interplay between subduction retreat and lateral extrusion tectonics of the western carpathians 1 analysis of brittle microstructures reveals three tertiary deformation events in the western carpathians 1 late paleogene bedding parallel extension 2 oligocene to middle miocene nne ssw compression and ese wnw extension 3 post mid miocene nw se extension these regional deformations applied to crustal blocks in the intra carpathian region resulted from forces which were induced by the coupled plate tectonic processes of subduction retreat beneath the carpathian arc and lateral extrusion from the eastern alps toward the carpathian region material flow from the alps spread toward east and ne guided by sinistral strike slip zones along the ne trending continental margin subduction retreat was terminated by mid miocene soft collision of the inner western carpathians with the european foreland ongoing subduction retreat beneath the eastern carpathians caused post mid miocene back arc extension forming the pannonian basin extension spread into the western carpathians by reactivating the extrusion related strike slip faults as normal faults

site effects in avcilar west of istanbul turkey from strong and weak motion data approximately 1000 people were killed in the collapse of buildings in istanbul turkey during the 17 august 1999 izmit earthquake whose epicenter was roughly 90 km east of the city most of the fatalities and damage occurred in the suburb of avcilar that is 20 km further west of the epicenter than the city proper to investigate this pattern of damage the u s geological survey in cooperation with the kandilli observatory earthquake research institute koeri deployed portable digital seismographs at seven free field sites in western istanbul to record aftershocks during the period from 24 august to 2 september the primary objective of this deployment was to study the site effects by comparing the aftershock ground motions recorded at sites inside and outside the damaged area and to correlate site effects with the distribution of the damaged buildings in addition to using weak motion data mainshock and aftershock acceleration records from the koeri permanent strong motion array were also used in estimating the site effects site effects were estimated using s waves from both types of records for the weak motion data set 22 events were selected according to the criteria of signal to noise ratio s n ratio and the number of stations recording the same event the magnitudes of these events ranged from 3 0 to 5 2 the acceleration data set consisted of 12 events with magnitudes ranging from 4 3 to 5 8 and included two mainshock events results show that the amplifying frequency band is in general less than 4 hz and the physical properties of the geologic materials are capable of amplifying the motions by a factor of 5 10 in this frequency band there is a good agreement among the spectral ratios obtained from the two mainshocks and their aftershocks the damage pattern for the 17 august izmit earthquake is determined by several factors however our study suggests that the site effects in avcilar played an important role in contributing to the damage manuscript received 30 august 2000

testing the ability of surface arrays to monitor microseismic activity recently there has been much interest in the use of data from surface arrays in conjunction with migration based processing methods for passive seismic monitoring in this study we use an example of this kind of data recorded whilst 18 perforation shots with a variety of positions and propellant amounts were detonated in the subsurface as the perforation shots provide signals with known source positions and origin times the analysis of these data is an invaluable opportunity to test the accuracy and ability of surface arrays to detect and locate seismic sources in the subsurface in all but one case the signals from the perforation shots are not visible in the raw or preprocessed data however clear source images are produced for 12 of the perforation shots showing that arrays of surface sensors are capable of imaging microseismic events even when the signals are not visible in individual traces we find that point source locations are within typically 45 m laterally of the true shot location however the depths are less well constrained 150 m we test the sensitivity of our imaging method to the signal to noise ratio in the data using signals embedded in realistic noise we find that the position of the imaged shot location is quite insensitive to the level of added noise the primary effect of increased noise being to defocus the source image given the migration approach the array geometry and the nature of coherent noise during the experiment signals embedded in noise with ratios 0 1 can be used to successfully image events furthermore comparison of results from data and synthetic signals embedded in noise shows that in this case prestack corrections of traveltimes to account for near surface structure will not enhance event detectability although the perforation shots have a largely isotropic radiation pattern the results presented here show the potential for the use of surface sensors in microseismic monitoring as a viable alternative to classical downhole methods

a comparison and test of various site response estimation techniques including three that are not reference site dependent abstract we compare various site response estimation techniques using after shock data of the 1989 loma prieta earthquake collected in oakland california because of recent interest in comparing results from weak and strong motion to infer any nonlinearity and between direct s and coda waves we pay particular attention to the uncertainties first sediment to bedrock spectral ratio estimates between pairs of sites are compared with those obtained from various generalized inversion approaches where the source and site effects of multiply recorded events are solved for simultaneously we find that the site amplification factors are very similar among these approaches but that the uncertainties can be significantly different depending on how the data are weighted we also examine and test three site response estimation techniques that do not rely on a reference site to estimate source and path effects the first involves a parameterized source and path effects inversion even when the bedrock data are excluded from consideration this approach is found to reveal the frequency dependence of site response at each of the sediment sites the second technique involves taking horizontal to vertical component spectral ratios receiver function type estimates of shear wave aftershock data these are also found to reveal the frequency dependence of site response at the sediment sites and the results for the bedrock site are relatively flat and near unity the third estimate is formed by taking horizontal to vertical component ratios of ambient seismic noise and these are shown to reveal the fundamental resonant frequency of the sediment sites unfortunately discrepancies exist among all of the site response estimates and with one dimensional predictions with respect to a frequency independent scaling factor nevertheless the highly frequency dependent character of site response is well constrained and the fact that non reference site dependent methods are capable of revealing this is promising for site specific hazard assessments in regions that lack adequate reference sites

dynamics of the polish and eastern slovakian parts of the carpathian accretionary wedge insights from palaeostress analyses the arcuate outer carpathian accretionary wedge formed in front of the east alpine carpathian pannonian alcapa megablock during the eocene sarmatian the wedge accreted sediments of the subducting remnants of the carpathian flysch basin a large oceanic tract left in front of the alpine orogen the palaeostress data for the orogenic hinterland particularly the data related to the early miocene extension that was expanding towards the ne combined with coeval subduction related volcanism that was expanding towards the ne indicate that the uneven roll back of the subduction zone was the main mechanism controlling the development of the northern west carpathian arc the palaeostress data for the tertiary accretionary wedge from the same time period are characterized by outward fanning 1 trajectories that changed gradually during the wedge development in contrast the palaeostress data for the hinterland are characterized by preferred directional stress events that changed abruptly during the wedge development these palaeostress results are in accordance with the behaviour of the wedge and the hinterland as the wedge behaved as a weak continuum and the hinterland behaved as a block mosaic with weak boundaries the fault traces of the northern west carpathian arc converge to both ends of the arc and suggest that the pre existing basin was the factor that controlled the arc location these fault trace patterns are asymmetric indicating a slightly oblique overall convergence in a ne sw direction in accordance with this convergence the palaeostress data for the accretionary wedge indicate that the western part of the wedge which is characterized by nw se oriented maximum principal compressional stress 1 was undergoing sinistral transpression meanwhile the eastern part which is characterized by ne sw oriented 1 was undergoing compression apparently the dynamics of the accretionary wedge was further influenced by the shape of an elongated ne sw trending alcapa megablock which was located behind the wedge and advanced in the direction of the general early miocene convergence during the most pronounced stages of the wedge development this megablock served as the local indenter as its strength surpassed that of the accretionary wedge located to its front further dynamic complexities were added because of the complex shape of the magura unit which was located in the most proximal portion of the wedge and was stronger than the units in front of it wedge outcrops indicate that the large scale shortening which is characterized by the development of detachments and ramps was preceded by an initial layer parallel shortening this is indicated by scaly fabrics and minor reverse faults that rotated into locked positions during the later accretion several outcrops with a wedge detachment fault indicate that there was a relatively low amount of friction during its development the decollement zone is several hundred metres thick and shows evidence of transient fluid flow that was driven by pressure gradients this is documented by frequent hydrofracturing sandstone dykes and fibrous veins that opened against the weight of the whole wedge all of which indicate cycles of higher pore fluid pressures that lowered the basal friction

the oligocene miocene tectonic evolution of the northern outer carpathian fold and thrust belt insights from compression and rotation analogue modelling experiments this paper presents the different analogue scenarios of the tectonic evolution of the northern outer carpathians i e the western and northern eastern outer carpathians which formed as an accretionary wedge in front of the east alpine carpathian pannonian alcapa block during oligocene miocene times currently this fold and thrust belt forms an arc which is asymmetrically convex to the north and wider in its eastern part palaeomagnetic investigations have suggested that the rocks of the arc underwent counter clockwise rotation along almost the whole arc which is difficult to explain as an effect of simple indentation of the triangular indenter in this case two branches of the arc should be rotated in the opposite directions the structural evolution of the western outer carpathians is characterized by superposition of two successive tectonic shortening events directed n s and ne sw the results of the presented analogue modelling suggest that two scenarios of the geodynamic evolution of the studied belt could explain the occurrence of such differently oriented shortening events 1 two phases of differently directed indentation first to the n then to the ne and 2 indenter movement to the ne with simultaneous counter clockwise rotation however the experiment in which the moving indenter is simultaneously rotated produces the most suitable model the counter clockwise rotation of the material is only possible in front of both sides of the convex indenter in this model the results of the analogue modelling also prove that rotation of the alcapa block started after formation of the magura nappe the innermost nappe of the western outer carpathians

automated seismic event location by waveform coherence analysis summary automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring since microseismic records are generally characterized bylowsignal to noiseratio automated locationmethods arerequested to be noise robust and sufficiently accurate most of the standard automated location routines arebasedontheautomatedpicking identificationandassociationofthefirstarrivalsofpands waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases although current methods can accurately pick p onsets the automatic picking of the s onset is still problematic especially when the p coda overlaps the s wave onset in this paper we propose a picking free earthquake location method based on the use of the short term average long term average sta lta traces at different stations as observed data for the p phases we use the sta lta traces of the vertical energy function whereas for the s phases we use the sta lta traces of a second characteristic function which is obtained using the principal component analysis technique in order to locate the seismic event we scan the space of possible hypocentral locations and origin times and stack the sta lta traces along the theoretical arrival time surface for both p and s phases iterating this procedure on a 3 d grid we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial coordinates of the seismic event a pilot application was performed in the campania lucania region southern italy using a seismic network irpinia seismic network with an aperture of about 150km we located 196 crustal earthquakes depth 20km with magnitude range 1 1 ml 2 7 a subset of these locations were compared with accurate manual locations refined by using a double difference technique our results indicate a good agreement with manual locations moreover our method is noise robust and performs better than classical location methods based on the automatic picking of the p and s waves first arrivals

the peak frequency of direct waves for microseismic events abstractdirect seismic waves p or s waves are used to locate and further characterize microseismic events the resolution of information obtained from direct waves depends on the peak frequencies of the waveforms the peak frequency results from combination of the source propagation and the receiver effects for frequencies below the corner frequency propagation effects control the peak frequency in observed seismograms of microseismic events the frequency dependence of direct body waves can be modeled by attenuation specifically the global attenuation factor this model is consistent with observed data along surface profiles explaining the difference between the peak frequencies of p and s waves in addition the model is consistent with the peak frequencies observed on downhole monitoring arrays this can be used to invert effective attenuation providing additional unique measurement from microseismic events the corner frequency can be estimated from the average stress drop and analytical sour

seismic imaging of melanges pieniny klippen belt case study the authors present results of the first high resolution deep seismic reflection survey in the pieniny klippen belt pkb in poland this survey sheds new light on the matter of olistostromes and the melange character of the pkb the sedimentary mass transport deposits represented by olistoliths and olistostromes manifest themselves by different petrophysical parameters of rocks velocity density and resistivity and seismic attributes seismic attributes are very effective in the interpretation of the geology of complex melanges the authors used selected attributes low pass filter energy energy gradient dip steered median filter prewitt filter laplacian edge enhancing filter and square root of the energy gradient these attributes emphasize changes of the seismic image inside melange zones the distinguished olistoliths are now inside imbricated thrust structures and they are tectonically rearranged polygenetic melanges in the pkb originated as a result of sedimentary and tectonic processes the pkb in the investigated area forms several north vergent thrust sheets belonging to the zlatne and hulina nappes both nappes contain large chaotic non reflective olistoliths as well as the smaller mainly high reflective olistoliths olistoliths are arranged parallel to the flysch layering and thrusts the results presented confirm the postulated two olistostrome belts within the pkb structure

stability of source mechanisms inverted from p wave amplitude microseismic monitoring data acquired at the surface we study the stability of source mechanisms inverted from data acquired at surface and near surface monitoring arrays the study is focused on p wave data acquired on vertical components as this is the most common type of acquisition we apply ray modelling on three models a fully homogeneous isotropic model a laterally homogeneous isotropic model and a laterally homogeneous anisotropic model to simulate three commonly used models in inversion we use geometries of real arrays one consisting in surface receivers and one consisting in buried geophones at the nearsurface stability was tested for two of the frequently observed source mechanisms strike slip and dip slip and was evaluated by comparing the parameters of correct and inverted mechanisms we assume these double couple source mechanisms and use quantitatively the inversion allowing non double couple components to measure stability of the inversion to test the robustness we inverted synthetic amplitudes computed for a laterally homogeneous isotropic model and contaminated with noise using a fully homogeneous model in the inversion analogously amplitudes computed in a laterally homogeneous anisotropic model were inverted in all three models we show that a star like surface acquisition array provides very stable inversion up to a very high level of noise in data furthermore we reveal that strike slip inversion is more stable than dip slip inversion for the receiver geometries considered here we show that noise and an incorrect velocity model may result in narrow bands of source mechanisms in hudson s plots

the pieniny klippen belt in the western carpathians of northeastern slovakia structural evidence for transpression abstract the pieniny klippen belt represents a 600 km long but only a few kilometers wide suture zone in the carpathian orogenic belt based on a quantitative analysis along a part of its nw trending segment in northeastern slovakia we present structural data supporting transpression the continuous interaction of strike slip shearing horizontal shortening and vertical lengthening as a major deformation style in its polyphase deformation history dextral transpression is expressed in the map scale and outcrop fault pattern the oblique orientation of fold axes to the faults bounding the klippen belt and extension parallel to the fold axes the transpression related strain field is described and quantified by the analysis of 1 orientation of rotated fold axes displaying an acute angle to the margins of the klippen belt 2 orientation and geometry of paleostress derived from mesoscale fault striae analysis e trend of 3 trajectories and flattening geometry and 3 the deformation history indicated by extension veins non coaxial regime different techniques using fault striae data quantify paleostress and subdivide heterogeneous data sets mathematically into homogeneous subsets the observed deformation history is modelled as a homogeneous transpression deformation the best fitting model requires a nw trending present day orientation external contraction direction e g plate slip vector and predicts 16 fold axes parallel extension and 23 axial plane normal shortening

possible paleostress tensor configurations derived from fault slip data in eastern vermont and western new hampshire the configuration of six possible paleostress tensors have been derived from 152 faults measured in eastern vermont and western new hampshire populations of potentially genetically related faults were separated using two techniques tensor configurations for each population were derived using a linear least squares inversion method based in part on the work of reches 1987 and a grid search inversion method which tests over 100 000 possible tensors for compatibility with all or portions of the data faults belonging to the oldest population set r n 24 occur primarily in high grade rocks this set is composed of semiductile northeast trending reverse and west northwest trending left lateral faults fault fabrics of quartz rods and thin mylonite layers suggest that the host rocks were at crustal levels of 8 10 km during faulting the derived tensor indicates a roughly east west 1 and near vertical 3 set r faults are offset by normal faults sets n1 and n2 and are interpreted to be pre mesozoic in age perhaps related to late paleozoic alleghanian compression normal and normal oblique faults mineralized with chlorite calcite and strained quartz n 73 have been separated into two populations sets n1 n 49 and n2 n 24 even though these faults are likely of similar age host rocks were probably at moderate crustal depths of perhaps 5 km during faulting faults of both sets are most likely related to mesozoic rifting tensor configurations indicate that 1 plunges steeply northwest n1 and southeast n2 and 3 plunges gently roughly east west these faults cut presumably mesozoic age dikes and are themselves offset by normal oblique faults set t and right lateral faults set rl strongly deviatoric near vertical 1 suggests a thermally driven tectonic regime during the development of normal faulting in new england set t n 25 is composed of normal oblique slip faults mineralized similarly as sets n1 and n2 the plunge of 1 is 50 n and 3 plunges gently east field relations indicate set t faults document the transition from normal sets n1 and n2 to strike slip faulting regimes set rl a compatible sequence of mesozoic stress fields is suggested de boer et al 1988 north northeast trending right lateral faults of set rl n 7 are mineralized with quartz limonite calcite chlorite calcite twins are bent and fractured and quartz grains show minor internal strain suggesting that these faults developed while host rocks were at relatively shallow crustal levels the plunge of 1 is gently northeast and 3 plunges gently east southeast seven distinctly mineralized feldspar siderite quartzoalcite 1imonite chlorite gently northwest dipping thrust faults of set f define the sixth tensor these faults are cut by essentially vertical east side up faults and are assumed to be mesozoic in age by analogy with similar faults in western massachusetts

full waveform earthquake location application to seismic streaks on the calaveras fault california 1 we use a novel technique based upon source array analysis to locate three moderate earthquakes that occur at the edge of previously identified streaks of seismicity on the calaveras fault california our method determines centroid locations for earthquakes in addition to the hypocenters previously determined using first break picks application of the method to smaller earthquakes indicates that the errors associated with the locations are on the order of 100 m much less than the rupture dimensions of the m 4 5 events that we have analyzed we treat high precision locations of microearthquakes near the earthquakes that we want to locate as source arrays and compute the slowness of waves leaving these source arrays we then use the slowness parameters to locate the earthquakes of interest we find that the medium magnitude events nucleate on the streaks and rupture into a zone devoid of seismicity on this basis we argue that streaks represent the boundary between creeping and locked sections of a fault our location technique has the potential for wide application including circumstances where it may be necessary or desirable to locate earthquakes without using direct arrivals

seismic event detection and source location using single station three component data the seismic event detection and source location scheme presented in this paper uses single station seismic data to analyze seismic events to detect events the detection scheme combines the signals on the horizontal components in a manner analogous to beam steering once an event is detected the location scheme estimates the location of the source with respect to the receiver by estimating the polarization direction of the pn phase the range estimate is then obtained from the relative timing of different phases

multiple low temperature thermochronology constraints on exhumation of the tatra mountains new implication for the complex evolution of the western carpathians in the cenozoic the tectonothermal evolution of the highest mountain range in the carpathian arc the tatra mountains is investigated by zircon and apatite fission track and zircon u th he zhe dating methods in order to unravel the disputed exhumation and geodynamic processes in the western carpathians our data in combination with geological evidences reveal a complex cenozoic history with four major tectonothermal events i a very low grade metamorphism of the crystalline basement at temperatures 240 c due to tectonic burial during the eo alpine collision in the late cretaceous 80 ma ii exhumation and cooling of the basement to temperatures 150 c after burial to 5 9 km depths by the paleogene fore arc basin iv final exhumation of the segmented basement blocks during oligocene miocene 32 11 ma owing to lateral extrusion of the north pannonian plate and its collision with the european foreland the spatial pattern of thermochronological data suggests asymmetric exhumation of the tatra mountains beginning in the northwest at 30 20 ma with low cooling rates 1 5 c ma and propagating toward the major fault bounding the range in the south where the youngest cooling ages 16 9 ma and fastest cooling rates 10 20 c ma are found our data prove that the tatra mountains shared cenozoic evolution of other crystalline core mountains in the western carpathians however the miocene zhe ages suggest that the tatra mountains were buried to the greatest depths in the paleogene early miocene and experienced the greatest amount of miocene exhumation

late cretaceous deformation of the pieniny klippen belt west carpathians abstract the late cretaceous position and dynamics of the pieniny klippen belt of the west carpathians which lies behind the palaeogene flysch accretionary prism are reconstructed as shown by the reconstruction based on structural sedimentological and palaeomagnetic data the pieniny klippen belt occupied a wnw ese to nw se trending zone during the late cretaceous which acted as an oblique convergent boundary between the ancestral west carpathians and the oceanic lithosphere attached to the north european platform sediments of the pieniny klippen belt were part of both the mountain belt and foredeep at that time known change from pelagic micritic limestone to a flysch sequence is progressively younger seawards in the thrust slice stack forming the pieniny klippen belt the syn sedimentary record includes flysch olistostrome and wildflysch sediments both the nw se thrusting along the ne sw striking faults and dextral strike slip faulting along the wnw ese to nw se striking faults were active in the late cretaceous in the area of the current pieniny klippen belt

klippen belt flysch belt and inner western carpathian paleogene basin relations in the northern slovakia by magnetotelluric imaging the paper presents the interpretation of magnetotelluric measurements along the sw ne profile near stara ubov a northern slovakia the profile passes through the outer carpathian flysch belt klippen belt and ends in the inner western carpathians paleogene nw from ru bachy horst structure the interpretation of the older measurements from profile mt4 was utilized and moreover the 3 d geoelectrical model of studied region was constructed the magnetotelluric data interpretations verified the northern inclination of flysch belt structures and their smaller thickness out of klippen belt in direction to the carpathian electrical conductivity zone axis we consider this as a consequence of the flower structure more precisely the southern branch of the suture zone related to mentioned conductivity zone northerly from this zone the thickness of the outer carpathian flysch belt increases and the structures have inclination to the south i e to the subduction zone the contact of flysch belt with klippen belt has a fault character and it is subvertical slightly inclined to the north the southern boundary between klippen belt and inner western carpathians has also fault character and is very steep we detect the continuation of the ru bachy horst to the ne in the basement of inner western carpathian paleogene the structural discordance between this horst and klippen belt direction is a result of younger tectonic processes according to our results the depth distribution of the pre tertiary basement below the inner western carpathian units is non uniform the basement is broken to a number of partial blocks horsts and grabens

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

kinematics of austro alpine cover nappes changing translation path due to transpression upper and middle austro alpine nappes of the eastern alps the structural uppermost subunits of the alps suffered two major superposed deformations d1 d2 during the eo alpine cretaceous orogeny d1 is characterized by nw to w directed thrusting and nappe internal rock flow d2 by large scale folding and imbrication toward the north and northeast structures strain metamorphic history microfabrics and stretching trajectories indicate that the superposition of d2 over d1 structures can be interpreted as a progressive deformation it is concluded that the emplacement of the nappes follows a curved translation path a model which emphasizes non coaxial deformation structures explains the detachment of the nappes the configuration of the separating thrust planes and the distribution of intense deformation zones the overall kinematic history of the austro alpine nappes fits a model in which strike slip shearing horizontal shortening and vertical lengthening act together continuously over a finite deformation zone transpressional model this model emphasizing a gradually changing strain regime eliminates the space problems encountered in models which consider simple south over north imbrication during the alpine orogeny the study stresses two interpretations 1 1 stretching lineations indicate nappe transport directions 2 2 transpression may be a common feature of orogenic belts

variable structural styles and tectonic evolution of an ancient backstop boundary the pieniny klippen belt of the western carpathians the pieniny klippen belt pkb and adjoining zones form a narrow but lengthy belt that separates the cretaceous nappe stack of the central austroalpine and the cenozoic accretionary wedge of the external western carpathians flysch belt the pkb shares units and structures of both in addition to the distinctive oravic units derived from a continental fragment in the middle penninic position in map view the northward convex pkb consists of two branches the western one striking roughly sw ne and the eastern one oriented in the nw se direction the western branch experienced a continuous nw se convergence and forward accretion of units derived from the foreland plate during the late cretaceous up to oligocene the developing accretionary wedge was supported by the backstop of the central carpathians in contrast the eastern branch originated by separation of pkb units and their dextral translation along the ne margin of the central carpathian block in the late eocene during the miocene reorganization of plate movements in the carpathian area the situation reversed the eastern formerly dextral transform margin was converted to the frontal backstop of the eastern part of the accretionary wedge in contrast the western previously orthogonally convergent branch was affected by along strike sinistral movements despite these considerable kinematic changes the pkb remained fixed to both backstop edges and records deformation structures and associated sediments differentiated into several evolutionary stages

reverse modelling for seismic event characterization summary the localization of seismic events is of utmost importance in seismology and exploration current techniques rely on the fact that the recorded event is detectable at most of the stations of a seismic network weak events not visible in the individual seismogram of the network are missed out we present an approach where no picking of events in the seismograms of the recording network is required the observed wavefield of the network is reversed in time and then considered as the boundary value for the reverse modelling assuming the correct velocity model the reversely modelled wavefield focuses on the hypocentre of the seismic event the origin time of the event is given by the time where maximum focussing is observed the spatial extent of the focus resembles the resolution power of the recorded wavefield and the acquisition this automatically provides the uncertainty in the localization with respect to the bandwidth of the recorded data the method is particularly useful for the upcoming large passive networks since no picking is required it has great potential for localizing very weak events not detectable in the individual seismogram since the reverse modelling sums the energy of all recorded traces and therefore enhances the signal to noise ratio similar to stacking in seismic exploration the method is demonstrated by 2 d and 3 d numerical case studies which show the potential of the technique events with a s n ratio smaller than 1 where the events cannot be identified in the individual seismogram of the network are localized very well by the method

a comparison of observations of ground response to weak and strong ground motion at coalinga california abstract measurements of the response to earthquake motion of an unsaturated soil in coalinga california indicate that this response is linear within the limits of random errors for frequencies below 10 hz and for accelerations up to 0 7 g the response of the soil site relative to a bedrock site was determined by dividing the amplitude spectrum of the soil site ground motion for a given event by the amplitude spectrum of the bedrock site ground motion for the same event the relative response of this pair of sites to 23 regional and small local earthquakes is the same in the 1 to 10 hz band as the response to seven strong motion events within a random error of a factor of 1 3 at 10 to 11 hz the relative response to strong motion is significantly reduced by as much as a factor of 2 from the relative response to the 23 regional and small local earthquakes at the 95 per cent confidence level suggesting the possibility of nonlinear response the response of the soil site is a factor of 2 to 3 times larger than that of the bedrock site the variation in the spectral ratios for strong motion events and for regional and small local events about their respective averages has a standard deviation of about a factor of 2

effect of soil conditions on predicted ground motion case study from western anatolia turkey abstract we present a site effect study for the city of izmir western anatolia turkey local amplification was evaluated using state of practice tools ten earthquakes recorded at 16 sites were analysed using spectral ratios relative to a reference site horizontal to vertical spectral ratios and an inversion scheme of the fourier amplitude spectra of the recorded s waves seismic noise records were also used to estimate site effects the different estimates are in good agreement among them although a basic uncertainty of a factor of 2 seems difficult to decrease we used our site effect estimates to predict ground motion in izmir for a possible m6 5 earthquake close to the city using stochastic modelling site effects have a large impact on psv pseudospectral velocity where local amplification increases amplitudes by almost a factor of 9 at 1 hz relative to the firm ground condition our results allow identifying the neighbourhoods of izmir where hazard mitigation measurements are a priority task and will also be useful for planning urban development

source parameters of loma prieta aftershocks and wave propagation characteristics along the san francisco peninsula from a joint inversion of digital seismograms abstract aftershock recordings from 10 digital seismographs deployed along the axis of the san francisco peninsula from the epicenter of the 18 october 1989 loma prieta earthquake to san francisco provide the data for a joint inversion for source wave propagation and site effects the inversion procedure is a least squares method using the singular value decomposition algorithm and is done in two parts the first solves only for the source and attenuation terms for all events and the second projects the residuals from the first inversion onto the site terms the coefficient of geometrical spreading is solved for as part of the model of attenuation residuals plotted versus distance and frequency provide a check on the appropriateness of the attenuation model the earthquakes are all located near the san andreas fault mostly in the aftershock zone of the loma prieta mainshock but some area near daly city on the peninsula the data set provided by geos recorders consists of 148 digital seismograms for 33 events from 10 sites that form a linear profile from the epicentral region to the city of san francisco a distance of approximately 100 km strong motion accelerograms are also available for the larger events body wave spectra are fit surprisingly well by our model especially at distances beyond about 20 km where differences due to radiation pattern effects and changes in angle of incidence become less important results from the inversion show that estimates of moment are only 1 higher for the p waves compared to the s waves apparently there are no major biases in the estimates as each is determined independently of the other p wave corner frequencies are 1 5 times higher than s wave corner frequencies on average stress drops with an average of 176 bars for events that range in magnitude from 1 7 to 4 2 are higher than those found in previous studies where site and path were not explicitly taken into account the exponents of geometrical spreading are very close to one 1 019 for p waves and 1 017 for s waves for this data set which extends to about 100 km the whole path q assumed to be frequency independent was about 800 for both p and s waves specifically 790 for p waves and 830 for s waves the average p wave attenuation at all sites is quantified by a t of 0 020 sec which compares to 0 03 sec for s waves t determined for each site range from a low of 0 008 sec at san bruno mountain a hard rock site to a high of 0 065 sec at corralitos in the epicentral area residuals of the model fits which are distance dependent show larger amplitudes near the epicenter but fall off with a minimum at about 30 km where amplitudes are about 30 to 60 lower than average at distances farther than 30 km amplitudes rise out to the limit of the data at about 105 km where amplitudes are about average at frequencies less than 10 hz but are slightly above average for higher frequencies the location of this low in amplitude can be explained as the boundary between the amplitude decay of direct arrivals and the emergence of wide angle reflections from the lower crust and moho which increase in amplitude beyond 30 km these amplitudes correlate with damage patterns from the mainshock as less damage was observed along the peninsula but appeared to increase towards san francisco even when damage in the marina and china basin districts of san francisco are not included in the damage census

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

temperature time history of subducted continental crust mount olympos region greece in the mt olympos region of northeastern greece continental margin strata and basement rocks were subducted and metamorphosed under blueschist facies conditions and thrust over carbonate platform strata during alpine orogenesis subsequent exposure of the subducted basement rocks by normal faulting has allowed an integrated study of the timing of metamorphism its relationship to deformation and the thermal history of the subducted terrane alpine low grade metamorphic assemblages occur at four structural levels three thrust sheets composed of paleozoic granitic basement and mesozoic metasedimentary cover were thrust over mesozoic carbonate rocks and eocene flysch thrusting and metamorphism occurred first in the highest thrust sheets and progressed downward as units were imbricated from ne to sw 40ar 39ar spectra from hornblende white mica and biotite samples indicate that the upper two units preserve evidence of four distinct thermal events 1 293 302 ma crystallization of granites with cooling from 550 c to 20 km extension in the olympos region was synchronous with extension in the mesohellenic trough and the aegean back arc and concurrent with westward progressing shortening in the external hellenides

sedimentology and hydrocarbon habitat of the submarine fan deposits of the central carpathian paleogene basin ne slovakia abstract the central carpathian paleogene basin accommodates a subsiding area of the destructive plate margin the basin history comprises marginal faulting and alluvial fan accumulation e 2 transgressive onlap by shoreface sediments and carbonate platform deposits e 2 glacio eustatic regression induced by cooling terminal eocene event forced regression tectonic subsidence and growth fault accumulation of basin floor and slope fans e 3 decelerating subsidence aggradation and sea level rising during the mud rich deposition o 1 high magnitude drop in sea level mid oligocene event retroarc backstep of depocenters and lowstand accumulation of sand rich fans and suprafans o 2 m 1 subduction related shortening and basin inversion along the northern margins affected by backthrusting and transpressional deformation o 2 m 1 the basin fill sequence has poor toc 0 5 to fair toc

40ar 39ar dating of white micas from an alpine high pressure metamorphic belt on naxos greece the resetting of the argon isotopic system overprinting of white micas from high pressure low to medium temperature m1 metamorphic assemblages in pelitic schists on naxos during subsequent thermal dome m2 metamorphism ranges from minor in the southeast of the island to complete recrystallization in the amphibolite facies rocks near the migmatites in the centre of the dome the original m1 minerals are phengites si4 6 7 7 0 and the overprinting minerals are muscovites si4 6 0 6 45 40ar 39ar step heating analyses of white mica separates from rocks in the area where phengite and muscovite occur together yield complex age spectra characterized by low apparent ages in the first and the last stages of gas release and high apparent ages in between these upward convex age spectra are shown to be caused by mixing of two generations of micas each of which has a different age spectrum and argon release pattern seemingly good plateaus in some age spectra from white micas of the area must be interpreted as providing meaningless intermediate ages further the upward convex age spectra have been used to trace the isotopic signature of phengites toward increasing m2 metamorphic grade and suggest that as long as phengites can be observed in the rocks upward convex age spectra occur on naxos crystallization of muscovite at the expense of phengite appears to be the main mechanism of resetting argon isotopic ages in white micas however there is also good evidence for argon loss by volume diffusion from phengites simple diffusion calculations suggest that the m2 metamorphism was caused by a shortlived heat source

tertiary subduction and slab break off model of the carpathian pannonian region abstract this paper illustrates the application of multidisciplinary data analysis to the carpathian pannonian region and presents a new tertiary development model that incorporates all multidisciplinary parameters during the late cretaceous eocene the future carpathian orogen was part of the larger alpine carpathian orogen formed by the southeastward subduction 135 55 ma of the penninic ocean and the ultimate collision 55 40 ma of the european and adriatic continents the subduction in the alpine region ended by the slab break off of the subducting oceanic lithosphere from the continental one and by the related magmatism 43 24 ma while the eocene alps were under continental collision the eocene remnant carpathian flysch basin rcfb was still subducting the carpathians and eastern parts of the alps started to occupy the region of the present carpathians during the early miocene the oceanic plate underlying the rcfb subducted southwestwards later westwards while the northeastward and eastward migration velocity of the accreting plate boundary decreased through time the slower subduction rate caused a steeper dip of the subducting slab the beginning of the eggenburgian 22 19 ma and following duration of extension in the orogenic hinterland accompanied by the asthenosphere upwelling the onset of the crustally derived volcanism above the risen asthenosphere and the younger mantle derived volcanism progressively less contaminated by the crustal material all contemporaneous with a shortening in the carpathian accretionary wedge the subduction of the rcfb finally led at the end of the early miocene to a collision with the continental margin along the westernmost part of the present carpathian arc the subduction roll back of the subducting slab of the rcfb under the advancing inner carpathians the oblique closure of the basin the progressive change of the subduction to collision from the west to the east along the carpathian arc drove a scissors like break off of the subducting oceanic slab along the west carpathians the break off in the east carpathians was driven by the weight of a subducting oceanic slab and buoyancy of the attached continental slab the break off started in the west of the carpathian arc in the early miocene ran along the arc to its present position in the bend area between the east and south carpathians and separated the oceanic slab that subducted passively under its own weight from the european continental margin the lateral propagation rate of the slab tear decreased with time the break off related volcanism was synchronous with the final stages of the collision

back projection stacking of p and s waves to determine location and focal mechanism of microseismic events recorded by a surface array we present an automatic method of processing microseismic data acquired at the surface by a star like array the back projection approach allows successive determination of the hypocenter position of each event and of its focal mechanisms one component vertical geophone groups and three component accelerometers are employed to monitor both p and s waves hypocenter coordinates are determined in a grid by back projection stacking of the short time average to long time average ratio of absolute amplitudes at vertical components and polarization norm derived from horizontal components of the p and s waves respectively to make the location process more efficient calculation is started with a coarse grid and zoomed to the optimum hypocenter using an oct tree algorithm the focal mechanism is then determined by stacking the vertical component seismograms corrected for the theoretical p wave polarity of the focal mechanism the mechanism is resolved in the coordinate space of strike dip and rake angles the method is tested on 34 selected events of a dataset of hydraulic fracture monitoring of a shale gas play in north america it was found that by including s waves the vertical accuracy of locations improved by a factor of two and is equal to approximately the horizontal location error a twofold enhancement of horizontal location accuracy is achieved if a denser array of geophone groups is used instead of the sparse array of three component seismometers the determined focal mechanisms are similar to those obtained by other methods applied to the same dataset

an assessment of the microseismic activity and focal mechanisms of the izmir smyrna area from a new local network izmirnet abstract izmir metropolitan area is one of the biggest cities of turkey in terms of population and industrial density amount of recordings and quality of located events increased since the new local seismic array izmirnet was installed in 2008 present study addresses to elucidate seismotectonics of izmir vicinity by a new data set and reveal first results of seismological analysis obtained for 4 5 years 930 small earthquakes are well located within less than 1 0 km horizontal error rms 0 15 s over a total of 1421 recorded events data were processed by using seisan earthquake analysis software implemented at seismolab of dokuz eylul university the orhanli tuzla fault zone and izmir faults are capable of producing a destructive earthquake events show clear clusters around the outer bay of izmir gulf and sigacik bay we also detected some dense clusters sigacik bay to the south and in the outer bay of izmir gulf along nw se direction we investigated kinematics of active faults around the izmir and foca areas by using 41 focal mechanism solutions from different algorithms foca is located 60 km in the nw direction of izmir mechanisms generally resulted in pure normal or dominant normal faulting with minor strike slip components in agreement with the kinematics of the other fault zones in western turkey a stress tensor study using selected fault plane solution indicates that the study area is under extension regime in an n s direction with 71 plunge for maximum compressive principal stress axis s1 and closer to horizontals for intermediate s2 and minimum compressive principal stress axis s3

continuity and episodicity in the early alpine tectonic evolution of the western carpathians how large scale processes are expressed by the orogenic architecture and rock record data

transition from convergence to escape field evidence from the west carpathians abstract the tertiary deformation of the west carpathians occurred during northeast directed convergence of the european and apulian plates and was complicated by space constraints imposed by orogen advance palaeostress fields computed from fault slip data and structural interpretation of known gravimetric magnetic seismic palaeomagnetic lithostratigraphic sedimentological fission track and borehole data indicate that during deformation the orogen consisted of both frontal thrust stacking zones and internal extensional trans tensional zones synthesis of available data indicates that the episodes of tectonism in litho tectonic units were both time and plate position related and were caused by conditions which varied in different areas ranging from the foreland to back arc region in each time period discrete deformation phases record the transition from convergent to tectonic escape tectonisrn principal horizontal stress trajectories were approximately co linear with the plate convergence vectors prior to escape the onset of escape conditions is indicated by 1 clockwise rotation of palaeostress orientations during the time of known escape in the eastern alps and 2 the cessation of thrusting of the flysch belt nappes onto the neogene foredeep in the westernmost part of the west carpathians tectonic escape along strike slip faults subparallel to the collision suture zone began in early badenian time in the west carpathians various regions along the orogenic belt were affected by escape that became progressively younger towards the east this agrees with the observations of various authors that the final phase of thrusting towards the european platform became younger to the east along the west carpathian arc in addition palaeostress trajectory patterns for various periods are similar to those modelled by a rigid block indenting a viscous half space an attempt is made to complete the mosaic of information on the cenozoic evolution of the alpine carpathian pannonian area which in the models given by ratschbacher royden horvath bergerat and others is based on extrapolated data the object is to detail the timing and complexity of the local time and plate position related mechanisms in the context of the entire orogen in order to update previous rather simplified models

geochronology of blueschists from west central baja california and the timing of uplift in subduction complexes a geochronologic study of blueschists from west central baja california has provided constraints on the timing of high pressure low temperature metamorphism and the subsequent uplift of this subduction complex mineral separates from coherent blueschists and blueschist blocks enclosed in serpentinite melange were analyzed by 40 ar 39 ar fission track and rb sr methods 40 ar 39 ar age spectra for white mica separated from four blueschist blocks and an overprinted eclogite block in serpentinite matrix melange show slow cooling gradients between 115 95 ma rb sr apparent ages for one block are concordant with these results 40 ar 39 ar ages of blue amphibole are primarily the result of the degassing of white mica intergrowths as confirmed by microprobe analyses apatite fission track ages indicate a blueschist block and an eclogite block cooled to a temperature below 100 c at 22 ma and 32 ma respectively subduction related metamorphism of the coherent blueschists occurred in la

u pb zircon geochronology and anomalous sr nd hf isotope systematics of late orogenic andesites pieniny klippen belt western carpathians south poland abstract late orogenic andesites and basaltic andesites in the pieniny klippen belt pkb in the western carpathians display atypical isotope systematics strongly departing from those observed among other neogene quaternary calc alkaline rocks in the carpathian pannonian region low end values 10 6 to 5 2 and low ehf values 19 6 to 5 2 are accompanied by unusually low 87 sr 86 sr ratios 0 7052 to 0 7059 major trace element isotope and geochronological data presented in this study indicate two magma sources evolving with low rb sr ratio from which the pkb calc alkaline rocks originated basaltic andesites showing less enriched signature and wider range of isotope compositions end 7 7 to 5 2 ehf 11 3 to 5 2 and 87 sr 86 sr 0 7052 0 7059 are interpreted as having originated from the partial melts derived from an ancient metasomatized sub continental lithospheric mantle which during emplacement were contaminated by the upper crustal material andesites whose precise timing of emplacement was constrained by in situ la icp ms u pb zircon dating at 11 2 0 2 to 12 1 0 3 ma show more enriched signature and narrow range of nd and hf isotope compositions end 10 6 to 10 1 ehf 19 6 to 18 3 accompanied by low 87 sr 86 sr 0 70531 0 70541 u pb dating of the inherited domains in zircons revealed the presence of late paleozoic precambrian and archean age components which support crustal origin of the pkb andesites in situ hf isotope analyses of zircons suggest that andesites could have been derived from enriched initial ehf 13 to 10 permian igneous domains in the lower crust generation of the calc alkaline magmas in the upper lithospheric mantle and in the thickened crust was triggered by decompression or crustal delamination following middle miocene collision of the alcapa block with southern margin of the european platform the pkb fault zone and its splays acted as conduits which enabled ascent of small volumes of andesitic magmas into the upper crust of the western carpathians

palaeomagnetic results from the fold and thrust belt of the western carpathians an overview the western carpathians are separated into an outer and inner carpathians both comprising several nappe systems by the extremely narrow and highly deformed pieniny klippen belt the main phase of deformation and thrusting took place during the late cretaceous in the inner carpathians at the end of cretaceous paleocene in the pieniny klippen belt and in the miocene in the outer carpathians in this paper a large amount of palaeomagnetic results of different quality available from several nappe stacks and from overstep sequences were reviewed and interpreted in terms of tectonics the data suggest that all three main units participated in two phases of anticlockwise rotation starting at 18 5 ma that is the outer carpathian nappes in front of the already consolidated alpine carpathian pannonian block became accreted to the block late cretaceous nappe transport neogene uplift of core mountains and possibly oroclinal bending of pre oligocene age can account for important differences in pre cenozoic palaeomagnetic declinations most of them exhibit less or no anticlockwise rotation suggested by the overstep sequences implying pre cenozoic clockwise rotations of variable angles

temporal and spatial variations of gutenberg richter parameter and fractal dimension in western anatolia turkey abstract the temporal and spatial variations of gutenberg richter parameter b value and fractal dimension dc during the period 1900 2010 in western anatolia was investigated the study area is divided into 15 different source zones based on their tectonic and seismotectonic regimes we calculated the temporal variation of b and dc values in each region using zmap the temporal variation of these parameters for the prediction of major earthquakes was calculated the spatial distribution of these parameters is related to the stress levels of the faults we observed that b and dc values change before the major earthquakes in the 15 seismic regions to evaluate the spatial distribution of b and dc values 0 50 0 50 grid interval were used the b values smaller than 0 70 are related to the aegean arc and eskisehir fault the highest values are related to sultandagi and sandikli faults fractal correlation dimension varies from 1 65 to 2 60 which shows that the study area has a higher dc value the lowest dc values are related to the joining area between aegean and cyprus arcs burdur fethiye fault zone some have concluded that b values drop instantly before large shocks others suggested that temporally stable low b value zones identify future large earthquake locations the results reveal that large earthquakes occur when b decreases and dc increases suggesting that variation of b and dc can be used as an earthquake precursor mapping of b and dc values provide information about the state of stress in the region i e lower b and higher dc values associated with epicentral areas of large earthquakes

kar and 40ar39ar study of metamorphic rocks associated with the oman ophiolite tectonic implications abstract k ar analyses on extracted minerals are reported for a variety of metamorphic rocks associated with the sumail ophiolite amphibolites lying at the sole of the ophiolite yield ages of 95 100 ma which are viewed as reflecting times of crystallization high pressure metamorphics of the saih hatat reveal complex results white micas range in age from 80 to 131 ma whereas blue amphiboles indicate ages that are systematically lower than those of coexisting white micas investigation of a few white micas by the 40 ar 39 ar step heating method yields rather intricate age spectra featuring low apparent ages in the first and the last stages of gas release and high apparent ages in between two explanations can be equally envisaged for these convex upward age spectra the first is the mixing of two generations of micas corresponding to two main metamorphisms the first one m1 is a low to medium temperature high pressure event which conceivably occurred between 130 and 114 m y ago the second m2 overprints m1 and has produced rocks typical of the greenschist facies it took place 80 m y ago and also affected the sole of the ophiolites the second is the presence of excess argon in mica mixtures with complex degassing properties thus the two metamorphic phases identified by microscopic inspection are not significantly different in age they occurred in the 70 80 ma interval moreover k ar dates on amphibole from gabbroic dikes intersecting the peridotites suggest that they are genetically linked to the mafic part of the ophiolites assuming that metamorphism is a tracer of tectonic events we view the infraophiolitic amphibolites as the result of an intraoceanic thrusting which took place near a spreading center nevertheless the uncertainty as to the age of the blueschist metamorphism precludes the possibility of indicating a timetable based on metamorphic ages for the motion shift of africa relative to eurasia during the late cretaceous a tentative model of the obduction of the sumail ophiolite is proposed assuming an age of about 130 ma for m1 we stress differences with respect to earlier reconstructions which advocated an 80 m y old blueschist metamorphism

the thermal significance of potassium feldspar k ar ages inferred from age spectrum results 40ar39ar age spectrum analyses of three microcline separates from the separation point batholith northwest nelson new zealand which cooled slowly 5 c ma 1 through the temperature zone of partial radiogenic 40ar accumulation are characterized by a linear age increase over the first 65 percent of gas release with the lowest ages 80 ma corresponding to the time that the samples cooled below about 100 c the last 35 percent of 39ar released from the microclines yields plateau ages 103 99 and 93 ma which reflect the different bulk mineral ages and correspond to cooling temperatures between about 130 to 160 c theoretical calculations confirm the likelihood of diffusion gradients in feldspars cooling at rates 5 c ma 1 diffusion parameters calculated from the 39ar release yield an activation energy e 28 8 1 9 kcal mol 1 and a frequency factor grain size parameter d0l2 5 6 3 9 14sec 1 this arrhenius relationship corresponds to a closure temperature of 132 13 c which is very similar to the independently estimated temperature from the observed diffusion compensation correlation this d0l2 implies an average diffusion half width of about 3 m similar to the half width of the perthite lamellae in the feldspars the range in microcline k ar ages from the separation point batholith is the result of relatively small temperature differences within the pluton during cooling comparison of the diffusion laws determined for microcline with those for anorthoclases and other homogeneous k feldspars e 40 to 52 kcal mol 1 reveals that ar diffusion is more highly temperature dependent in the disordered structural state than in the ordered structural state previously published u shaped age spectra are probably the result of the superimposition of excess 40ar upon diffusion profiles of the kind described here

kinematics of the alpine plate margin structural styles strain and motion along the penninic austroalpine boundary in the swiss austrian alps a structural and kinematic analysis of parts of the alpine suture zone i e the arosa zone and the edges of the overlying austroalpine and underlying penninic units is presented the arosa zone is interpreted as part of an accretionary wedge formed by the overriding of the austroalpine units the northern part of the adriatic plate over the penninic units structures strain and stretching trajectories indicate that two main deformation events followed each other discontinuously the earlier event was a wsw to nw directed thrusting under noncoaxial deformation and led to melange type structures the second event less penetrative in the arosa zone and with a downward increase in strain and noncoaxial flow formed n to ne verging folds and imbrication zones west directed displacement commenced in the early cretaceous and the motion changed to a prevailing northerly direction during the eocene as revealed by sediments involved in thrusting and by radiometric dating of the mylonites the kinematic history deduced from structural analysis agrees with the history obtained by recent work on plate margin sediments we correlate the anticlockwise rotation of the adriatic plate relative to europe between about 130 and 60 ma with the west directed motion in the arosa zone a change to relative n s motion during the lower tertiary led to the n to ne directed displacements a direct relationship thus exists between the motion of the adriatic plate and the resulting deformation along its northern margin during the early history of the eastern alps partitioning in brittle and ductile deformation and structural slicing under noncoaxial deformation is responsible for the melange type structures

40ar 39ar age spectrum analysis of detrital microclines from the southern san joaquin basin california an approach to determining the thermal evolution of sedimentary basins abstract detrital microcline grains from sedimentary strata preserve a record of thermal evolution in the temperature range 100 to 200 c which can be revealed by40ar 39ar age spectrum analysis microcline separates from deep drill hole intersections with eocene to miocene sediments in the basin and tejon blocks of the southern san joaquin valley california analysed by the age spectrum approach show radiogenic40ar 40ar gradients that record both the slow cooling of the uplifting sediment source 65 ma ago and a recent thermal event this information in conjunction with the observation of fission track annealing in the coexisting apatites allows estimation of the temperature time conditions of this thermal event at about 140 c for 200 ka present and paleotemperature data is in accord with heating related to several kilometers of pleistocene sediment deposition heat flow calculations suggest that this recent subsidence has depressed the thermal gradient from about 30 c km 1 to the present apparent gradient of 24 c km 1 40ar 39ar analysis of detrital microcline crystals yields thermochronological information in the temperature time range of petroleum maturation and provides this technique with potential as both a useful exploration tool and as a means of probing the fundamental geodynamic processes of basin evolution

quantitative reconstruction of orogenic convergence in the northeast carpathians abstract the ne outer carpathians form a fold and thrust belt of large displacement this mainly consists of deformed cretaceous tertiary deep water clastics and can be divided into an imbricate stack of four major supracrustal nappes the magura dukla silesian and skole nappes an extensive reflection seismic surface geological and drillhole database is used to constrain the deformed geometry of the two uppermost and southernmost allochthonous units the magura and dukla nappes a retro deformable cross section shows that the cretaceous tertiary sediment piles are detached along a single large decollement at about 5 7 km depth the rear and frontal parts of the magura nappe show steep imbricate fan geometries while the central part has a duplex structure with long thrust horses to the ne the dukla nappe is a stack of imbricate slices and is separated from the subjacent silesian nappe by a large thrust flat reverse modelling of deformation reveals that the magura nappe was horizontally shortened by at least 80 km and the dukla nappe by about 20 km in the ne sw direction together with previously published estimates of shortening in the silesian and skole nappes the total orogenic contraction in the ne outer carpathians is at least 260 km shortening was accumulated between the middle oligocene and the middle miocene almost all of the shortening can be balanced against contemporaneous back arc extension and eastward extrusion of rock masses from the eastern alps

microtremor array measurements for shallow s wave profiles at strong motion stations in hatay and kahramanmaras provinces southern turkey abstract we conducted microtremor array exploration of shallow s wave velocity profiles at 28 sites in hatay and kahramanmaras in the southern part of turkey to provide fundamental data to assess seismic hazards in the two areas a total of 16 and 12 sites were located in hatay and kahramanmaras provinces respectively we temporarily installed two small arrays to obtain simultaneous records of vertical microtremors the spatial autocorrelation method was applied to retrieve rayleigh wave phase velocity in a 1 30 hz frequency range the phase velocities at most of the sites in kahramanmaras province were high in the entire frequency range whereas those in hatay province were widely distributed suggesting significant variation in soil conditions low phase velocities were identified at sites near the coast in hatay subsequently the phase velocity observed at each site was inverted to a 1d s wave velocity profile to a depth of 100 m using a hybrid heuristic inversion most of the profiles in kahramanmaras had very thin near surface layers with s wave velocities of less than 300 m s and thicknesses of less than 10 m the top layers at the sites in hatay showed significant variation with different s wave velocities from 110 to 760 m s and thicknesses from 2 to 40 m these layers were thicker at the sites near the coastal area we finally discuss amplification factors of s waves using the inverted profiles the fundamental predominant periods of the amplification factors distributed across a wide frequency range from 0 8 to 10 hz in hatay the peak frequencies concentrated in a high frequency range of more than 5 hz in kahramanmaras the profiles observed were used to map average s wave velocities in the top 30 m at strong motion stations

fast location of seismicity a migration type approach with application to hydraulic fracturing data we propose a new approach for the location of seismic sources using a technique inspired by gaussian beam migration of three component data this approach requires only the preliminary picking of time intervals around a detected event and is much less sensitive to the picking precision than standard location procedures furthermore this approach is characterized by a high degree of automation the polarization information of three component data is estimated and used to perform initial value ray tracing by weighting the energy of the signal using gaussian beams around these rays the stacking is restricted to physically relevant regions only event locations correspond to regions of maximum energy in the resulting image we have successfully applied the method to synthetic data examples with 20 30 white noise and to real data of a hydraulic fracturing experiment where events with comparatively small magnitudes 0 were recorded

deep crustal structure beneath the central and inner west carpathians abstract the 150 km long deep seismic transect 2t crossing the central part of the slovakian west carpathians has revealed an important whole crustal seismic suture zone dipping to the south this zone is dominated by six large and several minor reflection events because of our good knowledge of the surface geology and a large number of comparative studies of the eastern alps it is clear that the upper reflections are due to overthrust sheets that originated during compression of the apulian passive margin tectonically deeper reflections are interpreted as being due to ligurian oceanic igneous and sedimentary rocks sheared in ductile domain during continental collision with the brianconnais passive margin and continental masses north of the central apulian west carpathians cwc behind a significant strike slip fault are the cenozoic structures of the pieniny klippen belt and the magura rhenodanubian flysch south of the cwc the inner tethyan west carpathians iwc are thrust over the cwc the iwc originated during the late jurassic early cretaceous closure of the tethyan ocean and the seismic image of the iwc is different from the highly reflective cwc suture these three pre neogene nappe systems amalgamated as one overthrust system during the neogene subduction of the moldavian sea as the moldavian accretionary wedge the vepor gemer block of the west carpathians where the cretaceous suture is observed has been untouched by any major cenozoic deformation and has remained relatively rigid this unique structure therefore enables us to observe seismically the cretaceous suture zone which elsewhere in the european alpine belt has been almost completely destroyed more general data about the beginning of subduction and subsequent collision processes are presented significant compression and partial subduction of the apulian upper plate passive margin lasted from the hauterivian to the beginning of the turonian for about 25 30 ma subduction of the ligurian ocean occurred from turonian to campanian times after the early campanian the collision of the apulian and brianconnais plates took place

neotectonic structures in izmir gulf and surrounding regions western turkey evidences of strike slip faulting with compression in the aegean extensional regime abstract of single channel 70 km and 900 km of multi channel seismic reflection data show that izmir gulf and surrounding regions are widely deformed by n s to ne sw trending active transpressional strike slip faults reverse faults and some e w normal faults normal faults are mapped offshore karaburun foca in inner part of izmir gulf offshore alacati teke and offshore kusadasi delimiting the southern scarp of lesvos basin izmir basin northern scarp of ikaria basin and continuation of kucuk menderes graben respectively normal faults are cut by strike slip faults the major strike slip faults are the n s oriented karaburun reverse fault bordering izmir gulf on the west and uplifting the karaburun peninsula and the ne sw oriented strike slip tuzla fault extending from doganbey promontory towards seferihisar ridge onland this fault pattern can be explained by pure shear model indicating that the area is under e w compression n s extension ne sw and nw se strike slip deformation moreover tuzla fault has a regional importance it separates ne sw trending structures of the study area from e w oriented gediz and kucuk menderes grabens and probably continues towards to iznik at north constituting a transition zone between northern transpressional region and southern extensional region in the western anatolia aegean sea

a general inversion scheme for source site and propagation characteristics using multiply recorded sets of moderate sized earthquakes abstract we derive an inversion scheme that fits the logarithms of seismic body wave spectra to 2 source shapes conditioned by anelastic attenuation with a frequency independent q the residuals from this fit are then projected onto the set of sources and sites with the source terms damped to estimate residual source spectra and site response spectra this two part inversion process is iterated until the square of the residuals summed over frequency for all recordings is minimized the absolute amplitudes of the source and site spectra are determined by fitting the site response spectra to estimates of the site amplification derived from geotechnical data we apply this inversion process to three sets of recordings of loma prieta aftershocks the first data set contains s waves recorded both in the marina district and at nearby hard rock stations we constrain the site response using the s wave velocity measured in a nearby borehole the absolute site amplifications for the marina stations are 15 to 20 at 1 hz and 10 at 2 5 hz the other two data sets comprise the p and s wave recordings from 28 aftershocks ranging in size from m d 2 1 to 4 6 obtained at accelerograph sites near the epicentral area the p and s wave attenuations determined from the inversions are q 414 and 380 while the average near site attenuations are t 0 012 and 0 026 sec respectively the average ratio of the s to p wave seismic moments is 1 1 0 1 the ratio of the p to s wave corner frequencies is 1 24 0 11 and the ratio of s to p wave radiated energy is 13 9 3 2 the brune stress drops for these aftershocks range from 8 to 800 bars the largest earthquakes exhibit the largest stress drops but there is no apparent dependence of stress drop on seismic moment for earthquakes with 10 19 m 0 21 dyne cm

a conjugate strike slip fault system within the extensional tectonics of western turkey summary three main shocks m 1 m 2 and m 3 17 october 2005 at 05 45 utc m w 5 4 17 october at 09 46 utc m w 5 8 and 20 october at 21 40 utc m w 5 9 and their associated after shocks within the gulf of si gacik 50 km southwest of izmir turkey were studied in detail a temporary seismic network deployed during the activity allowed the hypocentre of m 3 and subsequent aftershocks to be determined with high accuracy a relative relocation technique was used to improve the epicentres of m 1 and m 2 all three main shocks have strike slip mechanisms which agree with the linear trends of the aftershock locations two distinct zones were illuminated by the aftershock locations the zones contain clear echelon patterns with slightly different orientations from the trend of the aftershock distribution m 2 and m 3 rup tured along of the eastern rupture zone which aligns n45 e however the strike direction of m 1 is not clearly identified the alignment of the two rupture zones intersect at their southern terminus at an angle of 90 the fault zones form conjugate pair system and static triggering is considered as a probable mechanism for the sequential west to east occurrence of m 1 m 2 and m 3 this earthquake sequence provides seismological evidence for conjugate strike slip faulting co existing within a region dominated by north south extension and well developed east west trending normal faults

complex local moho topography in the western carpathians indication of the alcapa and the european plate contact seismic data from deep refraction and wide angle reflection profiles intersecting the western carpathians show distinct upper mantle pn phases with anomalous apparent velocities identified in the first and later arrivals their systematic analysis indicates that such phases are present in numerous seismic sections both for in line and off line shots they are observed in data from profiles intersecting the carpathians in the west at the contact with the bohemian massif similar feature was also found in data at the northern edge of the carpathians at the contact with the north european platform modelling of these anomalous pn phases shows that they originate due to local structural anomalies of the moho discontinuity detected in several places along the western carpathian arc such anomalies are located in close lateral proximity of the pieniny klippen belt representing the contact between the stable european plate in the north and the alcapa alpine carpathian pannonian microplate in the south thus the complex local moho topography modelled from the pn phases suggests tectonic relation to the formation of the carpathian orogen the result is supported by correlation with the large scale carpathian conductivity anomaly modelled in the carpathians at a mid crustal level relative lateral position of these two structures together with the pieniny klippen belt at the surface delineates a zone affected by deformations at various depths along the whole western carpathian arc

the choice of reference sites for seismic ground amplification analyses case study at parkway new zealand this article focuses on how close reference rock sites need to be to the sites of interest when using the standard spectral ratio technique to obtain consistent estimates of site amplifications reflecting behavior of seismic waves at the sites of interest taber and smith 1992 and chavez garcia et al 1999 obtained very different amplification factors for the parkway basin new zealand using reference sites only 2 km apart we analyze 34 earthquakes recorded by a dense 2d array of 19 soil sites in the basin and 4 rock sites fringing the basin spectral ratios are calculated separately relative to taber and smith9s reference site p01 2 km from the basin and to a hypothetical average rock site pr formed from the four local rock sites including reference site p25 of chavez garcia et al our spectral ratios of the soil sites relative to pr are remarkably consistent with a distribution of the dominant peaks at 8 4 2 0 at 1 7 0 3 hz in contrast the spectral ratios relative to p01 are much less consistent and the dominant peak ratios are widely scattered around two separate centers of 14 5 4 1 at 1 8 0 3 hz and 14 4 5 5 at 4 7 1 0 hz our results relative to the two references are similar to those obtained by chavez garcia et al and taber and smith respectively we find that extreme differences between the two are often associated with the occurrence of troughs in the amplitude spectra at p01 possibly due to topographic deamplification there relative to the parkway basin in some but not all earthquakes

reconstruction of cretaceous rifts incorporated in the outer west carpathian wedge by balancing abstract two balanced cross sections were constructed through the outer carpathians of poland in order to restore the early cretaceous rifts the rift fill is incorporated into the tertiary carpathian accretionary wedge the data compiled for this study confirm that the early cretaceous rifting in the silesian basin area was followed by late cretaceous paleocene basin inversion eocene pelagic deposition and oligocene syn orogenic deposition the original width of the silesian basin is about 130 138 km the overall wedge shortening ranges between 31 and 58 with 57 and 58 in the silesian nappe the rifting commenced at the jurassic cretaceous boundary and formed the horst and graben structures defined by nw se striking normal faults portions of the horsts become emergent at various times during rifting stages sedimentation rates in the grabens varied around 4 7 2 1 and 1 3 cm ka during three rifting stages while sedimentation rates on their slopes varied around 0 0 1 26 and 0 cm ka the altitude difference between horst tops and graben floors did not exceed 2 km the reconstructed widths of the horsts range between 17 5 and 18 3 km the reconstructed widths of several grabens in both cross sections have values 14 5 45 7 57 7 and 79 3 km the rifting related extension calculated from fault striae data was ne sw directed sometimes the very low 2 3 1 3 stress ratio of the driving stress configuration resulted in polydirectional extension when the value decreased below 0 1

reservoir characterization using surface microseismic monitoring microseismic monitoring of reservoir processes can be performed using surface or near surface arrays we review the published technical basis for the use of the arrays and the historical development of the method beginning with locating earthquakes through geothermal exploration to the growing field of hydraulic fracture monitoring practical considerations for the array deployment and data processing are presented the road ahead for the technology includes a move toward life of field buried arrays as well as opportunities for extended interpretation of the data particularly inversion for source mechanism estimation and measurement of anisotropy in the monitored subsurface

determination of the tectonic stress tensor from slip along faults that obey the coulomb yield condition a new method to calculate the stress tensor associated with slip along a population of faults is derived here the method incorporates two constraints first the stresses in the slip direction satisfy the coulomb yield criterion and second the slip occurs in the direction of maximum shear stress along the fault the computations provide the complete stress tensor normalized by the vertical stress and evaluation of the mean coefficient of friction and the mean cohesion of the faults during the time of faulting the present method is applied to three field cases dixie valley nevada wadi neqarot israel and yuli microearthquakes taiwan it is shown that the coefficieet of friction of the three cases varies between 0 1 to 0 8 further it is demonstrated that previous stress inversion methods implicitly assume zero friction along the faults

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

tertiary extension development and extension compression interplay in the west carpathian mountain belt abstract this paper describes palaeostresses calculated from fault striae data the inferred palaeostrain patterns and determines the inter relation of the compression and extension during the tertiary development of the west carpathians the calculated stress and inferred strain patterns for the palaeogene burdigalian indicate that the ancestral west carpathians formed a more or less straight orogenic belt this belt underwent contraction and uplift in its narrow frontal zone stretching along its strike during the paleocene chattian and regional contraction and uplift during the chattian burdigalian the strain stress pattern is similar to the collision related pattern known from the eastern alps for the paleocene burdigalian during the burdigalian tortonian the calculated and inferred west carpathian stress and strain patterns indicate narrow frontal contractional and lateral sinistral transpressional zones in the orogenic front and broad extensional and dextral transtensional zones in the orogenic interior the stress strain pattern is similar to the subduction related pattern known from areas such as the hellenic or sunda banda arcs

graphical determination of principal stress directions for slickenside lineation populations an attempt to modify arthaud s method abstract a new method of graphic determination of principal stress directions is proposed for slickenside populations produced in anisotropic rocks arthaud s concept of movement planes is advanced through studying variations in their pattern relative to the changing values of the principal stresses these variations are recognizable by means of a simple test based on the bott equation in contrast to arthaud s method the proposed procedure is applicable to fault populations resulting from stress fields geometrically reproducible by a triaxial ellipsoid a field example is given to demonstrate the practical utility of the method

paleogene and neogene kinematics of the alpine carpathian fold thrust belt at the alpine carpathian transition abstract in this study we analyze a 300 km long segment of the alpine carpathian orogen using novel outcrop data and regional seismic profiles from the west carpathians to unravel the kinematics and timing of eocene to late miocene deformation of the fold thrust belt comparison with data from the eastern alps and the vienna basin leads to an updated tectonic model for the paleogene and neogene of the alpine carpathian transition which includes three stages 1 eocene to early oligocene nnw directed foreland propagating thrusting thrusts are directed perpendicular to the strike of the european foreland in the outer west carpathians owc and sub parallel to thrusts observed in the eastern alps west of the vienna basin 2 continued late oligocene to early miocene nnw directed foreland propagating thrusting simultaneous with sinistral strike slip reactivation of former nappe boundaries in the hinterland of the active thrusts this deformation corresponds to the early stage of eastward lateral extrusion of the eastern alps the ene striking sinistral faults in the owc are kinematic equivalents of the semp fault system in the eastern alps which was active at the same time the latest stage of thrusting is characterized by sse directed out of sequence thrusts in the hinterland of the owc and the reactivation of variscan basement thrusts in the european foreland as sse directed backthrusts 3 formation of n ne striking sinistral strike slip faults which are kinematically linked to n ne directed out of sequence thrusts post dating nnw directed thrusting the sinistral faults formed coeval with the opening of the vienna pull apart basin during the middle to late miocene stage of lateral extrusion unlike proposed in previous studies the west carpathians do not appear to be affected by oligocene to early miocene crustal scale wrenching of the pieniny klippen belt our data show that the deformation of the pkb is in line with the eocene to late miocene tectonic evolution reconstructed for the owc

local site response in an alpine valley from recorded earthquakes and ambient noise analysis local response is estimated within the sediment fill of the tagliamento river valley thv northeastern italy using about 90 weak to medium local and regional earthquakes ground motion is recorded at six stations deployed in a linear array across the valley site amplification factors are determined using the standard spectral ratio the generalized inversion technique and evaluations of receiver functions results obtained from earthquake data are then compared with ambient noise analysis azimuthal effects in the seismic response are observed locally for waves coming from the east southeast aligned with the longitudinal axis of the valley the seismic responses evaluated at the mid valley and at the valley edge are then convolved with the 1976 m w 6 4 friuli mainshock recorded at accelerometric station tlm1 located close to the array the local response at the valley edge in the town of cavazzo carnico is responsible for an enhancement of the input motion of an average factor of about 4 in the frequency range from 2 to 8 hz the elastic demand from the current national regulation for a 475 year return period and specific for cavazzo carnico is overcome by the 5 damped pseudoacceleration response spectrum estimated at the valley edge the underestimation of the italian code is mostly due to a 2d amplification effect at the valley edge rather than a simple inadequacy of the v s 30 site classification online material figures showing locations of historical earthquakes distribution of fundamental frequency of vibration waveforms of the m d 5 1 kobarid earthquake s wave velocity versus depth and git and rf amplification median values and spectra tables of seismic station locations and soil type and of local and regional earthquakes

an experimental study of site effects near thessaloniki northern greece ground motion amplification by local geology conditions is investigated near thessaloniki greece using spectral ratios of s waves from local and regional earthquakes we present results for two different experiments using an array of five digital three component seismographs in the first instruments were installed across vasilika sedimentary valley southeast of thessaloniki three on sediments and two on rock sites outside the valley empirical transfer functions relative to one of the rock sites show significant amplification for low frequencies between 1 and 6 hz at the stations on the sediments and at high frequencies between 8 and 15 hz for a station on a weathered rock site our spectral ratios for local earthquakes have shapes similar to those for regional earthquakes but the amplification levels are different in the second experiment the seismographs were installed at five sites within the city of thessaloniki on four different geological formations according to our results site response does not vary significantly between gneiss quartzites and recrystallized limestone two stations on the same neogene formation a series of red silty clays with mica and calcareous concretionary bodies show relative amplification which attains a factor of 5 relative to the rock site but the shapes of the transfer functions are different between the two stations finally we show that our results correlate well with macroseismic information from the 1978 seismic sequence in thessaloniki consisting of both regional isoseismal maps and damage distribution within the city this substantiates the use of weak motion records to estimate local ground motion amplification in earthquake engineering

neotectonic structures in the area offshore of alacati doganbey and kusadasi western turkey evidence of strike slip faulting in the aegean extensional province abstract about 400 km of new seismic reflection data has been acquired in the study region offshore of alacati doganbey and kusadasi which enables investigation of the active crustal deformation in this region the deformation onshore in western turkey is dominated by crustal extension and clear evidence of this process is also now available from this offshore area however in the onshore area adjacent to this study region evidence of active right lateral strike slip faulting has also previously been observed this strike slip faulting has previously been thought only to accommodate variations in extension between adjacent normal faults however in the offshore area there is considerable evidence of zones of deformation some of which may link to the strike slip faulting onshore suggesting that strike slip faulting may be of greater importance in this region than previously thought

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

palaeotectonic reconstruction of the central alpine mediterranean belt for the neogene abstract the structural patterns of the central alpine mediterranean belt ranging from the eastern balearic sea to the western aegean sea have been reconstructed for 10 and 20 ma b p they have been obtained in the frame of the africa europe convergence through a step by step rigid plastic reconstruction using available geological and palaeomagnetic data all domains outlined in the present situation are shown in the palaeotectonic reconstructions while the structural pattern at 10 ma b p is similar to that of the present except for the tyrrhenian region that at 20 ma b p differs from it in most areas the well known adriatic promontory of the african plate is recognizable in both pictures and at 20 ma its original boundaries are revealed as strongly deformed flysch belts the adriatic promontory was broken up in the early or middle miocene into two microplates of comparable sizes the norther one is the adriatic microplate s s which suffered counter clockwise rotation by 20 relative to africa around the alpine apenninic whirl centre the southern one is the apulian microplate first outlined in the present work including the south apenninic and the apulian s s south of the gargano peninsula platforms which suffered no rotations relative to africa but which moved towards the northeast of it the primary reason for the break up of the adriatic promontory was most probably the opening of the balearic ligurian sea since 10 ma the adriatic and apulian microplates were again integral with africa or perhaps they moved towards the west relative to africa pushed by the turkish microplate the orogeny in the area discussed is mostly linked with collisional processes on the boundaries of the adriatic apulian unit

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

plate collision and paleostress trajectories in a fold thrust belt the foothills of taiwan abstract field analyses of compressional faulting and folding in the foothills of western taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events two main compressional events have contributed to the present structure of the fold thrust belt stratigraphic data show that these events are plio pliocene in age older normal faulting indicates nnw sse extension across the chinesse passive continental margin during the neogene the two main compressional events of the taiwan collision correspond to similar fan shaped distributions of maximum compressive stress trajectories with a counterclockwise shift of 30 50 between the two events using the relationship between recent stress trajectories and the direction of recent plate motion as a guide we reconstruct the direction of plate convergence for the older event we suspect that the relative motion philippine sea plate eurasia has rotated counterclockwise of at least 35 45 in taiwan during collision this conclusion is in agreement with independent plate tectonic reconstructions several problems provide objectives to further tectonic and paleomagnetic studies including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost taiwan

new paleomagnetic results from the upper cretaceous red marls of the pieniny klippen belt western carpathians evidence for general ccw rotation and implications for the origin of the structural arc formation abstract the pieniny klippen belt pkb is a narrow arcuate structure separating the central and outer western carpathians formed during several cenozoic deformational stages the primary aim of this study was to obtain paleomagnetic constraints for the mechanism of formation of the arc we investigate albian santonian red pelagic marls from 14 localities distributed along a strike length of ca 400 km ams measurements reveal a pattern characteristic of weakly deformed sedimentary rocks and magnetic lineations do not correlate with the general strike of the pkb paleomagnetic analysis revealed well defined hematite based ancient magnetization components at 13 localities which are dated using fold and inclination tests a within locality fold test is negative for two localities exhibiting large ccw rotations of similar magnitude situated at the two ends of the pkb remanences of pre folding age were documented for 11 localities with an overall mean paleomagnetic direction of d 311 i 53 and 95 11 the indicated general ccw rotation most probably took place during the miocene together with western central and outer carpathians paleolatitudes for the pkb indicate a considerable separation from the southern margin of stable europe leaving space for coordinated rotation a paleomagnetic oroclinal test involving all localities with primary magnetizations was negative when localities with monoclinal steep dips are omitted due to possible declination bias the overall mean paleomagentic direction does not change significantly but correlation is observed between the general trend of the pkb and the paleomagnetic declinations thus we conclude that the present shape of the arc can be partly due to oroclinal bending this must have happened before oligocene since paleomagnetic declinations for neighboring paleogene basins in the central and outer western carpathians reveal a uniform ccw rotation of ca 50 magnitude irrespective of the position of the localities in relation to the carpathian arc

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

ambient noise level and site characterization in northern egypt the characterization of the background seismic noise in any seismological network is an essential task for checking the performance of the recording stations hence a funded project from science and technology funding authority stdf was awarded by the national research institute of astronomy and geophysics nriag in 2017 to detect the recording capabilities of the egyptian national seismological network ensn established after the cairo earthquake which occurred in egypt on october 12 1992 this article covers the first output of the project which shows the results of noise assessment for nine broadband stations located in northern egypt for a proper assessment of seismic data quality for a part of the ensn network the passcal quick look extended pqlx software was used which is based on the calculation of power spectral density psd and probability density function pdf for the background noise the analysis covered almost one year of continuously recorded seismic data the results show that some stations have very low detectability and higher noise level in some frequency bands which affects the recording of seismic events while others show good performance complete site analysis for all stations was done to illustrate the present site response to be able to recommend whether to keep a station or to relocate it to achieve this the seismic noise data extracted from all stations of the considered zone was studied to determine the horizontal to vertical h v spectral ratio method to study the amplification parameters of the recording site the output of this study is useful for detecting operational problems in the northern part of the egyptian seismological network and could be relevant for the reconfiguration and optimization of ensn stations

strain partitioning along the western margin of the carpathians abstract four profiles across the obliquely convergent west carpathian external zone together with a field study of the area indicate the interrelation of thrusting and strike slip faulting in the transpressionally deformed wedge in the front of the wedge thrusting is dominant towards the hinterland a progressively greater proportion of strike slip faulting is found the resultant deformational paths are curvilinear diverging from the parallel with the northeast vergent orogen advance the external zone of the west carpathian arc consists of two parts first a zone of frontal compression perpendicular to the orogen advance vector and second a zone of lateral sinistral transpression which is at a lower angle to the orogen advance vector the displacement along correlated strike slip faults progressively decreases towards the zone of frontal compression

observed variations of earthquake motion across a sediment filled valley the response to earthquake motion of a site in one sediment filled valley was observed to depend strongly on frequency and the position of the site within the valley and weakly on the input signal s azimuth and incidence angles the observed input motion was weak varying between 10 5 and 10 3 g measurements of ground velocity were made on profiles across and along the valley and simultaneously on two nearby rock sites the valley was 400 m wide and 700 m long with a maximum sediment thickness of 60 m the average seismic impedance contrast between the sediments and underlying basement rock was about 6 1 ratios of fourier spectra from soil sites to spectra from nearby rock sites showed apparent site amplifications of as much as a factor of ten depending strongly on frequency and the distance of the site from the valley edge the scatter in spectral ratios for earthquakes with different azimuths and angles of incidence was about a factor of two thus local site effects that changed the amplitude of incident motion by a factor of two or more could be identified in the records of most earthquakes ground motion at valley edge and mid valley sites separated by less than 100 m differed by as much as a factor of five this difference could cause large differential motion in structures spanning these sites a theoretical flat layer model of sediment response predicts the average behavior of the middle of the valley but not that of the valley edge the lowest frequency responance apparently involves the sediments across the width of the valley not just the vertical column of soil beneath each site

microseismic imaging of a geothermal reservoir stimulation exploitation of geothermal heat energy from rocks at depths of several km has been the goal of vari ous projects since the mid 1970s to exploit the energy in these deep rocks poses technical challenges in drilling well completion creation of the heat exchange reservoir at depth and control of seismicity in spite of the difficulties what are now known as enhanced engineered geothermal systems egs offer almost limitless clean energy so it is not surprising that this technology continues to attract investors however commercial energy production from the greatest potential resource hot rock at depths 5 km or temperatures 200 c remains elusive

source parameters and scaling relations of local earthquakes from a strong motion network in izmir western turkey this study reports the estimation of source parameters in and around izmir western anatolia turkey using data recorded by 18 strong motion stations belonging to the local accelerometer array izmirnet the displacement spectra of sh waves are calculated for 55 earthquakes with a moment magnitude range mw of 3 4 to 5 7 recorded by at least ten stations the corner frequency f0 spectral level and fmax are acquired from the displacement spectra in order to analyse the source characteristics of the events using brune s source model seismic moment m0 values are computed between 12 74 and 17 93 nm spectral level 0 values are detected between 3 17 and 6 44 nm s source radius r values are calculated from 0 45 to 2 28 km and seismic energy values are estimated between 2 07 1013 and 6 45 1020 erg computed stress drop values vary from 0 72 to 346 9 bar and this result is significantly lower than the values of 0 017 and 647 6 bar reported for the marmara region northwestern anatolia turkey and slightly lower than the source sizes of the events of between 0 0862 and 5 1042 km however similar results were found for seismic moments koseoglu et al in j seismol 18 651 669 https doi org 10 1007 s10950 014 9435 2 2014 from the results of the present study it is concluded that scattering in seismic moment stress drop and hypocentral distance during large earthquakes is observed by an increase in f0 and fmax which is related to the complex tectonism of the study area

40ar 39ar dating of the inner carpathians variscan basement and alpine mylonitic overprinting abstract the 40ar 39ar dating method has been applied to mylonitic rocks from the carpathian mountains these are variscan metamorphic and magmatic rocks that were overprinted during the alpine orogeny the inner western carpathians are conventionally described as a nappe pile formed by northward movement and then subjected to intense strike slip and normal faulting resulting in the formation of mylonitic rocks precise stratigraphie ages provide clear constraints for the geodynamic interpretation related to the succession of alpine events such as the pre gosauian phase during the turonian 90 ma the 40ar 39ar method allows to define the age of the ancient variscan basement and the ages of the alpine overprinting in the high and low tatras mineral ages of around 340 350 ma are yielded by gneisses micaschists and amphibolites providing a younger limit for the variscan metamorphism the emplacement cooling of the variscan granites is defined between 305 and 335 ma these rocks are overprinted by several alpine tectonothermal events the major events are dated at 65 and 86 88 ma during which the mylonites were generated an older event around 140 ma earlier defined by the rb sr method is now confirmed by the 40ar 39ar method dating of phengites extracted from high pressure metamorphic triassic rocks from the kosice area yields new data for the age of this event at 155 ma