the effect of low velocity sediments on the mislocation vectors of the grf array summary the grf array is situated on jurassic limestone of the franconian alb in se germany the mislocation vectors show symmetry axes in their slowness and azimuth components for the slowness the line of separation is at about 95 against north the azimuth pattern shows a symmetry axis nearly perpendicular to the axis in the slowness pattern waves arriving from ne have a reduced slowness whereas waves from sw have a larger slowness the largest azimuth anomalies are found in the directions where the slowness components change direction these effects can to a large extent be modellfd by a low velocity sedimentary layer dipping to nne with about 0 8 dip such a sedimentary wedge correlates well with the geological data is able to reproduce the observed mislocation vector pattern and explains a major part of the observed traveltime residuals it furthermore demonstrates that local effects like the influence of sedimentary covers should be removed before inversion procedures and tomographic methods are applied

locating non volcanic tremor along the san andreas fault using a multiple array source imaging technique summary non volcanic tremor nvt has been observed at several subduction zones and at the san andreas fault saf tremor locations are commonly derived by cross correlating envelope transformed seismic traces in combination with source scanning techniques recently they have also been located by using relative relocations with master events that is low frequency earthquakes that are part of the tremor locations are derived by conventional traveltime based methods here we present a method to locate the sources of nvt using an imaging approach for multiple array data the performance of the method is checked with synthetic tests and the relocation of earthquakes we also applied the method to tremor occurring near cholame california a set of small aperture arrays i e an array consisting of arrays installed around cholame provided the data set for this study we observed several tremor episodes and located tremor sources in the vicinity of saf during individual tremor episodes we observed a systematic change of source location indicating rapid migration of the tremor source along saf

relative array analysis of upper mantle lateral velocity variations in southern california spatial averaging of short period teleseismic p wave arrivals across scarlet constrains upper mantle lateral velocity variations beneath southern california we compare dt d back azimuth and averaged arrival time estimates determined from the entire network for 154 events to the same parameters derived from small subsets of scarlet the resulting relative array diagrams and plots of net subarray delays computed for 171 overlapping subarrays exhibit large anomalies that vary smoothly as a function of subarray position implying substantial lateral heterogeneity under the network patterns of mislocation vectors for more than 100 subarrays permit identification of an east west striking high velocity antiform beneath the transverse ranges further constraints on both the lateral configuration and depth of the anomaly are obtained through thin lens analysis of the net delay data where all the time perturbations are assumed to originate at a single depth projection of 2798 net delays requires a lens deeper than 100 km a representative lens at 150 km depth features low velocities beneath the salton trough as well as a concentrated high velocity zone between 116 3 118 3 w and 33 7 34 8 n consistent with the relative array diagrams and the pkp delay contours of hadley and kanamori 1977 therefore the bulk of the high velocity material observed by hadley and kanamori may in fact lie at or deeper than 150 km rather than 40 100 km this possibility prompts renewed speculation regarding the relationship of this body to the plate tectonic history of the region

the deep structure of the north anatolian fault zone abstract multi scale full waveform inversion of complete continental and regional scale seismograms reveals the crustal and upper mantle signature of the north anatolian fault zone which shapes the neotectonics of turkey and the eastern mediterranean within the crust the fault zone is mostly bounded by several high velocity blocks suggesting that it developed along the edges of continental fragments with high rigidity below the crust the surface expression of the eastern and central parts of the north anatolian fault zone correlate with a pronounced low velocity band that extends laterally over 600 km around 100 km depth the low velocity band merges into the shallow anatolian asthenosphere thereby providing a link to the kirka afyon isparta volcanic field and the central anatolian volcanics we interpret the low velocity band beneath the north anatolian fault zone as the upper mantle expression of the tethyan sutures that formed 60 15 ma ago as a result of africa eurasian convergence the structurally weak suture facilitated the formation of the younger less than 10 ma crustal fault zone in this sense the north anatolian fault zone is not only a crustal feature but a narrow zone of weakness that extends into the upper mantle

new constraints on the active tectonic deformation of the aegean 1 site velocities from six separate global positioning system gps networks comprising 374 stations have been referred to a single common eurasia fixed reference frame to map the velocity distribution over the entire aegean we use the gps velocity field to identify deforming regions rigid elements and potential microplate boundaries and build upon previous work by others to initially specify rigid elements in central greece the south aegean anatolia and the sea of marmara we apply an iterative approach tentatively defining microplate boundaries determining best fit rigid rotations examining misfit patterns and revising the boundaries to achieve a better match between model and data short term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long term kinematics we find that present day aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them the rms misfit of model to data is about 2 sigma very good when compared to the typical match between coseismic fault models and gps data the simplicity of the microplate description of the deformation and its good fit to the gps data are surprising and were not anticipated by previous work which had suggested either many rigid elements or broad deforming zones that comprise much of the aegean region the isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain year nstrain year 10 9 year 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries lower strain rates may exist elsewhere within the microplates but are only resolved in anatolia where extension of 13 4 nstrain year is required by the data our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity active faulting fault geomorphology and earthquake fault plane solutions continental tectonics at least in the aegean is to first order very similar to global plate tectonics and obeys the same simple kinematic rules although the widespread distribution of aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized

strain partitioning and stress rotation at the north anatolian fault zone from aftershock focal mechanisms of the 1999 izmit mw 7 4 earthquake summary we investigate aftershock focal mechanisms of the m w 7 4 izmit earthquake of 1999 august 17 on the western north anatolian fault zone nafz spatial clustering and the orientation of 446 fault plane solutions are analysed the izmit mainshock occurred as a right lateral slip on an ew trending near vertical fault plane aftershock clusters define four individual fault segments focal mechanisms surrounding the epicentres of the izmit and subsequent duzce mainshock m w 7 1 1999 november 12 indicate predominantly strike slip but also normal faulting aftershocks in the area between the izmit and duzce segments are mainly related to ew oriented normal faulting delineating a small pull apart structure beneath the easternmost sea of marmara alignments of aftershocks suggest branching of the nafz into three or more active segments that differ significantly in terms of their focal mechanism characteristics the distribution of aftershock focal mechanisms corresponds to fault segmentation of the nafz in the izmit duzce region produced by coseismic slip areas with large amounts of coseismic slip show aftershocks that are predominantly strike slip but low slip barriers show mostly normal faulting aftershocks stress tensor inversions of the aftershock focal mechanisms show rotations of the local stresses following the izmit mainshock in the izmit sapanca area the maximum horizontal compressive stress axis is horizontally rotated counter clockwise by 8 with respect to the coseismic and long term regional stress field towards the eastern end of the rupture karadere duzce area stresses are rotated clockwise we conclude that the izmit earthquake caused significant stress partitioning along the rupture the direction of stress rotation is related to the orientation of the individual fault segments along the nafz

spatial variations in stress within the 1987 whittier narrows california aftershock sequence new techniques and results the ml 5 9 whittier narrows california earthquake of october 1 1987 triggered a complex aftershock sequence the aftershocks had many different focal mechanisms including thrusting on e w striking north dipping planes similar to the main shock right lateral motion on nw se striking planes similar to the ml 5 3 aftershock on october 4 1987 thrusting on n s striking planes and left lateral motion on n s striking planes i attempt to interpret these mechanisms in terms of a stress field that may have caused them previously stress inversion methods based on focal mechanisms assumed that the stress field was spatially uniform in order to test for the spatially varying effect of the main shock s dislocation on the aftershocks focal mechanisms a new inversion technique was developed that solves for a uniform stress field that is superimposed on a given spatially varying stress field a series of simulations were performed to test both the new method and an older method that uses only the uniform component of the stress field these simulations show that both techniques work but will be limited by the amount of noise in the data and the accuracy to which the given spatially varying stress field resembles the actual spatially varying stresses most importantly the simulations show that the older methods do work when the stress field has a uniform component that is at least as large as the spatially varying component the simulations also show that when applying the older stress inversion techniques one can determine if the results are valid and the amount of spatially varying stresses present by examining the misfit between the data and the model application of these techniques to the whittier narrows aftershocks suggests that the uniform component of the stress field and the complex faulting corresponds to the response of an elastic halfspace to a simple regional n s compression the misfit between the data and the uniform model demonstrate the presence of spatially varying stresses at whittier narrows however their form as shown by the simulations can not be determined with this data set and these techniques

processing of regional seismic events using data from small aperture arrays abstract a regional on line array processing package ronapp has been developed and tested on data from a small aperture seismic array noress at norsar consisting of 12 sensors spaced with distances up to about 2 km the processing package automatically detects and locates regional seismic events in the distance range from a few kilometers to the maximum propagation range of regional s type waves sn or lg the package contains a conventional sta lta detector which works on a set of filtered beams deployed at typical phase velocities of pn and lg sn 8 0 and 4 5 km sec when a detection is found data within a certain time window around the detection time are used for estimates of refined arrival time and signal frequency and a wavenumber analysis is then performed following a proper prefiltering this gives in addition to arrival time and frequency estimates of phase velocity azimuth and signal to noise ratio for each detection following each processed detection an event location based on azimuth and s p travel times is performed if the last detection is identified as an s type wave phase velocity below 6 km sec and a preceding p wave phase velocity above 6 km sec has been detected with about the same direction of approach appropriate procedures are developed to allow for several detections within the p and s coda to keep track of used and unused detections and to identify epicenter locations that override preliminary ones as the analysis progresses through the s wave train of the event the processing package has been tested off line and on line on a number of data intervals for various experimental noress array configurations the automatic processing package provides detection results for regional events that compare favorably with those from the full norsar array and location results that deviate from locations by the fennoscandian network of seismological stations by typically 30 km which is of the order of the location uncertainty of the network

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

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

establishment of a 3 83 ga magmatic age for the akilia tonalite southern west greenland a recurring challenge to ion microprobe u pb zircon geochronology has been to discriminate between preservation of original igneous zircon populations and inherited grains this has proved particularly problematic in studying the polyphase metamorphic rocks that dominate early archean gneissic terranes for example differing interpretations exist for the origin of complex zircon populations investigated by u pb ion microprobe zircon geochronology from a granitoid orthogneiss body previously used to establish a minimum age for a supracrustal enclave on akilia island in southern west greenland we describe a method whereby the geochemistry of the akilia orthogneiss coupled with a u th pb vs age depth profile in a zircon from the same rock permits direct assessment of zircon inheritance results reveal evidence for three phases of concentric zircon growth at 3 83 ga v3 6 ga and 2 7 2 5 ga zircon growth at both v3 6 ga and 2 7 2 5 ga is consistent with precipitation from a metamorphic fluid depth profile u th pb data demonstrate that only the s 3 8 ga zircon core could have crystallized from the host rock we conclude that the magmatic age of this rock is 3 83 7 0 01 ga not v3 65 ga as has been previously proposed the u th pb zircon depth profile technique has wider applications to resolving other geochronological debates in highgrade metamorphic terranes where zircons populations are diverse and individual grains record complex overgrowth and dissolution re precipitation features 2002 elsevier science b v all rights reserved

stress orientations obtained from earthquake focal mechanisms what are appropriate uncertainty estimates crustal stress orientations provide important information about the mechanics of regional deformation numerous methods exist for inverting earthquake focal mechanisms for stress orientation and the more widely used methods usually obtain similar results for similar data sets however error estimates are highly variable complicating the interpretation of results the southern california stress field for example contains much statistically significant spatial and temporal variability according to the error estimates of one method michael 1984 1987b but very little according to those of another gephart and forsyth 1984 to resolve whether the southern california stress field is generally homogeneous or heterogeneous we must determine which of the error estimates best reflects the true inversion uncertainty to do this we tested both methods on a suite of synthetic focal mechanism data sets containing random errors the method of gephart and forsyth 1984 usually provides more accurate estimates of stress orientation especially for high quality data sets but its confidence regions are in most cases too large the method of michael 1984 1987b is more accurate for very noisy data sets and provides a more appropriate estimate of uncertainty implying that the stress field in southern california is probably heterogeneous

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

seismotectonic investigation of biga peninsula in sw marmara region using steerable filter technique potential field data and recent seismicity we examine seismotectonic setting of biga peninsula in western anatolia canakkale region using the steerable filter technique and recent seismicity one of the most important issues in geophysics is to observe borders or margins of tectonic geologic discontinues for this purpose we apply this filter technique to gravity anomaly map of biga peninsula we observe undetected buried faults in biga peninsula using the steerable technique where they have never been seen in the geological maps before these buried faults comply with recent seismicity for this region focal mechanisms of past earthquakes m 3 5 are in good agreement with fault orientations this observation shows that we have to take into account these fault locations and consider for preparing future seismic hazard maps the geometry of fault segments reveals mostly strike slip faulting regime with ne sw trending direction of t axis in the entire study region according to high resolution hypocenter relocation of the biga earthquake sequences in the observation period between 5 january 2005 and 14 november 2015 extends from n to s direction the stress tensor inversion results indicate a predominant normal stress regime with a nw se oriented maximum horizontal compressive stress s h according to strong discrepancy of density in the biga peninsula is characterized by numerous small segmented secondary faults these buried or undetected fault locations indicate that these segments are large enough to increase earthquake stress failure towards nw se and n s directions respectively seismotectonic setting of biga peninsula is divided into sub regions by ne sw trending secondary faults with normal and major strike slip components this output is verified by steerable filter and local regional seismotectonic analysis we propose a new seismotectonic model for biga peninsula and update the orientation of active fault segments according to our model north anatolian fault zone cross cuts the southern marmara basins as a narrow fault segment and continues towards aegean sea

superresolution with seismic arrays using empirical matched field processing scattering and refraction of seismic waves can be exploited with empirical matched field processing of array observations to distinguish sources separated by much less than the classical resolution limit to describe this effect we use the term superresolution a term widely used in the optics and signal processing literature to denote systems that break the diffraction limit we illustrate superresolution with pn signals recorded by the arces array in northern norway using them to identify the origins with 98 2 accuracy of 549 explosions conducted by closely spaced mines in northwest russia the mines are observed at 340 410 kilometers range and are separated by as little as 3 kilometers when viewed from arces many are separated by just tenths of a degree in azimuth this classification performance results from an adaptation to transient seismic signals of techniques developed in underwater acoustics for localization of continuous sound sources matched field processing is a potential competitor to frequency wavenumber and waveform correlation methods currently used for event detection classification and location it operates by capturing the spatial structure of wavefields incident from a particular source in a series of narrow frequency bands in the rich seismic scattering environment closely spaced sources far from the observing array nonetheless produce distinct wavefield amplitude and phase patterns across the small array aperture with observations of repeating events these patterns can be calibrated over a wide band of frequencies e g 2 5 12 5 hertz for use in a power estimation technique similar to frequency wavenumber analysis the calibrations enable coherent processing at high frequencies at which wavefields normally are considered incoherent under a plane wave model

improvements to seismic monitoring of the european arctic using three component array processing at spits abstract the detectability of low magnitude seismic events in the european arctic is determined primarily by the small aperture international monitoring system arrays arces and spits in august 2004 the spits array was upgraded to a broadband array with an increase in the sampling rate from 40 to 80 hz most important however for the detection and location of small magnitude seismic events was the deployment of three component instruments at six of the nine sites detection and correct classification of secondary phases are of paramount importance for events observed by only a small number of stations at regional distances and in the absence of the strong lg phases typically observed for continental propagation paths multiple three component stations were deemed necessary to exploit the higher s phase amplitudes anticipated on the horizontal sensors we demonstrate improved signal to noise ratios snrs for s phases on horizontal beams for several events close to novaya zemlya horizontal component f k analysis improves direction estimates and phase classification for low snr signals we demonstrate secondary phases that are misidentified by vertical only f k analysis but which are correctly classified by three component array processing a significant problem with array processing at spits is the overlap in slowness space of regional p and s phases phase identification is improved greatly by comparing the coherence between vertical traces with the coherence between horizontal traces considerations in the routine array processing of spits data are reviewed including the need for elevation corrections in slowness estimation and the need to take into account azimuth dependent variation of apparent velocity estimates for regional phases

hyposat an enhanced routine to locate seismic events a program package called hyposat has been under development that attempts to use the maximum information possible to estimate the hypocenter of a seismic source the standard input parameters can be used arrival times of first and later onsets with backazimuths and ray parameters or apparent velocities in addition travel time differences between different phases observed at the same station can be optionally used the observed standard deviations are used to weight all input parameters and the inversion is done with a generalized matrix inversion code

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

seismotectonic setting of the karadere duzce branch of the north anatolian fault zone between the 1999 izmit and duzce ruptures from analysis of izmit aftershock focal mechanisms abstract we investigate aftershock focal mechanisms along the eastern part of the izmit mw 7 4 august 17 1999 rupture zone during the time period august 22 1999 october 17 1999 two spatial clusters of aftershock activity are analyzed representing the karadere fault kf and the duzce area da based on an aftershock hypocenter catalogue restricted to events with horizontal and vertical errors 10 km events north and east of the easternmost end of the karadere fault we observe a high variance in stress field orientation correlated with lower b values while the karadere fault reflects a predominant dextral strike slip regime with normal faulting components the duzce area further to the east that also hosted the forthcoming mw 7 2 mainshock 87 days after the izmit earthquake can be subdivided into a dominantly ne sw extensional normal faulting regime below the duzce basin db and a first order strike slip regime along the western duzce fault df we conclude that the duzce basin was set under tension by the izmit rupture and partly released the slip deficit by extensional faulting on karadere fault parallel to the coseismic displacement at the same time this area and in particular the duzce fault that bounds the duzce basin to the south reflects mostly strike slip events representing a major asperity along the north anatolian fault zone nafz before initiating the duzce rupture 87 days after the izmit event

details of stress directions in the alaska subduction zone from fault plane solutions we used the cumulative misfit method to divide a data set with heterogeneous stress orientations into subsets with homogeneous stress directions we propose that slope changes of the cumulative misfit as a function of earthquake number pinpoint the boundaries of homogeneous stresses using a synthetic data set of 50 fault plane solutions composed of two halves corresponding to two incompatible stress tensors we tested the validity and efficacy of the cumulative misfit method our acceptance criteria for results of stress tensor inversions are 1 the directions must be well constrained that is the 95 confidence regions of the greatest and least principal stresses do not overlap and 2 there must be evidence for homogeneity in the sample that is the average misfit of the inversion is less than 6 we estimated stress directions in the alaska wadati benioff zone wbz using 470 fault plane solutions which we determined for earthquakes with ml 3 and 67 published fault plane solutions for earthquakes with ms 5 we succeeded in subdividing the data set of the small and large earthquakes into 25 and 3 subsets with the average misfit ranging from 3 2 to 5 5 the average misfits of the subsets we accept as satisfying the assumption of homogeneity are smaller than the average misfit of the overall data set f 10 by factors of 2 to 3 we estimated the stress fields at two scales along the alaska wbz the stress directions measured by the large earthquakes ms 5 were homogeneous over large volumes with extension downdip and the direction of greatest compression along strike this unusual orientation of the greatest principal stress is attributed to the bend of the slab under central alaska which generates compressive stresses along strike the stress orientations revealed by small earthquakes in contrast exhibited a great deal of heterogeneity as a function of space although their general trend confirms the overall stress directions obtained from the large events we propose that the ratio of the dimensions of the stress field sensed by earthquakes to the rupture dimensions is about 20 to 50 the estimated stress directions of the crustal earthquakes corresponded to the following mechanisms 1 strike slip faulting with the greatest principal stress oriented n s near fairbanks and 2 thrusting with the greatest principal stress oriented nw se near mount mckinley

spatial correlation of the aeromagnetic anomalies and seismogenic faults in the marmara region nw turkey abstract previous investigations into the deep structure of the marmara sea region revealed an existence of a rigid barrier located at the centre of the marmara sea thus the north anatolian fault naf was divided into three segments to the west of this barrier seismological records of two 5 year periods 1998 2002 and 2003 2007 indicate a decrease of seismic activity on and around this barrier it was previously shown if the fault movement reaches to magma its fractures are filled with magmatic material causing magnetic anomalies in this study advance processing methods are utilized to observe the spatial correlation between the aeromagnetic anomalies and the faults of the marmara region these are the reduction to the pole transformation rtp and second vertical derivative svd methods in particular svd map shows alignments which can be correlated with the faults these faults are the northern boundary yalova armutlu imrali and edincik faults length of the northern boundary fault nbf is about 50 60 km thus this fault would not produce strong earthquakes the edincik fault extends from east to the west and bends through wsw the length of this fault in connection with the imrali armutlu and yalova faults in the east exceeds 300 km and named the main fault zone mfz by the authors of this study these faults as a whole may produce strong earthquakes some seismic gaps are observed along with the imrali and edincik faults from the earthquake distribution records of two 5 year periods 1998 2002 and 2003 2007 as a conclusion there are high potentials of strong earthquake occurrences in these regions

maximum earthquake magnitudes along different sections of the north anatolian fault zone abstract constraining the maximum likely magnitude of future earthquakes on continental transform faults has fundamental consequences for the expected seismic hazard since the recurrence time for those earthquakes is typically longer than a century such estimates rely primarily on well documented historical earthquake catalogs when available here we discuss the maximum observed earthquake magnitudes along different sections of the north anatolian fault zone nafz in relation to the age of the fault activity cumulative offset slip rate and maximum length of coherent fault segments the findings are based on a newly compiled catalog of historical earthquakes in the region using the extensive literary sources that exist owing to the long civilization record we find that the largest m7 8 8 0 earthquakes are exclusively observed along the older eastern part of the nafz that also has longer coherent fault segments in contrast the maximum observed events on the younger western part where the fault branches into two or more strands are smaller no first order relations between maximum magnitudes and fault offset or slip rates are found the results suggest that the maximum expected earthquake magnitude in the densely populated marmara istanbul region would probably not exceed m7 5 the findings are consistent with available knowledge for the san andreas fault and dead sea transform and can help in estimating hazard potential associated with different sections of large transform faults

constraints on the evolution and vertical coherency of deformation in the northern aegean from a comparison of geodetic geologic and seismologic data abstract we study the 3 d strain evolution of the northern aegean and the vertical coherency of deformation we observe that finite strain orientations in the mantle inferred from published shear wave sks fast polarization orientations mid to upper crustal stretching lineations in metamorphic core complexes of mainly miocene age and the gradient in regional crustal thickness variations are subparallel to one another this correlation suggests that the miocene phase of extension is imprinted in the anisotropic fabric i e lattice preferred orientation lpo of the lithospheric mantle and that the orientation of finite strain due to extension is nearly constant with depth the lateral variation of published seismic delay times shows a correlation with laterally varying finite strain in the crust inferred from topography and crustal thickness estimates this correlation suggests that lateral variations in finite crustal and mantle strain are correlated and may point at a pure shear extension mechanism involving the entire lithosphere we also present a new strain rate model for the northern aegean based on global positioning system gps velocities and additional geological constraints no length change orientations calculated from the model near the north anatolian fault naf and north aegean trough are not consistent with anisotropy orientations at depth present day extension orientations are systematically and significantly more n s oriented than the stretching lineations and sks splitting orientations we conclude that the current shear dominated surface deformation pattern is not yet reflected by significant anisotropy in the lithosphere based on some simple calculations we postulate that the present day deformation pattern cannot be older than 4 ma which is consistent with independent arguments on the timing of the propagation of the north anatolian fault into the aegean domain

stress tensor inversion using detailed microearthquake information and stability constraints application to olfus in southwest iceland using detailed microearthquake data we present a stress tensor inversion scheme with new methods for selecting the fault planes and allowing for errors in the focal mechanisms the nonuniqueness of earthquake focal mechanisms is accounted for in our inversion scheme through the introduction into the inversion of a range of well fitting focal mechanisms for each event the range of focal mechanisms significantly improves the quality of the estimated stress tensor relative localization of clusters of microearthquakes is used to obtain information about which nodal plane could be correct fault plane the clusters frequently fall on a common fault plane and if there are acceptable focal mechanisms where one nodal plane has orientation similar to the common plane we assume this is the correct fault plane for the event if there is no predefined fault plane we utilize a simple mohr coloumb failure criterion to obtain a physical choice of fault plane between the two nodal planes in the focal mechanism the nodal plane with highest relative instability is chosen as the fault plane differences between the instability and the standard slip angle criterion are investigated the new inversion scheme has been applied to microearthquake data from the olfus area in the vicinity of the southwest iceland triple junction we estimate an oblique strike slip state of stress maximum horizontal stress at n30 e and minimum horizontal stress at n60 w with significant normal faulting influence the instability fault selection criterion predicts very well the orientation of faults mapped by relative localization

coseismic stress changes induced by the 1989 loma prieta california earthquake earthquake focal mechanisms from before and after the 1989 loma prieta california earthquake are used to infer the coseismic stress change before the main shock most earthquakes correspond to right lateral slip on planes sub parallel to the san andreas fault and imply a generally n s most compressional stress axis and a vertical intermediate stress axis aftershocks within the main shock rupture zone however display almost every style and orientation of faulting implying an extremely heterogeneous stress field this suggests that the main shock relieved most if not all of the shear stress acting on its fault plane aftershocks that lie on the perimeter of the rupture agree with spatially uniform stress states but only when considered in three groups north south and above the main shock rupture area in each of these areas the stress state may reflect stress transfer by the main shock

properties of the aftershock sequence of the 1999 mw 7 1 hector mine earthquake implications for aftershock hazard we investigate the spatial and temporal seismicity parameters and the related probabilistic aftershock hazard for the aftershock sequence of the 1999 m w 7 1 hector mine mainshock and compare it with the neighboring 1992 m w 7 3 landers sequence using a catalog of 11 000 earthquakes we determine the earthquake size distribution b value the aftershock decay rate p value and the seismic activity rate a value the b values are high b 1 2 within the rupture area significantly lower b 0 7 north of the rupture area and increase with time since the mainshock probabilistic aftershock hazard maps computed automatically as early as 4 days after the mainshock identified the northernmost part of the sequence as the highest hazard region these maps show a good agreement between the forecasts and the recorded large aftershocks based on the asymmetrical b value and hazard patterns for both the hector mine and landers sequences we hypothesize that the mainshock rupture directivity and slip distribution influence aftershock hazard current static or dynamic stress triggering models cannot resolve this spatial and temporal evolution of the hazard stress tensor inversions of 1400 relocated first motion focal mechanisms show predominantly a strike slip stress state with a sw ne trend of the greatest principal stress the heterogeneity of the stress field is unusually high near the hector mine and landers mainshock ruptures particularly near patches of large slip

seismicity of the sea of marmara turkey since 1500 summary we use the earthquake history of the last 500 years to help evaluate the tectonic and hazard contexts of the1999 earthquakes at izmit and dzce in westernturkey the 20th century has been unusually active but over the 500 year period the seismic moment release can account for the known right lateral shear velocity across the marmara region observed by gps two areas of known late quaternary faulting stand out as unusually quiet over this period the northwest shore of the sea of marmara and the southern branch of the north anatolian fault system between bursa and mudurnu

the bursa gonen depression nw turkey a complex basin developed on the north anatolian fault in this study we show that the southern branch of the north anatolian fault has been active since late pliocene time and that evidence of activity is supported by geological and seismological data the southern branch of the north anatolian fault consists of four segments from west to east yenice gonen manyas mustafakemalpasa uluabat and bursa these faults delimit the bursa gonen depression with the bandirma mudanya uplift to the north and uludag sularya uplift to the south the bursa gonen depression includes upper pliocene to recent sediments that thicken to the south suggesting a deposition pattern under active fault control study of fault kinematics suggests that the bursa gonen depression started as a small pull apart basin during late pliocene time and then evolved to a large depression the faults delimiting this depression are still active and capable of producing future earthquakes

p wave backazimuth anomalies observed by a small aperture seismic array at pinyon flat southern california implications for structure and source location abstract seismograms of earthquakes and explosions recorded at local regional and teleseismic distances by a small aperture dense seismic array located on pinyon flat in southern california reveal large 15 backazimuth anomalies we investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques the broadband frequency wavenumber bbfk technique the polarization technique and the beamforming technique while each technique provided nearly the same direction as a most likely estimate the beamforming estimate was associated with the smallest uncertainties backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the anza and caltech seismic networks and the preliminary determination of epicenters pde bulletin these backazimuth anomalies have a simple sinelike dependence on azimuth with the largest anomalies observed from the southeast and northwest directions such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array a best fit model of a single interface has a dip and strike of 20 and 315 respectively and a velocity contrast of 0 82 km sec application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions suggesting that this is an upper crustal feature we confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

geodetic constraints on the tectonic evolution of the aegean region and strain accumulation along the hellenic subduction zone article i nfo we present evidence that gps velocity estimates of plate motions and fault slip rates agree to within uncertainties with geologic estimates during the most recent phase of the geologic evolution of the e mediterranean region post late miocene on this basis we use the gps differential velocities to estimate the timing of initiation of the principal structures in nw turkey the n aegean sea and central greece including the marmara sea the gulfs of evia goe and corinth goc and the kephalonia transform fault ktf we interpret these ages to indicate that the north anatolian fault propagated across the n aegean opening the goe and goc and initiating the ktf during the past 1 4 ma we further suggest that aegean extension that was earlier more distributed across the aegean basin became focused on this new fault system allowing the southern aegean and peloponnisos to translate sw with little internal deformation as observed today with gps this change in tectonic configuration may account for the clear geologic evidence for crustal thinning throughout the s aegean in apparent contradiction with low present day strain rates we further show that the low present day strain rate along the southern edge of the aegean micro plate requires substantial aseismic slip along the plate interface below crete consistent with the low level of historic subduction type earthquakes along this segment of the subduction zone

stress tensor inversions along the westernmost north anatolian fault zone and its continuation into the north aegean sea summary gephart forsyth s method has been applied to estimate stress orientations from earthquake fault plane solutions of the westernmost north anatolian fault zone nafz its westward continuation in the northern aegean sea where it interacts with the normal faulting of central greece and of the western coastal parts of anatolia in total 163 fault plane solutions were used to invert for the stress tensor of 9 seismotectonic subregions magnitudes range from 1 1 to 7 4 all events have shallow focal depths most occurred in the uppermost 15 km and very few in the 15 to 40 km depth range the region studied is characterized by strike slip nafz by transtension central greece and western anatolia and by a strong signature of transpression in the marmara area from nafz to central greece the 3 axis changes continuously and smoothly its orientation from n35 e in the westernmost nafz to nearly north south in continental central greece and the maximum horizontal stress hmax changes from wnw ese to e w the total angle of lateral variation in the direction of either hmax or 3 is 40 in central western anatolia the orientation of 3 is nne ssw n10 e while in southern western anatolia it is nnw sse n33 w in both cases the development of the major grabens simav gediz menderes is in agreement with the resolved stress tensor at the termination of the nafz against central greece the regime is complex the dextral shear motion transferred from the east crosses the pilion peninsula and northern evia island where it interacts with the major normal faults of continental greece these faults have variable orientations the e w trending quaternary fault system and the nw se trending fault system which is inherited from the past the latter faults under the presently acting stress field are reactivated either as strike slip faults with sinistral strike slip component when oriented at small angle in respect to 3 or as normal faults with small sinistral strike slip component when oriented at high angle in respect to 3 the occurrence of the recent 2001 july 26 skyros event which was clearly connected to a nnw sse fault with sinistral strike slip motion provides strong seismological evidence that the old structures can equally well be reactivated under the presently active stress field

seismic velocity structure and seismotectonics of the eastern san francisco bay region california the hayward fault system is considered the most likely fault system in the san francisco bay area california to produce a major earthquake in the next 30 years to better understand this fault system we use microseismicity to study its structure and kinematics we present a new 3d seismic velocity model for the eastern san francisco bay region using microseismicity and controlled sources which reveals a 10 velocity contrast across the hayward fault in the upper 10 km with higher velocity in the franciscan complex to the west relative to the great valley sequence to the east this contrast is imaged more sharply in our localized model than in previous regional scale models thick cenozoic sedimentary basins such as the livermore basin which may experience particularly strong shaking during an earthquake are imaged in the model the accurate earthquake locations and focal mechanisms obtained by using the 3d model allow us to study fault complexity and its implications for seismic hazard the relocated hypocenters along the hayward fault in general are consistent with a near vertical or steeply east dipping fault zone the southern hayward fault merges smoothly with the calaveras fault at depth suggesting that large earthquakes may rupture across both faults the use of the 3d velocity model reveals that most earthquakes along the hayward fault have near vertical strike slip focal mechanisms consistent with the large scale orientation and sense of slip of the fault with no evidence for zones of complex fracturing acting as barriers to earthquake rupture online material velocity model validation experiments and additional seismicity plots

slowness corrections one way to improve idc products the first step to identify and locate a seismic event is the association of observed onsets with common seismic sources this is especially important in the context of monitoring the comprehensive nuclear test ban treaty ctbt at the international data center idc being developed in vienna austria well defined slowness measurements are very useful for associating seismic phases to presumed seismic events shortly after installation of the first seismic arrays systematic discrepancies between measured and theoretically predicted slowness values were observed and therefore slowness measurements of seismic stations should be calibrated the observed slownesses measured with small aperture arrays some of which will be included in the international monitoring system ims now being implemented for verifying compliance with the ctbt show large scatter and deviations from theoretically expected values however in this study a method is presented by which mean slowness corrections can be derived which show relatively stable patterns specific to each array the correction of measured slowness values of these arrays clearly improved the single array location capabilities applying slowness corrections with seismic phases observed by arces fines geres and nores and associated to seismic events in the bulletins of the prototype international data center pidc in arlington va also clearly demonstrates the advantages of these corrections for arrays with large slowness deviations that are due to the influence of a dipping layer the corrections were modeled with a sine function depending on the measured azimuth in addition the measured values can be weighted with the corresponding uncertainties known from the process of deriving the mean corrections

investigation of azimuth residuals observed at stations of the gsett 3 alpha network the gsett 3 experiment was conducted for more than two years and the international data center idc reported more than 20 000 events for 1995 in the reviewed event bulletins reb we have used this data base to investigate the location bias of arrays and selected three component stations in the alpha network for which the recorded data is automatically processed to determine earthquake locations in near real time the alpha network which consists of 14 arrays provides estimates of event azimuths determined by f k processing we selected 19 three component stations that were operated all or most of 1995 and for which event azimuth was estimated by polarization analysis only events with epicentral distances of less than 100 were considered in order to exclude phases with steep incidence angles associated with unreliable azimuth estimates teleseismic p phases and the major regional and local phases were examined only data for which a signal to noise ratio was given were included in this analysis the signal to noise ratios were used as a weighting factor for the statistical parameters and the graphical representation of the azimuth residuals the preliminary analysis of azimuth residuals identified some arrays that give significantly erroneous azimuths in some cases the error is systematic in other cases it is random one array with systematic azimuthal bias is cmar this array shows positive residuals for event paths from the south while phases for events with paths from the north show negative residuals similar patterns which strongly suggest azimuthal bias are observed for pdar txar and spits in the case of mjar the large azimuthal errors observed particularly for regional and local distances are not a function of direction the scatter in the azimuth residuals is much larger for 3 c stations than for the arrays clear systematic errors were identified for schq and cpup which show constant offsets and at vnda which has negative residuals for events to the north and positive residuals for events from the south the most significant azimuth bias was observed for pdy where the azimuth residuals change from about 90 to more than 90 at backazimuths near 120 meaning that all rays appear from the northwest

neotectonics of the sw marmara region nw anatolia turkey this study reports on the geometric and structural characteristics of the north anatolian fault zone in the southwest marmara region the geometric and kinematic features of the faults in the region are described based on field observations in addition the neogene and quaternary basin fill which occupies large areas in the region has been determined and the tectonic regimes controlling these basins are explained the neotectonic regime is also explained considering different deformation phases affecting the region the n s extension and e w strike slip have affected the region possibly since the latest pliocene quaternary field observations show that these extensional tectonics around the south marmara region are related to right strike slip on the e w north anatolian fault zone and the n s aegean extensional system the faults in this zone trend approximately e w in the eastern part of the region and ne sw towards the west of the region indicating that they accommodate rotation in addition to differential movement between adjacent blocks

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

the yenice gonen active fault nw turkey active tectonics and palaeoseismology abstract the yenice gonen fault ygf is one of the most important active tectonic structures in the biga peninsula on march 18 1953 a destructive earthquake m w 7 2 occurred on the ygf which is considered to be a part of the southern branch of the north anatolian fault zone nafz a 70 km long dextral surface rupture formed during the yenice gonen earthquake yge in this study structural and palaeoseismological features of the ygf have been investigated the ygf surface ruptures have been mapped and three trenches were excavated at muratlar karakoy and seyvan sites according to the palaeoseismic interpretation and the results of 14 c ams dating seyvan trench shows that an earthquake of palaeoseismic age ca 620 ad ruptured a different strand of the 1953 fault producing rather significant surface rupture displacement while there are indications that at least two older events occurred during the past millennia another set of trenches excavated near gonen town muratlar village revealed extensive liquefaction not only during the 1953 event but also during a previous earthquake dated at 1440 ad the karakoy trench shows no indications of recent reactivations based on the trenching results we estimate a recurrence interval of 660 160 years for large morphogenic earthquakes creating linear surface ruptures the maximum reported displacement during the 1953 earthquake was 4 2 m taking into account the palaeoseismologically determined earthquake recurrence interval and maximum displacement slip rate of the ygf has been calculated to be 6 3 mm a which is consistent with present day velocities determined by gps measurements according to the geological investigations cumulative displacement of the ygf is 2 3 km this palaeoseismological study contributes to model the behaviour of large seismogenic faults in the biga peninsula

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

azimuth estimation capabilities of the arcess regional seismic array abstract the effect of local geology and noise conditions on the performance of a small regional array is investigated by comparing the regional p n backazimuth estimation capabilities of the arcess array in northern norway to the noress array a broadband frequency wavenumber estimator was used to calculate backazimuths from the p n arrival for each of 203 regional events recorded at arcess while varying element spacing frequency band and time window most of the errors in backazimuth are less than 20 when appropriate parameter combinations are used and mean backazimuth errors are close to zero the best results are obtained using a 13 element configuration that has a 1 4 km aperture and a maximum station spacing of about 600 m with the 13 element configuration and the data filtered to include frequencies between 3 and 10 hz the mean errors for the 203 event data set are less than 0 9 and s d are as small as 16 9 there are differences seen in the backazimuth estimation capabilities of arcess and noress with specific parameter combinations the larger aperture configurations 10 and 17 elements have smaller means at arcess although the precision is about the same the estimates using unfiltered data at arcess are poor because of local noise conditions that increase the level of background noise at low frequencies overall the precision is better at noress but both regional arrays have the best results using the 13 element configuration and filtering the data in the middle frequency range 3 to 10 hz other factors investigated include snr and source region backazimuth estimation statistics improve if only events with 5 db of snr are included in the data set at both arcess and noress the mean errors move closer to zero and standard deviations decrease the differences between the two arrays are not as pronounced there are some path effects from different source regions around the arcess array however combinations of small aperture configurations and middle 3 to 10 hz frequency bands work well for events over the entire distance range of 30 to 1200 km arcess and noress have similar backazimuth estimation capabilities even though there are differences in the local geology and noise conditions because a 13 element configuration produces reliable results for both arrays it would be reasonable to reduce the number of elements in a regional array this in turn will reduce the costs associated with building and deploying small regional arrays

estimating azimuth and slowness from three component and array stations abstract the capabilities of three component 3 c and array stations for estimating azimuth and slowness are compared for short period p type phases recorded at the noress array for vertical array data azimuth and slowness estimates are obtained from broadband frequency wavenumber f k analysis for 3 c data polarization analysis is performed the data processing is automated using arrival time and dominant frequency information from the noress bulletin independent determinations of azimuth and or slowness obtained from locations in the neis or regional network bulletins are used as reference estimates over 100 events are analyzed both teleseismic and regional they were selected from a variety of distances and azimuths and cover a wide range of signal to noise ratios snr the capability of 3 c stations for azimuth and slowness estimation critically depends on snr for snr below a threshold of 2 the scatter in the estimates is very large for both parameters and the slowness of teleseismic events tends to be overestimated also the results are site dependent within the noress array the array measurements obtained with the broadband f k method are not significantly affected by noise at the levels of snr considered for events with sufficient snr both methods compare well and only a slightly better performance is observed with the f k method

application of the multichannel wiener filter to regional event detection using norsar seismic array data seismic arrays for detection of small earthquakes bene t from reduced noise levels by array processing methods we present a frequency dependent multi channel wiener l tering mcwf technique which employs an adaptive least squares method to remove coherent noise in seismic array data the noise records on a number of reference chan nels are used to predict the noise on a primary channel which can then be subtracted from the observed data a sequence of aftershocks caused by a feb 21 2008 main shock in spitsbergen was recorded in 2008 by the arces array in northern norway this aftershock sequence was ltered using the multi channel wiener lters on both triggered and continuous modes the spitsbergen spits array at a much closer dis tance to the source region provides reliable reference information on the true number of detectable aftershocks the triggered procedure detects 631 aftershocks at arces in total where conventional delay and sum beamforming combined with a band pass lter could detect 513 aftershocks with 181 false alarms using a series of constraints signal to noise ratio snr back azimuth and slowness the multi channel wiener l tered results found 577 aftershocks with 165 false alarms using the same constraints a complete automatic multi channel wiener procedure is developed for event detec tion on continuous data the appropriate snr threshold for aftershock detection 2 7 is suggested the mcwf also demonstrates the advantage of reducing false alarms compared to the beamforming method when detecting the same number of aftershocks

the miocene to present kinematic evolution of the eastern mediterranean and middle east and its implications for dynamics the present kinematics in the eastern mediterranean and middle east is now well constrained by gps measurements and dominated by a circular counterclockwise motion while arabia rotates rigidly the rotational velocities increase from the levant to aegea causing extension in western anatolia we place the present pattern in light of the post middle miocene geological history and propose that in addition to the effects of the hellenic subduction and zagros collision subduction zones on driving the surface motion an underlying asthenospheric flow is also required this counterclockwise toroidal flow is expected to exist around the eastern edge of the african slab owing to subduction rollback and it helps explain the initiation of the north anatolia fault the extrusion and uplift of anatolia and the mid miocene to recent volcanism in eastern anatolia the afar plume had a similar effect on the acceleration of arabia at 40 mya