western hellenic subduction and cephalonia transform local earthquakes and plate transport and strain abstract focal parameters of local earthquakes in the region of the ionian islands of western greece are constrained with a temporary dense array of three component seismographs operated jointly offshore and onshore seismic deformation is documented to be confined to the east of the n20 e striking steep continental slope west of cephalonia island the right lateral cephalonia transform fault ctf inferred from large earthquakes the pre apulian continental material appears to be only deforming east of the transform fault where it is in upper plate position to the hellenic subduction east of the transform fault the transmission velocity tomography from local earthquakes compared in depth section with a previous marine reflection profile provides evidence in support of a shallow landward dipping boundary around 12 km deep under the ionian islands along which they may override the lower plate on either side of this interface local earthquakes occur with different focal mechanisms in support with its interpretation as the interplate under cephalonia island reverse faulting deforms the upper plate along nw se structures which may also be affected by left lateral bookshelf faulting small earthquakes show normal faulting along the western coast of cephalonia and its extension 20 km ssw the trace of the ctf as inferred from the occurrence of the large strike slip earthquakes another group of normal fault earthquakes locates in the lower plate from under cephalonia to zante just outboard of a possible change of interplate dip suggested from reflection seismics landward under the islands these normal fault earthquakes appear to coincide in position with that of the load imposed by the upper plate transported over them rather than occurring in an outer rise outboard the plate boundary and trench as observed in other subductions and attributed to the control by the flexural bending of the lower plate under the pull of the sinking slab interpretation has to consider several peculiar features of plate interaction in western greece with respect to a steady state model for major subduction zones in particular a fast deformation of the upper plate in front of an orogenically overthickened crust and of the southwestward push of extruding anatolia its transport which is the cause of the migration of the plate boundary rather than the roll back of a slab which has been proposed to be detached possibly a flat and ramp shape of the interplate the geometrical complexity of the shear limit across the ctf between subduction and collision and the nearby variation of the nature of the foreland crust

application of numerical wave propagation techniques to study local soil effects the case of benevento italy many of the numerical techniques used for seismic zonation studies treat one dimensional structural models and or the incidence of plane polarized body waves these techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest in such cases a more rigorous treatment of the combined effects of the source the path and the site response is needed this can be accomplished with a hybrid approach combining modal summation and the finite difference technique to demonstrate the differences between these techniques the ground motion in the city of benevento italy is modelled we first compare the results obtained with one and two dimensional structural models for vertical incidence of plane polarized body waves these results are then compared with those obtained with the hybrid approach for two dimensional structural models

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

deformation of western greece during neogene clockwise rotation and collision with apulia following an early miocene phase of n s extension affecting the entire hellenides 50 clockwise rotation affected western greece modern gps analyses show rapid southwestward motion in southwestern greece over subducting oceanic lithosphere and no motion in the northwest where greece collided with apulia we aim to identify the deformation history of western greece associated with the rotation and the collision with apulia the timing of the various phases of deformation is constrained via detailed analysis of vertical motions based on paleobathymetry evolution of sedimentary sequences overlying the evolving structures the results show that accompanying the onset of rotation compression was re established in western greece in the early langhian around 15 ma subsequently western greece collided with the apulian platform leading in the late miocene to a right lateral strike slip system running from the aliakmon fault zone in northern greece via the kastaniotikos fault and the thesprotiko shear zone to the kefallonia fault zone offshore western greece ne sw compression and uplift of the ionian islands was accompanied by ne sw extension in southwestern greece associated with faster southwestward motion in the south than in the north this led in the middle pliocene around 3 5 ma to collision without further shortening in northwestern greece from then onward nw se to n s extension east of apulia and gradually increasing influence of e w extension in the south accommodated motion of the hellenides around the apulian platform as a result curved extensional basin systems evolved including the gulf of amvrakikos sperchios basin gulf of evia system and the gulf of corinth saronic gulf system

focal mechanisms of small earthquakes beneath the japanese islands based on first motion polarities picked using deep learning knowledge of crustal stress field is essential for understanding tectonics and earthquake generation one way to estimate the crustal stress field is based on focal mechanisms of earthquakes this

site specific modeling of sh and p sv waves for microzonation study of kolkata metropolitan city india kolkata one of the oldest cities of india is situated over the thick alluvium of the bengal basin where it lies at the boundary of the zone iii and zone iv of the seismic zonation map of india an example of the study of site effects of the metropolitan kolkata is presented based on theoretical modeling full synthetic strong motion waveforms have been computed using a hybrid method that combines the modal summation and finite difference techniques the 1964 calcutta earthquake which was located at the southern part of kolkata is taken as the source region with the focal mechanism parameters of dip 32 strike 232 and rake 56 four profiles are considered for the computation of the synthetic seismograms from which the maximum ground acceleration a max is obtained response spectra ratios rsr are then computed using a bedrock reference model to estimate local amplifications effects the a max varies from 0 05 to 0 17 g and the comparison of the a max with the different intensity scales mm msk rf and mcs shows that the expected intensity is in the range from vii to x mcs for an earthquake of magnitude 6 5 at an epicentral distance of about 100 km this theoretical result matches with the empirical historical and recent intensity observations in kolkata the rsr as a function of frequency reaches the largest values largest amplification in the frequency range from 1 0 to 2 0 hz the largest site amplification is observed at the top of loose soil

variation of seismic coupling with slab detachment and upper plate structure along the western hellenic subduction zone abstract the western hellenic subduction zone is characterized by a trenchward velocity of the upper plate in the ionian islands segment complete seismic coupling is achieved as is predicted by standard plate tectonic models in which there is no slab pull force because the slab has broken off the moderate local seismic moment rate relates to a shallow downdip limit for the seismogenic interface this characteristic may be attributed to the ductility of the lower crust of the upper plate which allows a decollement between the upper crust of the overriding plate and the subducting plate farther south a deeper downdip limit of the seismogenic interface is indicated by thrust faulting earthquakes which persist much deeper in western crete a correspondingly larger downdip width of this seismogenic zone is consistent with the suggested larger maximum magnitude of earthquakes here however since the seismic moment release rate seems to be moderate in the peloponnese and western crete like in in the ionian islands this seismically active interface cannot maintain complete seismic coupling across its larger downdip width a cause may be the lateral addition of overweight to the part of the slab still attached in crete by the free fall of its part that has broken off from the surface further north this increased slab pull reduces the compressive normal stress across the seismogenic interface and thus causes partial seismic coupling in its shallower part however the width of this part may provide an additional area contributing to slip in large earthquakes which may nucleate deeper on stick slip parts of the interface hints at anomalies in structure and seismicity which need to be resolved may relate to the present location of the edge of the tear in the slab

active deformation of the continents whereas relatively narrow bands of deformation define oceanic plate boundaries in continental situations deformation is shown to be distributed over much broader zones the complex and heterogeneous nature of boundary regions between major plates is outlined with reference to the mediterranean and the himalayas relatively aseismic regions have traditionally been defined as microplates but although they are presently acting as rigid blocks undergoing slow deformation it is argued that this need not always have been the case and that deformation may simply have moved elsewhere broad zones of deformation surrounding rigid blocks are highlighted as fundamental to the analysis and interpretation of continental tectonics detailed theoretical consideration is given to the kinematics of distributed formation and the dynamics of continental deformation a j barker

first order seismic microzonation of haldia bengal basin india using a gis platform the seismic microzonation of the bengal basin haldia region india is carried out using the analytical hierarchy process ahp on the geographic information system gis three themes are used for the seismic microzonation namely peak ground acceleration pga predominant frequency and elevation map an analysis of the maximum magnitude mmax and the b value is carried out after preparing the earthquake catalogue from various sources on the basis of the tectonic set up and seismicity of the region five seismic zones are delineated which can be a threat to haldia they are broadly classified as zone 1 arakan yoma zone ayz zone 2 himalayan zone hz zone 3 shillong plateau zone spz zone 4 bay of bengal zone bbz and zone 5 shield zone sz the mmax for zones 1 2 3 4 and 5 are 8 30 0 51 9 09 0 58 9 20 0 51 6 62 0 43 and 6 61 0 43 respectively the pga value is computed for haldia following the attenuation relationship taking the mmax of each source zone the expected pga at haldia varies from 0 09 0 19 g the predominant frequency of haldia is also calculated using the h v ratio with a frequency ranging from 0 1 3 0 hz the elevation map of haldia is also generated using the shuttle radar topography mission strm data a first order seismic microzonation map of haldia is prepared in which four zones of hazard have been broadly classified for haldia as very high seismic hazard zone high seismic hazard zone moderate seismic hazard zone and less seismic hazard zone the very high seismic hazard zone is observed along the southern part of haldia where there are major industrial and port facilities the pga for the four hazard zones are 0 09 0 13 g for low hazard zone 0 13 0 15 g for moderate hazard zone 0 15 0 16 g for high hazard zone and 0 16 0 19 g for very high hazard zone

automatic bayesian polarity determination this work was funded under a natural environment research council nerc studentship as a case award with schlumberger seismometers were borrowed from the nerc seis uk loan 842 who also archive the data

stress fields in and around metropolitan osaka japan deduced from microearthquake focal mechanisms abstract present day stress fields in and around metropolitan osaka japan have been investigated based on 238 microearthquake focal mechanism solutions from approximately the past 10 years the successful retrieval of the focal mechanisms in the noisy urban area owed much to the clean seismic data recorded at four borehole observatories deeper than 500 m depth in osaka prefecture in which p wave onset polarity of the microearthquake could be clearly identified we found many microearthquakes with a pure reverse faulting mechanism which is consistent with the faulting style of major active faults within the area 42 km long east dipping uemachi and 38 km long east dipping ikoma fault zones however a considerable number of microearthquakes with strike slip components were also found to occur most of the p axes are oriented in the ese wnw to ene wsw directions sub horizontally conforming to the general tectonic trend of the area the analysis of a stress tensor inversion delineated small but noticeable differences in stress regime on a scale of at least 10 km where strike slip faulting prevails throughout the region but the middle and southern sections of the uemachi fault zone contain some reverse faulting components based on the estimated stress fields together with assumptions regarding the deep geometry of the uemachi fault zone we assessed the reactivation potential of the fault zone through slip tendency analysis the results indicate higher potential in the middle and southern sections of the fault zone which is related to the locally increased reverse component detected there

stress strain rate and anisotropy in kyushu japan abstract seismic anisotropy the directional dependence of wave speeds may be caused by stress oriented cracks or by strain oriented minerals yet few studies have quantitatively compared anisotropy to stress and strain over large regions here we compare crustal stress and strain rates on the island of kyushu japan as measured from inversions of focal mechanisms gps and shear wave splitting over 85 000 shear wave splitting measurements from local and regional earthquakes are obtained from the nied network between 2004 and 2012 and on aso sakurajima kirishima and unzen volcano networks strain rate measurements are made from the japanese geonet stations jma determined s arrival times processed with the mfast shear wave splitting code measure fast polarisations related to the orientation of the anisotropic medium and time delays dt related to the path length and the percent anisotropy we apply the tessa 2 d delay time tomography and spatial averaging code to the highest quality events which have nearly vertical incidence angles separating the 3455 shallow depth 40 km earthquakes using square grids with 30 km sides for all the inversions the best correlations are observed between splitting from shallow earthquakes and stress axes of maximum horizontal stress shmax and correlate with a coefficient c of 0 56 significant at the 99 confidence level their mean difference is 31 9 axes of maximum compressional strain rate and shmax are also well aligned with an average difference of 28 but they do not correlate with each other meaning that where they differ the difference is not systematic anisotropy strength is negatively correlated with the stress ratio parameter determined from focal mechanism inversion c 0 64 significant at the 99 confidence level the anisotropy and stress results are consistent with stress aligned microcracks in the crust in a dominantly strike slip regime eigenvalues of maximum horizontal strain rate correlate positively with stress ratio c 0 43 significant at 99 confidence all three orientations are e w in central kyushu where the compressional strain rate is highest both splitting and stress suggest plate boundary parallel maximum principal stress just off the coast of kyushu where strain rate measurements are sparse south western kyushu has the largest difference between directions of strain rate and stress from shallow and deep earthquakes are not well aligned suggesting that the deep earthquake waveforms are not simply split in the crust causes for the anisotropy may be olivine crystals aligned by drag of the subducting philippine sea plate in the mantle and stress aligned microcracks in the crust

evaluation of environmental seismic intensities of all known historical and recent earthquakes felt in zakynthos island greece using the environmental seismic intensity esi 2007 scale abstract the complete and detailed knowledge of the historical earthquakes the past earthquake environmental effects eee and the respective seismic intensities has become significant in recent years due to the fact that among others it serves as a valuable tool for revealing and highlighting sites of significant earthquake related hazards many efforts have been made to record the eee of individual recent earthquakes and evaluate their seismic intensity based on the environmental seismic intensity 2007 scale esi 2007 in greece and around the world but fewer studies have focused on the complete seismic history including historical and recent earthquakes of an area and the respective intensities based on the induced eee the central ionian islands western greece and especially zakynthos island are considered appropriate for the development of this approach the complete history of earthquakes with destructive impact on zakynthos from 1513 to present is presented emphasis is given on eee while the respective esi 2007 intensities are assigned based on the eee s distribution on the affected fault blocks it is concluded that eastern zakynthos has been affected more often and severely by earthquakes this selective distribution is attributed to the neotectonic setting of zakynthos the recording of the eee over the past five centuries and the study of possible correlation with the seismotectonic structure of the affected area could be used as a basic guide for the reduction of the future seismic risk and the risk from eee through effective land use planning and preparedness in earthquake prone areas

triassic evaporites and plio quaternary diapirism in western greece wide triassic evaporite outcrops run parallel to the strike of hellenide thrust faults in western greece they crop out along the leading edges of thrust sheets emplaced as part of the foreland migrating fold and thrust belt the evaporites acted as the plane of decollement for thrust sheet emplacement over much of the external hellenides plio quaternary diapirs occur locally within the broad outcrops of triassic evaporite they are the result of local mobilization of evaporite after its emplacement their rise may have been initially triggered by hellenide thrust sheet loading and subsequently accentuated by plio quaternary subsidence geophysical records and onland exposures show that diapiric rise controlled local sedimentation patterns above the sites of earlier hellenide thrusts the subsequent intrusion of diapirs into these cover sediments caused localized extensional structures to develop this is best seen in se zakinthos where strain hardened conjugate faults developed in friable pliocene sandstones early in the intrusion history principal strains calculated from these sets demonstrate patterns of extension sub orthogonal to intrusion margins they are comparable with patterns known from other field and experimental examples but contrast with some recent studies on diapir related strains

an overview on the seismic zonation and microzonation studies in india abstract the present study presents a review on the progressive development of the seismic zonation map of india both from official agencies and also from independent individual studies the zonation map have been modified and updated regularly with the occurrence of major destructive earthquakes over the years in the indian subcontinent with the addition of new data this study discusses the criteria chosen for the progressive zonation and the major earthquakes that were responsible for retrospection of the earlier published maps the seismic zonation maps of india have also been prepared by various independent workers by adopting different approaches to achieve the purpose of the zonation despite the endeavors from various sources to provide a solution for the problem of earthquake hazards in india there were many limitations on the zonation map as it gives the picture at a regional scale mostly on the bedrock level without addressing the local site conditions but nevertheless the seismic zonation map gives basic guidelines for any region to know the hazard scenario and if any city or urban population is under threat from seismic point of view further site specific seismic microzonation may be carried out in the international scenario the global seismic hazard assessment program gshap in 1999 prepared a hazard map for world in terms of peak ground acceleration pga with a 10 probability of exceedance in 50 years but it turned out to be an underestimation of the hazard parameter when compared with the observed pga to tackle the problem of seismic hazards there was a need to have a detail study on the local site conditions in terms of its geological geophysical and geotechnical properties with the advent of better instrumentation and knowledge on the mechanics of earthquakes it was possible to identify zones of hazards at a local level and this gives rise to the study of seismic microzonation seismic microzonation work has been carried out in india in some of the strategic important mega cities and industrial build up that has the potential of being damaged from future earthquakes as has been shown in the past though the microzonation map is not the final output map as it can still be updated at later stage with more input data it does provide a more realistic picture on the site specific seismic hazard

iterative deconvolution of regional waveforms and a double event interpretation of the 2003 lefkada earthquake greece the moment tensor inversion for multiple point sources based on kikuchi and kanamori 1991 was extended to full waveform data at regional or local distances the new code proved to be efficient for retrieving major source contributions of the 2003 lefkada greece earthquake the source model was derived from five three component regional stations epicentral distances 140 km at periods 10 20 s two main events dominated the rupture process one at the lefkada island comprising three subevents of total moment 0 9 1018 n m and the other at the cephalonia island comprising one subevent of 0 5 1018 n m their spatial and temporal separation is 40 km and 14 s respectively they can be understood as two earthquakes the uncertainty estimate based on reduced data sets repeatedly excluding a station shows that the cephalonia subevent and the major lefkada subevent are very well resolved regarding their position time and focal mechanism the source model explains well the aftershock distribution characterized by two clusters at the lefkada and cephalonia islands respectively the focal mechanisms of the two main subevents are predominantly right lateral strike slip of south southwest north northeast orientation the cephalonia subevent occurred on a less steeply dipping fault with a small thrust component large deviations from pure double couple were found but interpreted as artifacts the new software developed in this article fortran code and matlab graphic user interface is freely available online material color graphics and 3d visualization of the 2003 lefkada earthquake sequence

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

the world stress map database release 2016 crustal stress pattern across scales abstract knowledge of the present day crustal in situ stress field is a key for the understanding of geodynamic processes such as global plate tectonics and earthquakes it is also essential for the management of geo reservoirs and underground storage sites for energy and waste since 1986 the world stress map wsm project has systematically compiled the orientation of maximum horizontal stress shmax for the 30th anniversary of the project the wsm database has been updated significantly with 42 870 data records which is double the amount of data in comparison to the database release in 2008 the update focuses on areas with previously sparse data coverage to resolve the stress pattern on different spatial scales in this paper we present details of the new wsm database release 2016 and an analysis of global and regional stress pattern with the higher data density we can now resolve stress pattern heterogeneities from plate wide to local scales in particular we show two examples of 40 60 shmax rotations within 70 km these rotations can be used as proxies to better understand the relative importance of plate boundary forces that control the long wave length pattern in comparison to regional and local controls of the crustal stress state in the new wsm project phase iv that started in 2017 we will continue to further refine the information on the shmax orientation and the stress regime however we will also focus on the compilation of stress magnitude data as this information is essential for the calibration of geomechanical numerical models this enables us to derive a 3 d continuous description of the stress tensor from point wise and incomplete stress tensor information provided with the wsm database such forward models are required for safety aspects of anthropogenic activities in the underground and for a better understanding of tectonic processes such as the earthquake cycle

late cenozoic deformation of the hellenide foreland western greece the late cenozoic structural evolution of western greece involved the shortening of mesozoic passive continental margin and cenozoic foreland basin sequences in a foreland propagating fold and thrust system and superimposed neotectonic deformation related to the development of an active island arc although the pre apulian zone has been regarded as the undeformed western foreland to the thrust belt three dimensional exposures in the ionian islands of kephalonia and zakinthos afford evidence of significant late neogene and quaternary shortening including thrusting on reactivated normal faults time relations and fault kinematics show that these structures are compatible with the westward migration of the locus of hellenide thrusting beyond its previously recognized limit and outer arc compression related to active subduction the presence of the pre apulian zone in the west contrasts with other aegean foreland areas where no such intermediate block lay between the thrust pile and old mesozoic oceanic crust consequently the pre apulian block took up continued hellenide shortening in the late miocene while oceanic crust was being overridden subducted in southern parts of the arc to the east the pre apulian zone subsequently overrode the ocean floored ionian sea during the late neogene the confusion in determining driving mechanisms for late cenozoic deformation in western greece and the apparent conflict between evidence for the age of initial subduction in different parts of the arc are explained by this model which is consistent with regional considerations including structuration in adjacent areas and important paleomagnetic rotations in the arc

the main features of the local geological conditions can explain the macroseismic intensity caused in xiji langfu beijing by the ms 7 7 tangshan 1976 earthquake the special geological conditions in the xiji langfu area are the main reason for the anomalous high macroseismic intensity caused by the tangshan 1976 earthquake the area is formed by deep deposits mainly alluvium sands and clays poorly consolidated and with high water content that have been trapped by the xiadian fault from simulated ground motion we have computed quantities commonly used for engineering purposes like the acceleration maximum amplitude amax and the total energy of ground motion w which is related to the arias intensity the thick low velocity deposits are responsible for the large increment of the values of amax and w inside the basin on the two sides of the xiadian fault amax and w can vary by 200 and 700 respectively and these variations are quite stable with varying thickness of the sedimentary deposit used in the models with the existing relationships between acceleration amax and macroseismic intensity i our results can explain the large values of i observed in the xiji langfu area in connection with the tangshan earthquake

seismic structure and the active hellenic subduction in the ionian islands in the region of the ionian islands of western greece the active margin of the hellenic domain passes from oceanic subduction in the south to continental collision in the north linked by the right lateral cephalonia transform fault a slightly landward dipping interface revealed at 13 km depth by a single previous line in the channel between cephalonia and zante has been suggested as the interplate subduction boundary new marine multichannel reflection profiles and obs refraction and wide angle reflection data confirm the reflector as a regional feature these data evidence its extension to the south where large low angle thrust earthquakes occur offshore to zante the new profiles establish a coincidence between the focal depths of these large subduction events and the imaged bright reflective level confirming its tentative interpretation as the interplate boundary which generally appears with a positive reflection polarity in this context the ionian islands outcrop corresponds to a shallowing of the interplate boudary from south to north in the south offshore zante the interplate boundary comprises a stratified zone that may be considered as the sedimentary cover of the ionian basin oceanic like crust which forms the lower plate here the shallower position and single cycle reflection character of the interplate further north suggest that the lower plate could there be the apulian paleomargin to that basin

depth dependent stress field in and around the atotsugawa fault central japan deduced from microearthquake focal mechanisms evidence for localized aseismic deformation in the downward extension of the fault 1 focal mechanisms have been determined from p wave polarity data as well as body wave amplitudes for 154 microearthquakes that occurred around the atotsugawa fault in central japan between 2002 and 2004 while we found many microearthquakes with a pure strike slip mechanism that is similar to the faulting style of the atotsugawa fault a considerable number of microearthquakes with reverse faulting components are also occurring most of the p axes are horizontal and oriented in the wnw ese direction which conforms to the general tectonic trend in this area in contrast the t axes have a wide range of plunge suggesting that reverse faulting type earthquakes as well as strike slip ones are occurring the most conspicuous feature in the focal mechanism distribution is the depth dependence where shallow earthquakes are primarily reverse faulting and strike slip earthquakes become predominant with depth a stress tensor inversion reveals that the shallower part is characterized by a mixture of reverse and strike slip faulting regimes and that a pure strike slip faulting regime appears only around the bottom of the seismogenic zone together with other geophysical observational evidence for the fault we suggest that the existence of a localized aseismic deformation below the atotsugawa fault is the simplest scenario that can explain the observed stress fields this scenario provides a stress accumulation mechanism of disastrous shallow inland earthquakes in which the localized aseismic deformation accumulates stress onto the fault plane in the seismogenic zone during an earthquake cycle and the main shock would occur when the failure stress is reached on the fault

strike slip tectonics within the northernmost philippine sea plate in an arc continent collisional setting abstract the geological processes in the northernmost philippine sea plate which is bounded by the suruga and sagami troughs are a typical example of an active collision zone we attempt to illustrate the stress field through seismic estimations and geodetic analysis and propose the kinematic mode of the northernmost tip of the philippine sea plate seven events m 4 0 are chosen for waveform inversion by the isola software to distinguish the stress field in particular six of the chosen events which exhibit strike slip motion are distributed in the eastern area where few focal mechanisms have been reported by previous studies according to the available focal mechanisms strike slip faults with similar p and t axes are widely distributed in the study area the stress inversion suggests that the northern area is characterized by a nw se compression and a ne sw extension stress regime although some spatial differences exist as indicated by an analysis of the geodesy epicenters focal mechanisms gravity anomalies and velocity structure the deformation in the northernmost tip is mainly accommodated by several conjugate strike slip fault systems with steep dips that center on the izu volcanic line generally the maximum principal stress of the kinematics is derived from the collision between the philippine sea plate and central japan because of the different subduction angles rates and directions of the down going plate diverging slab pull forces along the suruga and sagami troughs may be causing the ne nne extension in most of the areas that are bounded by the two troughs the extension propagates southwards along the izu volcanic line and reaches the area adjacent to miyake jima

a deterministic seismic hazard map of india and adjacent areas a seismic hazard map of the territory of india and adjacent areas has been prepared using a deterministic approach based on the computation of synthetic seismograms complete with all main phases the input data set consists of structural models seismogenic zones focal mechanisms and earthquake catalogues there are few probabilistic hazard maps available for the indian subcontinent however this is the first study aimed at producing a deterministic seismic hazard map for the indian region using realistic strong ground motion modelling with the knowledge of the physical process of earthquake generation the level of seismicity and wave propagation in anelastic media synthetic seismograms at a frequency of 1 hz have been generated at a regular grid of 0 2 x 0 2 by the modal summation technique the seismic hazard expressed in terms of maximum displacement d m a x maximum velocity v m a x and design ground acceleration dga has been extracted from the synthetic signals and mapped on a regular grid over the studied territory the estimated values of the peak ground acceleration are compared with the observed data available for the himalayan region and are found to be in agreement many parts of the himalayan region have dga values exceeding 0 6 g the epicentral areas of the great assam earthquakes of 1897 and 1950 in northeast india represent the maximum hazard with dga values reaching 1 2 1 3 g the peak velocity and displacement in the same region is estimated as 120 177 cm s 1 and 60 90 cm respectively

3 d simulation of tectonic evolution of the mariana arc back arc system with a coupled model of plate subduction and back arc spreading abstract we developed a mechanical model for the nonlinear coupled system of plate subduction and back arc spreading on the basis of mathematical formulation for internal deformation due to a moment tensor in an elastic viscoelastic layered half space under gravity in our modeling the plate subduction and the back arc spreading are rationally represented by the increase of tangential displacement discontinuity at the plate interface and normal displacement discontinuity at the spreading center respectively through 3 d numerical simulation with this model we obtained a possible scenario for the tectonic evolution of back arc basins as follows at the first stage steady plate subduction gradually forms tensile stress fields in the back arc region when the accumulated tensile stress reaches a critical level back arc spreading starts at a structurally weak portion of the overriding plate the back arc spreading pushes out the frontal part of the overriding plate toward the plate boundary and leads to the increase of slip rates at the plate interface the local increase of slip rates at the plate interface produces additional tensile stress in the back arc region the incremental tensile stress is canceled out by further back arc spreading such a feedback mechanism is necessary to maintain steady back arc spreading the long duration of slip rate excess due to back arc spreading leads to the gradual protrusion of the plate boundary toward the descending plate trench retreat as the plate boundary moves away from the back arc spreading center the accumulation rate of tensile stress at the spreading center gradually decreases and the slip rate excess at the plate interface due to back arc spreading also decreases then the original back arc spreading center becomes less effective in releasing the tectonic tensile stress and new active back arc spreading will start somewhere closer to the plate boundary such a qualitative scenario accords with the evolution history of back arc basins in the mariana region we obtained the slip rate excess of 7 mm year at the plate interface and the 20 km trench retreat for the last 4 5 myr these simulation results are significantly smaller than observations in the mariana region the discrepancy between simulation results and observations can be ascribed to the effect of the negative buoyancy acting on cold descending slab which advances spontaneous plate subduction and directly increases the slip rate excess and the trench retreat in our model

cmt data inversion using a bayesian information criterion to estimate seismogenic stress fields summary we developed an inversion method to estimate the stress fields related to earthquake generation seismogenic stress fields from the centroid moment tensors cmt of seismic events by using akaike s bayesian information criterion abic on the idea that the occurrence of an earthquake releases some part of the seismogenic stress field around its hypocentre we define the cmt of a seismic event by a weighted volume integral of the true but unknown seismogenic stress field representing each component of the seismogenic stress field by the superposition of a finite number of 3 d basis functions tri cubic b splines we obtain a set of linear observation equations to be solved for the expansion coefficients model parameters we introduce prior constraint on the roughness of the seismogenic stress field and combine it with observed data to construct a bayesian model with hierarchic highly flexible structure controlled by hyper parameters the optimum values of the hyper parameters are objectively determined form observed data by using abic given the optimum values of the hyper parameters we can obtain the best estimates of model parameters by using a maximum likelihood algorithm we tested the validity of the inversion method through numerical experiments on two synthetic cmt data sets assuming the distribution of fault orientations to be aligned with the maximum shear stress plane in one case and to be random in the other case then we applied the inversion method to actual cmt data in northeast japan and obtained the pattern of the seismogenic stress field consistent with geophysical and geological observations

a hybrid method for the estimation of ground motion in sedimentary basins quantitative modeling for mexico city to estimate the ground motion in two dimensional 2d laterally heterogeneous anelastic media a hybrid technique has been developed that combines modal summation and the finite difference method in the calculation of the local wave field owing to a seismic event both for small and large epicentral distances it is possible to take into account the source path and local soil effects as a practical application we have simulated the ground motion in mexico city caused by the michoacan earthquake of september 19 1985 by studying the one dimensional 1d response of the two sedimentary layers present in mexico city it is possible to explain the difference in amplitudes observed between records for receivers inside and outside the lake bed zone these simple models show that the sedimentary cover produces the concentration of high frequency waves 0 2 to 0 5 hz on the horizontal components of motion the large amplitude coda of ground motion observed inside the lake bed zone and the spectral ratios between signals observed inside and outside the lake bed zone can only be explained by 2d models of the sedimentary basin in such models the ground motion is mainly controlled by the response of the uppermost clay layer the synthetic signals explain the major characteristics relative amplitudes spectral ratios and frequency content of the observed ground motion the large amplitude coda of the ground motion observed in the lake bed zone can be explained as resonance effects and the excitation of local surface waves in the laterally heterogeneous clay layer also for the 1985 michoacan event the energy contributions of the three subevents are important to explain the observed durations

heterogeneities in stress and strength in tohoku and its relationship with earthquake sequences triggered by the 2011 m9 tohoku oki earthquake inland tohoku has been recognized as under the wnw ese compressional stress state before the 2011 m9 tohoku oki earthquake earthquakes that occurred there were characterized by reverse faulting with the compressional axis oriented in almost the wnw ese direction the tohoku oki earthquake reduced this wnw ese compressional stress and therefore should have suppressed the earthquake occurrence however several intensive earthquake sequences were triggered in inland tohoku in this study we investigated the triggering mechanism of these remote earthquake sequences in the stress shadow based on the detailed distribution of stress orientations newly determined from pre mainshock focal mechanism data the spatial distribution of stress orientations shows that there exist some regions with anomalous stress fields even before the tohoku oki earthquake on the spatial scale of a few tens of kilometers this spatial heterogeneity in the stress field suggests that the differential stress magnitude in inland tohoku is low a few tens of mpa locations of the earthquake clusters tend to correspond to regions where the principal stress axis orientations of the pre mainshock period are similar to those of the static stress change by the tohoku oki earthquake this observation suggests that these earthquake sequences were triggered by a local increase in differential stress due to the static stress change however a few swarm sequences occurred in central tohoku with delays ranging from a few days to few weeks after the tohoku oki earthquake despite the reduction in differential stress these sequences have notable characteristics including upward migration of hypocenters such features are similar to the fluid injection induced seismicity the source regions of these swarms are located near the ancient caldera structures and major geological boundaries the swarm activities were probably triggered by the upward fluid movement along such pre existing structures these observations demonstrate that information about the temporal evolutions of both stress and frictional strength is necessary to understand the triggering mechanism of earthquakes

local stress concentration in the seismic belt along the japan sea coast inferred from precise focal mechanisms implications for the stress accumulation process on intraplate earthquake faults 1 spatial changes in the azimuth of the maximum principal stress 1 axis are found in the intraplate region of southwest japan it is inferred from stress inversions of numerous precise focal mechanisms that the azimuths of the 1 axis in the seismic belt along the japan sea coast are oriented in n110 e n130 e directions while in the surrounding region they are aligned in almost the ew direction n90 e n100 e maximum horizontal compressional stresses in an ew direction are widely observed in the shallow crust in the inland plate along the nankai trough however the maximum horizontal stress in a wnw ese direction is seen only in the seismic belt this spatial change in the stress field in and around the seismic belt is explained by the deformation of an aseismic fault or a ductile fault zone in the lower crust beneath the seismic belt

stress orientations in subduction zones and the strength of subduction megathrust faults subduction zone megathrust faults produce most of the world s largest earthquakes although the physical properties of these faults are difficult to observe directly their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them a global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward consistently making an angle of 45 to 60 with respect to the subduction megathrust fault these angles indicate that the megathrust fault is not substantially weaker than its surroundings together with several other lines of evidence this implies that subduction zone megathrusts are weak faults in a low stress environment the deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface

long period ground motion at bedrock level in delhi city from himalayan earthquake scenarios delhi the capital of india is prone to severe seismic hazards not only from local events but also from himalayan earthquakes at distances of 250 300 km standard techniques are not sufficiently reliable to completely characterize the seismic hazards in this case due to the difficulty of predicting the occurrence of earthquakes frequency magnitude relations and of properly treating the propagation of their effects attenuation laws especially their long period components in order to give a sound description of the seismic ground motion due to an earthquake in such a given range of distances and magnitudes we use modelling techniques developed from physics of the seismic source generation and propagation processes such models take into account the directivity effect of rupture propagation and the attenuation of long period ground motions the generated ground motion scenarios permit us to build a very important knowledge base to be fruitfully used by civil engineers since long period ground motions especially if amplified by deep sedimentary basins can represent a severe threat for large scale structures e g lifelines and bridges and tall buildings which are widespread in fast growing megacities in this study we simulate the ground motion at bedrock level in delhi city for an earthquake scenario corresponding to a source of mw 8 0 located in the central seismic gap of himalayas at an epicentral distance of about 300 km from delhi city by means of several parametric studies we simulate the time histories using size scaled point source space and time scaled point source and extended source models together with the complete time histories displacements velocities and accelerations from which the peak amplitudes have been extracted we have also used the displacement response spectrum to characterize the seismic input at delhi not only is the displacement response spectrum of great significance to modern displacement based design engineering approaches but it is probably the best parameter by which to characterize the destructiveness potential of earthquakes located at such great distances from the target sites of the order of 300 km since the energy of the seismic input is mainly concentrated at long periods in general greater than 1 s and it cannot be determined by straightforward integration of velocity or acceleration response spectra

modelling of seismic ground motion in santiago de cuba city from earthquakes in oriente fault seismic zone we present the results of complete p sv and sh waves modelling up to a maximum frequency of 1 hz along two profiles in santiago de cuba city the seismic sources are located in the depth range from 10 to 40 km on the oriente fault zone at distances of several tens of kilometres from the city the calculation has been made by a hybrid method modal summation in the regional anelastic model one dimensional where the source is buried and finite differences in the local sedimentary anelastic models two dimensional the analysis of the influence of the depth and of the distance of the source on the site effects shows that standard traditional methods based on the deconvolution analysis of the rock outcrop motion can lead to erroneous results

seismicity and geodynamics of western peloponnese and central ionian islands insights from a local seismic deployment abstract the tectonic setting of western peloponnese and central ionian islands greece is characterized by the subduction of the oceanic african plate beneath the aegean micro plate the transition from subduction to continental collision in northwestern greece is accommodated by the right lateral cephalonia transform fault in this work we exploit the recordings of a temporary seismic network composed of 15 stations operating from july 2016 until may 2017 to investigate the complex deformation of this region our local network fills in a major observational gap in one of the most tectonically active regions of the hellenic arc we detected and located more than 1200 local earthquakes and constrained five 1d optimum local velocity models the relocated seismicity including the aftershock sequence that followed the october 2018 mw 6 7 earthquake offshore zakynthos and associated focal mechanisms constrained for the major earthquakes point out a complex crustal deformation we propose a clockwise rotation of the ionian akarnania block accommodated by major marginal strike slip fault zones that appear segmented along their strike additionally left lateral motion is observed on the kyllini cephalonia fault along a north west direction finally the seismicity recorded in north cephalonia offshore myrtos and fiskardo suggests that the cephalonia transform fault is a large deformation zone where secondary wnw striking sinistral strike slip faults occur

accounting for site effects in probabilistic seismic hazard analyses of southern california overview of the scec phase iii report this article presents an overview of the southern california earthquake center scec phase iii effort to determine the extent to which probabilistic seismic hazard analysis psha can be improved by accounting for site effects the contri butions made in this endeavor are represented in the various articles that compose this special issue of bssa given the somewhat arbitrary nature of the site effect distinction it must be care fully defined in any given context with respect to psha we define the site effect as the response relative to an attenuation relationship averaged over all damaging earthquakes in the region a diligent effort has been made to identify any attributes that predispose a site to greater or lower levels of shaking the most detailed maps of quaternary geology are not found to be helpful either they are overly detailed in terms of distinguishing different amplification factors or present southern california strong motion observations are inadequate to reveal their superiority a map based on the average shear wave velocity in the upper 30 m however is found to delineate significantly different amplification factors a correlation of amplification with basin depth is also found to be significant implying up to a factor of two difference between the shallowest and deepest parts of the los angeles basin in fact for peak accel eration the basin depth correction is more influential than the 30 m shear wave ve locity questions remain however as to whether basin depth is a proxy for some other site attribute in spite of these significant and important site effects the standard deviation of an attenuation relationship the prediction error is not significantly reduced by making such corrections that is given the influence of basin edge induced waves subsur face focusing and scattering in general any model that attempts to predict ground motion with only a few parameters will have a substantial intrinsic variability our best hope for reducing such uncertainties is via waveform modeling based on first principals of physics finally questions remain with respect to the overall reliability of attenuation re lationships at large magnitudes and short distances current discrepancies between viable models produce up to a factor of 3 difference among predicted 10 in 50 yr exceedance levels part of which results from the uncertain influence of sediment nonlinearity

tectonics and sedimentation in the gulf of corinth and the zakynthos and kefallinia channels western greece abstract single channel seismic reflection profiling data are presented from the gulf of corinth and from the continental margin outside the gulf of patras different tectonic styles are exhibited in the two regions the gulf of corinth is occupied by a complex asymmetrical graben structure with major faults trending nearly perpendicular to the local tectonic zones of the internal hellenides the gulf is interpreted to have formed during the quaternary in response to approximately north south extensional stress the deep floor of the gulf is underlain by a sequence of turbidites up to 1 km thick affected by normal growth faulting that extends up to the sea floor the sea areas inside the ionian islands of zakynthos and kefallinia zakynthos and kefallinia channels occupy a broad structural depression that trends parallel to the local tectonic zones of the external hellenides and is situated on the continental side of the strophades continental margin rise the channels contain local nw se trending structural basins zakynthos and kefallinia basins whose geometry is controlled by reverse faults or thrusts with associated diapirism in triassic evaporites hydra bank is interpreted as a tilted fault block with a diapiric core and its faulted western margin can be traced into the zone of thrusting and diapirism in southeast kefallinia at the boundary between the ionian and pre apulian paxos zones of the external hellinides the zakynthos and kefallinia structural basins are filled with a variety of sediments including prodeltaic deposits in front of the modern delta complex of the acheloos river slumped masses and debris flow deposits and in the zakynthos basin occasional turbidites the boundary separating zones of extensional and compressional focal mechanisms for shallow earthquakes crosses the gulf of patras the inner part of which exhibits wnw ese trending graben tectonics apparently related to the gulf of corinth tectonic province onshore neotectonic studies around the gulf of patras are required in order to understand the nature and cause of the westward tectonic transition from wnw ese graben structures in the gulfs of corinth and patras to nw se oriented zones of subsidence with associated compressional tectonics and diapirism in the zakynthos and kefallinia channels

a kinematic model for evolution of island arc trench systems summary plate subduction zones are typically characterized by the patterns of surface topography and gravity anomalies consisting of island arc high trench low and outer rise gentle high these patterns are stable on the time scale of 106 107 yr at some subduction zones regardless of its age steady uplift of marine terraces formed by eustatic sea level changes during the last lo5 yr can be also observed the stable patterns of topography and gravity anomalies and the steady uplift of marine terraces seem to contradict each other we constructed a kinematic model which could explain the evolution process of island arc trench systems and demonstrated that this puzzle could be solved by considering the effect of accretion at plate boundaries in our model the lithosphere asthenosphere system is represented by a stratified visco elastic half space under gravity which consists of a high viscosity surface layer and a low viscosity substratum the rheological properties of both layers are assumed to be a maxwell fluid in shear and an elastic solid in bulk interaction between oceanic and continental plates is represented by the steady increase of discontinuity in tangential displacement across the plate boundary the other essential factors considered in our model are accretion of oceanic sediments at plate boundaries erosion on land and sedimentation on inner trench wall we computed the evolution process of island arc trench systems by using the kinematic model and obtained the following results the island arc trench systems grow at nearly constant rates in the early stage of plate subduction therefore at young subduction zones we can generally expect the steady uplift of marine terraces the stable patterns of topography and gravity anomalies are formed within several million years after the initiation of plate subduction when the accretion process continuously proceeds at plate boundaries these stable patterns gradually migrate seaward as a whole in such a case we can expect the steady uplift of marine terraces even at old subduction zones we demonstrate that our model can consistently explain the observed surface topography gravity anomalies and uplift rates of marine terraces at subduction zones

spatial variation of stress orientations in ne japan revealed by dense seismic observations abstract in order to investigate the spatial distribution of the crustal stress state across ne japan we determined 1370 focal mechanisms by picking p wave polarities from seismograms observed by temporary and permanent seismic networks densely deployed in this area we applied stress tensor inversions to these data plus to those routinely determined the results show that the stress state in ne japan is heterogeneous in space which is different from previous results that showed that the ne japan arc is characterized by margin normal compression the orientations of the maximum compressional stress 1 axes are significantly different with 95 confidence limits between the arc backarc region and the forearc region the arc backarc region is characterized by spatially uniform margin normal compression however the north and south parts of the forearc region have the 1 axis oriented nearly n s and vertical respectively the region in between has a similar stress orientation to the arc backarc region moreover the stress regime in the arc backarc region varies spatially in response to change in the surface altitude beneath regions of relatively low altitudes a reverse faulting stress regime is dominant however regions of higher altitudes are characterized by a strike slip faulting stress regime numerical model calculations in which gravitational and buoyancy forces caused by topography are incorporated show that differential stresses of about 15 25 mpa are needed to explain the lateral variation of the stress regime observed in the arc backarc region this suggests that the background deviatoric stress magnitude in ne japan is very low

estimation of regional stress state and young s modulus by back analysis of mining induced deformation abstract a method to evaluate regional stress state and young s modulus by analyzing the mining induced deformation of ground is proposed the effect of changes in regional strain state due to tectonic plate motion can be accounted for using the proposed method mining induced deformation can manifest itself as changes in ground surface geometry resulting from mining activity there are three underlying factors that can contribute to the deformation these being displacement induced by the effect of gravity displacement induced by the effect of horizontal regional strain and incremental change in the horizontal regional strain both regional strain and young s modulus can be simultaneously estimated because the displacement induced by the regional strain is independent of the young s modulus and the displacement induced by the gravity is inversely proportional to the young s modulus the relative displacement arising from the mining excavation at the torigatayama limestone mine in japan has been measured by gps both the regional stress state and young s modulus were estimated by back analysis of the relative displacement using a 3 d finite element method it was shown that back analysis based on changes in distance between the measurement points provides a more reliable estimation than that could be achieved based on the direct relative displacement

a two fault model of the 2003 leucas aegean arc earthquake based on topological inversion of gps data the fault pattern of the 2003 m w 6 2 leucas lefkada lefkas earthquake at the northwest edge of the aegean arc an area of very high seismicity rates was modeled using global positioning system gps data the rupture process of this earthquake is a matter of debate because of the complexities in the aftershock distribution and in the waveforms of the mainshock as well as the kinematics of the area are not well understood especially the characteristics of the cephalonia kefalonia keffalinia transform fault and its relationship with major discordant active thrusts representing the tectonic fabric of western greece our analysis was based on the topological inversion topinv algorithm which uses a deterministic hypergrid search to identify one or more clusters of n dimensional points around the true solution of the system of observation equations from these clusters optimal estimators of the variables defining okada type faults and their variance covariance matrices are computed as statistical moments and results are validated by minimum mean misfits faulting of the 2003 seismic sequence was approximated by two stepping essentially strike slip segments with a separation of 10 km this pattern is in agreement with fault rupture models based on inversion of seismological data and their main difference is a thrust component in the major segment well constrained by interferometric synthetic aperture radar and gps observations of uplift this thrust component may reflect either postseismic evaporite salt controlled slip or uncertainties in the inversion models the 2003 and other seismic sequences among them the 1953 m 7 2 cephalonia catastrophic earthquakes that were associated with major uplift seem to confirm previous views for an 100 km wide shear zone superimposed on compression along the edges of the aegean arc online material description of analytical inversion methodology the topological inversion algorithm topinv including a figure showing projection of hypergrids on planes

3 d modelling of plate interfaces and numerical simulation of long term crustal deformation in and around japan we developed a 3 d simulation model for long term crustal deformation due to steady plate subduction in and around japan by incorporating viscoelastic slip response functions into a realistic 3 d plate interface model constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes the lithosphere asthenosphere system is modelled by an elastic surface layer overlying a maxwellian viscoelastic half space kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity fault slip across the interfaces with this model giving the steady slip rates at plate interfaces calculated from nuvel 1a we simulated long term crustal deformation due to steady plate subduction in and around japan the simulated crustal deformation pattern is characterized by steep uplift at island arcs sharp subsidence at ocean trenches and gentle uplift at outer rises the numerical results show the strong dependence of the deformation pattern on the 3 d geometry of plate interfaces

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

temporal variation of frictional strength in an earthquake swarm in ne japan caused by fluid migration temporal variations of the fault frictional strength was investigated based on the diversity of focal mechanisms in the source area of the yamagata fukushima border earthquake swarm a significant earthquake swarm that occurred in central tohoku ne japan which started just after the 2011 m9 0 tohoku oki earthquake the focal mechanisms of events in this swarm activity were determined using p wave polarity data as well as short period 1 5 2 5 hz waveform data from the direct p wave the stress field in the source area of this swarm was estimated by applying stress tensor inversions to these focal mechanism data based on the estimated stress field and under the assumption of uniform stress we calculated relative frictional strengths for individual focal mechanisms the calculated relative frictional strengths vary over a wide range but their average value exhibits a characteristic temporal variation which is at first small but steadily increases with time for 100 to 150 days and then becomes approximately constant we confirmed this characteristic temporal variation of the average relative frictional strength by assuming the stress to be nonuniform similar temporal variations of the average relative frictional strength are obtained for even these cases confirming the variation the most likely cause for the observed temporal variation of the average relative frictional strength is the temporal variation of the pore fluid pressure in the source area of the swarm facilitated by the tohoku oki earthquake and the subsequent fluid diffusion

quantifying seismic vulnerability dynamical shear strain and liquefaction of the quaternary deposits in the doon valley near the main boundary thrust in the northwest himalaya india abstract erosion and deposition are two conjugate surface dynamical processes that affect differently to the soft soil site characteristics of quaternary deposits in the doon valley and at its northern topographic transition zone near the main boundary thrust mbt during an impending large magnitude earthquake what would be the seismic vulnerability and liquefaction susceptibility of the soft soil at both the regions we quantified seismic vulnerability index effective dynamical shear strain and the expected ground deformation in the valley soft soil through h v site characteristics using seismic ambient noise data at the in accessible topographic transition zone near the mbt site effects were studied using moderate and light magnitude earthquakes recorded by three broad band seismographs bbs results show unique dual peak mean resonant frequencies 1 11 and 1 38 hz and amplification factors 1 69 and 1 51 at the topographic transition zone which highlights a bimodal distribution of site effects where the top soil formation is influenced by erosion and deposition due to topographic slope instability apart from fluvial re working here relatively compact oldest doon gravel is present in the foothill terraces with the re worked fluvial deposition of the youngest doon gravel however in the valley and its terraces the soft soil formed under fluvial environ is relatively thick 10 to 2 and mean resonant frequency of 1 1 hz the spot resonant frequencies increases from 1 hz to more than 6 hz from the hft region to the mbt while the amplification factor decreases from 14 to 1 in general the valley soft soil is susceptible for liquefaction because the estimated dynamical shear strain is 15 25 millistrains under medium 2 2 m s 2 225 years and long 4 6 m s 2 2500 years term strong motion conditions which is much higher than the soil plasticity limit of ten millistrains that lead to liquefaction dynamical shear strain distribution with depth at eight boreholes in the valley indicate 20 m is the liquefaction potential depth where the pore pressure induced peak shear strain exceeds the threshold shear strain of 0 01 during the passage of seismic waves isolated locations in the valley like that at dharmawala h1 where all site parameters are very high and would be hazardously vulnerable to liquefaction however near the mbt the liquefaction possibility of soft soil is less but would experience ground deformation of more than 50 cm

a dislocation model for the earthquake cycle at convergent plate boundaries summary a kinematic model for the earthquake cycle at convergent plate boundaries has been constructed on the basis of dislocation theory we model the lithosphere asthenosphere system by a stratified semi infinite medium under gravity consisting of an elastic surface layer an intervening layer with maxwell viscoelasticity and an elastic substratum the steady motion of plate convergence is naturally represented by uniform slip at a constant rate on the upper boundary of the descending oceanic plate the occurrence of interplate earthquakes is regarded as a perturbation of the steady state plate motion and represented by a periodic sequence of step slips on a finite seismic zone of the plate interface based on dislocation theory we can show that the steady slip on the interface deeper than the lithosphereasthenosphere boundary does not contribute to surface deformation in the steady state accordingly the surface deformation associated with the earthquake cycle is given by the superposition of viscoelastic responses to the steady slip on the interface shallower than the lithosphere asthenosphere boundary the steady backslip on the seismic zone and the periodic sequence of seismic slips we have computed cyclic patterns of vertical displacements at the free surface for two representative cases taking account of gravity effects the patterns of vertical displacements differ notably in the latter stage of the cycle depending on whether or not the seismic zone extends through the entire thickness of the lithosphere after the completion of one earthquake cycle our model yields a certain amount of permanent deformation resulting from the steady plate convergence the pattern of the permanent deformation that is characterized by steep uplift on the continental side sharp subsidence at the plate boundary and gentle uplift on the oceanic side is irrespective of the cyclic process of stress accumulation and release repeated on the seismic zone the earthquake cycle model developed here provides a possible explanation for the formation of earthquake origin marine terraces

stress change before and after the 2011 m9 tohoku oki earthquake abstract megathrust systems hold important clues for our understanding of long and short term plate boundary dynamics and the 2011 m9 tohoku oki earthquake provides a data rich case in point here we show that the f net moment tensor catalog indicates systematic changes in crustal stress in the years leading up to the m9 due to the co seismic effect and for the last few years due to viscous relaxation we explore the match between imaged stress change and the perturbations that are expected from 3 d mechanical models of the visco elastic relaxation and afterslip effects of the m9 while these models were constructed based on geodetic and structural seismology constraints alone they match many characteristics of the seismicity inferred stress change this provides additional confidence in the modeling approach and new clues for our understanding of plate boundary dynamics for the japan trench the success of deterministic approaches for exploring crustal stress change also implies that joint inversions using stress from focal mechanisms and geodetic constraints may be feasible such future efforts should provide key insights into time dependent seismic hazard including earthquake triggering scenarios

the 1953 earthquake in cephalonia western hellenic arc coastal uplift and halotectonic faulting summary geomorphological marine biological and radiometric data in combination with earlier reports reveal that the m 7 2 1953 cephalonia earthquake the most destructive but least studied earthquake in greece this century was associated with a 0 3 0 7m quasi rigid body uplift and westward tilting of the central part of the island another palaeoseismic event around 1500 yr bp associated with coastal uplifts was also identified structural data indicate that the 1953 uplift is bounded by two subparallel east dipping major reverse faults and corresponds to a piston like motion this structurally unusual pattern of seismic deformation is detached from the deformation of the basement conspicuously a thrust and different from the long term deformation pattern of the area it is probably due to the particularities of salt tectonics a 1500m thick salt layer acts as a regional dccollement while thinner layers are sandwiched between the carbonate thrust sheets that compose the overburden and reduce their friction during fault movement this crustal anisotropy is responsible for the observed anomalous attenuation of seismic waves during the 1953 and historical earthquakes the 1953 seismic surface deformation mimics long term halotectonic patterns but is not directly indicative of the regional stress field for it reflects uplift induced stresses only

3 d simulation of tectonic loading at convergent plate boundary zones internal stress fields in northeast japan the evidence of east west compression in northeast japan has been reported by many investigators on the basis of geodetic geologic and geomorphic data but its origin still remains far from understood in the present study we have proposed a mechanical model of tectonic loading at convergent plate boundary zones and demonstrated its validity through the numerical simulation of internal stress fields in northeast japan with realistic 3 d geometry of plate interfaces at convergent plate boundary zones in general a part of plate convergence is consumed by steady slip along plate interfaces and the remaining part by inelastic deformation seismic faulting aseismic faulting and active folding of overriding plates such a plate boundary process to be called partial collision can be quantitatively described by introducing a collision rate defined as c 1 steady slip rate at plate interfaces plate convergence rate by this definition we can simply represent the mechanical process of partial collision which includes total subduction c 0 and total collision c 1 as two extreme cases in terms of steady slip rates at plate interfaces on the basis of elastic dislocation theory first we numerically computed the internal stress fields in northeast japan produced by the total subduction of the pacific plate beneath the north american plate however the computed stress pattern was opposite in sense to observations then we computed the internal stress fields by taking c 0 1 on average and succeeded in reproducing the observed east west compression in northeast japan this indicates that the concept of partial collision is essential to understand the mechanism of intraplate tectonic loading

the postearthquake stress state on the tohoku megathrust as constrained by reanalysis of the jfast breakout data the jfast drilling project endeavored to establish the stress state on the shallow subduction megathrust that slipped during the m9 tohoku earthquake borehole breakout data from the drillhole can constrain both the orientation and magnitude of the principal stresses here we reanalyze that data to refine our understanding of the stress state on the fault in particular we 1 improve the identification of breakouts 2 consider a fuller range of stress states consistent with the data and 3 incorporate new and more robust laboratory constraints on rock strength the original conclusion that the region is in a normal faulting regime after the earthquake is strengthened by the new analysis the combined analysis suggests the earthquake released sufficient elastic strain energy to reset the local stress field

a traverse of the ionian islands front with coincident normal incidence and wide angle seismics abstract marine vertical reflection profiling with a powerful airgun source augmented with a few wide angle seismometer stations on land has been applied along a 180 km line across the presently active deformation front of the subduction of the ionian sea plate beneath the western hellenides east of the ionian islands there is limited evidence for reflectivity down to 23 km interpreted as the base of a rather thin continental type crust under the western slope of the islands a major normal incidence reflector dips eastward first gently to the west of the islands then more steeply under them this reflector may be extrapolated southwestwards beneath a bulge that is thought to represent the modern pre apulian front located over the subduction zone the continuity signature and geometry of this reflector suggest that it may act as the lower limit of the western hellenides where they override the ionian sea quasi oceanic crust rather than just an intracrustal interface of a pre apulian crust the location of the previous deformation front the ionian thrust proposed in previous models can be constrained by the new seismic data the new data raise the possibility of a larger area of evaporite mobility than previously considered insofar as active block motion apparently related to halokinesis is recognized west of the zakynthos anticline diapirism decollement and westward directed over thrusting in the pre apulian crust may have been brought on by late pliocene quaternary reactivation of regional extension associated with the separation of the peloponnesus from northern greece as it was captured by the anatolian aegean rotation and associated also with the fast clockwise rotation of the ionian islands as they were sheared off the apulian domain to the southwest by the initiation of the kefallinia transform

coexistence of thin and thick skinned tectonics in zakynthos area western greece insights from seismic sections and regional seismicity abstract the structural style of the fold and thrust belt in the western part of the hellenic foreland in an area offshore the zakynthos island is assessed on the basis of two lithoseismic profiles earthquake data and field data in the broader area the compressional deformation in the area is due to the late phases of subduction and collision between aegean and african plates shortening is affecting a 6 7 km thick sedimentary succession of mesozoic carbonate rocks and evaporites as well as miocene to pleistocene foredeep clastic deposits structures accommodating shortening in the pre apulian and ionian zones comprise a blind imbricate thrust system and fault propagation folds that formed over a 10 11 km deep detachment the thrust system comprises an array of forward verging thrust faults which sole out in a low angle hinterland dipping decollement separating the mesozoic cover from the pre mesozoic basement in this tectonic context the triassic evaporitic layers seem to play an important role in the vertical partitioning of the deformation style acting as either detachment horizons or lining the imbricate thrust surfaces the concentration of recent seismic activity at a depth between 6 and 16 km implies that the pre mesozoic basement is also involved in the deformation in the form of upthrust basement slices suggesting a combination of thick and thin skinned deformation across this domain of the external hellenides fold and thrust belt the frontal part of the belt shows higher seismic activity along a low angle blind thrust as well as also in the areas where the individual thrust planes branch at depth to the basal decollement

the 3 d tectonic stress fields in and around japan inverted from centroid moment tensor data of seismic events 1 we can regard the occurrence of earthquakes as the partial release of tectonic stress by sudden brittle rupture in the framework of linear elasticity any indigenous source including earthquake rupture is represented by a moment tensor the moment tensor is mathematically equivalent to the volume integral of stress release over the whole elastic region surrounding the source and so we can quantitatively relate the centroid moment tensor cmt of seismic events with an unknown tectonic stress field on the basis of such an idea and bayesian statistical inference theory we developed an inversion method to estimate the 3 d pattern of tectonic stress from cmt data applying the cmt data inversion method to 12 500 seismic events in and around japan we obtained precise 3 d tectonic stress patterns that illuminate the present day quaternary complex tectonic motion of japanese islands the stress pattern of the kuril japan nankai arc is basically e w compression but the direction of intermediate principal stress changes from n s reverse faulting type in northeast japan to vertical strike slip faulting type in southwest japan on the other hand the stress pattern of the ryukyu and izu bonin back arc regions is basically trench perpendicular tension normal faulting type in addition to these basic stress patterns governed by mechanical interaction between the eurasian north american pacific and philippine sea plates we can recognize several characteristic local stress patterns corresponding to the horizontal motion of the kuril fore arc sliver the collision of the izu peninsula with the mainland of japan and the opening of the beppu shimabara rift zone

site specific microzonation study in delhi metropolitan city by 2 d modelling of sh and p sv waves delhi the capital of india lies on a severe earthquake hazard threat not only from local earthquakes but also from himalayan events just 200 250 km apart the seismic ground motion in a part of delhi city is computed with a hybrid technique based on the modal summation and the finite difference scheme for site specific strong ground motion modelling complete realistic sh and e5 e5 sv wave seismograms are computed along two geological cross sections 1 north south from inter state bus terminal isbt to sewanagar and 2 east west from tilak bridge to punjabi bagh two real earthquake sources of july 15 1720 mmi ix m 7 4 and august 27 1960 m 6 0 have been used in modelling the response spectra ratio rsr i e the response spectra computed from the signals synthesized along the laterally varying section and normalized by the response spectra computed from the corresponding signals synthesized for the bedrock reference regional model have been determined as expected the sedimentary cover causes an increase of the signal amplitude particularly in the radial and transverse components to further check the site effects we reversed the source location to the other side of the cross section and recomputed the site amplifications there are only a few sites where a large amplification is invariant with respect to the two source locations considered the rsr ranges between 5 to 10 in the frequency range from 2 8 to 3 7 hz for the radial and transverse components of motion along the ns cross section along the ew cross section rsr varies between 3 5 to 7 5 in the frequency range from 3 5 to 4 1 hz the amplification of the vertical component is considerable at high frequency 4 hz whereas it is negligible in lower frequency range

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

the april 2007 earthquake swarm near lake trichonis and implications for active tectonics in western greece abstract we investigate the properties of the april 2007 earthquake swarm mw 5 2 which occurred at the vicinity of lake trichonis western greece first we relocated the earthquakes using p and s wave arrivals to the stations of the hellenic unified seismic network husn and then we applied moment tensor inversion to regional broad band waveforms to obtain the focal mechanisms of the strongest events of the 2007 swarm the relocated epicentres cluster along the eastern banks of the lake and follow a distinct nnw ese trend the previous strong sequence close to lake trichonis occurred in june december 1975 we applied teleseismic body waveform inversion to obtain the focal mechanism solution of the strongest earthquake of this sequence i e the 31 december 1975 mw 6 0 event our results indicate that a the 31 december 1975 mw 6 0 event was produced by a nw se normal fault dipping to the ne with considerable sinistral strike slip component we relocated its epicentre i using phase data reported to isc and its coordinates are 38 486 n 21 661 e ii using the available macroseismic data and the coordinates of the macroseismic epicentre are 38 49 n 21 63 e close to the strongly affected village of kato makrinou b the earthquakes of the 2007 swarm indicate a nnw sse strike for the activated main structure parallel to the eastern banks of lake trichonis dipping to the ne and characterized by mainly normal faulting occasionally combined with sinistral strike slip component the 2007 earthquake swarm did not rupture the well documented e w striking trichonis normal fault that bounds the southern flank of the lake but on the contrary it is due to rupture of a nw se normal fault that strikes at a 45 angle to the trichonis fault the left lateral component of faulting is mapped for the first time to the north of the gulf of patras which was previously regarded as the boundary for strike slip motions in western greece this result signifies the importance of further investigations to unravel in detail the tectonics of this region

seismic sequence near zakynthos island greece april 2006 identification of the activated fault plane abstract the april 2006 earthquake sequence near zakynthos western greece is analysed to identify the fault plane s the sequence 33 events was relocated to assess physical insight into the hypocenter uncertainty moment tensor solution of three major events was performed simultaneously with the determination of the centroid position joint analysis of the hypocenter position centroid position and nodal planes indicated sub horizontal fault planes moment tensor solutions of 15 smaller events were performed under assumption that the source positions are those of the hypocenters without seeking centroids their focal mechanisms are highly similar and agree with the analysis of the three major events the preferable seismotectonic interpretation is that the whole sequence activated a single sub horizontal fault zone at a depth of about 13 km corresponding to the interplate subduction boundary considering that the ionian sea is a high seismicity area the identification of the seismic fault is significant for the seismic hazard investigation of the region

oblique subduction and collision forearc tectonics of the kuril arc the tectonics of the southwestern kuril arc are a result of the oblique subduction of the pacific plate at the kuril trench in association with forearc sliver migration caused by the oblique subduction collision tectonics occur at the leading margin of the sliver and tensional tectonics take place at the tapering margin as a result of the collision a deep crustal section of island arc is observed at the leading margin of the forearc sliver tectonics of the kuril arc related to oblique subduction are different from those of the western sunda arc where backarc spreading occurs at the leading margin this difference is due to margin morphology of the oblique subduction zone

extremely weak fault planes an estimate of focal mechanisms from stationary seismic activity in the san in district japan abstract in this paper using data from dense seismic observations in and around the seismic belt of the san in district japan we describe our analysis of focal mechanisms of stationary seismic activity estimated stress states and pore fluid pressures we found these focal mechanisms to be described by the estimated stress field suggesting that the stress field can be treated as uniform in each sub region of the study area we also found that events occurred even on unfavorably oriented fault planes with small shear stress further we inferred that pore fluid pressures of approximately 20 of the faults analyzed are greater than the magnitude of minimum principal stress when we assume 0 6 a possible explanation is localized high pore fluid pressure anomalies another is the coefficient of friction of at least a part of faults analyzed in the study area being substantially smaller than 0 6 which we view as more plausible since it is difficult to maintain pore fluid pressures higher than the magnitude of minimum principal stress for long periods of time

a unified interpretation of vertical movement in himalaya and horizontal deformation in tibet on the basis of elastic and viscoelastic dislocation theory abstract the present day convergence rate between the indian and the eurasian plates has been estimated to be about 50 mm year at the collision boundary extending along the himalayas about 40 of the total convergence is consumed by the subduction of the indian plate beneath the eurasian plate the rest of about 60 is consumed by the internal deformation of the eurasian plate the present crustal movement in this region is characterized by rapid uplift along the high himalayas and large scale horizontal deformation in and around tibet the fundamental causes of these two different types of crustal movement are the same interaction between the indian and the eurasian plates in this study we represent the plate interaction by steady increase in tangential displacement discontinuity dislocation across the interface that divides a surface layer overlying a viscoelastic half space into the indian and the eurasian plates first given a steady slip of 20 mm year at the plate interface with a ramp shaped undulation below the high himalayas we computed the profile of surface uplift rates along a line perpendicular to the himalayan arc the result accords with observed free air gravity anomalies and the intermediate and short term uplift rates estimated respectively from the present heights of river terraces and levelling data this means that the rapid uplift of the high himalayas is due to the steady slip along the ramp shaped plate interface below it second given the steady slips of 20 mm year along the 2000 km long collision boundary and 50 mm year along the remaining portions of the india eurasia plate boundary we computed the increase rates of horizontal deformation in and around tibet the result accords with the observed strikes and slip rates of major quaternary active faults this means that the horizontal deformation in and around tibet is due to the slip deficits of 30 mm year at the collision boundary from these two results we can conclude that the present rapid uplift of the high himalayas and large scale horizontal deformation in and around tibet are consistently explained by a single plate interaction model based on elastic and viscoelastic dislocation theory this study sheds new light on the driving mechanism of the crustal deformation in the india eurasia collision zone as follows the plate interaction on single plate interface consists of coexisting two different physical mechanisms 1 slip along the ramp undulation spatial changes in slip direction 2 slip deficit at the collision boundary spatial changes in slip rates as a consequence the two different types of crustal deformation in the india eurasia collision zone are driven by these two different physical mechanisms

deformation of an island arc rates of moment release and crustal shortening in intraplate japan determined from seismicity and quaternary fault data the historical record of large m 6 9 earthquakes and geologically determined rates of slip on quaternary faults in intraplate japan honshu and shikoku are used to estimate the average rate of seismic moment release m for the last 400 years and during the late quaternary respectively values of m estimated from the two data sets are similar in regions where seismic activity is concentrated on land we interpret this observation to suggest that m in intraplate japan has been constant during the late quaternary and is relatively free from secular variation when averaged over periods of several hundreds of years m in shikoku may be attributed almost solely to right lateral slip of the median tectonic line mtl the easterly strike of the mtl is consistent with a compressive stress field that trends northwest crustal shortening of the izu peninsula taken up on a set of strike slip faults that show north by northwest compression is 1 mm yr northeast honshu is characterized by a set of reverse type faults that trend northerly conversion of m in northeast japan to strain rates suggests that about 5 of the relative plate motion between japan and the pacific plate 9 7 cm yr is accommodated as a permanent east west shortening 5 mm yr of northeast honshu the predominant deformation in central and western honshu takes place as slip on a conjugate system of strike slip faults that strike northeast and southeast and show right lateral and left lateral motion respectively crustal shortening resulting from slip on faults in central and western honshu is 5 and 0 5 mm yr respectively in an easterly direction central and western honshu are in closest proximity to the nankai trough and hence the stress field in these regions cannot simply be attributed to the accommodation of the relative northwesterly convergence of the philippine sea plate the northward impingement of the izu peninsula into honshu may influence stresses in central and western japan but a conclusive explanation of the stress field in central and western honshu remains an enigma

stress orientations of taiwan chelungpu fault drilling project tcdp hole a as observed from geophysical logs 1 the taiwan chelungpu fault drilling project tcdp drilled a 2 km deep research borehole to investigate the structure and mechanics of the chelungpu fault that ruptured in the 1999 mw 7 6 chi chi earthquake geophysical logs of the tcdp were carried out over depths of 500 1900 m including dipole sonic imager dsi logs and formation micro imager fmi logs in order to identify bedding planes fractures and shear zones from the continuous core obtained from the borehole a shear zone at a depth of 1110 meters is interpreted to be the chelungpu fault located within the chinshui shale which extends from 1013 to 1300 meters depth stress induced borehole breakouts were observed over nearly the entire length of the wellbore these data show an overall stress direction n115e that is essentially parallel to the regional stress field and parallel to the convergence direction of the philippine sea plate with respect to the eurasian plate variability in the average stress direction is seen at various depths in particular there is a major stress orientation anomaly in the vicinity of the chelungpu fault abrupt stress rotations at depths of 1000 m and 1310 m are close to the chinshui shale s upper and lower boundaries suggesting the possibility that bedding plane slip occurred during the chi chi earthquake citation wu h y k f ma m zoback n boness h ito j h hung and s hickman 2007 stress orientations of taiwan chelungpu fault drilling project tcdp hole a as observed from geophysical logs geophys res lett 34 l01303 doi 10 1029 2006gl028050

seismicity and seismotectonics in epirus western greece results from a microearthquake survey during a twelve month passive tomography experiment in epirus in northwestern greece a total of 1368 microearthquakes were located the most accu rately located events and focal mechanisms are used here to understand the seismo tectonics of the area the seismicity shows a clear association with the main previously defined deformation zones a total of 434 well defined focal mechanisms were also used for the determination of the stress pattern in the area the computed stress field pattern is quite complex close to the surface and almost homogeneous at depths below 15 km for these depths the stress field is purely compressional in a west southwest direction whereas for shallow depths it is transpressional or even extensional for some smaller areas the abrupt change in the stress pattern which occurs as depth increases suggests the existence of a detachment surface which is provided by the evaporites that have intruded into the upper layers through the thrust zones the presence of the evaporites and their lateral extent is mapped by the seismicity distribution and con firmed by seismic tomography based on the findings we estimate a possible total evaporite thickness of almost 10 km at least for the central part of the study area such a result is important for the oil exploration efforts that have just started in epirus

estimation of site effects in bucharest caused by the may 30 31 1990 vrancea seismic events the vrancea region seismicity characterized by focal depths larger than 60 km and major events with magnitudes m w 6 9 is responsible for the most destructive effects experienced in the romanian territory and may seriously affect high risk construction located on a wide area from central to eastern europe this seismogenic volume must be taken into account both for seismic hazard analysis at the regional level southeastern europe and national level romania and bulgaria as well as for microzonation studies of the highly populated cities located in the range of influence of this source since about four destructive earthquakes occur every century in vrancea the microzonation of bucharest the main city exposed to the potential damages due to these strong intermediate depth shocks represents an essential step towards the mitigation of the local seismic risk two main approaches can be considered for the evaluation of the local seismic hazard a collection and extended use for engineering purposes of the recorded strong motion data and b advanced modelling techniques that allow us the computation of a realistic seismic input which can compensate for the lack of strong motion records actually available only for a few events that occurred in the last 20 30 years

stress rotations due to the m6 5 foreshock and m7 3 main shock in the 2016 kumamoto sw japan earthquake sequence a shallow m7 3 event with a m6 5 foreshock occurred along the futagawa hinagu fault zone in kyushu sw japan we investigated the spatiotemporal variation of the stress orientations in and around the source area of this 2016 kumamoto earthquake sequence by inverting 1 218 focal mechanisms the results show that the 3 axis in the vicinity of the fault plane significantly rotated counterclockwise after the m6 5 foreshock and rotated clockwise after the m7 3 mainshock in the hinagu fault segment this observation indicates that a significant portion of the shear stress was released both by the m6 5 foreshock and m7 3 mainshock it is estimated that the stress release by the m6 5 foreshock occurred in the shallower part of the hinagu fault segment which brought the stress concentration in its deeper part this might have caused the m7 3 mainshock rupture mainly along the deeper part of the hinagu fault segment after 28 hours

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

the egion june 15 1995 6 2m l earthquake western greece on june 15 1995 at 00 15 gmt a devastating earthquake 6 2m l occurred in the western end of the gulf of corinth this was followed 15 min later by the largest aftershock 5 4m l the main event was located by the university of patras seismological network patnet at the northern side of the gulf of corinth graben the second event 5 4m l was located also by patnet near the city of egion on a fault parallel to the eliki major fault that defines the south bound of the gulf of corinth graben a seismogenic volume that spans the villages of akrata se and rodini nw and extends to eratini ne was defined by the aftershock sequence which includes 858 aftershocks of magnitude greater than 2m l that occurred the first seventeen days the distribution of hypocentres in cross section does not immediately suggest a planar distribution but rather defines a volume about 15 km depth by 35 km nw se and by 20 km ne sw

sar revealed slip partitioning on a bending fault plane for the 2014 northern nagano earthquake at the northern itoigawa shizuoka tectonic line abstract by applying conventional cross track synthetic aperture radar interferometry insar and multiple aperture insar techniques to alos 2 data acquired before and after the 2014 northern nagano central japan earthquake a three dimensional ground displacement field has been successfully mapped crustal deformation is concentrated in and around the northern part of the kamishiro fault which is the northernmost section of the itoigawa shizuoka tectonic line the full picture of the displacement field shows contraction in the northwest southeast direction but northeastward movement along the fault strike direction is prevalent in the northeast portion of the fault which suggests that a strike slip component is a significant part of the activity of this fault in addition to a reverse faulting clear displacement discontinuities are recognized in the southern part of the source region which falls just on the previously known kamishiro fault trace we inverted the sar and gnss data to construct a slip distribution model the preferred model of distributed slip on a two plane fault surface shows a combination of reverse and left lateral fault motions on a bending east dipping fault surface with a dip of 30 in the shallow part and 50 in the deeper part the hypocenter falls just on the estimated deeper fault plane where a left lateral slip is inferred whereas in the shallow part a reverse slip is predominant which causes surface ruptures on the ground the slip partitioning may be accounted for by shear stress resulting from a reverse fault slip with left lateral component at depth for which a left lateral slip is suppressed in the shallow part where the reverse slip is inferred the slip distribution model with a bending fault surface instead of a single fault plane produces moment tensor solution with a non double couple component which is consistent with the seismically estimated mechanism

computation of ground motion amplification scenario in nct delhi for earthquake engineering purposes and seismic microzonation this paper presents a scenario for the spatial variation of the fundamental frequency of the sediment deposits above the basement and the corresponding amplification as well as the average spectral amplification in different frequency bandwidths for the national capital territory delhi the capital of india the exposed central quartzite ridge and the yamuna river channel are responsible for very large spatial variations of the fundamental frequency in the eastern part of the national capital territory delhi at 20 of the considered sites a good match is obtained between the fundamental frequency computed numerically using available s wave velocities to a certain depth and their extrapolation and that obtained experimentally the computed fundamental and dominant frequencies reveal that both medium rise 5 10 storey and high rise 10 storey buildings in the western part and medium rise buildings lying in the localities east of or very near to the yamuna river may suffer heavy to very heavy damage due to the occurrence of the double resonance phenomenon furthermore 1 2 storey buildings lying on the weathered exposed quartzite rock may also suffer heavy damage during local earthquakes because of the occurrence of double resonance the possible reasons behind the lack of earthquake damage to the qutab minar the tallest brick masonry minaret in the world over the last 800 years may be the nonoccurrence of double resonance and almost no amplification in the low frequency range there are two localities in the western part of the national capital territory delhi namely kanganheri chhawla and buradi wherein all sorts of buildings are highly vulnerable to earthquake damage for the closed chhatarpur basin and a semiclosed basin to its northeast formed due to exposed quartzite rock three dimensional 3d simulations are required to predict the characteristics of basin generated surface waves and their focusing effects in the chhatarpur basin the average spectral amplification map developed for the 0 10 hz bandwidth depicts a range of 2 25 4 82 in the national capital territory delhi and may be directly used to transfer the estimated seismic hazard at basement to the free surface

computing a large refined catalog of focal mechanisms for southern california 1981 2010 temporal stability of the style of faulting using the method developed by hardebeck and shearer 2002 2003 termed the hash method we calculate focal mechanisms for earthquakes that occurred in the southern california region from 1981 to 2010 when available we use hypocenters refined with differential travel times from waveform cross correlation using both the p wave first motion polarities and the s p amplitude ratios computed from three component seismograms we determine mechanisms for more than 480 000 earthquakes and analyze the statistical features of the whole catalog we filter the preliminary catalog with criteria associated with mean nodal plane uncertainty and azimuthal gap and obtain a high quality catalog with approximately 179 000 focal mechanisms as more s p amplitude ratios become available after 2000 the average nodal plane uncertainty decreases significantly compared with mechanisms that include only p wave polarities in general the parameters of the focal mechanisms have been stable during the three decades the dominant style of faulting is high angle strike slip faulting with the most likely p axis centered at n5 e for earthquakes of m 2 5 events using the 210 moment tensor solutions in tape et al 2010 as benchmarks we compare the focal plane rotation angles of common events in the catalog seventy percent of common earthquakes match well with rotation angles less than the typical nodal plane uncertainty the common events with relatively large rotation angles are either located around the edge of the scsn network or poorly recorded

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

moment tensor inversion of the 1983 january 17 kefallinia event of ionian islands greece summary the source parameters of the recent 1983 january 17 ionian island event are obtained by the inversion of body waves an optimum source depth of 8 km is determined and the source parameters of the major double couple are strike 60 dip 47 rake 174 and seismic moment m0 7 3 1025 dyne cm this mechanism implies a strike slip dextral fault with a small thrust component this solution ascertains the existence of a transform fault connecting the northwestern edge of the hellenic are with the compressional zone which is produced by the collision of the apulian plate with the eurasian plate along the adriatic north ionian coast this right lateral strike slip fault probably terminates the hellenic subduction zone

3d crustal structure from local earthquake tomography around the gulf of arta ionian region nw greece during summer of 1995 local seismicity was recorded in the area around the gulf of arta in northwestern greece by a dense temporary seismic network of the 441 local events observed at 37 stations 232 well locatable events with a total of 2776 p phase readings were selected applying the criteria of a minimum of 6 p observations and an azimuthal gap less than 180 this data set is used to compute a minimum 1d velocity model for the region several tests are conducted to estimate model stability and hypocenter uncertainties leading to the conclusion that relative hypocenter location accuracy is about 500 m in latitude and longitude and 1 km in depth the minimum 1d velocity model serves as initial model in the non linear inversion for three dimensional p velocity crustal structure by iteratively solving the coupled hypocenter velocity problem in a least squares sense careful analysis of the resolution capability of our data set outlines the well resolved features for interpretation the resulting 3d velocity model shows generally higher average crustal velocities in the east and the well resolved area of the eastern gulf of arta exhibits a homogeneous velocity around 6 km s for the whole upper crust a pronounced north south trending zone of low velocities in the upper 5 10 km is observed in the area of the katouna fault zone kfz at greater depths below 10 km the kfz is underlain by high velocity material e w profiles suggest a horst graben structure associated with the kfz

a rigid block rotation model for the gps derived velocity field along the ryukyu arc abstract using a gps derived velocity field we try to estimate the kinematic features of the ryukyu arc and discuss its implications to the spreading of the okinawa trough the gps derived strain rate field implies that internal deformation within the ryukyu arc is not significant therefore we adopt a rigid block rotation model for the motion of the ryukyu arc the velocity field in the ryukyu arc is best explained by a model with three blocks rather than one with only one block the estimated block rotations predict the spreading along the okinawa trough the predicted spreading is slow 10 mm per year in the north and fast 50 mm per year in the southwest the direction of the predicted spreading is normal to the okinawa trough n170 e n180 e in the southwest while in the north the direction of the spreading is oblique to the okinawa trough n150 e n180 e