seismic evidence for reactivation of a buried hydrated fault in the pacific slab by the 2011 m9 0 tohoku earthquake 1 we employ seismic tomography to estimate detailed 3d seismic velocity structures in the focal area of an intraslab earthquake m7 1 which occurred on april 7 1 month after the 2011 tohoku earthquake m9 0 near its source area the results show a low velocity zone around the focal area of the m7 1 event and that the aftershock activity is limited to the upper 15 km of the oceanic mantle the lateral extent of the low velocity zone is comparable to the distribution of aftershocks suggesting a concentration of fluids in the aftershock area the angle between the aftershock alignment and the dip of the slab surface is estimated to be 60 which is consistent with the dip of an oceanward dipping normal fault observed at the outer trench slope these observations suggest that the m7 1 intraslab event occurred as a result of reactivation of a buried hydrated fault that formed prior to subduction the upper 15 km of the oceanic mantle may be locally hydrated by bending related tensional faulting at the outer trench slope

quasi real time fault model estimation for near field tsunami forecasting based on rtk gps analysis application to the 2011 tohoku oki earthquake mw 9 0 1 real time crustal deformation monitoring is extremely important for achieving rapid understanding of actual earthquake scales because the measured permanent displacement directly gives the true earthquake size seismic moment mw information which in turn provides tsunami forecasting we have developed an algorithm to detect estimate static ground displacements due to earthquake faulting from real time kinematic gps rtk gps time series the new algorithm identifies permanent displacements by monitoring the difference of a short term average sta to a long term average lta of the gps time series we assessed the noise property and precision of the rtk gps time series with various baseline length conditions and orbits and discerned that the real time ephemerides based on the international gnss service igs are sufficient for crustal deformation monitoring with long baselines up to 1 000 km we applied the algorithm to data obtained in the 2011 off the pacific coast of tohoku earthquake mw 9 0 to test the possibility of coseismic displacement detections and further we inverted the obtained displacement fields for a fault model the inversion estimated a fault model with mw 8 7 which is close to the actual mw of 9 0 within five minutes from the origin time once the fault model is estimated tsunami waveforms can be immediately synthesized using pre computed tsunami green s functions the calculated waveforms showed good agreement with the actual tsunami observations both in arrival times and wave heights suggesting that the rtk gps data by our algorithm can provide reliable rapid tsunami forecasting that can complement existing tsunami forecasting systems based on seismic observations

source spectral characteristics of two large intra slab earthquakes along the southern kurile hokkaido arc abstract in 1993 and 1994 two large earthquakes occurred along the southern kurile hokkaido arc the 1993 kushiro oki earthquake 15 january mw 7 6 and the 1994 shikotan earthquake 4 october mw 8 2 these were intra slab earthquakes that ruptured through a substantial part of the subducting oceanic lithosphere we study source spectral characteristics of these large intra slab earthquakes based on strong motion records for the kushiro oki earthquake the s wave spectra on three rock site stations are directly compared with the theoretical spectra based on the omega squared source model and the source parameters estimated from long period seismic waves the observed spectra are roughly consistent with the theoretical ones at low frequencies

earthquakes a chilean surprise initiation of the great 2010 chile earthquake occurred within the rupture zone of the 1835 event experienced by charles darwin however the peak fault slip was to the north of the epicentre not where it was expected to occur

full interseismic locking of the nankai and japan west kurile subduction zones an analysis of uniform elastic strain accumulation in japan constrained by permanent gps we analyze permanent global positioning system gps data obtained over japan between 1995 and 1997 to estimate the instantaneous interseismic coupling ratio of the seismogenic zones due to the subduction of the pacific and philippine sea plates below the japanese islands we first derive the gps strain rate fields that characterize the crustal deformation of southern and northern japan and invert them to determine the effective subduction velocity along the central nankai trough on one side and the japan west kurile trench on the other these reference free velocities are close to those predicted by plate motion models with respect to eurasia we conclude that the eurasian reference frame gives a good approximation to the subduction motion and that to first order both subduction zones were fully locked during the period of measurements we then test whether the coupling ratio shows local variations within the seismogenic zones to do this we divide the subduction interface into 35 km 30 km elements that we model by point source groups and we invert the gps velocity field referenced to eurasia to derive the coupling ratio between 0 and 1 on each fault element the results are coherent over the 3 years and confirm that both the central nankai and the japan west kurile seismogenic zones are homogeneously fully locked most of the coupling ratios are close to 1 and a few are close to 0 intermediate values are rare the zones of decoupling correspond either to strong postseismic afterslip associated with the 1994 sanriku oki interplate earthquake japan trench or to a small overestimation of the actual lower limit of the locked zone we conclude that within the resolution of the gps data and the model 1 partial coupling did not exist during these 3 years along the nankai and japan west kurile trenches 2 the small seismic coupling ratio previously derived from earthquakes analysis for the japan and kurile trenches may indicate that a significant part of the elastic energy is dissipated silently through slow earthquakes and postseismic afterslip and 3 the heterogeneous coseismic slip pattern observed for the large and great earthquakes that rupture both subduction zones is in great contrast to the homogeneous loading finally we discuss the nonelastic residual deformation within the frame of the long term deformation of the japanese islands

the diversity of large earthquakes and its implications for hazard mitigation with the advent of broadband seismology and gps significant diversity in the source radiation spectra of large earthquakes has been clearly demonstrated this diversity requires different approaches to mitigate hazards in certain tectonic environments seismologists can forecast the future occurrence of large earthquakes within a solid scientific framework using the results from seismology and gps such forecasts are critically important for long term hazard mitigation practices but because stochastic fracture processes are complex the forecasts are inevitably subject to large uncertainty and unexpected events will continue to surprise seismologists recent developments in real time seismology will help seismologists to cope with and prepare for tsunamis and earthquakes combining a better understanding of earthquake diversity with modern technology is the key to effective and comprehensive hazard mitigation practices

the dynamic rupture process of the 1993 kushiro oki earthquake we have constructed a dynamic rapture model of the 1993 kushiro oki earthquake mw 7 6 that is consistent with the observed seismograms this earthquake occurred beneath the city of kushiro japan at a depth of about 100 km and the aftershocks are limited to a horizontal plane between a double seismic zone in the subducting slab excellent near field strong motion records are available in our analysis a kinematic inversion is followed by a dynamic crack calculation and this pair of operations is repeated until convergence to the data is obtained two different conditions concerning the dynamic stress drop were considered in the dynamic calculation and a dynamic model was constructed for each condition the difference in these conditions has little effect on the results the final dynamic model shows that this earthquake occurred with a localized high stress drop of about 40 mpa in the subducting slab which indicates that the region between the double seismic zone is strong enough to sustain such a high stress one of the two high strength regions in the final model lies near the upper plane of the double seismic zone and represents a barrier due to a substantial change of stress state in the slab in the region where the initial breaks occurred 5 s before the main rupture both the strength and the stress drop are smaller than in the adjacent region this implies that before the main rupture the accumulated stress had already been released in the area of the initial breaks the aftershocks tend to occur near the high strength area in some of them the p wave first motions are opposite to those of the main shock

earthquakes as self organized critical phenomena a cellular automation model with threshold elements previously proposed by bak et al 1988 which generates 1 f noise and self organizes into a critical state is studied as a model for earthquake occurrence the model explains some of fractal features of earthquakes such as the power law distribution of the size of the earthquake the model is modified so that every earthquake may trigger aftershocks the modified trigger model explains other fractal features of earthquakes such as the power law decay of aftershock frequency and the power law decay of aftershock frequency and the power law correlation of the hypocenter distribution

elevated bacterial abundance and exopolymers in saline frost flowers and implications for atmospheric chemistry and microbial dispersal 1 frost flowers ff have been studied for their potential influence on ice surface reflectivity and roles in atmospheric chemistry but not as microbial habitats we examined ff grown in a freezer laboratory from a bacteria containing saline solution and ff formed naturally in the coastal april and central arctic ocean september all ff contained bacteria up to 3 46 106 ml 1 in natural ff with densities 3 6 fold higher than in underlying ice bacterial abundance correlated strongly with salinity in ff p values 0 001 a correlation that held for all components of the surface ice environment p 0 0001 coastal samples concentrations of extracellular polysaccharides were also elevated in ff and brine skim relative to underlying ice up to 74 fold higher here we consider implications of finding microbes and exopolymers within the chemically reactive surface ice environment to the photolytic production of oxidants and long range transport of potential ice nucleating particles in the atmosphere

the 1994 java tsunami earthquake and its normal aftershocks 1 we compare the source spectra of the 1994 java tsunami earthquake mw 7 9 and its two largest aftershocks the source spectra of the aftershocks from teleseismic p waves can be fit remarkably well by a standard 2 model however the mainshock shows a lower moment release at periods of 1 20 sec than its aftershocks although its total moment is 1000 times larger we analyze this discrepancy by exploring two mechanisms that in a simple haskell rupture model will decrease one of the corner frequencies of the source spectrum 1 lowering the rupture velocity and 2 lowering the particle slip velocity both changes maintain an identical spectral drop off and static stress drop and result in the characteristic spectral shape of a slow earthquake these kinematic models can be related to physical rupture parameters by considering the earthquake energy budget in both cases the radiated seismic energy is lowered either due to a higher frictional stress during the break down phase increasing the fracture energy case 1 or by an increase in the sliding stress case 2 we do not suggest that either of these simplified models is the only possible interpretation but want to illustrate the danger in directly interpreting slow earthquakes as having a low rupture velocity

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

the 2009 samoa tonga great earthquake triggered doublet great earthquakes having seismic magnitudes of at least 8 usually involve abrupt sliding of rock masses at a boundary between tectonic plates such interplate ruptures produce dynamic and static stress changes that can activate nearby intraplate aftershocks as is commonly observed in the trench slope region seaward of a great subduction zone thrust event1 the earthquake sequence addressed here involves a rare instance in which a great trench slope intraplate earthquake triggered extensive interplate faulting reversing the typical pattern and broadly expanding the seismic and tsunami hazard on 29 september 2009 within two minutes of the initiation of a normal faulting event with moment magnitude 8 1 in the outer trench slope at the northern end of the tonga subduction zone two major interplate underthrusting subevents both with moment magnitude 7 8 with total moment equal to a second great earthquake of moment magnitude 8 0 ruptured the nearby subduction zone megathrust the collective faulting produced tsunami waves with localized regions of about 12 metres run up that claimed 192 lives in samoa american samoa and tonga overlap of the seismic signals obscured the fact that distinct faults separated by more than 50 km had ruptured with different geometries with the triggered thrust faulting only being revealed by detailed seismic wave analyses extensive interplate and intraplate aftershock activity was activated over a large region of the northern tonga subduction zone

modeling the anisotropic brine microstructure in first year arctic sea ice 1 cross borehole dc resistivity tomography has recently been used to monitor the temporal variation of the anisotropic bulk electrical resistivity of first year arctic sea ice during the period of spring warming these measurements cannot be explained by standard models of sea ice microstructure which treat the brine phase as isolated ellipsoidal pores a simple structural model which does satisfy the observed electrical data shows that the brine phase must be connected both vertically and horizontally calculation of the temporal and thermal evolution of the microstructure suggests that although vertical connectivity is through pore tubes and sheets with widths of 100 m horizontal connectivity is through much thinner connections which are interpreted as inter and intragranular brine layers as the temperature increases the width of vertical channels increases smoothly in contrast at temperatures above about 2 c there is a rapid increase in the thickness of horizontal connections which we interpret as a change from conduction through intergranular brine layers to the development of horizontal pores the electrical data also broadly exhibit a percolation transition predicted by mathematical models however the critical brine volume fraction for vertical electrical connection is very small while that for horizontal electrical connection is derived to be about 0 5 the difference between these and the critical threshold of 5 for fluid permeability is presumed to arise because of the strong dependence of the latter on brine channel width

characteristics of strong ground motion across a thrust fault tip from the september 21 1999 chi chi taiwan earthquake near fault tip strong motion records from the northern part of the major earthquake mw 7 6 namely the chi chi earthquake on september 21 1999 in central taiwan demonstrated systematic differences on the hanging wall and footwall and simulated by the finite element method the extraordinary ground motion differences on either side of the northern fault tip can be explained by a 2 dimension kinematic source model with fault rupture breaking to surface in this study the earthquake faulting was considered as bilateral from the center of a low angle thrust fault which is 30 km in length with a dip angle of 31 based on waveform modeling the source rupture velocity rise time and dislocation of 2 0 km sec 5 sec and 6 meters respectively are suggested the results of this study show that on the northern part of the chi chi earthquake fault there was lower rupture velocity and longer rise time of the fault slip than that previously reported furthermore the effects of surface breaking from the fault movement contributed large ground deformations near the fault tip and consequently induced extensive damage

seasonal and regional manifestation of arctic sea ice loss abstractthe arctic ocean is currently on a fast track toward seasonally ice free conditions although most attention has been on the accelerating summer sea ice decline large changes are also occu

seismic gap hypothesis ten years after the seismic gap hypothesis states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries one of the earliest and clearest applications of the seismic gap theory to earthquake forecasting was by mccann et al 1979 who postulated zones of high medium and low seismic potential around the pacific rim in the 10 years since there have been over 40 large m 7 0 earthquakes enough to test statistically the earlier forecast we also analyze another forecast of long term earthquake risk that by kelleher et al 1973 the hypothesis of increased earthquake potential after a long quiet period can be rejected with a large confidence the data suggest that contrary to these forecasts places of recent earthquake activity have larger than usual seismic hazard whereas the segments of the circum pacific belt with no large earthquakes in recent decades have remained relatively quiet the clustering of earthquake times does not contradict the plate tectonic model which constrains only the long term average slip rate not the regularity of earthquakes

a habitat for psychrophiles in deep antarctic ice microbes some of which may be viable have been found in ice cores drilled at vostok station at depths down to approximately 3 600 m close to the surface of the huge subglacial lake vostok two types of ice have been found the upper 3 500 m comprises glacial ice containing traces of nutrients of aeolian origin including sulfuric acid nitric acid methanosulfonic acid msa formic acid sea salts and mineral grains ice below approximately 3 500 m comprises refrozen water from lake vostok accreted to the bottom of the glacial ice nutrients in the accretion ice include salts and dissolved organic carbon there is great interest in searching for living microbes and especially for new species in deepest antarctic ice i propose a habitat consisting of interconnected liquid veins along three grain boundaries in ice in which psychrophilic bacteria can move and obtain energy and carbon from ions in solution in the accretion ice with an age of a few 10 4 years and a temperature a few degrees below freezing the carbon and energy sources in the veins can maintain significant numbers of cells per cubic centimeter that are metabolizing but not multiplying in the 4 x 10 5 year old colder glacial ice at least 1 cell per cm 3 in acid veins can be maintained with fluorescence microscopy tuned to detect nadh in live organisms motile bacteria could be detected by direct scanning of the veins in ice samples

near simultaneous great earthquakes at tongan megathrust and outer rise in september 2009 the tsunami that struck the samoan and northern tongan islands in september 2009 was preceded by a magnitude 8 earthquake on the outer slope of the oceanic trench where the pacific plate bends as it enters the subduction zone this was initially thought to be the sole source of the tsunami but a more complex picture is emerging two groups report the occurrence of two earthquakes a triggered doublet at nearly the same time and place what is not clear is which triggered the other beavan et al use an analysis of global positioning system station displacements and tsunami models to show that the outer rise earthquake was accompanied possibly triggered by a near simultaneous mega thrust earthquake in the adjacent tonga subduction zone lay et al analyse the available seismic data and their model suggests that the outer rise event triggered megathrust faulting either way this dual strike suggests a mechanism for the occasional large tsunamis generated at the tonga subduction zone on 29 september 2009 a tsunami devastated the samoan and northern tongan islands it is shown here that an unusual earthquake sequence preceded this tsunami a magnitude 8 earthquake in the outer rise intraplate region occurred almost simultaneously with rupture of the shallow subduction interplate interface equivalent to a magnitude 8 earthquake the findings provide information on strain release mechanisms at subduction zones and a possible mechanism for the occasional large tsunamis generated at the tonga subduction zone the earth s largest earthquakes and tsunamis are usually caused by thrust faulting earthquakes on the shallow part of the subduction interface between two tectonic plates where stored elastic energy due to convergence between the plates is rapidly released1 2 the tsunami that devastated the samoan and northern tongan islands on 29 september 2009 was preceded by a globally recorded magnitude 8 normal faulting earthquake in the outer rise region where the pacific plate bends before entering the subduction zone preliminary interpretation suggested that this earthquake was the source of the tsunami3 here we show that the outer rise earthquake was accompanied by a nearly simultaneous rupture of the shallow subduction interface equivalent to a magnitude 8 earthquake that also contributed significantly to the tsunami the subduction interface event was probably a slow earthquake with a rise time of several minutes that triggered the outer rise event several minutes later however we cannot rule out the possibility that the normal fault ruptured first and dynamically triggered the subduction interface event our evidence comes from displacements of global positioning system stations and modelling of tsunami waves recorded by ocean bottom pressure sensors with support from seismic data and tsunami field observations evidence of the subduction earthquake in global seismic data is largely hidden because of the earthquake s slow rise time or because its ground motion is disguised by that of the normal faulting event earthquake doublets where subduction interface events trigger large outer rise earthquakes have been recorded previously4 but this is the first well documented example where the two events occur so closely in time and the triggering event might be a slow earthquake as well as providing information on strain release mechanisms at subduction zones earthquakes such as this provide a possible mechanism for the occasional large tsunamis generated at the tonga subduction zone5 where slip between the plates is predominantly aseismic6

stress regime in the philippine sea slab beneath kanto japan 1 we determine the focal mechanisms of earthquakes within the philippine sea slab beneath the tokyo metropolitan area and perform stress tensor inversions to investigate the detailed stress field within the slab the results show a characteristic spatial variation in earthquake generating stress slab stress in northeastern part of the phs slab is characterized by down dip tension ddt except for the uppermost tip of the seismic portion of the slab where down dip compression ddc stress is dominant we interpret that ddt is caused by the net slab pull and ddc is attributable to local resistance to subduction at the tip of the slab in southwestern part of the phs slab 1 and 3 are generally rotated oblique to the dip of the slab suggesting that earthquakes occur under stress conditions of neither ddc nor ddt the rotations in 1 and 3 may be related to stress accumulation by the slip deficit along the asperity of the 1923 kanto earthquake m7 9

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

dissolved organic matter in antarctic sea ice sea ice supports highly dynamic and at times highly productive assemblages of auto and heterotrophic organisms central to the biogeochemical cycling of carbon and nitrogen within sea ice is the production and lability of dissolved organic matter dom dom is produced through excretion mortality cell lysis and amplified by inefficient feeding by grazers it has been hypothesised that there are significant dom pools in sea ice systems although measurements of dom in sea ice have only rarely been made the significance of dom for ice based productivity and carbon turnover therefore remains highly speculative the dissolved organic carbon and nitrogen doc don of sea ice from the amundsen bellingshausen and weddell seas were investigated in 1992 1994 and 1997 measurements were made on melted sea ice sections in 1994 and 1997 and in sea ice brines in 1992 these studies confirm that doc and don can reach up to 30 and 8 times higher concentrations compared to those in surface waters respectively this dom tends to be carbon enriched with a mean doc don ratio of 14 measurements made on a limited data set showed that carbohydrates constitute on average 35 of the doc pool with highly variable contributions

the 25 october 2010 mentawai tsunami earthquake from real time discriminants finite fault rupture and tsunami excitation 1 the moment magnitude 7 8 earthquake that struck offshore the mentawai islands in western indonesia on 25 october 2010 created a locally large tsunami that caused more than 400 human causalities we identify this earthquake as a rare slow source tsunami earthquake based on 1 disproportionately large tsunami waves 2 excessive rupture duration near 125 s 3 predominantly shallow near trench slip determined through finite fault modeling and 4 deficiencies in energy to moment and energy to duration cubed ratios the latter in near real time we detail the real time solutions that identified the slow nature of this event and evaluate how regional reductions in crustal rigidity along the shallow trench as determined by reduced rupture velocity contributed to increased slip causing the 5 9 m local tsunami runup and observed transoceanic wave heights observed 1600 km to the southeast

a great earthquake doublet and seismic stress transfer cycle in the central kuril islands temporal variations of the frictional resistance on subduction zone plate boundary faults associated with the stick slip cycle of large interplate earthquakes are thought to modulate the stress regime and earthquake activity within the subducting oceanic plate here we report on two great earthquakes that occurred near the kuril islands which shed light on this process and demonstrate the enhanced seismic hazard accompanying triggered faulting on 15 november 2006 an event of moment magnitude 8 3 ruptured the shallow dipping plate boundary along which the pacific plate descends beneath the central kuril arc the thrust ruptured a seismic gap that previously had uncertain seismogenic potential although the earlier occurrence of outer rise compressional events had suggested the presence of frictional resistance within minutes of this large underthrusting event intraplate extensional earthquakes commenced in the outer rise region seaward of the kuril trench and on 13 january 2007 an event of moment magnitude 8 1 ruptured a normal fault extending through the upper portion of the pacific plate producing one of the largest recorded shallow extensional earthquakes this energetic earthquake sequence demonstrates the stress transfer process within the subducting lithosphere and the distinct rupture characteristics of these great earthquakes illuminate differences in seismogenic properties and seismic hazard of such interplate and intraplate faults

interplate seismogenic zones along the kuril japan trench inferred from gps data inversion stress accumulation between earthquakes results from slip that is insufficient to fully accommodate plate movement an inverse analysis of gps data from the kuril japan trench reveals a trench parallel belt of stress accumulation with six peaks in the depth range of 10 40 km suggesting potential source regions for future earthquakes in the subduction zones around japan where four plates interact with one another large earthquakes have occurred repeatedly1 these interplate earthquakes are part of the process of tectonic stress accumulation and release that is driven by relative plate motion2 3 4 stress accumulation between earthquakes results from slip deficit slip that is insufficient to fully accommodate plate movement for the prediction of large earthquakes it is therefore important to monitor the distribution of slip deficit on plate interfaces here we apply an inversion method based on bayesian modelling using direct and indirect prior information on the magnitude and distribution of fault slip5 to horizontal and vertical velocities from global positioning system data for the seismically calm period between 1996 and 2000 we obtain a precise distribution of slip deficit rates on the interface between the north american and pacific plates around japan which reveals a trench parallel belt of slip deficit with six peaks in the depth range of 10 40 km these peaks agree with the source regions of past large interplate earthquakes along the kuril japan trench we conclude that the slip deficit zones identified with our method are potential source regions of large earthquakes

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

the 1994 java tsunami earthquake slip over a subducting seamount on june 2 1994 a large subduction thrust earthquake ms 7 2 produced a devastating tsunami on the island of java this earthquake had a number of unusual characteristics it was the first recorded large thrust earthquake on the java subduction zone all of the aftershock mechanisms exhibit normal faulting no mechanisms are similar to the main shock also the large tsunami and the relatively low energy radiated by the main shock have led to suggestions that this earthquake might have involved slow shallow rupture near the trench similar to the 1992 nicaragua earthquake we first relocate the main shock and the aftershocks we then invert long period surface waves and broadband body waves to determine the depth and spatial distribution of the main shock slip a dip of 12 hypocenter depth of 16 km and moment of 3 5 l020 n m mw 7 6 give the best fit to the combined seismic data and are consistent with the plate interface geometry the source spectrum obtained from both body and surface waves has a single corner frequency between 10 and 20 mhz implying a stress drop of 0 3 mpa the main energy release was preceded by a small subevent lasting 12 s the main slip occurred at 20 km depth downdip and to the nw of the hypocenter this area of slip is collocated with a prominent high in the bathymetry that has been identified as a subducting seamount we interpret the java earthquake as slip over this subducting seamount which is a locked patch in an otherwise decoupled subduction zone we find no evidence for slow shallow rupture no thrust aftershocks are expected if the entire locked zone slipped during the main shock but extension of the subducting plate behind the seamount would promote normal faulting as observed it seems probable that such a source model could also explain the size and timing of the observed tsunami

real time inversion of gps data for finite fault modeling and rapid hazard assessment 1 responses to recent great earthquakes and ensuing tsunamis in sumatra chile and japan with the resulting loss of life and damage to infrastructure demonstrate that our ability to ascertain the full extent of slip of catastrophic earthquakes and their tsunamigenic potential in the first minutes after the initiation of rupture is problematic regional gps networks such as those in western north america and japan are complementary to seismic networks by being able to directly measure displacements close to the source during large earthquakes in real time we report on rapid modeling of two large earthquakes the 2003 mw 8 3 tokachi oki earthquake 100 km offshore hokkaido island using 356 geonet stations and the 2010 mw 7 2 el mayor cucapah earthquake in northern baja california using 95 crtn stations in southern california about 75 km northwest of the epicenter working in a simulated real time mode we invert for finite fault slip in a homogeneous elastic half space using green s functions obtained from okada s formulation we compare two approaches the first starts with a catalog of pre defined faults while the second uses a rapid centroid moment tensor solution to provide an initial estimate of the ruptured fault plane in either case we are able to characterize both earthquakes in less than two minutes reducing the time necessary to obtain finite fault slip and moment magnitude for medium and greater earthquakes compared to traditional methods by an order of magnitude

inter plate coupling in the nicoya peninsula costa rica as deduced from a trans peninsula gps experiment abstract we investigated the state of plate coupling at the subduction zone beneath the nicoya peninsula northwestern costa rica from 1 5 years of trans peninsula gps campaign experiments this area is recognized as a seismic gap located between the rupture areas of two m 7 earthquakes that occurred in the early 1990s and it has not ruptured since 1950 we carried out campaign gps observations beginning in autumn 2001 to obtain the profile of site velocities across the peninsula for the interseismic period the obtained velocity field indicates a strong coupling at the plate interface however velocity directions deflect counterclockwise which suggests a trench parallel forearc sliver motion of nicoya peninsula at 8 5 mm year an inversion analysis to infer inter plate coupling at nicoya seismic gap shows that the strongly coupled zone agrees well with seismogenic zone inferred from seismicity cumulative slip deficits since 1950 at the nicoya seismic gap would produce a thrust earthquake as large as m w 7 5

the 17 july 2006 java tsunami earthquake the 17 july 2006 java earthquake involved thrust faulting in the java trench and excited a deadly tsunami 5 8 m that inundated the southern coast of java the earthquake s size estimates vary significantly with seismic wave period very long period signals 300 500 s indicate a seismic moment of 6 7 10 20 nm m w 7 8 m s 20 s 7 2 m b 1 s 6 2 while shaking intensities 3 10 hz were mmiv the large tsunami relative to ms characterizes this event as a tsunami earthquake like previous tsunami earthquakes the java event had an unusually low rupture speed of 1 0 1 5 km s and occurred near the up dip edge of the subduction zone thrust fault most large aftershocks involved normal faulting the rupture propagated 200 km along the trench with several pulses of shorter period seismic radiation superimposed on a smooth background rupture with an overall duration of 185 s

the 2010 mw 7 8 mentawai earthquake very shallow source of a rare tsunami earthquake determined from tsunami field survey and near field gps data 1 the mw 7 8 october 2010mentawai indonesia earthquake was a tsunami earthquake a rare type of earthquake that generates a tsunami much larger than expected based on the seismicmagnitude itproducedalocallydevastatingtsunami withrunupcommonlyinexcess of 6 m we examine this event using a combination of high rate gps data from instruments located on the nearby islands and a tsunami field survey the gps displacement time series are deficient in high frequency energy and show small coseismic displacements 16 m our modeling results show that the combination of the small gps displacements and large tsunami can only be explained by high fault slip at very shallow depths far from the islands and close to the oceanic trench inelastic uplift of trench sediments likely contributed to the size of the tsunami recent results for the 2011 mw 9 0 tohoko oki earthquake have also shown shallow fault slip but the results from our study which involves a smaller earthquake provide much stronger constraints on how shallow the rupture can be with the majority of slip for the mentawai earthquake occurring at depths of 6 km this result challenges the conventional wisdom that the shallow tips of subduction megathrusts are aseismic and therefore raises important questions both about the mechanical properties of the shallow fault zone and the potential seismic and tsunami hazard of this shallow region

selective retention in saline ice of extracellular polysaccharides produced by the cold adapted marine bacterium colwellia psychrerythraea strain 34h the retention of salts in laboratory grown ice was compared to the retention of extracellular polysaccharide substances eps produced by the cold adapted marine gammaproteo bacterium colwellia psychrerythraea strain 34h saline ice was formed by means of a cold finger apparatus from artificial sea water solutions containing either native dissolved eps from strain 34h the same eps but heat treated or dissolved eps from the uninoculated growth medium results indicated that only the native unheated eps of strain 34h was retained preferentially in the ice temperature and volumetric measurements of the ice further suggested a link between the heat labile fraction of this eps of marine bacterial origin and potential habitat alteration bacterial eps may join algal eps in our understanding of how extracellular polymers help to establish and sustain the microbial community that inhabits sea ice