the 5 september 2012 nicoya costa rica mw 7 6 earthquake rupture process from joint inversion of high rate gps strong motion and teleseismic p wave data and its relationship to adjacent plate boundary interface properties 1 on 5 september 2012 a large thrust earthquake mw 7 6 ruptured a densely instrumented seismic gap on the shallow dipping plate boundary beneath the nicoya peninsula costa rica ground motion recordings directly above the rupture zone provide a unique opportunity to study the detailed source process of a large shallow megathrust earthquake using very nearby land observations hypocenter relocation using local seismic network data indicates that the event initiated with small emergent seismic waves from a hypocenter 10 km offshore 13 km deep on the megathrust a joint finite fault inversion using high rate gps strong motion ground velocity recordings gps static offsets and teleseismic p waves reveals that the primary slip zone slip 1 m is located beneath the peninsula the rupture propagated downdip from the hypocenter with a rupture velocity of 3 0 km s the primary slip zone extends 70 km along strike and 30 km along dip with an average slip of 2 m the associated static stress drop is 3 mpa the seismic moment is 3 5 1020 nm giving mw 7 6 the coseismic large slip patch directly overlaps an onshore interseismic locked region indicated by geodetic observations and extends downdip to the intersection with the upper plate moho at deeper depths below the upper plate moho seismic tremor and low frequency earthquakes have been observed most tremor locates in adjacent areas of the megathrust that have little coseismic slip a region of prior slow slip deformation to the southeast also has no significant coseismic slip or aftershocks an offshore locked patch indicated by geodetic observations does not appear to have experienced coseismic slip and aftershocks do not overlap this region allowing the potential for a comparable size rupture offshore in the future

distortions rotations and crustal thinning at ridge transform intersections when an oceanic ridge intersects a transform fault the newly formed oceanic crust may be severely distorted frequently exhibiting major rotations of fault blocks1 4 such effects typically extend over a 10 km wide strip parallel to the transform by contrast studies of contemporary oceanic transforms suggest that deformation is restricted to a single fault trace within the transform domain5 9 this apparent inconsistency can be reconciled if the rotations occurred at the ridge transform intersection during accretion of the crust here i develop a kinematic model that considers the effect of an ephemeral period of stretching on a region that broadens as the transform is approached along the ridge the strains calculated from this model indicate extension at the ridge simple shear at the transform and composite strains in the region of distributed deformation the model predicts very rapid rotation rates 100 in 104 105 yr the implications for the topography and structure of ridge transform intersections are considered and the alternating periods of extension by stretching and by intrusion are illustrated by reference to contemporary transforms on the mid atlantic ridge the model may also explain the common occurrence of cross cutting dykes near transform faults in ophiolites

rupture characteristics of the a d 1912 murefte ganos earthquake segment of the north anatolian fault western turkey abstract the ganos fault is the westernmost segment of the north anatolian fault naf that generated the 9 august 1912 murefte ganos earthquake mw 7 4 we study the 1912 earthquake characteristics using co seismic fault slip and fault segmentation coupled with an analysis of historical seismic records surface ruptures with small releasing and restraining structures and 1 5 to 5 5 m right lateral offsets have been measured at 45 sites of the onland 45 km long fault section similar structures are delineated by fresh fault scarps and prominent pull apart basins in the sea of marmara and saros bay a second shock with mw 6 8 occurred on 13 september 1912 implying 20 to 40 km long rupture the damage distribution and analysis of seismic records suggest an epicenter located further west near saros bay which indicates the location of western termination of the 9 august rupture our modeling of historical seismic records reveals a relative source time function between the two events and indicates a 40 second rupture duration in agreement for a 120 30 km long fault rupture for the 9 august shock an estimated total rupture length of 150 30 km for the two earthquakes combined with onshore and offshore fault segmentation allow us to better constrain the western limit of the marmara sea seismic gap and related potential for producing a large earthquake that was sharply increased by the devastating 1999 izmit earthquake in the east

imaging supershear rupture for the 2014 mw 6 9 northern aegean earthquake by backprojection of strong motion waveforms the seismic source spatiotemporal evolution of the mw 6 9 event on 24 may 2014 in northern aegean is imaged by backprojection of strong motion envelopes the results indicate that the event ruptured on two different fault segments in the first one rupture propagated from the hypocenter westward for 20 km in the second delayed segment to the east rupture propagated eastward for 65 km with a supershear velocity 5 5 km s at the end of this rupture the largest stacking amplitudes are imaged associated with possible stopping phases from the abrupt cessation of a fast slip low aftershock seismicity on the supershear segment implies a simple and linear fault geometry there this is the third large event in the northern aegean trough northern anatolian fault zones that has ruptured with supershear speed this characteristic should be taken into account in studying past events and estimating seismic hazard in this area

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

onset of aseismic creep on major strike slip faults time series analysis of spaceborne synthetic aperture radar sar data gps measurements and field observations reveal that the central section of the izmit turkey fault that slipped with a supershear rupture velocity in the a d 1999 m w 7 4 izmit earthquake began creeping aseismically following the earthquake rapid initial postseismic afterslip decayed logarithmically with time and appears to have reached a steady rate comparable to the pre earthquake full fault crossing rate suggesting that it may continue for decades and possibly until late in the earthquake cycle if confirmed by future monitoring these observations identify postseismic afterslip as a mechanism for initiating creep behavior along strike slip faults long term afterslip and or creep has significant implications for earthquake cycle models recurrence intervals of large earthquakes and accordingly seismic hazard estimation along mature strike slip faults in particular for istanbul which is believed to lie adjacent to a seismic gap along the north anatolian fault in the sea of marmara

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

geodetic evidence for low coupling on the hellenic subduction plate interface we develop a block model for the aegean and surrounding areas constrained by global positioning system gps in order to investigate the degree of coupling on the hellenic subduction interface i e the fraction of the motion across the plate boundary accommodated by elastic strain accumulation we use previously published models and seismicity to define the geometry of the interface separating the down going nubian slab from the overriding aegean this model provides a good fit to the gps observations for the 200 000 km2 aegean block the wrms of the residual velocities is 1 4 mm yr for 80 gps velocity estimates approximately the 95 level of the gps velocity uncertainties we investigate the degree of coupling on the seismically active plate interface the hellenic trench splay fault believed to be the source of the 365 ad great crete earthquake and tsunami and the kephalonia transform fault by comparing the modeled gps residual velocity field for a range of coupling values the gps observations are almost insensitive to coupling on the kephalonia transform fault because of the vertical dip of the fault that creates interseismic deformation only close to the fault where few gps sites exist the absence of resolvable shortening of the leading edge of the aegean plate precludes coupling of more than 0 2 20 of the full nubia aegean convergence rate on the modeled plate interface because of the shallow dip of the plate interface and trench splay fault and high rate of convergence if these boundaries were fully coupled high elastic strain rates would be expected to extend well into the overriding aegean plate based on our preferred value for the degree of coupling 0 1 and assuming characteristic earthquake behavior we estimate a recurrence time for great earthquakes with slip similar to that for the 365 crete event of 5700 8300 yr consistent with the absence of subsequent great earthquakes on this segment of the subduction zone

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

recalculated probability of m 7 earthquakes beneath the sea of marmara turkey 1 new earthquake probability calculations are made for the sea of marmara region and the city of istanbul providing a revised forecast and an evaluation of time dependent interaction techniques calculations incorporate newly obtained bathymetric images of the north anatolian fault beneath the sea of marmara le pichon et al 2001 armijo et al 2002 newly interpreted fault segmentation enables an improved regional a d 1500 2000 earthquake catalog and interevent model which form the basis for time dependent probability estimates calculations presented here also employ detailed models of coseismic and postseismic slip associated with the 17 august 1999 m 7 4 izmit earthquake to investigate effects of stress transfer on seismic hazard probability changes caused by the 1999 shock depend on marmara sea fault stressing rates which are calculated with a new finite element model the combined 2004 2034 regional poisson probability of m 7 earthquakes is 38 the regional time dependent probability is 44 18 and incorporation of stress transfer raises it to 53 18 the most important effect of adding time dependence and stress transfer to the calculations is an increase in the 30 year probability of a m 7 earthquake affecting istanbul the 30 year poisson probability at istanbul is 21 and the addition of time dependence and stress transfer raises it to 41 14 the ranges given on probability values are sensitivities of the calculations to input parameters determined by monte carlo analysis 1000 calculations are made using parameters drawn at random from distributions sensitivities are large relative to mean probability values and enhancements caused by stress transfer reflecting a poor understanding of large earthquake aperiodicity index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 8150 tectonophysics plate boundary general 3040 keywords earthquake probability sea of marmara seismic hazard turkey stress interaction north anatolian fault

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

space time distribution of afterslip following the 2003 tokachi oki earthquake implications for variations in fault zone frictional properties 1 gps time series following the september 25 2003 ut tokachi oki earthquake m w 8 0 reveal significant deformation we use the network inversion filter to invert for the spatial and temporal evolution of afterslip in the 30 days following the earthquake afterslip is concentrated adjacent to the coseismic rupture zone between the 2003 rupture and the inferred source regions of the 1968 tokachi oki and the 1973 nemuro oki earthquakes the inversion shows a rapid decay of slip rate in the 2003 rupture zone with slower deceleration in the surrounding regions the stress velocity paths for the afterslip regions approximately follow d d in v 0 6 mpa suggestive of steady state velocity strengthening friction the complementary spatial pattern of coseismic rupture and afterslip may indicate along strike spatial variations of frictional properties although other interpretations can not be ruled out

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

repeating earthquake finite source models strong asperities revealed on the san andreas fault 1 we investigate the rupture process of a sequence of repeating mw 2 1 earthquakes on the san andreas fault in parkfield spanning the occurrence of the september 28 2004 mainshock by inverting seismic moment rate functions obtained from empirical green s function deconvolution the results show that these events have extremely concentrated slip patches with radii on the order of 10 20 m with peak slip between 8 4 and 11 4 cm the rupture speed and rise time are consistent with values of larger earthquakes the spatial distribution of stress drop for the events shows low average values 2 5 5 6 mpa and very large peak values of 66 7 93 9 mpa the results show that strong asperities can exist at small scales on an otherwise weak fault and helps reconcile differences between traditional spectra based and tectonic loading methods for determining the stress drop of small repeating earthquakes

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

the 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

partial rupture of a locked patch of the sumatra megathrust during the 2007 earthquake sequence the great sumatra andaman earthquake and tsunami of 2004 was a dramatic reminder of the importance of understanding the seismic and tsunami hazards of subduction zones 1 2 3 4 in march 2005 the sunda megathrust ruptured again producing an event 5 of moment magnitude mw 8 6 south of the 2004 rupture area which was the site of a similar event in 1861 ref 6 concern was then focused on the mentawai area where large earthquakes had occurred in 1797 mw 8 8 and 1833 mw 9 0 6 7 two earthquakes one of mw 8 4 and twelve hours later one of mw 7 9 indeed occurred there on 12 september 2007 here we show that these earthquakes ruptured only a fraction of the area ruptured in 1833 and consist of distinct asperities within a patch of the megathrust that had remained locked in the interseismic period this indicates that the same portion of a megathrust can rupture in different patterns depending on whether asperities break as isolated seismic events or cooperate to produce a larger rupture this variability probably arises from the influence of non permanent barriers zones with locally lower pre stress due to the past earthquakes the stress state of the portion of the sunda megathrust that had ruptured in 1833 and 1797 was probably not adequate for the development of a single large rupture in 2007 the moment released in 2007 amounts to only a fraction both of that released in 1833 and of the deficit of moment that had accumulated as a result of interseismic strain since 1833 the potential for a large megathrust event in the mentawai area thus remains large

time dependent model of creep on the hayward fault from joint inversion of 18 years of insar and surface creep data 1 spatial and temporal variations of aseismic fault creep influence the size and timing of large earthquakes along partially coupled faults to solve for a time dependent model of creep on the hayward fault we invert 18 years of surface deformation data 1992 2010 obtained by interferometric processing of 52 and 50 sar images acquired by the ers1 2 and envisat satellites respectively and surface creep data obtained at 19 alinement and 4 creepmeter stations for multi temporal analysis of the sar data we developed a method for identifying stable pixels using wavelet multi resolution analysis we also implement a variety of wavelet based filters for reducing the effects of environmental artifacts using a reweighted least squares approach we inverted the interferometric data to generate a time series of surface deformation over the san francisco bay area with a precision of better than a few millimeters to jointly invert the insar displacement time series and the surface creep data for a time dependent model of fault creep we use a robust inversion approach combined with a kalman filter the time dependent model constrains a zone of high slip deficit that may represent the locked rupture asperity of past and future m 7 earthquakes we identify several additional temporal variations in creep rate along the hayward fault the most important one being a zone of accelerating slip just northwest of the major locked zone we estimate that a slip rate deficit equivalent to mw 6 3 6 8 has accumulated on the fault since the last event in 1868

rupture process of the 1999 mw 7 1 duzce earthquake from joint analysis of spot gps insar strong motion and teleseismic data a supershear rupture with variable rupture velocity we analyze the rupture process of the 1999 m w 7 1 duzce earthquake using seismological remote sensing and geodetic data ground deformation measured from the subpixel cross correlation of satellite pour l observation de la terre spot images reveals a 55 km long fault trace and smooth surface slip distribution peaking at 3 5 4 m the westernmost segment overlaps for over 10 km with ruptures from the m w 7 4 izmit earthquake the 15 km long easternmost segment which cuts across mountainous topography had not been reported previously we determine a well constrained source model using a four segment fault geometry using constraints on surface fault slip and inverting global positioning system and interferometric synthetic aperture radar data along with strong motion records our results show that some variability of the rupture velocity and an eastward supershear velocity are required to fit the strong motion data the rise time up to 6 sec correlates with cumulative slip suggesting a sliding velocity of about 1 m sec the source model predicts teleseismic waveforms well although early by 2 sec this time shift is probably due to the weak beginning of the earthquake that is not observable at teleseismic distances strong motion records are relatively well predicted from a source model derived from the teleseismic data using the fault geometry derived from the satellite images this study demonstrates the benefit of using accurate fault geometries to determine finite fault source models

cosmogenic radionuclide chronology of pre last glacial cycle moraines in the western arthur range southwest tasmania cosmogenic 10be and 26al exposure ages of 12 boulders from two moraine complexes in the western arthur range of southwest tasmania which previously were considered to have been deposited during the last glacial maximum predate the last glacial cycle zero erosion minimum exposure ages range from 95 ka to 232 ka based on weighted mean 10be and 26al ages per boulder for a reasonable choice of erosion rates 10be boulder ages range from 105 to 326 ka respectively although a direct association of moraine construction to a specific marine isotope stage mis glaciation is not definitive erosion corrected exposure ages indicate glacial advances commensurate with mis 6 and 10 although the latter advance may be attributable to mis 8 if the erosion rate correction is an over estimate given the relatively close proximity of the dated moraines to their source cirques this new cosmogenic glacial chronology implies a very limited extent for any younger glacial advances that occurred in the western arthur range during the last glacial cycle post mis 5 including the global lgm

fault structure and mechanics of the hayward fault california from double difference earthquake locations 1 the relationship between small magnitude seismicity and large scale crustal faulting along the hayward fault california is investigated using a double difference dd earthquake location algorithm we used the dd method to determine high resolution hypocenter locations of the seismicity that occurred between 1967 and 1998 the dd technique incorporates catalog travel time data and relative p and s wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events the relocated seismicity reveals a narrow near vertical fault zone at most locations this zone follows the hayward fault along its northern half and then diverges from it to the east near san leandro forming the mission trend the relocated seismicity is consistent with the idea that slip from the calaveras fault is transferred over the mission trend onto the northern hayward fault the mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the calaveras fault at calaveras reservoir in some locations discrete structures adjacent to the main trace are seen features that were previously hidden in the uncertainty of the network locations the fine structure of the seismicity suggests that the fault surface on the northern hayward fault is curved or that the events occur on several substructures near san leandro where the more westerly striking trend of the mission seismicity intersects with the surface trace of the aseismic southern hayward fault the seismicity remains diffuse after relocation with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation the seismicity is highly organized in space especially on the northern hayward fault where it forms horizontal slip parallel streaks of hypocenters of only a few tens of meters width bounded by areas almost absent of seismic activity during the interval from 1984 to 1998 when digital waveforms are available we find that fewer than 6 5 of the earthquakes can be classified as repeating earthquakes events that rupture the same fault patch more than one time these most commonly are located in the shallow creeping part of the fault or within the streaks at greater depth the slow repeat rate of 2 3 times within the 15 year observation period for events with magnitudes around m 1 5 is indicative of a low slip rate or a high stress drop the absence of microearthquakes over large contiguous areas of the northern hayward fault plane in the depth interval from 5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large magnitude earthquakes

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

the seismic activity of the marmara sea region over the last 2000 years we examined the seismicity of the region of the sea of marmara in northwest turkey over the last 2000 yr using the historical record of the region we found no evidence for truly large earthquakes of a size comparable to those in the north anatolian fault zone in the marmara basin events are smaller in keeping with the known fault segmentation of the basin over the last 2000 yr seismic mo ment release accounted for the known right lateral shear velocity across the marmara region observed by global positioning system measurements its average rate is relatively constant and varies between 1 6 and 2 4 cm yr the long term seismicity in the marmara sea region shows that large earthquakes are less frequent than pre dicted from the 100 yr long instrumental period

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

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

modeling afterslip and aftershocks following the 1992 landers earthquake one way to probe the rheology of the lithosphere and fault zones is to analyze the temporal evolution of deformation following a large earthquake in such a case the lithosphere responds to a known stress change that can be assessed from earthquake slip models constrained from seismology and geodesy here we model the postseismic response of a fault zone that is assumed to obey a rate strengthening rheology where the frictional stress varies as a ln e e being the deformation rate and a 0 a rheological parameter the model is simple enough that these parameters can be estimated by inversion of postseismic geodetic data we apply this approach to the analysis of geodetic displacements following the m w 7 3 1992 landers earthquake the model adjusts well the measured displacements and implies a 0 47 0 53 mpa in addition we show that aftershocks and afterslip follow the same temporal evolution and that the spatiotemporal distribution of aftershocks is consistent with the idea that they are driven by reloading of the seismogenic zone resulting from frictional afterslip

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