accurate relocation of izmit earthquake mw 7 4 1999 aftershocks in cinarcik basin using double difference method 1 we relocated part of the aftershock activity in cinarcik basin and surrounding areas that are associated with the 1999 izmit earthquake mw 7 4 double difference relocation algorithm is used to relocate the aftershocks the data set was obtained from a temporary seismic network deployed 10 days after the main shock by cooperation between bogazici university kandilli observatory and earthquake research institute lgit grenoble and ipgp paris for a better station coverage additional data set was obtained from a network operated by tubitak marmara research center differential travel times were calculated using both arrival time readings and waveform cross correlation method we relocated 1145 of the aftershocks and interpreted the results with emphasis on the yalova and tuzla cluster located within the marmara sea the results show better focused seismicity patterns for the yalova cluster providing clear evidence for the proposed models we present a revised location of the 1963 cinarcik earthquake which took place in area of yalova cluster finally we propose that the activity of tuzla cluster represents a parallel subsidiary fault of the main marmara fault

seismic interaction and delayed triggering along the north anatolian fault 1 the deformation of northwestern turkey is the result of the encounter of the westward extrusion of the anatolian plate with the north south extension of the aegean domain while the north anatolian fault localizes the former type of deformation and has been the site of more large earthquakes 9 events of magnitude 7 than any other continental fault over the past 100 years the extension is diffuse and is characterized by spatial clusters of smaller earthquakes and near continuous activity we study the evolution of seismicity along the fault and in the clusters neighboring the fault before and after the two large earthquakes of 1999 we observe that the un ruptured section of the fault and the extension clusters respond very differently to the earthquakes while significant aftershock activity on the fault segments adjacent to the rupture only occurs at relatively short distance from the rupture 30 km the clusters can be activated at much larger distances 300 km remarkably their triggering is not immediate after the earthquake but is delayed in time their peak seismic activation may occur weeks or months after the earthquake this distant and delayed triggering which is consistent with recent gps observations may help resolve some of the previously unexplained characteristics of the 1939 1999 sequence of large earthquakes along the fault

propagation of a strike slip plate boundary within an extensional environment the westward propagation of the north anatolian fault we document the establishment of the aegea anatolia eurasia plate boundary in pliocene pleistocene time before 2 ma no localized plate boundary existed north of the aegean portion of the anatolia plate and the shear produced by the motion of anatolia aegea with respect to eurasia was distributed over the whole width of the aegean west anatolian western portion in 4 5 ma a shear zone comparable to the gulf of corinth was formed in the present sea of marmara the initial extensional basins were cut by the strike slip main marmara fault system after 2 5 ma shortly after the plate boundary migrated west of the sea of marmara along the northern border of aegea from the north aegean trough to the gulf of corinth area and to the kefalonia fault there it finally linked with the northern tip of the aegean subduction zone completing the system of plate boundaries delimiting the anatolia aegea plate we have related the change in the distribution of shear from miocene to pliocene to the formation of a re

global distribution of volcanic centers and mountains on io control by asthenospheric heating and implications for mountain formation abstract jupiter s moon io possesses numerous tectonic mountains in addition to its ubiquitous volcanoes and volcanic features remarkably a distinct global anticorrelation exists between the spatial distribution of mountains and volcanic centers on io this relationship indicates an explicit connection between volcanism and mountain formation even though the mountains are tectonic in origin predominantly upthrusted crustal blocks spherical harmonic analysis shows the distribution of mountains and volcanic centers have statistically significant power at degree 2 this result is especially striking for the volcanic center distribution and directly implicates models of asthenospheric tidal heating the latter predict enhanced heat flux along the equator in a degree two pattern that matches observations mountain formation on io appears to be a form of dominantly vertical tectonism unique in the modern solar system continual burial by widespread volcanism drives the crust inward which leads to strong compression and at discrete locations mountains correlation coefficients between the volcanic and mountain distributions indicate statistically meaningful anticorrelation at low spectral degrees l 1 2 4 and 6 the anticorrelation is especially significant between the longitudinal sectorial l 2 components when considered on their own we compare this anticorrelation with published models that link volcano and mountain formation while consistent in part with l 2 convection models which predict such an anticorrelation in principle such low degree anticorrelations are also if not more compatible with mountain formation due to or influenced by thermal expansion of io s crust and deep compression and thrust faulting in regions of lower than average volcanic heat piping positive correlations between mountain and volcanic center distributions at high spectral degree may reflect structural links between a good fraction of mountain blocks and adjacent volcanic paterae whereas the anticorrelation at low degree implies that most volcanic features which are far more numerous overall form independently of mountains

magma transport of heat on io a mechanism allowing a thick lithosphere models indicate that the high heat flow from io would result in a very thin approximately 5 km silicate lithosphere overlying a molten interior if all heat was transported through the lithosphere via conduction however the presence of mountains with relief in excess of 10 km would seem to demand a thick lithosphere at least locally a significant fraction of io s heat flow may be transported via advection through volcanoes advective heat transfer permits a thicker lithosphere than does pure conduction possibly reconciling io s high heat flow with the rugged topography

seismic imaging of the three dimensional architecture of the cinarcik basin along the north anatolian fault the cinarcik basin is a transtensional basin located along the northern branch of the northern north anatolian fault naf in the sea of marmara the eastern half of which has been identified as a seismic gap during the seismarmara 2001 experiment a dense grid of multichannel seismic reflection profiles was shot covering the whole cinarcik basin and its margins the new seismic images provide a nearly three dimensional view of the architecture of the basin fault system at depth and sedimentary infill and provide insight into its tectonic evolution along both northern and southern margins of the basin seismic reflection data show deep penetrating faults hence long lived features which have accommodated a large amount of extension there is no indication in the data for a single throughgoing strike slip fault neither a cross basin fault nor a pure strike slip fault running along the northern margin faster opening is presently observed in the eastern part of the basin the cinarcik basin seems to have developed as a transtensional basin across strike slip segments of the northern naf for the last few million years

seven years of postseismic deformation following the 1999 m 7 4 and m 7 2 izmit duzce turkey earthquake sequence 1 we report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode gps observations for the 1999 izmit duzce earthquake sequence resolvable time dependent postseismic changes to the preearthquake interseismic velocity field extend at least as far as the continuous gps station in ankara 200 km southeast of the izmit rupture seven years after the earthquake sequence the relative postseismic velocity across the north anatolian fault naf reaches 10 12 mm a roughly 50 of the steady state interseismic rate with the highest postseismic velocities within 40 km of the coseismic ruptures we use a sequence of logarithmic time functions to fit gps site motions up to three logarithmic terms with decay constants of 1 150 and 3500 days are necessary to fit all the transient motion observed at the continuous gps stations the first term is required for the component of site motion parallel to the naf at near field sites strongly implicating rapid shallow afterslip the intermediate and longer term postseismic velocity components reflect more broadly distributed strain with a symmetric double couple pattern suggestive of either localized deep afterslip or viscoelastic relaxation of the upper mantle and or lower crust in two areas including the marmara sea this pattern is superimposed on north south extension centered on the naf we speculate that this extension may result from aseismic dip slip along coseismically weakened faults driven by the background tectonic stress

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

uplift and subsidence from oblique slip the ganos marmara bend of the north anatolian transform western turkey abstract bends that locally violate plate motion parallel geometry are common structural elements of continental transform faults we relate the vertical component of crustal motion in the western marmara sea region to the nnw pointing 18 bend on the northern branch of the north anatolian fault naf n between the ganos segment which ruptured in 1912 and the central marmara segment a seismic gap crustal shortening and uplift on the transpressive west side of the bend results in the ganos mountain crustal extension and subsidence on the transtensional east side produce the tekirdag basin we propose that this vertical component of deformation is controlled by oblique slip on the non vertical north dipping ganos and tekirdag segments of the north anatolian fault we compare holocene with quaternary structure across the bend using new and recently published data and conclude the following first bend related vertical motion is occurring primarily north of the naf n this suggests that this bend is fixed to the anatolian side of the fault second current deformation is consistent with an antisymmetric pattern centered at the bend up on the west and down on the east accumulated deformation is shifted to the east along the right lateral naf n however leading to locally opposite vertical components of long and short term motion uplift has started as far west as the landward extension of the saros trough current subsidence is most intense close to the bend and to the ganos mountain while the basin deepens gradually from the bend eastward for 28 km along the fault the pattern of deformation is time transgressive if referenced to the material but is stable if referenced to the bend the lag between motion and structure implies a 1 1 1 4 ma age for the basin at current dextral slip rate 2 0 2 5 cm year third the tekirdag is an asymmetric basin progressively tilted down toward the naf n which serves as the border fault progressive tilt suggests that the steep northward dip of the fault decreases with depth in a listric geometry at the scale of the upper crust and is consistent with reactivation of paleogene suture related thrust faults fourth similar thrust fault geometry west of the bend can account for the ganos mountain anticline monocline as hanging wall block folding and back tilting oblique slip on a non vertical master fault may accommodate transtension and transpression associated with other bends along the naf and other continental transforms

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

new estimates for io eruption temperatures implications for the interior abstract the initial interpretation of galileo data from jupiter s moon io suggested eruption temperatures 1600 c tidal heating models have difficulties explaining io s prodigious heat flow if the mantle is 1300 c although we suggest that temperatures up to 1450 c may be possible in general io eruption temperatures have been overestimated because the incorrect thermal model has been applied much of the thermal emission from high temperature hot spots comes from lava fountains but lava flow models were utilized we apply a new lava fountain model to the highest reported eruption temperature the ssi observation of the 1997 eruption at pillan this resets the lower temperature limit for the eruption from 1600 to 1340 c additionally viscous heating of the magma may have increased eruption temperature by 50 100 c as a result of the strong compressive stresses in the ionian lithosphere while further work is needed it appears that the discrepancy between observations and interior models is largely resolved

link between coulomb stress changes and seismic activation in the eastern marmara sea after the 1999 izmit turkey earthquake 1 we investigate the effect of dynamic and static stress changes produced by the 1999 izmit earthquake on four preexisting seismic clusters located in the eastern marmara sea beyond the western termination of the earthquake rupture these four clusters show long lasting modifications in their seismicity rate we observe that these seismic activity variations are related to stress changes dynamic stress pulses activate strike slip faulting instantaneously but in the absence of a concomitant static coulomb stress increase this activation is short lived indeed a large dynamic stress combined with a negative static coulomb stress may result in an immediate activation followed by the occurrence of a seismicity shadow in contrast the activation of extensional clusters begins slowly and takes a few days to fully develop it is also remarkably long lasting and does not follow a classical omori decay more than 10 years after the earthquake the extensional clusters located near the termination of the rupture where static stress and pressure changes were high are still activated

asymmetric thermal evolution of the moon 1 the moon possesses a clear dichotomy in geological processes between the nearside and farside hemispheres the most pronounced expressions of this dichotomy are the strong concentration of radioactive heat sources on the nearside in a region known as the procellarum kreep terrane pkt and the mare basaltic lava flows that erupted in or adjacent to this terrane we model the thermochemical evolution of the moon using a 3 d spherical thermochemical convection code in order to assess the consequences of a layer enriched in heat sources below the pkt on the moon s global evolution we find that in addition to localizing most of the melt production on the nearside such an enriched concentration of heat sources in the pkt crust has an influence down to the core mantle boundary and leaves a present day temperature anomaly within the nearside mantle moderate gravitational and topographic anomalies that are predicted in the pkt but not observed may be masked either by crustal thinning or gravitational anomalies from dense material in the underlying mantle our models also predict crystallization of an inner core for sulfur concentrations less than 6 wt

evolution of the seismicity in the eastern marmara sea a decade before and after the 17 august 1999 izmit earthquake we review the long term evolution of seismicity in the eastern marmara sea over a decade before and after the 1999 mw 7 6 izmit earthquake we analyze large scale space time variations of seismicity in the region and illustrate the impact of the recent large strike slip earthquakes on the background activity composed of distinct pre existing seismic clusters two types of aftershocks activity are observed the first type of enhancement is on strike slip fault segments izmit fault princes island section of the main marmara fault gemlik fault immediately following the main shock and related to coulomb stress transfer the second type of enhancement is attached to extensional clusters yalova tuzla with a few days delay in the onset of strong activation probably related to pore pressure increase we observe a fast decay of the activity on strike slip segments and slower evolution of seismic clusters with extensional features two years after the izmit earthquake seismic activity returned to the pre earthquake pattern with most of the activity occurring within extensional clusters it appears that the influence of the last large strike slip event on the spatial seismicity distribution in the eastern marmara sea is less significant than the effect of the long term regional extension

the crustal structure of the eastern marmara region turkey by teleseismic receiver functions summary we study the crustal structure of eastern marmara region by applying the receiver function method to the data obtained from the 11 broad band stations that have been in operation since the 1999 earthquake the stacked single event receiver functions were modelled by an inversion algorithm based on a five layered crustal velocity model to reveal the firstorder shear velocity discontinuities with a minimum degree of trade off we observe crustal thickening from west 29 32 km to east 34 35 km along the north anatolian fault zone nafz but we observe no obvious crustal thickness variation from north to south while crossing the nafz the crust is thinnest beneath station ter 29 km located near the black sea coast in the west and thickest beneath station tar 35 km located inland in the southeast the average crustal thickness and s wave velocity for the whole regions are 31 2 km and 3 64 0 15 km s 1 respectively the eastern marmara region with its average crustal thickness high heat flow value 101 11 mw m 2 and with its remarkable extensional features seems to have a basin and range type characteristics but the higher average shear velocities 3 64 km s 1 and crustal thickening from 29 to 35 km towards the easternmost stations indicate that the crustal structure shows a transitional tectonic regime therefore we conclude that the eastern marmara region seems to be a transition zone between the marmara sea extensional domain and the continental anatolian inland region

crustal anisotropy in the eastern sea of marmara region in northwestern turkey abstract the north anatolia fault zone nafz is a transform zone 1600 km in length representing the plate boundary between the westward moving anatolian plate and stable eurasia almost the entire fault zone has failed during the last century except for the sea of marmara section which is located in direct vicinity to the city of istanbul in this study we investigate the crustal anisotropy along the eastern marmara section of the nafz based on shear wave splitting we measure seismic anisotropy parameters namely the fast polarization direction pd and time delay td by analyzing local seismicity recorded at selected seismographs operated throughout the eastern sea of marmara region our shear wave splitting sws observations indicate a predominant northwest southeast oriented pd which is sub parallel to both the orientation of the regional s hmax in northwest turkey and the local nafz strike along the princes islands segment toward the south at the armutlu peninsula we find a different pd pattern reflecting local fault strikes s hmax as well as strain asymmetry between different crustal blocks across the fault zone applying strict quality criteria enables us to identify robust preferred fast pds which suggests that initially observed pd heterogeneities are sometimes caused by second order effects in the data rather than by varying pds comparing td and hypocentral depth distribution we find the depth extent of the anisotropy is confined to the uppermost 10 km depth of crust we combine our sws results with those from previous studies conducted along the san andreas fault saf and nafz in order to investigate the relation of angular deviations of the pds from regional s hmax and local fault strikes with fault zone distance we find that fast pds are mainly controlled by the local fault structure in close proximity to a fault zone 5 and 10 km while they are controlled by crustal stress at off fault locations 5 and 10 km

spatial variation of aftershock activity across the rupture zone of the 17 august 1999 izmit earthquake turkey we examined the spatial variation in the aftershock activity from the 17 august 1999 izmit turkey earthquake we found that this aftershock sequence is non uniform both in space and time aspects that need to be taken into account in any further statistical analysis other aspects of this aftershock sequence are similar to other aftershock sequences namely low b values and a high degree of spatial variation we have detected three zones of relatively high b values two of which coincide with asperities revealed by previous slip inversion studies the third zone with an anomalous b value is located beyond the fault rupture and indicates a weakened fractured zone in the yalova tuzla area this b value analysis provided no evidence for any significant difference that may exist between the two sides of the mainshock fault plane d 2004 elsevier b v all rights reserved

tidal dissipation surface heat flow and figure of viscoelastic models of io abstract the distribution of hot spots on io s surface and io s figure constrain models of io s interior voyager observations indicate that most hot spots and volcanic plumes are close to the equator recently however it has been proposed that a large low albedo feature in the south polar region may be the source of 40 of the surface heat flow we calculate spatial distributions of the dissipation rate surface heat flow and the figures of three and four layer maxwell rheology models of io by using the correspondence principle the models are required to satisfy the observed surface heat flow constraint and are consistent with the composition of a dehydrated c2 chondrite they consist of an inviscid fe fes core and viscoelastic silicate mantle and lithosphere layers a comparison of the calculated equilibrium figure with the observed figure of io supports the chosen core radius of 980 km in addition the four layer model has a partially molten asthenosphere a few tens of kilometers thick the preferred three layer model has a mantle shear modulus of 10 10 pa and a viscosity of 2 10 16 pa s consistent with rock properties the tidal dissipation rate for this model is largest along the polar axis integration of the dissipation rate over radius gives a surface heat flow with maxima at the poles and minima near the sub jovian and anti jovian points in contrast the dissipation rate in a molten or partially molten incompressible asthenosphere has maxima near the equator and is close to zero at the poles the asthenosphere dissipation rate is mainly a function of asthenosphere viscosity and thickness the thinner the asthenosphere the smaller is the required viscosity a 50 km thick asthenosphere requires a viscosity of about 10 8 pa s a strong south polar hot spot if it can be confirmed by infrared observation favors dissipation in the mantle but does not exclude dissipation in a partially molten asthenosphere equatorial hot spots and the concentration of prometheus type plumes near the equator favor asthenosphere heating but do not rule out deep mantle dissipation both asthenosphere and deep mantle heating may contribute to io s surface heat flow the properties of magma transport through the lithosphere and the planform of mantle convection might exert a control on the surface expression of heating at greater depth

seismotectonics of the armutlu peninsula marmara sea nw turkey from geological field observation and regional moment tensor inversion abstract the armutlu peninsula located in the eastern marmara sea coincides with the western end of the rupture of the 17 august 1999 izmit mw 7 6 earthquake which is the penultimate event of an apparently westward migrating series of strong and disastrous earthquakes along the nafz during the past century we present new seismotectonic data of this key region in order to evaluate previous seismotectonic models and their implications for seismic hazard assessment in the eastern marmara sea long term kinematics were investigated by performing paleo strain reconstruction from geological field investigations by morphotectonic and kinematic analysis of exposed brittle faults short term kinematics were investigated by inverting for the moment tensor of 13 small to moderate recent earthquakes using surface wave amplitude spectra our results confirm previous models interpreting the eastern marmara sea region as an active transtensional pull apart environment associated with significant nne ssw extension and vertical displacement at the northern peninsula long term deformation pattern did not change significantly since pliocene times contradicting regional tectonic models which postulate a newly formed single dextral strike slip fault in the marmara sea region this area is interpreted as a horsetail splay fault structure associated with a major normal fault segment that we call the waterfall fault apart from the waterfall fault the stress strain relation appears complex associated with a complicated internal fault geometry strain partitioning and reactivation of pre existing plane structures at the southern peninsula recent deformation indicates active pull apart tectonics constituted by ne sw trending dextral strike slip faults earthquakes generated by stress release along large rupture zones seem to be less probable at the northern but more probable at the southern peninsula additionally regional seismicity appears predominantly driven by plate boundary stresses as transtensional faulting is consistent with the southwest directed far field deformation of the anatolian plate

perturbation of the izmit earthquake aftershock decaying activity following the 1999 mw 7 2 duzce turkey earthquake triggering and quiescence patterns of seismicity in western turkey following the occurrence of the 12 november 1999 m w 7 2 duzce earthquake are investigated the changes in seismicity rate are analyzed along the north anatolian fault segments that had ruptured 3 months earlier during the 17 august 1999 m w 7 4 izmit earthquake detection of triggering and quiescence is done by comparing the seismicity rate that would be expected if the duzce earthquake had not happened to the actual observed rate the expected rates are estimated by extrapolating the preexisting seismicity pattern using two complementary models a simple omori utsu s law and the etas model fault segments located to the east of the izmit epicenter show a mild case of quiescence following the duzce earthquake these segments had previously experienced an anomalous triggering episode in the 5 days preceding the duzce earthquake correlated with the occurrence of two strong m w 5 izmit aftershocks however it is not clear whether this observed quiescence is real or spurious as it coincides with a local reconfiguration of the seismological network a temporary increase of 0 1 to 0 15 in completeness magnitude would be enough to explain this apparent deactivation fault segments located to the west of the izmit epicenter exhibit triggering of seismicity following the duzce earthquake this observed triggering is mostly restricted to a cluster of events located in the geothermal area of yalova the increase of seismicity rate is delayed by 18 hours after the waves travelling from the duzce rupture had hit this zone our analysis suggests that this 15 day long reactivation can be explained by a short lived perturbation the local seismic activity then sustaining itself for the remaining 15 days we argue that this particular behavior is likely to correspond to a case of dynamic triggering by the end of year 1999 the yalova cluster shows a significant quiescence that lasted for several months this shutting down does not coincide with the occurrence of any local earthquake that would be large enough to stress shadow this area suggesting an aseismic cause to this pattern these results highlight the fact that 1 seismicity triggered by a major earthquake is not restricted to areas loaded by static stress and 2 that seismic activity associated with geothermal geological settings is highly sensitive to stress perturbations but also to aseismic processes that can both delay reactivation and cause this activity to suddenly decrease

layered convection in io implications for short wavelength surface topography and heat flow abstract io one of the four galilean moons of jupiter is remarkable for its extensive volcanism and extreme interior tidal heating the tidal heating likely yields a very low viscosity asthenosphere and consequently a very high rayleigh number of o 10 12 for convection in the interior in a state of quasi steady balance the internally generated heat must be transported from the interior to the base of the io lithosphere and exhausted to space the mechanisms whereby the convective radial heat transfer is evacuated involve both conduction and volcanism despite io s ubiquitous volcanism only 4 of its mountains montes appear to have a volcanic origin and most of the mountainous regions seem to be related to tectonic processes by employing an original control volume based numerical model we investigate the style of convection in the interior of io and the correlation of the scale of convection with the ionian surface heat flux and topography our control volume results support the existence of significant asthenospheric heating and demonstrate that short wavelength features of the surface heat flux are well correlated in scale to an expected layered intra lithospheric style small scale convection these numerical analyses suggest that the amplitude of the short wavelength topography of io is expected to be on the order of a few hundreds of meters the model results also demonstrate that the ionian highs cannot be produced by a lithospheric flexure process above the hot upwellings and therefore other tectonic events such as have previously been suggested must be responsible for the formation of the high ionian mountains that reach in excess of 17 km in elevation

constraints on mantle plumes on venus implications for volatile history abstract the analysis of venus gravity field and topography suggests the presence of a small number of deep mantle plumes 9 this study predicts the number of plumes formed at the core mantle boundary their characteristics and the production of partial melt from adiabatic decompression numerical simulations are performed using a 3d spherical code that includes large viscosity variations and internal heating this study investigates the effect of several parameters including the core mantle boundary temperature the amount of internal heating and the mantle viscosity the smallest number of plumes is achieved when no internal heating is present however scaling earth s radiogenic heating to venus suggests a value of 16 tw cases with internal heating produce more realistic lid thickness and partial melting but produce either too many plumes or no plumes if a high mantle temperature precludes the formation of a hot thermal boundary layer mantle viscosity must be reduced to at least 10 20 pa s in order to include significant internal heating and still produce hot plumes in all cases that predict melting melting occurs throughout the upper mantle only cases with high core temperature 1700 k produce dry melting over time the upper mantle may have lost significant volatiles depending on the water content of the lower mantle deep plumes may contribute to present day atmospheric water via volcanic outgassing assuming 50 ppm water in mantle 10 plumes with a buoyancy flux of 500 kg s continuously erupting for 4 myr will outgas an amount of water on the order of that in the lower atmosphere a higher level of internal heating than achieved to date as well as relatively low mantle viscosity may be required to achieve simulations with 10 plumes and a thinner lid alternatively if the mantle is heating up due to the stagnant lid the effect is equivalent to having lower rates of internal heating a temperature increase of 110 k byr is equivalent to 13 tw this value along with the internal heating of 3 tw used in this study may represent the approximate heat budget of venus mantle

new constraints on the rupture process of the 1999 august 17 izmit earthquake deduced from estimates of stress glut rate moments summary this paper illustrates the use of integral estimates given by the stress glut rate moments of total degree 2 for constraining the rupture scenario of a large earthquake in the particular case of the 1999 izmit mainshock we determine the integral estimates of the geometry source duration and rupture propagation given by the stress glut rate moments of total degree 2 by inverting long period surface wave lpsw amplitude spectra kinematic and static models of the izmit earthquake published in the literature are quite different from one another in order to extract the characteristic features of this event we calculate the same integral estimates directly from those models and compare them with those deduced from our inversion while the equivalent rupture zone and the eastward directivity are consistent among all models the lpsw solution displays a strong unilateral character of the rupture associated with a short rupture duration that is not compatible with the solutions deduced from the published models with the aim of understand this discrepancy we use simple equivalent kinematic models to reproduce the integral estimates of the considered rupture processes including ours by adjusting a few free parameters controlling the western and eastern parts of the rupture we show that the joint analysis of the lpsw solution and source tomographies allows us to elucidate the scattering of source processes published for this earthquake and to discriminate between the models our results strongly suggest that 1 there was significant moment released on the eastern segment of the activated fault system during the izmit earthquake 2 the apparent rupture velocity decreases on this segment

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

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

a study of microearthquake seismicity and focal mechanisms within the sea of marmara nw turkey using ocean bottom seismometers obss we have carried out seismological observations within the sea of marmara nw turkey in order to investigate the seismicity induced after gflcqk iuzmit kocaeli earthquake mw 7 4 of august 17 1999 using ocean bottom seismometers obss high resolution hypocenters and focal mechanisms of microearthquakes have been investigated during this marmara sea obs project involving deployment of 10 obss within the cvnarcvk eastern marmara sea and central tekirdagu western marmara sea basins during april july 2000 little was known about microearthquake activity and their source mechanisms in the marmara sea we have detected numerous microearthquakes within the main basins of the sea of marmara along the imaged strands of the north anatolian fault naf we obtained more than 350 well constrained hypocenters and nine composite focal mechanisms during 70 days of observation microseismicity mainly occurred along the main marmara fault mmf in the marmara sea there are a few events along the southern shelf seismic activity along the main marmara fault is quite high and focal depth distribution was shallower than 20 km along the western part of this fault and shallower than 15 km along its eastern part from high resolution relative relocation studies of some of the microearthquake clusters we suggest that the western main marmara fault is subvertical and the eastern main marmara fault dips to south at 458 composite focal mechanisms show a strike slip regime on the western main marmara fault and complex faulting strike slip and normal faulting on the eastern main marmara fault d 2004 elsevier b v all rights reserved

surface changes on io during the galileo mission abstract a careful survey of galileo ssi global monitoring images revealed more than 80 apparent surface changes that took place on io during the 5 year period of observation ranging from giant plume deposits to subtle changes in the color or albedo of patera surfaces explosive volcanic activity was discovered at four previously unrecognized centers an unnamed patera to the south of karei that produced a pele sized red ring a patera to the west of zal that produced a small circular bright deposit a large orange ring detected near the north pole of io and a small bright ring near io s south pole only a handful of io s many active volcanoes produced large scale explosive eruptions and several of these erupted repeatedly leaving at least 83 of io s surface unaltered throughout the galileo mission most of the hot spots detected from ssi nims and ground based thermal observations caused no noticeable surface changes greater than 10 km in extent over the five year period surface changes were found at every location where active plumes were identified including acala which was never seen in sunlight and was only detected through auroral emissions during eclipse two types of plumes are distinguished on the basis of the size and color of their deposits confirming post voyager suggestions by mcewen and soderblom icarus 55 1983 191 smaller plumes produce near circular rings typically 150 200 km in radius that are white or yellow in color unless contaminated with silicates and frequently coat their surroundings with frosts of fine grained so2 the larger plumes are much less numerous limited to a half dozen examples and produce oval orange or red sulfur rich rings with maximum radii in the north south direction that are typically in the range from 500 to 550 km both types of plumes can be either episodic or quasi continuous over a five year period repeated eruptions of the smaller so2 rich plumes likely contribute significantly to io s resurfacing rate whereas dust ejection is likely dominated by the tenuous giant plumes both types of plume deposits fade on time scales of months to years through burial and alteration episodic seepages of so2 at haemus montes zal montes dorian montes and the plateau to the north of pillan patera may have been triggered by activity at nearby volcanic centers

states of local stresses in the sea of marmara through the analysis of large numbers of small earthquakes abstract we invert the present day states of stresses for five apparent earthquake clusters in the northern branch of the north anatolian fault in the sea of marmara as the center of the sea of marmara is prone to a devastating earthquake within a seismic gap between these selected clusters sensitive analyses of the understanding of the stress and strain characteristics of the region are all important we use high quality p and s phases and p wave first motion polarities from 398 earthquakes with ml 1 5 using at least 10 p wave first motion polarities fmps and a maximum of 1 inconsistent station obtained from a total of 105 seismic stations including 5 continuous obss we report here on large numbers of simultaneously determined individual fault plane solutions fpss and orientations of principal stress axes which previously have not been determined with any confidence from the basins of the sea of marmara and prominent fault branches we find ne sw trending transtensional stress structures predominantly in the earthquake clusters of the eastern tekirdag basin eastern cinarcik basin yalova and gemlik areas we infer that a dextral strike slip deformation exist in the eastern ganos offshore cluster furthermore we analyze fpss of four ml 4 0 earthquakes occurred in seismically quiet regions after 1999 izmit earthquake stress tensor solutions from a cluster of small events that we have obtained correlate with fpss of these moderate size events as a demonstration of the effectiveness of the small earthquakes in the derivation of states of local stresses consequently our analyses of seismicity and large numbers of fpss using the densest seismic network of turkey contribute to better understanding of the present states of the stresses and seismotectonics of the sea of marmara

insights into the dynamics of planetary interiors obtained through the study of global distribution of volcanoes ii tectonic implications from venus abstract the distribution of volcanic features is ultimately controlled by processes taking place beneath the surface of a planet for this reason characterization of volcano distribution at a global scale can be used to obtain insights concerning dynamic aspects of planetary interiors until present studies of this type commonly have focused on volcanic features of a specific type e g large volcanoes in venus or hot spot volcanism on earth or have concentrated on relatively small regions i e vent distribution within individual volcanic fields but no comparison of extensive databases has been made by using the same tools in both planets in this work the description of the distribution of volcanic features observed over the entire surface of venus is made using the same tool used for earth and is applied to an extensive database the analysis is based on density contours obtained with the fisher kernel as a result several groupings of volcanoes are identified refining the already documented concentration of volcanoes on the bat zone in particular some doughnut like patterns are observed that might be related to the action of mantle plumes the occurrence of such features on earth as well as the existence of a uniform distribution of background volcanism on both planets suggests similarities on their geodynamic behavior that had not been identified previously

internal structure of io and the global distribution of its topography abstract the distribution of equatorial long wavelength topography on io consists of alternating basins and swells similar to the pattern expected if tidal heating in a thin asthenosphere controls the elevation of the surface through a conductive lithosphere in isostatic equilibrium the equatorial basin swell pattern is shifted in longitude with respect to theoretical tidal heating patterns however making the correlation between theoretical heat flow and elevation unclear we calculate global topography for multilayer io models with dissipation occurring in a viscous asthenosphere and a solid mantle two models are considered a thermal swell model in which topography and heat flow are positively correlated and a differentiated lithosphere model in which topography and heat flow are negatively correlated both models match the observed pattern of alternating basins and swells along the equator and moderate polar topography if about two thirds of the tidal heating occurs in the asthenosphere and about one third occurs in the underlying solid mantle the mean thicknesses of the model lithospheres are 35 km in the differentiated model and 150 km in the thermal swell model polar topography and the hypsometric distribution of elevations in the differentiated lithosphere model match the observations better than the thermal swell model in a differentiated lithosphere model consistent with the topography the asthenosphere is at least 50 km thick with viscosity about 100 mpa sec and is about 7 more dense than the lithosphere the mantle density exceeds the asthenosphere density by at least 10 the shift of the equatorial basin swell pattern suggests that io s lithosphere has recently undergone a zonal rotation of about 25

influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions the influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions has been investigated by performing a series of high temperature triaxial compression experiments samples with melt fractions of 0 02 0 12 were deformed under water saturated conditions at temperatures between 1373 and 1473 k and a confining pressure of 300 mpa in a gas medium apparatus at constant differential stress and temperature the rate of deformation increased rapidly but systematically with increasing melt fraction in the diffusion creep regime at a given differential stress samples with melt fractions of 0 02 and 0 12 deformed a factor of 2 and 20 respectively faster than a melt free sample in the dislocation creep regime a sample with a melt fraction of 0 12 deformed a factor of 40 faster than a melt free sample for partially molten olivine basalt aggregates deformed under hydrous conditions the dependence of creep rate on melt fraction can be expressed in the form 0 exp where 26 for diffusion creep and 31 for dislocation creep the results of this study combined with reasonable estimates for the spatial variation in the concentrations of water and melt as well as for the geotherm and the activation volume for creep provide constraints on the viscosity structure of earth s upper mantle as an example we present a viscosity profile for the mantle wedge above a subducting plate demonstrating that the viscosity in that region can vary by 3 orders of magnitude over a depth of 60 km due to the combined effects of water and melt weakening

variations of seismic b value at different stages of the seismic cycle along the north anatolian fault zone in northwestern turkey abstract we studied spatiotemporal b value variations along the north anatolian fault zone nafz in northwestern turkey with a focus on the combined 1999 izmit and duzce rupture and the eastern sea of marmara we used a local seismicity catalog of the izmit duzce region covering a time span from 2 5 years prior to the izmit until 14 months after the duzce mainshock and a four year hypocenter catalog in the eastern sea of marmara we consistently calculated moment magnitudes to ensure a homogeneous dataset and applied strict quality criteria this allows studying variations of b values throughout the region and at different stages of the seismic cycle with a standard gridding technique b value maps depth sections and time series were calculated which reveal a very heterogeneous b value distribution in the study area the variety of b value observations cannot be interpreted unambiguously given that the b value most likely depends on a combination of fault zone characteristics like local stress conditions heterogeneity of the crust and damage distribution by presenting a comprehensive set of possible interpretations we point out that a biased discussion of the results towards stress or another individual parameter may lead to erroneous conclusions furthermore the applied data discretization scheme influences the appearance of the final b value distribution leading to potential misinterpretations

insights into the dynamics of planetary interiors obtained through the study of global distribution of volcanoes i empirical calibration on earth abstract the distribution of volcanic features is ultimately controlled by processes taking place beneath the surface of a planet for this reason characterization of volcano distribution at a global scale can be used to obtain insights concerning dynamic aspects of planetary interiors until present studies of this type have focused on volcanic features of a specific type or have concentrated on relatively small regions in this paper the first of a series of three papers we describe the distribution of volcanic features observed over the entire surface of the earth combining an extensive database of submarine and subaerial volcanoes the analysis is based on spatial density contours obtained with the fisher kernel based on an empirical approach that makes no a priori assumptions concerning the number of modes that should characterize the density distribution of volcanism we identified the most significant modes using those modes as a base the relevant distance for the formation of clusters of volcanoes is constrained to be on the order of 100 to 200 km in addition it is noted that the most significant modes lead to the identification of clusters that outline the most important tectonic margins on earth without the need of making any ad hoc assumptions consequently we suggest that this method has the potential of yielding insights about the probable occurrence of tectonic features within other planets

living stained deep sea foraminifera from the sea of marmara a preliminary study abstract in this preliminary study we investigate living stained foraminifera from the sea of marmara we focus on the faunal composition and geochemical signatures trace elements carbon and oxygen stable isotopes in foraminiferal tests at two deep sea sites 329 and 1240 m depth respectively documented by rov observations and sampling both study areas are heterogeneous including bacterial mats and carbonate concretions proximal to cold seeps and consist of dysoxic bottom water o2

the sinuous bedrock channel of the tapi river central india its form and processes abstract the tapi gorge lies in the monsoon dominated region of the indian subcontinent because of the seasonality of rainfall and flows all the fluvial activity in the bedrock gorge is confined to the monsoon season in general and during a few high magnitude monsoon floods in particular field investigations along a 30 km reach of the sinuous bedrock gorge indicate that the river displays all the morphologic properties of a meandering alluvial channel albeit with a much higher level of energy expenditure considering the perimeter lithology and channel morphology two types of reaches are evident in the field a predominantly rocky and relatively straight reach close to the gorge head and a longer sinuous reach of gravel deposition downstream hydraulic modeling of a rainfall induced dam failure flood indicates that large magnitude events that exceed the threshold of bedrock resistance for a sustained length of time are capable of erosion it appears that the overall channel and gorge morphology is adjusted to two types of thresholds a threshold of boulder transport which is associated with large floods that are competent to entrain boulders but are incapable of bedrock erosion and another higher threshold that is exceeded by truly high energy processes that generate large total energy and exceed the threshold of bedrock resistance the later threshold is exceeded only episodically with fairly long periods of little or no bedrock erosion in between interestingly meso scale erosional features such as inner channels and well developed potholes are nearly absent or inconspicuous within the gorge section whilst this could be partly attributed to the bedrock resistance it appears that under the present hydro geomorphic conditions the dominant fluvial activity is not directed towards the channel bed but towards the banks this is evident from the concentration of erosion on the outer banks and deposition of coarse gravel on the inner banks and armoring of the channel bed the main conclusion of the study is that the bedrock channel is increasing the flow resistance and energy losses by developing and enhancing the meandering pattern

strain localization in the sea of marmara propagation of the north anatolian fault in a now inactive pull apart 1 the sea of marmara is presently the site of pure dextral strike slip faulting that connects the izmit fault in the east to the ganos fault in the west along a linear strike slip fault that is part of the northwestern branch of the north anatolian fault this active main marmara fault mmf cuts across a succession of depocenters and highs analysis of a large data set that includes multichannel seismic lines sparker and deep towed high definition seismics shows that most of the n120 e trending normal faults framing these depocenters are now inactive as they are sealed by an average thickness of 300 m of sediments the highs correspond to a series of ne sw trending anticlines and reverse faults blanketed by a thin cover of undeformed sediments we interpret these structures as inverted former transfer faults of the now inactive sea of marmara pull apart system depocenters and highs are the relicts of a former pull apart basins and transfer faults system that accommodated the north anatolian fault motion within the sea of marmara prior to the formation of the mmf we propose that a relatively short a few hundreds of thousands of years period of basin inversion accompanied the localization of strain along the present main marmara fault until it was fully formed 200 100 kyr ago the preexisting pull apart basin system accounts for about 30 km of motion along this fault system and thus probably appeared sometime in late pliocene or early pleistocene as a reactivated portion of the old thrace basin during the plio quaternary the sea of marmara has been the site of progressive localization of strain

new constraints on micro seismicity and stress state in the western part of the north anatolian fault zone observations from a dense seismic array with the aim of extensively investigating the crustal structure beneath the western segment of the north anatolian fault zone where it splays into northern and southern branches a temporary seismic network dense array for north anatolia dana consisting of 70 stations was deployed in early may 2012 and operated for 18 months in the sakarya region during the faultlab experiment out of 2437 events contaminated by explosions we extracted 1371 well located earthquakes the enhanced station coverage having a nominal station spacing of 7 km lead to a minimum magnitude calculation of 0 1 horizontal and vertical location uncertainties within the array do not exceed 0 8 km and 0 9 km respectively we observe considerable seismic activity along both branches of the fault where the depth of the seismogenic zone was mostly confined to 15 km using our current earthquake catalog we obtained a b value of 1 we also mapped the b value variation with depth and observed a gradual decrease furthermore we determined the source parameters of 41 earthquakes with magnitudes greater than 1 8 using p wave first motion polarity method regional moment tensor inversion method was also applied to earthquakes with magnitudes greater than 3 0 focal mechanism solutions confirm that sakarya and its vicinity is stressed by a compressional regime showing a primarily oblique slip motion character stress tensor analysis indicates that the maximum principal stress is aligned in wnw ese direction and the tensional axis is aligned in nne ssw direction

tectonic evolution of the ganos segment of the north anatolian fault nw turkey we analyzed the paleostress field ongoing deformation meso to micro scale faulting cataclasis fault rock alteration and veining within turbidite and limestone sequences at the ganos fault which represent a major branch of the north anatolian fault zone in nw turkey fault damage was found to occur across a several kilometers wide zone effects of faulting are shown by localized subsidiary brittle faults and fault rock alteration in the turbidites as well as fault breccia formation in the limestone sequence microseismicity along the ganos fault cluster at two locations the more pronounced being located offshore at a fault bend associated with a change from a transpressional to a transtensional regime kinematic analysis reveals a dextral strike slip regime with components of normal and thrust faulting along strike paleostress orientation at the ganos fault is rather uniform deformation mechanisms and fluid inclusion data from quartz and calcite veins suggest that fault related quartz veins were formed at temperatures between 170 and 250 c and pressures between 40 and 120 mpa fault related calcite vein

seismic imaging of the 1999 izmit turkey rupture inferred from the near fault recordings we use near fault accelerograms to infer the space time history of rupture on the fault during the izmit earthquake the records show that the ground displacement and velocity near the fault were surprisingly simple rupture propagated toward the west at a velocity of about 3 km s and toward the east at a remarkably high average velocity of 4 7 km s over a distance of about 45 km before decelerating to about 3 1 km s on the eastern segment slip on the fault is particularly large down to a depth of 20 km on the central portion of the fault where it reaches about 7 m slip is large also below 10 km on the eastern fault segment and this may have contributed to the loading of shear stress on the duzce fault on the western fault segment large slip seems confined to shallow depths

the aftershock signature of supershear earthquakes recent studies show that earthquake faults may rupture at speeds exceeding the shear wave velocity of rocks this supershear rupture produces in the ground a seismic shock wave similar to the sonic boom produced by a supersonic airplane this shock wave may increase the destruction caused by the earthquake we report that supershear earthquakes are characterized by a specific pattern of aftershocks the fault plane itself is remarkably quiet whereas aftershocks cluster off the fault on secondary structures that are activated by the supershear rupture the post earthquake quiescence of the fault shows that friction is relatively uniform over supershear segments whereas the activation of off fault structures is explained by the shock wave radiation which produces high stresses over a wide zone surrounding the fault

estimating slip distribution for the izmit mainshock from coseismic gps ers 1 radarsat and spot measurements we use four geodetic satellite systems global positioning system gps european remote sensing ers radarsat and satellite pour l9observation de la terre spot to measure the permanent deformation field produced by the izmit earthquake of 17 august 1999 we emphasize measurements from interferometric analysis of synthetic aperture radar sar images acquired by ers and radarsat and their geodetic uncertainties the primary seismological use of these data is to determine earthquake source parameters such as the distribution of slip and the fault geometry after accounting for one month9s postseismic deformation tropospheric delay and orbital gradients we use these data to estimate the distribution of slip at the time of the izmit mainshock the different data sets resolve different aspects of the distribution of slip at depth although these estimates agree to first order with those derived from surface faulting teleseismic recordings and strong motion careful comparison reveals differences of 40 in seismic moment we assume smooth parameterization for the fault geometry and a standard elastic dislocation model the root mean square residual scatter is 25 mm and 11 mm for the ers and radarsat range changes respectively our estimate of the moment from a joint inversion of the four geodetic data sets is m 0 1 84 10 20 n m a moment magnitude of m w 7 50 these values are lower than other estimates using more realistic layered earth models given the differences between the various models we conclude that the real errors in the estimated slip distributions are at the level of 1 m the prudent geophysical conclusion is that coseismic slip during the izmit earthquake tapers gradually from approximately 2 m under the hersek delta to 1 m at a point 10 km west of it we infer that the yalova segment west of the hersek delta may remain capable of significant slip in a future earthquake

io heat flow from small volcanic features abstract we identify nine new faint thermal sources on io via color ratio images constructed from relatively high spatial resolution galileo nims data acquired late in the mission all of these identifications are associated with small dark paterae we utilize nims data to quantify their volcanic thermal emission as 0 53 1012 w or 0 5 of io s total heat flow in addition we refine our previous estimates of the thermal emission from 47 hot spots and highlight several hot spots within the amirani flow field small dark paterae still out number faint close to the limit of detection hot spots identified in high spatial resolution multi wavelength nims data in particular we point out 24 small dark paterae that were scanned by nims at resolutions down to 17 km pixel but had no detectable volcanic thermal emission all dark paterae are expected to have some volcanic thermal emission but the small size and finite number of detectable faint sources limit their contribution to the total heat flow on io compared to small paterae small dark flows are more numerous but must have significantly lower surface temperatures finally we update and summarize our results for the global heat flow on io due to 242 recently active volcanic features including other dark paterae as well as large dark flows the volcanic thermal emission from known hot spots undetected scanned dark patera and outbursts can account for only 56 2 1012 w or 54 of io s total heat flow approximately 49 1012 w or 46 of io s heat flow remains an enigma

coseismic and postseismic fault slip for the 17 august 1999 m 7 5 izmit turkey earthquake we use global positioning system gps observations and elastic half space models to estimate the distribution of coseismic and postseismic slip along the izmit earthquake rupture our results indicate that large coseismic slip reaching 5 7 meters is confined to the upper 10 kilometers of the crust correlates with structurally distinct fault segments and is relatively low near the hypocenter continued surface deformation during the first 75 days after the earthquake indicates an aseismic fault slip of as much as 0 43 meters on and below the coseismic rupture these observations are consistent with a transition from unstable episodic large earthquakes to stable fault creep sliding at the base of the seismogenic zone

sedimentary record of late holocene seismicity and uplift of hersek restraining bend along the north anatolian fault in the gulf of izmit abstract the north anatolian fault naf in the gulf of izmit eastern marmara sea consists of three subsegments linked by bends the present study focuses on the hersek peninsula which is a ridge of pleistocene and holocene deposits emerged by tectonic uplift at a left stepping 7 restraining double bend between the karamursel and darica segments of the naf the hersek bend has acted as a local barrier to westward rupture propagation whereby the marine substrate was deformed by transpressional thrusting combined with underwater slumping the record of the hersek ridge emergence has been analyzed in excavation trenches by the methods of sedimentology geomorphology and radiocarbon dating the time of initial emergence is unknown but the highest recognized palaeoshoreline terrace indicates that around 2250 yrs bc a narrow ridge was already standing at least 13 m above the sea level the uplift rate of the ridge is about 3 5 m kyr for the past 4250 years the development of the three lower lying successively younger palaeoshoreline terraces involved episodes of uplift accompanied and or followed by tsunami events the ridge s stepwise uplift above the sea level amounted to at least 28 m on the basis of radiocarbon dates the deciphered seismotectonic events have been tentatively correlated to the region s historical earthquakes which allowed the fault bend s behavior to be reconstructed and time constrained the study gives new insights into the dynamics of an naf restraining bend and the non characteristic behavior of the naf segments in the quake stricken region of eastern marmara sea

a unified earthquake catalogue for the sea of marmara region turkey based on automatized phase picking and travel time inversion seismotectonic implications abstract the marmara section of the north anatolian fault zone nafz is late in its seismic cycle and can be expected to produce a magnitude m up to 7 4 earthquake during the next decades in direct vicinity to the 15 million population center istanbul this setting translates the seismic hazard into very high risk and makes a thorough understanding of the current seismotectonic setting of this nafz section a pressing task the absence of near fault stations along the most part of the offshore marmara section limits the reliability of existing seismicity catalogues for this region for the first time we combine the different regional permanent networks thereby optimizing azimuthal coverage and present a refined hypocenter catalogue for the sea of marmara on this basis compared to the original locations adoption of a refined automated technique to determine precise onset times for the different body waves and an iterative travel time inversion scheme lead to substantial improvement of 6812 absolute earthquake locations particularly in the epicentral distribution the automated processing is explained in detail further optimization is achieved through relative relocation of 4407 earthquakes our catalogue covers more than a decade 2006 2016 with a regional moment magnitude of completeness of mc 2 1 the epicentral distribution delineates the marmara section i e the northern nafz branch as the seismically most active fault strand we identify several aseismic fault patches that are interpreted to represent locked parts of the fault seismic activity in the past decade predominantly occurs off the main fault on the edges of the aseismic patches supporting previous studies that the marmara section of the nafz contains both locked and creeping fault portions single event focal mechanisms 2 7 mw 4 5 indicate that currently both strike slip and normal faulting occur confirming the transtensional setting of the region

the effect of elastic layering on inversions of gps data for coseismic slip and resulting stress changes strike slip earthquakes we investigate the effect of depth dependent elasticity on slip inversions and coseismic stress change estimates for large strike slip earthquakes using a series of hypothetical models and the 1999 izmit turkey earthquake as examples slip inversions are performed using both semianalytical and finite element solutions for surface displacements due to a shear dislocation in layered and uniform elastic earth models we find that incorporating realistic increases to shear modulus with depth in our inversions increases recovered centroid depth and seismic potency relative to uniform elastic half space models recovered seismic moment is up to 40 greater for models incorporating depth dependent than it is for uniform elastic half space models incorporating depth dependent also increases our estimate of the maximum slip depth for the izmit turkey earthquake to at least 20 km our estimates of coseismic stress change in the upper crust do not change significantly when we incorporate depth dependent elasticity in our inversions as long as slip at depth is tuned increased to match surface displacements coseismic differential stresses in the lower crust increase by up to a factor of 3 in the near field but further from the fault stresses from layered and uniform elastic models are approximately equal with increasing depth in the mantle the ratio of modeled differential stresses for the layered and uniform elastic models approaches the ratio of mantle values for these two models we conclude that models of postseismic viscoelastic relaxation following large strike slip earthquakes should incorporate depth dependent elasticity but that uniform elastic half space models are adequate to calculate coseismic coulomb stresses in the upper crust for most triggering studies

a tomographic image of the shallow crustal structure in the eastern marmara 1 we present a 2 d tomographic seismic velocity image in eastern marmara region along a n s trending 120 km long seismic refraction profile which traverses the northern branches of north anatolian fault naf and tectonically active cinarcik basin in the sea of marmara the 2 d velocity model which is constrained down to upper crustal depth of 7 km shows significant heterogeneities in the upper crust displayed by well constrained velocity anomalies the seismicity observed following the 17 august 1999 izmit earthquake concentrates in three distinct zones and takes place near the inferred low velocity zones and below high velocity anomalies obtained from tomographic inversion this correlation is interpreted as a result of intensely sheared zones of deformation imposed by strike slip motion of the northern branches of the north anatolian fault

formation of mountains on io variable volcanism and thermal stresses abstract thermal stresses are potentially important drivers of io s tectonics and mountain building it has been hypothesized that sustained local or regional shut down of heat pipe volcanism on io could lead to deep crustal heating and large compressive stresses mckinnon w b schenk p m dombard a j 2001 geology 29 103 106 such large stresses would then be relieved by thrust faulting and uplifting of crustal blocks producing mountains like those observed on io here we analyze the tectonic consequences of the heat pipe model in detail considering both the initial thermal stress state of a basalt or peridotite crust created by heat pipe volcanism and relative roles of subsidence stresses due to burial of preexisting layers and thermal stresses arising from variable volcanism and changes in crustal lithosphere thickness we limit the magnitude of the potential subsidence stresses in our study because the magnitude of subsidence stresses can be quite large if not dominant results indicate that for a fixed crustal thickness the region of failure and faulting moves closer to the surface as eruption rate decreases and time increases when the crust melts at its base as volcanism decreases as might occur under steady state tidal heating resulting in crustal thinning the region of failure is brought even closer to the surface naturally when compressive subsidence stresses are included the vertical extent of crust in brittle failure thickens to include most of the lithosphere in contrast increases in eruption rate cause the extent of the region in compressional failure to decrease and be driven very deep in the crust in the absence of sufficient subsidence stress therefore regions of declining volcanism are more likely to produce mountains whereas regions of extensive or increasing volcanism are less likely to do so this is consistent with the observation of a global anticorrelation between mountains and volcanic centers on io finally we find that the choice of crustal composition rheology dry basalt vs dry peridotite has little effect on our results implying that basalt peridotite and komatiite are all similarly stiff in the io environment

characterization of aftershock fault plane orientations of the 1999 izmit turkey earthquake using high resolution aftershock locations 1 joint inversion for hypocentral parameters and the velocity field is nowadays a state of the art tool to obtain high resolution images of seismically active regions in this study we focus on the location accuracy of aftershocks of the 1999 mw 7 4 izmit nw turkey earthquake we obtained a new velocity model for the region and depicted its improvement on absolute locations in terms of uncertainty and misfit two well developed aftershock clusters located in the akyazi area and karadere duzce region were analyzed in detail based on a waveform cross correlation approach that allowed improving the location accuracy by a factor of 6 relocation results reveal that hypocenters form narrow planes of activity that can be correlated with focal mechanisms of the larger aftershocks as well as nearby clouds of activity with no internal structure down to the resolved scale of 300 m

seismicity and source parameters for small scale earthquakes along the splays of the north anatolian fault naf in the marmara sea summary major discrepancy between present day fault models in the marmara sea is closely related to structural development of depression areas beneath the sea therefore in this study the marmara sea and especially its major basins are investigated by means of recent seismological observations consisting of microseismicity 1 2 md 3 6 2002 may 2006 may focal mechanisms 2 4 md 5 0 1999 2006 and stress analysis based on the focal mechanisms in the cinarcik basin where either pull apart model or negative flower structure is proposed northeastern margin is represented by strike slip sources having a nw alignment probably corresponding to a cross basin strike slip fault developing in a matured pull apart basin this suggestion is directly relevant to experiments of sand box analogue models these experiments indicate that such a cross basin strike slip fault is produced after the pull apart basins attain their mature stage eventually resulting in less vertical displacements attributed to normal faults bounding the basin this experimental decline may be corroborated by the paucity of normal mechanisms in the basin extensional motion in this region is more influential outside of the basin especially to the area where an onshore seismic activity is monitored on the land on the other hand another strike slip activity in the cinarcik basin is distributed on a possible strand parallel to the northern coastline of the marmara sea in the armutlu peninsula this may indicate that one or more short strands of the northern splay extend to the west by bounding the basin from the south in the central basin the existence of a right lateral strike slip faulting on an east west trending fault is supported by similar strike slip focal mechanisms located at both extremities of the basin to the west dominant style of deformation gradually shifts from strike slip faulting to transpression along the western coastline of the marmara sea where the northern splay joins with the offshore continuation of the ganos fault finally focal mechanisms in the marmara sea are inverted for the best fitting stress tensor characterized by a subvertical 2 axis and two subhorizontal stress axes of 1 and 3 oriented nw se and ne sw respectively conclusively this study infers that the current tectonics of the marmara sea is mainly governed by a strike slip regime ascribed to both submarine splays of the naf and partly dominated by extensional and compressional features indicating shallow processes at local scales

stress inversion of regional seismicity in the sea of marmara region turkey in this study we derive the stress tensor and its local variations throughout the marmara region turkey based on a recently compiled 10 year earthquake catalogue we directly invert first motion polarity data and quantify confidence intervals for the principal stress orientations we find a combined strike slip and normal faulting stress field for the marmara region generally reflecting the overall transtensional setting however the results clearly show moderate local variations of the stress field the largest sigma 1 and intermediate sigma 2 principal stresses show an average regional trend of n 125 circ e and locally varying plunges the least principal stress sigma 3 is well resolved in its confidence interval and consistent throughout the region with an average trend of sim n 35 circ e and a subhorizontal plunge the eastern sea of marmara shows local stress field orientations with pronounced strike slip northern part and normal faulting southern part components along the central marmara region normal faulting tends to dominate while a well resolved strike slip stress regime is found in the western sea of marmara region regarding the faulting mechanism of an earthquake with magnitude up to 7 4 which is expected in this area in direct vicinity of the istanbul metropolitan region our results imply that neither strike slip nor normal faulting kinematics can be excluded

can a combination of convective and magmatic heat transport in the mantle explain io s volcanic pattern tidal dissipation makes jupiter s moon io the most volcanically active body in the solar system most of the heat generated in the interior is lost through volcanic activity in this study we aim to answer the questions can convection and melt migration in the mantle explain the spatial characteristics of io s observed volcanic pattern and if so what constraints does this place on the viscosity and thickness of the convective layer we examine three different spatial characteristics of io s volcanic activity i the presence of global volcanism ii the presence of large scale variations in io s volcanic activity and iii the number of io s volcanic systems our study relies on the assumptions that melt in the mantle controls io s global volcanism that the large scale variations of io s volcanic activity are caused by nonuniform tidal heating and that the spatial density of volcanoes correlates with the spatial density of convective anomalies in the mantle the results show that the observed small and large scale characteristics of io s volcanic pattern can be explained by sublithospheric anomalies influenced and caused by convective flow solutions that allow for active volcanism and io s specific large scale variations in volcanic activity range from a thick mantle of a high viscosity formula presented pa s to a thin asthenosphere of a low viscosity formula presented pa s provided that io s volcanoes are induced by convective anomalies in the mantle we find that more than 80 of io s internal heat is transported by magmatic processes and that io s upper mantle needs to be thicker than 50 km

gas driven water volcanism and the resurfacing of europa we have analyzed the problem of how pathways are created for the resurfacing by water or volatiles for a europa model in which there is an ocean underlying a thin ice shell 10 km thickness open cracks propagating downward cannot reach the ocean unless the relative tension in the ice is both very high 100 bar and applied very rapidly 10 4 10 5sec there is no known way to satisfy these criteria water filled cracks propagating upward can approach the surface for relative tensions of 5 10 bar comparable to the stresses induced by the eccentricity tide exsolution of plausible gas species co 2 co ch 4 so 2 can then occur at the crack tip the application of linear elastic fracture mechanics shows that the gas filled portion of the crack pinches off from the water filled portion and may rise rapidly to the surface entraining some water many of these cracks may end up as intrusions rather than extrusions because of partial freeze out of co 2 and water on the walls of the crack the resulting eruption is initially gas dominated but may include a subsequent less extended eruption of foam there may not be a direct relationship between the resurfacing process described here and the currently known geologic features observed on the surface the main problem with this or any model for tapping the ocean is the propagation of cracks through the soft ice immediately overlying the ocean

joint inversion of insar and teleseismic data for the slip history of the 1999 izmit turkey earthquake the slip history of the izmit earthquake is investigated by jointly inverting sar and teleseismic data with a multi segment variable slip finite fault model surface offsets are used as an added constraint the highest slip values 5 to 7 m of right lateral displacement are associated with a strong central asperity surrounding the hypocenter the bilateral breaking of this main asperity which lasted about 10 sec dominates the source time function from the golcuk izmit area to lake sapanca a relatively good correspondence is observed between slip at depth and at the surface but farther to the west and to the east slip tends to be confined to the near surface slip in the easternmost part of the rupture duzce segment is not well resolved our analysis finds the insar and teleseismic data to be compatible and complementary this study shows the potential of the joint inversion of both data sets for a rapid determination of the spatio temporal history of large earthquakes

north anatolian fault in the gulf of izmit turkey rapid vertical motion in response to minor bends of a nonvertical continental transform 1 the catastrophic rupture of the north anatolian fault east of the marmara sea on 17 august 1999 highlighted a need for mapping the underwater extension of that continental transform a new bathymetric map of izmit gulf indicates that the fault follows the axis of the gulf with a few minor bends submerged shorelines and shelf breaks that formed during the last glacial maximum provide markers to quantify vertical deformation variable tilting of these horizons reveals that vertical deformation is highest just south of the fault a correlation between vertical deformation of the southern fault block and distance to fault bends can be accounted for by a fault dipping steeply to the south hence subsidence uplift of the southern hanging wall block would be expected where the fault strikes at a slightly transtensional transpressional orientation to relative plate motion subsidence reaches about 8 mm yr west of the town of golcuk and might be accommodated in 1 2 m subsidence events during large earthquakes that scenario is compatible with the tsunami runups and the coseismic subsidence of the southern shore that occurred in 1999 seafloor morphology also suggests that earthquakes are accompanied by widespread gas and fluid release the periphery of the deepest basin displays a hummocky texture diagnostic of sediment fluidization and mud volcanoes occur west of hersek peninsula that might be activated by earthquakes finally the backscatter imagery reveals a series of lineaments midway through the gulf that are interpreted as products of the 1999 surface rupture the seafloor is undisturbed farther west suggesting that surface slip decreased to an insignificant level beyond hersek possibly the stress shadow from the 10 july 1894 earthquake which was felt strongly along the western izmit gulf contributed to arrest the 1999 surface rupture

a conceptual model for the relationship between coronae and large scale mantle dynamics on venus 1 among the most enigmatic features on venus are the more than 500 quasi circular structures collectively referred to as coronae associated volcanism and tectonism suggest that coronae result from small transient mantle plumes although only about 20 have clearly associated positive gravity anomalies indicative of current activity coronae are concentrated within a region defined by the dynamically active highland areas of beta atla and themis regiones bat coronae avoid the lowest or highest topography and geoid subsets of the corona population indicate that the spatial distribution of coronae has evolved from a previously less concentrated global distribution to the current bat concentration recent laboratory experiments on thermal convection at high rayleigh number using fluids with temperature dependent viscosity suggest a straightforward interpretation of these relationships small scale upwellings from a hot lower thermal boundary layer tend to be excluded by longer wavelength downwelling structures from the cold upper boundary layer the relative paucity of coronae in the broad lowland plains regions is consistent with the inference of mantle downwellings beneath the plains coronae are largely excluded from compensated highlands perhaps because the thickened crust is not easily disrupted in these regions laboratory experiments indicate that small transient boundary layer instabilities can coexist with and be focused toward large scale upwellings possibly explaining the spatial concentration of coronae in the bat region thus coronae provide important insights into interacting scales of convective flow in venus s mantle and into the evolution of venus s mantle dynamics direct tests of our model are possible through geological mapping

space and time evolution of rupture and faulting during the 1999 izmit turkey earthquake we use the records of the ground motion obtained at near fault accelerometers to study the space and time evolution of rupture and faulting during the izmit earthquake we find that the rupture propagated at the sub rayleigh speed of about 3 km sec on the western and eastern segments of the fault but that the central segment izmit sapanca lake sakarya nearly 50 km long broke at the supershear speed of about 4 8 km sec this value within the range of uncertainties is the one theoretically predicted sqrt 2 v mathrm s in fracture dynamics for stable shear crack growth at intersonic speed we infer an average fault slip of about 2 9 m over a total rupture length of about 150 km with the largest values of up to 6 m occurring in the golcuk area to the west and in the sakarya region to the east the strong motion data also indicate that the slip diminished gradually to the west beyond the hersek peninsula over about 30 km whereas it stopped abruptly at depth at the termination of the eastern karadere segment the slip duration is between 2 and 4 sec except in the hypocentral area which slipped in about 1 sec the seismic moment inferred is about 2 5 10 20 n m

gas emissions and active tectonics within the submerged section of the north anatolian fault zone in the sea of marmara the submerged section of the north anatolian fault within the marmara sea was investigated using acoustic techniques and submersible dives most gas emissions in the water column were found near the surface expression of known active faults gas emissions are unevenly distributed the linear fault segment crossing the central high and forming a seismic gap as it has not ruptured since 1766 based on historical seismicity exhibits relatively less gas emissions than the adjacent segments in the eastern sea of marmara active gas emissions are also found above a buried transtensional fault zone which displayed micro seismic activity after the 1999 events remarkably this zone of gas emission extends westward all along the southern edge of cinarcik basin well beyond the zone where 1999 aftershocks were observed the long term monitoring of gas seeps could hence be highly valuable for the understanding of the evolution of the fluid fault coupling processes during the earthquake cycle within the marmara sea

istanbul s earthquake hot spots geodetic constraints on strain accumulation along faults in the marmara seismic gap during the past century a series of predominantly westward migrating m 7 earthquakes broke an 1000 km section of the north anatolian fault naf the only major remaining seismic gap along the fault is under the sea of marmara main marmara fault mmf we use 20 years of gps observations to estimate strain accumulation on fault segments in the marmara sea seismic gap we report the first direct observations of strain accumulation on the princes islands segment of the mmf constraining the slip deficit rate to 10 15 mm yr in contrast the central segment of the mmf that was thought to be the most likely location for the anticipated gap filling earthquakes shows no evidence of strain accumulation suggesting that fault motion is accommodated by fault creep we conclude that the princes islands segment is most likely to generate the next m 7 earthquake along the sea of marmara segment of the naf

analysis of izmit aftershocks 25 days before the november 12th 1999 duzce earthquake turkey abstract we investigate spatial clustering of 2414 aftershocks along the izmit mw 7 4 august 17 1999 earthquake rupture zone 25 days prior to the duzce earthquake mw 7 2 november 12 1999 we analyze two spatial clusters namely sakarya sc and karadere duzce kdc we determine the earthquake frequency magnitude distribution b value for both clusters we find two high b value zones in sc and one high b value zone in kdc which are in agreement with large coseismic surface displacements along the izmit rupture the b values are significantly lower at the eastern end of the izmit rupture where the duzce mainshock occurred these low b values at depth are correlated with low postseismic slip rate and positive coloumb stress change along kdc since low b values are hypothesized with high stress levels we propose that at the depth of the duzce hypocenter 12 5 km earthquakes are triggered at higher stresses compared to shallower crustal earthquake the decrease in b value from the karadere segment towards the duzce basin supports this low b value high stress hypothesis at the eastern end of the izmit rupture consequently we detect three asperity regions which are correlated with high b value zones along the izmit rupture according to aftershock distribution the half of the duzce fault segment was active before the 12 november 1999 duzce mainshock this part is correlated with low b values which mean high stress concentration in the duzce basin this high density aftershock activity presumably helped to trigger the duzce event mw 7 2 after the izmit mw 7 4 mainshock

coseismic and early post seismic slip associated with the 1999 izmit earthquake turkey from sar interferometry and tectonic field observations summary we use combined tectonic field observations and sar data to determine an improved model of the slip associated with the 1999 izmit earthquake which ruptured the north anatolian fault at the eastern end of the sea of marmara the leading goal is to understand the main features of the coseismic and post seismic deformation which are captured together in the sar data to achieve this we make a critical analysis of the ers1 2 sar data which allows atmospheric effects to be identified and removed we also use detailed field mapping and measurements of the earthquake surface rupture dislocations in elastic half space and a forward modelling strategy allow us to obtain a slip model by steps a trial and error approach is combined with conventional inversion techniques to determine the slip in the different regions of the fault the sar data are well explained with three main zones of high slip along the fault releasing a total moment of 2 3 10 20 nm mw 7 6 which is higher than the seismological estimates 1 7 2 0 10 20 n m the inhomogeneous slip distribution correlates with fault segments identified at the surface the izmit rupture appears to have extended 30 km west of the hersek peninsula into the sea of marmara with slip tapering fro m2mt ozero the western end of the rupture is located 40 km sse from istanbul we show that some features seen near to mudurnu and gevye and previously interpreted as slip on secondary faults are explained mostly as atmospheric effects correlated with the topography using our approach and the available gps data we obtain a slip model that represents the coseismic slip alone which suggests that the moment release during the main shock was 1 9 10 20 nm mw 7 5 consistent with the seismological estimates we conclude that the sar data include the effects of 2 m of fast after slip during the month following the main shock within a zone of the fault located 12 24 km below the epicentral region near the hypocentre at a depth of 18 km the fault appears to have experienced dynamic slip of 1 m associated with the main shock followed by 2 m of rapidly decelerating post seismic shear during the following month we suggest that the distribution of heterogeneous slip and loading along the different fault segments may be important factors controlling the propagation of large earthquake ruptures along the north anatolian fault

gravitational spreading bookshelf faulting and tectonic evolution of the south polar terrain of saturn s moon enceladus abstract despite a decade of intense research the mechanical origin of the tiger stripe fractures tsf and their geologic relationship to the hosting south polar terrain spt of enceladus remain poorly understood here we show via systematic photo geological mapping that the semi squared spt is bounded by right slip left slip extensional and contractional zones on its four edges discrete deformation along the edges in turn accommodates translation of the spt as a single sheet with its transport direction parallel to the regional topographic gradient this parallel relationship implies that the gradient of gravitational potential energy drove the spt motion in map view internal deformation of the spt is expressed by distributed right slip shear parallel to the spt transport direction the broad right slip shear across the whole spt was facilitated by left slip bookshelf faulting along the parallel tsf we suggest that the flow like tectonics to the first approximation across the spt on enceladus is best explained by the occurrence of a transient thermal event which allowed the release of gravitational potential energy via lateral viscous flow within the thermally weakened ice shell

microseismicity at the north anatolian fault in the sea of marmara offshore istanbul nw turkey 1 the north anatolian fault zone nafz below the sea of marmara forms a seismic gap where a major earthquake is expected to occur in the near future this segment of the fault lies between the 1912 ganos and 1999 izmit ruptures and is the only nafz segment that has not ruptured since 1766 to monitor the microseismic activity at the main fault branch offshore of istanbul below the cinarcik basin a permanent seismic array pires was installed on the two outermost prince islands yassiada and sivriada at a few kilometers distance to the fault in addition a temporary network of ocean bottom seismometers was deployed throughout the cinarcik basin slowness vectors are determined combining waveform cross correlation and p wave polarization we jointly invert azimuth and traveltime observations for hypocenter determination and apply a bootstrap resampling technique to quantify the location precision we observe seismicity rates of 20 events per month for m 2 5 along the basin the spatial distribution of hypocenters suggests that the two major fault branches bounding the depocenter below the cinarcik basin merge to one single master fault below 17 km depth on the basis of a cross correlation technique we group closely spaced earthquakes and determine composite focal mechanisms implementing recordings of surrounding permanent land stations fault plane solutions have a predominant right lateral strike slip mechanism indicating that normal faulting along this part of the nafz plays a minor role toward the west we observe increasing components of thrust faulting this supports the model of nw trending dextral strike slip motion along the northern and main branch of the nafz below the eastern sea of marmara

geomechanical model of the marmara sea region ii 3 d contemporary background stress field summary we present the contemporary 3 d background stress field of the marmara sea region derived from a geomechanical model the background stress field i e the component of the absolute stress state that is time independent over the seismic cycle primarily depends on the distribution of density and elastic parameters on the acting far field stresses from plate boundary forces and on fault geometries we take these into account to predict the 3 d background stress field including its spatial variations technically our model concept involves the definition of an appropriate initial stress state accounting for the gravitational reference stress state of the crust which is then changed by plate tectonics until the 3 d background stress field has evolved the modelled stress field agrees well with observations from earthquake focal mechanism solutions and their formal stress inversion with orientation of maximum horizontal stress and with the distribution of seismicity in the marmara sea in particular in the vicinity of fault bends the stress field deviates considerably from the regional nw se oriented maximum horizontal stress and exhibits variability of the stress regime our model results are consistent not only with dynamic observations but also with kinematic ones various kinematic observations are understandable from the stress field we show that a stress regime that indicates normal faulting in the basins is nonetheless reconcilable with almost pure strike slip motion on the main marmara fault the distribution of seismicity in the marmara sea can be explained in first order by the distribution of critical differential stress which is closely related to local fault geometries we refer the wide absence of seismicity between the bend of the main marmara fault near istanbul and the central basin to the relatively plane fault geometry of that segment normal stress on the main marmara fault is highly variable along strike which makes segment wise rupture more likely than a rupture of the seismic gap at once comparably low normal stress on the prince s islands segment indicates a shorter interevent time for this fault segment than for the central segment of the main marmara fault