ionospheric structure observed by rocsat the observed longitudinal variation of the crest to trough ratio of the average background eia structure in the 1800 1900 lt sector fails to correlate with the longitudinal variation of the postsunset equatorial irregularity occurrences in a season there is also no correlation found between the seasonal variations of the crest to trough ratio and the irregularity occurrence at almost all longitudes except at the longitudes of south america atlantic sector where some correlation seems to exist

p and s wave tomography and anisotropy in northwest pacific and east asia constraints on stagnant slab and intraplate volcanism we determined three dimensional p and s wave velocities and p wave azimuthal anisotropic tomography of the northwest pacific subduction zones by inverting 1 225 086 p wave and 335 117 s wave arrival times from 13 413 earthquakes our results show some differences between p and s wave images for the stagnant pacific slab in the mantle transition zone mtz beneath northeast china the stagnant slab looks thicker in the p wave image than that in the s wave image which may reflects the effects of both hydration and lower temperature in the mtz though differences in the resolution of p and s wave tomography may also have some effects the changbai intraplate volcanism is caused by hot and wet upwelling in the big mantle wedge above the stagnant pacific slab our p wave anisotropy tomography shows that the fast velocity direction fvd in the subducting philippine sea plate beneath the ryukyu arc is ne sw trench parallel which is consistent with the spreading direction of the west philippine basin during its initial opening stage suggesting that it may reflect the fossil anisotropy a striking variation of the fvd with depth is revealed in the subducting pacific slab beneath the northeast japan arc which may be caused by slab dehydration that changed elastic properties of the slab with depth the fvd in the mantle wedge beneath the northeast japan and ryukyu arcs is trench normal which reflects subduction induced convection beneath the kuril and izu bonin arcs where oblique subduction occurs the fvd in the mantle wedge is nearly normal to the moving direction of the downgoing pacific plate suggesting that the oblique subduction together with the complex slab morphology have disturbed the mantle flow

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

the mechanism of partial rupture of a locked megathrust the role of fault morphology assessment of seismic hazard relies on estimates of how large an area of a tectonic fault could potentially rupture in a single earthquake vital information for these forecasts includes which areas of a fault are locked and how the fault is segmented much research has focused on exploring downdip limits to fault rupture from chemical and thermal boundaries and along strike barriers from subducted structural features yet we regularly see only partial rupture of fully locked fault patches that could have ruptured as a whole in a larger earthquake here we draw insight into this conundrum from the 25 april 2015 m w 7 8 gorkha nepal earthquake we invert geodetic data with a structural model of the main himalayan thrust in the region of kathmandu nepal showing that this event was generated by rupture of a decollement bounded on all sides by more steeply dipping ramps the morphological bounds explain why the event ruptured only a small piece of a large fully locked seismic gap we then use dynamic earthquake cycle modeling on the same fault geometry to reveal that such events are predicted by the physics depending on the earthquake history and the details of rupture dynamics however great earthquakes that rupture the entire seismogenic zone are also possible these insights from nepal should be applicable to understanding bounds on earthquake size on megathrusts worldwide

the fine structure of the subducted investigator fracture zone in western sumatra as seen by local seismicity the sumatran margin suffered three great earthquakes in recent years aceh andaman 26 december 2004 mw 9 1 nias 28 march 2005 mw 8 7 bengkulu 12 september 2007 mw 8 5 here we present local earthquake data from a dense amphibious local seismic network covering a segment of the sumatran margin that last ruptured in 1797 the occurrence of forearc islands along this part of the sumatran margin allows the deployment of seismic land stations above the shallow part of the thrust fault in combination with ocean bottom seismometers this station geometry provides high quality hypocentre location for the updip end of the seismogenic zone in an area where geodetic data are also available in this region the investigator fracture zone ifz which consists of 4 sub ridges is subducted below the sunda plate this topography appears to influence seismicity at all depth intervals a well defined linear streak of seismicity extending from 80 to 200 km depth lies along the prolongation of closely spaced ifz sub ridges more intermediate depth seismicity is located to the southeast of this string of seismicity and is related to subducted rough oceanic seafloor the plate interface beneath siberut island which ruptured last in 1797 is characterised by almost complete absence of seismicity

an analysis of the scale heights in the lower topside ionosphere based on the arecibo incoherent scatter radar measurements 1 we statistically analyze the ionospheric scale heights in the lower topside ionosphere based on the electron density ne and temperature profiles observed from the incoherent scatter radar isr at arecibo 293 2e 18 3n puerto rico in this study a database containing the arecibo isr observations from 1966 to 2002 has been used in order to investigate the diurnal and seasonal variations and solar activity dependences of the vertical scale height vsh which is deduced from the electron concentration profiles

on the mechanical role of smectite in subduction zones smectites a group of hydrated phyllosilicate minerals are often a main component of sediments entering a subduction zone they are common in hemipelagic sediments and consist of an authigenetic component that arises from the alteration of volcanic ash intercalated in the sediment and a detrital component smectite rich strata are structurally weak retain water and are highly porous a review of sediment lithology in subduction zones around the world suggests that decollement zones may preferentially form in smectite rich horizons one consequence of this observation is that the assignment of high frictional resistance to materials in a decollement may be unwarranted at deeper structural levels smectite is transformed to illite a mechanically stronger mineral estimates of the depth of this transition coincide with the depth at which earthquakes are first detected along plate interfaces i speculate that the smectite illite transition in subduction zones may be an important component of sediment consolidation processes that trigger interplate seismicity

time varying interseismic strain rates and similar seismic ruptures on the nias simeulue patch of the sunda megathrust fossil coral microatolls from fringing reefs above the great m w 8 6 megathrust rupture of 2005 record uplift during the historically reported great earthquake of 1861 such evidence spans nearly the entire 400 km strike length of the 2005 rupture which was previously shown to be bounded by two persistent barriers to seismic rupture moreover at sites where we have constrained the 1861 uplift amplitude it is comparable to uplift in 2005 thus the 1861 and 2005 ruptures appear to be similar in both extent and magnitude at one site an uplift around ad 1422 also appears to mimic the amount of uplift in 2005 the high degree of similarity among certain ruptures of this nias simeulue section of the sunda megathrust contrasts with the substantial disparities amongst ruptures along other sections of the sumatran portion of the sunda megathrust at a site on the northwestern tip of nias reefs also rose during an earthquake in ad 1843 known historically for its damaging tsunami along the eastern coast of the island the coral microatolls also record interseismic vertical deformation at annual to decadal resolution spanning decades to more than a century before each earthquake the corals demonstrate significant changes over time in the rates of interseismic deformation on southern simeulue interseismic subsidence rates were low between 1740 and 1820 but abruptly increased by a factor of 4 10 two to four decades before the 1861 rupture this may indicate that full coupling or deep locking of the megathrust began only a few decades before the great earthquake in the banyak islands near the pivot line separating coseismic uplift from subsidence in 2005 ongoing interseismic subsidence switched to steady uplift from 1966 until 1981 suggesting a 15 year long slow slip event with slip velocities at more than 120 of the plate convergence rate

forearc structure and morphology along the sumatra andaman subduction zone the sunda subduction margin the location of recent magnitude 8 9 megathrust earthquakes is characterized by major changes in prism and forearc morphology and structure along its 5000 km length on the sumatra andaman section measurements of prism width and surface slope indicate along strike segments inclu1ding abrupt changes of prism morphology 1 a narrow and steep prism between burma and the andamans 2 broad with an averaged gentle slope in the andamans nicobars and north sumatra 3 steep and narrow in central sumatra and 4 wider and less steep offshore south sumatra decreasing in width to west java prism width varies from 90 to 180 km and average surface slope from 1 to 3 with a strong inverse correlation between width and slope also observed globally the prism deviates from typical taper geometry in parts of the margin notably offshore north sumatra where it is characterized by a steep toe and broad plateau along strike changes in morphology are strongly linked to input sediment thickness sections of the prism toe represent key global examples of unusual landward vergent thrusting these sections correspond to a thick sediment input and to a wide prism with shallow surface slope a low basal shear stress or backstop mechanism may drive this style of faulting prism morphology and structure appear to be driven predominantly by input sediment thickness linked to oceanic basement topography with sediment properties plate smoothness and orthogonal subduction rate and obliquity also contributing and no clear role of plate age or dip

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

global frequency of magnitude 9 earthquakes for decades seismologists have sought causal relationships between maximum earthquake sizes and other properties of subduction zones with the underlying notion that some subduction zones may never produce a magnitude 9 or larger event the 2004 andaman m w 9 2 earthquake called into question such ideas given multicentury return times of the greatest earthquakes ignorance of those return times and our very limited observation span i suggest that we cannot yet make such determinations present evidence cannot rule out that any subduction zone may produce a magnitude 9 or larger earthquake based on theoretical recurrence times i estimate that one to three m9 earthquakes should occur globally per century and the past half century with five m9 events reflects temporal clustering and not the long term average

thermal regime of the southwest japan subduction zone effects of age history of the subducting plate abstract during a mid miocene at about 15 ma tectonic reorganization an ocean spreading ridge perpendicular to the strike of the nankai trough subduction zone stopped spreading since that time there has been subduction of the cooling fossil spreading ridge in the present study we have developed a time dependent thermal subduction model for this region using the finite element method there are good seismological and geological constraints for the plate geometry and for the subduction history of the past 15 ma boundary conditions are specified so that the oceanic plate subducting at the nankai trough becomes cooler as it gets older the model results agree with the present heat flow trend that decreases landward and explain the paleothermal regime of high mid miocene temperatures inferred from land geological studies the tectonics of the region prior to 15 ma has some uncertainties assuming subduction of an active spreading ridge or an 80 ma old lithosphere prior to 15 ma give the same results for the present thermal regime of the seaward portion of the forearc but different results for the most landward region 250 km the thermal history of the forearc since 15 ma can be summarized as a rapid warming period as a consequence of ridge subduction followed by a cooling trend to the present as a result of the aging of the subducting plate the results illustrate the thermal consequences of one type of ridge subduction they also demonstrate that the thermal regime of a subduction zone depends critically on the age history of the subducting oceanic lithosphere especially if it is young as well as such parameters as the subducting plate dip angle and thickness of insulating sediments on the incoming oceanic crust this dependence is especially important when the thermal regime is used to constrain the seismogenic behaviour of the subduction thrust fault

revisiting the structure age and evolution of the wharton basin to better understand subduction under indonesia understanding the subduction processes along the sunda trench requires detailed constraints on the subducting lithosphere we build a detailed tectonic map of the wharton basin based on reinterpretation of satellite derived gravity anomalies and marine magnetic anomalies the wharton basin is characterized by a fossil ridge dated 36 5 ma offset by n s fracture zones magnetic anomalies 18 to 34 38 84 ma are identified on both flanks although a large part of the basin has been subducted we analyze the past plate kinematic evolution of the wharton basin by two plate india australia and three plate india australia antarctica reconstructions despite the diffuse plate boundaries within the indo australian plate for the last 20 ma we obtain finite rotation parameters that we apply to reconstruct the subducted wharton basin and constrain the thickness buoyancy and rheology of the subducting plate the lower subductability of younger lithosphere off sumatra has important consequences on the morphology with a shallower trench forearc islands and a significant inward deviation of the subduction system this deviation decreases in the youngest area where the wharton fossil spreading center enters subduction the discontinuous magmatic crust and serpentinized upper mantle consequences of the slow spreading rates at which this area was formed weaken the mechanical resistance to subduction and facilitate the restoration of the accretionary prism deeper effects include the possible creation of asthenospheric windows beneath the andaman sea in relation to the long offset fracture zones and east of 105 e as a result of subduction of the spreading center

coseismic slip and afterslip of the great mw 9 15 sumatra andaman earthquake of 2004 we determine coseismic and the first month postseismic deformation associated with the sumatra andaman earthquake of 26 december 2004 from near field global positioning system gps surveys in northwestern sumatra and along the nicobar andaman islands continuous and campaign gps measurements from thailand and malaysia and in situ and remotely sensed observations of the vertical motion of coral reefs the coseismic model shows that the sunda subduction mega thrust ruptured over a distance of about 1500 km and a width of less than 150 km releasing a total moment of 6 7 7 0 10 22 n m equivalent to a magnitude m w 9 15 the latitudinal distribution of released moment in our model has three distinct peaks at about 4 n 7 n and 9 n which compares well to the latitudinal variations seen in the seismic inversion and of the analysis of radiated t waves our coseismic model is also consistent with interpretation of normal modes and with the amplitude of very long period surface waves the tsunami predicted from this model fits rela tively well the altimetric measurements made by the jason and topex satellites neither slow nor delayed slip is needed to explain the normal modes and the tsunami wave the near field geodetic data that encompass both coseismic deformation and up to 40 days of postseismic deformation require that slip must have continued on the plate interface after the 500 sec long seismic rupture the postseismic geodetic moment of about 2 4 10 22 nm mw 8 8 is equal to about 30 5 of the coseismic moment release evolution of postseismic deformation is consistent with rate strengthening frictional afterslip online material summary of geodetic data used in this study

robust features of the source process for the 2004 parkfield california earthquake from strong motion seismograms summary we explore a recently developed procedure for kinematic inversion based on an elliptical subfault approximation in this method the slip is modelled by a small set of elliptical patches each ellipse having a gaussian distribution of slip we invert near field strong ground motion forthe2004september28mw 6 0parkfield california earthquake thedatasetconsistsof10 digital three component 18 s long displacement seismograms the best model gives a moment of 1 21 10 18 n m with slip on two distinct ellipses one with a high slip amplitude of 0 91 m located 20 km northwest of the hypocentre the average rupture speed of the rupture process is 2 7 kms 1 we find no slip in the top 5 km at this depth a lineation of small aftershocks marks the transition from creeping above to locked below in the interseismic period the highslip patch coincides spatially with the hypocentre of the 1966 mw6 0 parkfield california earthquake the larger earthquakes prior to the 2004 parkfield earthquake and the aftershocks of the 2004 earthquake mw 3 also lie around this high slip patch where our model images a sharp slip gradient this observation suggests the presence of a permanent asperity that breaks during large earthquakes and has important implications for the slip deficit observed on the parkfield segment which is necessary for reliable seismic hazard assessment

footprints of past earthquakes revealed in the afterslip of the 2010 mw 7 8 mentawai tsunami earthquake the 2010 mw 7 8 mentawai tsunami earthquake marks one of the first tsunami earthquakes to have postseismic deformation observed by geodetic instruments the sumatran gps array sugar has recorded the postseismic deformation following this event continuously for 5 years the spatio temporal evolution of the postseismic deformation is well explained by velocity strengthening frictional sliding on the sunda megathrust our results show that the 2010 afterslip progressed downdip relative to the 2010 coseismic rupture the southeastern portion of the afterslip region overlaps the area that slipped during the mainshock and afterslip of the 2007 mw 8 4 bengkulu earthquake while the northwestern portion slipped an area without recent large earthquakes by incorporating pre earthquake stress conditions into quasi dynamic models we demonstrate that the preceding cumulative slip from the 2007 sequence might have caused a 0 1 mpa difference in pre earthquake coulomb stress between the southeastern and northwestern portions of the afterslip region

tectonic evolution and mantle structure of the caribbean we investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic p wave velocity structure under the caribbean region in the upper mantle positive seismic anomalies are imaged under the lesser antilles and puerto rico these anomalies are interpreted as remnants of atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the lesser antilles island arc during the past 45 myr the imaged lesser antilles slab consists of a northern and southern anomaly separated by a low velocity anomaly across most of the upper mantle which we interpret as the subducted north america south america plate boundary the southern edge of the imaged lesser antilles slab agrees with vertical tearing of south america lithosphere the northern lesser antilles slab is continuous with the puerto rico slab along the northeastern plate boundary this results in an amphitheater shaped slab and it is interpreted as westward subducting north america lithosphere that remained attached to the surface along the northeastern boundary of the caribbean plate at the muertos trough however material is imaged until a depth of only 100 km suggesting a small amount of subduction the location and length of the imaged south caribbean slab agrees with proposed subduction of caribbean lithosphere under the northern south america plate an anomaly related to proposed oligocene subduction at the nicaragua rise is absent in the tomographic model beneath panama a subduction window exists across the upper mantle which is related to the cessation of subduction of the nazca plate under panama since 9 5 ma and possibly the preceding subduction of the extinct cocos nazca spreading center in the lower mantle two large anomaly patterns are imaged the westernmost anomaly agrees with the subduction of farallon lithosphere the second lower mantle anomaly is found east of the farallon anomaly and is interpreted as a remnant of the late mesozoic subduction of north and south america oceanic lithosphere at the greater antilles aves ridge and leeward antilles the imaged mantle structure does not allow us to discriminate between an intra americas origin and a pacific origin of the caribbean plate key points tectonic reconstructions for the caribbean validated by seismic tomography cenozoic lesser antilles and mesozoic greater antilles subduction confirmed tomography gives insight into geodynamics of lesser antilles

interseismic coupling segmentation and mechanical behavior of the central chile subduction zone global positioning system gps measurements carried out in chile over the last two decades showed that an entire portion of the nazca south america subduction zone 38 s 24 s was locked over this period of time the induced accumulation of elastic deformation in the upper plate was not released until the recent maule earthquake of 27 february 2010 mw 8 8 that ruptured the southern part of this section locking or coupling between the two plates varies both with depth and along strike here we use our own gps data an updated solution of our extended network in central chile combined with other published data sets to quantify the spatial variations of the coupling that prevailed before the maule earthquake using a simple elastic model based on the back slip assumption we show that coupling variations on the subduction plane are sufficient to explain the observed surface deformation with no need of a sliver in central chile we identify four segments characterized by higher coupling and separated by narrow areas of lower coupling this segmentation is in good agreement with historical and recent seismicity in chile in particular the narrow zones of lower coupling seem to have stopped most large seismic ruptures including maule s these zones are often associated with irregular bathymetric or coastal features fracture zones or peninsulas finally coseismic and early post seismic slip distribution of the maule earthquake occurring either in previously highly or weakly coupled zones map a complex distribution of velocity weakening and velocity strengthening patches on the subduction interface

slab breakoff as a mechanism for flipping of subduction polarity in taiwan we propose a model that involves breakoff of the east dipping eurasian slab beneath the taiwan orogen to account for the flipping of subduction polarity in northern taiwan the breakoff was initiated in southern ryukyu in the early pliocene and then propagated southwestward into taiwan like an opening zipper detachment of the eurasian slab has created a mantle window for the north dipping philippine sea plate to move in laterally causing a switch in the subduction polarity slab breakoff not only provides a testable model for the lithospheric structure of taiwan but also accounts for the high heat flow rapid uplift synorogenic extension deep focus earthquakes and north diminishing crustal contraction in the taiwan mountain belt

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

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

historical seismograms for unravelling a mysterious earthquake the 1907 sumatra earthquake history of instrumental seismology is short seismograms are available only for a little more than 100 years high quality seismograms are available only for the last 50 years and the seismological database is very limited in time to extend the database seismograms of old events are of vital importance many unusual earthquakes are known to have occurred but their seismological characteristics are poorly known the 1907 sumatra earthquake is one of them 1907 january 4 m 7 6 gutenberg and richter located this event in the outer rise area of the sunda arc this earthquake is known to be anomalous because of its extensive tsunami which is disproportionate of its magnitude the tsunami affected the coastal areas over 950 km along the sumatran coast we investigated this earthquake using the historical seismograms we could collect from several seismological observatories we examined the p wave arrival times listed in the strassburg bulletin 1912 and other station bulletins the scatter of the observed computed traveltime residuals ranges from 30 to 30 s too large to locate the event accurately the uncertainty of the epicentre estimated from an s p grid search relocation study is at least 1 110 km we interpreted the omori seismograms from osaka mizusawa and tokyo and the wiechert seismograms from gottingen and uppsala by comparing them with the seismograms simulated from modern broad band seismograms of the 2002 2008 and two 2010 sumatra earthquakes which occurred near the 1907 earthquake from the amplitude of rayleigh waves recorded on the omori seismograms we conclude that the magnitude of the 1907 earthquake at about 30 to 40 s is about 7 8 i e 7 5 to 8 0 the sh waveforms recorded on the gottingen and uppsala seismograms suggest that the 1907 earthquake is a thrust earthquake at a shallow depth around 30 km the most likely scenario is that the 1907 earthquake initiated on the subduction interface and slowly ruptured up dip into the shallow sediments and caused the extensive tsunami although their quantity and quality are limited historical seismograms provide key quantitative information about old events that cannot be obtained otherwise this underscores the importance of preserving historical seismograms

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

implications of the diffuse deformation of the indian ocean lithosphere for slip partitioning of oblique plate convergence in sumatra oblique plate convergence between indian ocean lithosphere and continental crust of the sunda plate is distributed between subduction on the sunda megathrust and upper plate strike slip faulting on the sumatran fault zone in a classic example of slip partitioning over the last decade a destructive series of great earthquakes has brought renewed attention to the mechanical properties of these faults and the intervening forearc crustal block while observations of forearc deformation over the earthquake cycle indicate that the forearc crust is fundamentally elastic the spatial pattern of slip vector azimuths for earthquakes sourced by rupture of the sunda megathrust is strongly inconsistent with relative motion of two rigid plates permanent and distributed deformation therefore occurs in either the downgoing lithospheric slab or the overriding forearc crust previous studies have inferred from geodetic velocities and geological slip rates of the sumatran fault that the forearc crust is undergoing rapid trench parallel stretching using new geological slip rates for the sumatran fault and an updated decadal gps velocity field of sumatra and the forearc islands we instead show that permanent deformation within the forearc sliver is minor and that the sumatran fault is a plate boundary strike slip fault the kinematic data are best explained by diffuse deformation within the oceanic lithosphere of the wharton basin which accommodates convergence between the indian and australian plates and has recently produced several large earthquakes well offshore of sumatra the slip partitioning system in sumatra is fundamentally linked with the mechanical properties of the subducting oceanic lithosphere

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

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

okinawa trough backarc basin early tectonic and magmatic evolution the okinawa trough lying between japan and taiwan is a backarc basin formed by extension within the continental lithosphere behind the ryukyu trench arc system stress directions associated with the two last extensional phases in the southwestern okinawa trough have been deduced from a comparison with analog modeling the direction of extension is n 150 o for the pleistocene phase of extension 2 0 1 ma and n 170 o for the late pleistocene holocene phase of extension 0 1 0 ma the present day ryukyu volcanic arc a narrow continuous feature extending from japan to taiwan is located on the eastern side of the okinawa trough 80 100 km above the wadati benioff zone the minimum depth for emplacement of arc magmatism scarce present day backarc volcanism appears in the middle and southern okinawa trough within linear en echelon bathymetric depressions a n045 o oriented seamount volcanic chain cuts across obliquely the southwestern okinawa trough and lies in the direct line of extension of the gagua ridge a n s linear volcanic feature of the philippine sea plate associated with this extension of the gagua ridge a large reentrant located at the base of the ryukyu prism the uplift of part of the nanao forearc basin and the deformation of the sedimentary arc suggest that the voluminous cross backarc volcanism could be tied to the subduction of the gagua ridge located there at a depth of 80 100 km beneath the backarc basin a second area of anomalous volcanism has been identified in the middle okinawa trough in the ene extension of the daito ridge a wnw ese 400 km long volcanic feature of the philippine sea plate we suggest that the gagua and daito ridges initially induced stress at the base of the arc which is still brittle and cracks propagated through the overlying brittle lithosphere allowing magmas with arc affinities to erupt at the seafloor this excessive magmatism reaches the seafloor through conduits which preferentially follow in their shallowest portion the crustal normal faults of the backarc rifts the okinawa trough is consequently still in an early stage of evolving from arc type to backarc activity

the finite kinematic rupture properties of great sized earthquakes since 1990 abstract here i present a database of 160 finite fault models for all earthquakes of m 7 5 and above since 1990 created using a consistent modeling approach the use of a common approach facilitates easier comparisons between models and reduces uncertainties that arise when comparing models generated by different authors data sets and modeling techniques i use this database to verify published scaling relationships and for the first time show a clear and intriguing relationship between maximum potency the product of slip and area and average potency for a given earthquake this relationship implies that earthquakes do not reach the potential size given by the tectonic load of a fault sometimes called moment deficit calculated via a plate rate over time since the last earthquake multiplied by geodetic fault coupling instead average potency or slip scales with but is less than maximum potency dictated by tectonic loading importantly this relationship facilitates a more accurate assessment of maximum earthquake size for a given fault segment and thus has implications for long term hazard assessments the relationship also suggests earthquake cycles may not completely reset after a large earthquake and thus repeat rates of such events may appear shorter than is expected from tectonic loading this in turn may help explain the phenomenon of earthquake super cycles observed in some global subduction zones

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

afterslip following the 2007 mw 8 4 bengkulu earthquake in sumatra loaded the 2010 mw 7 8 mentawai tsunami earthquake rupture zone the 12 september 2007 mw 8 4 bengkulu earthquake in sumatra marked the first in a modern series of large earthquakes along the mentawai section of the sunda megathrust understanding the spatial distribution of coseismic slip and ensuing afterslip is important for assessing seismic hazard in neighboring unruptured regions of the megathrust we re estimate the spatial distribution of coseismic slip during this earthquake with improved coseismic offsets from the sumatran gps array sugar and estimate afterslip following this earthquake with sugar postseismic time series spanning 6 3 years after the earthquake we invert for the spatio temporal distribution of afterslip with the principal component analysis based inversion method pcaim and we take into account viscoelastic deformation by incorporating into the inversion the estimation of strain within ductile deforming blocks located at asthenospheric depths our results suggest cumulative afterslip concentrated within updip and downdip of the 2007 coseismic rupture area and shallow afterslip that borders and overlaps the 2010 mw 7 8 mentawai earthquake rupture zone the cumulative contribution of stress changes due to the coseismic event and the ensuing afterslip likely increased strain rates in the shallow portion of the megathrust adjacent to the mentawai earthquake rupture area potentially promoting its rupture in 2010

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

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

deformation and slip along the sunda megathrust in the great 2005 nias simeulue earthquake seismic rupture produced spectacular tectonic deformation above a 400 kilometer strip of the sunda megathrust offshore northern sumatra in march 2005 measurements from coral microatolls and global positioning system stations reveal trench parallel belts of uplift up to 3 meters high on the outer arc islands above the rupture and a 1 meter deep subsidence trough farther from the trench surface deformation reflects more than 11 meters of fault slip under the islands and a pronounced lessening of slip trenchward a saddle in megathrust slip separates the northwestern edge of the 2005 rupture from the great 2004 sumatra andaman rupture the southeastern edge abuts a predominantly aseismic section of the megathrust near the equator

earthquake rupture stalled by a subducting fracture zone we showed that the rupture produced by the great peru earthquake moment magnitude 8 4 on 23 june 2001 propagated for 70 kilometers before encountering a 6000 square kilometer area of fault that acted as a barrier the rupture continued around this barrier which remained unbroken for 30 seconds and then began to break when the main rupture front was 200 kilometers from the epicenter the barrier had relatively low rupture speed slip and aftershock density as compared to its surroundings and the time of the main energy release in the earthquake coincided with the barrier s rupture we associate this barrier with a fracture zone feature on the subducting oceanic plate

topside ionospheric scale heights retrieved from constellation observing system for meteorology ionosphere and climate radio occultation measurements 1 the vertical scale height vsh in the topside ionosphere can be derived from electron density profiles in this study the electron density profiles retrieved from the cosmic formosat 3 a constellation observing system for meteorology ionosphere and climate mission c f3 for short ionospheric radio occultation iro observations have been collected to investigate the local time seasonal latitudinal and longitudinal variations of the vsh with the postprocessed c f3 iro electron density profiles during the interval from day of year doy 194 in 2006 to doy 60 in 2008 we conduct an analysis on the behaviors of vsh at an altitude of 400 km there are appreciable latitudinal variations in vsh a new finding is a significant peak around dip equator during daytime in four seasons away from the equatorial peak it is obvious that the vsh generally increases at higher latitudes the equatorial vsh undergoes a significant diurnal variation with a local noon maximum the peak shifts to sunrise time with increasing dip latitude and the values of daytime vsh become comparable with those at nighttime at low latitude in both hemispheres which is somewhat different from the feature revealed from arecibo incoherent scatter radar observations one of the crucial findings in our results is the most outstanding feature of vsh that is the presence of a substantial longitudinal structure in equatorial regions a wave like longitudinal feature is found in equatorial vsh during the daytime in four seasons while it becomes weaker or absent at other local time intervals and at higher latitudes this investigation also confirms that the behaviors of vsh are not strongly consistent with those of the neutral or plasma scale heights

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

empirical model of the thermospheric mass density based on champ satellite observations 1 the decadal observations from champ satellite have provided ample information on the earth s upper thermosphere reshaping our understandings of the vertical coupling in the atmosphere and near earth space an empirical model of the thermospheric mass density is constructed from these high resolution observations using the multivariable least squares fitting method it describes the density variation with latitude longitude height local time season and solar and geomagnetic activity levels within the altitude range of 350 420 km it represents well prominent thermosphere structures like the equatorial mass density anomaly ema and the wave 4 longitudinal pattern furthermore the empirical model reveals two distinct features first the ema is found to have a clear altitude dependence with its crests moving equatorward with increasing altitude second the equinoctial asymmetry is found to strongly depend on solar cycle with its magnitude and phase being strongly regulated by solar activity levels the equinoctial density maxima occur significantly after the actual equinox dates toward solar minimum which may signal growing influence from the lower atmosphere forcing this empirical model provides an instructive tool in exploring thermospheric density structures and dynamics it can also be easily incorporated into other models to have a more accurate description of the background thermosphere for both scientific and practical purposes

thermal modeling of the sw ryukyu forearc taiwan implications for the seismogenic zone and the age of the subducting philippine sea plate huatung basin subduction mega thrust earthquakes in the sw ryukyu trench pose a seismic and tsunami hazard one of the objectives of this study is to estimate the downdip width of the seismogenic zone using numerical modeling to determine the temperature distribution along the plate interface however this approach depends strongly on the thermal parameters of the subducting slab while the philippine sea plate psp subducting beneath the central and eastern ryukyu arc is of eocene age 35 50 ma its age west of the gagua ridge is uncertain with proposed ages ranging from lower cretaceous 140 ma to upper eocene 35 ma since the sparse available heat flow data are insufficient to resolve this debate both end member hypotheses are tested as input parameters we examined two transects at 122 5 e and 123 5 e on either side of the n s trending 4 km high gagua ridge the shallow forearc geometry is obtained from wide angle seismic data the deep slab geometry was obtained from hypocenter distribution and tomography for an eocene slab age we obtain a 100 km and 110 km wide seismogenic zone between the 150 c and 350 c isotherms west and east of gagua ridge respectively this is in good agreement with the observed distribution of hypocenters using a cretaceous slab west of gagua ridge predicts a deep seismogenic zone 25 km 60 km depth inconsistent with observed thrust earthquakes tomographic images at 122 5 e and 123 5 e show a similar slab thickness of 70 80 km suggesting that the oceanic lithosphere has a young eocene thermal age the westernmost psp huatung basin may have been thermally rejuvenated by mantle convection near the slab corner the tectonic history since 6 ma transition from subduction to collision beneath taiwan may have also perturbed the thermal structure

physical characteristics of subduction interface type seismogenic zones revisited 1 based on global earthquake catalogs the hypocenters nodal planes and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007 assuming that the seismogenic zone coincides with the distribution of 5 5 m 7 earthquakes the subduction interface seismogenic zones were mapped for 80 of the trench systems and characterized with geometrical and mechanical parameters using this database correlations were isolated between significant parameters to identify cause effect relationships empirical laws obtained in previous studies were revisited in light of this more complete accurate and uniform description of the subduction interface seismogenic zone the seismogenic zone was usually found to end in a fore arc mantle rather than at a moho depth the subduction velocity was the first order controlling parameter for variations in the physical characteristics of plate interfaces determining both the geometry and mechanical behavior as such the fast subduction zones and cold slabs were associated with large and steep plate interfaces which in turn had large seismic rates the subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches events with mw 8 5 preferentially occurred in the vicinity of slab edges where the upper plate was continental and the back arc strain was neutral this observation was interpreted in terms of compressive normal stresses along the plate interface large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally

geometrical effects of a subducted seamount on stopping megathrust ruptures 1 we have numerically simulated dynamic ruptures along a slip weakening megathrust fault with a subducted seamount of realistic geometry demonstrating that seamounts can act as a barrier to earthquake ruptures such barrier effect is calculated to be stronger for increased seamount normal stress relative to the ambient level for larger seamount height to width ratio and for shorter seamount to nucleation distance as the seamount height increases from 0 to 40 of its basal width the required increase in the effective normal stress on the seamount to stop ruptures drops by as much as 20 we further demonstrate that when a seamount is subducted adjacent to the earthquake nucleation zone coseismic ruptures can be stopped even if the seamount has a lower effective normal stress than the ambient level these results indicate that subducted seamounts may stop earthquake ruptures for a wide range of seamount normal stress conditions including the case of the thrust fault being lubricated by seamount top fluid rich sediments as suggested from observations in the japan and sunda trenches

persistent termini of 2004 and 2005 like ruptures of the sunda megathrust to gain insight into the longevity of subduction zone segmentation we use coral microatolls to examine an 1100 year record of large earthquakes across the boundary of the great 2004 and 2005 sunda megathrust ruptures simeulue a 100 km long island off the west coast of northern sumatra indonesia straddles this boundary northern simeulue was uplifted in the 2004 earthquake whereas southern simeulue rose in 2005 northern simeulue corals reveal that predecessors of the 2004 earthquake occurred in the 10th century ad in ad 1394 2 and in ad 1450 3 corals from southern simeulue indicate that none of the major uplifts inferred on northern simeulue in the past 1100 years extended to southern simeulue the two largest uplifts recognized at a south central simeulue site around ad 1422 and in 2005 involved little or no uplift of northern simeulue the distribution of uplift and strong shaking during a historical earthquake in 1861 suggests the 1861 rupture area was also restricted to south of central simeulue as in 2005 the strikingly different histories of the two adjacent patches demonstrate that this boundary has persisted as an impediment to rupture through at least seven earthquakes in the past 1100 years this implies that the rupture lengths and hence sizes of at least some future great earthquakes and tsunamis can be forecast these microatolls also provide insight into megathrust behavior between earthquakes revealing sudden and substantial changes in interseismic strain accumulation rates

deriving the effective scale height in the topside ionosphere based on ionosonde and satellite in situ observations chapman scale height is a valuable key parameter measuring the shape of the profile of plasma density in the f2 layer ionosphere currently the data of chapman scale height are routinely derived from ionogram observations at many ionosonde stations in terms of the sao explorer software in this report we collected the in situ observations of plasma density at altitudes around 600 km from the rocsat 1 satellite and of simultaneous f peak parameters from an ionosonde operated at wuhan 30 6 n 114 4 e a low latitude station in central china to estimate the topside plasma density profiles by using the chapman function and further retrieve chapman scale height evident solar cycle seasonal variation and local time variation are presented in the retrieved chapman scale height over wuhan the climatological features of the derived chapman scale height are significantly different from those from the ground based ionograms such significant discrepancy suggests that further improvements are required in the present extrapolating topside electron density profiles from ionosonde observations furthermore the attempt to constructing plasma density profiles through combining ionosonde and satellite in situ observations provides a new way to reanalyze observations from different sources and normalize plasma density recorded at varying altitudes to specified altitudes which is critical and more convenient for ionospheric climatology studies

the updip seismic aseismic transition of the sumatra megathrust illuminated by aftershocks of the 2004 aceh andaman and 2005 nias events great subduction earthquakes exhibit segmentation both within the rupture of individual events and in the long term history of the margin the 2004 december 26 aceh andaman and 2005 march 28 nias event in northern sumatra are two of the largest earthquakes in recent years with both co and post seismic displacements constrained in unprecedented detail using aftershock locations from a temporary seismic array in the boundary region between both events and waveform modelling of large aftershocks we demonstrate that the vast majority of aftershocks in the study region occur on the plate interface within a narrow band 20 km seaward of the outer arc high comparing the seismicity distribution to the co and post seismic displacements we infer that the seismic band marks the transition between the seismogenic zone and stable sliding the location of the band and therefore the transition appears to be correlated with the 500 m bathymetry contour this close correspondence is disrupted at the boundary between the two great earthquakes where the transition to seismogenic behaviour occurs further landward by 25 km to the west of simeulue where seafloor bathymetry throughout the forearc is deeper than 500 m the seismic band terminates abruptly and the focus of aftershock activity is found near the trench the seismic efficiency of afterslip varies dramatically along strike the segment below the banyak islands in the gap between the two main asperities of the nias earthquake accommodates a much larger proportion of afterslip seismically