regional moment tensor inversion for strong aftershocks of the august 17 1999 izmit earthquake mw 7 4 we analyzed the source mechanisms of the thirty largest aftershocks 4 0 ml 6 2 of the august 17 1999 izmit earthquake mw 7 4 by applying the regional moment tensor inversion method using data from near regional broadband stations the inversion solutions were compared to 17 well constrained first motion solutions and were seen to be in good agreement we found that the dominance of strike slip motion is the main characteristic of the izmit earthquake sequence significant aftershock activity was recorded to the west and east of the un ruptured extremities in the east the aftershocks located near the town of duzce represent an early replica of the november 12 1999 duzce earthquake mw 7 2 in terms of locations and source mechanisms in the marmara sea where the fault geometry is still very poorly resolved most aftershocks have right lateral strike slip solutions with strike direction parallel to the submerged branches of the north anatolian fault

implementing the effect of the rupture directivity on psha for the city of istanbul turkey abstract in the present study we improve the probabilistic seismic hazard assessment psha taking into account fault rupture related parameters that sensibly affect the azimuthal variability of the ground motion the study area is the marmara region turkey characterized by one of the highest levels of seismic risk in europe and the mediterranean region the seismic hazard in the city of istanbul is mainly associated with two active fault segments having well defined geometry focal mechanism and rate of activity deterministic dynamic models are also available in this area aochi and ulrich 2015 that aimed at evaluating the seismic potential of the marmara region these models provide the statistical distribution for the hypocenter position which is particularly relevant for rupture directivity the aim of this work is to incorporate all the available information about the seismic potential of the marmara region in a psha framework we use an analytical model for directivity spudich and chiou 2008 spudich et al 2013 to integrate rupture related parameters inside the psha standard procedure because the directivity effect is conditional on the hypocenter position which is not a priori known we assume at first ad hoc gaussian distributions centered in the western eastern or middle part of the two fault segments our results show that the correction for directivity introduces a significant contribution up to 25 of relative increase at 2 s to the hazard maps computed with the standard psha practice given in terms of pseudospectral accelerations having 10 probability of exceedance in 50 years the hazard maps sensibly change when we use the distribution for the hypocenter position informed by the statistical treatment of dynamic simulations thus integrating new variables in the psha in combination with properly informed probability density functions is not only feasible but also recommended for a comprehensive psha

an active deep marine strike slip basin along the north anatolian fault in turkey the tekirdag depression within the marmara sea in the mediterranean region is an active rhomb shaped strike slip basin along the north anatolian fault with a basin floor at a water depth of 1150 m new multichannel seismic reflection data and on land geological studies indicate that the basin is forming along a releasing bend of the strike slip fault and is filled with syntransform sediments of pliocene quaternary age the basin is bounded on one side by the north anatolian fault and on the other side by a subparallel normal fault which forms the steep submarine slope in cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2 5 km adjacent to the north anatolian fault seismic sections also show that the slope forming normal fault connects at depth to the north anatolian fault implying that the basin is completely detached from its substratum the whole structure can be envisaged as a huge rather flat negative flower structure the releasing bend of the north anatolian fault responsible for the formation of the basin is flanked by a constraining bend along the constraining bend the syntransform strata are being underthrust implying a recent change in the direction of the regional displacement vector this thrusting is responsible for the uplift of the submarine slope to a height of 924 m possibly by a mechanism of elastic rebound regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays the anomalous present depth of the tekirdag depression is due to reduced quaternary sedimentation coupled with high rates of displacement along the north anatolian fault which amounts to 20 mm yr in the marmara sea region

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

rates of crustal deformation in western turkey as deduced from major earthquakes abstract western turkey has undergone dominantly n s extension probably since the late miocene this extensional regime caused the formation of e w trending grabens and similarly orientated normal faults the rates of deformation of the seismogenic layer caused by the major earthquakes ms 5 5 during the period between 1943 and 1983 are calculated for western anatolia this region is first analysed as a single system and then divided into two provinces namely the marmara and southwestern anatolian provinces which are investigated as two separate seismotectonic units the dominant mode of deformation in the marmara province is amounting to right lateral displacement 24 0 mm yr other modes of upper crustal deformation in this province can be explained by an average 7 1 mm yr n s extension 10 0 mm yr e w contraction and 0 13 mm yr thinning of a 10 km seismogenic layer the dominant mode of deformation in southwestern anatolia is about 13 5 mm yr extension in the n s direction this region is also undergoing e w extension of about 3 6 mm yr justifying the separation of marmara and southwestern anatolian provinces as two different seismotectonic provinces the average rate of thinning of the seismogenic layer in this area is 0 5 mm yr which is consistent with large scale normal faulting observed here it is found that n s extension in western anatolia increases from north to south while e w compression in the marmara province changes to e w extension in southwestern anatolia it is suggested that these kinematics may explain the present bending of the north anatolian transform forming a transtensional basin between the marmara and southwestern anatolian provinces

long term seismicity of istanbul and of the marmara sea region we examine the long term seismicity of the marmara sea region in turkey over a period of twenty centuries to attempt to answer two questions 1 how well recorded in history is the earthquake activity of this region and 2 does seismicity over this long period of time differ from that over the present century we study this densely populated and fast developing region because it is one of the most tectonically active regions on the continents that appears today to be relatively quiescent

the seismicity in the eastern marmara sea after the 17 august 1999 izmit earthquake we used seismic stations that we deployed after the izmit earthquake along the shores and islands of the izmit bay cinarcik basin to study the seismic activity that took place after the earthquake in the eastern marmara sea the aftershock distribution indicates the existence of three clusters of activity there in the days that followed the earthquake one of the clusters shows the extension of the e w trending izmit rupture into the eastern marmara sea the seismic activity there clearly outlines the fault plane of the main rupture and shows its termination 35 km beyond the hersek peninsula two other clusters of activity are present in the region one is in the armutlu peninsula and the other one is located a few kilometers southwest of the tuzla peninsula beneath the northern slope of the cinarcik basin the focal mechanism solutions indicate strike slip faulting along the main branch of the izmit rupture and normal faulting within the two swarms the presence of the different mechanisms suggests the existence of slip partitioning in the region a remarkable feature of the aftershock data is the absence of seismicity above 4 km in the marmara sea manuscript received 30 august 2000

seismic tomography and deformation modeling of the junction of the san andreas and calaveras faults local earthquake p traveltime data is inverted to obtain a three dimensional tomographic image of the region centered on the junction of the san andreas and calaveras faults the resulting velocity model is then used to relocate more than 17 000 earthquakes and to produce a model of fault structure in the region these faults serve as the basis for modeling the topography using elastic dislocation methods the region is of interest because active faults join it marks the transition zone from creeping to locked fault behavior on the san andreas fault it exhibits young topography and it has a good spatial distribution of seismicity the tomographic data set is extensive consisting of 1445 events 96 stations and nearly 95 000 travel time readings tomographic images are resolvable to depths of 12 km and show significant velocity contrasts across the san andreas and calaveras faulls a low velocity zone associated with the creeping section of the san andreas fault and shallow low velocity sediments in the southern santa clara valley and nonhem salinas valley relocated earthquakes only occur where vp s kmls and indicate that portions of the san andreas and calaveras faults are non vertical although we cannot complctcly cxclude the possibility hat all or parr of this rcsults from ray uacing problems the new dips are more consistent with geological observations that dipping faults intcrscct thc surfacc where surface traces have been mapped the topographic modeling predicts extensive subsidence in regions characterized by shallow low velocity material presumably the result of recent sedimentation some details of the topography at the junction of the san andreas and calaveras faults are not consisknl with lhe modeling results suggesting that the current position or this triple junction has changed with time the model also predicts those parts of the fault subject to contraction or extension perpendicular to the fault strike and hence the sense of any dip slip component in each locality the relative vertical motion accross the fault is consistent with the fault dips found with the new hypocentral locations

viscoelastic gravitational deformation by a rectangular thrust fault in a layered earth previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered elastic gravitational earth model this paper extends these methods to the calculation of fully time dependent vertical surface deformation from a rectangular dipping thrust fault in an elastic gravitational layer over a viscoelastic gravitational half space the elastic gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the laplace transform domain the technique used here to invert the displacements into the time domain is the prony series technique wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials purely viscoelastic results obtained are checked against results found previously using a different inverse transform method and agreement is excellent the major advantage in using the prony series technique is that deformations can be computed for arbitrary time intervals a series of results are obtained for a rectangular 30 dipping thrust fault in an elastic gravitational layer over viscoelastic gravitational half space time dependent displacements are calculated out to 50 half space relaxation times a or 100 maxwell times 2 m a significant effects due to gravity are shown to exist in the solutions as early as several a the difference between the purely viscoelastic solution and the viscoelastic gravitational solutions grows as time progresses typically the solutions with gravity reach an equilibrium value after 10 20 relaxation times when the purely viscoelastic solutions are still changing significantly additionally the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic gravitational problem two independent length scales one of which changes with time are now seen to characterize the problem

investigation of the tectonics of the main marmara fault by means of deep towed seismic data abstract we report a study of the active principal deformation zone pdz of the main marmara fault mmf in the sub basins of the sea of marmara by means of deep towed seismic pasisar as well as multi beam bathymetry data collected by ifremer s r v le suroit in september 2000 our main objective is to investigate the active deformation within the uppermost sedimentary layers with a much higher resolution than hitherto has been available to the west of the sea of marmara the pdz is located along the southern flank of the tekirdag basin where the sediments are affected by steep reverse faults dipping toward the north e w strike slip faults are also observed in the central part of the tekirdag basin and thrusting occurs along its n50 trending margin we interpret these structures in terms of a slight clockwise rotation in the basin north of the pdz to the east the pdz enters the central basin and follows a steep scarp along the southern flank of a tectonic depression the scarp consists of an en echelon fault system with a normal component these faults are combined with small parallel anticlines and synclines that extend along the southern portion of the depression the northern scarp of the depression is made of a mixed system of faults with both normal and reverse components associated with anticlines and synclines these faults are best interpreted as right lateral strike slip faults with a vertical component that is dominantly normal these faults and the sigmoid shape of the depression are compatible with a clockwise rotation above the pdz this recent tectonic structure appears to be superimposed over a pre existing graben that is now essentially deactivated the pdz continues eastwards out of the central basin as a n50 e trending nw verging thrust system toward the kumburgaz basin that is located on a restraining bend of the pdz this shortening zone consists of two main n60 e trending branches the northern one is more pronounced and composed of two successive restraining bends the southern branch is smoother and forms a gently curved connection between the two segments of the pdz this suggests that the pdz migrates southward to cut through this restraining bend further east the pdz enters the cinarcik basin along its northern scarp active deformation observed on the pasisar profiles along the 290 trending eastern portion of this scarp consists of n110 5 trending dextral strike slip faults connecting short segments of active n130 140 normal faults that control elongated depocenters along the southern flank of the cinarcik basin the e w izmit fault enters the basin from the east pasisar data confirm the extension of the izmit strike slip fault into the cinarcik basin and the large development of normal faulting along the southern flank of the basin some of the normal faulting observed here may be related to horse tail termination of the izmit fault while most of it is the expression of strain partitioning

evidence for a minimum 52 1 km of total offset along the northern branch of the north anatolian fault in northwest turkey abstract the north anatolian fault naf splits into two major branches in northwestern turkey with most of the present strain accumulation and holocene displacement being along the northern branch naf n estimates of total offset along the naf n range between 4 km and 70 km in the marmara sea region these different estimates lead to different interpretations on the formation of marmara sea basins in this study we use cretaceous faults sub perpendicular to the naf n as precise offset markers based on these faults as well as the offset of the middle eocene volcanic belt we report a minimum 52 1 km cumulative dextral displacement along the naf n east of marmara sea near 31 e longitude the displacement of the middle eocene volcanic belt shows that the offset is post middle eocene if we assume an additional 15 km dextral displacement on the second strand of the naf n duzce fault the total offset along the naf n can be estimated as 67 km in the eastern marmara region adding the published offsets that range from 16 to 26 km on the southern branch of the naf give a total offset estimate of whole naf zone as 88 5 km in the eastern marmara region the gps velocity estimate indicates 23 mm yr 1 of total plate motion across and near eastern marmara sea that would take 3 9 million years to accumulate 88 km of displacement on the naf additionally the anatolian plate would not have instantaneously accelerated to its modern rate of motion thus initiation of transform displacement must somewhat pre date 3 9 ma

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

morphology displacement and slip rates along the north anatolian fault turkey 1 geological and geomorphological offsets at different scales are used to constrain the localization of deformation total displacement and slip rates over various timescales along the central and eastern north anatolian fault naf in turkey the naf total displacement is reevaluated using large rivers valleys 80 15 km and structural markers pontide suture 85 25 km tosya vezirkopru basins 80 10 km these suggest a neogene slip rate of 6 5 mm yr over 13 myr the river network morphology shows offsets at a range of scales 20 m to 14 km across the main fault trace and is also used to estimate the degree to which deformation is localized at a smaller scale the morphology associated with small rivers is offset by 200 m along the naf the age of these features can be correlated with the holocene deglaciation and a slip rate of 18 3 5 mm yr is determined this is consistent with a rate of 18 5 mm yr deduced independently from the 14c dating of stream terrace offsets over the short term gps data gives a similar rate of 22 3 mm yr all our results tend to show that most of the deformation between the anatolian and eurasian lithospheric plates has been accommodated along or very close to the active trace of the naf the difference between the neogene and the holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the naf

subsurface imaging reveals a confined aquifer beneath an ice sealed antarctic lake liquid water oases are rare under extreme cold desert conditions found in the antarctic mcmurdo dry valleys here we report geophysical results that indicate that lake vida one of the largest lakes in the region is nearly frozen and underlain by widespread cryoconcentrated brine a ground penetrating radar survey profiled 20 m into lake ice and facilitated bathymetric mapping of the upper lake basin an airborne transient electromagnetic survey revealed a low resistivity zone 30 100 m beneath the lake surface based on previous knowledge of brine chemistry and local geology we interpret this zone to be a confined aquifer situated in sediments with a porosity of 23 42 discovery of this aquifer suggests that subsurface liquid water may be more pervasive in regions of continuous permafrost than previously thought and may represent an extensive habitat for microbial populations

the active main marmara fault abstract this paper presents selections from and a synthesis of a high resolution bathymetric sparker and deep towed seismic reflection data set recently acquired by the french ifremer r v le suroit in an e w deep trough that forms the northern half of the sea of marmara in nw turkey it includes the first high resolution complete bathymetric map of this area a single throughgoing dextral strike slip fault system which is the western continuation of the northern branch of the north anatolian fault cuts this trough lengthwise and joins the 1999 8 17 kocaeli earthquake fault with the 1912 8 09 arkoy murefte earthquake fault both of which display strike slip offset in its eastern one fourth the structure follows closely the northern margin of the deep trough whereas in the west it hugs its southern margin the eastern one fourth of the structure has a minor component of its displacement distributed across the deep trough owing to a possible original bend in the course of the dextral structure the present course of the north anatolian fault in the sea of marmara originated some 2 105 a ago by cutting across the older basin fabric generated by a dominant nne ssw extension before it began taking up major motion in the pliocene

the sea of marmara a plate boundary sea in an escape tectonic regime abstract the sea of marmara is dissected by two major fault systems the first consists of two east west striking transtensional boundary faults and a number of secondary faults subparallel to them the second is made up of ne sw trending subvertical strike slips and their conjugates oriented nw se that offset the first system these fault systems segment the deep marmara sea into 5 blocks that are either rhomboidal lazy z or wedge shaped three of these blocks may be interpreted as pull apart basins characterized by transtension while the other two sill areas which separate the basins are transpressional push up structures the blocks are subjected to rapid episodic subsidence but they also undergo pervasive vertical motions and possible rotations relative to one another the sedimentary column above the acoustic basement mapped within the sea of marmara can be divided into 3 seismic units a folded and truncated pre transform unit and two syn transform units the lower thick syn transform unit exhibits 3 distinct seismic facies a well stratified basin fill facies cut by subvertical growth faults a push up facies with a contorted or chaotic internal configuration and a slump facies the observed neotectonic and sedimentary regimes result from compressional movement between eurasia and africa which has led to major dextral transform movements along the north anatolian fault zone escape tectonics and from the fact that this fault zone splinters into two overlapping right stepping oblique master faults at the eastern and western border of the sea of marmara respectively

slip partitioning in the sea of marmara pull apart determined from gps velocity vectors summary dislocation modelling is used to examine the gps velocity vectors for the marmara sea region first the vectors due to the known anatolia eurasia rotation are reproduced by introducing structures that approximate the large scale tectonics observed features of the smaller scale fault system in the marmara region are then progressively included with slip amplitudes and directions adjusted to fit an 80 vector subset of the gps data the motion in the marmara sea region is partitioned with the faults that bound the north of the basin carrying more strike slip motion than predicted from the anatolia eurasia plate motion and faults to the south having a greater perpendicular component taken together however there is no net opening across the marmara sea perpendicular to the overall trend of the boundary and thus deformation in the marmara region results only from the pull apart geometry of the north anatolian fault no extension related to the aegean system is needed to explain the observations the gps results are consistent with motion over the last 5 myr that has been determined from geological reconstructions

seismic hazard in the marmara sea region following the 17 august 1999 izmit earthquake on 17 august 1999 a destructive magnitude 7 4 earthquake occurred 100 km east of istanbul near the city of izmit on the north anatolian fault this 1 600 km long plate boundary 1 2 slips at an average rate of 2 3 cm yr 1 refs 3 5 and historically has been the site of many devastating earthquakes 6 7 this century alone it has ruptured over 900 km of its length 6 models of earthquake induced stress change 8 combined with active fault maps 9 had been used to forecast that the epicentral area of the 1999 izmit event was indeed a likely location for the occurrence of a large earthquake 9 10 here we show that the 1999 event itself significantly modifies the stress distribution resulting from previous fault interactions 9 10 our new stress models take into account all events in the region with magnitudes greater than 6 having occurred since 1700 ref 7 as well as secular interseismic stress change constrained by gps data 11 these models provide a consistent picture of the long term spatio temporal behaviour of the north anatolian fault and indicate that two events of magnitude equal to or greater than the izmit earthquake are likely to occur within the next decades beneath the marmara sea south of istanbul

structural relationship between the sea of marmara basin and the north anatolian fault zone the north anatolian fault naf zone is 1500 km long extending almost up to the greek mainland in the west it is a seismically active right lateral strike slip fault that accommodates the relative motion between the turkish block and black sea plate the sea of marmara lies along the western part of the naf and shows evidence of subsidence in this area pure strike slip motion of the fault zone changes into extensional strike slip movement that is responsible for the creation of the sea of marmara and the north aegean basins the northern half of the sea of marmara is interpreted as a large pull apart basin this basin is subdivided into three smaller basins separated by strike slip fault segments of uplifted blocks ne sw basinal areas are covered by horizontally layered sedimentary sequences uplifted blocks have undergone compressional stress all the blocks are subsiding and are undergoing vertical motions and rotations relative to one another the uplifted blocks exhibit positive bouguer gravity anomalies according to gravity interpretation there is relative crustal thinning under the sea of marmara the northern side of the sea of marmara is marked by a distinctive deep rooted magnetic anomaly which is dissected and shifted southward by strike slip faulting the southern shelf areas of the sea of marmara are dominated by short wavelength magnetic anomalies of shallow origin

the seismotectonics of the marmara region turkey results from a microseismic experiment the marmara region is an active tectonic zone characterised by the transition between the dextral strike slip regime of the north anatolian fault naf and the extension regime of the aegean sea strong historical earthquakes m 7 and the presence of known seismic gaps imply a high level of seismic hazard a synthesis of recent studies of active tectonics in the region is presented including inland and underwater observations the branching of the naf is explained in terms of increasing influence of the extension historical information and instrumental seismicity are reinterpreted in order to have a critical appraisal of the existence of large seismic gaps in the central and eastern marmara sea focal mechanisms of strong earthquakes are used to obtain orientation and shape factor of the deviator of the stress tensor the resulting tensor is in shear regime s 2 vertical but close to extension r 0 93 with s 1 oriented n145 0 a microseismic experiment with 48 stations distributed around the marmara sea was carried out in october december 1995 a total of 137 microearthquakes were located and 23 of those were selected to obtain focal mechanism solutions the epicentral distribution indicates activity along the system of pull apart basins north of the marmara sea the segment between marmara sea and the saros bay activated in 1912 and the gulf of izmit site of the 1754 earthquake are now silent seismic activity is very linear along the northern branch of the naf but it is more divused on the bursa and iznik branches southeast of the marmara sea the stress tensor obtained from the focal mechanisms of the micro earthquakes is compared to the one inverted from teleseismic data the microseismic stress is compatible with a shear intermediate regime like the one obtained from strong earthquakes though not as well constrained one of the acceptable solutions having the same orientation but diverent shape r 0 5 2000 elsevier science b v all rights reserved

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

submarine fault scarps in the sea of marmara pull apart north anatolian fault implications for seismic hazard in istanbul earthquake scarps associated with recent historical events have been found on the floor of the sea of marmara along the north anatolian fault naf the marmarascarps cruise using an unmanned submersible rov provides direct observations to study the fine scale morphology and geology of those scarps their distribution and geometry the observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north marmara extensional step over between the strike slip ganos and izmit faults smaller strike slip segments and pull apart basins alternate within the main step over commonly combining strike slip and extension rapid sedimentation rates of 1 3 mm yr appear to compete with normal faulting components of up to 6 mm yr at the pull apart margins in spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief sets of youthful earthquake scarps extend offshore from the ganos and izmit faults on land into the sea of marmara our observations suggest that they correspond to the submarine ruptures of the 1999 izmit mw 7 4 and the 1912 ganos ms 7 4 earthquakes while the 1999 rupture ends at the immediate eastern entrance of the extensional cinarcik basin the 1912 rupture appears to have crossed the ganos restraining bend into the sea of marmara floor for 60 km with a right lateral slip of 5 m ending in the central basin step over from the gulf of saros to marmara the total 1912 rupture length is probably about 140 km not 50 km as previously thought the direct observations of submarine scarps in marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the naf next to istanbul coulomb stress modeling shows a zone of maximum loading with at least 4 5 m of slip deficit encompassing the strike slip segment 70 km long between the cinarcik and central basins that segment alone would be capable of generating a large magnitude earthquake mw 7 2 other segments in marmara appear less loaded

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

high resolution seismic profiling in the sea of marmara northwest turkey late quaternary sedimentation and sea level changes high resolution sparker seismic profiling was carried out in the sea of marmara northwest turkey to study the late quaternary tectonics and sedimentation of this important active basin at the western end of the north anatolian fault zone a sedimentary unit interpreted as the clinoforms of a prograding delta was observed in places along the outer part of the southern shelf the topset foreset transitions of the latest clinoforms cluster around 100 m below present sea level they were probably deposited during the last glacial maximum and early phase of deglaciation between 25 and 13 k y b p when the level of the aegean was below that of the dardanelles sill 60 70 m below sea level at present therefore the sea of marmara was isolated from the aegean during the last glacial maximum but it is possible that a fluvial overflow existed across the dardanelles during this time stabilizing the level of the marmara lake and allowing the delta progradation rivers that drain into the sea of marmara from the south have a much greater combined drainage basin area and sediment flux than those draining the region to the north this may explain the much broader shelf to the south half graben bounded by north dipping normal faults observed within the southern shelf would tend to trap sediment sourced from the south and subdue any sea bed morphology on the shelf

using mechanical modeling to constrain fault geometries proposed for the northern marmara sea 1 in recognition of potential seismic hazard along the north anatolian fault within the marmara sea geophysical surveys have recently been conducted to collect high resolution bathymetry and seismic reflection data despite the high quality of the data fault interpretations by different authors are varied and a conclusive fault geometry within the marmara sea remains elusive this paper presents a mechanical modeling method for constraining proposed fault geometry interpretations in the model crustal faults within the marmara sea slip in accordance with gps constrained slip rates along deep plate boundary dislocations we test three fault models proposed by others and show that an interpretation with a series of pull apart basins along a master strike slip fault best produces the observed deformation pattern within the marmara sea the locations and relative subsidence of the basins along the northern marmara trough are well matched the computed slip vectors on the faults in the best fitting model indicate that except for small faults bounding the tekirdag basin the faults have dominantly right lateral slip with rakes within 15 of horizontal on the local scale this suggests that interaction between the segmented strike slip faults is the dominant mechanism producing the observed vertical deformation in the marmara sea on the regional scale if the marmara sea faults behaved in this manner over geologic timescales then right lateral plate boundary motion without an additional component of north south extension associated with the aegean sea is sufficient to produce the marmara sea pull apart basin morphology

slip distribution along the north anatolian fault associated with the large earthquakes of the period 1939 to 1967 abstract between 1939 and 1967 six large fault ruptures formed a westward migrating sequence of events along a 900 km long nearly continuous portion of the north anatolian fault for these events the 1939 erzincan 1942 niksar erbaa 1943 tosya 1944 bolu gerede 1957 abant and 1967 mudurnu valley earthquakes i have compiled a record of dextral slip which contains nearly 100 points these data indicate that the amount of slip is irregularly distributed along the 1939 to 1967 rupture zone the maximum slip 7 5 m occurred during the 1939 earthquake in the eastern 150 km of the 900 km long rupture zone dextral offsets diminish very abruptly eastward but very gradually westward the rate of westward decrease in the 1939 to 1967 offsets is only slightly greater than the rate of westward decrease of post miocene displacement along the north anatolian fault this suggests that westward decrease in slip can be expected to be a general characteristic of earthquake ruptures along the north anatolian fault in the future nevertheless within the 1939 to 1967 slip distribution there are three regions that had less slip than the neighboring regions these i interpret as possible sites of large future earthquakes one of these seismic gaps has already experienced another earthquake in 1951 and subsequent creep

susehri basin an active fault wedge basin on the north anatolian fault zone turkey abstract the susehri section of the north anatolian fault zone nafz is dominated by an active fault wedge basin its recent configuration is a quaternary strike slip depression superimposed on a larger fault controlled fluvial to lacustrine setting inherited from the pliocene in and around the susehri fault wedge basin the nafz is characterized by the north anatolian master fault namf or principal displacement zone pdz and four second order fault sets namely the kelkit akcaa il beyde irmeni and ekenek fault sets the namf cuts through the basin the fault sets border the margins of the basin and impart a double divergence character to the namf which is proposed as an evolutionary model for the susehri fault wedge basin the susehri basin fill deposits of pliocene age rest on the quiet and shallow marine limestones of burdigalian age with a sharp angular unconformity besides the upper half of the pliocene basin fill deposits is dominated by the well developed syndepositional mesofractures which reveal the existence of a right lateral shearing at the time of deposition these observations also imply the emergence of a new tectonic regime after the burdigalian by which time the susehri basin had experienced a subsidence of about 660 m to 1150 m during its evolution on the other hand at the south easternmost end of the susehri basin the lutetian volcano sedimentary sequence of the yesilyayla group is cut and displaced right laterally by about 35 km which is the detectable minimum offset on the nafz finally during the 1939 12 27 erzincan earthquake the erzincan erbaa segment of the nafz was reactivated and several modern faults were produced along these modern faults some natural and man made features were displaced right laterally these offsets vary in decreasing order from 7 5 m near the epicenter at the southeastern end to 3 7 m away from it at the northwestern end of the erzincan erbaa segment of the nafz

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

the north anatolian fault within the sea of marmara a new interpretation based on multi channel seismic and multi beam bathymetry data abstract we analyze 2200 km of multi channel seismic reflection profiles that have become recently available in the sea of marmara this analysis benefits from the recent acquisition of multi beam bathymetric data covering the axial portion of the northern basins we conclude that the northern sea of marmara is at present cut by an active continuous strike slip fault system that we call the marmara fault it links the 270 izmit portion of the northern branch of the north anatolian fault to the east of the sea to the 245 ganos fault to the west the marmara fault itself consists of two main parts the western one is a single 80 km long fault it follows a 265 direction that differs by 20 from the direction of the ganos fault at its northeastern extremity it turns toward the northern margin of the cinarcik basin this western part of the fault is seismically quite active the eastern part is more complex it extends over 65 km in a 280 direction there is thus a 10 clockwise rotation with respect to the 270 izmit fault strand that should result in a slight extensional component within the eastern cinarcik basin this part of the marmara fault has two parallel branches 10 km apart the northern one near the foot of the northern slope the southern one near the foot of the southern slope a shortening zone occupies the northwestern corner of the cinarcik basin and much of the adjacent eastern central high and separates the northern branch from the western one the southern branch on the other hand may cross the eastern central high along a narrow 280 valley the data we have provide no definitive evidence on which of these two branches carries most of the motion the establishment of the present trace of the fault through the marmara basin is contemporaneous with a recent phase of deposition of deep giant ripples parallel to the bathymetric slope contours and adjacent to the turbidites basin deposits the base of these deep basins sedimentary deposits is marked by a widespread erosional unconformity below which lies a gently folded sedimentary sequence that may consist of shallow thrace basin deposits

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

physical analog modeling of pull apart basin evolution abstract pull apart basins are structural depressions formed by localized extension along strike slip fault systems typically at releasing bends or steps in the fundamental strike slip system analog modeling is used to evaluate the sequence of structural evolution of pull apart basins and factors that control their degree of structural asymmetry and geometry basin evolution internal structure and overall symmetry are investigated for oblique releasing step angles and with varying rates of displacement between brittle and ductile crust on opposing sides of the strike slip system while maintaining relative rates between brittle crust on opposing sides of the basin pull apart basin evolution is separated into three stages incipient early and mature incipient pull apart basins are characterized by formation of a normal fault bounded graben or half graben parallel to the oblique step between main strike slip zones in the early stage of formation additional normal faults form toward the basin interior from the original bounding faults and cross basin strike slip faults cut diagonally across the basin interior basin bounding normal fault systems are characterized by lateral variations of fault throw and localized relay ramps in the mature stage of evolution strike slip and normal faults join to completely bound the pull apart basin analog model results indicate that displacement associated with cross basin faults causes development of a through going strike slip fault that links the two main strike slip displacement zones ultimately resulting in a decline in normal fault activity asymmetric symmetric and hybrid pull apart basins all follow the same overall deformation sequence just described the asymmetry of a pull apart basin is controlled by the degree of decoupling between brittle and ductile crust beneath the two crustal blocks in relative motion this is modeled by maintaining a constant relative rate of motion between opposing fault blocks in all models but varying the rate between the blocks and the fixed model basement absolute rate models in which one side of the detachment is fixed with respect to the basement form asymmetric pull apart basins defined by a half graben with the master fault on the mobile side in models where opposing sides of the fault system are equally decoupled from the basement symmetrical pull apart basins form defined by horst and graben structures and master fault dominance switching sides along the length of the basin fault segmentation associated with relatively immature pull apart basins may be capable of arresting earthquake rupture late linkage of main strike slip zones by a cross basin fault could extend potential rupture area dramatically increasing the possibility for large magnitude earthquakes

asymmetric slip partitioning in the sea of marmara pull apart a clue to propagation processes of the north anatolian fault between 1939 and 1999 the north anatolian fault naf experienced a westward progression of eight large earthquakes over 800 km of its morphological trace the 2000 km long north anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale 10 myr the sea of marmara is a large pull apart that appears to have been a geometrical mechanical obstacle encountered by the naf during its propagation the present paper focuses on new high resolution data on the submarine fault system that forms a smaller pull apart beneath the northern sea of marmara between two well known strike slip faults on land izmit and ganos faults the outstandingly clear submarine morphology reveals a segmented fault system including pull apart features at a range of scales which indicate a dominant transtensional tectonic regime there is no evidence for a single continuous purely strike slip fault this result is critical to understanding of the seismic behaviour of this region of the naf close to istanbul additionally morphological and geological evidence is found for a stable kinematics consistent both with the long term displacement field determined for the past 5 myr and with present day anatolia eurasia motion determined with gps however within the sea of marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull apart the loading associated with the westward propagation process of the naf may have provided a favourable initial geometry for such a slip separation

geomechanical model of the marmara sea region i 3 d contemporary kinematics summary we investigate by means of a 3 d geomechanical model the relationship between structural elements and contemporary kinematics in the marmara sea region northwest turkey the recently imaged fault system beneath the marmara sea is incorporated into the model as frictional surfaces with varying strike and dip the main marmara fault is implemented as through going and is accompanied by mostly non vertical second order faults topography basement topography and the moho become mechanically effective through changes in density and elastic parameters across these horizons the model is subjected to gravity and kinematic boundary conditions the ultimate goal of this study is to set up a 3 d model that is consistent with both kinematic observations and stress data the stress results are presented in a complementary paper in this paper we present the modelled long term 3 d kinematics in terms of fault slip rates rotations vertical motion and sense of fault slip the model results agree with global positioning system velocities geological fault slip rates palaeomagnetic measurements and with the observed pattern of subsidence and uplift furthermore our tectonically driven vertical velocities can be linked to landscape and basin evolution and to features of sedimentation our results indicate that the main marmara fault can be interpreted as a through going fault that slips almost purely in a strike slip sense nevertheless and not contradictory to the previous statement there is significant dip slip motion at some sections of the main marmara fault the agreement of the modelled 3 d kinematics with model independent observations supports that the main structural details of the fault system are accounted for sensitivity analysis of model parameters reveals that changes in rock properties and the initial stress state have minor influence on the 3 d kinematics we conclude that the 3 d structure of the fault system is the key control of the kinematics the slip rate of the main marmara fault from our model is lower than previous estimates and shows high variability along strike 12 8 17 8 mm a 1 the latter indicates that stress accumulation is non uniform along strike

m 7 earthquake rupture forecast and time dependent probability for the sea of marmara region turkey we forecast time independent and time dependent earthquake ruptures in the marmara region of turkey for the next 30 years using a new fault segmentation model we also augment time dependent brownian passage time bpt probability with static coulomb stress changes cff from interacting faults we calculate mw 6 5 probability from 26 individual fault sources in the marmara region we also consider a multisegment rupture model that allows higher magnitude ruptures over some segments of the northern branch of the north anatolian fault zone beneath the marmara sea a total of 10 different mw 7 0 to mw 8 0 multisegment ruptures are combined with the other regional faults at rates that balance the overall moment accumulation we use gaussian random distributions to treat parameter uncertainties e g aperiodicity maximum expected magnitude slip rate and consequently mean recurrence time of the statistical distributions associated with each fault source we then estimate uncertainties of the 30 year probability values for the next characteristic event obtained from three different models poisson bpt and bpt cff using a monte carlo procedure the gerede fault segment located at the eastern end of the marmara region shows the highest 30 year probability with a poisson value of 29 and a time dependent interaction probability of 48 we find an aggregated 30 year poisson probability of m 7 3 earthquakes at istanbul of 35 which increases to 47 if time dependence and stress transfer are considered we calculate a twofold probability gain ratio time dependent to time independent on the southern strands of the north anatolian fault zone

analog modeling of pull apart basins scaled sandbox models have successfully simulated the geometries and progressive evolution of pull apart basins developed in a weak sedimentary cover above right stepping releasing dextral strike slip fault systems in rigid basement synkinematic basin infill was added progressively as the models were deformed vertical and horizontal sectioning of the completed models has allowed the full three dimensional architecture of the pull apart system to be analyzed we present three representative end member experiments 30 underlapping releasing sidestep 90 sharp nonoverlapping releasing sidestep and 150 overlapping releasing sidestep the pull apart basin geometries are typically sigmoidal to rhombic grabens the geometries of which are dependent upon the architecture of the underlying basement fault systems underlapping releasing sidestepping faults offset angles of 30 75 typically form elongate rhomboidal grabens 90 releasing offset sidesteps produce shorter squat rhomboid pull apart basins and overlapping releasing sidesteps 115 150 produce box like grabens with highly kinked basin sidewalls the pull apart basins are bounded by terraced oblique slip extensional sidewall fault systems that link the laterally offset principal displacement zones pdz of the main dextral strike slip faults the sidewall faults show changes in kinematics from dominantly dip slip extension in copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received june 24 1996 revised manuscript received november 20 1996 final acceptance june 10 1997 2fault dynamics project geology department royal holloway university of london egham surrey tw20 oex united kingdom supported by the fault dynamics project sponsored by arco british limited petrobras u k ltd bp exploration conoco u k limited mobil north sea limited and sun oil britain we also acknowledge additional funding from sun oil britain landsat thematic mapper data courtesy of rtz mining and exploration limited south american division jurrian reijs is thanked for field data relating to the salina del fraile pull apart basin chris elders is thanked for reviewing earlier versions of this manuscript and j crowell c morley and k biddle are thanked for constructive reviews of the manuscript the contents of this paper have been

interaction between faulting and sedimentation in the sea of marmara western turkey 1 the aegean region is one of the most rapidly deforming continental areas in the world in the sea of marmara interaction between strike slip and extensional faulting has led to a complicated style of local deformation to the east the continental plate containing eastern and central turkey is moving westward with respect to eurasia with little internal deformation tectonic deformation is restricted to a narrow zone along the dominantly strike slip north anatolian fault however in the vicinity of the sea of marmara both surface mapping of faults and earthquake fault plane solutions indicate that extensional motions presumably related to back arc extension behind the hellenic subduction zone create a much wider zone of deformation which reaches hundreds of kilometers in width we use a regional grid of high resolution seismic reflection profiles to map the fault systems as they cross the sea of marmara and show how they divide the sea of marmara into separate deep basins with distinctive sediment sources and depositional styles in the southern sea of marmara these basins are half graben formed on north dipping fault planes which have trapped sediment coming into the sea of marmara from the south no evidence is found in the data set for the existence of a single strike slip fault through the sea of marmara or for the existence of a northern boundary fault along the tekirdag and central marmara basins we conclude that a single strike slip fault would be incapable of accommodating the relative motion and extension observed between western turkey and eurasia

airborne and ground geophysical mapping of coastal clays in eastern friesland germany coastal areas such as the german bight are at risk from storms and rising sea level that may affect the hydrogeologic setting because knowledge of the distribution of clayey sediments is important for understanding the current status of this dynamic setting the german federal institute for geosciences and natural resources bgr has focused on geophysical research projects on the north sea coast applying airborne and ground geophysics the airborne system operated by bgr was used to survey a 20 by 31 km large coastal area in eastern friesland germany including the islands of langeoog and spiekeroog helicopter borne electromagnetic hem data were collected at six frequencies in addition the leibniz institute for applied geophysics commissioned a skytem survey covering a 2 km wide north south strip on the island of langeoog ground geophysical methods such as transient electromagnetics tem and magnetic resonance soundings mrs were used to investigate the hydrogeologic setting in greater detail onshore the airborne electromagnetic results clearly outlined a complex electrically conductive pattern occurring at a shallow depth comparison with borehole results provided by the state authority for mining energy and geology confirmed that these conductors were caused by clayey material particularly down to an approximate 20 m depth this pattern continues offshore and it is likely that the saltwater is linked to stripes of clayey sediments and the fresh groundwater flows out to the wadden sea in between on the islands the hem results revealed the freshwater lenses and showed some indications for clay layers within these freshwater lenses the application of tem and mrs helped to distinguish lithology from salinity and confirmed the existence of these clay layers we demonstrated the usefulness of combining the spatial airborne data with geophysical and borehole data available at sparsely distributed sites on the ground to investigate hydrogeologic settings

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

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

evaluation of earthquake potential along the northern anatolian fault zone in the marmara sea using comparisons of gps strain and seismotectonic parameters abstract seismotectonic parameters including the gutenberg richter b value and multifractal dimensions d2 and d15 of seismicity patterns both spatial and temporal were compared to gps derived maximum shear and dilatation strains measured in the marmara sea region of western turkey along the northern anatolian fault zone nafz comparisons of seismotectonic parameters and gps derived maximum shear and dilatation strain along the nafz in the vicinity of the 1999 m7 4 izmit earthquake reveal a positive correlation r 0 5 p 0 05 between average dilatation and the gutenberg richter b value significant negative correlation r 0 56 p 0 03 and r 0 56 p 0 02 was also observed between the spatial fractal dimension d2 and gps derived maximum geodetic and shear strain this relationship suggests that as maximum geodetic and shear strains increase seismicity becomes increasingly clustered anomalous interrelationships are observed in the marmara sea region prior to the izmit event along a bend in the nafz near the eastern end of the marmara sea known as the northern boundary fault nbf an asperity is located near the northwest end of the nbf along the 50 km length of the nbf gps strains become slightly compressive the correlation between b value and gps derived dilatation suggests that regions in compression have increased probability of larger magnitude rupture the nbf appears to serve as an impediment to the transfer of strain from east to west along the nafz recurrence times for large earthquakes along the nbf are larger than in surrounding areas temporal clustering of seismicity in the vicinity of the nbf may represent foreshocks of an impending rupture

generation of 3 d hydrostratigraphic zones from dense airborne electromagnetic data to assess groundwater model prediction error we present a new methodology to combine spatially dense high resolution airborne electromagnetic aem data and sparse borehole information to construct multiple plausible geological structures using a stochastic approach the method developed allows for quantification of the performance of groundwater models built from different geological realizations of structure multiple structural realizations are generated using geostatistical monte carlo simulations that treat sparse borehole lithological observations as hard data and dense geophysically derived structural probabilities as soft data each structural model is used to define 3 d hydrostratigraphical zones of a groundwater model and the hydraulic parameter values of the zones are estimated by using nonlinear regression to fit hydrological data hydraulic head and river discharge measurements use of the methodology is demonstrated for a synthetic domain having structures of categorical deposits consisting of sand silt or clay it is shown that using dense aem data with the methodology can significantly improve the estimated accuracy of the sediment distribution as compared to when borehole data are used alone it is also shown that this use of aem data can improve the predictive capability of a calibrated groundwater model that uses the geological structures as zones however such structural models will always contain errors because even with dense aem data it is not possible to perfectly resolve the structures of a groundwater system it is shown that when using such erroneous structures in a groundwater model they can lead to biased parameter estimates and biased model predictions therefore impairing the model s predictive capability

oscillating quaternary water levels of the marmara sea and vigorous outflow into the aegean sea from the marmara sea black sea drainage corridor abstract detailed interpretation of single channel air gun and deep tow boomer profiles demonstrates that the marmara sea turkey experienced small amplitude 70 m fluctuations in sea level during the later quaternary limited in magnitude by the sill depth of the strait of dardanelles moderate subsidence along the southern shelf and quaternary glacio eustatic sea level variations created several stacked deltaic successions separated by major shelf crossing unconformities which developed during the transitions from global glacial to interglacial periods near the strait of dardanelles a series of sand prone deposits are identified beneath an uppermost holocene transparent mud drape the sandy deposits thicken into mounds with the morphology and cross sectional geometries of barrier islands sand waves and current generated marine bars all cross stratification indicates unidirectional flow towards the dardanelles prior to the deposition of the transparent drape which began 7000 years bp in strong support of the notion that the marmara sea flowed westwards into the aegean sea through the dardanelles at times of deglaciation in northern europe the global sea level curve shows that at 11 000 and 9500 years bp sea level rose to the sill depths of the straits of dardanelles and bosphorus respectively the effect from 11 000 to 9500 years bp was seawater incursion into the marmara sea drowning and formation of algal serpulid bioherms atop lowstand barrier islands and transgression of shelves and lowstand deltas at 9500 years bp glacial meltwater temporarily stored in the black sea lake developed into a vigorous southward flow toward the aegean sea forming west directed sandy bedforms in the western marmara sea and initiating deposition of sapropel s1 in the aegean sea this strong outflow persisted until 7000 years bp after which a mud drape began to accumulate in the marmara sea and euryhaline mediterranean mollusks successfully migrated into a progressively more saline black sea where sapropel deposition began most eastern mediterranean sapropels from s1 to s11 appear to correlate with periods of rising sea level and breaching or near breaching of the bosphorus sill these events are believed to coincide with times of vigorous outflow of low salinity fresh surface waters transiting the black sea marmara sea corridor and ultimately derived from melting of northern european ice sheets

the landscape geometry and active tectonics of northwest greece when a region is tectonically deformed its geometry changes some of these changes produce easily identified and often readily datable morphological features such as regions of rapid uplift and subsidence sediment ponds or river terraces these features are usually secondary to the main active structures and consequently do not provide information about them directly we show however that simple models using boundary element methods can be adapted to relate the evolution of these minor features to motion on major structures this adds substantially to the information available to determine motion on such features in this paper we apply the technique to northwest greece we show that in addition to the long recognized compressional component of motion in epirus a substantial left lateral strike slip component of motion must be present the modeling allows us to identify a regional slip vector of n275 e this slip vector suggests that the plate configuration assumed by previous workers must be modified a new configuration is proposed that remains consistent with the data used for earlier interpretations and our new data it is proposed that the medina wrench is a significant active structure and that a period of quiescence explains the low seismic activity at present the plate configuration and angular rotation rates that we suggest require that the gulf of arta is associated with a triple junction using the slip vectors we have defined for the plates meeting at this junction we model the regions of uplift and subsidence in the region the ability of this model to explain many features associated with the gulf provides assurance that our overall tectonic model is correct

understanding the hydrogeology of the venice lagoon subsurface with airborne electromagnetics abstract the occurrence of alternating dry wet conditions in transitional environments such as wetlands deltas and lagoons usually challenges the use of traditional direct and geophysical surveys for comprehensive hydrogeologic investigations moreover significant mixing between continental fresh groundwater and marine salty surface waters generally takes place in these flat coastal areas airborne electromagnetics aem is a promising tool in this respect as it provides in a fast and cost effective manner large scale distribution of bulk electrical conductivities that can be used profitably to develop hydrogeologic models the results of a skytem aem survey in the venice lagoon italy show the capability of this technique to significantly improve the knowledge of the hydrogeologic setting of the lagoon and nearby coastland subsurface irrespective of the different features characterizing the area the environment consists of salt marshes mud flats shallows tidal channels islands together with reclaimed farmlands crossed by natural watercourses and drainage channel networks in particular the aem shows i the presence of fresh water with resistivity larger than 20 m underneath the central part of the lagoon at depths from 10 to 25 m below m s l ii the interface between different relevant stratigraphic units e g the clayey layer bounding the holocene pleistocene sedimentation and iii the occurrence of areas with possible submarine fresh groundwater discharge moreover the source and inland extent of the saltwater contamination in the shallow coastal aquifers along the southern margin of the lagoon are clearly revealed aem data were complemented with very high resolution seismic vhrs acquisitions the integrated analysis of the two data sets allows distinguishing between lithostratigraphic heterogeneity and variability of the subsurface fluids

clues of postseismic relaxation for the 1915 fucino earthquake central italy from modeling of leveling data 1 we study five high precision leveling lines located around the epicentral area of 13 january 1915 mw 6 7 fucino earthquake italy that possibly recorded late stage postseismic relaxation movements the geodetic signal is expected to comprise both large scale uplift of the apennines and postseismic relaxation effects in order to verify this hypothesis and to estimate the amount of each contribution we compute gravitational visco elastic postseismic relaxation by inverting leveling data results indicate that the elastic upper crust is relatively thin about 10 km and post seismic contribution could be set at 30 of the geodetic signal model parameters are consistent with previous knowledge of the 1915 fucino earthquake source local seismic hypocentral determinations and crustal models derived from surface waves

moment tensor inversion of recent small to moderate sized earthquakes implications for seismic hazard and active tectonics beneath the sea of marmara summary we retrieve the moment tensors of 64 small to moderate sized events that occurred mostly beneath the sea of marmara using near field data recorded at strong motion and broad band seismic stations the near field displacement records are inverted to their sources utilizing kuge s method where the best fit between the synthetic and observed seismograms is achieved through searching a centroid moment tensor cmt point in a grid scheme we also analyse the stress fields acting in the eastern and western parts of the sea of marmara by inverting the p and t axes of the focal mechanisms obtained significant biases in the stress tensors are obtained the nearly horizontal maximum compressive axis 1 in the western part is rotated 16 counter clockwise compared with 1 in the eastern part the 2 axis is close to vertical shear tectonic regime in the east and the plunge of 2 axis in the west is 36 transpressive tectonic regime changes in the 3 axis are also observed that is it is close to horizontal in the east and dips 49 in the west the spatial distribution of the focal mechanisms suggests that the stress field in the eastern part of the sea of marmara is homogenous compared with the western part and we identify five distinct subsidiary faults 1 a wnw ese striking right lateral strike slip fault located a few kilometres sw of the princes islands 2 a wsw ene striking right lateral strike slip fault named the yalova hersek fault 3 an e w striking normal fault located onshore between

the 1999 izmit earthquake sequence in turkey seismological and tectonic aspects the izmit duzce earthquake sequence is the largest sequence recorded by modern digital networks in the history of turkish earthquakes the m w 7 4 izmit mainshock occurred at 29 967 e and 40 729 n and 13 km depth at 00 hr 01 min 38 7 sec utc on 17 august 1999 and was preceded by at least eight immediate foreshocks of magnitude m l 3 0 aftershock locations show that a large region has become seismically very energetic following the mainshock and that most of the aftershock zone developed quickly in the first 3 days the distribution of the aftershocks illuminates numerous seismotectonic structures associated with the various branches of the north anatolian fault naf in the aftershock zone the seismicity pattern defines a rupture plane that extends about 80 km east and 75 km west of the mainshock epicenter confirming bilateral rupture during the mainshock the western aftershock activity is almost entirely located offshore extending along the axis of the izmit bay we show that the westernmost extent of the mainshock rupture reached the offshore region just 10 km south of the princes islands the dominance of strike slip motion is one of the main characteristics of the izmit sequence a number of significant aftershock clusters occur off the inferred mainshock rupture plane the spatial and temporal occurrence of these clusters show that they are triggered by the complex redistribution of stresses and dynamic strains imposed by the dislocation of the mainshock the focal mechanisms of the events located in the western end of the rupture zone show both strike slip and normal faulting mechanisms we infer that the yalova cluster was triggered by the mainshock the dominance of the normal faulting mechanisms supports the notion that dynamic extensional strains played a major role in triggering this cluster four events located off the princes islands indicate similar source mechanisms characterized by right lateral strike slip motion parallel to the strike of the northern boundary fault nbf and local trend of aftershock distribution this observation leads to a first order seismotectonic evidence that the nature of the nbf which is known to be a transtensional feature at the surface is dominated by strike slip motion at depth the coexistence of strike slip and extensional seismotectonic features in the sea of marmara highlights the importance of strain partitioning amongst shallow transtentional structures accommodating north south extension and deeper structures associated with the naf accommodating east west right lateral shear manuscript received 22 september 2000

surface water groundwater exchange in transitional coastal environments by airborne electromagnetics the venice lagoon example 1 a comprehensive investigation of the mixing between salt fresh surficial water and groundwater in transitional environments is an issue of paramount importance considering the ecological cultural and socio economic relevance of coastal zones acquiring information which can improve the process understanding is often logistically challenging and generally expensive and slow in these areas here we investigate the capability of airborne electromagnetics aem at the margin of the venice lagoon italy the quasi 3d interpretation of the aem outcome by the spatially constrained inversion sci methodology allows us to accurately distinguish several hydrogeological features down to a depth of about 200 m for example the extent of the saltwater intrusion in coastal aquifers and the transition between the upper salt saturated and the underlying fresher sediments below the lagoon bottom are detected the research highlights the aem capability to improve the hydrogeological characterization of subsurface processes in worldwide lagoons wetlands deltas

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

active faults and evolving strike slip basins in the marmara sea northwest turkey a multichannel seismic reflection study abstract the north anatolian fault is a 1200 km long transform fault forming the boundary between the anatolian and eurasian plates near its western end it strikes through the marmara sea and is responsible for the creation of three deep marine depressions the north anatolian fault system and the linked basins in the eastern marmara sea were studied using newly acquired multi channel seismic reflection data in the marmara sea the north anatolian fault consists of a main strand and a few subsidiary branches the main strand is made up of the ganos 15 km long central marmara 105 km and north boundary 45 km fault segments the north boundary fault joins in the east to the izmit segment which was ruptured during the m s 7 4 earthquake on 17 8 1999 the north boundary fault is highly oblique to the regional displacement vector which results in the generation of a symmetrical fault wedge basin this cinarcik basin is a wedge shaped deep marine depression south of istanbul it is about 50 km long up to 20 km wide and 1250 m deep and is filled with pliocene to quaternary sediments over 3 km thick the north boundary fault joins in the west to the transpressional central marmara fault around the restraining segment boundary the syntransform sediments are being deformed into a large anticlinorium the cinarcik basin started to form when the westward propagating north anatolian fault intersected a northwest trending pre existing fault zone during the pliocene and bifurcated into nw and sw trending segments forming a transform transform transform type triple junction dextral strike slip movement along the arms of the triple junction led to the development of the cinarcik basin the present fault geometry in the marmara region was achieved later during the mid pliocene following the termination of the triple junction geometry south of the main north anatolian fault system there is a second active strike slip fault in the marmara sea made up of several segments a highly asymmetrical fault bend basin comprising pliocene quaternary sediments over 2 5 km thick is forming along a releasing fault segment of this south boundary fault system

the morphology of strike slip faults examples from the san andreas fault california fault zones are seldom straight nor are fractures within them continuous permanent strain fields are imprinted near a fault of complex geometry as a result of continued slip these strain fields may be manifest as vertical deformation near the fault strain fields that increase area result in subsidence and strain fields that reduce area result in uplift although these effects are modified by erosion and deposition the general features of fault zone morphology are a consequence of the geometry and slip distribution along strike graphical views of strain fields associated with simple vertical strike slip faults are derived using boundary element methods if the fault is straight and parallel to the applied shear strain the hills and valleys resulting from finite fault rupture are separated by the fault trace this is rarely observed in nature instead strike slip faults cut through hills and valleys apparently of their own making we show this to be a consequence of segments of the fault being nonparallel to each other and to the overall applied shear strain coseismic strains are large but transient since they are substantially annulled by rupture on contiguous fault segments we test our theory with examples from parts of the san andreas fault system in california the morphologies of the parkfield region and the southern san andreas fault in the coachella valley are shown to be consistent with plausible distributions of slip on mapped surface faults the location of the salton sea appears to be a consequence of a reduction of slip on the san andreas fault toward the brawley seismic zone

strike slip fault geometry in turkey and its influence on earthquake activity the geometry of turkish strike slip faults has been reviewed and described from this data set it appears that fault geometry the distribution of discontinuities such as bends and stepovers along the main fault trace plays an important role in controlling the location of large earthquake rupture segments along the fault zones large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 more important than the size of each discontinuity however is the total geometric pattern i e the distribution of adjacent bends and stepovers based not only on distance from one another but also on relative discontinuity size certain geometric patterns restraining single or double bends are particularly common and can be viewed as responsible for strain accumulation along portions of the fault zone fault geometry not only plays a role in the extent of earthquake rupture but also in characteristics of earthquake behavior for example large earthquake epicenters often occur near restraining bends or double bends furthermore aftershocks and swarm activity can often be associated with releasing areas areas along the strike slip fault that are undergoing a relatively large amount of extension

estimates of seismic potential in the marmara sea region from block models of secular deformation constrained by global positioning system measurements we model the geodetically observed secular velocity field in north western turkey with a block model that accounts for recoverable elastic strain ac cumulation the block model allows us to estimate internally consistent fault slip rates and locking depths the northern strand of the north anatolian fault zone nafz carries approximately four times as much right lateral motion 24 mm yr as does the southern strand in the marmara sea region the data show strain accu mulation to be highly localized we find that a straight fault geometry with a shallow locking depth of 6 7 km fits the observed global positioning system velocities better than does a stepped fault geometry that follows the northern and eastern edges of the sea this shallow locking depth suggests that the moment release associated with an earthquake on these faults should be smaller by a factor of 2 3 than previously inferred assuming a locking depth of 15 km online material an updated version of velocity field data

gps and geologic estimates of the tectonic activity in the marmara sea region nw anatolia a dense network of 52 global positioning system gps sites is used to determine the velocity field and strain rate pattern at the western end of the north anatolian fault zone nafz in the marmara sea region nw anatolia based on four gps campaigns carried out biannually between 1990 and 1996 the detailed kinematic field of crustal motion is calculated the southernmost station shows an average rate of 22 3 mm yr oriented westward relative to istanbul eurasia this value is indicative of the dextral strike slip motion of nw anatolia relative to the black sea the gps velocity field reveals that the sites located on the thrace black sea block show negligible motion relative to istanbul the gps based deformation pattern of three sections crossing the westward prolongation of the nafz is compared with neotectonic data both the gps and the neotectonic data give clear evidence that most of the deformation occurs along a relatively narrow e w oriented zone this belt extends from the single fault trace of the nafz through the gulf of izmit the marmara sea the arkoy region and the gulf of saros into the north aegean trough nat in addition the cross sections show the increasing influence of the n s oriented extension in the aegean sea region from the comparison of the directions and rates of shear and normal strain deduced from gps data with geologic and seismic observations we conclude that the most active zone of dextral shear follows a line along mudurnu valley the northern marmara sea and the saros trough where it joins the nat

quantifying geophysical inversion uncertainty using airborne frequency domain electromagnetic data applied at the province of zeeland the netherlands an accurate understanding of the fresh saline distribution of groundwater is necessary for effective groundwater management airborne electromagnetic aem surveys offer a rapid and cost effective method with which to map this offering valuable additional information about the subsurface to convert aem data into electric conductivity and ultimately groundwater salinity an inversion is undertaken a number of algorithms are available for this purpose however these are affected by significant uncertainty owing to inherent nonunique characteristics of this process the most commonly used inversion codes in hydrogeophysical studies were quantitatively tested using frequency domain aem and ground data from the province of zeeland the netherlands these include ubc1dfm code and quasi 2d laterally constrained inversions following an investigation of inversion parameter settings data were inverted for four inversion methods and interpolated into 3 d volumes using geological data and empirical electrical conductivity and water salinity relationships each inversion was converted into groundwater electrical conductivity and split into fresh brackish saline regions for groundwater volume estimates out of a total volume of 2 8 billion m3 a fresh groundwater estimate could differ by as much as 178 million m3 depending on the inversion used the primary factor here was the choice of model smoothness which was shown to affect the thickness of the brackish interval fresh brackish saline interfaces were consistently mapped with an accuracy of 3 m the brackish being the most accurately resolved the few layer method was less successful at resolving smoothly varying salinity distributions but more successful at mapping the brackish interface at greater depth

active faults in the sea of marmara western turkey imaged by seismic reflection profiles turkey is moving westward relative to eurasia thereby accommodating the collision between arabia and eurasia this motion is mostly taken up by strike slip deformation along the north and east anatolian faults the sea of marmara lies over the direct westward continuation of the north anatolian fault zone just east of the sea of marmara the north anatolian fault splits into three strands two of which continue into the sea while the locations of the faults are well constrained on land it has not yet been determined how the deformation is transferred across the sea of marmara onto the faults on the west coast of turkey we present results from a seismic reflection survey undertaken to map the faults as they continue through the three deep marmara sea basins of clnarclk central marmara and tekirdag in order to determine how the deformation is distributed across the sea of marmara and how it is taken up on the western side of the sea the data show active dipping faults with associated tilting of sedimentary layers connecting the north anatolian fault to strike slip faults that cut the biga and gallipoli peninsulas

rupture progression along discontinuous oblique fault sets implications for the karadere rupture segment of the 1999 izmit earthquake and future rupture in the sea of marmara abstract large earthquakes in strike slip regimes commonly rupture fault segments that are oblique to each other in both strike and dip this was the case during the 1999 izmit earthquake which mainly ruptured e w striking right lateral faults but also ruptured the n60 e striking karadere fault at the eastern end of the main rupture it will also likely be so for any future large fault rupture in the adjacent sea of marmara our aim here is to characterize the effects of regional stress direction stress triggering due to rupture and mechanical slip interaction on the composite rupture process we examine the failure tendency and slip mechanism on secondary faults that are oblique in strike and dip to a vertical strike slip fault or master fault for a regional stress field well oriented for slip on a vertical right lateral strike slip fault we determine that oblique normal faulting is most favored on dipping faults with two different strikes both of which are oriented clockwise from the strike slip fault the orientation closer in strike to the master fault is predicted to slip with right lateral oblique normal slip the other one with left lateral oblique normal slip the most favored secondary fault orientations depend on the effective coefficient of friction on the faults and the ratio of the vertical stress to the maximum horizontal stress if the regional stress instead causes left lateral slip on the vertical master fault the most favored secondary faults would be oriented counterclockwise from the master fault for secondary faults striking 30 oblique to the master fault right lateral slip on the master fault brings both these secondary fault orientations closer to the coulomb condition for shear failure with oblique right lateral slip for a secondary fault striking 30 counterclockwise the predicted stress change and the component of reverse slip both increase for shallower angle dips of the secondary fault for a secondary fault striking 30 clockwise the predicted stress change decreases but the predicted component of normal slip increases for shallower angle dips of the secondary fault when both the vertical master fault and the dipping secondary fault are allowed to slip mechanical interaction produces sharp gradients or discontinuities in slip across their intersection lines this can effectively constrain rupture to limited portions of larger faults depending on the locations of fault intersections across the fault intersection line predicted rakes can vary by 40 and the sense of lateral slip can reverse application of these results provides a potential explanation for why only a limited portion of the karadere fault ruptured during the izmit earthquake our results also suggest that the geometries of fault intersection within the sea of marmara favor composite rupture of multiple oblique fault segments