constitutive relationships and physical basis of fault strength due to flash heating 1 we develop a model of fault strength loss resulting from phase change at asperity contacts due to flash heating that considers a distribution of contact sizes and nonsteady state evolution of fault strength with displacement laboratory faulting experiments conducted at high sliding velocities which show dramatic strength reduction below the threshold for bulk melting are well fit by the model the predicted slip speed for the onset of weakening is in the range of 0 05 to 2 m s qualitatively consistent with the limited published observations for this model earthquake stress drops and effective shear fracture energy should be linearly pressure dependent whereas the onset speed may be pressure independent or weakly pressure dependent on the basis of the theory flash weakening is expected to produce large dynamic stress drops small effective shear fracture energy and undershoot estimates of the threshold slip speed stress drop and fracture energy are uncertain due to poor knowledge of the average contact dimension shear zone thickness and gouge particle size at seismogenic depths

effect of normal stress during rupture propagation along nonplanar faults 1 we study a symmetrical three forked shear fault under simple triaxial stress rupture initiates in the central primary plane and propagates toward the branching point one of the two branches is in the compressional quadrant while the other is in the tensional domain we study the following question does rupture always prefer propagating along the tensional branch because of the effect of normal stress when the primary plane is located in the most favorable direction as determined by mohr coulomb criterion one finds that the compressional branch is almost always preferred for various dynamic coefficients and confining pressures simultaneous rupture propagation on both branches appears only under a very special condition found by aochi et al 2000b these results indicate that shear stress changes produced by the rupture front dominate during dynamic rupture propagation compared to normal stress changes this result depends completely on the orientation of the whole fault system in all cases we can explain the branch selection by analyzing the applied initial shear stress and the fault properties change of normal stress may play a role similar to shear stress change for disjoint faults since the effect of normal stress change sometimes dominates

spontaneous rupture processes on a bending fault 1 we simulated spontaneous rupture processes on a vertical bending strike slip fault in a three dimensional half space using a finite difference method rupture area and overall slip distribution on the fault vary with the initial stress field which depends on strike change at the bend rupture velocity and detailed slip distribution around the bend on the other hand are affected by time dependent normal stress change caused by rupture this dynamic stress change plays an important role in the rupture process ahead of the bend as well as in the resulting ground motion the numerical simulation method demonstrated here in a simplified geometry is equally applicable to modeling strong ground motion from geometrically complex ruptures in realistic earth models

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

earthquakes and relative sealevel changes 1 using a spherical model of postseismic deformation for the first time we have computed the global contribution of large earthquakes to the relative sealevel variations in the twentieth century we have found that great earthquakes have the overall tendency to produce a sealevel rise and that they affect the measurements taken at those tide gauge sites that are commonly employed to obtain global estimates of sealevel rise though on a global scale most of the signal is associated with thrust events on a regional scale the effects of great transcurrent earthquakes cannot be neglected depending on the viscosity of the asthenosphere the contribution of earthquakes to the long term sealevel changes amounts to at least 0 1 mm yr thus the climate driven long term sealevel changes deduced by tide gauge observations may be slightly but not negligibly overestimated

the equivalent strength of geometrical barriers to earthquakes we present a quantitative framework for evaluating the influence of non planar fault geometry on repeated seismic ruptures we model quasistatic ruptures on a non planar fault trace imbedded in a two dimensional elastic medium under in plane strain because of the presence of fault segments that are not parallel to the regional shear stress i e bends the apparent strength at a given point on the fault is not fixed but fluctuates with normal stress compressional features behave as increasingly strong barriers to fracture unless the stored normal stress is released in order to unlock the fault since slip on the fault itself cannot get rid of the normal stress this is achieved through the action of off fault morphological features such as secondary faulting folding and vertical motions that we introduce parametrically in the form of an aseismic relaxation the apparent strength of a fault bend will stabilize in a narrow interval of values after repeated ruptures characterized by a non dimensional hardness parameter whereby the relaxation rate is scaled by the tectonic loading rate on a fault structure having several small widely separated bends three families of events can be identified whose frequency and magnitude depend on the hardness relaxation parameter and the geometry small events that cluster in the tension zones of the bends intermediate size ruptures involving a single interbend segment and large ruptures that break through bends and link on or more interbend segments large multi segment events are most likely to occur for low values of the hardness i e fast relaxation and slow loading rate regions with compressional features act as barriers that stop most ruptures stress is stored at these sites until they themselves break and initiate motion on the smoother long reaches of the fault

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

rupture termination and jump on parallel offset faults proper evaluation of seismic hazard depends on accurate estimates of potential earthquake size in areas with complex multisegment fault systems such an estimate in turn depends on an ability to predict the circumstances under which rupture may jump between fault segments many observational and numerical studies have analyzed the phenomenon of jumping rupture but none has focused on how the process of rupture termination on the primary nucleating fault segment affects the ability of rupture to jump to a secondary fault segment in the current study i model the dynamics of a simple 2d strike slip fault system with two parallel segments arranged with either a compressional or extensional stepover i vary the suddenness with which the initial shear stress tapers to zero on the primary section if the initial shear stress goes to zero over a very small 100 m distance rupture readily jumps both compressional and extensional stepovers of 1 km if the initial shear stress tapers to zero over 1 km rupture can jump the compressional stepover but not the extensional stepover if the initial shear stress tapers to zero over 2 5 km rupture cannot jump either the compressional or the extensional stepover the results illustrate the importance of the slip gradient and the resultant static stress field and the acceleration of the rupture front and the resultant generation of stopping phases in determining the probability of jumping rupture

fault geometry rupture dynamics and ground motion from potential earthquakes on the north anatolian fault under the sea of marmara summary using the 3 d finite element method we develop dynamic spontaneous rupture models of earthquakes on the north anatolian fault system in the sea of marmara turkey considering the geometrical complexity of the fault system in this region we find that the earthquake size rupture propagation pattern and ground motion all strongly depend on the interplay between the initial static regional pre stress field and the dynamic stress field radiated by the propagating rupture by testing several nucleation locations we observe that those far from an oblique normal fault stepover segment near istanbul lead to large through going rupture on the entire fault system whereas nucleation locations closer to the stepover segment tend to produce ruptures that die out in the stepover however this pattern can change drastically with only a 10 rotation of the regional stress field our simulations also reveal that while dynamic unclamping near fault bends can produce a new mode of supershear rupture propagation this unclamping has a much smaller effect on the speed of the peak in slip velocity along the fault finally we find that the complex fault geometry leads to a very complex and asymmetric pattern of near fault ground motion including greatly amplified ground motion on the insides of fault bends the ground motion pattern can change significantly with different hypocentres even beyond the typical effects of directivity the results of this study may have implications for seismic hazard in this region for the dynamics and ground motion of geometrically complex faults and for the interpretation of kinematic inverse rupture models

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

late quaternary paleoenvironmental records from the chatanika river valley near fairbanks alaska abstract perennially frozen deposits are considered as excellent paleoenvironmental archives similar to lacustrine deep marine and glacier records because of the long term and good preservation of fossil records under stable permafrost conditions a permafrost tunnel in the vault creek valley chatanika river valley near fairbanks exposes a sequence of frozen deposits and ground ice that provides a comprehensive set of proxies to reconstruct the late quaternary environmental history of interior alaska the multi proxy approach includes different dating techniques radiocarbon accelerator mass spectrometry ams 14 c optically stimulated luminescence osl thorium uranium radioisotope disequilibria 230 th u as well as methods of sedimentology paleoecology hydrochemistry and stable isotope geochemistry of ground ice the studied sequence consists of 36 m thick late quaternary deposits above schistose bedrock main portions of the sequence accumulated during the early and middle wisconsin periods the lowermost unit a consists of about 9 m thick ice bonded fluvial gravels with sand and peat lenses a late sangamon mis 5a age of unit a is assumed spruce forest with birch larch and some shrubby alder dominated the vegetation high presence of sphagnum spores and cyperaceae pollen points to mires in the vault creek valley the overlying unit b consists of 10 m thick alternating fluvial gravels loess like silt and sand layers penetrated by small ice wedges osl dates support a stadial early wisconsin mis 4 age of unit b pollen and plant macrofossil data point to spruce forests with some birch interspersed with wetlands around the site the following unit c is composed of 15 m thick ice rich loess like and organic rich silt with fossil bones and large ice wedges unit c formed during the interstadial mid wisconsin mis 3 and stadial late wisconsin mis 2 as indicated by radiocarbon ages post depositional slope processes significantly deformed both ground ice and sediments of unit c pollen data show that spruce forests and wetlands dominated the area the macrofossil remains of picea larix and alnus incana ssp tenuifolia also prove the existence of boreal coniferous forests during the mid wisconsin interstadial which were replaced by treeless tundra steppe vegetation during the late wisconsin stadial unit c is discordantly overlain by the 2 m thick late holocene deposits of unit d the pollen record of unit d indicates boreal forest vegetation similar to the modern one the permafrost record from the vault creek tunnel reflects more than 90 ka of periglacial landscape dynamics triggered by fluvial and eolian accumulation and formation of ice wedge polygons and post depositional deformation by slope processes the record represents a typical wisconsin valley bottom facies in central alaska

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

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

dynamic transfer of rupture across differently oriented segments in a complex 3 d fault system 1 we simulate spontaneous dynamic propagation of rupture across two adjacent fault segments subject to a triaxial compressive stress regime these segments have different orientations and hence different focal mechanisms vertical strike slip and dipping thrust numerical simulations using a biem boundary integral equation method have revealed that under a typical triaxial homogeneous compressive stress regime where the magnitude of the intermediate principal stress lies halfway between those of the maximum and minimum ones ruptures of different focal mechanisms are not likely to occur simultaneously in a single rupture event propagation of rupture from a vertical strike slip fault segment to a pure dip slip normal reverse fault segment is possible only when the stress field is close to uniaxial compression or when the intermediate stress magnitude is close either to the minimum or the maximum one these findings are useful for evaluating possible earthquake scenarios along fault systems with complex 3d geometries

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

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

dynamic seismic ruptures on melting fault zones 1 we present a physical model that describes the behavior of spontaneous earthquake ruptures dynamically propagating on a fault zone and that accounts for the presence of frictional melt produced by the sliding surfaces first we analytically derive the solution for the temperature evolution inside the melt layer which generalizes previous approximations then we incorporate such a solution into a numerical code for the solution of the elastodynamic problem when a melt layer is formed the linear slip weakening law initially governing the fault and relying on the coulomb friction is no longer valid therefore we introduce on the fault a linearly viscous rheology with a temperature dependent dynamic viscosity we explore through numerical simulations the resulting behavior of the traction evolution in the cohesive zone before and after the transition from coulomb friction and viscous rheology the predictions of our model are in general agreement with the data from exhumed faults we also find that the fault after undergoing the breakdown stress drop controlled by the slip weakening constitutive equation experiences a second traction drop controlled by the exponential weakening of fault resistance due to the viscous rheology this further drop enhances the instability of the fault increasing the rupture speeds the peaks in fault slip velocity and the fracture energy density

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

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