empirical ground motion relations for subduction zone earthquakes and their application to cascadia and other regions ground motion relations for earthquakes that occur in subduction zones are an important input to seismic hazard analyses in many parts of the world in the cascadia region washington oregon northern california and british columbia for example there is a significant hazard from megathrust earthquakes along the subduction interface and from large events within the subducting slab these hazards are in addition to the hazard from shallow earthquakes in the overlying crust we have compiled a response spectra database from thousands of strong motion record ings from events of moment magnitude m 5 8 3 occurring in subduction zones around the world including both interface and in slab events the 2001 m 6 8 nis qually and 1999 m 5 9 satsop earthquakes are included in the database as are many records from subduction zones in japan kyoshin net data mexico guerrero data and central america the size of the database is four times larger than that available for previous empirical regressions to determine ground motion relations for subduc tion zone earthquakes the large dataset enables improved determination of attenu ation parameters and magnitude scaling for both interface and in slab events soil response parameters are also better determined by the data we use the database to develop global ground motion relations for interface and in slab earthquakes using a maximum likelihood regression method we analyze regional variability of ground motion amplitudes across the global database and find that there are significant regional differences in particular amplitudes in cascadia differ by more than a factor of 2 from those in japan for the same magnitude distance event type and national earthquake hazards reduction program nehrp soil class this is believed to be due to regional differences in the depth of the soil profile which are not captured by the nehrp site classification scheme regional correction factors to account for these differences are proposed for cascadia and japan the results of this study differ significantly from previous analyses based on more limited data and have important implications for seismic hazard analysis the ground motion relations predict that a great megathrust earthquake m 8 at a fault distance of about 100 km would produce pseudoacceleration psa 5 damped horizontal component on soil sites of about 110 cm sec 2 at 0 5 hz 660 cm sec 2 at 2 5 hz and 410 cm sec 2 at 5 hz with a peak ground acceleration of about 180 cm sec 2 these damaging levels of motion would be experienced over a very large area corresponding to a rectangular area about 300 km wide by 500 km long large in slab events m 7 5 would produce even higher psa values within 100 km of the fault but the in slab motions attenuate much more rapidly with distance thus the hazard posed by moderate to large in slab events such as the 2001 nisqually earth quake is modest compared to that of a cascadia megathrust earthquake of m 8 in terms of the area that would experience damaging levels of ground motion

interseismic coupling and seismic potential along the central andes subduction zone we use about two decades of geodetic measurements to characterize interseismic strain build up along the central andes subduction zone from lima peru to antofagasta chile these measurements are modeled assuming a 3 plate model nazca andean sliver and south america craton and spatially varying interseismic coupling isc on the nazca megathrust interface we also determine slip models of the 1996 m w 7 7 nazca the 2001 m w 8 4 arequipa the 2007 m w 8 0 pisco and the m w 7 7 tocopilla earthquakes we find that the data require a highly heterogeneous isc pattern and that overall areas with large seismic slip coincide with areas which remain locked in the interseismic period with high isc offshore lima where the isc is high a m w 8 6 8 8 earthquake occurred in 1746 this area ruptured again in a sequence of four m w 8 0 earthquakes in 1940 1966 1974 and 2007 but these events released only a small fraction of the elastic strain which has built up since 1746 so that enough elastic strain might be available there to generate a m w 8 5 earthquake the region where the nazca ridge subducts appears to be mostly creeping aseismically in the interseismic period low isc and seems to act as a permanent barrier as no large earthquake ruptured through it in the last 500 years in southern peru isc is relatively high and the deficit of moment accumulated since the m w 8 8 earthquake of 1868 is equivalent to a magnitude m w 8 4 earthquake two asperities separated by a subtle aseismic creeping patch are revealed there this aseismic patch may arrest some rupture as happened during the 2001 arequipa earthquake but the larger earthquakes of 1604 and 1868 were able to rupture through it in northern chile isc is very high and the rupture of the 2007 tocopilla earthquake has released only 4 of the elastic strain that has accumulated since 1877 the deficit of moment which has accumulated there is equivalent to a magnitude m w 8 7 earthquake this study thus provides elements to assess the location size and magnitude of future large megathurst earthquakes in the central andes subduction zone caveats of this study are that interseismic strain of the forearc is assumed time invariant and entirely elastic also a major source of uncertainty is due to fact that the available data place very little constraints on interseismic coupling at shallow depth near the trench except offshore lima where sea bottom geodetic measurements have been collected suggesting strong coupling

jurassic cretaceous boundary age and mid ocean ridge type mantle source for shatsky rise basalt sills cored in lowermost berriasian sediments on shatsky rise in the northwest pacific yield a mean 4 0 ar 3 9 ar incremental heating age of 144 6 0 8 ma providing a minimum estimate on the age of the jurassic cretaceous boundary the largest part of the rise was emplaced at rates similar to those of several continental flood basalts the rise formed at an oceanic triple junction and the sills as well as lavas from two dredge sites exhibit an ocean ridge type nd pb sr isotope signature this signature is provisionally consistent with either a perisphere or meteorite impact model but is not predicted by the plume head model of plateau formation however no model can yet be rejected given the very sparse sampling of shatsky rise

the andean subduction zone between 22 and 25 s northern chile precise geometry and state of stress abstract one year of seismicity recorded by a local network is used to obtain more precision about the geometry and the stress regime of the andean subduction between 22 and 25 s in the northern chile seismic gap a sharp image of the wadati benioff zone wbz is obtained down to 270 km in depth a seismically quasi quiescent zone is observed in the wbz below the volcanic arc between 150 and 210 km in depth hypocentres of distant intermediate depth earthquakes located with the local network are compared with worldwide seismic network hypocentres in order to evaluate the accuracy of the wbz image at depth greater than 100 150 km in depth no shallow microearthquakes have been observed in the continental crust but some seismic activity is likely to occur locally at the deep root of the atacama fault the stress field and the characteristics of faulting along the subducted slab are investigated underthrusting and localized reverse faulting earthquakes define the seismically coupled plate interface from 20 to 50 km in depth locked zone downdip intra slab normal faulting prevails tensile zone but some strike slip faulting is observed a transition between normal faulting with variable fault azimuth and normal faulting with nearly homogeneous nnw to nw oriented fault plane is found at about 80 km in depth it is found that the stress axes 1 and 3 in the locked zone are oriented in the convergence direction 75 80 e downdip in the tensile zone 3 has a mean azimuth 60 65 e there the slab is hence submitted to a tensional force slab pull oblique relatively to the convergence the transition between seismic underthrusting and intraplate normal faulting downdip occurs at the depth where the continental moho encounters the wadati benioff zone suggesting that a relationship exists between seismic coupling and the presence of continental crust at the plate interface the pre seismic state of this segment of the andean subduction zone is confirmed by the occurrence of strong earthquakes located by the global network around the presumed rupture area and by the stress regime found along the wadati benioff zone

ndsha a new paradigm for reliable seismic hazard assessment abstract a new paradigm is needed for reliable seismic hazard assessment rsha not only from consideration of a the huge human losses experienced in the many recently destructive earthquakes worldwide but also from b theoretical considerations of seismic wave generation and propagation phenomena through often non homogeneous media within the earth s crust particularly when large and more complex fault ruptures occur the neo deterministic seismic hazard assessment ndsha method proposed some twenty years ago is found to reliably and realistically simulate the wide suite of earthquake ground motions that may impact civil populations as well as their heritage buildings the scenario based ndsha modeling technique is developed from comprehensive physical knowledge of i the seismic source process ii the propagation of earthquake waves and iii their combined interactions with site effects thus ndsha effectively accounts for the tensor nature of earthquake ground motions a formally described as the tensor product of the earthquake source functions and the green s functions of the transmitting pathway medium and b more informally described as mathematical arrays of numbers or functions indices that transform according to certain rules under a change of coordinates importantly ndsha therefore uses all available information about the spacial distribution of large magnitude earthquake phenomena including a maximum credible earthquake mce which is based on seismic history and seismotectonics and b geological and geophysical data thus it does not rely on scalar empirical ground motion attenuation models gmpes as these are often both a weakly constrained by available observations and b fundamentally unable to account for the tensor nature of earthquake ground motions

a probabilistic seismic hazard assessment of southern peru and northern chile abstract southern peru and northern chile 17 30 s 67 74 w make up a seismically active region due to the convergence of the nazca plate and the south american plate the region has experienced a number of destructive earthquakes and tsunamis over the past few centuries which have caused loss of human life and significant damage to infrastructure highlighting the importance of seismic hazard assessment in the region in fact a reliable seismic hazard assessment is critical for developing policies for seismic hazard mitigation and risk reduction in this study we performed a probabilistic seismic hazard assessment psha of the study area based on an earthquake catalog that was very carefully analyzed in earlier studies we demonstrated that inappropriate treatment of the earthquake catalog can result in a serious bias in evaluations of seismicity parameters e g a bias of up to 42 in the b parameter of the gutenberg richter law to address this issue we compiled a homogenous earthquake catalog consisting of 39 977 events during the 1513 2016 period and accounted for site specific local effects by developing site specific scaling relationships between different measures of magnitude e g mb ms md and moment magnitude mw the study area was subdivided into 15 seismogenic zones accounting for site specific seismicity patterns the parameters a and b of the gutenberg richter law were estimated for each zone based on independent earthquake events the psha was performed using a standard logic tree approach which allowed us to systematically take into account the model based uncertainty and its influence on the estimated ground motion parameters uniform hazard spectra for return periods of 475 and 2475 years were estimated for peak ground accelerations and spectral accelerations at 0 2 s and 1 0 s to meet the definitions of seismic hazards provided by the international building code ibc international code council icc 2009 this study is expected to provide a basis for design maps for building codes and emergency planning

interseismic coupling segmentation and mechanical behavior of the central chile subduction zone global positioning system gps measurements carried out in chile over the last two decades showed that an entire portion of the nazca south america subduction zone 38 s 24 s was locked over this period of time the induced accumulation of elastic deformation in the upper plate was not released until the recent maule earthquake of 27 february 2010 mw 8 8 that ruptured the southern part of this section locking or coupling between the two plates varies both with depth and along strike here we use our own gps data an updated solution of our extended network in central chile combined with other published data sets to quantify the spatial variations of the coupling that prevailed before the maule earthquake using a simple elastic model based on the back slip assumption we show that coupling variations on the subduction plane are sufficient to explain the observed surface deformation with no need of a sliver in central chile we identify four segments characterized by higher coupling and separated by narrow areas of lower coupling this segmentation is in good agreement with historical and recent seismicity in chile in particular the narrow zones of lower coupling seem to have stopped most large seismic ruptures including maule s these zones are often associated with irregular bathymetric or coastal features fracture zones or peninsulas finally coseismic and early post seismic slip distribution of the maule earthquake occurring either in previously highly or weakly coupled zones map a complex distribution of velocity weakening and velocity strengthening patches on the subduction interface

continuing megathrust earthquake potential in chile after the 2014 iquique earthquake the 2014 iquique event was not the earthquake that had been expected to fill the regional seismic gap given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure the seismic gap theory1 identifies regions of elevated hazard based on a lack of recent seismicity in comparison with other portions of a fault it has successfully explained past earthquakes see for example ref 2 and is useful for qualitatively describing where large earthquakes might occur a large earthquake had been expected in the subduction zone adjacent to northern chile3 4 5 6 which had not ruptured in a megathrust earthquake since a m 8 8 event in 1877 on 1 april 2014 a m 8 2 earthquake occurred within this seismic gap here we present an assessment of the seismotectonics of the march april 2014 iquique sequence including analyses of earthquake relocations moment tensors finite fault models moment deficit calculations and cumulative coulomb stress transfer this ensemble of information allows us to place the sequence within the context of regional seismicity and to identify areas of remaining and or elevated hazard our results constrain the size and spatial extent of rupture and indicate that this was not the earthquake that had been anticipated significant sections of the northern chile subduction zone have not ruptured in almost 150 years so it is likely that future megathrust earthquakes will occur to the south and potentially to the north of the 2014 iquique sequence

modeling of seismic hazard for turkey using the recent neotectonic data abstract recent developments in the neotectonic framework of turkey introduced new tectonic elements necessitating the reconstruction of turkey s seismic hazard map in this regard 14 seismic source zones were delineated maximum earthquake magnitudes for each seismic zones were determined using the fault rupture length approximation regression coefficients of the earthquake magnitude frequency relationships for the seismic zones were compiled mostly from earlier works along with these data a strong ground motion attenuation relationship developed by joyner and boore joyner w b boore d m 1988 measurement characterization and prediction of strong ground motion earthquake engineering and soil dynamics 2 recent advances ground motion evaluation pp 43 102 was utilized to model the seismic hazard for turkey using the probabilistic approach for the modeling the earthquake location uncertainty concept was employed a grid of 5106 points with 0 2 intervals was constituted for the area encompassed by the 25 46 e longitudes and 35 43 n latitudes for the return periods of 100 and 475 years the peak horizontal ground acceleration pga in bedrock was computed for each grid point isoacceleration maps for the return periods of 100 and 475 years were constructed by contouring the pga values at each node

paleo pacific subduction accretion evidence from geochemical and u pb zircon dating of the nadanhada accretionary complex ne china the nadanhada terrane located along the eastern margin of eurasia contains a typical accretionary complex related to paleo pacific plate subduction accretion the yuejinshan complex is the first stage accretion complex that consists of meta clastic rocks and metamafic ultramafic rocks whereas the raohe complex forms the main parts of the terrane and consists of limestone bedded chert and mafic ultramafic rocks embedded as olistolith blocks in a weakly sheared matrix of clastic meta sedimentary rocks geochemical data indicate that the yuejinshan metabasalts have normal mid ocean ridge basalt n morb affinity whereas the raohe basaltic pillow lavas have an affinity to ocean island basalts oib sensitive high resolution ion microprobe shrimp u pb zircon analyses of gabbro in the raohe complex yield a weighted mean 206pb 238u zircon age of 216 5 ma whereas two samples of granite intruded into the complex yield weighted mean 206pb 238u zircon ages of 128 2 and 129 2 ma laser ablation inductively coupled plasma mass spectrometry la icpms u pb zircon analyses of basaltic pillow lava in the raohe complex define a weighted mean age of 167 1 ma two sandstone samples in the raohe complex record younger concordant zircon weighted mean ages of 167 17 and 137 3 ma these new data support the view that accretion of the raohe complex was between 170 and 137 ma and that final emplacement of the raohe complex took place at 137 130 ma the accretion of the yuejinshan complex probably occurred between the 210 and 180 ma suggesting that paleo pacific plate subduction was initiated in the late triassic to early jurassic

ground motion prediction equation for the chilean subduction zone abstract a ground motion prediction equation for the horizontal component of the response spectral values from the chilean subduction zone is developed the dataset contains 3774 recordings from 473 earthquakes including the latest megathrust events that occurred in the country i e 2010 m w 8 8 maule 2014 m w 8 1 iquique and 2015 m w 8 3 illapel the functional form for the median model follows the proposal by abrahamson et al 2016 site effects are estimated based on v s 30 an additional model is built using only ground motions associated with measured values of v s 30 and reliable m w estimates termed the high quality hq model the standard deviation of the hq model is much lower than the main model particularly the component of the standard deviation that corresponds to site to site variability indicating that better site characterization can significantly reduce the overall uncertainty in ground motion estimation electronic supplement tables of regression coefficients for the high quality hq model and 95 confidence intervals for model s coefficients and matlab implementation of the ground motion prediction equation gmpe

the late jurassic magmatic protoliths of the mikabu greenstones in sw japan a fragment of an oceanic plateau in the paleo pacific ocean abstract the mikabu greenstones form accreted fragments of an ancient oceanic plateau which are currently incorporated within the cretaceous high p t type sanbagawa metamorphic belt in sw japan previous geological and petrological studies indicate that protoliths of the mikabu greenstones were mafic ultramafic volcano plutonic rocks of oceanic plateau and or islands despite their rock assemblage and metamorphic nature their protolith age has been poorly constrained by measuring u pb age of igneous zircon grains using la icpms this study identified for the first time a late jurassic age for the protoliths of the mikabu greenstones in the eastern kii peninsula the shurei complex with an overlap within 2 sigma error measured u pb ages of zircon grains have a weighted mean age of 154 6 1 6 ma the kimmeridgian late jurassic which is slightly younger than the radiolarian ages middle jurassic of deep sea pelagic cherts associated with the mikabu greenstones this age difference indicates that mafic magmas intruded pelagic deep sea sediments to form a volcanic edifice onto the pre existing oceanic lithosphere new measurements of trace element composition of the dated zircon grains further confirmed that the dated zircon grains are more similar to those in oceanic crusts rather than in continental crusts in addition the trace element composition suggests that the host mafic magma of the zircon grains was derived from depleted mantle similar to the mid oceanic ridge type source rather than fertile mantle source like hawaii and iceland on the basis of the common occurrence of similar mafic rocks from the shatsky rise in the modern nw pacific ocean we conclude that the protoliths of the mikabu greenstones had formed a part of an oceanic plateau island which was generated by the late jurassic intra plate mafic magmatism in ancient mid pacific probably together with the shatzky rise

attenuation relations of strong ground motion in japan using site classification based on predominant period a spectral acceleration attenuation model for japan is presented in the present study the data set includes a very large number of strong ground motion records up to the 2003 off tokach main and aftershocks site class terms instead of individual site correction terms are used the site classes of recording stations are from a recent study on site classification for strong motion recording stations in japan according to a classification scheme that has been used in japanese engineering design the use of site class terms enables tectonic source type effects to be identified and accounted for in the present model the effects of a faulting mechanism for crustal earthquakes also are accounted for for crustal and interface earthquakes a simple form of an attenuation model with respect to distance is able to capture the main strong motion characteristics and achieves unbiased estimates for subduction slab events a simple distance modification factor is employed to achieve plausible and unbiased predictions the effects of source depth tectonic source type and faulting mechanism of crustal earthquakes are significant the need for magnitude squared terms is evaluated and the use of magnitude squared terms reduces the interevent error further

syncollisional rapid granitic magma formation in an arc arc collision zone evidence from the tanzawa plutonic complex japan the tanzawa plutonic complex tpc central japan is a suite of tonalitic gabbroic plutons exposed in a globally unique arc arc collision zone where an active intraoceanic izu bonin mariana ibm arc is colliding against the honshu arc the tpc has been widely accepted as an exposed middle crust section of the ibm arc chiefly because of geochemical similarities between the tpc and ibm rocks and previously reported precollisional miocene k ar ages however new zircon u pb ages show that the main pulse of tpc magmatism was syncollisional and that plutons were emplaced rapidly and cooled soon after pliocene collision trace element compositions of tpc zircon show distinctively elevated th nb ratios compared to zircon from other noncollisional ibm silicic plutonic rocks indicating the involvement of continental sediments from the honshu arc in their magma genesis

transformative geomorphic research using laboratory experimentation abstract laboratory experiments in geomorphology is the theme of the 46th annual binghamton geomorphology symposium bgs while geomorphic research historically has been dominated by field based endeavors laboratory experimentation has emerged as an important methodological approach to study these phenomena employed primarily to address issues related to scale and the analytical treatment of the geomorphic processes geomorphic laboratory experiments can result in transformative research several examples drawn from the fluvial and aeolian research communities are offered as testament to this statement and these select transformative endeavors often share very similar attributes the 46th bgs will focus on eight broad themes within laboratory experimentation and a diverse group of scientists has been assembled to speak authoritatively on these topics featuring several high profile projects worldwide this special issue of the journal geomorphology represents a collection of the papers written in support of this symposium

historical and recent large megathrust earthquakes in chile abstract recent earthquakes in chile 2014 mw 8 2 iquique 2015 mw 8 3 illapel and 2016 mw 7 6 chiloe have put in evidence some problems with the straightforward application of ideas about seismic gaps earthquake periodicity and the general forecast of large megathrust earthquakes in northern chile before the 2014 iquique earthquake 4 large earthquakes were reported in written chronicles 1877 1786 1615 and 1543 in north central chile before the 2015 illapel event 3 large earthquakes 1943 1880 1730 were reported and the 2016 chiloe earthquake occurred in the southern zone of the 1960 valdivia megathrust rupture where other large earthquakes occurred in 1575 1737 and 1837 the periodicity of these events has been proposed as a good long term forecasting however the seismological aspects of historical chilean earthquakes were inferred mainly from old chronicles written before subduction in chile was discovered here we use the original description of earthquakes to re analyze the historical archives our interpretation shows that a priori ideas like seismic gaps and characteristic earthquakes influenced the estimation of magnitude location and rupture area of the older chilean events on the other hand the advance in the characterization of the rheological aspects that controlled the contact between nazca and south american plate and the study of tsunami effects provide better estimations of the location of historical earthquakes along the seismogenic plate interface our re interpretation of historical earthquakes shows a large diversity of earthquakes types there is a major difference between giant earthquakes that break the entire plate interface and those of mw 8 0 that only break a portion of it

mesozoic tectonothermal development of the sambagawa mikabu and chichibu belts south west japan evidence from 40ar 39ar whole rock phyllite ages five whole rock 40ar 39ar plateau ages from low grade sectors of the sambagawa belt besshi nappe complex range between 87 and 97 ma two whole rock phyllite samples from the mikabu greenstone belt record well defined 40ar 39ar plateau ages of 96 and 98 ma together these ages suggest that a high pressure metamorphism occurred in both the sambagawa and mikabu belts at c 90 100 ma the northern chichibu sub belt may consist of several distinct geochronological units because metamorphic ages increase systematically from north c 110 ma to south c 215 ma the northern chichibu sub belt is correlated with the kuma nappe complex sambagawa belt two whole rock phyllite samples from the kurosegawa terrane display markedly older metamorphic ages than either the sambagawa or the chichibu belts accretion of sambagawa chichibu protoliths began prior to the middle jurrasic depositional ages decrease from middle jurassic kuma chichibu nappe complex to c 100 ma oboke nappe complex toward lower tectonostratigraphic units the ages of metamorphic culmination also decrease from upper to lower tectonostratigraphic units the kurosegawa belt and the geological units to the south belong to distinctly different terrances than the sambagawa chichibu belts these have been juxtaposed as a result of transcurrent faulting during the cretaceous

probabilistic seismic hazard assessment for northeast india region northeast india bounded by latitudes 20 30 n and longitudes 87 98 e is one of the most seismically active areas in the world this region has experienced several moderate to large sized earthquakes including the 12 june 1897 shillong earthquake mw 8 1 and the 15 august 1950 assam earthquake mw 8 7 which caused loss of human lives and significant damages to buildings highlighting the importance of seismic hazard assessment for the region probabilistic seismic hazard assessment of the region has been carried out using a unified moment magnitude catalog prepared by an improved general orthogonal regression methodology geophys j int 190 1091 1096 2012 probabilistic seismic hazard assessment of northeast india region ph d thesis department of earthquake engineering iit roorkee roorkee 2013 with events compiled from various databases isc neic gcmt imd and other available catalogs the study area has been subdivided into nine seismogenic source zones to account for local variation in tectonics and seismicity characteristics the seismicity parameters are estimated for each of these source zones which are input variables into seismic hazard estimation of a region the seismic hazard analysis of the study region has been performed by dividing the area into grids of size 0 1 0 1 peak ground acceleration pga and spectral acceleration sa values for periods of 0 2 and 1 s have been evaluated at bedrock level corresponding to probability of exceedance pe of 50 20 10 2 and 0 5 in 50 years these exceedance values correspond to return periods of 100 225 475 2475 and 10 000 years respectively the seismic hazard maps have been prepared at the bedrock level and it is observed that the seismic hazard estimates show a significant local variation in contrast to the uniform hazard value suggested by the indian standard seismic code indian standard criteria for earthquake resistant design of structures fifth edition part i bureau of indian standards new delhi 2002 not only holistic treatment of earthquake catalog and seismogenic zones has been performed but also higher resolution in spatial distribution could be achieved the cov maps have been provided with the strong ground motion maps under various conditions to show the confidence in the results obtained results obtained in the present study would be helpful for risk assessment and other disaster mitigation related studies

on the occurrence trace element geochemistry and crystallization history of zircon from in situ ocean lithosphere we characterize the textural and geochemical features of ocean crustal zircon recovered from plagiogranite evolved gabbro and metamorphosed ultramafic host rocks collected along present day slow and ultraslow spreading mid ocean ridges mors the geochemistry of 267 zircon grains was measured by sensitive high resolution ion microprobe reverse geometry at the usgs stanford ion microprobe facility three types of zircon are recognized based on texture and geochemistry most ocean crustal zircons resemble young magmatic zircon from other crustal settings occurring as pristine colorless euhedral type 1 or subhedral to anhedral type 2 grains in these grains hf and most trace elements vary systematically with ti typically becoming enriched with falling ti in zircon temperature ti in zircon temperatures range from 1 040 to 660 c corrected for a tio2 0 7 a sio2 1 0 pressure 2 kbar intra sample variation is typically 60 150 c decreasing ti correlates with enrichment in hf to 2 wt while additional hf enrichment occurs at relatively constant temperature trends between ti and u y ree and eu eu exhibit a similar inflection which may denote the onset of eutectic crystallization the inflection is well defined by zircons from plagiogranite and implies solidus temperatures of 680 740 c a third type of zircon is defined as being porous and colored with chaotic cl zoning and occurs in 25 of rock samples studied these features along with high measured la cl s ca and fe and low sm la n ratios are suggestive of interaction with aqueous fluids non porous luminescent cl overgrowth rims on porous grains record uniform temperatures averaging 615 26 c 2sd n 7 implying zircon formation below the wet granite solidus and under water saturated conditions zircon geochemistry reflects in part source region elevated hree coupled with low u concentrations allow effective discrimination of 80 of zircon formed at modern mors from zircon in continental crust the geochemistry and textural observations reported here serve as an important database for comparison with detrital xenocrystic and metamorphosed mafic rock hosted zircon populations to evaluate provenance

seismic hazard map of turkey using the deterministic approach abstract because the instrumental records of turkey are far from being satisfactory for modeling the seismic hazard using the probabilistic approach an attempt was made in this study to accomplish it through the deterministic way in this regard all active faults of turkey small and large were evaluated together to obtain major fault systems then the procedure suggested by wells and coppersmith bull seismol soc am 4 1994 975 applied to those faults to obtain the maximum magnitude earthquake that they can generate to do this it was assumed that 1 3 of the total fault length would rupture to yield the maximum earthquake following that seven different attenuation relationships of the strong ground motion were utilized to calculate the maximum horizontal ground accelerations for the whole turkey at 0 2 intervals using the computer model tumdes written in basic programming language the computed peak ground acceleration pga values were contoured and the iso acceleration map based on sadigh et al seismol res lett 1 1997 180 relationship was selected as the new seismic hazard map of turkey on which the seismic zonations were determined as following pga 0 3 g zone 1 0 3 g

variety and origin of magmas on shatsky rise northwest pacific ocean 1 shatsky rise consists of thick 30 km maximum basaltic crust with various geochemical compositions geochemistry data indicate that four magma types exist on the plateau namely normal low ti high nb and u1349 types the normal type is the most abundant in volume and appears on all three large edifices of the plateau tamu ori and shirshov massifs composition of the normal type is similar to normal mid ocean ridge basalt n morb composition but with slight relative enrichment of the more incompatible elements the low ti type is distinguished from the normal type basalt by slightly lower ti content at a given mgo composition of the high nb type is characterized by distinctively high contents of incompatible trace elements u1349 type basalts are composed of more primitive and depleted compositions compared with the others the normal type basalts constitute 94 of the lava units of the oldest tamu massif and non normal types i e the other three types basalts comprise 57 on the younger ori massif implying that geochemical compositions may have become heterogeneous with time petrological examination demonstrates that compositions of the normal low ti and high nb type basalts evolved through fractional crystallization of olivine plagioclase and augite in shallow magma chambers 200 mpa model calculations of immobile trace elements estimate that the normal type basalt can be formed by 15 melting of a depleted mantle source in the presence of residual garnet this degree of melting is similar to n morb but the larger effect of residual garnet during petrogenesis implies that a greater depth of melting

accreted oceanic materials in japan abstract the phanerozoic circum pacific orogenic belts contain numerous ocean derived materials accreted through plate converging processes japanese islands in particular display various kinds of oceanic materials of different origins including fragments of seamounts oceanic reef limestone morb like rocks and oceanic mantle and pelagic sediments the compilation of these rocks in many subduction complexes of late permian to the present led to following conclusions accretion processes work effectively only for materials primarily composing the upper portion of subducting oceanic crust i e layer 1 and layer 2 many fragments of seamount with alkali basalt 600 hot spot seamount 26 oceanic reef limestone 291 morb like basalt 200 and numerous cherts more than 1000 are recognized as ancient oceanic materials accreted to the japanese islands however gabbros and mantle materials of layer 3 and lower parts of the oceanic lithosphere scarcely occur in subduction accretion complexes except for a few examples of back arc basin or fore arc origin accretion occurs episodically in southwest japan oceanic materials were accreted intermittently in 1 a end permian 2 b middle late jurassic 3 c late cretaceous times 4 d at ca 50 ma and 5 e in miocene times while in northeast japan and hokkaido this occurred in b middle late jurassic c late cretaceous and f early cretaceous times in contrast to the general belief on accretion of younger oceanic plates the majority of japanese subduction accretion complexes were formed during the subduction of plates up to 160 ma old the accretionary events in end permian and middle late jurassic times coincide with northward collision of ancient island arcs oceanic rises or seamount chains of hot spot origin with the asian continent accretion relevant to subduction of older plates may be controlled by the collision subduction process of these topographic reliefs on an oceanic plate in addition the chronological coincidence with the continent collision amalgamation between the sino korean and siberian platforms and between the sino korean and yangtze blocks also implies collision induced voluminous supply of elastics from back arc regions and its contribution to the formation of huge accretionary complexes accreted fragments of ancient seamounts are much smaller than the average size of modern seamounts this implies that most parts of a colliding seamount are not accreted but subducted together with the underlying oceanic crust to much deeper levels with respect to the metamorphic grades for japanese subduction complexes oceanic materials have less than 1 vol in the zeolite facies 15 20 in the prehnite pumpellyite metagraywacke facies and ca 30 in the greenschist glaucophane schist facies and albite epidote amphibolite fades this relationship indicates that the major process for landward accretion of oceanic materials is not off scraping or sedimentary mixing at the trench but underplating subcretion at much deeper levels of a subduction zone