relocation and assessment of seismicity in the iran region summary more than 2000 instrumentally recorded earthquakes occurring in the iran region during the period 1918 2004 have been relocated and reassessed with special attention to focal depth using an advanced technique for 1 d earthquake location a careful review of starting depths association of teleseismic depth phases and the effects of reading errors on these phases are made and when necessary waveforms have been examined to better constrain ehb focal depths uncertainties in ehb epicentres are on the order of 10 15 km in the iran region owing to the earth s lateral heterogeneity and uneven station distribution uncertainties of reviewed ehb focal depth estimates are on the order of 10 km as compared to about 4 km for long period p and sh body waveform inversions nevertheless these ehb depth estimates are sufficiently accurate to resolve robust differences in focal depth distribution throughout the iran region and within their errors show patterns that are in agreement with the smaller number of earthquakes whose depths have been confirmed by body wave modelling or local seismic networks the importance of this result is that future earthquakes with apparently anomalous depths can easily be identified and checked if necessary most earthquakes in the iranian continental lithosphere occur in the upper crust with the crustal shortening produced by continental collision accommodated entirely by thickening and distributed deformation in the zagros mountains nearly all earthquakes are confined to the upper crust depths 20 km and there is no evidence for a seismically active subducted slab dipping ne beneath central iran by contrast in southeastern iran where the arabian seafloor is being subducted beneath the makran coast low level earthquake activity occurs in the upper crust as well as to depths of at least 150 km within a northward dipping subducting slab near the oman line a region transitional between the zagros and the makran seismicity extends to depths of up to 30 45 km in the crust consistent with low angle thrusting of arabian basement beneath central iran in north central iran along the alborz mountain belt seismic activity occurs primarily in the upper crust but with some infrequent events in the lower crust particularly in the western part of the belt the talesh where the south caspian basin underthrusts nw iran earthquakes that occur in a band across the central caspian following the apscheron balkhan sill between azerbaijan and turkmenistan have depths in the range 30 100 km deepening northwards these are thought to be connected with either incipient or remnant northeast subduction of the south caspian basin basement beneath the east west trending apscheron balkhan sill curiously in this region of genuine mantle seismicity there is no evidence for earthquakes shallower than 30 km

global mantle heterogeneity and its influence on teleseismic regional tomography abstract a new global p wave tomography model is determined using a flexible grid parameterization this new model better reveals the mantle structure under the polar regions than the previous tomographic models the subducting slabs are generally imaged clearly as high velocity high v zones the young slabs are still subducting in the upper mantle and the mantle transition zone mtz whereas the old and ancient slabs are either stagnant in the mtz or have subducted down to the lower mantle even reaching the core mantle boundary low velocity low v anomalies are generally revealed in the mantle under the hotspot regions it seems that a variety of mantle upwelling plumes exist some strong plumes are visible in the whole mantle under the long living hotspots such as those in south central pacific africa hawaii and iceland whereas weak plumes are visible in only some depth range under the minor hotspots under the intraplate volcanoes in east eurasia bering sea and west alaska significant low v anomalies are revealed in the upper mantle which may reflect hot and wet upwelling associated with corner flows in the big mantle wedge bmw above the stagnant pacific slab in the mtz and perhaps deep slab dehydration as well the subduction triggered magmatism in the bmw may be a new class of mantle plumes we also used the new global model to investigate the influence of whole mantle heterogeneity on the determination of upper mantle tomography under japan with a teleseismic inversion method the results show that the mantle heterogeneities outside the target volume of regional tomography can cause significant changes 0 2 0 4 s to the observed relative travel time residuals of a distant earthquake the pattern of regional tomography remains the same even after correcting for the whole mantle heterogeneity but there are some changes in the amplitude of velocity anomalies in the regional tomography hence it is necessary to correct for the mantle heterogeneities outside the target volume so as to obtain a better regional tomography

the scotia antarctica plate boundary from 35 w to 45 w abstract a compilation of available multichannel seismic profiles acquired along the southern margin of the scotia sea east of the south orkney microcontinent has allowed identifying and mapping the main morphological and structural features of the central segment of the scotia antarctica plate boundary this margin is composed by several bathymetric highs of variable size and uncertain crustal nature separated by deep troughs and restricted oceanic basins some of these troughs represent pull apart basins three main segments oriented wnw ese the western sector ene wsw the central sector here named bruce deep and ne sw the eastern sector have been described these segments are separated by nnw sse trending release zones disposed in an en echelon geometry which represent mostly strike slip faults the western segment corresponds to the northern margin of the south orkney microcontinent where a subduction zone seems to be present even if its present day activity is unclear the segment further to the east corresponds to an ene oriented basin bruce deep which separates the bruce bank from the eastern promontory of the south orkney continental platform to the south of the bruce deep a wide deformation zone with n verging folds and thrusts here named jane thrust belt has been identified from seismic data the eastern segment of the plate boundary is structurally the less constrained and may be composed by a series of tectonic lineaments of different lengths from the bruce bank to the east focal mechanisms maintain a prevalent left lateral strike slip motion combined with an extensional component in this sector earthquakes are located in a 150 km wide area and on a local scale are difficult to follow unambiguously at the plate boundary lithologic analyses on dredged material recovered along a flank of one of the morphological relieves present south of the discovery bank to 35 w here collectively named irizar highs yielded a dominant granitic composition a similar composition characterizes the rocks collected in the southern flank of the south easternmost jane bank this suggests a continental crust nature for these bathymetric highs now dispersed along this sector of the scotia antarctica plate boundary we propose here a tectonic evolution for this margin dominated since the early miocene by the northward subduction of the weddell sea oceanic crust the development of a dextral en echelon transform fault system facilitated the process of fragmentation and dispersion of the crustal blocks dismembered the subduction zone and possibly inverted the direction of convergence therefore the scotia plate would subduct beneath the antarctic plate in the western sector and weddell sea would subduct beneath scotia plate in the eastern sector finally the activation of left lateral transtensional strike slip lineaments generated narrow pull apart basins in the fore arc sectors of the convergent zones

tectonics of the scotia antarctica plate boundary constrained from seismic and seismological data abstract the plate boundary between the scotia and antarctic plates runs along the broadly e w trending south scotia ridge it is a mainly transcurrent margin that juxtaposes thinned continental and transitional crust elements with restricted oceanic basins and deep troughs seismic profiles and regional scale seismological constraints are used to define the peculiarities of the crustal structures in and around the southern scotia sea and focal solutions from recent earthquakes help to understand the present day geodynamic setting the northern edge of the western south scotia ridge is marked by a sub vertical left lateral master fault locally a narrow wedge of accreted sediments is present at the base of the slope this segment represents the boundary between the scotia plate and the independent south shetland continental block along the northern margin of the south orkney microcontinent the largest fragment of the south scotia ridge an accretionary prism is present at the base of the slope which was possibly created by the eastward drift of the south orkney microcontinent and the consequent subduction of the transitional crust present to the north east of the south orkney microcontinent the physiography and structure of the plate boundary are less constrained here the tectonic regime exhibits mainly strike slip behavior with some grade of extensional component and the plate boundary is segmented by a series of nnw sse trending release zones which favored the fragmentation and dispersion of the crustal blocks seismic data have also identified along the north western edge of the south scotia ridge an elevated region the ona platform which can be considered along with the terror rise as the conjugate margin of the tierra del fuego before the drake passage opening we propose here an evolutionary sketch for the plate boundary from the late oligocene to the present encompassing the segment from the elephant island platform to the herdman bank

establishing a 14 6 0 2 ma age for the nordlinger ries impact germany a prime example for concordant isotopic ages from various dating materials abstract 40ar 39ar dating of recrystallized k feldspar melt particles separated from partially molten biotite granite in impact melt rocks from the approximately 24 km nordlinger ries crater southern germany yielded a plateau age of 14 37 0 30 0 32 ma 2 this new age for the nordlinger ries is the first age obtained from 1 monomineralic melt 2 separated from an impact metamorphosed target rock clast within 3 ries melt rocks and therewith extends the extensive isotopic age data set for this long time studied impact structure the new age goes very well with the 40ar 39ar step heating and laser probe dating results achieved from mixed glass samples suevite glass and tektites and is slightly younger than the previously obtained fission track and k ar and ages of about 15 ma as well as the k ar and 40ar 39ar age data obtained in the early 1990s taking all the 40ar 39ar age data obtained from ries impact melt lithologies into account data from the literature and this study we suggest an age of 14 59 0 20 ma 2 as best value for the ries impact event

the vakkejokk breccia an early cambrian proximal impact ejecta layer in the north swedish caledonides the 27 m thick vakkejokk breccia is intercalated in autochthon lower cambrian along the caledonian front north of lake tornetrask lapland sweden the spectacular breccia is here interpreted as a proximal ejecta layer associated with an impact crater probably 2 3 km in size located below caledonian overthrusts immediately north of the main breccia section the impact would have taken place in a shallow marine environment 520 ma ago the breccia comprises i a strongly disturbed lower polymict subunit with occasional in themselves brecciated crystalline mega clasts locally exceeding 50 m surrounded by contorted sediments ii a middle commonly normally graded crystalline rich polymict subunit in turn locally overlain by iii a thin fine grained quartz sandstone 30 cm thick the upper sandstone is sporadically either overlain or replaced by a conglomerate in progressively more distal parts of the ejecta layer the lower subunit is better described as only slightly disturbed strata the lower subunit is suggested to have formed by ejecta bombardment of the strata surrounding the impact crater even causing some net outwards mobilization of the sediments the middle subunit and the uppermost quartz sandstone are considered resurge deposits the top conglomerate may be caused by subsequent wave reworking and slumping of material from the elevated rim quartz grains showing planar deformation features are present in the graded polymict subunit and the upper sandstone that is the inferred resurge deposits

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

surface deformation of the barren island volcano andaman sea 2007 2017 constrained by insar measurements evidence for shallow magma reservoir and lava field subsidence abstract barren island situated in the andaman sea is the northernmost active volcano of the sunda arc the oldest known eruption of the volcano was during the period 1787 1832 after about 150 years of quiescence volcanic activity resumed in 1991 and continues since then the magmatic plumbing system of this volcano is largely unknown due to lack of geophysical experiments owing to its remote location we report for the first time time series surface deformation measurements of barren island volcano from interferometric synthetic aperture radar insar during epochs 2007 2011 and 2015 2017 line of sight los deformation of 50 mm yr during 2007 2011 at the cinder cone is interpreted as the co eruptive pressure changes associated with the 2008 2010 eruptions bayesian inversion suggests a shallow magma reservoir at a depth of 578 100 300 m below the summit the depth of the magma reservoir is shallower than that of other volcanoes of the sunda arc probably due to the extensional stress regime imposed by the oblique subduction based on the present studies and previous works we propose a plausible source model for barren island volcano we also discuss potential biases in the present source parameter estimation due to the lack of high quality insar data from both ascending and descending directions significant deformation 15 to 150 mm yr observed along the lava delta of barren island volcano for both the epochs are interpreted as post emplacement subsidence of the lava flow further we characterise the lava flow including volcanic deposits by mapping its spatial extent and elevation changes during 1979 2000 and 2000 2017 periods using geodetic measurements

shocked quartz grains in the early cambrian vakkejokk breccia sweden evidence of a marine impact here we present a study of the abundance and orientation of planar deformation features pdfs in the vakkejokk breccia a proposed lower cambrian impact ejecta layer in the north swedish caledonides the presence of pdfs is widely accepted as evidence for shock metamorphism associated with cosmic impact events and their presence confirms that the vakkejokk breccia is indeed the result of an impact the breccia has previously been divided into four lithological subunits from bottom to top viz lower polymict breccia lpb graded polymict breccia gpb top sandstone ts and top conglomerate tc here we show that the lpb contains no shock metamorphic features indicating that the material derives from just outside of the crater and represents low shock semi autochthonous bombarded strata in the overlying more fine grained gpb and ts quartz grains with pdfs are relatively abundant 2 5 of the grain population and with higher shock levels in the upper parts suggesting that they have formed by reworking of more distal ejecta by resurge of water toward the crater in a marine setting the absence of shocked quartz grains in the tc indicates that this unit represents later slumps associated with weathering and erosion of the protruding crater rim sparse shocked quartz grains 0 2 were also found in sandstone beds occurring at the same stratigraphic level as the vakkejokk breccia 15 20 km from the inferred crater site it is currently unresolved whether the sandstone at these distal sites is related to the impact or just contains rare reworked quartz grains with pdfs less

evolution of the southern segment of the philippine trench constraints from seismic tomography a high resolution model of three dimensional p wave tomography of the crust and upper mantle beneath the southern part of the philippine trench is determined by inverting 22 960 arrival times of 2 789 local earthquakes and 4 660 traveltime residuals of 751 teleseismic events simultaneously the tomographic method tomog3d is used to obtain the tomographic model that has a lateral resolution of 0 6 degrees or better as shown by extensive checkerboard resolution tests a model recovery synthetic test is also performed which indicates that main features of our tomographic images are quite robust our results show that the philippine sea slab has subducted down to depths of 450 600km with an overturned dip angle along the southern segment of the philippine trench indicating that the subduction of the philippine sea plate along the southern segment of the philippine trench initiated at 20 25ma contemporaneous with the sangihe trench the subduction initiation of the philippine sea plate at the central philippine trench resulted from the collision between the philippines and the palawan block at similar to 10ma the subduction completion of the molucca sea slab propagated from the south to the north at similar to 5ma which presumably resulted in the subduction reorganization of the philippine sea plate along the southern segment of the philippine trench and subduction initiation of the philippine sea plate along the northern segment of the philippine trench

the rhombohedral framework of the scandinavian caledonides and their foreland the baltic shield of northern europe is transsected by approximately n s and nw se striking proterozoic fault and fracture zones that were remobilized during the late precambrian opening of the iapetus ocean and the se directed thrusting of the caledonian nappes in mid paleozoic time remobilizations of these older structures account for a distinct subsidence history and sedimentological evolution over each fault bounded basement segment during opening of the iapetus and for a distinct metamorphic and structural development found within each block during overthrusting of the caledonian nappes and the exhumation of the orogen the two fault sets define basement blocks with rhombus like plan sections which had individual subsidence histories during iapetus rifting as is expressed by their late precambrian riphean and vendian to silurian sedimentary cover of contrasting thickness and facies this contrasting subsidence history of the various basement blocks may have contributed to differences in thrusting level thrust excision nappe size and tectonic style correlative caledonian nappes from adjacent faultbounded basement blocks were thrust diachronously resulting in transport transverse to the general thrusting direction thrusting oblique to the nw se fault zones and orogen parallel extension resulted in lateral ramp folds in the cover and reactivation along the nw se faults imbricated the overlying nappes the extent of basement imbrication and duplex formation is variable in the different segments within single segments the basement imbrication and duplex formation defined basement highs that roughly align in two parallel zones within the orogen the site of the basement duplexes is probably controlled by older n s fracture zones while the pinch and swell structure parallel to the orogen is caused by the individual deformation and thrusting behavior of the basement and cover sequences that are bound by the nw se fault zones thus the caledonian orogen appears to have inherited the precambrian structural grain of the underlying baltic shield

aseismic deep subduction of the philippine sea plate and slab window abstract we have made great efforts to collect and combine a large number of high quality data from local earthquakes and teleseismic events recorded by the dense seismic networks in both south korea and west japan this is the first time that a large number of korean and japanese seismic data sets are analyzed jointly as a result a high resolution 3 d p wave velocity model down to 700 km depth is determined which clearly shows that the philippine sea phs plate has subducted aseismically down to 460 km depth under the japan sea tsushima strait and east china sea the aseismic phs slab is visible in two areas one is under the japan sea off western honshu and the other is under east china sea off western kyushu however the aseismic phs slab is not visible between the two areas where a slab window has formed the slab window is located beneath the center of the present study region where many teleseismic rays crisscross detailed synthetic tests were conducted which indicate that both the aseismic phs slab and the slab window are robust features using the teleseismic data recorded by the japanese stations alone the aseismic phs slab and the slab window were also revealed zhao et al 2012 though the ray paths in the japanese data set crisscross less well offshore the slab window may be caused by the subducted kyushu palau ridge and kinan seamount chain where the phs slab may be segmented hot mantle upwelling is revealed in the big mantle wedge above the pacific slab under the present study region which may have facilitated the formation of the phs slab window these novel findings may shed new light on the subduction history of the phs plate and the dynamic evolution of the japan subduction zone

resurge deposits associated with the shallow marine early cambrian vakkejokk impact north sweden the lower cambrian vakkejokk breccia is a proximal ejecta layer from a shallow marine impact it is exposed for 7 km along a steep mountainside in lapland northernmost sweden in its central parts the layer is up to 27 m thick here the breccia shows a vertical differentiation into 1 a lower subunit consisting of strongly deformed target sediments mixed with up to decameter size mainly crystalline basement clasts i e lower polymict breccia lpb 2 a middle subunit consisting of a polymict blocky to gravelly breccia commonly graded i e graded polymict breccia gpb that in turn is sporadically overlain by 3 a few dm thick sandy bed i e top sandstone ts previous work interpreted the graded beds as deposited by resurging water during early crater modification we made three short 1 35 m core drillings through the graded beds the line logging technique previously used on cores from other marine target craters was complemented by logging of equal sized cells in photos made along the cores granulometry and clast lithology determinations provide further evidence for the top beds of the breccia being resurge deposits however the magnitude of this resurge can only be assessed by future deep core drilling of the infill of the crater hidden below the mountain less

the 2004 earthquakes offshore of the kii peninsula japan hypocentral relocation source process and tectonic implication on 5 september 2004 two major earthquakes of mw 7 2 and mw 7 3 referred to as the foreshock and the mainshock hereafter occurred close to the nankai trough in southwest japan this earthquake sequence is located within the subducting philippine sea plate phs with an aftershock distribution that overlapped a portion of the source region of the 1944 tonankai earthquake mw 7 9 we relocate 53 events with magnitudes greater than 4 2 by combining a single event location method for depth and a multiple event location method for epicenter and origin time source mechanisms and rupture histories of the foreshock and the mainshock are investigated by using a waveform modeling method which allows for mechanism changes during the rupture process the mw 7 2 foreshock and the mw 7 3 mainshock are relocated in the uppermost mantle of the phs on primary high angle reverse faults focal mechanisms are consistent with the horizontal and vertical projects of the distribution of aftershocks we speculate that this earthquake sequence was due to the collision reaction between the phs and the zenisu ridge

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

delineating complex spatiotemporal distribution of earthquake aftershocks an improved source scanning algorithm summary conventional earthquake location methods depend critically on the correct identification of seismic phases and their arrival times from seismograms accurate phase picking is particularly difficult for aftershocks that occur closely in time and space mostly because of the ambiguity of correlating the same phase at different stations in this study we introduce an improved source scanning algorithm issa for the purpose of delineating the complex distribution of aftershocks without time consuming and labour intensive phase picking procedures the improvements include the application of a ground motion analyser to separate p and s waves the automatic adjustment of time windows for brightness calculation based on the scanning resolution and a modified brightness function to combine constraints from multiple phases synthetic experiments simulating a challenging scenario are conducted to demonstrate the robustness of the issa the method is applied to a field data set selected from the ocean bottom seismograph records of an offshore aftershock sequence southwest of taiwan although visual inspection of the seismograms is ambiguous our issa analysis clearly delineates two events that can best explain the observed waveform pattern

estimating average shock pressures recorded by impactite samples based on universal stage investigations of planar deformation features in quartz sources of error and recommendations planar deformation features pdfs in quartz are the most widely used indicator of shock metamorphism in terrestrial rocks they can also be used for estimating average shock pressures that quartz bearing rocks have been subjected to here we report on a number of observations and problems that we have encountered when performing universal stage measurements and crystallographically indexing of pdf orientations in quartz these include a comparison between manual and automated methods of indexing pdfs an evaluation of the new stereographic projection template and observations regarding the pdf statistics related to the c axis position and rhombohedral plane symmetry we further discuss the implications that our findings have for shock barometry studies our study shows that the currently used stereographic projection template for indexing pdfs in quartz might induce an overestimation of rhombohedral planes with low miller bravais indices we suggest based on a comparison of different shock barometry methods that a unified method of assigning shock pressures to samples based on pdfs in quartz is necessary to allow comparison of data sets this method needs to take into account not only the average number of pdf sets grain but also the number of high miller bravais index planes both of which are important factors according to our study finally we present a suggestion for such a method which is valid for nonporous quartz bearing rock types which consists of assigning quartz grains into types a e based on the pdf orientation pattern and then calculation of a mean shock pressure for each sample less

systematic relocation of early instrumental seismicity earthquakes in the international seismological summary for 1960 1963 abstract we have relocated 2556 events that were reported in the bulletins of the international seismological summary iss during the period 1960 1963 using the phase arrival time data listed in the bulletins parts of the data were already available in digital form and the rest we obtained by scanning the printed bulletins and applying an optical character recognition procedure earthquakes were then relocated with a teleseismic location method that uses an improved 1d global travel time earth model depth phases and corrections for ellipticity bounce point bathymetry topography and station elevation the aspherical velocity structure below stations was partially taken into account through the use of teleseismic station patch corrections the quality of the newly obtained locations and the improvements in data fit are similar to relocations of earthquakes in the early bulletins of the international seismological centre isc the most significant improvement of the new locations is in focal depth and a significant number of blatant mislocations such as earthquakes deeper than 100 km below midocean ridges have also been corrected the relocations presented here extend by 10 the time period for which homogeneous and reliable hypocenters are available on a global basis this is the first of a series of studies addressed towards relocating using the same methodology all the instrumentally recorded earthquakes listed in the bulletins of the iss 1918 1963

teleseismic relocation and assessment of seismicity 1918 2005 in the region of the 2004 mw 9 0 sumatra andaman and 2005 mw 8 6 nias island great earthquakes the m w 9 0 2004 sumatra andaman islands and m w 8 6 nias island great earthquake sequences have generated over 5000 catalog reported earthquakes along 1700 km of the sumatra andaman and western sunda regions studies of prior regional seismicity have been limited to global catalog locations that often have poorly constrained epicenters and depths approximately 3650 teleseismically well recorded earthquakes occurring in this region during the period 1918 2005 are relocated with special attention to focal depth reduced uncertainties of epicenters and depths in the region on the order of 15 and 10 km respectively foster interpretation of focal mechanism data and provide additional details about the subducting indian and australian plates the revised earthquake dataset reveals a sharp delineation between aftershocks of the 2004 and 2005 earthquakes near simeulue island and a steepening in slab dip from south to north the downdip width of the aftershock zone of the 2004 m w 9 0 earthquake varies from 200 km at its northern end to 275 km at its southern end and events located between 35 and 70 km focal depth occur more frequently in the southernmost section of this aftershock zone outer rise and near trench normal and strike slip faulting earthquakes also increase in frequency following the 2004 and 2005 earthquakes earthquake swarms triggered along the andaman backarc spreading center both north of sumatra and near siberut island 100 km south of the nias island aftershock sequence illustrate the complex and variable nature of seismicity following these great earthquakes

imaging the subducting slabs and mantle upwelling under the japan islands summary a high resolution p wave tomography of the crust and mantle down to 700 km depth beneath the japan islands is determined using a large number of high quality arrival time data from local earthquakes and teleseismic events simultaneously the tomography shows that the philippine sea slab is subducting aseismically down to 430 km depth under southwest japan though the seismicity within the slab ends at 180 km depth a low velocity low v zone in the mantle wedge under tohoku and kyushu is found to extend westward from the volcanic front to the backarc under the japan sea and east china sea significant low v anomalies are revealed in the deep portion of the mantle wedge 400 500 km depth above the pacific slab under southwest japan which may reflect hot mantle upwelling associated with fluids from the deep dehydration of the pacific slab low v anomalies appear at 420 700 km depths beneath the pacific slab under eastern japan which may reflect hot mantle upwelling associated with the deep subduction of the pacific slab and its collapsing down to the lower mantle