an attenuation relationship based on turkish strong motion data and iso acceleration map of turkey abstract this paper presents an attenuation relationship of peak ground acceleration pga derived from turkish strong motion data for rock soil and soft soil sites and an iso acceleration map of turkey based on this relationship for the purpose among all the three component accessible records 221 records from 122 earthquakes that occurred in turkey between 1976 and november 2003 were selected the database was compiled for earthquakes with moment magnitudes m w and pga values ranging between 4 1 and 7 5 and 20 and 806 gal and distances to epicenter considered in the database were between 5 and 100 km from the regression analysis of the data an attenuation equation of pga considering rock soil and soft soil conditions was developed the pga values predicted from the equation suggested in this study and those both from a few domestic equations and some imported equations were compared in addition an iso acceleration map of turkey was constructed using the suggested attenuation equation and considering both known active faults and epicenter locations of the earthquakes that have occurred in turkey

evaluation of site amplification and site period using different methods for an earthquake prone settlement in western turkey abstract seismic micro hazard zonation for urban areas is the first step towards a seismic risk analysis and mitigation strategy essential here is to obtain a proper understanding of the local subsurface conditions and to evaluate ground shaking effects in this study present and future settlement areas of yenisehir which is located in the earthquake prone marmara region of turkey were evaluated with respect to site amplification and site period borings in conjunction with in situ penetration tests seismic velocity measurements resistivity surveys and microtremor studies were performed and available data from previous investigations were complied to determine the variation of the soil profile as well as the characteristics of the soil layers within the study site in addition new empirical correlations between shear wave velocity v s and number of blows from standard penetration test spt n were also developed to be used for the estimation of amplification factors site amplification was assessed using empirical methods based on estimated values of v s 1 d site response numerical modeling program and microtremor measurements among the three methods employed the numerical technique and microtremor method yielded considerably higher amplification factors when compared to those obtained from the empirical method this situation is considered as a limitation of the empirical methods the survey of site response suggests ground amplification the microzonation map based on soil site amplification suggests amplification factors between 1 6 and 5 in the present settlement while the areas at the north and south of the settlement generally amplify the motion 5 to 9 times the site periods obtained from microtremor studies vary from 0 51 to 0 8 s throughout the settlement in addition the comparison between fundamental site periods and fundamental building periods which were measured in a few buildings and estimated from an empirical expression indicate that prime attention should be paid to resonance phenomena particularly for the northern part of the settlement where high rise buildings are still in construction

liquefaction resistance of soils from shear wave velocity a simplified procedure using shear wave velocity measurements for evaluating the liquefaction resistance of soils is presented the procedure was developed in cooperation with industry researchers and practitioners and evolved from workshops in 1996 and 1998 it follows the general format of the seed idriss simplified procedure based on standard penetration test blow count and was developed using case history data from 26 earthquakes and 70 measurement sites in soils ranging from fine sand to sandy gravel with cobbles to profiles including silty clay layers liquefaction resistance curves were established by applying a modified relationship between the shear wave velocity and cyclic stress ratio for the constant average cyclic shear strain suggested by r dobry these curves correctly predicted moderate to high liquefaction potential for 95 of the liquefaction case histories and are shown to be consistent with the standard penetration test based curves in sandy soils a case study is provided to illustrate application of the procedure additional data are needed particularly from denser soil deposits shaken by stronger ground motions to further validate the simplified procedure

changes in depositional systems and sequences in response to basin evolution in a rifted and inverted basin an example from the neogene niigata shin etsu basin northern fossa magna central japan abstract the niigata shin etsu basin which occurs along the eastern margin of the sea of japan was generated in middle miocene time as a failed rift basin in relation to the backarc opening of the japan arc and was converted to a compressional basin in late miocene time the basin filling succession can be divided into four tectonostratigraphic units stages based on characteristics of depositional systems depositional sequences tectonic subsidence rate and sediment supply these units coincide in time with major tectonic events during backarc rifting and subsequent basin inversion unit i 16 13 5 ma represents a syn rift stage characterized by rapid basin subsidence the rate of accommodation exceeded the rate of accumulation resulting in a retrogradational stacking pattern of muddy slope to basin floor systems unit ii 13 5 6 5 ma represents a post rift thermal subsidence stage the rate of accommodation nearly equaled the rate of accumulation resulting in an aggradational stacking pattern of five third order depositional sequences mainly comprising submarine fan turbidite systems affected by supply of coarse clastics unit iii 6 5 1 ma represents the basin inversion stage showing no subsidence or uplift the accumulation rate exceeded the rate of accommodation resulting in rapid progradation of depositional sequences composed of slope shelf shallow marine delta and fluvial systems unit iv 1 ma present represents an intense compressional stress field sedimentation has been restricted to a synclinal area due to syndepositional folding and uplift changes in basin subsidence rate and sediment supply resulting from tectonics and climate change in the basin and the provenance strongly affected characteristics of the depositional systems and sequences the change in basin subsidence also created a basinwide depositional cycle whereas eustasy affected relative sea level changes created higher order depositional sequences during relatively stable phases of tectonics

uplift of the ou backbone range in northeast japan at around 10 ma and its implication for the tectonic evolution of the eastern margin of asia abstract the late cenozoic uplift history of a sedimentary basin located in the axial part of the ou backbone range northeast japan was studied using detailed mapping fission track dating and basin analysis the subsidence analysis of the basin clarified the more complex stepwise uplift of the ou backbone range three stages of uplift have been recognized and are interpreted to be the result of compressional stress possibly accompanied by basin inversion the three stages are identified as 1 a phase of surface uplift and regional unconformity 12 9 ma 2 a stage of differential uplift and compression 6 5 3 ma and 3 an intense compression stage 3 ma in the first stage the eastern sector of the backbone range uplifted and a notable unconformity was formed at 10 ma the western sector remained submerged suggesting that the eastern sector uplifted earlier than the western sector although the first uplift stage has been regarded as a tectonically quiet period in northeast japan this tectonic event at 10 ma is supposed to have a regional origin because coeval tectonic events took place across all northeast japan as well as on the eastern margin of asia this study thus provides new insights into the neogene tectonic evolution in the eastern margin of asia

the migration history of the nazca ridge along the peruvian active margin a re evaluation abstract the collision zone of the 200 km wide and 1 5 km high nazca ridge and the peruvian segment of the convergent south american margin between 14 s and 17 s is characterized by deformation of the upper plate and several hundred meters of uplift of the forearc this is evident by a narrowing of the shelf a westward shift of the coastline and the presence of marine terraces as the nazca ridge is oblique with respect to both trench and convergence direction of the nazca plate it migrates southward along the active plate boundary for reconstructing the migration history of the nazca ridge this study uses updated plate motion data resulting from a revision of the geomagnetic time scale the new model suggests that the ridge crest moved laterally parallel to the margin at a decreasing velocity of 75 mm a before 10 8 ma 61 mm a 10 8 4 9 ma and 43 mm a 4 9 ma to present intra plate deformation associated with mountain building in the peruvian andes since the miocene reduces the relative convergence rate between nazca plate and peruvian forearc taking an intra plate deformation at a rate of 10 mm a estimated from space geodetic and geological data into account does not significantly reduce these lateral migration velocities constraining the length of the original nazca ridge by its conjugate feature on the pacific plate yields a length of 900 km for the subducted portion of the ridge using this constraint ridge subduction began 11 2 ma ago at 11 s therefore the nazca ridge did not affect the northern sites of ocean drilling program odp leg 112 located at 9 s this is supported by benthic foraminiferal assemblages in odp leg 112 cores indicating more than 1000 m of subsidence since at least middle miocene time and by continuous shale deposition on the shelf from 18 to 7 ma recorded in the ballena industrial well at 11 5 s the model predicts the passage of the ridge crest 9 5 ma ago this agrees with the sedimentary facies and benthic foraminiferal stratigraphy of odp leg 112 cores which argue for deposition on the shelf in the middle and late miocene with subsequent subsidence of a minimum of several hundred meters onshore at 12 s the sedimentary record shows at least 500 m uplift prior to the end of the miocene also in agreement with the model

liquefaction potential of quaternary alluvium in bolu settlement area turkey groundwater bearing alluvial units in the seismically active settlement areas may bring out probable damage on the urban and built environment due to liquefaction bolu settlement area and surroundings are located in the north anatolian fault zone geotechnical boreholes were drilled in order to determine the distribution of the geological units to obtain representative soil samples and to measure groundwater level quaternary aged alluvium is the main geological unit in the south of study area stiffness and consistency of the soils were determined by standart penetration test p and s wave velocities of soil have been measured along the seismic profiles the index and physical properties of the samples have also been tested in the laboratory liquefaction potential and safety factor of the sandy levels in quaternary aged alluvium were investigated by different methods based on spt and v s liquefaction seems to be a significant risk in case of an earthquake with a max 0 48 g and m w 7 5 at different levels of the boreholes this situation may bring out environmental problems in the future

liquefaction potential evaluation of the quaternary alluvium western ankara turkey liquefaction of the soils is a major problem during and after earthquakes and can lead to severe damage a wide range of experience in dealing with natural hazards was gained in the capital city of ankara after several earthquakes occured in kaman 1938 gerede 1944 and duzce 1999 and in later events the recent findings after the orta 2000 and bala 2005 2007 earthquakes proved that ankara should not be designated as a nonseismic hazard zone as it has been previously the quaternary age alluvium is located in the nearby suburbs of etimesgut macunkoy cuglu avdan and kazan a high density of population and structures is spread over this alluvium which contains a high percentage of cohesive soils associated with sand and gravel lenses the depths of the groundwater level ranges between 6 0 and 8 0 m in west etimesgut 3 0 m in macunkoy 5 0 to 7 0 8 0 m in cuglu avdan and 4 5 7 0 m in southern kazan the average s wave velocities of the alluvium derived from the remi were 140 m s in etimesgut 200 m s in macunkoy 134 m s in cuglu avdan and 200 m s in kazan respectively liquefaction evaluation is conducted by standard penetration blow count shear wave velocity and threshold acceleration varying horizontal accelerations of the input motions in the soil stratigraphy were generated via the quad4m program geotechnical investigation and proper soil improvement should be carried out in order to prevent structural damage

active forearc shortening in tohoku japan constraints on fault geometry from erosion rates and fluvial longitudinal profiles abstract convexities in the longitudinal profiles of actively incising rivers are typically considered to represent the morphologic signal of a transient response to external perturbations in tectonic or climatic forcing distinguishing such knickzones from those that may be anchored to the channel network by spatial variations in rock uplift however can be challenging here we combine stream profile analysis 10be watershed averaged erosion rates and numerical modeling of stream profile evolution to evaluate whether knickzones in the abukuma massif of northeast japan represent a temporal or spatial change in rock uplift rate in relation to forearc shortening knickzones in channels that drain the eastern flank of the abukuma massif are characterized by breaks in slope area scaling and separate low gradient alluvial upper channel segments from high gradient deeply incised lower channel segments average erosion rates inferred from 10be concentrations in modern sediment below knickzones exceed erosion rates above knickzones by 20 50 although profile convexities could be interpreted as a transient response to an increase in rock uplift rate associated with slip on the range bounding fault geologic constraints on the initiation of fault slip and the magnitude of displacement cannot be reconciled with a recent spatially uniform increase in slip rate rather we find that knickzone position stream profile gradients and basin averaged erosion rates are best explained by a relatively abrupt spatial increase in uplift rate localized above a flat ramp transition in the fault system these analyses highlight the importance of considering spatially non uniform uplift in the interpretation of stream profile evolution and demonstrate that the adjustment of river profiles to fault displacement can provide constraints on fault geometry in actively eroding landscapes

constraints on the evolution of the japan sea based on 40ar 39ar ages and sr isotopic ratios for volcanic rocks of the yamato seamount chain in the japan sea 40 ar 39 ar and sr isotope analyses were performed on basalts and andesites dredged from the yamato seamount chain in the japan sea the 40 ar 39 ar plateau ages range from about 11 to 17 ma though most samples show ages between 10 and 14 ma the seamounts seem to have formed within a period of a few million years although some of them might have formed earlier based on the present results together with previously reported radiometric age data it is thought that the yamato basin formed during some period prior to 17 ma and probably later than around 25 ma taking into account the radiometric age data on rocks from the japan basin it is conjectured that the opening of the japan sea might have started almost at this time or a little earlier the observed 87 sr 86 sr ratios range from 0 70357 to 0 70388 suggesting incorporation of some time integrated components enriched in incompatible elements such as continental crustal materials this may indicate that in the japan sea area at least the yamato basin had not developed enough to show the characteristics of typical n type morb source materials without being affected by pre existing continental crustal materials

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

relationship between tectonics volcanism sedimentation and basin development late cenozoic central part of northern honshu japan abstract a pronounced interplay between tectonics volcanism and sedimentation can be established in the volcanic arc region of the central part of northern honshu during the early miocene to quaternary interval four stages are recognized with the type of volcanism and sedimentation varying according to the tectonic stress regime 1 1 rifting stage 22 15 ma ns trending half grabens were formed under an extensional stress regime related to the rifting of the sea of japan basins were rapidly filled by intermediate to felsic volcanic products which are often associated with subaerial fluvial and lacustrine sediments 2 2 back arc basin opening stage 15 13 ma with more advanced stagess of rifting subsidence from crustal stretching resulted in marked marine incursion and an overall transgressive succession developed during this stage the back arc side of northern honshu subsided rapidly to middle bathyal environments at the same time associated with the opening of the sea of japan large volumes of regionally extensive mafic lavas and associated hyaloclastites were erupted within submarine grabens in contrast in the present backbone ranges felsic volcanism occurred within bathyal to shallow marine environments igneous rock types in this stage display a bimodal mafic felsic chemistry 3 3 transitional stage 13 2 4 ma a thermal subsidence substage 13 8 ma an intermediate stress regime developed which included phases of both weak extension and compression consequently grabens along the sea of japan ceased to form later lithospheric cooling eventually led to thermal subsidence of the back arc region and hemipelagic sediments mantled the previously active mafic volcanic apron volcanism at this time was mainly restricted to a narrow zone along the present backbone ranges where felsic to intermediate volcanic products accumulated within shallow marine environments b incipient compressional substage 8 2 4 ma hemipelagic sedimentation continued on the back arc side of northern honshu along the present backbone ranges the intermediate stress regime continued with formation of many large caldera structures associated with subaerial felsic volcanism 4 4 shortening deformation stage 2 4 ma present the change of the absolute direction of motion of the pacific plate at the early to middle pliocene changed the regional stress regime of the volcanic arc from intermediate to compression movement of back arc thrusts along the sea of japan coast began 2 3 ma and led to uplift of the volcanic arc continued compression in the volcanic arc produced narrow uplifted zones with associated basins bounded by reverse faults these basins were filled rapidly by terrestrial sediments containing upward coarsening sequences under this highly compressional tectonic stress regime volcanism became intermediate mafic in composition with large stratovolcanoes becoming prominent

dynamics of plate bending at the trench and slab plate coupling 1 the bending strength of subducting lithosphere plays a critical role in the earth s plate tectonics and mantle convection modulating the amount of slab pull transmitted to the surface and setting the boundary conditions under which plates move and deform however it is the subject of a lively debate how much of the potential energy of the downgoing plate is consumed in bending the plate and how the lithospheric strength is defined during this process we model the subduction of a viscoelastic lithosphere driven solely by the downgoing plate s buoyancy freely sinking in a passive mantle represented by drag forces to investigate the dynamics of bending 1 we vary the density and the viscosity profile within the plate from isoviscous where strength is distributed to strongly layered where strength is concentrated in a thin core and 2 we map the stress strain and dissipation along the downgoing plate the effective plate strength during bending is not a simple function of average plate viscosity but is affected by rheological layering and plate thinning earth like layered plates allow for the transmission of large fractions of slab pull 75 80 through the bend and yield a net slab pull of fspnet 1 to 6 1012 n m 1 which varies with the buoyancy of plates in all models only a minor portion of the energy is dissipated in the bending surprisingly bending dissipation hardly varies with lithospheric viscosity because in our dynamic system the plates minimize overall dissipation rate by adjusting their bending curvature as a result bending dissipation b is mainly controlled by the bending moment work rate exerted by slab pull we propose a new analytical formulation that includes a viscosity dependent bending radius which allows for assessment of the relative bending dissipation in the earth s subduction zones using parameters from a recent global compilation this yields estimates of b tot 20 these results suggest that plates on earth weakly resist bending yet are able to propagate a large amount of slab pull

upper plate deformation and seismic barrier in front of nazca subduction zone the chololo fault system and active tectonics along the coastal cordillera southern peru abstract the south america plate boundary is one of the most active subduction zone the recent mw 8 4 arequipa 2001 earthquake ruptured the subduction plane toward the south over 400 km and stopped abruptly on the ilo peninsula in this exact region the subduction seismic crisis induced the reactivation of continental fault systems in the coastal area we studied the main reactivated fault system that trends perpendicular to the trench by detailed mapping of fault related geomorphic features also at a longer time scale a recurrent quaternary transtensive tectonic activity of the cfs is expressed by offset river gullies and alluvial fans the presence of such extensional fault systems trending orthogonal to the trench along the coastal cordillera in southern peru is interpreted to reflect a strong coupling between the two plates in this particular case stress transfer to the upper plate at least along the coastal fringe appears to have induced crustal seismic events that were initiated mainly during and after the 2001 earthquake the seafloor roughness of the subducting plate is usually thought to be a cause of segmentation along subduction zones however after comparing and discussing the role of inherited structures within the upper plate to the subduction zone segmentation in southern peru we suggest that the continental structure itself may exert some feedback control on the segmentation of the subduction zone and thus participate to define the rupture pattern of major subduction earthquakes along the southern peru continental margin

characterization of dolomitizing fluids in the carboniferous of the cantabrian zone nw spain a fluid inclusion study with cryo raman spectroscopy abstract a late diagenetic dolomitization pervasively affected carboniferous carbonates of the variscan cantabrian zone nw spain the process generated replacive and void filling dolomite phases spatially related with various calcite cements the nature of the diagenetic fluids has been investigated by cryo raman spectroscopy i e a combination of raman spectroscopy and low temperature microthermometry which reveals in great accuracy the salinity and the major types of dissolved cations and anions in single fluid inclusions fluid properties obtained only from microthermometry are distinctively different the study demonstrates that this improved analytical method of fluid inclusions is a valuable contribution for the interpretation of fluids in dolomite research in primary fluid inclusions of the cantabrian dolomites hydrohalite and two unknown salt hydrates one of which resembles mgcl2 12h2o were detected by cryo raman spectroscopy whereas only hydrohalite appeared in the calcite primary inclusions the presence of cacl2 hydrates is suspected only from low eutectic temperatures dolomite formed from an evolving fluid as reflected by the highly variable equivalent na ca ratios calculated at high and nearly constant total salinities the approximately constant na ca ratio in the first calcite cement reflects a homogeneous source for the salts cryo raman spectroscopy reveals that different cooling procedures may induce the formation of different phase assemblages within the same fluid inclusion in both dolomite and calcite consequently fluid inclusions display different melting behaviors corresponding to different values of calculated salinities salinity calculation only from microthermometry may lead to an underestimation of true salinities according to an assumed hydrostatic geothermal gradient maximum formation conditions for the dolomites are 150 30 c and 40 10 mpa corresponding to a depth of 3 9 1 0 km the first calcite formed at 130 20 c and 35 5 mpa corresponding to a depth of 3 4 0 6 km the minimum t p of formation is defined by the homogenization conditions

thermal modeling of the geometry of subduction with implications for the tectonics of the overriding plate the path which subducting lithosphere follows can be broken into three zones zone i a subhorizontal region of nearly constant dip near the trench zone ii a region of rapidly increasing dip and zone iii a region generally deeper than 125 km again of nearly constant dip we have modeled the thermal evolution of slabs as they pass through these three zones using the method of lines a numerical technique well suited to the solution of time dependent partial differential equations by use of appropriate initial conditions and time dependent boundary conditions we can simulate subduction with variations in age of subducting lithosphere slab velocities and paths followed by the slab thermal modeling results indicate that the geometry of the slab in region ii can be empirically related directly to the thermal structure of the slab in that region and thus indirectly to age and velocity it follows that low angle subduction can extend several hundred kilometers inland only in cases of high convergent velocities 15 cm yr 1 and old 120 m y lithosphere we further suggest that rapid variations in the convergence velocities can provide an enabling mechanism for back arc spreading while slow changes in convergence velocities and or age variations in the subducting lithosphere lead to migration of volcanic arcs

crustal earthquake triggering by pre historic great earthquakes on subduction zone thrusts triggering of earthquakes on upper plate faults during and shortly after recent great m 8 0 subduction thrust earthquakes raises concerns about earthquake triggering following cascadia subduction zone earthquakes of particular regard to cascadia was the previously noted but only qualitatively identified clustering of m 6 5 crustal earthquakes in the puget sound region between about 1200 900 cal years b p and the possibility that this was triggered by a great cascadia thrust subduction thrust earthquake and therefore portends future such clusters we confirm quantitatively the extraordinary nature of the puget sound region crustal earthquake clustering between 1200 900 cal years b p at least over the last 16 000 we conclude that this cluster was not triggered by the penultimate and possibly full margin great cascadia subduction thrust earthquake however we also show that the paleoseismic record for cascadia is consistent with conclusions of our companion study of the global modern record outside cascadia that m 8 6 subduction thrust events have a high probability of triggering at least one or more m 6 5 crustal earthquakes

relationship between outer forearc subsidence and plate boundary kinematics along the northeast japan convergent margin 1 tectonic erosion along convergent plate boundaries whereby removal of upper plate material along the subduction zone interface drives kilometer scale outer forearc subsidence has been purported to explain the evolution of nearly half the world s subduction margins including part of the history of northeast japan here we evaluate the role of plate boundary dynamics in driving forearc subsidence in northeastern japan a synthesis of newly updated analyses of outer forearc subsidence the timing and kinematics of upper plate deformation and the history of plate convergence along the japan trench demonstrate that the onset of rapid fore arc tectonic subsidence is contemporaneous with upper plate extension during the opening of the sea of japan and with an acceleration in convergence rate at the trench in plio quaternary time relative uplift of the outer forearc is contemporaneous with contraction across the arc and a decrease in plate convergence rate the coincidence of these changes across the forearc arc backarc system appears to require an explanation at the scale of the entire plate boundary similar observations along other western pacific margins suggest that correlations between forearc subsidence and major changes in plate kinematics are the rule rather than the exception we suggest that a significant component of forearc subsidence at the northeast japan margin is not the consequence of basal tectonic erosion but instead reflects dynamic changes in plate boundary geometry driven by temporal variations in plate kinematics if correct this model requires a reconsideration of the mass balance and crustal recycling of continental crust at nonaccretionary margins

a summary of cenozoic tectonic history along the ipod japan trench transect along the international program of ocean drilling ipod japan trench transect a mid cenozoic period of tectonism without arc volcanism separated an earlier cretaceous to paleogene and a later neogene period of plate convergence and subduction the cretaceous to early paleogene period of convergence is evidenced by andesitic volcanism associated with a large syncline probably a forearc basin the seaward flank of the basin is a tectonically thickened sediment sequence inferred to be an accretionary complex the arc the syncline and the thickened sediment sequence resemble an arc trench system of the size and structure of the great valley forearc basin and franciscan accretionary complex of california and they were probably continuations of the yezo geosyncline and associated sequences exposed to the north on hokkaido the arc trench system is contemporaneous with the adjacent shimanto arc trench system southwest of tokyo bay in the early paleogene volcanism ceased and part of the thickened sediment sequence of the cretaceous paleogene margin was emergent as a 160 km wide landmass which is recognized in seismic records as a later paleogene sediment source at the end of the paleogene this landmass began to subside and volcanism began again but it was located first briefly on the east and then on the west of the cretaceous arc along the present arc of northern honshu the land mass erosion surface is clearly visible as an angular unconformity in multichannel seismic reflection records the sequence of neogene sediment explosive volcanism and benthic foraminiferal assemblages recording subsidence from subareal conditions to the present bathyal depths have been studied in deep sea drilling project dsdp cores cretaceous subduction appears to have resulted in a very extensive accretionary complex whereas the neogene subduction period appears to have been marked by little net accretion in the forearc area but massive subsidence and some erosion of the front of the convergent margin

slip inversion along inner fore arc faults eastern tohoku japan funding was provided by a grant from the national science foundation tectonics program grant ear 0809939 to d m f and e k geologic society of america graduate research grants and the p d krynine memorial fund the authors thank gaku kimura kyoko tonegawa hiroko watanabe jun kameda and asuka yamaguchi for scientific and logistical support and kristin morell for comments on early versions of the manuscript we also thank yuzuru yamamoto and kohtaro ujiie for their detailed reviews and suggestions for improvement to the manuscript the authors acknowledge the use of the move software suite granted by midland valley s academic software initiative geologic structural stratigraphic and chronologic data used herein are accessible in manuscript figures and in the citations therein input geologic data for trishear kinematic modeling can be accessed in table 1 and in the supporting information ear 0809939 national science foundation tectonics program grant geologic society of america graduate research grants p d krynine memorial fund

faster better shear wave velocity to 100 meters depth from refraction microtremor arrays current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites they require large sources to be effective in noisy urban settings or specialized independent recorders laid out in an extensive array this work shows that microtremor noise recordings made on 200 m long lines of seismic refraction equipment can estimate shear velocity with 20 accuracy often to 100 m depths the combination of commonly available equipment simple recording with no source a wavefield transformation data processing technique and an interactive rayleigh wave dispersion modeling tool exploits the most effective aspects of the microtremor spectral analysis of surface wave sasw and multichannel analysis of surface wave masw techniques the slowness frequency wavefield transformation is particularly effective in allowing accurate picking of rayleigh wave phase velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities higher mode rayleigh waves body waves air waves and incoherent noise two locations illustrate the application of this technique in detail coincident with a large accelerometer microtremor array in reno nevada and atop a borehole logged for shear velocity in newhall california refraction equipment could duplicate microtremor results above 3 hz but could not estimate velocities deeper than 100 m refraction microtremor cannot duplicate the detail in the velocity profile yielded by a suspension logger but can match the average velocity of 10 to 20 m depth intervals and suggest structure below the 100 m logged depth of the hole eight additional examples from southern california and new zealand demonstrate that the refraction microtremor technique quickly produces good results from a wide range of hard and soft sites

permanent fore arc extension and seismic segmentation insights from the 2010 maule earthquake chile 1 geologists have long known that young normal faults are an important structural element of the andean coastal cordillera but their relationship to the subduction seismic cycle is still unclear some of the largest aftershocks of the 2010 mw 8 8 maule earthquake in central chile were nucleated on upper plate normal faults including the mw 6 9 and 7 0 events of the pichilemu earthquake sequence we use the available coseismic gps displacements moment tensor sums and slip distribution models for the maule earthquake to compute the static strain and stress fields imposed on the upper plate by slip on the subduction interface the extensional strains calculated from coseismic gps and from a moment tensor sum of the pichilemu events have similar orientations and orders of magnitude the normal coulomb stress increment csi on the pichilemu fault has maximum positive stresses as high as 4 9 mpa regionally the maule event produced a semi elliptical radial pattern of static extension and deviatoric tension csi 1 5 mpa along the coastal cordillera enclosing the rupture area this elliptical pattern mimics the trends of the major upper crustal structures the static deformation field produced by a great subduction earthquake is an effective mechanism for generating permanent extension above the seismogenic zone reactivating suitably oriented long lived normal faults we suggest that the semi elliptical outline of the first order structures along the coastal cordillera may define the location of a characteristic long lived megathrust segment this observation implies a persistence at least over the quaternary of great subduction ruptures along the maule segment

south kitakami region an allochthonous terrane in japan the pre cretaceous geology of the japanese islands may be interpreted as an accretion complex in which many terranes of several origins are juxtaposed and a number of allochthonous blocks are involved the south kitakami and abukuma regions of northeast japan and probably also silurian and devonian blocks in the kurosegawa fault zone and the border fault zone of the hida metamorphic terrane are the allochthonous blocks the stratigraphic sequence and paleobiofacies of the regions are similar to each other and their lithologic characters are of continental affinity but however are quite different from those of the other terranes having oceanic characters the south kitakami and abukuma regions have been fragments of a lost continent less remotely situated to gondwana during the middle paleozoic and may have drifted and incorporated with the other part of the japanese islands before late mesozoic to early tertiary igneous activity

propagation of an earthquake triggering front from the 2011 tohoku oki earthquake 1 increases in seismicity have been widely observed at varying distances from the source area following large earthquakes the increased number of earthquakes are usually called aftershocks if the area is within a rupture length of the mainshock and called remotely triggered events if they are well beyond that distance these earthquakes can be explained as being induced by static and or dynamic stress changes due to the mainshock however clear observations of dynamic triggering have been inadequate to differentiate between the two mechanisms this study shows that early post seismic events triggered by the 2011 mw 9 0 tohoku oki earthquake systematically propagated over japan in a southwestern direction associated with the strong seismic waves from the source the propagation front was consistent with the arrivals of large amplitude surface waves traveling at 3 1 to 3 3 km s and extending to a distance of 1 350 km there were no observations of triggered earthquakes in the northern direction dynamic stress changes toward the north were comparable to or smaller than those necessary for triggering in the southwestern direction static stress changes were one to two orders smaller than dynamic stress changes at remote distance indicating that static stress was not the main mechanism of the triggering furthermore the dynamic stress strain changes play an important role for remote triggering if the value is more than 500 kpa in stress or 10 6 in strain

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

do subducting seamounts generate or stop large earthquakes seamount subduction is a common process in subduction zone tectonics contradicting a widely held expectation that subducting seamounts generate large earthquakes seamounts subduct largely aseismically producing numerous small earthquakes on rare occasions when they do produce relatively large events the ruptures tend to be complex suggesting multiple rupture patches or faults we explain that the seismogenic behavior of these seamounts is controlled by the development and evolution of an adjacent fracture network during subduction and cannot be described using the frictional behavior of a single fault the complex structure and heterogeneous stresses of this network provide a favorable condition for aseismic creep and small earthquakes but an unfavorable condition for the generation and propagation of large ruptures

quantifying crustal extension and shortening in the back arc region of northeast japan 1 the northeast japan nej arc has experienced strong extension in the early to middle miocene time and contractive deformation since pliocene time we determine the amounts of the miocene extension and pliocene contraction along four transects across the nej arc by area balancing restoration using seismic reflection gravity and surface geologic data we find that the miocene extension is as much as 31 56 km while the pliocene quaternary contraction is only 10 15 km the style of the miocene extension in the back arc region of nej is highly asymmetric the zone of concentrated extension is characterized by a breakaway fault on the west a rollover basement anticline on the east and abnormally deep 10 km basins and strongly rotated fault blocks in between suggesting the existence of a large scale detachment fault at a mid crustal level beneath the extended zone we reveal that the pliocene quaternary contractive surface deformation in the back arc region of nej resulted principally from positive tectonic inversion of the underlying detachment fault previous works have suggested that andean type orogens have often experienced negative and positive inversions alternately in their back arc regions although the former has been well documented for example for the cenozoic north american cordillera the latter has rarely been reported because subsequent contraction has obscured the older structures since the nej arc is still at an incipient stage and hence its older structures are well preserved our study provides an important example of positive tectonic inversion of andean type orogens

normal and reverse faulting driven by the subduction zone earthquake cycle in the northern chilean fore arc 1 despite its location in a convergent tectonic setting the coastal cordillera of northern chile between 21 s and 25 s is dominated by structures demonstrating extension in the direction of plate convergence in some locations however normal faults have been reactivated as reverse faults complicating the interpretation of long term strain in order to place these new observations in a tectonic context we model stress changes induced on these faults by the subduction earthquake cycle our simulations predict that interseismic locking on the plate boundary encourages normal slip on fore arc faults which may result from elastic rebound due to interplate earthquakes or from seismic or aseismic motion that takes place within the interseismic period conversely stress generated by strong subduction zone earthquakes such as the 1995 mw 8 1 antofagasta event provides a mechanism for the reverse reactivation we document here upper plate fault slip in response to the low magnitude stress changes induced by the subduction earthquake cycle suggests that the absolute level of stress on these faults is very low furthermore seismic hazard analysis for northern chile requires consideration of not only the plate boundary earthquake cycle but also the cycle on fore arc faults that may or may not coincide with the interplate pattern though the relationships between permanent strain and deformation calculated using elastic models remain unclear the compatibility of modeled stress fields with the distribution of fore arc faulting suggests that interseismic strain accumulation and coseismic deformation on the subduction megathrust both play significant roles in shaping structural behavior in the upper plate

large extensional aftershocks in the continental forearc triggered by the 2010 maule earthquake chile summary the mw 8 8 maule earthquake occurred off the coast of central chile on 2010 february 27 and was the sixth largest earthquake to be recorded instrumentally this subduction zone event was followed by thousands of aftershocks both near the plate interface and in the overriding continental crust here we report on a pair of large shallow crustal earthquakes that occurred on 2010 march 11 within 15 min of each other near the town of pichilemu on the coast of the o higgins region of chile field and aerial reconnaissance following the events revealed no distinct surface rupture we infer from geodetic data spanning both events that the ruptures occurred on synthetic sw dipping normal faults the first larger rupture was followed by buried slip on a steeper fault in the hangingwall the fault locations and geometry of the two events are additionally constrained by locations of aftershock seismicity based on the international maule aftershock data set the maximum slip on the main fault is about 3 m and consistent with field results the onshore slip is close to zero near the surface satellite radar data also reveal that significant aseismic afterslip occurred following the two earthquakes coulomb stress modelling indicates that the faults were positively stressed by up to 40 bars as a result of slip on the subduction interface in the preceding megathrust event in other words the pichilemu earthquakes should be considered aftershocks of the maule earthquake the occurrence of these extensional events suggests that regional interseismic compressive stresses are small several recent large shallow crustal earthquakes in the overriding plate following the 2011 mw 9 0 tohoku oki earthquake in japan may be an analogue for the triggering process at pichilemu

backarc deformation along the eastern japan sea margin offshore northern honshu abstract the structural evolution of the eastern japan sea margin offshore northern honshu is discussed on the basis of single channel seismic profiles backarc structures evolved in response to late oligocene middle miocene extension which was generated at high angles to the arc trench system the evolution of a late miocene recent compressional plate tectonic regime resulted in widespread basement inversion the eastern japan sea margin is characterized by variable inverted half graben systems which are obliquely oriented to the island arc the area is underlain by three major structural blocks which are separated by a nw and a wnw trending structural discontinuity these blocks experienced a northward increase in extension the two southern blocks contain nne ne oriented reverse faults while the northern block is underlain by n nnw trending reverse faults the orientation and geometry of basement faults compares well with faults mapped onshore honshu the evaluation of the eastern japan sea margin can be explained by early miocene ese directed extension followed by a middle miocene sse directed extension pliocene recent east dipping reverse faults extend along the base of the continental slope and form a discontinuous thrust front which is characterized by minor fault offsets these reverse faults are locally associated with small active arc volcanoes

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

microzonation for earthquake hazards yenisehir settlement bursa turkey abstract detailed geological hydrogeological and geotechnical studies were performed for the assessment of the foundation conditions of the present and future settlement areas of yenisehir yenisehir is located 50 km east of bursa turkey within an east west trending elliptical sedimentary basin the present and future development areas of yenisehir cover 10 km 2 the topography of the settled area is quite smooth and the slopes are generally less than 10 yenisehir is located within a first degree earthquake zone of turkey according to the seismic design code the seismicity of the town is mainly controlled by the geyve iznik and bursa fault zones the study also involves trial pitting drilling in situ testing and laboratory testing borehole logs index properties of soils standard penetration test results and groundwater level measurements were used for activity and liquefaction assessments of the foundation material based on the evaluation of the data two geotechnical zones were distinguished the northern part of the area is characterized by cohesive soils of high expansion behaviour and the southern part by alternation of cohesive and non cohesive soils showing high liquefaction potential

development of a geotechnical and geophysical database for seismic zonation of the ankara basin turkey engineering geological and geotechnical site characteristics were assessed and seismic hazard studies performed for the upper pliocene to pleistocene fluvial and quaternary alluvial and terrace deposits for a site west of ankara turkey sediment conditions were determined and a soil profile was characterized by surface geophysical methods these studies were integrated with existing in situ characterization studies to create a seismic and geotechnical database for the site a seismic zonation map of the site was then prepared site classification systems were assigned to account for site effects in relation to seismic hazard assessments the consequences of the seismic hazards were investigated and recommendations were presented

compressional and shear wave velocity versus depth relations for common rock types in northern california abstract this article presents new empirical compressional and shear wave velocity vp and vs versus depth relationships for the most common rock types in northern california vp versus depth relations were developed from borehole laboratory seismic refraction and tomography and density measurements and were converted to vs versus depth relations using new empirical relations between vp and vs the relations proposed here account for increasing overburden pressure but not for variations in other factors that can influence velocity over short distance scales such as lithology consolidation induration porosity and stratigraphic age standard deviations of the misfits predicted by these relations thus provide a measure of the importance of the variability in vp and vs caused by these other factors because gabbros greenstones basalts and other mafic rocks have a different vp and vs relationship than sedimentary and granitic rocks the differences in vs between these rock types at depths below 6 or 7 km are generally small the new relations were used to derive the 2005 u s geological survey seismic velocity model for northern california employed in the broadband strong motion simulations of the 1989 loma prieta and 1906 san francisco earthquakes initial tests of the model indicate that the vp model generally compares favorably to regional seismic tomography models but that the vp and vs values proposed for the franciscan complex may be about 5 too high

seamount subduction erosion in the nankai trough and its potential impact on the seismogenic zone seamount subduction along subduction zone plate boundary thrusts has long been implicated as a mechanism for abrasion and tectonic erosion of the base of the overriding plate however tectonic erosion processes have not been examined in detail with high quality three dimensional 3 d seismic reflection imaging in 1999 we acquired 3 d seismic reflection data from the nankai trough subduction zone to image the plate boundary fault and the overlying accretionary wedge structure fortuitously these data reveal a small to 1 km high basement ridge that has subducted to 7 km subseafloor updip from the basement ridge a 1 km thick sequence of sediment from the base of the accretionary wedge appears to be missing we interpret these data as evidence for tectonic erosion of the base of the accretionary wedge following the basement ridge subduction tectonic erosion has removed more than 25 km 3 from the updip edge of the seismogenic zone and carried it down into the seismogenic zone the tectonically eroded sediments are presumed to enhance fault zone fluid content potentially reducing fault zone effective stress and may temporarily inhibit earthquake rupture potential after the passage of the ridge the boundary fault returns to its former position in a period of enhanced underplating

widespread seismicity excitation throughout central japan following the 2011 m 9 0 tohoku earthquake and its interpretation by coulomb stress transfer 1 we report on a broad and unprecedented increase in seismicity rate following the m 9 0 tohoku mainshock for m 2 earthquakes over inland japan parts of the japan sea and izu islands at distances of up to 425 km from the locus of high 15 m seismic slip on the megathrust such an increase was not seen for the 2004 m 9 1 sumatra or 2010 m 8 8 chile earthquakes but they lacked the seismic networks necessary to detect such small events here we explore the possibility that the rate changes are the product of static coulomb stress transfer to small faults we use the nodal planes of m 3 5 earthquakes as proxies for such small active faults and find that of fifteen regions averaging 80 by 80 km in size 11 show a positive association between calculated stress changes and the observed seismicity rate change 3 show a negative correlation and for one the changes are too small to assess this work demonstrates that seismicity can turn on in the nominal stress shadow of a mainshock as long as small geometrically diverse active faults exist there which is likely quite common

evaluation of ground deformations induced by the 1999 kocaeli earthquake turkey at selected sites on shorelines the kocaeli earthquake m w 7 4 of 17 august 1999 occurred in the eastern marmara region of turkey along the north anadolu fault and resulted in a very serious loss of life and property one of the most important geotechnical issues of this event was the permanent ground deformations because of both liquefaction and faulting these deformations occurred particularly along the southern shores of izmit bay and sapanca lake between the cities of yalova and adapazari in the west and east respectively in this study three sites founded on delta fans namely degirmendere nose yenikoy tea garden at seymen on the coast of izmit bay and vakif hotel site on the coast of sapanca lake were selected as typical cases the main causes of the ground deformations at these sites were then investigated geotechnical characterization of the ground derivation of displacement vectors from the pre and post earthquake aerial photographs liquefaction assessments based on field performance data and analyses carried out using the sliding body method have been fundamental in this study the displacement vectors determined from photogrammetric evaluations conducted at degirmendere and seymen showed a combined movement of faulting and liquefaction but except the movements in the close vicinity of shorelines the dominant factor in this movement was faulting the results obtained from the analyses suggested that the ground failure at degirmendere was a submarine landslide mainly because of earthquake shaking rather than liquefaction on the other hand the ground failures at the yenikoy tea garden on the coast of seymen and the hotel area in sapanca town resulted from liquefaction induced lateral spreading it was also obtained that the ground deformations estimated from the sliding body method were quite close to those measured by aerial photogrammetry technique