site amplifications observed in the gubbio basin central italy hints for lateral propagation effects abstract in this study we investigate the site amplification effects observed in the gubbio plain central italy the recordings of 140 local earthquakes 1 2 ml 4 7 observed by two linear arrays installed along the longitudinal and perpendicular basin axis are analyzed both in the time and frequency domains to determine the spatial variation of the local site effects in the basin the time series recorded in the gubbio plain are characterized by locally generated surface waves which cause a significant increase in both ground motion duration and amplitude with respect to a nearby reference station on a rock site in the middle of the basin where the sedimentary cover is thickest ca 600 m the peak ground velocity is amplified on average by a factor of 5 with respect to the reference station installed on rock and the duration is increased by a factor of about 2 the analyses in the frequency domain show that the spectral energy of the basin generated waves is mainly distributed over the range 0 4 2 hz and affects both horizontal and vertical components the site responses estimated by applying two reference site methods show that the overall shape of the amplification functions is similar for the sites located inside the basin with a difference in the amplification levels which can reach values as high as 30 in the middle of the valley amplifications up to a factor of 10 affect the vertical component of ground motion over a broad frequency range for nearly all basin sites with the maximum amplifications occurring at around 1 hz finally although the horizontal to vertical spectral ratios were found to provide a reliable estimation of the fundamental resonance frequency of the site they fail to estimate the shape of the site transfer function

comparison of different site response estimation techniques using aftershocks of the 1999 izmit earthquake on 17 august 1999 the m w 7 4 izmit earthquake occurred in northwestern turkey a temporary seismic network was installed to improve the geometry of a previously installed network in this study 262 aftershocks of the izmit earthquake with magnitude m l ranging between 0 4 and 4 5 were analyzed using digital recordings from 17 stations of these networks s wave and p wave spectral records corrected for path attenuation function were inverted by means of the generalized inversion technique git the git site responses were compared with those calculated by horizontal to vertical h v ratios applied to both earthquake data and to pre event noise in most cases the h v of the earthquake data provided site responses with shapes consistent with those obtained using git however the level of amplification was occasionally found to be different in general these discrepancies can be explained either by the amplification affecting the vertical component of the ground motion that we detected by git or by the waves having a propagation in almost the vertical direction using the h v ratio applied to noise for most cases we obtained not only the peaks for the fundamental resonance frequencies but site responses with shapes similar to those obtained by git the detected level of amplifications using the h v ratio showed a tendency not to exceed those calculated by the inversion finally amplifications up to a factor 5 are found for stations placed over complex topography for these sites amplifications are not always correctly identified by the h v technique using either earthquakes or noise

tectonic evolution of the gediz graben field evidence for an episodic two stage extension in western turkey western turkey is one of the most spectacular regions of widespread active continental extension in the world the most prominent structures of this region are e w trending grabens e g gediz and buyuk menderes grabens and intervening horsts exposing the menderes massif this paper documents the result of a recent field campaign field geological mapping and structural analysis along the southern margin of the modern gediz graben of pliocene 5 ma age this work provides field evidence that the presently low angle ductile brittle detachment fault is cut and displaced by the high angle graben bounding normal faults with total displacement exceeding 2 0 km the evolution of the n s extension along the gediz graben occurred during two episodes each characterized by a distinct structural styles 1 rapid exhumation of menderes massif in the footwall of low angle normal fault core complex mode during the miocene 2 late stretching of crust producing e w grabens along high angle normal faults rift mode during pliocene quaternary times separated by a short time gap the later phase is characterized by the deposition of now nearly horizontal sediments of pliocene age in the hanging walls of the high angle normal faults and present day graben floor sediments the evolution of extension is at variance with orogenic collapse and or back arc extension followed by the combined effect of tectonic escape and subduction rollback processes along the aegean cyprean subduction zone consequently it is misleading to describe the miocene sediments exhumed on shoulders of the gediz graben as simple graben fill

site response of strong motion stations in the umbria central italy region we used near field and regional records from 16 earthquakes m l 4 6 5 9 located in the epicentral area of the 1997 umbria marche sequence to estimate the site response of 40 strong motion stations the distribution of hypocenters covers a distance range from 5 to 100 km we estimated site amplification factors using two techniques namely a generalized spectral inversion method and horizontal to vertical component spectral ratios hvsrs of ground acceleration for the first approach we inverted observed spectral amplitudes for site q and source using a reference site since the site response estimated using hvsrs assumes that the vertical component of motion is amplification free we also separated source and site effects by inverting the vertical component of the acceleration spectra we found that although most of the stations do not show important amplifications on the vertical component a few of them have a significant vertical amplification at low frequencies f q representative of the s wave train shows a frequency dependence that can be approximated by the relation q s 31 2 f 1 2 between 0 3 and 9 5 hz however at high frequencies f 10 hz this dependence weakens and q s takes an approximately constant value of 438

an active bivergent rolling hinge detachment system central menderes metamorphic core complex in western turkey two symmetrically arranged detachment systems delimit the central menderes metamorphic core complex and define a bivergent continental breakaway zone in the anatolide belt of western turkey structural analysis and apatite fission track thermochronology show that a large east trending syncline within the alpine nappe stack in the central part of the orogen is related to late miocene early pliocene to recent core complex formation the syncline formed as a result of two opposite facing rolling hinges in the footwalls of each of the two detachments back rotation of the syncline limbs suggests that the detachments rotated from an initial dip of 408 608 to a currently shallow orientation of 08 208

crustal structure and local seismicity in western anatolia summary western anatolia is one of the most seismically active continental regions in the world and much of it has been undergoing ns directed extensional deformation since early miocene time in a cooperative study seismologists from saint louis university usa and dokuz eylul university turkey deployed five broad band and 45 short period seismic stations in western anatolia between 2002 november and 2003 october the present paper uses data collected by this network and the data from five permanent stations operated by the kandilli observatory and earthquake research institute to map the hypocentral distribution of local earthquakes and to determine crustal structure of western anatolia we obtained a 1 d p wave crustal velocity model using a generalized scheme for simultaneously obtaining earthquake locations and a crustal velocity model our velocity model is characterized by crustal velocities that are significantly lower than average continental values the low velocities may be associated with high crustal temperatures a high degree of fracture or the presence of fluids at high pore pressure in the crust we located 725 local earthquakes and classified them in three categories we found that the level of seismic activity in western anatolia is higher than previously reported station delays resulting from the inversion process correlate with near surface geology and the thickness of sediments throughout the region the hypocentral distribution of the events indicates that peak seismicity for the region occurs at depths of about 10 km

timing of tectonic events in the menderes massif western turkey implications for tectonic evolution and evidence for pan african basement in turkey the menderes massif forms the western of the two large metamorphic culminations within the turkish alpide orogen it has three major lithologic units with a gneissic core at the base and a schist and a marble envelope overlying it successively although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the massif we present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the massif to constrain the timing of major tectonic events that shaped the massif since the late proterozoic pt3 in the southern part of the massif sensu stricto three episodes of deformation and metamorphism are distinguished whereas in its northern part there are four the first episode occurred at 500 10 ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis in the central part of the massif the 470 9 ma old now highly deformed tonalitic and granitic intrusions mark the end of this episode on a cambrian reconstruction of continents around the eastern mediterranean the menderes massif forms the southern end of the pan african orogenic collage of northeastern africa and arabia the area of earliest palaeozoic deformation in the menderes may connect with the northwest african orogenic collage along the strike via the bozburun and saricicek diabases arkoses and schists in the center of the karacahisar dome interpreted herein as fragments of a pan african suture the earliest palaeozoic deformations to affect the rocks were probably related to the last pan african collisions and associated postcollisional convergence the southern part of the massif was undeformed from early ordovician to the early later eocene whereas the northern part was deformed metamorphosed and intruded possibly during the late triassic related to the closure of the karakaya marginal basin of palaeo tethys the next major event affecting the whole of the massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts and only greenschist grade in the outermost envelope this metamorphism here called the main menderes metamorphism mmm is biostratigraphically constrained between early eocene and early oligocene time rb sr isotopic data show a spread of ages between 60 ma and 25 ma with the greatest number of determinations around 35 5 ma this number is in excellent agreement with the stratigraphic evidence and shows that mmm took place during latest eocene time or at the transition from eocene to oligocene time along the northern border of the massif deformation and metamorphism had already taken place during the late cretaceous in a high pressure low temperature hp lt metamorphic belt northernmost part of menderes massif sensu lato which was then covered by palaeocene molasse the evolution of the hp lt belt was probably related to the obduction of the bozkir ophiolites from the izmir ankara branch of the neo tethys ocean and preceded terminal collision in the evolution of the massif the mmm was a product of the latest palaeocene collision across neo tethys and the consequent internal imbrication of the menderes taurus block that resulted in the burial of the menderes massif area beneath the lycian nappe complex a low grade metamorphic event dated at 10 to 5 ma is interpreted to be related to the extensional deformation in the aegean and western turkey which has been dated stratigraphically to have begun during the tortonian 11 5 ma

lead and strontium isotope geochemistry of paleozoic sicker group and jurassic bonanza group volcanic rocks and island intrusions vancouver island british columbia whole rock and galena lead isotope analyses have been obtained from the sicker group paleozoic island arc volcanic package and from a jurassic island arc represented by the bonanza group volcanics and island intrusions galena lead isotope analyses from the volcanogenic ore deposits at the buttle lake mining camp in the sicker group provide estimates of the initial lead ratios for the sicker group lead isotope signatures are uniform within each of the major orebodies but the myra orebody is less radiogenic than the older h w orebody this has major significance in terms of ore genesis for these important deposits there are significant differences in isotopic composition between the sicker group and devonian island arc type rocks in the shasta district california which rules out direct correlations between the rock units of these two areas relatively high initial values of 207 pb 204 pb 15 56 and 208 pb 204 pb 38 00 suggest that large quantities of crustal lead must have been involved in the formation of the sicker group volcanic rocks thus it is proposed that the trench related to the paleozoic island arc had a substantial input of continental detritus and may have lain near a continent the jurassic island arc is characterized by low 207 pb 204 pb ratios 207 pb 204 pb versus 206 pb 204 pb and 208 pb 204 pb versus 206 pb 204 pb plots if interpreted as due to isotopic mixing the more radiogenic end member has a composition that is lower in 207 pb 204 pb and higher in 206 pb 204 pb than typical upper continental crust assimilation of sicker group material during the emplacement of the jurassic arc can explain the mixing trend

study of basin edge effects on the ground motion characteristics using 2 5 d modelling this paper presents the role of basin edge geometry in the generation of surface waves using 2 5 d modelling the simulated responses of various basin edge models revealed surface wave generation near the basin edge and their propagation normal to the edge seismic responses of basin edge models using different fundamental frequency of soil along with spectral analysis of differential ground motion confirmed that surface waves start generating near the basin edge when body wave frequency exceeds the fundamental frequency of soil spectral analysis of differential ground motion also confirmed the generation of high frequency surface wave an increase of surface wave amplitude with soil thickness was obtained large ground displacement observed near the basin edge may be due to the interference of surface diffracted waves with the direct waves and their multiples the effect of edge roughness on the surface wave characteristics was found to be negligible as compared with the edge geometry simulated results revealed a decrease of surface wave amplitude with edge slope particularly in the case of surface waves caused by s waves surface wave generation near the basin edge was obtained for all four considered angles of incidence at the same time it was also inferred that the characteristics of these surface waves depend on the angle of incidence to some extent the findings of this paper reveal that basin edge effects deserve a particular attention for the purpose of earthquake resistant design and seismic microzonation

seismotectonics of western turkey from high resolution earthquake relocations and moment tensor determinations 1 we have relocated 364 earthquakes in western turkey between 2002 and 2003 using more than 45 000 accurate p and s differential travel times we also have determined moment tensors for 71 of these earthquakes using their broadband regional waveforms after relocation the events are highly concentrated in three clusters and delineate two nearly vertical faults their strikes agree with the strike of one of the fault planes of the averaged fault plane solution of the cluster which allowed us to pick the true fault plane and the slip direction we identified a nnw striking left lateral strike slip fault near buldan that connects the gediz graben in the north and the eastern end of the buyuk menderes graben in the south the other right lateral strike slip fault near izmir strikes ene wsw direction our results indicate that part of the n s extension occurring in western turkey is accommodated by strike slip faults and is accompanied by e w shortening

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

3d gravity modeling of buyuk menderes basin in western anatolia using parabolic density function abstract a method to model 3d sedimentary basins with parabolic density contrast is applied to buyuk menderes basin in western anatolia the measured gravity fields reduced to a horizontal plane are assumed to be available at grid nodes of a rectangular square mesh juxtaposed 3d vertical prisms with their geometrical epicenters on top coincide with grid nodes of a mesh to approximate a sedimentary basin the algorithm based on newton s forward difference formula automatically calculates the initial depth estimates of a sedimentary basin assuming that 2d infinite horizontal slabs can generate the measured gravity fields and among these slabs the density contrast varies with depth the lower boundary of a sedimentary basin is formulated by estimating the depth values of the 3d prisms with in predetermined limits measured gravity fields pertaining to the buyuk menderes basin turkey where the density contrast varies with depth are interpreted to show the applicability of the method

flow and mixing in juan de fuca canyon washington we report breaking internal lee waves strong mixing and hydraulic control associated with wind driven up canyon flow in juan de fuca canyon washington unlike the flow above the canyon rim which shows a tidal modulation typical on continental shelves the flow within the canyon is persistently up canyon during our observations with isopycnals tilted consistent with a geostrophic cross canyon momentum balance as the flow encounters a sill near the canyon entrance at the shelf break it accelerates significantly and undergoes elevated mixing on the upstream and downstream sides of the sill on the downstream side a strong lee wave response is seen with displacements of o 100 m and overturns tens of meters high the resulting diffusivity is o 10 2 m2 s 1 sufficient to substantially modify coastal water masses as they transit the canyon and enter the salish sea estuarine system

sediment thicknesses of the western anatolia graben structures determined by 2d and 3d analysis using gravity data abstract western turkey is tectonically one of the most active and rapidly deforming regions of continental crust in the world the most pronounced structural and morphological features of this region are defined by normal faulting in an e w direction which creates the boundaries of the buyuk menderes kucuk menderes and gediz grabens the graben systems may have become active between 11 7 ma and are now deeper than the surrounding topography the gediz and buyuk menderes grabens exhibit negative bouguer gravity anomalies the bouguer gravity anomalies increase towards the center of the aegean sea in a regional sense the grabens are filled with recent sediments giving rise to relative negative gravity anomalies these anomalies were interpreted using 2d and 3d gravity inversion techniques in order to determine the depth to the metamorphic basement inversion of geophysical anomalies implies fitting the observed data to theoretical anomalies possibly produced by subsurface bodies inversion of gravity anomalies is a non linear problem in the sense that body parameters are not linearly related to the anomalies gravity anomalies caused by structures are mostly determined by a 2d model which has an n sided polygonal cross section for non linear problems theoretically it is more suitable to determine the parameters of the structure by a series of juxtaposing prisms or vertical dykes extending to infinity rather than using a single n side polygonal model the depths to the top surfaces of a rectangular prisms with infinite depth represent the relief of the basement the basement relief can be computed on the basis of density contrast if the reference depth is assessed as a result of 3d analysis of the bouguer gravity map the maximum thickness of sedimentary cover appears to be more than 2 0 and 1 5 km for the gediz and buyuk menderes grabens respectively towards the saraykoy kizildere area the sedimentary thickness cover thickens to more than 2 0 km 2d analysis of the bouguer gravity profiles indicate that the maximum thickness of the sedimentary cover is between 2 5 and 3 5 km in the buyuk menderes graben and between 0 5 and 2 0 km in the gediz graben

investigation of 3 d basin structures in the izmit bay area turkey by single station microtremor and gravimetric methods summary we investigate 3 d basin structures and site resonance frequencies in the izmit bay area of turkey by new geophysical surveys based on 239 single station microtremor and 405 point gravity measurements a fundamental resonance frequency map of the izmit bay was produced from the main peak in the horizontal to vertical component spectral ratio hvsr of microtremors the hvsr analysis of the microtremor data reveals single double broad peaked or no peak type hvsr curves varying in accordance with the surface geology and spatial extent of the three basins present in the izmit bay area in the deepest sections of the izmit golcuk and derince basins of the izmit bay the fundamental resonance frequencies are dominantly 0 24 0 30 hz these resonance frequencies should be taken into consideration along with higher mode frequencies to construct earthquake resistant structures in the izmit bay area the 3 d gravimetric bedrock depth map of the izmit basin shows that the basin has an asymmetric shape with its deepest section coinciding with the surface trace of the north anatolian fault the northern shoulder of the basin has a gentle dip on the kocaeli peneplain side and the southern shoulder is much steeper and it is bounded by the samanli mountains we derive a power law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the gravity and shear wave velocity data in the izmit bay we use this relationship to estimate bedrock depths beneath golcuk and derince basins our estimation of maximum basin depths is 1400 m for the izmit and is 800 m for the golcuk and derince basins finally we have analysed a converted sp phase from a local earthquake recording made at site cmp to calculate and verify the sediment thickness estimations obtained from our gravimetric and microtremor analyses this calculation shows close agreement with that of the gravimetric and microtremor results our results show that the basins in the izmit bay area have a very thick sedimentary cover with very low shear velocities underlined by hard bedrock forming a sharp impedance contrast we anticipate that these results will be a key contribution to the quantitative assessment of seismic hazard for the izmit bay area before the occurrence of strong earthquakes in the marmara region

spectral ratio estimates for site effects on the horst graben system in west turkey recordings of micro and moderate size local earthquakes have been used to quantify site effects in the central west turkey which contains one of the world s best examples of a rapid intra continental extension with its high population and industrial potential we analyzed 436 earthquakes with local magnitudes ranging between 2 0 and 5 6 using three component digital recordings from 32 stations site functions were obtained using two different spectral ratio approaches horizontal to vertical spectral ratio hvsr and standard spectral ratio ssr hvsr estimates of transverse and radial s waves were compared with one another epicentral distance magnitude and back azimuth dependencies of site functions were also evaluated in general hvsr values from transverse and radial s waves are similar within a factor of 2 the back azimuth dependencies of transverse s wave hvsr results are more significant than distance and magnitude dependencies on the other hand averaging of transverse and radial s wave hvsr results eliminates systematic back azimuth dependencies caused by source radiation effects distributions of hvsr estimates along n s linear array which traversed main grabens in the region with a station spacing of 3 4 km reflect subsurface geological complexities in the region the sites located near the basin edges are characterized by broader hvsr curves broad hvsr peaks could be attributed to the complexity of wave propagation related to significant 2d 3d velocity variations at the sediment bedrock interface near the basin edges the results also show that even if the site is located on a horst the presence of weathered zones along the surface could cause moderate frequency dependent site effects comparison of hvsr and ssr estimates for the stations on the graben sites showed that ssr estimates give larger values at lower frequencies which could be attributed to lateral variations in regional velocity and attenuation values caused by basin geometry and edge effects

evolution of the miocene sedimentary fill of the gediz graben sw turkey abstract the gediz graben is a continental extensional basin filled with miocene to recent sediments the evolution of the graben can be expressed in terms of two phases i miocene half graben phase and ii post miocene graben phase the miocene half graben phase was governed by the southern margin structure evolution of which significantly controlled the stratigraphic variability in the basin alluvial fluvial and lacustrine systems developed in the graben as a function of distance to the southern margin thus alluvial deposits with coarse grained facies dominate the southern margin and grade into finer fractions of fluvial and or lacustrine deposits to the north this depositional architecture repeated three times during the miocene and deposited alasehir caltilik and gediz formations these formations depict distinct thickness and grain size decrease from south to north to emphasize the half graben configuration for the favour of the southern margin the post miocene graben phase started with the faulting of the northern margin this resulted in relatively balanced partitioning of the subsidence between the two margins although the preceding asymmetry was inherited by the graben sediment influx became bipolar and alluvial fan systems developed along the both margins

bivergent extension in orogenic belts the menderes massif southwestern turkey the central menderes massif is characterized by an overall dome shaped foliation pattern and a north northeast trending stretching lineation the asymmetry of shear bands and quartz c axis fabrics on either side of the structural dome demonstrate a top to thenorth northeastshearsenseinthenorthernpartandatoptothesouth southwestshear sense in the southern part of the submassif i e a bivergent downdip movement this suggests a symmetric collapse of the alpine menderes orogenic belt along two extensional shearzones conjugateshearbandsandsymmetricquartzc axisfabricsintheeast trendingtransitionzonedemonstrateacoaxialdeformationbetweenthetwoextensiondomains bivergent extension in the menderes massif is in contrast to asymmetric extension in the aegeansea here thestill activehellenicsubductionzoneevolvedfromanadvancingplate boundary associated with crustal thickening into a retreating plate boundary in oligocene miocene time southward rollback of the subducting plate during continuous northward subduction allowed asymmetric top to the north northeast extension in the back arc region during the exhumation of the cycladic core complexes in western turkey the arrival of the thick continental crust of the menderes massif halted subduction and probably caused the symmetric collapse of the massif because the high potential energy of the thickened crust was no longer supported by subduction

high altitude plio quaternary fluvial deposits and their implication on the tilt of a horst western anatolia turkey abstract this study investigates the origin and regional tectonic implications of high altitude plio quaternary fluvial deposits developed over the bozdag horst which is an important structural element within the horst graben system of western anatolia turkey a total of 23 deposits occur near the modern drainage divide comprising fluvial to occasionally lacustrine deposits the deposits are all elongated in n s direction with a width length ratio of 1 10 the largest of them is of 13 km in length with a maximum observable thickness of about 100 110 m morphological lithological deformational characteristics of these deposits and the drainage system of the area all suggest that the deposits were formed due to uplift and southward tilting of the bozdag horst this tilting which is estimated as 1 2 to 2 2 caused accumulation of the stream load along channels flowing from south to north all the deposits were later dissected by the same streams with the exception of one deposit which still preserves its original lake form these deposits are of quaternary age which corresponds to the latest n s directed extensional tectonic phase in the region