earthquake scaling laws for creeping and non creeping faults the dependence of the summed moment release on the fault dimension differs between non creeping faults and creeping faults or volcanic regions this can be attributed to different earthquake scaling laws the number n of events with fault length l scales for non creeping faults as n l l 2 and for creeping faults as n l l 3 this difference offers a means for mapping the distribution of creep in the seismogenic crust

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

strong motion records and synthetic isoseismals of the pyrgos peloponnisos southern greece earthquake sequence of march 26 1993 in this work several seismological observations are presented in order to explain characteristic features of the earthquake sequence which occurred in march 1993 in southwestern greece very close to the city of pyrgos fault plane solutions of the largest fore and aftershocks and the main shock as well as the directions at which the maximum ground accelerations were recorded suggest that this earthquake sequence has been developed by rupturing three distinct focal planes with different focal mechanisms the first focal plane located in the off shore area strikes nw se dips se and includes most of the foreshock activity the foreshock activity migrated to the northeastern part of the city of pyrgos and took place on planes with a predominant direction ne sw the main shock ofm x 5 5 occurred in a focal plane located between the two above mentioned areas strong motion records of significant shocks of the sequence show peak acceleration values on components consistent with the relevant fault plane solutions furthermore the observed macroseismic field has been compared with synthetic isoseismals computed by using a certain velocity model and the focal mechanism parameters of the main shock

temporal variations in the fractal properties of seismicity in the north anatolian fault zone between 31 e and 41 e we investigate the nature of temporal variations in the statistical properties of seismicity associated with the north anatolian fault zone between longitudes 31 41 e during the instrumental period 1900 1992 temporal variations in the seismicb value and the fractal correlation dimensiondc of earthquake epicenters are examined for earthquakes of magnitudems 4 5 using sliding windows of 100 consecutive events b varies temporally between 0 6 and 1 0 anddc between 0 6 and 1 4 both representing significant fluctuations above the errors in measurement technique a strong negative correlation r 0 85 is observed betweenb anddc consistent with previous observation of seismicity in japan and southern california major events early in this century ms 7 are associated with lowb and highdc respectively consistent with greater stress intensity and greater spatial clustering of epicenters both implying a greater degree of stress concentration at this time

stress transfer by the 1988 1989 m 5 3 and 5 4 lake elsman foreshocks to the loma prieta fault unclamping at the site of peak mainshock slip we study the stress transferred by the june 27 1988 m 5 3 and august 8 1989 m 5 4 lake elsman earthquakes the largest events to strike within 15 km of the future loma prieta rupture zone during 74 years before the 1989 m 6 9 loma prieta earthquake we find that the first lake elsman event brought the rupture plane of the second event 0 3 1 6 bars 0 03 0 16 mpa closer to coulomb failure but that the lake elsman events did not bring the future loma prieta hypocentral zone closer to failure instead the lake elsman earthquakes are calculated to have reduced the normal stress on or undamped the loma prieta rupture surface by 0 5 1 0 bar 0 05 0 10 mpa at the site where the greatest slip subsequently occurred in the loma prieta earthquake this association between the sites of peak unclamping and slip suggests that the lake elsman events did indeed influence the loma prieta rupture process unclamping the fault would have locally lowered the resistance to sliding such an effect could have been enhanced if the lowered normal stress permitted fluid infusion into the undamped part of the fault although less well recorded the ml 5 0 1964 and ml 5 3 1967 corralitos events struck within 10 km of the southwest end of the future loma prieta rupture no similar relationship between the normal stress change and subsequent loma prieta slip is observed although the high slip patch southwest of the loma prieta epicenter corresponds roughly to the site of calculated coulomb stress increase for a low coefficient of friction the lake elsman loma prieta result is similar to that for the 1987 m 6 2 elmore ranch and m 6 7 superstition hills earthquakes suggesting that foreshocks might influence the distribution of mainshock slip rather than the site of mainshock nucleation

atmospheric boundary layer modification in the marginal ice zone a case study of the andreas et al 1984 data on atmospheric boundary layer modification in the marginal ice zone is made our model is a two dimensional multilevel linear model with turbulence lateral and vertical advection and radiation good agreement between observed and modeled temperature cross sections is obtained in contrast to the hypothesis of andreas et al we find the air flow is stable to secondary circulations adiabatic lifting and at long fetches cloud top longwave cooling not an air to surface heat flux dominate the cooling of the boundary layer the accumulation with fetch over the ice of changes in the surface wind field is shown to have a large effect on estimates of the surface wind stress we speculate that the andreas et al estimates of the drag coefficient over the compact sea ice are too high

displacement of surface monuments vertical motion several measurements of vertical ground motion at pinon flat observatory california indicate the overall weakness and instability of the earth s weathered surface with respect to the underlying rock cumulative long period motions of order 0 5 mm per year dominate these records though smaller elastic deformations caused by precipitation loading atmospheric loading and tidal strains are evident at higher frequencies all of these help to characterize the near surface material the long period records suggest that near surface weathering is the dominant influence on monument motion at least at this site on crystalline rock in a semi arid environment rainfall loading gives an average vertical modulus of 2 6 gpa for the material in the uppermost 26 m of the ground compared with 88 gpa for granite under moderate confining stress atmospheric loading gives similar results but indicates the ground is permeable to airflow at periods longer than a few hours earth tide records show poisson s ratio to be 0 09 in contrast to the normative range of 0 2 0 25 establishing that horizontal strains couple only weakly into vertical ones so that vertical strains near the surface are a poor measure of areal strain the form of the ground surface displacement power spectrum indicates that analyses of geodetic surveys would be improved with the inclusion of a monument positioning error budget that increases with time because of ground instability and the generally small rate of crustal tectonic motions deeply emplaced monuments will be needed for observational programs designed to detect short term changes in crustal deformation over baselengths of order 10 km and less

a slow earthquake sequence on the san andreas fault earthquakes typically release stored strain energy on timescales of the order of seconds limited by the velocity of sound in rock over the past 20 years observations1 13 and laboratory experiments14 have indicated that rupture can also occur more slowly with durations up to hours such events may be important in earthquake nucleation15 and in accounting for the excess of plate convergence over seismic slip in subduction zones the detection of events with larger timescales requires near field deformation measurements in december 1992 two borehole strainmeters close to the san andreas fault in california recorded a slow strain event of about a week in duration and we show here that the strain changes were produced by a slow earthquake sequence equivalent magnitude 4 8 with complexity similar to that of regular earthquakes the largest earthquakes associated with these slow events were small local magnitude 3 7 and contributed negligible strain release the importance of slow earthquakes in the seismogenic process remains an open question but these observations extend the observed timescale for slow events by two orders of magnitude

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

mapping the b value anomaly at 100 km depth in the alaska and new zealand subduction zones a positive anomaly in the frequency magnitude distribution b value is detected at approximately 90 100 km depth in two subduction zones the b value in this anomalous zone is 40 higher than in adjacent volumes we use regional catalogs with a magnitude of completeness of 2 6 central alaska and cook inlet 2 0 shumagin islands and 3 5 new zealand to resolve the b value as a function of space in more detail we project all earthquakes onto planes perpendicular to the strike of the slab these cross section views of the b value distribution locate the high b value anomalies at a depth of 90 100 km on the upper surface of the wadati benioff zone at these depths slab dehydration may increase pore pressure thus lowering the effective stress and increasing the b value increased pore pressure would also lower the liquidus in the overlying asthenosphere giving rise to the volcanism that occurs directly above this zone

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

variations in the frequency magnitude distribution with depth in two volcanic areas mount st helens washington and mt spurr alaska the frequency magnitude distribution of earthquakes characterized using the b value is examined as a function of space beneath mount st helens 1988 1996 and mt spurr 1991 1995 at mount st helens two volumes of anomalously high b b 1 3 can be observed at depths of 2 6 3 6 km below the crater floor and below 6 4 km these anomalies coincide with 1 the depth of vesiculation of ascending magma and 2 the suggested location of a magma chamber at mount st helens study of mt spurr reveals an area of high b value b 1 3 at a depth of about 2 3 4 5 km below the crater floor of the active vent crater peak we propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b value at shallow depths alternatively interaction of magma with groundwater may have increased pore pressure and lowered the effective stress the deeper anomaly at mount st helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber our results indicate that detailed mapping of the frequency magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

mapping active magma chambers by b values beneath the off ito volcano japan the b value of the frequency magnitude relation and thus the mean magnitude in the off ito volcanic area is not uniform based on detailed b value tomography using about 10 000 events in an area of 10 km radius and in the upper 15 km of the crust a high b value anomaly b 15 below 7 km depth and with a radius of about 2 km located below the coast southeast of ito contrasts with lower values of typically b 0 7 north of it and at shallower depths on the basis of surface deformations a tensile crack dislocation source was located above 7 km depth thus we surmise that the magma chamber in the off ito area was located below 7 km depth the correlation of a high b value anomaly with this model supports our hypothesis that active magma chambers may be mapped by high b value anomalies the magma body may be described as consisting of two parts a lower well established chamber below 11 km depth and a shallower part 11 7 km depth the b value in the volume surrounding the magma chamber increased from 0 7 during the 1980s to 1 5 during the earthquake swarms of the 1990s this may reflect a trend of increasing crack density due to the intrusion activity

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

spatial variations of the fractal properties of seismicity in the anatolian fault zones abstract the anatolian fault zones are seismically active strike slip fault zones transcending the anatolian plate in e w and n s directions we investigate the spatial variations of seismicity along these zones in an attempt to investigate fault complexity along strike quantified by the gutenberg richter b value and the fractal correlation dimension of earthquake epicentres using the maximum likelihood method and the correlation integral respectively the investigation covers instrumentally recorded carthquakes of magnitude m 4 5 occurring between 1900 and 1992 we find systematic spatial variations which may be related to structural or mechanical variability along strike in particular the large change in strike at the northern apex of the north anatolian fault zone is associated with the highest correlation dimension and lowest b value for seismicity this century the correlation dimension and b value show a negative correlation with respect to each other similar to results reported in other regional studies of japan and southern california this statistical correlation is stronger when more objective seismic zoning is carried out based on number of events rather than more subjective seismotectonic zoning in common use in seismic hazard analysis

fault plane structure of the antofagasta chile earthquake of 1995 from a large dataset of aftershocks in the rupture area of the mw 8 0 1995 antofagasta earthquake we derived the spatial distribution of hypocenters and a b value map along the fault plane we further examined various focal mechanisms of the aftershock sequence the b value distribution on the fault plane clearly indicates the heterogeneity of the rupture area we found a positive correlation between the b value variations and the main shock source time function determined by delouis 1996 where zones of high b value are related to high slip with these results we propose to have found evidence for the segmentation of the fault plane and suggest that the mapped inhomogeneities could have played the role of asperities prior to the main shock rupture

seismic observations at an overstep of the western north anatolian fault abant sapanca region turkey the course of the active north anatolian fault system from lake abant to lake sapanca was traced by its high micro earthquake activity if approaching from the east this section includes a broad south to north overstep fault offset of the main fault

correlating variations of b values and crustal deformations during the 1990s may have pinpointed the rupture initiation of the mw 7 4 izmit earthquake of 1999 august 17 summary the b value increases from 1 1 along straight segments to 1 7 along a releasing bend of the north anatolian fault system between 30 1 e and 30 8 e the tensional nature of the bend is corroborated by extension rates of 0 3 strain yr 1 as obtained from global positioning system gps data fault plane solutions in this area change from abundant right lateral strike slip to oblique slip with normal components in the central part of the bend compatible with the formation of a pull apart basin we suggest that this crustal volume is highly fractured corresponding to a short mean crack length due to the superposition of horizontal and normal faulting as a consequence of low normal stress on the existing cracks frictional sliding is assumed to be the predominant mechanism for the generation of seismic events resulting in high b values the lowest b values b 0 8 in the area investigated are found at the junction between the fault bend and the adjoining segment which runs through the epicentre of the 1999 izmit earthquake at the junction a localized stress concentration is expected from numerical models of seismicity along geometrical barriers thus the site of lowest b has been considered to be the most likely place for a major earthquake a conclusion that is confirmed by the izmit earthquake with epicentre located about 13 km from the anticipated site in early 1992 the spatially averaged b value started to increase along the central and northwestern parts of the fault bend and there was a corresponding period of intensified horizontal extension since no large earthquake was recorded in 1992 it is assumed that the anomalous extension and the associated change in stress have been caused by aseismic fault creep in view of the available seismotectonic information surface displacements due to a slow dislocation at depth were calculated the gps data are reasonably explained by a source of normal fault type at a depth of 10 km and equivalent magnitude mw 5 9 stress changes at seismogenic depths are calculated under the assumption that an increase in b is most likely to be observed along those segments where both deviatoric and mean stress are reduced while the coulomb stress change is positive that is the fault is brought closer to failure for right lateral strike slip the stress condition is fulfilled at the sites of the largest b value increase the surface rupture of the izmit earthquake is associated with known fault traces only in the west and in the east of the study area along the fault bend it detaches itself from mapped fault traces and runs through the regions of positive coulomb stress change caused by the inferred 1992 slow event maximum surface slip 5 m is observed in the immediate vicinity of sites of maximum coulomb stress change 3 bar indicating that the 1992 event could have partially unclamped the rupture plane of the subsequent izmit earthquake we propose that the strong differences in b observed along the complex fault bend can be used to characterize different states of tectonic deformation in space and time

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

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

temporal variations in seismic event rate and b values from stress corrosion constitutive laws abstract main i g meredith p g and sammonds p r 1992 temporal variations in seismic event rate and b values from stress corrosion constitutive laws in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 233 246 a model is developed to characterise the state of damage for a fractal population of cracks in terms of a mean energy release rate g which depends on the stress the event rate n and the seismic b value n is assumed to be proportional to the total number of potentially active cracks and b to be proportional to the exponent d of the crack length distribution g is then positively correlated with n and negatively correlated with b consistent with experimental observation based on stress intensity as a constitutive variable the model predicts that higher b values are associated either with lower stress intensity or greater material heterogeneity both experiment and theory predict intermediate term seismic quiescence of similar magnitude to that observed in the field 45 90 for only a small simultaneous reduction in stress and stress intensity 2 7 or the equivalent mean energy release rate the theoretical model predicts three different types of quiescence associated with increasing constant or decreasing b value the first two are associated with stable intermediate term quiescence due to a reduction in g and the third is associated with unstable short term quiescence associated with constant or increasing g the theory can be used to infer relative changes in g from acoustic emissions in the laboratory experiments to date show that quiescence of the order 10 can be seen in the laboratory at strain rates of 10 5 s 1 but that this has the characteristics of short term rather than intermediate term quiescence