effects of source faulting and fringing reefs on the 2009 south pacific tsunami inundation in southeast upolu samoa the subduction zone along the northern tonga trench has the highest plate convergence rate in the world but limited records of its seismic and tsunamigenic activities in 2009 a tsunami generated

detailed rupture imaging of the 25 april 2015 nepal earthquake using teleseismic p waves we analyze the rupture process of the 25 april 2015 nepal earthquake with globally recorded teleseismic p waves the rupture propagated east southeast from the hypocenter for about 160 km with a duration of 55 s backprojection of both high frequency hf 0 2 to 3 hz and low frequency lf 0 05 to 0 2 hz p waves suggest a multistage rupture process from the low frequency images we resolve an initial slow downdip northward rupture near the nucleation area for the first 20 s stage 1 followed by two faster updip ruptures 20 to 40 s for stage 2 and 40 to 55 s for stage 3 which released most of the radiated energy northeast of kathmandu the centroid rupture power from lf backprojection agrees well with the global centroid moment tensor solution the spatial resolution of the backprojection images is validated by applying similar analysis to nearby aftershocks the overall rupture pattern agrees well with the aftershock distribution a multiple asperity model could explain the observed multistage rupture and aftershock distribution

source model of the 2007 mw 8 0 pisco peru earthquake implications for seismogenic behavior of subduction megathrusts we use interferometric synthetic aperture radar teleseismic body waves tsunami waveforms recorded by tsunameters field observations of coastal uplift subsidence and runup to develop and test a refined model of the spatiotemporal history of slip during the mw 8 0 pisco earthquake of 15 august 2007 our preferred solution shows two distinct patches of high slip one patch is located near the epicenter while another larger patch ruptured 60 km further south at the latitude of the paracas peninsula slip on the second patch started 60 s after slip initiated on the first patch we observed a remarkable anticorrelation between the coseismic slip distribution and the aftershock distribution determined from the peruvian seismic network the proposed source model is compatible with regional runup measurements and open ocean tsunami records from the latter data set we identified the 12 min timing error of the tsunami forecast system as being due to a mislocation of the source caused by the use of only one tsunameter located in a nonoptimal azimuth the comparison of our source model with the tsunami observations validate that the rupture did not extend to the trench and confirms that the pisco event is not a tsunami earthquake despite its low apparent rupture velocity 1 5 km s we favor the interpretation that the earthquake consists of two subevents each with a conventional rupture velocity 2 4 km s the delay between the two subevents might reflect the time for the second shock to nucleate or alternatively the time it took for afterslip to increase the stress level on the second asperity to a level necessary for static triggering the source model predicts uplift offshore and subsidence on land with the pivot line following closely the coastline this pattern is consistent with our observation of very small vertical displacement along the shoreline when we visited the epicentral area in the days following the event this earthquake represents to our knowledge one of the best examples of a link between the geomorphology of the coastline and the pattern of surface deformation induced by large interplate ruptures

coseismic slip model of the 2007 august pisco earthquake peru as constrained by wide swath radar observations summary the pisco earthquake m w 8 0 2007 august 15 occurred offshore of peru s southern coast at the subduction interface between the nazca and south american plates it ruptured a previously identified seismic gap along the peruvian margin we use wide swath insar observations acquired by the envisat satellite in descending and ascending orbits to constrain coseismic slip distribution of this subduction earthquake the data show movement of the coastal regions by as much as 85 cm in the line of sight of the satellite distributed slip model indicates that the coseismic slip reaches values of about 5 5 m at a depth of 18 20 km the slip is confined to less than 40 km depth with most of the moment release located on the shallow parts of the interface above 30 km depth the region with maximum coseismic slip in the insar model is located offshore close to the seismic moment centroid location the geodetic estimate of seismic moment is 1 23 10 21 nm m w 8 06 consistent with seismic estimates the slip model inferred from the insar observations suggests that the pisco earthquake ruptured only a portion of the seismic gap zone in peru between 13 5 s and 14 5 s hence there is still a significant seismic gap to the south of the 2007 event that has not experienced a large earthquake since at least 1687

a reappraisal of the 2005 kashmir mw 7 6 earthquake and its aftershocks seismotectonics of nw himalaya abstract we study the source properties of the 2005 kashmir earthquake and its aftershocks to unravel the seismotectonics of the nw himalayan syntaxis the mainshock and larger aftershocks have been simultaneously relocated using phase data we use back projection of high frequency energy from multiple teleseismic arrays to model the spatio temporal evolution of the mainshock rupture our analysis reveal a bilateral rupture which initially propagated se and then nw of the epicenter with an average rupture velocity of 2 km s 1 the area of maximum energy release is parallel to and bound by the surface rupture incorporating rupture propagation and velocity we model the mainshock as a line source using p and sh waveform inversion our result confirms that the mainshock occurred on a ne dipping 35 fault plane with centroid depth of 10 km integrated source time function show that majority of the energy was released in the first 20 s and was confined above the hypocenter from waveform inverted fault dimension and seismic moment we argue that the mainshock had an additional 25 km blind rupture beyond the nw himalayan syntaxis combining this with findings from previous studies we conjecture that the blind rupture propagated nw of the syntaxis underneath a weak detachment overlain by infra cambrian salt layer and terminated in a wedge thrust all moderate to large aftershocks nw of the mainshock rupture are concentrated at the edge of the blind rupture termination source modeling of these aftershocks reveal thrust mechanism with centroid depths of 2 10 km and fault planes oriented sub parallel to the mainshock rupture to study the influence of mainshock rupture on aftershock occurrence we compute coulomb failure stress on aftershock faults all these aftershocks lie in the positive coulomb stress change region this suggest that the aftershocks have been triggered by either co seismic or post seismic slip on the mainshock fault

transoceanic wave propagation links iceberg calving margins of antarctica with storms in tropics and northern hemisphere 1 we deployed seismometers on the ross ice shelf and on various icebergs adrift in the ross sea including b15a a large 100 km by 30 km fragment of b15 which calved from the ross ice shelf in march 2000 the data reveal that the dominant energy of these floating ice masses is in the 0 01 to 0 1 hz band and is associated with sea swell generated in the tropical and extra tropical pacific ocean in one example a strong storm in the gulf of alaska on 21 october 2005 approximately 13 500 km from the ross sea generated swell that arrived at b15a immediately prior to and during its break up off cape adare on 27 october 2005 if sea swell influences iceberg calving and break up a teleconnection exists between the antarctic ice sheet mass balance and weather systems worldwide

combining seismic arrays to image the high frequency characteristics of large earthquakes summary this study investigates the source properties of the 2007 8 0 pisco peru 2007 8 4 and 7 9 mentawai islands indonesia 2009 8 1 samoa islands and 2010 8 8 maule chile earthquakes using a backprojection technique that utilizes data from multiple seismic arrays combining seismic arrays increases azimuth and distance coverage and improves lateral resolution the four subduction interface events show rupture propagation towards the bottom of the seismogenic zone in addition all of the earthquakes show evidence of multiple rupture segments with varying rupture speeds and directions relating these segments to the specific features of the subduction zones e g interseismic coupling suggests that asperity sizes may be controlled by subtle features of the subducted slab

complex rupture of the 13 november 2016 m w 7 8 kaikoura new zealand earthquake comparison of high frequency and low frequency observations abstract we apply a back projection analysis to determine the locations and timing of the sources of short period 0 5 to 2 s energy generated by the 13 november 2016 mw 7 8 kaikoura new zealand earthquake using data from australian and southeast asia the sources of strong short period energy are distributed northeast of the epicenter at distances of 70 to 80 km during the time period of 70 to 80 s after the initiation the locations of sources of long period energy derived from global seismic and local gps data are close to the northeastern edge of the source area and complementary to the areas of short period energy which occur in the converging region of the upper kowhal papatea and jordan thrust faults the obvious frequency dependence might be attributed to complexities in fault geometry possible rupture in the subduction interface or varying focal mechanisms during the earthquake

the 2010 maule chile coseismic gap and its relationship to the 25 march 2012 mw 7 1 earthquake abstract a backprojection method is applied to the 27 february 2010 m w 8 8 and 25 march 2012 m w 7 1 maule chile earthquakes using high frequency 0 8 2 hz usarray data during the 2010 event highest energy release occurred north of the epicenter with two subevents comprising this rupture the gap between these subevents was about 100 km and 15 s suggesting that p waves from the first subevent dynamically triggered the second subevent this triggering can be explained as a consequence of stopping phases generated at the terminus of subevent 1 as the rupture encounters a region of low interseismic coupling this argument is supported by the occurrence of the 2012 m w 7 1 event which is the largest interface earthquake since the 2010 mainshock and ruptured an area that completely filled the gap left from the mainshock seismic gaps regions between the slip areas of past giant earthquakes are known to have a higher potential for generating future large events the results of this study show that a coseismic gap behaves similarly and detailed imaging of rupture propagation can be used to identify areas that may produce large earthquakes a comparable coseismic gap to the 2010 chile gap is identified for the 2011 m w 9 0 tohoku japan earthquake that may be the site of a large event in the near future online material figures showing point source synthetic tests for the back projection method station location and distribution of energy release

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

back projection imaging of earthquakes back projection analysis of earthquakes is a type of array processing that images the source of seismic waves coherently recorded at stations throughout the seismic network the method was developed following the magnitude 9 2 sumatra andaman earthquake in 2004 although properties of earthquakes have been investigated using array data prior to the introduction of the back projection method this technique differs from other approaches because it makes limited assumptions and allows detailed and complex rupture propagation to be examined these advantages have led several researchers to apply the method to many of the largest earthquakes to occur this century the method has also been effective for the detection of smaller events a critical component of the success of back projection has been the development of large scale dense seismic arrays further improvements and future applications of the method will depend greatly on the continued maintenance and development of these networks

imaging the rupture of the mw 6 3 april 6 2009 l aquila italy earthquake using back projection of teleseismic p waves 1 we present rupture details of the mw 6 3 april 6 2009 l aquila earthquake derived by back projecting teleseismic p waves this technique has previously been applied to large magnitude earthquakes but this is the first application to a moderate size event we processed vertical component seismograms for 60 broadband stations obtained from the incorporated research institutions for seismology iris data center the traces were aligned and normalized using a multi channel cross correlation algorithm and 4th root stacking was used to image the rupture we found that the l aquila earthquake ruptured towards the south and that a second discrete pulse of energy occurred 20 25 km east of the epicenter about 17 18 s after the nominal origin time the spatial extent of the rupture image correlates well with a post seismic survey of damage in the region because the technique is potentially very fast images can be produced within 20 30 minutes of the origin time it may be useful to governmental agencies tasked with emergency response and rescue

effects of kinematic constraints on teleseismic finite source rupture inversions great peruvian earthquakes of 23 june 2001 and 15 august 2007 two great underthrusting earthquakes that occurred along the coast of peru in 2001 and 2007 involve spatiotemporal slip distributions that differ from the predominantly unilateral or bilateral rupture expansion of many great events commonly used finite source rupture model parameterizations with specified rupture velocity and or short duration of slip at each grid point applied to the seismic data for these two events lead to incorrect slip distributions or inaccurate estimation of rupture velocities as a result of intrinsic kinematic constraints imposed on the model slip distributions guided by large aperture array back projections of teleseismic broadband p wave signals that image slip locations without imposing a priori kinematic constraints on the rupture process we exploit the availability of large global broadband body and surface wave data sets to consider the effects of varying the kinematic constraints in teleseismic finite source waveform inversions by allowing longer than usual rupture durations at each point on the fault using a flexible subfault source time function parameterization we find that the anomalous attributes of the 2001 and 2007 peru earthquake ruptures are readily recognized and accounted for by compound rupture models the great 23 june 2001 m w 8 4 8 4 earthquake involved an initial modest size event that appears to have triggered a much larger secondary event about 120 km away that developed an overall slip distribution with significant slip located back along the megathrust in the vicinity of the initial rupture the great 15 august 2007 m w 8 0 8 0 earthquake was also a composite event with a modest size initial rupture followed by a 60 sec delayed larger rupture that initiated 50 60 km away and spread up dip and bilaterally when back projections indicate greater rupture complexity than captured in a simple slip pulse type rupture model one should allow for possible long subfault slip duration or composite triggered sequences and not overly constrain the earthquake slip distribution

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

geomorphic evidence for plio quaternary compression in the andean foothills of the southern neuquen basin argentina the southern central andes foothills are made of imbricate thick and thin skinned fold and thrust belts they were formed during cretaceous and miocene compressive periods by successive eastward propagation episodes of the orogenic front we analyze remnant terraces and alluvial deposits of the neuqun river and its tributaries to study the plio quaternary tectonic regime in the southern neuqun basin topographic profiles of remnant terraces show a crustal scale tens of kilometers anomaly above the chihuido south anticline this anomaly is accompanied by sedimentary aggradations downstream and upstream of the anticline another anomaly in the terrace profiles correlated with a knickpoint in the current neuqun river is observed farther east near aelo we interpret these anomalies to be the consequence of a plio quaternary uplift of the chihuidos and aelo anticlines folding and surface faulting of plio quaternary alluvial deposits show that this uplift is concomitant with the reactivation of the miocene orogenic front and of the predominantly thin skinned agrio fold and thrust belt from these data we infer that the southern neuqun basin is still shortening under a compressive stress regime and that the andean orogenic front is migrating farther to the east extensional features in the study area correspond mainly to thin skinned gravitational gliding resulting from crustal uplift thus we argue that the tectonic compressive regime is preserved in the southern neuqun basin throughout the plio quaternary though the slab may have steepened during this period

the 2015 illapel earthquake central chile a type case for a characteristic earthquake on 16 september 2015 the mw 8 2 illapel megathrust earthquake ruptured the central chilean margin combining inversions of displacement measurements and seismic waveforms with high frequency hf teleseismic backprojection we derive a comprehensive description of the rupture which also predicts deep ocean tsunami wave heights we further determine moment tensors and obtain accurate depth estimates for the aftershock sequence the earthquake nucleated near the coast but then propagated to the north and updip attaining a peak slip of 5 6 m in contrast hf seismic radiation is mostly emitted downdip of the region of intense slip and arrests earlier than the long period rupture indicating smooth slip along the shallow plate interface in the final phase a superficially similar earthquake in 1943 with a similar aftershock zone had a much shorter source time function which matches the duration of hf seismic radiation in the recent event indicating that the 1943 event lacked the shallow slip

the 2007 pisco peru earthquake m8 0 seismology and geodesy summary we investigate the 2007 pisco peru earthquake m8 0 using seismological and geodetic data analysis of teleseismic records indicates that the earthquake is characterized by a steadily increasing moment rate with the maximum occurring between about 55 and 70 s and the associated slip occurring about 40 km south of the epicentre we combine insar data from l band alos and c band envisat satellites to produce a 3 d image of the ground displacements caused by the earthquake distributed slip inversions of the interferograms identify a single large patch of slip in the location of the maximum moment rate identified by seismology despite a clear spatial coincidence between the location of the coseismic slip and the anomalously high topography of the paracas peninsula we find no evidence that the earthquake was directly responsible for motion on any upper plate faults

the 2010 mw 8 8 chile earthquake triggering on multiple segments and frequency dependent rupture behavior 1 multi frequency back projection results of the february 27 2010 mw 8 8 chile earthquake reveal that this earthquake consists of distinct subevents with different slip characteristics the subevent south of the epicenter releases its energy at low frequencies 0 05 0 1 hz implying slow slip and has a rupture speed around 0 8 km s two subevents north of the epicenter are characterized by high frequency energy 1 5 hz release the first of these subevents appears to trigger slip on the second segment to the north which has higher amplitude energy release and a fast propagation speed of about 2 9 km s in addition to these rupture details high frequency energy release is observed at the rupture front followed by lower frequency energy release this observation suggests that the rupture of large earthquakes involves dynamic weakening of faults and hence their rupture properties may not be related easily to those of small earthquakes these distinct slip behaviors point out the need to consider data from a wide range of frequencies to fully assess the rupture process and associated hazards of giant earthquakes

multiple branching rupture of the 2009 tonga samoa earthquake several source models have been proposed to explain the enigmatic 2009 tonga samoa earthquake the long period data require a composite source model and can be fit with a normal faulting subevent followed by one or more reverse faulting subevents the short period data in contrast indicate a more compact rupture pattern around the epicenter the lack of a unified source model reflects the complexity of the event we analyze the spatiotemporal evolution of this earthquake with p wave back projection from globally distributed stations in different frequency bands low frequency 0 05 0 2 hz high frequency 0 2 2 hz and a multiple moment tensor inversion the rupture propagation revealed by back projection exhibits frequency dependent behavior with two branches of high frequency enriched bilateral rupture around the epicenter and a high frequency deficient rupture branch at the subduction interface a composite source model with one mw 8 0 normal faulting earthquake east of the trench axis seaward followed by one mw 8 1 reverse faulting earthquake along the subduction interface west of the trench axis landward can explain the very long period data 200 500 s combined with high resolution swath bathymetry data the back projection images show that the azimuth of rupture branches east of the trench axis were controlled by the geometry of bending related faults on the pacific plate and that the rupture branch west of the trench axis may correlate with the along strike fore arc segmentation the rupture along the subduction interface was triggered by the seaward rupture and a partially subducted normal fault may have played a key role in facilitating the triggering the apparent normal reverse faulting interactions pose a higher seismic risk to this region than their individual strands at the northernmost corner of the tonga subduction zone

the 2015 april 25 gorkha nepal earthquake and its aftershocks implications for lateral heterogeneity on the main himalayan thrust the mw 7 8 gorkha nepal earthquake on 2015 april 25 initiated 80 km northwest of the capital city of katmandu and ruptured 150 km of the frictionally locked downdip segment of the main himalayan thrust mht beneath the central nepal himalaya avouac et al 2015 the earthquake resulted in 4 m of average slip of the himalayan mountains over the indian plate in the ssw direction mitra et al 2015 the main shock fault spanned between the meisoseismal zone of the 1505 mw 8 5 earthquake to its west kumar et al 2006 and the rupture zone of the 1934 mw 8 2 8 4 nepal earthquake to its east bilham wallace 2005 sapkota et al 2013 the last known great earthquake in this region of nepal occurred in 1833 m 7 5 ambraseys douglas 2004 and has a significant overlap with the rupture area of the gorkha main shock adhikari et al 2015 the main shock was followed by a series of moderate to strong aftershocks the largest one mw 7 3 occurred 18 d after the main shock on 2015 may 12 fig 1 albeit the loss of life and property inflicted by this damaging earthquake and its aftershocks it has provided an unprecedented opportunity to study the source properties of himalayan mega thrust earthquake and its relationship to the geometry of the mht which so far is poorly understood

a study of the 2006 and 2007 earthquake sequence of pisco peru with insar and teleseismic data 1 we combine interferometric synthetic aperture radar insar and teleseismic body waves to study the largest earthquake mw 8 1 in a sequence of events on the subduction megathrust near pisco peru our analysis includes some of the first insar data from the alos satellite and wide swath data from the envisat satellite the teleseismic data indicate the slip maximum occurred 60 90 seconds after the mainshock started the insar data constrain the main slip patch to be about 70 km from the hypocenter suggesting an extremely low rupture velocity 1 5 km s or long slip rise time no large earthquake has occurred in the 2007 rupture area since at least 1746 and possibly 1687 suggesting significant aseismic deformation in the area the slip deficit apparently cannot be filled with rapid after slip in addition the area where the nazca ridge is subducting appears to be either a seismic gap or a persistent area of aseismic slip

fault interactions and triggering during the 10 january 2012 mw 7 2 sumatra earthquake the 10 january 2012 mw 7 2 sumatra earthquake in the wharton basin occurred 3 months before the great mw 8 6 and mw 8 2 earthquakes in the same region which had complex ruptures and are the largest strike slip earthquakes ever recorded teleseismic p wave back projection of the mw 7 2 earthquake images a unilateral rupture lasting 40 s without observable frequency dependency low frequency 0 05 0 3 hz high frequency 0 3 1 hz in addition to radiation bursts during the mw 7 2 main shock coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about 143 km northeast of the main shock rupture and landward of the trench analysis of globally recorded p waves in both 0 02 0 05 hz velocity records and 1 5 hz stacked envelope functions confirms the presence of coherent sources during the time windows the observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface both dynamic and static triggering could have induced these early aftershocks as they initiated after the surface wave passed by and the coulomb stress perturbations from the mw 7 2 main shock promote earthquakes in the observed locations the earthquake sequence is a clear example of a seaward intraplate strike slip earthquake triggering landward intraplate earthquakes in the same region in contrast to previously reported normal reverse or reverse normal interactions at subduction zones

a high frequency secondary event during the 2004 parkfield earthquake by using seismic records of the 2004 magnitude 6 0 parkfield earthquake we identified a burst of high frequency seismic radiation that occurred about 13 kilometers northwest of the hypocenter and 5 seconds after rupture initiation we imaged this event in three dimensions by using a waveform back projection method as well as by timing distinct arrivals visible on many of the seismograms the high frequency event is located near the south edge of a large slip patch seen in most seismic and geodetic inversions indicating that slip may have grown abruptly at this point the time history obtained from full waveform back projection suggests a rupture velocity of 2 5 kilometers per second energy estimates for the subevent together with long period slip inversions indicate a lower average stress drop for the northern part of the parkfield earthquake compared with that for the region near its hypocenter which is in agreement with stress drop estimates obtained from small magnitude aftershocks

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

volcanism in a compressional andean setting a structural and geochronological study of tromen volcano neuquen province argentina we document evidence for growth of an active volcano in a compressional andean setting our data are surface structures and 39ar 40ar ages of volcanic products on tromen volcano tromen is an active back arc volcano in the andean foothills of neuquen province argentina its volcanic products are unconformable upon mesozoic strata of the neuquen basin the volcano straddles a n s trending pop up which formed during e w shortening the main underlying structures are eastward verging thrusts their traces curve around the eastern foot of the volcano minor folds and faults also occur in the volcanic cover of tromen as a result of e w shortening new 39ar 40ar ages for these volcanic rocks are younger than 2 27 0 10 ma and show that tromen has been active almost continuously from the late pliocene to the holocene we conclude that volcanism and thrusting have been coeval and that magma must have reached the surface in a tectonic setting of horizontal compression our results have wider implications for magmatic processes in such settings

heterogeneous coupling of the sumatran megathrust constrained by geodetic and paleogeodetic measurements geodetic and paleogeodetic measurements of interseismic strain above the sumatran portion of the sunda subduction zone reveal a heterogeneous pattern of coupling annual banding in corals provides vertical rates of deformation spanning the last half of the 20th century and repeated gps surveys between 1991 and 2001 and continuous measurements at gps stations operated since 2002 provide horizontal velocities near the equator the megathrust is locked over a narrow width of only a few tens of kilometers in contrast the locked fault zone is up to about 175 km wide in areas where great interplate earthquakes have occurred in the past formal inversion of the data reveals that these strongly coupled patches are roughly coincident with asperities that ruptured during these events the correlation is most spectacular for rupture of the m w 8 7 nias simeulue earthquake of 2005 which released half of the moment deficit that had accumulated since its previous rupture in 1861 suggesting that this earthquake was overdue beneath the mentawai islands strong coupling is observed within the overlapping rupture areas of the great earthquakes of 1797 and 1833 the accumulated slip deficit since these events is slowly reaching the amount of slip that occurred during the 1833 earthquake but already exceeds the slip that occurred during the 1797 earthquake thus rerupture of part of the mentawai patch in september 2007 was not a surprise in contrast coupling is low below the batu islands near the equator and around enggano island at about 5 s where only moderate earthquakes m w 8 0 have occurred in the past two centuries the correlation of large seismic asperities with patches that are locked during the interseismic period suggests that they are persistent features this interpretation is reinforced by the fact that the large locked patches and great ruptures occur beneath persistent geomorphologic features the largest outer arc islands depth and convergence rate dependent temperature might influence the pattern of coupling through its effect on the rheology of the plate interface but other influences are required to account for the observed along strike heterogeneity of coupling in particular subduction of the investigator fracture zone could be the cause for the low coupling near the equator

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

array back projection imaging of the 2007 niigataken chuetsu oki earthquake striking the world s largest nuclear power plant the 2007 niigataken chuetsu oki earthquake occurred near the kashiwazaki kariwa nuclear power plant in japan the largest in the world the strong motions were recorded by seven seismometers installed at the foundation slab base mat of the plant and exceeded the design level of the ground motion for the plant the strong motion observed by the seismographs in and around the plant show high coherency with three significant pulses in order to understand the cause of these pulses the rupture process of the earthquake was estimated using these seismograms the seismograph network was taken into account as a dense array and semblance enhanced waveform stacking was performed by projecting the power of the stacked waveforms onto the fault plane the asperities that generated significant pulses were successfully separated the first and third pulses were generated at the hypocenter and the southwest edge of the rupture zone respectively the rupture propagated toward the southwest and terminated offshore from the power plant the overall pattern of the imaged asperities coincides well with the slip distribution determined by conventional waveform inversions

the 15 august 2007 peru earthquake and tsunami influence of the source characteristics on the tsunami heights the tsunami caused by the 2007 peru earthquake mw 8 0 provoked less damage than by the seismic shaking itself numerous casualties due to the earthquake in the vicinity of pisco however it propagated across the pacific ocean and small waves were observed on one tide gauge in taiohae bay nuku hiva marquesas french polynesia we invert seismological data to recover the rupture pattern in two steps the first step uses surface waves to find a solution for the moment tensor and the second step uses body waves to compute the slip distribution in the source area we find the slip distribution to consist of two main slip patches in the source area the inversion of surface waves yields a scalar moment of 8 9 1020 nm and body wave inversion gives 1 4 1021 nm the inversion of tsunami data recorded on a single deep ocean sensor also can be used to compute a fault slip pattern yielding a scalar moment of 1 1 1021 nm we then use these different sources to model the tsunami propagation across the pacific ocean especially towards nuku hiva while the source model taken from the body wave inversion yields computed tsunami waves systematically too low with respect to observations on the central pacific ocean dart buoy as on the polynesian tide gauge the source model established from the surface wave inversion is more efficient to fit the observations confirming that the tsunami is sensitive to the low frequency component of the source finally we also discuss the modeling of the late tsunami arrivals in taiohae bay using several friction coefficients for the sea bottom

hidden aftershocks of the 2011 mw 9 0 tohoku japan earthquake imaged with the backprojection method 1 the first 25 h of the aftershock sequence following the 11 march 2011 mw 9 0 tohoku japan earthquake is investigated using a backprojection method in total 600 aftershocks are imaged during this time period these aftershocks are distributed over a 500 by 300 km area and include many events in the outer rise the backprojection events are compared with the japan meteorological agency jma catalogue which is composed of earthquakes recorded by local seismic networks in japan surprisingly half of the backprojection events are not found in the jma catalogue these events cluster near the japan trench and in the outer rise and fill in gaps in the spatial distribution of the early aftershock sequence where large main shock slip is thought to have occurred these results show that the jma magnitude of completeness is very high near the trench following the 2011 tohoku main shock and earthquakes as large as magnitude 6 8 went undetected by local seismic networks

rupture details of the 28 march 2005 sumatra mw 8 6 earthquake imaged with teleseismic p waves 1 we image the rupture of the 28 march 2005 sumatra mw 8 6 earthquake by back projecting teleseismic p waves recorded by the global seismic network and the japanese hi net to their source the back projected energy suggests that the rupture started slowly had a total duration of about 120 s and propagated at 2 9 to 3 3 km s from the hypocenter in two different directions first toward the north for 100 km and then after a 40 s delay toward the southeast for 200 km our images are consistent with a rupture area of 40 000 km2 the locations of the first day of aftershocks and the harvard cmt mw of 8 6 which implies an average slip of 6 m the earthquake is similar in its location size and geometry to a mw 8 5 event in 1861 our estimated average slip is consistent with a partially coupled subduction interface gps forearc velocities and the 59 mm yr convergence rate if the 2005 earthquake released elastic strain that accumulated over many hundreds of years rather than just since the last 1861 event

partial rupture of a locked patch of the sumatra megathrust during the 2007 earthquake sequence the great sumatra andaman earthquake and tsunami of 2004 was a dramatic reminder of the importance of understanding the seismic and tsunami hazards of subduction zones 1 2 3 4 in march 2005 the sunda megathrust ruptured again producing an event 5 of moment magnitude mw 8 6 south of the 2004 rupture area which was the site of a similar event in 1861 ref 6 concern was then focused on the mentawai area where large earthquakes had occurred in 1797 mw 8 8 and 1833 mw 9 0 6 7 two earthquakes one of mw 8 4 and twelve hours later one of mw 7 9 indeed occurred there on 12 september 2007 here we show that these earthquakes ruptured only a fraction of the area ruptured in 1833 and consist of distinct asperities within a patch of the megathrust that had remained locked in the interseismic period this indicates that the same portion of a megathrust can rupture in different patterns depending on whether asperities break as isolated seismic events or cooperate to produce a larger rupture this variability probably arises from the influence of non permanent barriers zones with locally lower pre stress due to the past earthquakes the stress state of the portion of the sunda megathrust that had ruptured in 1833 and 1797 was probably not adequate for the development of a single large rupture in 2007 the moment released in 2007 amounts to only a fraction both of that released in 1833 and of the deficit of moment that had accumulated as a result of interseismic strain since 1833 the potential for a large megathrust event in the mentawai area thus remains large

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

acoustic imaging of earthquake sources from the chalfant valley 1986 aftershock series summary following the chalfant valley earthquake of 1986 july 21 ml 6 4 the usgs deployed 120 vertical component seismometers to obtain dense array recordings of aftershocks from this data set we selected three events with the best station coverage to obtain acoustic images of the earthquake sources the events were relocated using a layered velocity model and models with a constant velocity and a constant gradient to obtain minimum traveltime residuals all models performed similarly well preprocessing of the data prior to the extrapolation consisted of applying static corrections lowpass filtering and spatial interpolation as well as spatial tapering at the edges of the recording line for the back projection of the recorded wavefield we used a second order finite difference reverse time extrapolation technique similar to mcmechan 1982 while for two events no focusing of the energy could be obtained an acoustic image of one earthquake source was retrieved in order to obtain a better understanding of the physical meaning of acoustic imaging we applied the same processing and extrapolation scheme to synthetic seismograms calculated using the reflectivity method for the present data set these tests indicate that the influence of the 1 d velocity model on the focusing quality is very low the most severe limitations however are due to the finite aperture and gaps of the recording line the spatial sampling of the wavefield limits the frequency range used for extrapolation so that the resolution is beyond the scale of the source processes the finite aperture leads to polarity reversals in the final source image which makes an interpretation of the radiation pattern at the time of focusing from the reconstructed image impossible

rapid identification of earthquake rupture plane using source scanning algorithm summary accurate identification of an earthquake s rupture plane is critical in many aspects ranging from scientific such as seismology and plate tectonics to societal such as emergency rescue planning we modify the recently developed source scanning algorithm ssa to rapidly image the rupture pattern of an earthquake using waveform data recorded at local and regional distances the method calculates the brightness function of a grid point by summing the observed amplitudes of the p wave envelopes at the corresponding predicted arrival times at all stations the composite image consisting of brightness functions of all grid points within a prescribed source volume and time interval illuminates the locations on the rupture plane where significant seismic energy is emitted synthetic tests indicate that the proposed method is robust even under the presence of hypocentral mislocation and origin time errors application of this method to the 2003 san simeon and 2004 parkfield earthquakes both occurred in central california clearly identifies the nw se striking planes as the actual rupture planes a conclusion consistent with all available evidences limited azimuthal distribution of seismic stations will not severely affect the identification result making this method ideal for offshore earthquake studies because the proposed method is able to identify the rupture plane using seismic waveform data only it is perfectly suited for near real time operation and may enable routine report of earthquake rupture planes by local seismic networks in the future

short period energy of the 25 april 2015 mw 7 8 nepal earthquake determined from backprojection using four arrays in europe china japan and australia abstract we apply a backprojection analysis to determine the locations and timing of the sources of short period 0 5 5 s energy generated by the 2015 nepal earthquake we use data from four different arrays at varying azimuths in europe china japan and australia which show generally consistent features for the rupture propagation the sources of strong short period energy are generally distributed east of the epicenter at distances of 10 100 km during the time period of 25 55 s after the initiation the rupture speed was 1 0 km s for the first 20 s then accelerated to 3 0 km s for the remaining 30 40 s the locations of sources of short period energy are close to the down dip edge of the fault and are complementary to the areas of large fault slip that occur further up dip the nepal earthquake might be another example in which regions of large fault slip do not coincide with the source areas of short period energy which are likely associated with the damaging strong ground motions online material animations of backprojections for the 2015 nepal earthquake using four different arrays

contemporary stress orientations in the andean retroarc between 34 s and 39 s from borehole breakout analysis 1 in this paper we present the results of the analysis of borehole breakouts from 115 wells drilled within neuquen basin in the andean retroarc between 34 and 39 s argentina the first order present day stress orientation in the andean retroarc is expected to be mainly controlled by the plate boundary forces azimuth 80 and the topographic forces e w the obtained maximum horizontal stress shmax has a preferred trend with a resultant direction of azimuth 88 7 and a 95 confidence interval of 13 3 consistent with the expected trend the horizontal stress trajectory map achieved for this region shows that the shmax along the study area is not completely uniform to the north of colorado river the shmax shows an ese tendency interpreted as significant influenced by the topographic forces to the south of colorado river shmax has an ene trend similar to the expected based on plate boundary forces to the southeast of the region a ne direction was found probably showing a basement structural control in the stress field geometry the stress orientations obtained for the whole region show that plate boundary forces drag basal and topographic forces are strongly controlling the stress direction distribution

hypocenter depths of large interplate earthquakes and their relation to seismic coupling we examine locations of hypocenters of large interplate earthquakes mv 7 5 at subduction zones relative to their rupture areas to obtain a relation between the hypocentral depth and the seismic coupling coefficient which is the ratio of the long term slip rate estimated from cumulative seismic moment of large earthquakes to the relative plate motion we find 1 that the hypocentral depth is close to the bottom of the depth extent of the rupture area when the seismic coupling coefficient is nearly equal to 1 0 and 2 that the hypocentral depth relative to the depth extent of the rupture area shows a large scatter from shallow to deep when the seismic coupling coefficient is smaller than about 0 5 to interpret these observations we conduct a numerical simulation of seismic cycles of interplate earthquakes where the frictional stress on the plate boundary is assumed to obey a laboratory derived rate and statedependent friction law the observed result 1 is reproduced in the simulation when the critical fault length which is the size of the fault where the slip nucleation process takes place is much shorter than the seismogenic zone of the plate boundary in this case the plate boundary is strongly locked during an interseismic period and accordingly the calculated seismic coupling coefficient is close to 1 0 seismic slip starts near the bottom of the seismogenic zone because the maximum shear stress concentration is generated near the bottom of the seismogenic zone due to deeper steady plate motion on the other hand when the critical fault length is large appreciable aseismic sliding occurs in the seismogenic zone and therefore the calculated seismic coupling coefficient becomes significantly smaller than 1 0 the hypocentral depths of simulated large earthquakes tend to be shallow for large critical fault lengths heterogeneous frictional properties on the plate boundary may produce non uniform aseismic sliding during an interseismic period in this case the seismic coupling is small and seismic slip starts in various portions of the seismogenic zone this can explain the observed result 2 2 2003 elsevier science b v all rights reserved

complex and diverse rupture processes of the 2018 mw 8 2 and mw 7 9 tonga fiji deep earthquakes author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 46 5 2019 2434 2448 doi 10 1029 2018gl080997

secarb co 2 injection test in mature coalbed methane reservoirs of the black warrior basin blue creek field alabama abstract the secarb black warrior field verification test employed a diverse suite of well testing and monitoring procedures designed to determine the injectivity capacity heterogeneity and performance of mature coalbed methane reservoirs a total of 3250 bbl of water and 252 t of co2 were injected into coal in a battery of slug tests these tests demonstrate that significant injectivity exists in black warrior coalbed methane reservoirs and that reservoir heterogeneity is a critical factor to consider when implementing co2 sequestration and co2 enhanced recovery programs the primary test well produces coalbed methane at wellhead pressures just above atmospheric and yet desorption testing indicates that less than 20 of the original gas in place has been recovered by primary production injection of co2 was conducted at sustained rates of about 90 t d of co2 reservoir pressure declined exponentially following the emplacement of each co2 slug slug and pressure buildup tests verify that permeability decreases exponentially with depth and also decreased during injection monitoring operations included multi zone pressure logging and gas sampling in deep observation wells and groundwater sampling in a shallow observation well results indicate that significant permeability anisotropy exists in each coal group in the black creek coal pressure response was greatest in the dominant natural fracture direction in the pratt coal group pressure response was dominated by hydrofractures co2 broke through to the observation wells only in the pratt coal group and only along the major fracture directions no significant flow of co2 out of zone was detected and no impact on shallow groundwater resources was identified

teleseismic p wave imaging of the 26 december 2004 sumatra andaman and 28 march 2005 sumatra earthquake ruptures using the hi net array 1 seismograms from a dense high quality seismic network in japan are used to investigate the characteristics of the 26 december 2004 sumatra andaman and the 28 march 2005 sumatran earthquakes the onset of the p waveforms are aligned through cross correlation and a simple concept of back projecting seismic energy to a grid of potential source locations is applied the waveform alignment removes the effects due to lateral variations in wave speed between the hypocenter and each station to better approximate the effects of three dimensional heterogeneity for paths originating from grid points away from the hypocenter cross correlation results of the p waveforms from aftershocks are introduced this additional information leads to improved resolution of smaller scale features near many of the aftershocks by reducing wavefront distortion the back projection analysis provides a quick assessment of the spatiotemporal extent and variability of relative high frequency energy release which can be translated into an estimate of the moment magnitude as well as an unparalleled view of high frequency rupture propagation the results are in general consistent with those obtained from more involved source inversion methods the 2004 sumatra andaman earthquake released most energy in a region northwest of the sumatra island and the rupture extended to the northern andaman islands about 1300 km from the epicenter this northern portion of the rupture radiated a considerable amount of energy but there is little evidence of slow slip the 2005 event is imaged to have bilateral rupture with northwestern slip occurring for about 50 s before it moved to the southeast of the epicenter

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

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

insights into the mechanism of intermediate depth earthquakes from source properties as imaged by back projection of multiple seismic phases 1 this study investigates the spatial and temporal distribution of energy release of large intermediate depth earthquakes using a modified back projection technique first used to study the 2004 sumatra andaman megathrust event multiple seismic phases are included in the back projection analysis which provides the capability to determine the energy distribution with respect to depth and time a total of 22 intermediate depth earthquakes with moment magnitudes greater than or equal to 6 5 are investigated with hypocentral depths between 100 and 300 km for most of these events the vertical extent of energy release is either below the resolution of this study 5 km or slightly above 15 km this observation agrees with previous studies that find large intermediate depth earthquakes have subhorizontal rupture planes the results also show a significant portion of the events have multiple rupture planes that are well separated in depth the closeness in time of the ruptures on separate planes and the distance between the planes suggest dynamic triggering where the p waves from the first rupture initiate rupture on the second plane we propose that a dehydration embrittlement mechanism combined with preferentially hydrated subhorizontal faults can explain the observations of dominant subhorizontal rupture planes and the frequent occurrence of rupture complexity involving multiple subevents

limited overlap between the seismic gap and coseismic slip of the great 2010 chile earthquake the mw 8 8 chile earthquake on 27 february 2010 occurred in a broad region where tectonic loading has been accumulating since the great 1835 earthquake a joint inversion of tsunami and geodetic data suggests that the 2010 earthquake rupture only partly overlapped with the zone of preseismic locking

characteristics of subevents and three stage rupture processes of the 2015 mw 7 8 gorkha nepal earthquake from multiple array back projection abstract on 25 april 2015 an mw 7 8 earthquake occurred in nepal and caused about 9000 casualties this earthquake ruptured part of the main himalaya thrust fault which is due to the convergence of the subducting indian plate to the overriding eurasian plate and showed thrust mechanism with a very small fault dip angle about 7 10 we apply teleseismic multiple array back projection analysis to study the rupture process of this earthquake and find 6 clear high frequency radiation sources subevents our results illustrate a simple unilateral eastward rupture of 160 km with relative stable rupture speed of 2 8 km s and a duration of 56 s the entire rupture processes can be divided into 3 stages the high frequency radiation appears to be mainly located at the edge of the large slip area but the subevents have different characteristics in the western and eastern rupture areas for this 2015 nepal earthquake the scales of asperities appear to be mainly controlled by depth which dominates the overall patterns of slip and high frequency radiation we finally propose a multiple scale asperity model with stress and structural heterogeneities along the rupture direction to explain the distribution of high frequency subevents co seismic slip and aftershocks

the 15 august 2007 peru tsunami runup observations and modeling 1 on 15 august 2007 an earthquake with moment magnitude mw of 8 0 centered off the coast of central peru generated a tsunami with locally focused runup heights of up to10 m a reconnaissance team was deployed two weeks after the event and investigated the tsunami effects at 51 sites three tsunami fatalities were reported south of the paracas peninsula in a sparsely populated desert area where the largest tsunami runup heights were measured numerical modeling of the earthquake source and tsunami suggest that a region of high slip near the coastline was primarily responsible for the extreme runup heights the town of pisco was spared by the paracas peninsula which blocked tsunami waves from propagating northward from the high slip region the coast of peru has experienced numerous deadly and destructive tsunamis throughout history which highlights the importance of ongoing tsunami awareness and education efforts to ensure successful self evacuation

insight into complex rupturing of the immature bending normal fault in the outer slope of the japan trench from aftershocks of the 2005 sanriku earthquake mw 7 0 located by ocean bottom seismometry 1 the distribution of aftershocks of a large mw 7 0 normal faulting earthquake beneath the outer slope of the japan trench in 2005 measured in 2007 using ocean bottom seismographs indicates that the earthquake was involved with a set of conjugate normal faults although the faults reach to the upper mantle the estimated vp and vp vs show no remarkable changes that can be related to extensive hydration in the crust or uppermost mantle the absence of horst graben topographic structure in the rupture area suggests that immaturity of the bending fault system is responsible for the relatively unhydrated lithosphere several earthquakes below the aftershock zone may belong to the lower plane seismicity of the shallow double seismic zone because no earthquakes were recorded in the area for more than 80 years before the 2005 event shallow extensional and deep compressive earthquakes may be activated concurrently in the focal area of this earthquake

illuminating the near sonic rupture velocities of the intracontinental kokoxili mw 7 8 and denali fault mw 7 9 strike slip earthquakes with global p wave back projection imaging 1 the denali and kokoxili strike slip earthquakes are two of the longest recent intracontinental ruptures previous studies report a range of rupture velocities here we image these earthquakes by reverse time migration of the intermediate frequency p wave train recorded by global broadband seismometers this technique permits a relatively direct measure of rupture velocity speed and direction as constrained by the radiated seismic energy free from restrictive assumptions or rupture speed bounds placed on the solution we compare our results with published seismic gps displacement and surface slip inversion results both ruptures were initially subshear and transitioned over a distance no longer than 40 km to supershear speeds close to the p wave speed of 5 6 km s we investigate the accuracy of our results with synthetic data and experiment with using different imaging parameters and seismic subnetworks these tests allow us to rule out the possibility of subshear speeds along the supershear segments although we cannot exclude supershear speeds of 4 5 6 5 km s our most reliable rupture velocities of 5 6 km s are close to the local p wave speeds we hypothesize that these intracontinental faults have weak shear strengths or high breakdown slips or crustal rigidities and experience at least moderate slip or slip rate weakening our observations and previous published results lead us to speculate that very long surface extending faults with general homogeneity in prestress and fault strength together with smaller adjacent fault segments to provide triggering may be necessary ingredients for the sub rayleigh to supershear rupture speed transition in strike slip earthquakes

tracking earthquake source evolution in 3 d summary starting from the hypocentre the point of initiation of seismic energy we seek to estimate the subsequent trajectory of the points of emission of high frequency energy in 3 d which we term the evocentres we track these evocentres as a function of time by energy stacking for putative points on a 3 d grid around the hypocentre that is expanded as time progresses selecting the location of maximum energy release as a function of time the spatial resolution in the neighbourhood of a target point can be simply estimated by spatial mapping using the properties of isochrons from the stations the mapping of a seismogram segment to space is by inverse slowness and thus more distant stations have a broader spatial contribution as in hypocentral estimation the inclusion of a wide azimuthal distribution of stations significantly enhances 3 d capability we illustrate this approach to tracking source evolution in 3 d by considering two major earthquakes the 2007 mw 8 1 solomons islands event that ruptured across a plate boundary and the 2013 mw 8 3 event 610 km beneath the sea of okhotsk in each case we are able to provide estimates of the evolution of high frequency energy that tally well with alternative schemes but also to provide information on the 3 d characteristics that is not available from backprojection from distant networks we are able to demonstrate that the major characteristics of event rupture can be captured using just a few azimuthally distributed stations which opens the opportunity for the approach tobeusedinarapidmodeimmediatelyafteramajoreventtoprovideguidancefor forexample tsunami warning for megathrust events

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

tracking the rupture of the mw 9 3 sumatra earthquake over 1 150 km at teleseismic distance on 26 december 2004 a moment magnitude mw 9 3 earthquake occurred along northern sumatra the nicobar and andaman islands resulting in a devastating tsunami in the indian ocean region the rapid and accurate estimation of the rupture length and direction of such tsunami generating earthquakes is crucial for constraining both tsunami wave height models as well as the seismic moment of the events compressional seismic waves generated at the hypocentre of the sumatra earthquake arrived after about 12 min at the broadband seismic stations of the german regional seismic network grsn located approximately 9 000 km from the event here we present a modification of a standard array seismological approach and show that it is possible to track the propagating rupture front of the sumatra earthquake over a total rupture length of 1 150 km we estimate the average rupture speed to be 2 3 2 7 km s 1 and the total duration of rupture to be at least 430 s and probably between 480 and 500 s

rupture imaging of the mw 7 9 12 may 2008 wenchuan earthquake from back projection of teleseismic p waves 1 the mw 7 9 wenchuan earthquake of 12 may 2008 was the most destructive chinese earthquake since the 1976 tangshan event tens of thousands of people were killed hundreds of thousands were injured and millions were left homeless here we infer the detailed rupture process of the wenchuan earthquake by back projecting teleseismic p energy from several arrays of seismometers this technique has only recently become feasible and is potentially faster than traditional finite fault inversion of teleseismic body waves therefore it may reduce the notification time to emergency response agencies using the iris dmc we collected 255 vertical component broadband p waves at 30 95 from the epicenter we found that at periods of 5 s and greater nearly all of these p waves were coherent enough to be used in a global array we applied a simple down sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function arf we also considered three regional subarrays of seismometers in alaska australia and europe that had apertures less than 30 and p waves that were coherent to periods as short as 1 s individual arfs for these subarrays were skewed toward the subarrays however the linear sum of the regional subarray beams at 1 s produced a symmetric arf similar to that of the groomed global subarray at 5 s for both configurations we obtained the same rupture direction rupture length and rupture time we found that the wenchuan earthquake had three distinct pulses of high beam power at 0 23 and 57 s after the origin time with the pulse at 23 s being highest and that it ruptured unilaterally to the northeast for about 300 km and 110 s with an average speed of 2 8 km s it is possible that similar results can be determined for future large dip slip earthquakes within 20 30 min of the origin time using relatively sparse global networks of seismometers such as those the usgs uses to locate earthquakes in near real time

a window into the complexity of the dynamic rupture of the 2011 mw 9 tohoku oki earthquake the 2011 mw 9 tohoku oki earthquake recorded by over 1000 near field stations and multiple large aperture arrays is by far the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in earthquake source dynamics here we conduct a high resolution array analysis based on recordings from the usarray and the european network the mutually consistent results from both arrays reveal rupture complexity with unprecedented resolution involving phases of diverse rupture speed and intermittent high frequency bursts within slow speed phases which suggests spatially heterogeneous material properties the earthquake initially propagates down dip with a slow initiation phase followed by sustained propagation at speeds of 3 km s the rupture then slows down to 1 5 km s for 60 seconds a rich sequence of bursts is generated along the down dip rim of this slow and roughly circular rupture front before the end of the slow phase an extremely fast rupture front detaches at about 5 km s towards the north finally a rupture front propagates towards the south running at about 2 5 km s for over 100 km key features of the rupture process are confirmed by the strong motion data recorded by k net and kik net the energetic high frequency radiation episodes within a slow rupture phase suggests a patchy image of the brittle ductile transition zone composed of discrete brittle asperities within a ductile matrix the high frequency is generated mainly at the down dip edge of the principal slip regions constrained by geodesy suggesting a variation along dip of the mechanical properties of the mega thrust fault or their spatial heterogeneity that affects rise time

multiarray rupture imaging of the devastating 2015 gorkha nepal earthquake sequence a rapid robust multiarray backprojection method was applied to image the rupture pattern of the 2015 gorkha nepal mw7 8 main shock and its mw7 3 aftershock backprojected teleseismic p wave trains from three regional seismic arrays in europe australia and alaska show that both earthquakes ruptured unilaterally and primarily eastward with rupture speeds potentially decreasing with depth the rupture of the main shock first extended eseward at 3 5 km s over 120 km with later rupture propagation further downdip on the eastern segment at 2 1 km s the aftershock ruptured the fault se of the main shock s ruptured plane it began to rupture updipward for 20 km at a speed around 1 2 km s then it may have accelerated to 3 5 km s for the next 50 km the apparent depth dependent rupture speeds of the two earthquakes may be caused by along dip heterogeneities in fault strength with a higher stress concentration on the updip part of the nepalese main himalayan thrust

tectonic control of the subducting juan fernandez ridge on the andean margin near valparaiso chile near the latitude of valparaiso chile a fundamental change in configuration of the benioff zone volcanic arc activity and the structure of the continental margin occurs opposite the subducting juan fernandez ridge upper plate tectonics related to subduction of the ridge were studied by an international group of geoscientists in the two degree segment offshore valparaiso extending from the shelf edge seaward across the eastern end of juan fernandez ridge near the o higgins group of seamounts the juan fernandez ridge strikes northeast rather than continuing its east west trend across the pacific basin the ridge uplifts the upper plate and sediments of the valparaiso basin are deformed against its southern flank this deformation is consistent with the southward migration required by an oblique trending ridge and the nearly trench normal vector of plate convergence in the trench axis the ridge forms a basement barrier behind which sediments 2 5 km deep have ponded the lower slope over the ridge appears eroded whereas the margin not yet affected by ridge subduction is fronted by an accretionary prism about 25 km wide nazca plate relief clearly influences tectonism of the margin where it subducts beneath thin continental crust its relation to deeper processes segmenting the andean orogen appears to involve prior tectonic events

real time earthquake location using kirchhoff reconstruction real time location of earthquakes can be achieved by using direct imaging of the recorded wave field based on a kirchhoff reconstruction method similar to that used in the migration of seismic reflection data the standard method of event location requires the wave arrival at each sensor to be picked and associated with an event by using direct imaging the event is identified once in the imaged wave field the computation is independent of the level of seismic activity and can be carried out on a typical desktop computer the procedure has been successfully demonstrated in two and three dimensions using data from the southern california seismic network trinet at higher resolutions the reconstruction method can identify finite source effects further work considers extending the method by implementing full elastic theory and solving for moment tensors at all locations in the mesh

coherent seismic arrivals in the p wave coda of the 2012 m w 7 2 sumatra earthquake water reverberations or an early aftershock

earthquake triggering during preparation for great earthquakes seismic quiescence has been proposed as a precursor to many large earthquakes in this paper we present two cases in which precursory quiescence is interrupted several years prior to great earthquakes by triggered events in the upcoming rupture areas this triggering results in complex precursory patterns which include seismic quiescence and triggered events prior to the kermadec earthquake of 1976 ms 8 0 events in the rupture zone were triggered by a quake on the outer rise and one near the future mainshock epicenter events were triggered by an earthquake on an adjacent segment of the plate interface and by one near the epicenter of the new hebrides earthquake of 1980 ms 8 0 we propose that two preconditions must be fulfilled for triggering to occur first the stress in the region must be close to the failure stress and second nearby events must occur which are large enough to affect the stress field but not large enough to cause an immediate mainshock

radiated energy of great earthquakes from teleseismic empirical green s function deconvolution we expand on the empirical green s function deconvolution method of ide et al 2011 to estimate radiated energy for the six largest earthquakes worldwide over the last 10 years 2011 m w 9 0 tohoku oki 2004 m w 9 1 sumatra 2010 m w 8 8 maule 2005 m w 8 7 nias 2007 m w 8 5 bengkulu and 2012 m w 8 6 off sumatra deconvolution of p sv and sh components gives consistent energy results that are comparable to estimates found independently by other researchers apparent stress for the five great thrust earthquakes is between 0 4 and 0 8 mpa while the 2012 off sumatra strike slip earthquake has a higher apparent stress of 3 mpa which is consistent with other studies that find a tendency for strike slip events to be more energetic our results are within the spread of apparent stress from the wider global earthquake population over a large magnitude range the azimuthal distribution of energy in each case shows signs of directivity and in some cases shows less energy radiated in the trench ward direction which may suggest enhanced tsunami potential we find that egfs as small as m 6 5 can be used for teleseismic deconvolution and that an egf mainshock magnitude difference of 1 5 units yields stable results this implies that m 8 is the minimum mainshock size for which teleseismic egf deconvolution will work well we propose that a database of egf events could be used to calculate radiated energy and apparent stress of great hazardous events in near real time i e promptly enough that it could contribute to rapid response measures

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