source spectra and spectral attenuation of seismic waves from mexican earthquakes and evidence of amplification in the hill zone of mexico city it is well known that seismic waves are enormously amplified at lake bed sites with respect to hill zone sites in mexico city it has been suggested that even hill zone sites suffer amplification in this paper we use eight recent well recorded earthquakes to determine spectral attenuation of seismic waves and to quantify the suggested amplification in the hill zone results show that indeed spectral amplitudes at these sites are roughly 10 times greater than expected for sites outside mexico city at similar hypocentral distances this implies that lake bed sites are amplified by a factor of 100 to 500 at some frequencies between 0 2 to 0 7 hz the source spectra retrieved from the regression analysis agree well with those obtained from epicentral recordings alone for two of the largest earthquakes ms 8 1 and 7 6 whose seismic moments are well determined and whose source spectra can be patched in a very broad band of frequencies 0 015 to 20 hz we observe clear deviation from an 2 model the spectra at intermediate frequencies from about 0 05 to 2 hz show a sag whether the observed spectra deviate from an 2 model for events with ms 6 depends on the reliability of the reported long period seismic moments if they are considered reliable then these events also deviate from the model if however the reported seismic moments of smaller events are ignored then the observed spectra can be fitted well with the 2 model

insights into the causal relationship between slow slip and tectonic tremor in guerrero mexico similar to other subduction zones tectonic tremors tts and slow slip events sses take place in the deep segment of the plate interface in guerrero mexico however their spatial correlation in this region is not as clear as the episodic tremor and slip observed in cascadia and japan in this study we provide insights into the causal relationship between tts and sses in guerrero by analyzing the evolution of the deformation fields induced by the long term 2006 sse together with new locations of tts and low frequency earthquakes lfes unlike previous studies we find that the sse slip rate modulates the tt and lfe activity in the whole tremor region this means that the causal relationship between the sse and the tt activity directly depends on the stressing rate history of the tremor asperities that is modulated by the surrounding slip rate we estimated that the frictional strength of the asperities producing tremor downdip in the sweet spot is around 3 2 kpa which is 2 3 times smaller than the corresponding value updip in the transient zone partly explaining the overwhelming tremor activity of the sweet spot despite that the slow slip there is smaller based on the lfe occurrence rate history during the interlong term sse period we determined that the short term sses in guerrero take place further downdip about 35 km than previously estimated with maximum slip of about 8 mm in the sweet spot this new model features a continuum of slow slip extending across the entire tremor region of guerrero

lithospheric structure of the chaco and parana basins of south america from surface wave inversion surface wave data from a portable broadband array have been used to invert for the velocity structure of the crust and upper mantle beneath the chaco and parana basins of central south america the upper mantle velocity structure beneath the parana basin is cratonic in character whereas that beneath the chaco basin is tectonic or asthenospheric in character the surface wave analysis used broadband recordings from a subset of a 14 station array deployed in a roughly east west sawtooth arrangement along 20 s latitude with a total e w aperture of 1 400 km results from receiver function analysis as well as direct p wave regional travel time data were used in the inversions to help constrain moho depths and crust and upper mantle velocities s wave structure for the intracratonic parana basin was determined using interstation phase and group velocities for rayleigh waves fundamental and first higher mode and love waves fundamental mode only based on seven events with paths which traverse the eastern parana basin and one event with a path across the western parana basin the average moho depth in the eastern parana basin is 42 km the high velocity upper mantle lid has a maximum s wave velocity of 4 7 km s with no resolvable low velocity zone to at least 200 km depth this cratonic velocity structure indicates the presence of a lithospheric root beneath the parana basin despite emplacement of the parana plume the limited data from the western parana basin are consistent with a homogeneous upper mantle structure throughout the parana basin waveform inversion of fundamental mode and first higher mode rayleigh waves from a single subandean event was used to obtain estimates for pure path dispersion along propagation paths through the chaco basin and the western half of the parana basin the data were partitioned to isolate the partial path contribution of the phase and group velocities for the chaco basin the phase and group velocities from this somewhat sparse data set were inverted to obtain a velocity depth model for the chaco basin the distinguishing features of the chaco model consist of a rather shallow moho depth 32 km and low asthenospheric upper mantle s wave velocities about 4 2 km s with velocity increasing only slightly to about 4 3km s at 150 km depth

seismotectonics of western anatolia regional stress orientation from geophysical and geological data abstract available fault plane solutions of shallow earthquakes occurring in the central part of western anatolia were reviewed in order to determine the stress directions active in this region data on 66 shocks were used for numerical analysis with the p and t dihedra method some of these data being used in further determination of stress tensors through numerical methods despite uncertainties on depth determinations results were found consistent and in agreement with those of geological analyses independently carried out on recent and active faults selections from the data were adopted on the basis of areal distribution magnitude and depth of earthquakes variations in stress axes orientation with depth seem significant and related to increasing influence of crustal anisotropy near the surface the dominant trend of the present day extension in this region as indicated by the analysis of available earthquake mechanisms is nne ssw with a corresponding azimuth of the 3 axis n25 e the stress regime is extensional with dominant normal fault motions and increasing importance of strike slip faults from south to north this pattern of stress in western turkey is consistent with kinematic reconstructions indicating a westward and southwestward motion of anatolia and aegea relative to eurasia

seismicity and structure in central mexico evidence for a possible slab tear in the south cocos plate the morphology of the transition from flat to normal subduction in eastern central mexico is explored using intraslab earthquakes recorded by temporary and permanent regional seismic arrays observations of a sharp transition in slab dip near the abrupt end of the trans mexican volcanic belt tmvb suggest a possible slab tear located within the subducted south cocos plate the eastern lateral extent of a thin ultra slow velocity layer usl imaged atop the cocos slab in recent studies along the meso america subduction experiment array is examined here using additional data we find an end to this usl which is coincident with the western boundary of a zone of decreased seismicity and the end of the tmvb near the sharp transition in slab dip waveform modeling of the 2 d structure in this region using a finite difference algorithm provides constraints on the velocity and geometry of the slab s seismic structure and confirms the location of the usl analysis of intraslab seismicity patterns reveals clustering sudden increase in depth variable focal mechanism orientations and faulting types and alignment of source mechanisms along the sharp transition in slab dip the seismicity and structural evidence suggests a possible tear in the south cocos slab this potential tear together with the tear along the orozco fracture zone to the northwest indicates a slab rollback mechanism in which separate slab segments move independently allowing for mantle flow between the segments

global positioning system measurements of present day crustal movements in the arabia africa eurasia plate collision zone we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1994 at 54 sites extending east west from the caucasus mountains of southern russia georgia and armenia to the aegean coast of turkey and north south from the southern edge of the eurasian plate pontus block to the northern edge of the arabian platform viewed from a eurasia fixed reference frame sites on the northern arabian platform move n38 13 w at 20 3 mm yr roughly consistent with the velocity implied by nuvel 1a circuit closure n23 7 w at 24 2 mm yr the motion of arabia appears to be transferred directly to the region of turkey north of the suture however eastern turkey is characterized by distributed deformation while central western turkey is characterized by coherent plate motion involving westward displacement and counterclockwise rotation of the anatolian plate internal deformation within the central part of the anatolian plate is less than 2 mm yr the anatolian plate is decoupled from eurasia along the right lateral strike slip north anatolian fault naf this different response in eastern and western turkey to the collision of arabia may result from the different boundary conditions the hellenic arc forming a free boundary to the west and the asian continent and oceanic lithosphere of the black and caspian seas forming a resistant boundary to the north and east we derive a best fitting euler vector for anatolia eurasia motion of 29 2 0 8 n 32 9 0 4 1 3 0 1 m y the mapped surface trace of the naf corresponds well to a small circle about this pole the new euler vector implies an upper bound for naf slip rate of 30 2 mm yr i e assuming all relative motion is accommodated along the naf using the nuvel 1a euler vector for arabia eurasia and the gps euler vector for anatolia eurasia we determine an arabia anatolia euler vector of 31 2 n 45 2 e 0 9 0 1 m y and an upper bound on the east anatolian fault slip rate of 15 3 mm yr the aegean trough region of western turkey deviates significantly from coherent plate rotation in addition to rotating with anatolia this region shows roughly n s extension at a rate of 14 5 mm yr taken together with satellite laser ranging results along the hellenic arc the contemporary pattern of deformation indicates increasing motions toward the arc suggesting that the westward displacement and counterclockwise rotation of anatolia is driven both by pushing from the arabian plate and by pulling or basal drag associated with the foundering african plate along the hellenic subduction zone

shear velocity structure in the aegean area obtained by inversion of rayleigh waves summary the purpose of this work is to derive a 3 d tomographic image of the shear wave velocity structure of the crust uppermost mantle in the aegean area using the group velocities of rayleigh wave fundamental mode the database consists of 185 regional earthquakes recorded at broad band stations that were installed for a period of 6 month in the aegean area within the framework of a large scale experiment in a previous work karagianni et al 2002 an averaged group velocity has been determined using the method of frequency time analysis ftan for each epicentre station ray path and the data were used in order to determine the local group velocities for different periods over the area covered by the seismic ray paths taking into account additional resolution results obtained for the local group velocities a grid of 0 5 was adopted for the aegean area and a local dispersion curve was defined for each gridpoint more than 80 local dispersion curves were finally inverted using a non linear inversion approach deriving the corresponding 1 d shear velocity models the interpolation of these models resulted in a 3 d s wave tomographic image of the crust and uppermost mantle in the broader aegean area as expected as a result of the complex tectonic setting of the aegean area strong lateral variations of the s wave velocities of the crust and uppermost mantle of the studied area are found in the southern aegean sea as well as in a large part of the central aegean sea a thin crust of approximately 20 22 km is observed whereas the remaining aegean sea area exhibits a crustal thickness less than 28 30 km on the contrary a crustal thickness of 40 46 km is observed in western greece along the hellenides mountain range whereas in the eastern continental greece the crust has a typical thickness of approximately 30 34 km for shallow depths 10 km low s wave velocities are observed under the sedimentary basins of the north aegean sea the gulf of thermaikos axios basin and western greece at depths ranging from 10 to 20 km low s wave velocities are mainly found in western greece under peloponnesus as well as in rhodes this low velocity zone seems to extend along the hellenic arc and can be correlated to the hellenides mountain range and the alpine orogenesis in agreement with previous p wave tomographic results in the southern aegean sea very low s wave velocities 3 6 4 0 km s 1 are observed at depths of approximately 30 40 km just below the moho discontinuity while in the rest of the inner aegean sea and continental greece the uppermost mantle is characterized by velocities around 4 3 4 4 km s 1 this low velocity zone in the southern aegean sea can be associated with the high temperatures and the presence of significant percentage partial melt in the mantle wedge of the southern aegean subduction zone in agreement with previous studies

a study of crustal and upper mantle structure of northwestern turkey the crustal thickness and uppermost mantle p wave velocity at several seismic stations in northwestern turkey were estimated using the established travel time distance relation method the data suggest a flat layered crust of average thickness 28 4 3 45 km with an average uppermost mantle p wave velocity of 8 05 0 17 km s this is similar to results obtained for the north aegean sea and suggests a close structural link between the two areas

continental vs oceanic lithosphere beneath the eastern mediterranean sea implications from rayleigh wave dispersion measurements abstract tectonics of the eastern mediterranean are strongly influenced by subduction of oceanic lithosphere with slab pull as a prominent driving force the current distribution of remnants of oceanic lithosphere and the properties of african mantle lithosphere beneath the eastern mediterranean basin have been a matter of debate previous studies variously found continental as well as oceanic lithosphere in this region a set of 1 d s wave velocity models is determined in order to characterize the mantle lithosphere in the area between crete and the middle east for seven paths starting from cyprus and running to crete to anatolia as well as to the middle east broad band average phase velocity curves of the fundamental rayleigh mode are obtained in the frequency range of about 3 mhz to 90 mhz by a two station method in addition an east west oriented path crossing southern anatolia and a path running parallel to the dead sea fault zone are considered phase velocity curves are inverted for path average 1 d s wave velocity models resolution is investigated with the neighbourhood algorithm comparing the resulting 1 d models cold oceanic mantle lithosphere showing s wave velocities above 4 6 km s 1 can be distinguished from mantle lithosphere with low s wave velocities oceanic lithosphere is found west of cyprus beneath the herodotus basin as indicated by benioff zones it is subducting towards northwest in the southeastern aegean and towards northeast beneath southwestern anatolia to the east of cyprus the mantle lithosphere beneath the easternmost mediterranean sea shows low s wave velocities no indications for cold oceanic mantle lithosphere are found beneath the levant basin in the region of the dead sea fault zone and the levant basin the lithosphere asthenosphere boundary is located at shallow depths of about 60 km to 80 km the dsfz is situated in a region of thinned lithosphere underlain by an asthenosphere with anomalous low s wave velocities low s wave velocities beneath southern anatolia extend down to at least 150 km depth as expected for a back arc setting inferred moho depths vary for the different paths between 28 km and 41 km

s wave velocity structure of the crust and upper mantle under southeastern china by surface wave dispersion analysis abstract group velocity dispersion data of fundamental mode rayleigh and love waves for 12 wave paths within southeastern china have been measured by applying the multiple filter technique to the properly rotated three component digital seismograms from two seismic research observatory stations tato and chto the generalized surface wave inversion technique was applied to these group velocity dispersion data to determine the s wave velocity structures of the crust and upper mantle for various regions of southeastern china the results clearly demonstrate that the crust and upper mantle under southeastern china are laterally heterogeneous the southern china region south of 25 n and the eastern china region both have a crustal thickness of 30 km the eastern tibet plateau along the 100 e meridian has a crustal thickness of 60 km central china consisting mainly of the yangtze and sino korean platforms has a crustal thickness of 40 km a distinct s wave low velocity layer at 10 20 km depth in the middle crust was found under wave paths in southeastern china on the other hand no such crustal low velocity layer is evident under the eastern tibet plateau this low velocity layer in the middle crust appears to reflect the presence of a sialic low velocity layer perhaps consisting of intruded granitic laccoliths or possibly the remnant of the source zone of widespread magmatic activities known to have taken place in these regions since the late carboniferous

an estimate of shear wave q of the mantle wedge in mexico we utilize earthquake recordings at two broadband seismographs located on the coast of the gulf of mexico to estimate q of the mantle wedge from the data at a station situated in the laguna verde nuclear power plant lvig about 100 km northwest of veracruz and at the eastern edge of the mexican volcanic belt we estimate an upper bound of shear wave q of the mantle wedge q f 120 f 0 75 0 1 f 10 hz as compared with q f 251 f 0 58 for the average path through subducted slab and continental lithosphere curiously the estimated q of the mantle wedge at station scig which is located on the yucatan block is about the same as the average q in southern mexico there are several possible explanations for the difference 1 very few recordings at scig 2 a site effect at scig masking the effect of low q of the mantle wedge and 3 relatively high mantle q beneath the yucatan block the third possibility is supported by surface wave tomography that reveals a thick cold mantle lithosphere below the yucatan block and near absence of mantle lithosphere in the backarc region of central mexico a higher density of seismographs along the gulf coast is needed to resolve these issues our study predicts diminished ground motions at the laguna verde nuclear power plant if the seismic waves pass through the mantle wedge or traverse below the popocatepetl or orizaba volcanoes

active crustal deformation from the azores triple junction to the middle east the co seismic crustal deformation along the africa eurasia eurasia arabia plate boundary from the azores triple junction 30 w up to the karliova triple junction 41 e is examined based on the moment tensor summation of mainly post 1964 earthquakes with ms 5 0 strain rates range from 10 8 yr to 10 6 yr while values exceeding 10 7 yr were calculated for the back arc aegean area and for the north anatolian fault zone a remarkable stability in the azimuth of the component of compression and of extension is observed in the area that extends west of italy 17 e up to the azores triple junction along this region the deformation is taken up by compression along a mean direction of n140 with rates from 1 1 to 2 8 mm yr and by extension along a mean direction of n50 with rates from 2 4 to 12 0 mm yr at the gloria fault and in the surrounding area dextral strike slip motion occurs at a rate of 11 mm yr from sicily up to the eastern end of the hellenic arc the crust is compressed at azimuths in the range n20 n31 with an average value of 26 5 this compression is occurring at a rate of 1 21 mm yr with an average value of 9 8 mm yr in the back arc aegean area extension is occurring along a mean azimuth of n156 with a rate of 5 2 3 8 mm yr the average shortening rate along the convex side of the hellenic arc is 12 mm yr from the eastern end of the north anatolian fault 41 e up to the northern aegean trough extension along n68 n179 and compression along n158 n89 occurs which results in dextral strike slip motion the rate of extension reduces from east to west from 30 mm yr to 5 mm yr while the rate of compression reduces from 17 mm yr to 5 mm yr the northwards motion of arabia results in a n31 trending compression at a rate of 7 mm yr along the east anatolian fault zone

repeating seismicity in the shallow crust modulated by transient stress perturbations abstract recent studies have reported seismic phenomena that are modulated by small stress perturbations 10 kpa revealing their critically stressed nature such observations have been principally limited to plate interfaces with their occurrence linked to high fluid pore pressure in this study we report observations of nine repeating seismic sources in the shallow crust in guerrero mexico that emit events at rates comparable to other seismic phenomena in low stress environments testing their susceptibility to small stress perturbations we find that all nine sources appear to be modulated by mining activity tides and a large slow slip event mw 7 5 our results suggest that the fault conditions necessary for low effective stress seismicity can occur away from plate interfaces

seismic velocity and poisson s ratio tomography of the crust beneath east anatolia abstract eastern anatolia is a region in the early stages of continent continent collision and so provides a unique opportunity to study the early development of continental plateau located within the alpine himalayan fold thrust fault belt the anatolian plateau is geologically very complex with over half of the surface area covered with late cenozoic volcanics of diverse composition the plateau is also seismically active and is dissected by numerous seismogenic faults predominantly of strike slip motion in this study we determine 3 d tomographic images of the crust beneath eastern anatolia by inverting a large number of arrival time data of p and s waves from the obtained p and s wave velocity models we estimated the poisson s ratio structures for a more reliable interpretation of the obtained velocity anomalies our tomographic results are generally consistent with the major tectonic features of the region high p and s wave velocity anomalies are recognized near the surface while at deeper crustal layers low seismic wave velocities are widely distributed poisson s ratio exhibits significant structural heterogeneities compared to the imaged velocity structure the seismic activity is intense along highly heterogeneous zones and is closely associated with pre existing faults in the central and western parts of the study area results of the checkerboard resolution test indicate that the imaged anomalies are reliable features down to a depth of about 40 km the low velocity high poisson s ratio zones in the middle to lower crust are consistent with many geophysical observations such as strong sn attenuation low pn and sn velocity and the absence of mantle lid implying the presence of partial melt in the uppermost mantle

active tectonics of the north and central aegean sea summary in this paper we examine the connection between the westward motion of turkey relative to europe and the extension in and around the aegean sea the principal new data available since the last attempt to synthesize the tectonics of this region by mckenzie 1978 are much improved focal mechanisms of earthquakes constrained by p and sh body wave modelling as well as by first motions these mechanisms show that the faulting in the western part of the aegean region is mostly extensional in nature on normal faults with a nw to wnw strike and with slip vectors directed nnw to nne there is evidence from palaeomagnetism that this western region rotates clockwise relative to stable europe in the central and eastern aegean and in nw turkey distributed right lateral strike slip is more prevalent on faults trending ne to ene and with slip vectors directed ne palaeomagnetic data in this eastern region is more ambiguous but consistent with very small or no rotations in the northern part and possibly anticlockwise rotations relative to europe in the south the strike slip faulting that enters the central aegean from the east appears to end abruptly in the sw against the nw trending normal faults of greece the kinematics of the deformation is controlled by three factors the westward motion of turkey relative to europe the continental collision between nw greece albania and the apulia adriatic platform in the west and the presence of the hellenic subduction zone to the south as the right lateral slip on the north anatolian fault enters the aegean region it splays out becoming distributed on several parallel faults the continental shortening in nw greece and albania does not allow the rotation of the western margin of the region to be rapid enough to accommodate this distributed e w right lateral shear and thus leads to e w shortening in the northern aegean which is compensated by n s extension as the southern aegean margin can move easily over the hellenic subduction zone the dynamics of the system once initiated is self sustaining being driven by the high topography in eastern turkey and by the roll back of the subducted slab beneath the southern aegean the geometry of the deformation resembles the behaviour of a system of broken slats attached to margins that rotate in spite of its extreme simplicity a simple model of such broken slats is able to reproduce quantitatively most of the features of the instantaneous velocity field in the aegean region including the slip vectors and nature of the faulting in the eastern and western parts the senses and approximate rates of rotation the overall extensional velocity across the aegean and the distribution of strain rates as seen in the seismicity and topography or bathymetry and using geodetic measurements as part of this study we re examined the relation between the surface faulting and the focal parameters determined seismologically for the three large 1981 gulf of corinth earthquakes and reassessed the evidence for associating particular earthquakes in the sequence with observed surface faulting an important result is that in one of the events there is a resolvable discrepancy between the slip vector measured at the surface and that determined from the seismic body waves

structure and anisotropy of the mexico subduction zone based on rayleigh wave analysis and implications for the geometry of the trans mexican volcanic belt 1 we develop a three dimensional model of shear wave velocity and anisotropy for the mexico subduction zone using rayleigh wave phase velocity dispersion measurements this region is characterized by both steep and flat subduction and a volcanic arc that appears to be oblique to the trench we give a new interpretation of the volcanic arc obliqueness and the location of the tzitzio gap in volcanism based on the subduction morphology we employ the two station method to measure rayleigh phase velocity dispersion curves between periods of 16 s to 171 s the results are then inverted to obtain azimuthally anisotropic phase velocity maps and to model 3 d variations in upper mantle velocity and anisotropy our maps reveal lateral variations in phase velocity at all periods consistent with the presence of flat and steep subduction we also find that the data are consistent with two layers of anisotropy beneath mexico a crustal layer with the fast directions parallel to the north american absolute plate motion and a deeper layer that includes the mantle lithosphere and the asthenosphere with the fast direction interpreted in terms of toroidal mantle flow around the slab edges our combined azimuthal anisotropy and velocity model enables us to analyze the transition from flat to steep subduction and to determine whether the transition involves a tear resulting in a gap between segments or is a continuous deformation caused by a lithospheric flexure our anisotropy results favor a tear which is also consistent with the geometry of the volcanic belt

crustal s wave structure beneath eastern black sea region revealed by rayleigh wave group velocities abstract in this study the crustal s wave structure beneath the eastern black sea region including the eastern black sea basin ebsb and eastern pontides ep has been revealed using inversion of single station fundamental mode rayleigh wave group velocities in the period range of 4 40 seconds we used digital broadband recordings of 13 regional earthquakes that recently occurred in the easternmost ebsb recorded at stations of the kandilli observatory and earthquake research institute koeri the average group velocity dispersion curves were generated from 26 paths for the ebsb and 16 paths for the ep and they were inverted to determine the average 1 d shear wave structure of the region we have created a pseudo section roughly depicting the crustal structure of the region based on the group velocity inversion results of all station earthquake paths the thickness of the sedimentary layer reaches 12 km in the center of ebsb vs 2 5 3 1 km s and decreases 4 km in the ep there is a thin sedimentary layer in the ep vs 2 7 km s a consolidated thin crust that exists in the ebsb possesses a high seismic velocity vs 3 8 km s while a thin 26 km and transitional crust exists beneath the ebsb a thick about 42 km continental crust exists beneath the ep where the conrad is clearly seen at about a 24 km depth thick continental crust in the ep region is clearly distinguished from a gradational velocity change vs 3 4 3 8 km s the moho dips approximately southwards and the vs velocity 4 25 4 15 km s beneath the moho discontinuity decreases from the ebsb to the ep in the n s direction this may be an indication of a southward subduction

estimation of ground motion in mexico city from a repeat of the m 7 0 acambay earthquake of 1912 abstract the acambay earthquake of 1912 m 7 0 which occurred in the central trans mexican volcanic belt ctmvb about 100 km west northwest of mexico city has been thought to be a critical scenario event in the estimation of seismic hazard of the city we use seismograms of two small earthquakes located near actopan 15 december 2003 18 may 2010 and recorded at station cuig a hill zone site in mexico city as empirical green s functions egfs for the acambay region because actopan like acambay is situated in the ctmvb and both are located at about the same distance from cuig the use of the recordings of the actopan earthquakes as egfs is partly justified we first analyze data of the two small earthquakes at a local station dhig to estimate their seismic moment and stress drop as there is considerable uncertainty in the estimated stress drops of the two events we choose a reasonable range of values for them and apply a technique of random summation of egfs to simulate ground motion at cuig from a postulated m w 7 earthquake the estimated geometric mean horizontal peak ground acceleration pga and peak ground velocity pgv at cuig range from 2 7 to 9 7 cm s 2 and from 1 1 to 3 0 cm s respectively ground motion maps for the entire city are presented using a simulated trace at cuig and the known transfer functions of many sites within the city the results are consistent with reported seismic intensities in mexico city and pga and peak ground displacement pgd at a 2 s period at the seismic station of tacubaya during the acambay earthquake estimated ground motions suggest that a repeat of the event does not present significant hazard to mexico city

low frequency earthquakes in the mexican sweet spot 1 we use data from the meso america subduction experiment to detect and locate low frequency earthquakes lfes in the mexican subduction zone we use visually identified templates to perform a network waveform correlation search that produced 17 000 robustly detected lfes that form 15 distinct families stacking an lfe family s corresponding detections results in seismograms with high signal to noise ratios and clear p and s wave arrivals we use these travel times to locate the sources the resulting locations superpose a previously identified region of permanent non volcanic tremor nvt activity husker et al 2012 called this region a sweet spot suggesting that the local conditions are adequate to continuously generate nvt the lfe hypocenters have been located at a depth of 40 45 km in an area that is surrounding the upper slab plate interface we characterize their focal mechanisms by comparing their stacked seismograms to synthetic seismograms this analysis reveals a common low dipping focal mechanism

horizontal subduction and truncation of the cocos plate beneath central mexico 1 based on analysis of data from a trans mexico temporary broadband seismic network centered on mexico city we report that the subducting cocos plate beneath central mexico is horizontal and tectonically underplates the base of the crust for a distance of 250 km from the trench it is decoupled from the crust by a very thin low viscosity zone the plate plunges into the mantle near mexico city but is truncated at a depth of 500 km probably due to an e w propagating tear in the cocos slab unlike the shallow slab subduction in peru and chile there is active volcanism along the trans mexican volcanic belt tmvb that lies much further inland than regions to either side where subduction dip is not horizontal geodynamical modeling indicates that a thin weak layer such as imaged by the seismic experiment can explain the flat subduction

regional wave propagation in turkey and surrounding regions this paper was published by the american geophysical union agu copyright 2000 agu see also http www agu org journals gl gl0003 1999gl008375 pdf 1999gl008375 pdf http atlas geo cornell edu turkey publications gok et al 2000 htm

variations in the crustal structure beneath western turkey summary we use teleseismic receiver functions to investigate the crustal structure at two locations in westernturkey using seismic data recorded on small arrays of temporary broad band seismographs the results from these analyses are compared with receiver function results from the gdsn station anto on the anatolian plateau in central turkey the crust is 30 km thick in the region of western turkey where active normal faulting reveals present day extension in the upper crust and alkali basaltic volcanism reveals recent extension within the subcrustal lithosphere the crust is 34 km thick further east where crustal extension is still evident but less pronounced in the anatolian plateau which is not currently extending the crust is 38 km thick the level of extension estimated from these measurements of crustal thickness implies a b factor of 1 2 this value agrees with the amount of extension estimated in the upper crust from the integrated seismic strain rate b factor of 1 3 from surface faulting b factor of 1 25 and from the amount of extension in the subcrustal lithosphere estimated from the volcanism b factor 2 all indicating that the extension is approximately uniformly distributed vertically throughout the lithosphere the moho transition in this region appears to thin slightly as the degree of extension increases westwards

crust and upper mantle structure of north africa europe and the middle east from inversion of surface waves summary we estimate the crust and upper mantle seismic velocity structure in north africa southern europe and the middle east using our surface wave dispersion tomography results from a previous study the surface wave tomography study provided high resolution coverage across the region from more than 6800 rayleigh and 3800 love wave paths over the period range from 10 60 s we have also included additional tomography results from 65 to 120 s the tomography model provides average rayleigh and love wave dispersion curves for each 2 2 block in the region we use these results to determine velocity structure by fitting the synthetic curves from simplified crust and upper mantle models to the tomographic data for each block via a grid search the grid search technique was chosen in order to map out the complete error space and to easily incorporate other data sets or a priori information the initial grid search is conducted over sediment thickness crustal velocity crustal thickness and upper mantle velocity to keep the grid search computationally reasonable other parameters are held fixed sediment velocity poisson s ratios and density despite the well known trade off between crustal thickness and crustal velocity that occurs when fitting surface wave data the initial grid search is quite successful in retrieving first order features such as ocean continent crustal thickness differences and crustal thickening in all but the oldest orogenic zones we can resolve major sedimentary basins active ridges and see differences based on crustal age e g archean cratons vs phanarozoic crust to better control the trade off inherent in fitting group velocity curves we also explore using other information to better constrain the grid searches in particular we use a global sediment depth and velocity model to fix those parameters and a regional pn tomography to constrain the upper mantle velocities in this constrained grid search we vary crustal thickness upper and lower crustal velocities and upper mantle poisson s ratio this produces a somewhat better fit to the dispersion curves while simultaneously satisfying several datasets while there are many similarities in the unconstrained and constrained model results overall we believe the constrained grid search model is a better representation of reality finally we compare and contrast our preferred velocity model with a number of other published models for this region within the resolution of the various models they appear to be similar

transitional continental oceanic structure beneath the norwegian sea from inversion of surface wave group velocity data summary we have analysed the fundamental mode of love and rayleigh waves generated by 12 earthquakes located in the mid atlantic ridge and jan mayen fracture zone using the multiple filter analysis technique we isolated the rayleigh and love wave group velocities for periods between 10 and 50 s the surface wave propagation paths were divided into five groups and average group velocities calculated for each group the average group velocities were inverted and produced shear wave velocity models that correspond to a quasi continental oceanic structure in the greenland norwegian sea region although resolution is poor at shallow depth we obtained crustal thickness values of about 18 km in the norwegian sea area and 9 km in the region between svalbard and iceland the abnormally thick crust in the norwegian sea area is ascribed to magmatic underplating and the thermal blanketing evect of sedimentary layers maximum crustal shear velocities vary between 3 5 and 3 9 km s 1 for most paths an average lithospheric thickness of 60 km was observed which is lower than expected for oceanic type structure of similar age we also observed low shear wave velocities in the lower crust and upper mantle we suggest that high heat flow extending to depths of about 30 km beneath the surface can account for the thin lithosphere and observed low velocities anisotropy coeycients of 1 5 per cent in the shallow layers and 7 per cent in the upper mantle point to the existence of polarization anisotropy in the region

geometry and seismic properties of the subducting cocos plate in central mexico the geometry and properties of the interface of the cocos plate beneath central mexico are determined from the receiver functions rfs utilizing data from the meso america subduction experiment mase the rf image shows that the subducting oceanic crust is shallowly dipping to the north at 15 for 80 km from acapulco and then horizontally underplates the continental crust for approximately 200 km to the trans mexican volcanic belt tmvb the crustal image also shows that there is no continental root associated with the tmvb the migrated image of the rfs shows that the slab is steeply dipping into the mantle at about 75 beneath the tmvb both the continental and oceanic moho are clearly seen in both images and modeling of the rf conversion amplitudes and timings of the underplated features reveals a thin low velocity zone between the plate and the continental crust that appears to absorb nearly all of the strain between the upper plate and the slab by inverting rf amplitudes of the converted phases and their time separations we produce detailed maps of the seismic properties of the upper and lower oceanic crust of the subducting cocos plate and its thickness high poisson s and vp vs ratios due to anomalously low s wave velocity at the upper oceanic crust in the flat slab region may indicate the presence of water and hydrous minerals or high pore pressure the evidence of high water content within the oceanic crust explains the flat subduction geometry without strong coupling of two plates this may also explain the nonvolcanic tremor activity and slow slip events occurring in the subducting plate and the overlying crust

structure of central and southern mexico from velocity and attenuation tomography the 3d v p v p vs p and s wave attenuation structure of the cocos subduction zone in mexico is imaged using earthquakes recorded by two temporary seismic arrays and local stations direct p wave arrivals on vertical components and direct s wave arrivals on transverse components from local earthquakes are used for velocity imaging relative delay times for p and pkp phases from teleseismic events are also used to obtain a deeper velocity structure beneath the southern seismic array using a spectral decay method we calculate a path attenuation operator t for each p and s waveform from local events and then invert for 3d spatial variations in attenuation q p 1 and q s 1 inversion results reveal a low attenuation and high velocity cocos slab the slab dip angle increases from almost flat in central mexico near mexico city to about 30 in southern mexico near the isthmus of tehuantepec high attenuation and low velocity in the crust beneath the trans mexico volcanic belt correlate with low resistivity and are probably related to dehydration of the slab and melting processes the most pronounced high attenuation low v p and high v p v s anomaly is found in the crust beneath the veracruz basin a high velocity structure dipping into the mantle from the side of gulf of mexico coincides with a discontinuity from a receiver functions study and provides an evidence for the collision between the yucatan block and mexico in the miocene

a surface wave dispersion study of the middle east and north africa for monitoring the comprehensive nuclear test ban treaty we present results from a large scale study of surface wave group velocity dispersion across the middle east north africa southern eurasia and the mediterranean our database for the region is populated with seismic data from regional events recorded at permanent and portable broadband three component digital stations we have measured the group velocity using a multiple narrow band filter on deconvolved displacement data overall we have examined more than 13 500 seismograms and made good quality dispersion measurements for 6817 rayleigh and 3806 love wave paths we use a conjugate gradient method to perform a group velocity tomography our current results include both love and rayleigh wave inversions across the region for periods from 10 to 60 seconds our findings indicate that short period structure is sensitive to slow velocities associated with large sedimentary features such as the mediterranean sea and persian gulf we find our long period rayleigh wave inversion is sensitive to crustal thickness such as fast velocities under the oceans and slow along the relatively thick zagros mts and turkish iranian plateau we also find slow upper mantle velocities along known rift systems accurate group velocity maps can be used to construct phase matched filters along any given path the filters can improve weak surface wave signals by compressing the dispersed signal the signals can then be used to calculate regionally determined m s measurements which we hope can be used to extend the threshold of m b m s discriminants down to lower magnitude levels other applications include using the group velocities in the creation of a suitable background model for forming station calibration maps and using the group velocities to model the velocity structure of the crust and upper mantle

propagation characteristics of short period sn and lg in the middle east abstract we present propagation characteristics of the short period regional seismic phases sn and lg for the middle east digital waveform data from the iranian long period array ilpa and the global seismic network gsn stations abkt alibek turkmenistan anto ankara turkey keg kottamya egypt and kiv kislovodsk georgia were used in this study three component rotated seismograms were bandpass filtered 0 5 to 5 0 hz and examined for the presence and strength amplitude of sn and lg relative to the pn and pg phases the short period sn and lg waveforms show great variability sn propagates efficiently for paths crossing the mediterranean black and caspian seas as well as for paths passing north of the greater caucasus alborz and kopet dag mountains generally sn is not observed or propagates inefficiently for paths with segments beneath the turkish plateau and northern iranian plateau consistent with a previous study by kadinsky cade et al 1981 this study finds that the zone of inefficient sn propagation coincides with a zone of low pn velocities pn tomography lg is consistently not observed for paths crossing the mediterranean black and caspian seas lg propagates efficiently for paths crossing the northern arabian shield generally lg propagates efficiently for paths contained within the turkish iranian plateau paths in the middle east greater than about 2000 km consistently show no or little lg energy the correspondence of zones of inefficient sn propagation and low pn velocities suggests that high temperatures and partial melt lie at shallow depths in the upper mantle beneath the turkish plateau and northern iranian plateau the presence of water presumably due to subduction of hydrated oceanic crust lowers the solidus temperature and enhances partial melt lg is blocked by oceanic crustal structures as well as by structural and topographic variations associated with tectonic boundaries

crustal and uppermost mantle structures in the frontal himalaya and indo gangetic basin using surface wave tectonic implications abstract characteristics of dispersion curves of rayleigh and love waves of 2005 kashmir earthquake and its aftershocks are utilized to investigate the sub surface structural variations within the northern margin of the indian continent i e indo gangetic plains and the frontal part of the northwestern himalaya surface waves of these earthquakes recorded in the broad band seismometers bbs installed at ajmer delhi and shimla were used for this investigation estimated group velocities along three paths from earthquake source region to these stations are in the range of 2 17 km s to 3 94 km s which are sufficient to investigate the crustal and uppermost mantle structures paths covering northern margin of the indian continent has very low group velocities for periods less than 10 s that indicate presence of thick sediments high differences are observed between love and rayleigh wave group velocities for the paths crossing himalayan wedge that can be ascribed to the effect of anisotropy due to india eurasia collision the inversion of dispersion curves was performed to investigate sub surface shear wave velocity structure and variation of anisotropy with depth for crust and uppermost mantle a 6km thick sediments divided into two layers unconsolidated and consolidated are seen in the indo gangetic plain deposited above underthrusting indian plate the conrad and moho depths increase from ajmer the southernmost station in the igp to shimla the station lying in the himalayan wedge this shows the dipping geometry of the indian plate the average moho depth along these paths from earthquake source to ajmer station is 42 5 km to delhi station is 44 km and to shimla station is at 46 km average values of conrad depth for these ray paths are 18 5 km 19 5 km and 26 5 km respectively the s wave velocity along ajmer path is higher than that along the other two paths this may be due to lateral heterogeneity of the crust and mantle for the study area frontal western himalaya is anisotropic in nature whereas the igp region is not anisotropy effect in the western himalaya is most pronounced in the lower crustal material of the underthrusted indian plate it is quite large in the uppermost mantle below the frontal himalayan region we infer that anisotropy in the lower crust and uppermost mantle could be due to development of preferably oriented folds faults and fractures and possible reorientation of crystals as a consequence of ongoing deformation caused by continent continent collision

seismic evidence of nonlinear crustal deformation during a large slow slip event in mexico repeated cross correlations of ambient seismic noise indicate a long term seismic velocity change associated with the 2006 m7 5 slow slip event sse in the guerrero region mexico because the sse does not radiate seismic waves the measured velocity change cannot be associated with the response of superficial soil layers to strong shaking as observed for regular earthquakes the perturbation observed maximized at periods between 7 s and 17 s which correspond to surface waves with sensitivity to the upper and middle crust the amplitude of the relative velocity change 10 3 was much larger than the volumetric deformation 10 6 at the depths probed 5 20 km moreover the time dependence of the velocity perturbation indicated that it was related to the strain rate rather than the strain itself this suggests that during strong slow slip events the deformation of the overlying crust shows significant nonlinear elastic behavior

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

generation of talc in the mantle wedge and its role in subduction dynamics in central mexico geophysical evidence shows the presence of low seismic velocity material at the surface of slabs in subduction zones in the central mexican subduction zone this appears as a thin 4 km low velocity zone that absorbs nearly all of the strain the p to s velocity ratio as a function of s wave velocity distinguishes among the various candidate hydrous low strength minerals the thin layer in the flat slab region is most consistent with a layer showing enrichment in talc overlying normal morb like gabbro based on available thermodynamic data for equilibria for talc its generation at the trench is nearly impossible and hence we propose it originates from the mantle wedge during the slab flattening process coupled with trench rollback the evolution of this low strength zone has important implications for the dynamics of the slab flattening process as well as the geochemistry of the mantle wedge and arc in central mexico

crustal structure variation in western turkey inferred from the receiver function analysis abstract we have used receiver function analysis employing teleseismic waveforms to investigate variations in crustal and upper mantle velocity structure beneath the western turkey the genetic algorithm is adopted to avoid the inherent non uniqueness problems of the inversion the total of 50 teleseismic waveforms recorded by 25 permanent stations is analyzed and the selected records of earthquakes distributed in three quadrants from each seismic station in the years from 2007 to 2008 are analyzed 2 d images of moho variation beneath the western turkey along two profiles are 700 and 300 km long and extended from the aegean sea coast to the central anatolia and southeastern anatolia respectively are estimated the depth migrated receiver function showed almost well resolved moho for the two profiles although the limited quantity of data is used to short periods the resolution and confidence level is not so bad for the one profile that extended from the aegean sea coast to central anatolia we obtain moho depths between 25 and 35 km on the other profile along the western coast the moho depths range from 20 and 30 km shear wave speed was found to vary between 3 3 km s and 3 7 km s in the lower crust and between 4 1 km s and 4 4 km s uppermost mantle we concluded that the moho depth is increasing from western anatolia to central anatolia considering inversion results and 2 d depth migrated receiver functions

a new intracontinental transcurrent structure the central anatolian fault zone turkey abstract recent neotectonic studies including remote sensing aerial photographs geological field mapping on various scales and measured stratigraphic section substantiate the existence of a large sinistral intracontinental transcurrent structure which we call the central anatolian fault zone cafz this is an approximately 730 km long 2 km to 80 km wide ne trending active sinistral strike slip fault zone that cuts across the anatolian plateau between duzyayla in the northeast and anamur county in the southwest it continues onward beneath the eastern mediterranean sea and determines the boundary of the antalya and adana basins as far as to the west of cyprus the cafz is a very young neotectonic structure it resulted from the reactivation and propagation of an older paleotectonic structure the so called ecemi s corridor in both nne and sw directions across the inner tauride suture in the plio quaternary times based on geometric discontinuities the cafz is divided into 24 segments each of them is characterized by a number of strike slip morphotectonic features reflecting recent motions the easternmost part of the anatolian platelet is being deformed internally by several dextral to sinistral intraplate strike slip faults these are the lake salt fault zone lsfz the salanda fault sf the cafz the goksu yazyurdu fault zone gyfz and the malatya ovacik fault zone mofz they take up lesser motion and are younger than boundary faults of the anatolian platelet the gyfz and mofz splay from the natf cut across the anatolian platelet and then meet to the eatf whereas other faults are confined into the anatolian platelet and seem to be independent structures however present day structural pattern of all these intraplate faults and boundary faults of the anatolian platelet indicates a regional strain pattern of nnw sse directed shortening and ene wsw directed extension and they seem to have developed to accommodate northward motion of the arabian plate since late early pliocene times

biogenic and lithogenic magnetic minerals in atlantic and pacific deep sea sediments and their paleomagnetic significance the carrier of the natural magnetization of deep sea sediments was characterized by mineralogical electron microscopic and rock magnetic investigations magnetic single domain sd and pseudo single domain psd particles which are most important for the stable remanent magnetization were separated from the magnetic coarse fraction and concentrated as magnetic fine fraction the magnetic coarse fraction consists of lithogenic magnetite and titanomagnetite which often contains exsolution lamellae of ilmenite both minerals are partially maghematized and occur isolated in the sediment or embedded in rock particles in regionally different concentrations the magnetic fine fraction consists of lithogenic magnetite and titanomagnetite and biogenic magnetite magnetofossils fossil bacterial magnetosomes the latter generally maghematized

seismic velocity and q model for the shallow structure of the arabian shield from short period rayleigh waves the shear velocity and q sub beta structure for the upper 1 km in different tectonic regions of the arabian shield have been investigated using high frequency vertical component records of rayleigh waves 1 20 hz which were recorded at source to receiver separations 55 80 km during a deep seismic refraction survey group and phase velocities of the fundamental and first higher modes were inverted for the shear wave velocity structure rayleigh wave attenuation coefficients were determined from the decay of the amplitude spectrum of the fundamental mode and used to invert for the q sub beta structure models derived from the data were tested by calculating synthetic seismograms for the fundamental and the first higher modes from surface wave theory with a center of compression used to represent the source both band pass filtered step and dirac delta source time functions were tested modeling indicates that the shear wave velocity of the shield increases from 2 6 km s to 3 4 km s in the upper 400 m of the crust q sub beta increases from 30 in the upper 50 m to 150 at 500 m depth the underlying material has a q sub beta of 400 500 for the outcropping igneous rocks such as granite and may reach values higher than 700 for the metamorphic green schist rock a band pass filtered dirac delta source time function produces the synthetic that is the best fit with observations

comparative study of tectonic tremor locations characterization of slow earthquakes in guerrero mexico deep tectonic tremor in guerrero mexico has been observed using dense temporal seismic networks i e the meso american subduction experiment and guerrero gap experiment g gap arrays during two different time periods we apply a set of seismic waveform analysis methods to these data sets to constrain the locations of tremors and determine the associated moment tensors first we detect and locate the tremors next very low frequency vlf signals are identified by stacking waveform data during tremor bursts and their moment tensors are determined finally to better investigate the link between tremors and vlf earthquakes we detect vlf events using a matched filtering algorithm to search continuous seismic records none of the 11 vlf events detected by this method occurred in the absence of tremor bursts suggesting they are indeed part of the same phenomena unlike previous investigations our results for the g gap period reveal that downdip tremor activity i e in the so called sweet spot is segmented into two patches separated by 40 km in the along trench direction indicating possible variations in the geometry of the plate interface and or slab effective pressure moment tensors of vlf signals are consistent with shear slip on the near horizontal plate interface but source depths are about 5 km deeper than the established plate interface the slip directions of the vlf events are slightly 10 counterclockwise of the plate convergence direction indicating that strain energy promoting left lateral strike slip motion may accumulate in the continental crust during the interseismic period

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

the relative density to shear velocity scaling in the uppermost mantle we perform inversions of gravity data geopotential model egm96 and seismic tomography model s16rlbm for the scaling factor which relates relative density anomalies to relative s wave velocity anomalies the gravity data and tomographic model are anti correlated below continents down to a depth of z 200 km this anti correlation is not present below oceans except for smoothness which is controlled by a damping factor no a priori information is added to the inversion data are filtered between degrees 11 and 16 of the spherical harmonic expansion this spectral window is well suited for the study of intermediate size 2000 4000 km anomalies in the uppermost mantle calculations are made separately for sub continental and sub oceanic mantle the sub continental and sub oceanic scaling factors are significantly different at depths shallower than 260 km in both cases the magnitude of is around 0 05 the sub continental scaling factor has a positive root down to z 220 km whereas the sub oceanic scaling factor yields positive values down to z 140 km only at depth shallower than 350 km models of do not depend on the damping factor or the viscosity model at depths greater than 350 km the resolution of z decreases significantly and low degrees 2 4 add information from large scale anomalies and from the lower mantle as a result the shape and values of for 2 16 and 11 16 are significantly different at depths greater than 350 km a possible explanation of the discrepancies between the sub continental and sub oceanic scaling factor is that intermediate scale anomalies are more important in the continental uppermost mantle than in the oceanic uppermost mantle 2001 elsevier science b v all rights reserved

scattering of teleseismic body waves by the lateral crustal heterogeneity at the pacific trench of mexico we examine the scattered field generated at the pacific trench of mexico upon the incidence of teleseismic body waves and the waveguide properties associated with the structure of the subduction zone in this study we analyze seismic records from a portable array perpendicular to the trench that show a distinctive phase with a phase velocity of graphic 1 following body wave phases this signal is better observed following phases with high incident angles such as ps sp and ss arriving from the ocean side of the trench and for events at teleseismic distances with magnitudes larger than m w 7 0 although weak scattered signals were detected for events down to m w 6 2 and for direct p and s phases we found that the lateral transition between the dipping slab and continental crust with an inclined boundary formed by the subducting slab at the trench generates a strong discontinuity that scatters seismic waves generating a secondary field with amplitude comparable to the incident wave this phase appears for incident body wave arrivals with characteristic wavelength comparable to the thickness of the continental crust analysis of the observed scattered field shows that the trapped waves are vertically polarized surface waves numerical modeling suggests that the impedance contrast at the trench and the geometry of the subducting slab form a waveguide like structure that efficiently generates and transmits trapped seismic waves along the continental margin 1 embed inline graphic 1 gif

anatolian surface wave evaluated at geofon station isp isparta turkey abstract we have studied seismic surface waves of 255 shallow regional earthquakes recently recorded at geofon station isp isparta turkey and have selected these 52 recordings with high signal to noise ratio for further analysis an attempt was made by the simultaneous use of the rayleigh and love surface wave data to interpret the planar crust and uppermost mantle velocity structure beneath the anatolian plate using a differential least square inversion technique the shear wave velocities near the surface show a gradational change from approximately 2 2 to 3 6 km s 1 in the depth range 0 10 km the mid crustal depth range indicating a weakly developed low velocity zone has shear wave velocities around 3 55 km s 1 the moho discontinuity characterizing the crust mantle velocity transition appears somewhat gradual between the depth range 25 45 km the surface waves approaching from the northern anatolia are estimated to travel a crustal thickness of 33 km whilst those from the southwestern anatolia and part of east mediterranean sea indicate a thicker crust at 37 km the eastern anatolia events traveled even thicker crust at 41 km a low sub moho velocity is estimated at 4 27 km s 1 although consistent with other similar studies in the region the current velocities are considerably slower than indicated by the preliminary reference earth model prem in almost all depth ranges

rayleigh wave group velocity tomography in the aegean area data from a large scale experiment which took place in greece during the period january july 1997 have been used to investigate the structure of the aegean area using surface waves during this experiment 30 seismic broadband instruments were deployed throughout the whole greek area additional data during the period 1996 2000 from other temporary networks have been included in the dataset one hundred eighty five events with magnitudes 4 0vmwv5 5 recorded by these stations have been collected and processed the individual dispersion curves of the group velocity of rayleigh waves for each source station path have been calculated producing more than 700 paths covering the studied region these curves have been used to determine rayleigh group velocity maps using a 2d tomography method on the basis of a regionalization of the dispersion measurements local averaged dispersion curves have been obtained and non linearly inverted to obtain models of shear wave velocity versus depth since the dispersion curves in the period range 5 svtv30 s are mostly affected by the crustal structure the model velocities are estimated down to a depth of approximately 35 45 km the results from the non linear hedhehog inversion as applied to a few local dispersion curves show a crustal thickness of approximately 32 km for the northern aegean sea and a relatively thin crust of approximately 22 24 km for the southern aegean sea d 2002 elsevier science b v all rights reserved

seismic imaging of the cocos plate subduction zone system in central mexico broadband data from the meso america subduction experiment mase line in central mexico were used to image the subducted cocos plate and the overriding continental lithosphere beneath central mexico using a generalized radon transform based migration our images provide insight into the process of subducting relatively young oceanic lithosphere and its complex geometry beneath continental north america the converted and reverberated phase image shows complete horizontal tectonic underplating of the cocos oceanic lithosphere beneath the north american continental lithosphere with a clear image of a very thin low velocity oceanic crust 7 8 km which dips at 15 20 degrees at acapulco then flattens approximately 300 km from the middle america trench farther inland the slab then appears to abruptly change from nearly horizontal to a steeply dipping geometry of approximately 75 degrees underneath the trans mexican volcanic belt tmvb where the slab bends underneath the tmvb the migrated image depicts the transition from subducted oceanic moho to continental moho at 230 km from the coast neither of which were clearly resolved in previous seismic images the deeper seismic structure beneath the tmvb shows a prominent negative discontinuity fast to slow at 65 75 km within the upper mantle this feature which spans horizontally beneath the arc 100 km may delineate the top of a layer of ponded partial melt

the horizontal velocity field in the deforming aegean sea region determined from the moment tensors of earthquakes we use the spatial distribution of seismic moment tensors of earthquakes in the aegean region over the time interval 1909 1983 to recover a continuous horizontal velocity field that describes the overall deformation of the lithosphere at large length scales the calculated velocity field is dominated by two effects 1 an e w right lateral shear of the eastern aegean related to motion on the north anatolian fault becoming distributed as it enters the aegean and 2 a n s extension probably related to the sinking of the slab in the hellenic trench the southern part of the central aegean is found to be moving in a sw direction relative to europe at a rate of about 30 mm yr probably a lower bound with an error of around 10 mm yr and rotating clockwise in the seismogenic upper crust this velocity field is accommodated by right lateral strike slip faults in the eastern aegean and by normal faults that rotate clockwise in central greece a comparison of paleomagnetic declination data with the expected rotation of rigid elongate inclusions in the velocity field shows in most places an agreement in sense and approximate agreement in rate of rotation expected rotation rates of line elements are sometimes too low probably because our derived velocity field is smoothed and unable to match locally high strain rates there is only one part of the region where line elements are predicted to rotate in either clockwise or counterclockwise directions depending on their orientation this is in western turkey which coincident ally is the only place where paleomagnetic rotations in both directions have been observed this coincidence in particular suggests to us that the analogy of rigid elongate inclusions in the velocity field responding to forces on their bases may be useful in predicting the senses and approximate rates of rotation of crustal blocks in deforming continental regions the velocity field we obtain preserves the strike directions of the major faults as directions of zero length change in spite of considerable smoothing we use this observation to speculate that the interaction between the upper crust and the rest of the lithosphere beneath it may involve an interplay of effects on one hand the variation of strength with direction in the crust may control the strike directions of faults that form or become reactivated and may also limit the velocity fields that are allowable on the other hand the fault bounded blocks may rotate in the velocity field in response to forces on their bases which would require the velocity field to change with time if the directions of zero length change are fixed to the blocks

seismic velocity changes strain rate and non volcanic tremors during the 2009 2010 slow slip event in guerrero mexico summary we use ambient noise cross correlations to monitor small but reliable changes in seismic velocities and to analyse non volcanic tremor nvt intensities during the slow slip event sse that occurred in 2009 and 2010 in guerrero we test the sensitivity of the seismic velocity to strain variations in absence of strong motions the 2009 2010 sse presents a complex slip sequence with two subevents occurring in two different portions of the fault from a seismic array of 59 seismometers installed in small antennas we detect a velocity drop with maximum amplitude at the time of thefirst subevent we analyse the velocity change at different period bands and observe that the velocity perturbation associated with the sse maximizes for periods longer than 12 s then a linearized inversion of the velocity change measured at different period bands is applied in order to determine the depth of the portion of the crust affected by this perturbation no velocity change in the first 10km is detected below the velocity perturbation increases with depth affecting the middle and lower crust finally we compute the transient deformation produced by the sse in an elastic model using the slip evolution recovered from the inversion of continuous gps the comparison between the velocity changes and the deformation suggests that the velocity change is correlated with the strain rate rather than with the strain this result is similar to what was observed during the 2006 sse in the same region and suggests a non linear behaviour of the crust the velocity changes can be interpreted together with other observables such as nvts during the 2009 2010 sse we measure nvt activity using continuous seismic records filtered between 2 and 8 hz we observe a correlation between velocity changes for period band greater than 14 s and tremor activity whereas no correlation exists between velocity changes and seismic noise energy measured at long periods these observations suggest that both seismic velocity change and nvt can be used as indication of transient deformation at depth

crustal structure of mexico and surrounding regions from seismic ambient noise tomography summary using continuous seismic data from newly available broadband stations in mexico and central america we have obtained group and phase velocity maps of fundamental mode rayleigh wave for the region these new maps have been calculated for periods between 8 and 60 s from cross correlations of seismic ambient noise between 100 broadband stations and stacked for 30 months from 2006 to 2008 the tomographic inversion of the obtained dispersion measurements has been carried out on a 1 1 grid resulting in maps with resolution better than 250 km in the well sampled regions of the model for short periods 8 16 s dispersion maps show good correlation with surface structural features low velocity anomalies correlate with sedimentary basins around the gulf of mexico and colorado embayment high velocity anomalies at short periods correlate with mountain ranges and regions of thin extended crust such as the gulf of california both the lowest and highest group velocity anomalies at these periods reach values of up to 15 per cent for periods between 25 and 40 s velocity anomalies are related to variations in crustal thickness and temperature the most prominent low velocity anomaly correlates with thick crust and high mantle temperatures associated with the trans mexican volcanic belt and the central american volcanic arc the most remarkable features for longer periods 40 60 s are the differences between high velocity anomalies beneath the mayan block the gulf of mexico and the cratonic part of the united states and low velocity anomalies beneath the chortis block and northern mexico the long wavelength features of our model agree well with previous global and continental scale studies however because of the increased station density of the data set used we are able to obtain reliable dispersion maps for shorter periods and to image smaller scale features

seismic gaps and recurrence periods of large earthquakes along the mexican subduction zone a reexamination abstract seismic gaps and recurrence periods of large shallow interplate earthquakes along the mexican subduction zone are reexamined after combining information from a catalog of nineteenth century9s earthquakes some relocated epicenters of the early part of this century source parameters of recent large earthquakes and redetermined magnitudes of great shallow earthquakes of this century tehuantepec and michoacan gaps have not experienced a large shock in this century and perhaps none in the past century they are either aseismic or have anomalously large repeat times guerrero jalisco and ometepec regions presently appear to have a high seismic potential observed average repeat times of large earthquakes m s 7 4 in six regions east central and west oaxaca san marcos petatlan and colima are between 32 to 56 yr data of this century indicate that the strain is released mostly in large events m s 7 4 a simple dislocation model with parameters obtained from the studies of recent earthquakes explains the observed recurrence periods quite well the b value for this zone is not meaningful an observation which is of significance for seismic risk estimation most of seismic moment or equivalently seismic energy release since 1800 appears to occur for 15 yr followed by relative quiescence in the next 15 yr

the crustal structure of the east anatolian plateau turkey from receiver functions an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018192 shtml http atlas geo cornell edu turkey publications zor et al 2003 htm

long term elasticity in the continental lithosphere modelling the aden ridge propagation and the anatolian extrusion process summary the evolution of the gulf of aden and the anatolian fault systems are modelled using the principles of elastic fracture mechanics usually applied to smaller scale cracks or faults the lithosphere is treated as a plate and simple boundary conditions are applied that correspond to the known plate boundary geometry and slip vectors the models provide a simple explanation for many observed geological features for the gulf of aden the model predicts why the ridge propagated from east to west from the owen fracture zone towards the afar and the overall form of its path the smaller en echelon offsets can be explained by upward propagation from the initially created mantle dyke while the larger ones may be attributed to the propagating rupture interacting with pre existing structures for anatolia the modelling suggests that the east anatolian fault was created before the north anatolian fault could form once both faults were formed however activity could switch between them the time scales over which this should take place are not known but evidence for switching can be found in the historical seismicity for aden and anatolia pre existing structures or inhomogeneous stress fields left from earlier orogenic events have modified the processes of propagation and without an understanding of the existence of such features the propagation processes cannot be fully understood furthermore a propagating fault can extend into an active region where it would not have initiated the north anatolian fault encountered slow but active extension when it entered the aegean about 5 ma and the stress field associated with the extending fault has progressively modified aegean extension in the central aegean activity has been reduced while to the north west on features such as the gulfs of evvia and corinth activity has been increased the field observation that major structures propagate and the success of simple elastic models suggest that the continental crust behaves in an elastic brittle or elastic plastic fashion even though laboratory tests may be interpreted to suggest viscous behaviour there are major problems in scaling from the behaviour of small homogeneous samples to the large heterogeneous mantle and large scale observations should be treated more seriously than extrapolations of the behaviour of laboratory experiments over many orders of magnitude in space and time the retention of long term elasticity and localised failure suggests a similar gross rheology for the oceanic and continental lithospheres even though it is incorrect to attribute differences in behaviour to the former being rigid i e elastic and the latter viscous oceanic and continental lithosphere behave in different ways unlike oceanic crust continental crust is buoyant and cannot be simply created or destroyed the process of thickening or thinning works against gravity preventing large displacements on extensional or contractional features in the upper mantle the equivalents of ridge or subduction systems are suppressed before they can accommodate large displacements and activity must shift elsewhere on the other hand strike slip boundaries and extrusion processes are favoured

constraining crustal and uppermost mantle structure beneath station tbz trabzon turkey by receiver function and dispersion analyses summary we jointly invert teleseismic radial component receiver functions and regional rayleigh and love surface wave group velocities for 1 d shear wave velocity structure beneath station tbz located on the northern side of the eastern pontides an influence factor is employed to control the relative influence of receiver function and surface wave dispersion on the resultant velocity depth profile radial and transverse component receiver functions at station tbz exhibit an azimuthal amplitude and polarity pattern consistent with 2 d receiver structure that has a general dip direction towards approximately south the radial component receiver functions are least affected by the dipping structures along the strike direction and thereby we prefer teleseismic events sampling along strike structures to alleviate the deflecting effect of dipping interfaces on the 1 d solution the 1 d inversion effectively reveals the two layer nature of the crust which is perturbed by high and low velocity layers and serves as a provisional model for the 2 d forward modelling minor to moderate changes to the 1 d model such as changing depth to and velocity contrast across an interface are needed to achieve the results with the 2 d modelling dipping interfaces and seismic anisotropy are included in the 2 d modelling to fit both radial and transverse component receiver functions the upper crust is characterized by a shear velocity of 3 5 km s 1 and cut through by a 4 km thick high velocity i e 3 8 km s 1 layer overlying the upper crust the sedimentary cover i e the top 5 km has velocities within the range 2 0 3 5 km s 1 a mid crustal velocity discontinuity between the upper granitic crust and the lower basaltic crust is identified at 16 km depth this boundary is analogous to the mid crustal discontinuity found under the black sea basin across which the shear velocity jumps from 3 5 to 4 1 km s 1 a relatively thick i e 12 km low velocity layer in the lower crust with a velocity reversal from 4 1 to 3 7 km s 1 is needed to better explain reverberations off this depth range we infer a 2 d moho discontinuity placed at 35 km depth beneath the station the proposed dip angle for the moho is rather steep i e 25 although coincident with regional gravity studies the associated sn velocity i e 4 4 km s 1 is rather low indicating disturbed upper mantle structure beneath the region initial amplitudes of transverse component receiver functions are rather energetic for which we propose substantial p and s velocity anisotropy 12 per cent for the topmost depths 5 km

crustal thickness variations in the aegean region and implications for the extension of continental crust 1 we installed 5 broadband and 45 short period temporary seismic stations distributed partly as a dense 100 km long n s linear array and partly as a regional network throughout the menderes massif of western turkey in order to study crust upper mantle structure and seismicity in this study we have combined teleseismic waveform data from these stations with data from several permanent seismic stations to determine crustal thickness variations in the aegean region receiver function studies at seven broadband stations using the h stacking method have yielded crustal thicknesses and vp vs ratios over a broad region of the aegean a more detailed crustal image was obtained in the central menderes massif where we applied common conversion point stacking to receiver functions obtained from the n s linear array the results show a general trend of westward crustal thinning from 36 km in central anatolia to 28 30 km in the central menderes massif to 25 km beneath the aegean sea the results also indicate that crustal thinning in the aegean is not uniform in the n s extensional direction the crust is thinner in the central menderes massif 28 30 km of crustal thicknesses and the cycladic massif 25 26 km than in surrounding regions where crustal thicknesses are 32 34 km the long lived elevated moho under the metamorphic core complexes suggests that the lower crust in the aegean region is at least 3 times more viscous than that in the basin and range province where the moho is much flatter

distribution of hydrous minerals in the subduction system beneath mexico abstract teleseismic converted phases are used to probe the composition of the downgoing oceanic crust as a function of depth along the cocos slab in central and southern mexico previously modeling of the receiver function rf conversion amplitude of the flat cocos slab beneath central mexico at 45 km depth revealed a thin low velocity upper oceanic crust of a thickness of 4 1 km which has much lower seismic velocities 20 30 reduction in shear wave velocities than normal lower crust high vp vs ratio 2 0 also suggested a large concentration of hydrous minerals such as talc in combination of high pore fluid pressure in the horizontal segment we extend this previous effort to examine seismic properties of both the steeply subducting cocos oceanic crust beneath the trans mexican volcanic belt tmvb in central mexico and the shallowly dipping crust beneath southern mexico inverted seismic velocities using the converted amplitudes at the top and bottom of the dipping oceanic crust are compared with experimentally constrained seismic velocities of candidate mineral phases in a range of likely pressures and temperatures the composition of the oceanic crust downdip in the steep part of slab beneath the tmvb includes the minerals such as lawsonite and zoisite at 60 100 km depth and the eclogitization occurs around 100 km depth this is related to arc volcanism in the tmvb directly above the slab as well as the slab rollback in contrast the dominant mineral phase in the upper oceanic crust of southern mexico beneath the isthmus of tehauntepec is amphibole on top of unaltered gabbroic oceanic crust the difference in mineral assemblages of the subducted oceanic crust may help explain the difference in slab geometries between central and southern mexico

seismic velocity and q structure of the middle eastern crust and upper mantle from surface wave dispersion and attenuation observed velocities and attenuation of fundamental mode rayleigh waves in the period range 7 82 sec were inverted for shear wave velocity and shear wave q structure in the middle east using a two station method additional information on q structure variation within each region was obtained by studying amplitude spectra of fundamental mode and higher mode rayleigh waves we obtained models for the turkish and iranian plateaus region 1 areas surrounding and including the black and caspian seas region 2 and the arabian peninsula region 3 the effect of continent ocean boundaries and mixed paths in region 2 may lead to unrealistic features in the models obtained there at lower crustal and upper mantle depths shear velocities are similar in all three regions shear velocities vary significantly in the uppermost 10 km of the crust being 3 21 2 85 and 3 39 km s for regions 1 2 and 3 respectively q models obtained from an inversion of interstation attenuation data show that crustal shear wave q is highest in region 3 and lowest in region 1 q s for the upper 10 km of the crust are 63 71 and 201 for regions 1 2 and 3 respectively crustal q s at 30 km depth for the three regions are about 51 71 and 134 the lower crustal q values contrast sharply with results from stable continental regions where shear wave q may reach one thousand or more these low values may indicate that fluids reside in faults cracks and permeable rock at lower crustal as well as upper crustal depths due to convergence and intense deformation at all depths in the middle eastern crust

q of lg waves in the central mexican volcanic belt from seismograms of nine shallow coastal earthquakes recorded at a pair of broadband stations we estimate q of lg waves in the part of central mexican volcanic belt mvb that includes the valley of mexico the two stations straddle the central mvb and are located on cretaceous limestone a weighted least square fit to the q 1 f data in the frequency range 0 25 to 8 hz yields q f 98 f 0 72 this estimate of q is lower than the corresponding q in the forearc region that is given by q f 273 f 0 66 note that our estimate of q f corresponds to a 200 km wide zone of the mvb the result of this study sheds light on the characteristics of seismic waves as they traverse through the mvb where they undergo dramatic amplification in the valley of mexico it also provides one of the critical elements needed in the estimation of expected ground motions at sites to the north of the mvb from future coastal earthquakes the lower q of lg waves in the mvb as compared with the forearc region seems correlated with lower resistivity reported in the mvb relative to the forearc region

shape of the subducted rivera and cocos plates in southern mexico seismic and tectonic implications the geometry of the subducted rivera and cocos plates beneath the north american plate in southern mexico was determined based on the accurately located hypocenters of local and teleseismic earthquakes the hypocenters of the teleseisms were relocated and the focal depths of 21 events were constrained using a body wave inversion scheme the suduction in southern mexico may be approximated as a subhorizontal slab bounded at the edges by the steep subduction geometry of the cocos plate beneath the caribbean plate to the east and of the rivera plate beneath north america to the west the dip of the interplate contact geometry is constant to a depth of 30 km and lateral changes in the dip of the subducted plate are only observed once it is decoupled from the overriding plate on the basis of the seismicity the focal mechanisms and the geometry of the downgoing slab southern mexico may be segmented into four regions 1 the jalisco region to the west where the rivera plate subducts at a steep angle that resembles the geometry of the cocos plate beneath the caribbean plate in central america 2 the michoacan region where the dip angle of the cocos plate decreases gradually toward the southeast 3 the guerrero oaxaca region bounded approximately by the onshore projection of the orozco and o gorman fracture zones where the subducted slab is almost subhorizontal and underplates the upper continental plate for about 250 km and 4 the southern oaxaca and chiapas region in southeastern mexico where the dip of the subduction gradually increases to a steeper subduction in central america these drastic changes in dip do not appear to take place on tear faults suggesting that smooth contortions accommodate these changes in geometry the inferred 80 and 100 km depth contours of the subducted slab lie beneath the southern front of the trans mexican volcanic belt suggesting it is directly related to the subduction thus the observed nonparallelism with the middle american trench is apparently due to the changing geometry of the rivera and cocos plates beneath the north american plate in southern mexico and not to zones of weakness in the crust of the north american plate as some authors have suggested

the moho of north america a brief review focused on recent studies abstract recent national programs in canada lithoprobe and the u s earthscope are providing vast quantities of data and many new scientific insights concerning crustal and lithospheric mantle structure and evolution more modest but significant results are also being produced in and about mexico this paper primarily focuses on results published since 2005 and presents an updated moho map of north america this overview of crustal structure does reveal a number of interesting observations for example two buried distinct crustal blocks have been discovered in the past 20 years one was caught in a precambrian suture zone in canada and the other is buried under the gulf coast region and is still of unknown origin the precambrian assembly of the continent has been documented by the mapping of numerous suture zones and shallow portions of subducted slabs have been preserved in several cases not surprisingly the internal structure of these suture zones is complex and highly variable isostatic adjustment has been shown to be a complex process involving the lithospheric mantle not just crustal structure variations specifically the correlation of crustal thickness with elevation is only approximate at best several crustal blocks that have been stable over very long periods of time possess unusually thick crust whose lower portion is usually fast vp 7 0 km s rifting has been shown to affect the crust in a variety of ways ranging from the massive magmatic modification that produced the mid continent rift system to the broad region of extension in the basin and range province crustal structure along the active modern western margin of north america is highly complex as would be expected as a result of transitions between subduction and transform faulting and variations in volcanism and intraplate magmatism we clearly still have a lot to learn about the structure and evolution of this continent

surface waveform tomography of the turkish iranian plateau summary the middle east is a tectonically complex region consisting of terrains as diverse as precam brian shields and young orogens the dominant tectonic feature is the turkish iranian plateau a recently elevated seismically active region along the zagros bitlis suture which results from the collision of the arabian plate with eurasia in this study we use surface waveform tomography to elucidate the upper mantle shear wave velocity structure beneath the turkish iranian plateau and adjacent regions the main large scale feature in the tomographic model is a low shear wave velocity anomaly in the uppermost mantle beneath the plateau this low velocity feature correlates with a long wavelength free air gravity anomaly and with recent volcanism whose geochemistry has a lower lithospheric mantle signature seismology gravity and volcanism all suggest the presence of a thin lithosphere and warm upper mantle beneath the turkish iranian plateau the upper mantle low shear wave velocity zone the high free air gravity and the deep lithospheric source depth for the basaltic volcanism are all consistent with a partial delamination of the lithosphere as a result of earlier lithospheric thickening resulting from the continental collision

s wave velocity structure below central mexico using high resolution surface wave tomography shear wave velocity of the crust below central mexico is estimated using surface wave dispersion measurements from regional earthquakes recorded on a dense 500 km long linear seismic network vertical components of regional records from 90 well located earthquakes were used to compute rayleigh wave group velocity dispersion curves a tomographic inversion with high resolution in a zone close to the array obtained for periods between 5 and 50 s reveals significant differences relative to a reference model especially at larger periods 30 s a 2 d s wave velocity model is obtained from the inversion of local dispersion curves that were reconstructed from the tomographic solutions the results show large differences especially in the lower crust among back arc volcanic arc and fore arc regions they also show a well resolved low velocity zone just below the active part of the trans mexican volcanic belt tmvb suggesting the presence of a mantle wedge low densities in the back arc inferred from the low shear wave velocities can provide isostatic support for the tmvb

geometry of the benioff zone and state of stress in the overriding plate in central mexico analysis of depths and focal mechanisms of 16 small earthquakes in central mexico along with previous data shows that a the subducted cocos plate becomes subhorizontal between 110 and 275 km from the trench reaching a depth of about 50 km and b the bottom part of the overriding continental plate is in tensional stress regime neotectonic structures in central mexico and stress orientations estimated from borehole elongations cinder cone alignments and fault slip analysis in the trans mexican volcanic belt which lies in the northeastern portion of the area under study also indicate the same stress regime absolute motion of the north american plate in the region has a component normal to the trench of 20 mm yr which if true would result in compressional stress in the upper plate if the trench position is fixed in an absolute frame of reference if we allow for seaward retreat of the trench then the tensional stress in the overriding plate and the observed geometry of the benioff zone can be explained this however implies that seaward retreat of a trench is possible even for a young 15 m y old subducting slab alternatively tectonic erosion of the leading edge of the continent which has been proposed to explain truncated igneous and metamorphic continental terrane could give rise to the tensional stress but would not explain the geometry of the benioff zone

flat slab subduction topography and mantle dynamics in southwestern mexico topography above subduction zones arises from the isostatic contribution of crustal and lithospheric buoyancy as well as the dynamic contribution from slab driven mantle flow we evaluate those effects in southwestern mexico where a segment of the cocos slab subducts horizontally the eastern part of the volcanic arc the trans mexican volcanic belt stands at an average elevation of 2 3 km nearly 1 3 km above the fore arc lateral changes in bulk crustal density are relatively small and seismic imaging shows that there is little variation in crustal thickness between these two regions thus the elevation difference between the arc and the fore arc should arise from differences in mantle properties we present finite element models of flat slab subduction that provide a simultaneous match to topography plate velocities and stress state in the overriding plate we find that the dynamic effects are primarily controlled by the amount of coupling at the subduction interface and in the mantle wedge the lack of slab anchoring into the lower mantle and the absence of continental mantle lithosphere with a mantle wedge and a subduction interface that are respectively 2 and 4 orders of magnitude weaker than the asthenosphere the flat slab exerts a downward pull that can explain most of the elevation difference between the fore arc and the arc we infer that lateral viscosity variations play a significant role in shaping dynamic topography in complex tectonic settings and that sublithospheric dynamics can influence the topography at wavelengths that are significantly shorter than previously recognized

one dimensional models of shear wave velocity for the eastern mediterranean obtained from the inversion of rayleigh wave phase velocities and tectonic implications summary on a sw ne profile from the libyan coast towards central turkey phase velocity curves of the fundamental rayleigh mode were measured using a two station method the inversion of phase velocity curves yields 1 d models of shear wave velocity down to approximately 200 km depths that may be interpreted as estimates of average models between neighbouring stations on the profile strong lateral variations in the shear wave velocity structure are imaged along the profile the subducted oceanic african mantle lithosphere is indicated in 1 d models for the region around crete by significantly enlarged shear wave velocities it is also imaged by an average model of the structure between stations on crete and santorini on a path crossing the libyan sea south of crete the resulting model is slower than a model expected for 110 myr old oceanic lithosphere the passive african margin is thus assumed to extend northwards beneath the libyan sea anomalous low shear wave velocities are found for the uppermost mantle beneath central turkey down to a depth of approximately 130 km using two stations on crete the average depth of the oceanic moho within the subducting slab is estimated to be at approximately 50 km beneath crete for this arc parallel path an enlarged standard deviation of the measured phase velocities of approximately 0 2 km s 1 between 10 and 30 mhz is observed that is probably caused by strong lateral heterogeneity related to the subducting slab in addition in this frequency range an anomalous propagation of the fundamental rayleigh mode is detected that is indicated by measured phase velocities that are approximately one standard deviation faster than phase velocities expected from a great circle approximation an average shear wave velocity of approximately 3 5 km s 1 is observed above the oceanic moho in order to explain the recent lithospheric structure of the hellenic subduction zone a tectonic model is assumed for the ne sw striking profile considered it is based on the calculated 1 d models tectonic reconstructions and on a model derived from the metamorphic history of rocks exposed on crete the suggested model summarizes the tectonic development at a lithospheric scale starting in the late cretaceous accretion of crustal material of two microcontinents to eurasia is assumed while continuous subduction of the oceanic lithosphere of different ocean basins and possibly of the mantle lithosphere of the microcontinents resulted in a single slab the length of the oceanic lithosphere that was subducted south of crete is estimated to be not greater than approximately 550 km

evidence for shallow isostatic compensation of the southern rocky mountains from rayleigh wave tomography in the past decade seismologists have found that the topography in colorado correlates with seismic velocities in the upper mantle not with crustal thickness and postulated that isostatic compensation of the southern rocky mountains takes place largely in the mantle to test the validity of this hypothesis we use rayleigh wave phase and amplitude data recorded in the rocky mountain front passcal experiment to obtain crustal thickness and shear wave structure in the crust and upper mantle the thickest crust in the model is beneath one of the two most elevated regions the san juan volcanic field the other most elevated region in central colorado the sawatch range is underlain by crust of anomalously low velocity the seismically defined mantle lithosphere is thicker beneath the great plains than beneath the colorado plateau and is largely absent beneath the southern rocky mountains but the correlation of topography with mantle velocities is weaker than the correlation with crustal anomalies we construct a model that matches the observed bouguer gravity anomaly primarily with variations in crustal thickness and density by assuming that density anomalies are proportional to the observed velocity anomalies the anomalous mantle may also contribute to maintaining regional isostasy in colorado but its contribution may be much less important than the crust

seismic attenuation structure in central mexico image of a focused high attenuation zone in the mantle wedge velocity spectra from moderate sized earthquakes were used to investigate the p wave attenuation structure in central mexico in particular we included regional events with magnitudes in the range of 4 5 to 6 1 recorded from 2005 to 2007 on the middle american subduction experiment mase array which consists of 100 broadband sensors across central mexico from acapulco to tempoal near the gulf of mexico by assuming a brune type source a frequency independent t value was obtained for each seismogram in the frequency band 1 to 30 hz these measurements were then inverted for two dimensional spatial variations in q p in the cross section along the mase array perpendicular to the trench the model has uniform 20 km vertical grid spacing down to a depth of 200 km and 50 km or 100 km horizontal grid spacing depending on ray coverage the inversion results show low attenuation in the subducting slab and high attenuation in the mantle wedge and the crust below and to the north of the volcanic belt the focused high attenuation zone q p 200 in the mantle wedge lies away from the top of the slab between depths of 80 km and 120 km beneath the volcanic belt and is likely to be related to relatively high temperature fluids and partial melts produced in subduction process the high attenuation region in the lower crust correlates with the low resistivity and low velocity region and could be caused by partial melts and fluids from dehydration and magmatic processes

crust and upper mantle seismic anisotropy variations from the coast to inland in central and southern mexico subduction zones are among the most dynamic tectonic environments on earth deformation mechanisms of various scales produce networks of oriented structures and faulting systems that result in a highly anisotropic medium for seismic wave propagation in this study we combine shear wave splitting inferred from receiver functions and the results from a previous sks wave study to quantify and constrain the vertically averaged shear wave splitting at different depths along the 100 station mesoamerican subduction experiment array this produces a transect that runs perpendicular to the trench across the flat slab portion of the subduction zone below central and southern mexico strong anisotropy in the continental crust is found below the trans mexican volcanic belt tmvb and above the source region of slow slip events we interpret this as the result of fluid melt ascent the upper oceanic crust and the overlying low velocity zone exhibit highly complex anisotropy while the oceanic lower crust is relatively homogeneous regions of strong oceanic crust anisotropy correlate with previously found low v p v s regions indicating that the relatively high v s is an anisotropic effect upper mantle anisotropy in the southern part of the array is in trench perpendicular direction consistent with the alignment of type a olivine and with entrained subslab flow the fast polarization direction of mantle anisotropy changes to n s in the north likely reflecting mantle wedge corner flow perpendicular to the tmvb

crustal structure beneath the eastern part of the coast ranges diablo range of central california from explosion seismic and near earthquake data abstract seismic refraction and near earthquake data of the u s geological survey for central california have been compiled into record sections along profiles and interpreted in terms of crustal structure the profiles are located northeast of the san andreas fault of central california and run parallel to the general structures for the explosion seismic line through the centre of the diablo range an uppermost layer franciscan formation with p velocities of 3 6 5 0 km s 1 decreases in thickness towards the northwest the lower boundaries of layers with constant velocities of 5 75 and 6 8 km s 1 are found at almost constant depths of 12 and 21 km respectively between 21 and 26 km depth a well defined low velocity zone appears whose velocity is estimated as 5 3 km s 1 with the aid of a hedgehog inversion and the calculation of amplitudes this zone is underlain by a layer 3 5 km thick with a velocity of 7 6 km s 1 the upper mantle velocity beneath the moho at 29 30 km depth is 8 2 km s 1 the near earthquake profiles located 20 km southwest and parallel to the explosion seismic line follow more or less the hayward and calaveras fault systems the velocity depth distribution derived for the earthquake data is very similar to that found beneath the diablo range however the low velocity zone at 21 26 km depth does not seem to exist everywhere along the line the moho is not disturbed beneath the calaveras hayward and silver creek faults it rises slightly from the diablo range towards the southwest

using systematically characterized low frequency earthquakes as a fault probe in guerrero mexico studies of low frequency earthquakes lfes have focused on detecting events within previously identified tectonic tremor however the principal lfe detection tools of matched filter searches are intrinsically incapable of detecting events that have not already been characterized previously as a template event in this study we therefore focus on generating the largest number possible of lfe templates by uniformly applying a recently developed lfe template detection method to a 2 5 yearlong data set in guerrero mexico using each of the detected templates in a matched filter search we then form event families that each represents a single source we finally develop simple empirical statistics to select the event families that represent lfes our resulting catalog contains 1120 unique lfe sources and a total of 1 849 486 detected lfes over the 2 5 yearlong data set the locations of the lfe sources are then divided into subcatalogs based on their distance from the subduction trench considering each lfe as a small unit of slip along the subduction interface we observe discrete episodes of lfe activity in the region associated with large slow slip events this is in direct contrast to the near continuous activity observed 35 km farther downdip within the previously identified lfe tremor sweet spot

shear wave velocity structures of the arabian peninsula abstract the shear velocity structures of the different tectonic provinces of the arabian peninsula has been studied using surface wave data recorded by the ryd riyadh station the inversion of rayleigh wave group velocities indicates that the arabian shield can be modeled by two layers each of which is 20 km thick with a shear velocity of 3 61 km s in the upper crust and 3 88 km s in the lower crust the underlying upper mantle velocity is 4 61 km s inversion of both love and rayleigh waves group velocities shows that the arabian platform upper and lower crusts are comparable in their thicknesses to those of the shield but with shear velocities of 3 4 and 4 km s respectively the upper mantle velocity beneath the platform is 4 4 km s and the average total thickness of the crust is 45 km

crustal structure below the valley of mexico estimated from receiver functions abstract receiver functions rfs from two permanent stations cuig and zaig of the mexican broadband network were calculated to infer the crustal structure at both sites the data were stacked to allow uncertainty estimations and inverted using two global optimization algorithms simulated annealing and genetic algorithms strong and systematic azimuthal dependence was observed in the stacked functions at cuig site which is located in the mexican volcanic belt mvb assuming a one dimensional five layer model per azimuthal stack these variations were explained with the same upper crustal structure including a superficial 2 km thick low velocity layer associated with the mvb and a well defined conrad interface around 15 km depth different depths for the moho discontinuity and variations in both the s wave velocity and poisson s ratio for the upper mantle our inversion of observed rfs at cuig and theoretical considerations suggest an eastward crustal thickening of at least 5 km below the valley of mexico we tested the sensitivity of the modeling procedure by applying it to the recordings at zaig station in this case no azimuthal dependence was noticed in the stacked functions after a simultaneous inversion of three different azimuthal stacks a single four layer model satisfactorily explained all data thus revealing a flat one dimensional crustal model below the mexican mesa central where zaig station is located these results support the resolution and robustness of the applied method at both sites

mineral composition in cognate inclusions in late miocene early pliocene potassic lamprophyres with affinities to lamproites from the denizli region western anatolia turkey implications for uppermost mantle processes in a back arc setting abstract mineral assemblages of both cognate inclusions and host lamprophyres with lamproitic affinity in kocapinar district denizli western anatolia consist of phlogopitic mica diopsidic clinopyroxene k feldspar apatite opaque and carbonates calcite dolomite two distinct types of cognate inclusions have been defined in host lamprophyres clinopyroxene rich cci and clinopyroxene phlogopite rich cpci whole rock compositions of inclusions show a near primitive nature with high mgo 7 56 15 1 wt cr 195 2270 ppm ni 213 335 ppm contents and a potassic character k2o 2 0 2 8 wt na2o 0 4 2 2 wt data imply that the inclusions crystallized from magmas formed by melting of phlogopite bearing pyroxenites in a peridotitic mantle source however the presence of reverse zoning in clinopyroxenes with salitic fe rich green cores in host lamprophyres and cpci inclusions suggest that the denizli lavas represent mixtures of distinct probably ultrapotassic and alkali basaltic magmas estimated geobarometric constraints inferred from clinopyroxene compositions in cci and cpci inclusions indicate moderate pressures of pyroxene crystallization ranging between 1 7 and 2 2 gpa and corresponding to 53 70 km depths under low pressure magma fractionation results reveal that i the origin of denizli lamprophyres with transitional between arc type and intra plate type geochemical signatures is consistent with a shallow level mantle petrogenesis rather than a deep seated origin related to mantle convection ii the source was a highly refractory and metasomatized peridotitic mantle present at the base of the lower crust iii metasomatic agents that affected the mantle lithosphere beneath denizli region are distinct from those beneath other western anatolia orogenic centers and iv the transitional character of kocapinar denizli lamprophyric rocks were probably formed as a result of either underplating or contamination of asthenospheric magma at the base of the mantle lithosphere or assimilation of delaminated continental edge lithospheric mantle via ascending asthenosphere denizli lamprophyres are interpreted to have formed during the formation of a basin graben structure in the latest miocene early pliocene just after late miocene exhumation of menderes massif

crustal structure and possible anisotropy in turkey from seismic surface wave dispersion summary the velocity structure of two regions of turkey are determined using single station measurements of rayleigh and love wave group velocities in the period range 8 50s a differential inversion scheme yields models for turkey in which crustal and upper mantle shear wave velocities are slower than those of most of europe comparisons of upper mantle shear wave velocities we have obtained with reported p velocities leads to poisson s ratio values in the upper mantle between 0 29 and 0 30 for eastern turkey and between 0 27 and 0 31 for western turkey crustal velocities are slightly slower and upper mantle velocities are slightly faster in western turkey than in eastern turkey the crust mantle boundary obtained in our studies is gradational but if a shear velocity of 4 2 km s l is taken to define the upper mantle then the crust appears to be about 40 km thick throughout all of turkey a sharp crust mantle boundary may occur but cannot be resolved the data of this study require neither a low velocity zone in the upper mantle nor polarization anisotropy in the crust or upper mantle azimuthal variations of rayleigh and love wave group velocities in western turkey are consistent with velocities predicted by an azimuthally anisotropic upper crust in which vertical cracks are orientated in an approximate e w direction this interpretation is consistent with geological information fault plane solutions lineations mapped from satellite observations and reported heat flow values but the possibility that these variations are caused by lateral changes of velocity in the crust of western turkey cannot be completely ruled out at the present time

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models

geodetic determination of the kinematics of central greece with respect to europe implications for eastern mediterranean tectonics we use a new satellite laser ranging global positioning system slr gps solution at seven sites in anatolia and aegea to obtain a better definition of the extrusion motion of the anatolian aegean block with respect to europe we show that this motion can be described in a first approximation by a counterclockwise rotation which transfers most of the motion of arabia to anatolia we combine 78 displacement vectors obtained at common points of two triangulation nets measured in central greece in 1895 and 1975 with the slr gps measurements to compute the velocity field over greece with respect to europe these measurements indicate that central greece is a zone of extension between the anatolian aegean counterclockwise rotation to the south and the northern greece clockwise rotation to the north this extension is principally localized within the gulf of corinth to the east but is distributed to the west we then extrapolate this velocity field to the whole aegea and western anatolia using recently published gps results as well as the slr results the narrow dextral north anatolian fault which limits the velocity field to the north progressively gives way to a much wider boundary zone where extension becomes dominant we show that the collision between the mediterranean ridge and africa began 3 6 ma and we describe the modifications that this collision has produced on the kinematic pattern both in aegea and on the mediterranean ridge