applying the coulomb failure function with an optimally oriented plane to the 2008 mw 7 9 wenchuan earthquake triggering the coulomb failure function cff quantitatively describes static stress changes in secondary faults near the source fault of an earthquake cff can be employed to monitor how static stress transfers and then shed some light on the probability of successive events occurring around a source fault in this paper we focus on the cff and particularly on optimally oriented planes we present a unified model to determine an optimally oriented plane and its corresponding coulomb stress then apply the model to the 2003 mw 6 6 bam iran earthquake and the 2008 mw 7 9 wenchuan china earthquake thereby checking its effectiveness our results show that spatial correlation between positive coulomb stress changes and aftershocks are for the 2003 bam earthquake 47 06 when elastic coulomb stress changes are resolved on uniform planes and 87 53 when these are resolved on optimally oriented planes at depth for the 2008 wenchuan earthquake the correlations are 45 68 and 58 20 respectively it is recommended that account be taken of optimally oriented planes when drawing a coulomb stress map for analyzing earthquake triggering effects

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

coulomb stress changes caused by repeated normal faulting earthquakes during the 1997 umbria marche central italy seismic sequence 1 we investigate fault interaction through elastic stress transfer among a sequence of moderate magnitude main shocks 5 mw 6 which ruptured distinct normal fault segments during a seismic sequence in the umbria marche region central apennines we also model the spatial pattern of aftershocks and their faulting mechanisms through coulomb stress changes we compute stress perturbations caused by earthquake dislocations in a homogeneous half space our modeling results show that seven out of eight main shocks of the sequence occur in areas of enhanced coulomb stress implying that elastic stress transfer may have promoted the occurrence of these moderate magnitude events our modeling results show that stress changes caused by normal faulting events reactivated and inverted the slip of a secondary n s trending strike slip fault inherited from compressional tectonics in its shallowest part 1 3 km of the 1517 available aftershocks 82 are located in areas of positive stress changes for optimally oriented planes oops for coulomb failure however only 45 of the 322 available fault plane solutions computed from polarity data is consistent with corresponding focal mechanisms associated with the oops the comparison does not improve if we compute the optimally oriented planes for coulomb failure by fixing the strike orientation of oops using information derived from structural geology our interpretation of these modeling results is that elastic stress transfer alone cannot jointly explain the aftershock spatial distribution and their focal mechanisms

the impact of static stress change dynamic stress change and the background stress on aftershock focal mechanisms the focal mechanisms of earthquakes in southern california before and after four m 6 7 main shocks provide insight into how fault systems respond to stress and changes in stress the main shock static stress changes have two observed impacts on the seismicity changing the focal mechanisms in a given location to favor those aligned with the static stress change and changing the spatial distribution of seismicity to favor locations where the static stress change aligns with the background stress the aftershock focal mechanisms are significantly aligned with the static stress changes for absolute stress changes of 0 02 mpa for up to 20 years following the main shock the dynamic stress changes have similar although smaller effects on the local focal mechanisms and the spatial seismicity distribution dynamic stress effects are best observed at long periods 30 60 s and for metrics based on repeated stress cycling in the same direction this implies that dynamic triggering operates at least in part through cyclic shear stress loading in the direction of fault slip the background stress also strongly controls both the preshock and aftershock mechanisms while most aftershock mechanisms are well oriented in the background stress field 10 of aftershocks are identified as poorly oriented outliers which may indicate limited heterogeneity in the postmain shock stress field the fault plane orientations of the outliers are well oriented in the background stress while their slip directions are not implying that the background stress restricts the distribution of available fault planes

a study of the coulomb stress and seismicity rate changes induced by the 2008 m w 7 9 wenchuan earthquake sw china abstract correlations between the calculated coulomb stress changes and observed seismicity rate changes after the wenchuan earthquake are investigated in this article three improvements are made in the calculation of static stress change including employing a dislocation method with triangular elements rather than traditional rectangular elements setting up a more realistic source slip model and a more complete receiver fault model and resolving stress changes on assumed receiver faults with spatially variable focal mechanisms based on well determined focal mechanisms at different calculation points the recorded aftershocks are mapped for comparison with the spatial distribution of stress changes the results indicate that the wenchuan earthquake encourages not only three major fault systems the east kunlun south of xianshuihe and west of qinling southern frontal but also several other regions including tazang north of min jiang north of pingwu qingchuan and west of chongqing in particular the eastern segment of longriba is shown to be quite dangerous with dramatic stress increase the influence of depth and frictional coefficient is analyzed the depth of calculation beyond the depth range of the source model will make a significant difference to the stress change map and thus cannot be neglected many aftershocks occurring in the stress shadow zone near the main rupture can be attributed to dynamic stress triggering and the fractal structure of the main fault the observed seismicity rate changes are compared with the static stress changes the results show that high background seismicity rates will amplify the effect of stress change the observed seismicity rate changes support the forecast rate of 10 year seismicity after the wenchuan earthquake based on the rate and state dependent friction model coulomb stresses increase on the focal mechanisms away from the main rupture which demonstrates the influence of the wenchuan earthquake over a wide range especially the focal mechanism for lushan earthquake undergoes a stress increase by more than 2 0 bars which suggests that the lushan earthquake has been effectively promoted by the wenchuan earthquake

tectonic implications of post 30 ma pacific and north american relative plate motions the pacific plate moved northwest relative to north america since 42 ma the rapid half rate of pacific farallon spreading allowed the ridge to approach the continent at about 29 ma extinct spreading ridges that occur offshore along 65 of the margin lonsdale 1991 document that fragments of the subducted farallon slab became captured by the pacific plate and assumed its motion prior to the actual subduction of the spreading ridge this plate capture process can be used to explain much of the post 29 ma cordilleran north america extension strike slip and the inland jump of oceanic spreading in the gulf of california the pacific and north american contact zone lengthened with each successive plate capture event underpinning the parts of western north america directly inland with a strong plate undergoing pacific relative motion we suggest that much of the post 29 ma continental tectonism is the result of the strong traction imposed on the deep part of the continental crust by the gently inclined slab of subducted oceanic lithosphere as it moved to the northwest relative to the overlying continent the plate capture hypothesis is distinctly different from theories involving shallow slab gaps kinematic problems associated with shallow slab gap models cause us to question them this conclusion is consistent with seismic refraction interpretations that suggest there is an inclined layer with high velocities like that of basalt or gabbro at the base of the continental crust beneath much of the californian margin and the documented reduction of slab pull forces and density associated with young subducting slabs thermal and rheologic modeling suggests that coastal california was a strong zone at all depths allowing it to be firmly linked to pacific motion our model shows that deformed regions such as the basin and range and borderland provinces developed in predicted weak parts of the crustal section but they have been incompletely linked to the deep plate across the ductile middle and lower crustal layer

resolving fault plane ambiguity for small earthquakes summary we have developed an automated procedure to resolve fault plane ambiguity for small to medium sized earthquakes 2 5 ml 5 using synthetic green s tensors computed in a 3 d earth structure model and applied this procedure to 35 earthquakes in the los angeles area for 69 per cent of the events we resolved fault plane ambiguity of our cmt solutions at 70 per cent or higher probability for some earthquakes the fault planes selected by our automated procedure were confirmed by the distributions of relocated aftershock hypocentres in regions where there are no precisely relocated aftershocks or for earthquakes with few aftershocks we expect our method to provide the most convenient means for resolving fault plane ambiguity our procedure does not rely on detecting directivity effects therefore it is applicable to any types of earthquakes

sensitivity of coulomb stress change to the parameters of the coulomb failure model a case study using the 2008 mw 7 9 wenchuan earthquake the coulomb stress change has been widely employed to interpret mainshock mainshock and mainshock aftershock triggering as well as interactions amongst earthquake faults and volcanoes this quantitative index is computed based on the coulomb failure criterion and is a function of fault parameters including the source and receiver fault geometries the friction coefficient on the receiver fault and skempton s coefficient of the host rock thus for the robust determination of the coulomb stress change the sensitivity of the coulomb stress change to these model parameters should be thoroughly assessed however notwithstanding numerous case studies almost no systematic investigation of the sensitivity of the coulomb stress change has been performed here we present an error estimator for the coulomb stress change and then quantitatively investigate the sensitivity of the coulomb stress change to the fault model parameters for the 2008 mw 7 9 wenchuan earthquake our results indicate that for this case the coulomb stress change is the most sensitive to the uncertainty in the dip angle of the receiver fault while the influences of the uncertainties in the slip model of the source fault the strike and rake angles of the receiver fault and the friction and skempton s coefficients cannot be neglected accordingly it is crucial to perform a realistic estimate of the uncertainty in the coulomb stress change by performing such calculation future coulomb stress analyses such as the stress triggering of earthquake sequence and the likelihoods of potential earthquakes could be based on more robust coulomb stress change maps

the significance of linear trends and clusters of fault related mesothermal lode gold mineralization gold deposits from the laverton region western australia form both linear trends and cluster like distributions in map view associated with regional scale shear zone systems clusters of deposits are common and they form 5 5 km domains spaced every 15 to 20 km in contrast there is also a linear trend of mineralization that can be traced continuously for 20 km along a shear zone in detail mineralization is found in a range of different rock types and is hosted in fault shear zone networks that are smaller than the adjacent regionalscale shear zones by several orders of magnitude a mixture of different fault types comprise these mineralized fault shear networks often within the same gold field although thrust and reverse faults are a common component of the richer deposits e g sunrise dam wallaby granny smith the seismogenic behavior of fault systems during mineralization can explain these observations illustrated by simple stress transfer models that show the location of aftershock distributions around different fault types strike slip ruptures on regional scale structures can repeatedly trigger restricted clusters of aftershocks these aftershock clusters describe vertical pipe like domains in three dimensions in contrast regional scale thrust or reverse ruptures trigger continuous more diffuse domains of aftershocks along the full strike of the rupture thus ruptures along regional strike slip structures are able to trigger ruptures on preexisting thrust faultsshears at the deposit scale when they do so the thrust aftershocks generate a vertical domain of elevated permeability over the depth of the crust where the individual flow paths are likely to be highly tortuous increasing the potential for fluid rock interaction or fluid mixing the existence of linear trends and cluster like distributions of deposits at laverton may be consistent with two different ages of mineralization in this gold camp the results also show that distributions of deposits provide an indication of the kinematics of the regional fault systems that they relate to and that stress transfer modeling is a simple non computationally demanding technique that is easily adapted to exploration for fault related mineral deposits

response of the san andreas fault to the 1983 coalinga nunez earthquakes an application of interaction based probabilities for parkfield 1 the parkfield cholame section of the san andreas fault site of an unfulfilled earthquake forecast in 1985 is the best monitored section of the world s most closely watched fault in 1983 the m 6 5 coalinga and m 6 0 nunez events struck 25 km northeast of parkfield seismicity rates climbed for 18 months along the creeping section of the san andreas north of parkfield and dropped for 6 years along the locked section to the south right lateral creep also slowed or reversed from parkfield south here we calculate that the coalinga sequence increased the shear and coulomb stress on the creeping section causing the rate of small shocks to rise until the added stress was shed by additional slip however the 1983 events decreased the shear and coulomb stress on the parkfield segment causing surface creep and seismicity rates to drop we use these observations to cast the likelihood of a parkfield earthquake into an interaction based probability which includes both the renewal of stress following the 1966 parkfield earthquake and the stress transfer from the 1983 coalinga events we calculate that the 1983 shocks dropped the 10 year probability of a m 6 parkfield earthquake by 22 from 54 22 to 42 23 and that the probability did not recover until about 1991 when seismicity and creep resumed our analysis may thus explain why the parkfield earthquake did not strike in the 1980s but not why it was absent in the 1990s we calculate a 58 17 probability of a m 6 parkfield earthquake during 2001 2011 index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 7260 seismology theory and modeling keywords coalinga earthquake parkfield stress change earthquake probability seismicity rate

evidence of a large triggered event in the nepal himalaya following the gorkha earthquake implications toward enhanced seismic hazard a dc double couple constrained multiple point source moment tensor inversion is performed on the band passed 0 008 0 10 hz displacement data of the 25 april mw 7 8 2015 nepal mainshock from 17 broadband stations in india our results reveal that the 25 april event strike 324 dip 14 rake 88 ruptured the north dipping main himalayan thrust mht at 16 km depth we modeled the coulomb failure stress changes cfs produced by the slip on the fault plane of the 25 april nepal mainshock a strong correlation with occurrences of aftershocks and regions of increased positive cfs is obtained below the aftershock zone of the 2015 nepal mainshock we notice that predicted cfs at 16 km depth show a positive coulomb stress of 0 06 mpa at the location of the 12 may 2015 event these small modeled stress changes can lead to trigger events if the crust is already near to failure but these small stresses can also advance the occurrence of future earthquakes the main finding of our cfs modeling implies that the 25 april event increased the coulomb stress changes by 0 06 mpa at 16 km depth below the site of the 12 may event and thus this event can be termed as triggered we propose that the seismic hazard in the himalaya is not only caused by the mainshock slip on the mht rather the occurrence of large triggered event on the mht can also enhance our understanding of the seismic hazard in the nepal himalaya

modeling seismicity rate changes during the 1997 umbria marche sequence central italy through a rate and state dependent model 1 we model the spatial and temporal pattern of seismicity during a sequence of moderate magnitude normal faulting earthquakes which struck in 1997 the umbria marche sector of northern apennines italy by applying the dieterich 1994 rate and state dependent constitutive approach the goal is to investigate the rate of earthquake production caused by repeated coseismic stress changes computed through a 3 d elastic dislocation model in a homogeneous half space the reference seismicity rate is assumed time independent and it is estimated by smoothing the seismicity that occurred in the previous decade without declustering we propose an analytical relation for deriving the stressing rate directly from the reference seismicity rate this allows us to perform a tuning of the constitutive parameter a where a accounts for the direct effect of friction in the rate and state dependent model and is the effective normal stress into the dieterich model through a maximum likelihood method which yields for this seismic sequence a best fitting value equal to 0 04 mpa our computations show that although seven out of eight main shocks are located in areas of increased rate of earthquake production numerous aftershocks are located in seismicity shadows our simulations point out that the adopted value of a strongly affects the pattern of both seismicity shadow and areas of enhanced rate of earthquake production we conclude that solely accounting for static stress changes caused by the main shocks of this seismic sequence is not sufficient to forecast the complex spatial and temporal evolution of seismicity

three dimensional model of the late cenozoic history of the death valley region southeastern california the accumulation of a large database on the timing and kinematics of late cenozoic deformation in the death valley region of southeastern california indicates a complex three dimensional history on the basis of paleogeographic reconstructions we suggest the system was initiated as a localized pull apart between two conjugate strike slip faults the garlock and furnace creek faults and evolved into a system characterized by distributed transtension related to the eastern california shear zone our reconstructions differ from previous models in the incorporation of significant vertical axis rotations of a number of crustal blocks to explain paleomagnetic data from the region the model may resolve 1 a long standing problem of the eastern termination of the garlock fault which is explained here as a complex system of splays that initially terminated in the pull apart between the furnace creek and garlock systems and 2 the complex architecture of the black mountains which is explained here in terms of initial extreme attenuation between the garlock and furnace creek systems with overprinting by a fold and normal fault system that operated simultaneously as a result of distributed transtension this model suggests much of the displacement field is taken up in rotations and translations and the actual crustal thinning in our model is relatively small 50 66 of original thickness

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

seismic cycle stress change in western taiwan over the last 270 years 1 the island of taiwan is affected by intense seismic activity which includes large events as the disastrous 1999 chi chi earthquake to improve seismic hazard assessment in this area we estimate the effect of both interseismic loading and major events since 1736 on the state of stress of major active faults we focus our approach on western taiwan which is the most densely populated part of taiwan we pay a specific attention to faults geometry and to both interseismic and coseismic slip distributions our results suggest that both earthquakes and interseismic loading before 1999 increase the coulomb stress in the north western part of the chelungpu fault a region which experienced the highest coseismic slip during the chi chi earthquake more importantly our results reveal a coulomb stress increase in the southern part of the changhua thrust fault below a densely populated area

an example of triggered earthquakes in western turkey 2000 2015 afyon aksehir graben earthquake sequences abstract we investigate significant earthquake sequences in the observation period between 2000 and 2015 along the afyon aksehir graben system in western anatolia these sequences include a series of strong events with moment magnitudes m w larger than 5 5 e g eber m w 5 8 sultandagi m w 6 5 and cay m w 5 8 earthquakes the mainshocks are shallow focus normal events at depths of 8 15 km focal depths of aftershocks range from 2 to 30 km the focal mechanisms of the aftershocks are mainly normal faulting with variable strike slip components the geometry of focal mechanisms reveals a normal faulting regime with nne ssw trending direction of t axis in the entire activated region a stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the afyon aksehir graben stress field the stress tensor inversion results display a predominant normal stress regime with a nw se oriented maximum horizontal compressive stress s h according to high resolution hypocenter relocations of the afyon aksehir graben seismic sequences six clusters are revealed the aftershock activities in the observation period between 17 january 2000 and 26 october 2015 extend from east to west direction seismic cross sections show that a complex pattern of the hypocenter distribution with the activation of sultandagi fault segments the western clusters are associated with a fault plane trending mainly e w and dipping towards se while the eastern clusters are related to a fault plane trending nw se and dipping towards vertical the best constrained focal depths are mainly confined in the crust depth

source mechanisms and stress fields of the 15 16 june 2013 crete earthquake sequence along hellenic subduction zone 15 june 2013 mw 6 1 off shore southern crete earthquake and its aftershock sequence along hellenic subduction zone are examined centroid moment tensors cmts for 40 earthquakes with moment magnitudes mw between 3 5 and 6 1 are determined by applying a waveform inversion method the mainshock is shallow focus thrust event with a minor strike slip component at a depth of 20 km the seismic moment mo of the mainshock is estimated as 2 07 1018 nm and rupture duration of the mainshock is 4 s the focal mechanisms of aftershocks are mainly thrust faulting with a strike slip component the geometry of the moment tensors mw 3 5 reveals a thrust faulting regime with n s trending direction of p axis in the entire activated region according to high resolution cmt solutions of the off shore southern crete earthquake sequence one main cluster consisting of 40 events is revealed the aftershock activity in the observation period between 15 june and 15 july 2013 extends from n to s and nw to se directions seismic cross sections indicate a complex pattern of the hypocenter distribution with the activation of two segments the subduction interface is clearly revealed with high resolution hypocenter source relocation and moment tensor solution the best constrained focal depths indicate that the aftershock sequence is mainly confined in the upper plate depth 30 km and is ranging from about 5 28 km depth a stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the off shore southern crete stress field the stress tensor inversion results indicate a predominant thrust stress regime with a ne sw oriented maximum horizontal compressive stress sh according to variance of the stress tensor inversion to first order the southern crete region is characterized by a homogeneous interplate stress field we also investigate the coulomb stress change associated with the mainshock to evaluate any significant enhancement of stresses along southern crete and surrounding regions positive lobes with stress more than 0 3 bars are obtained for the mainshock indicating that these values are large enough to increase the coulomb stress failure toward wnw ese direction

assessing vertical axis rotations in large magnitude extensional settings a transect across the death valley extended terrane california models for neogene crustal deformation in the central death valley extended terrane southeastern california differ markedly in their estimates of upper crustal extension versus shear translations documentation of vertical axis rotations of range scale crustal blocks or parts thereof is critical when attempting to reconstruct this highly extended region to better define the magnitude aerial extent and timing of vertical axis rotation that could mark shear translation of the crust in this area paleomagnetic data were obtained from tertiary igneous and remagnetized paleozoic carbonate rocks along a roughly east west traverse parallel to about 36 n latitude sites were established in 7 to 5 ma volcanic sequences greenwater canyon and brown s peak and the 10 ma chocolate sundae mountain granite in the greenwater range 8 5 to 7 5 ma and 5 to 4 ma basalts on the east flank of the black mountains the 10 6 ma little chief stock and upper miocene basalts in the eastern panamint mountains and paleozoic pogonip group carbonate strata in the north central panamint mountains at the site level most materials yield readily interpretable paleomagnetic data group mean directions after appropriate structural corrections suggest no major vertical axis rotation of the greenwater range e g d 359 i 46 95 8 0 n 12 7 normal n 5 reversed r polarity sites little post 5 ma rotation of the eastern black mountains e g d 006 i 61 95 4 0 n 9 n 6 r sites and no significant post 10 ma rotation of the panamint range e g d 181 i 51 95 6 5 n 9 r sites in situ data from the greenwater canyon volcanic rocks chocolate sundae mountain granite funeral peak basalt rocks the little chief stock and paleozoic carbonate rocks remagnetized are consistent with moderate south east side down tilting of the separate range blocks during northwest directed extension the paleomagnetic data reported here suggest that the panamints shared none of the 7 ma to recent clockwise rotation of the black mountains crystalline core as proposed in recent models for transtensional development of the central death valley extended terrane

the 16 april 2015 m w 6 0 offshore eastern crete earthquake and its aftershock sequence implications for local regional seismotectonics we examine the 16 april 2015 m w 6 0 offshore eastern crete earthquake and its aftershock sequence in southern aegean sea centroid moment tensors for 45 earthquakes with moment magnitudes m w between 3 3 and 6 0 are determined by applying a waveform inversion method the mainshock is shallow focus thrust event with a strike slip component at a depth of 30 km the seismic moment m o of the mainshock is estimated as 1 33 1018 nm and rupture duration of the mainshock is 3 5 s the focal mechanisms of aftershocks are mainly thrust faulting with a strike slip component the geometry of the moment tensors m w 3 3 reveals a thrust faulting regime with ne sw trending direction of t axis in the entire activated region according to high resolution hypocenter relocation of the eastern crete earthquake sequence one main cluster consisting of 352 events is revealed the aftershock activity in the observation period between 5 january 2015 and 7 july 2015 extends from n to s direction seismic cross sections indicate a complex pattern of the hypocenter distribution with the activation of three segments the subduction interface is clearly revealed with high resolution hypocenter relocation and moment tensor solution the best constrained focal depths indicate that the aftershock sequence is mainly confined in the upper plate depth 40 km and are ranging from about 4 5 to 39 km depth a stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the offshore eastern crete stress field the stress tensor inversion results indicate a predominant thrust stress regime with a nw se oriented maximum horizontal compressive stress s h according to variance of the stress tensor inversion to first order the crete region is characterized by a homogeneous interplate stress field we also investigate the coulomb stress change associated with the mainshock to evaluate any significant enhancement of stresses along crete and surrounding regions positive lobes with stress more than 3 bars are obtained for the mainshock indicating that these values are large enough to increase the coulomb stress failure toward ne sw and nw se directions respectively

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

aftershock modeling based on uncertain stress calculations 1 we discuss the impact of uncertainties in computed coseismic stress perturbations on the seismicity rate changes forecasted through a rate and state dependent frictional model we aim to understand how the variability of coulomb stress changes affects the correlation between predicted and observed changes in the rate of earthquake production we use the aftershock activity following the 1992 m7 3 landers california earthquake as a case study to accomplish these tasks we first analyze the variability of stress changes resulting from the use of different published slip distributions we find that the standard deviation of the uncertainty is of the same size as the absolute stress change and that their ratio the coefficient of variation cv is approximately constant in space this uncertainty has a strong impact on the forecasted aftershock activity if a rate and state frictional model is considered we use the early aftershocks to invert for friction parameters and the coefficient of variation by means of the maximum likelihood method we show that when the uncertainties are properly taken into account the inversion yields stable results which fit the spatiotemporal aftershock sequence the analysis of the 1992 landers sequence demonstrates that accounting for realistic uncertainties in stress changes strongly improves the correlation between modeled and observed seismicity rate changes for this sequence we measure a friction parameter asn 0 017 mpa and a coefficient of stress variation cv 0 95

a search for evidence of secondary static stress triggering during the 1992 mw7 3 landers california earthquake sequence secondary triggering of aftershocks is widely observed and often ascribed to secondary static stress transfer however small to moderate earthquakes are generally disregarded in estimates of coulomb stress changes cfs either because of source parameter uncertainties or a perceived lack of importance we use recently published high quality focal mechanisms and hypocenters to reassess the role of small to moderate earthquakes for static stress triggering of aftershocks during the 1992 mw7 3 landers california earthquake sequence we compare the cfs imparted by aftershocks 2 m 6 onto subsequent aftershocks with the total cfs induced by the m 6 main shocks we find that incremental stress changes between aftershock pairs are potentially more often positive than expected over intermediate distances cumulative aftershock stress changes are not reliable for receivers with nearby aftershock stress sources because we exclude unrealistic aftershock stress shadows that result from uniform slip models nonetheless 27 of aftershocks receive greater positive stress from aftershocks than from the main shocks overall 85 of aftershocks are encouraged by the main shocks while adding secondary stress encourages only 79 we infer that source parameter uncertainties of small aftershocks remain too large to convincingly demonstrate or rule out that secondary stress transfer induces aftershocks an important exception concerns aftershocks in main shock stress shadows well resolved secondary stress from detected aftershocks rarely compensates negative main shock stress these aftershocks require a different triggering mechanism

stress coupling between earthquakes in northwest turkey and the north aegean sea we have investigated the coulomb stress interactions of 29 earthquakes m s greater than or equal to 6 0 that have occurred in the region of northwest turkey and north aegean sea since 1912 of these events 23 may be related to earlier events and 16 are clearly related to earlier events all events after 1967 are related to previous events events in the early part of our time interval that show no correlation could be related to historical events as yet unidentified in some cases faults that have received a stress reduction from earlier events are prepared for an event by an earthquake occurring a few years before that creates a local coulomb stress rise thus regions of coulomb stress shadow can become regions where a damaging earthquake may occur the relation between smaller events and the coulomb stress distribution is less clear but may be related to poor data quality and practical limitations of our modeling technique nonetheless there are 4 times as many events per unit area in regions of enhanced stress than where stress is reduced we discuss the contemporary distribution of coulomb stress and argue that it is possible to identify the likely locations of future damaging earthquakes including identifying the most likely candidate faults

the 10 june 2012 fethiye mw 6 0 aftershock sequence and its relation to the 24 25 april 1957 ms 6 9 7 1 earthquakes in sw anatolia turkey abstract the 10 june 2012 mw 6 0 aftershock sequence in southwestern anatolia is examined centroid moment tensors for 23 earthquakes with moment magnitudes mw between 3 7 and 6 0 are determined by applying a waveform inversion method the mainshock is a shallow focus strike slip with reverse component event at a depth of 30 km the seismic moment mo of the mainshock is estimated as 1 28 1018 nm and rupture duration of the fethiye mainshock is 38 s the focal mechanisms of the aftershocks are mainly strike slip faulting with a reverse component the geometry of the focal mechanisms reveals a strike slip faulting regime with ne sw trending direction of t axis in the entire activated region a stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the fethiye earthquake stress field the stress tensor inversion results indicate a predominant strike slip stress regime with a nw se oriented maximum horizontal compressive stress sh according to variance of the stress tensor inversion to first order the fethiye earthquake area is characterized by a homogeneous interplate stress field the coulomb stress change associated with the mainshock and the largest aftershock are also investigated to evaluate any significant enhancement of stresses along the gulf of fethiye and surrounding region positive lobes with stress more than 0 4 bars are obtained indicating that these values are large enough to increase the coulomb stress failure towards nnw sse and e w directions

methods for measuring seismicity rate changes a review and a study of how the m w 7 3 landers earthquake affected the aftershock sequence of the m w 6 1 joshua tree earthquake the development of fault interaction models has triggered the need for an accurate estimation of seismicity rate changes following the occurrence of an earthquake several statistical methods have been developed in the past to serve this purpose each relying on different assumptions e g stationarity gaussianity pertaining to the seismicity process

a new hypothesis for the amount and distribution of dextral displacement along the fish lake valley northern death valley furnace creek fault zone california nevada 1 the fish lake valley northern death valley furnace creek fault zone a 250 km long predominantly right lateral structure in california and nevada is a key element in tectonic reconstructions of the death valley area eastern california shear zone and walker lane and central basin and range province total displacement on the fault zone is contested however with estimates ranging from 30 to 63 km or more here we present a new synthesis of available constraints preextensional thrust faults folds and igneous rocks indicate that offset reaches a maximum of 50 km neogene rocks constrain its partitioning over time most offset is interpreted as 13 10 ma accruing at 3 5 mm yr in the middle of the fault zone and more slowly toward the tips the offset markers imply 68 14 km of translation between the cottonwood mountains and resting spring nopah range 60 14 km since 15 ma through a combination of strike slip and crustal extension this suggests that a previous interpretation of 104 7 km based on the middle miocene eagle mountain formation is an overestimate by 50 our results also help to mitigate a discrepancy in the 12 0 ma strain budget for the eastern california shear zone displacement has previously been estimated at 100 10 km and 67 6 km for the basin and range and mojave portions of the shear zone respectively our new estimate of 74 17 km for the basin and range is within the uncertainty of the mojave estimate

probing coulomb stress triggering effects for a mw 6 0 earthquake sequence from 1997 to 2014 along the periphery of the bayan har block on the tibetan plateau abstract recently there have occurred the manyi kangding earthquake sequence including the 1997 manyi 2001 kokoxili 2008 yutian 2008 wenchuan 2010 yushu 2013 lushan 2014 yutian and 2014 kangding earthquakes along the periphery of the bayan har block on the northern tibetan plateau we employ the coulomb failure model to probe the stress triggering effects on this sequence in terms of coseismic postseismic and interseismic coulomb stress changes we examine the coulomb stress changes from both the manyi kangding sequence and other large earthquakes from 1411 to 2012 around the bayan har block and interseismic tectonic stressing we use a stratified spherical postseismic relaxation model to compute postseismic coulomb stress changes we develop an explicit spherical least squares collocation model to calculate interseismic coulomb stress changes our results indicate that when merely considering triggering effects because of earthquakes from the manyi kangding sequence the compounded coulomb stress changes of the coseismic and postseismic coulomb stress changes are generally insignificant except for the 2013 lushan earthquake 0 14 bar this general insignificance of coulomb stress changes imparted by the manyi kangding sequence agrees with previous studies although interseismic coulomb stress changes always load each hypocenter on the other hand when surrounding prior m 6 0 earthquakes are considered we found that the compounded coulomb stress changes become significant ranging from 0 14 to 10 4 bars according to the constant apparent friction coulomb failure model with an intermediate coefficient of 0 4 therefore all eight earthquakes are well explained by coulomb stress changes when thoroughly considering large earthquakes around the bayan har block our findings indicate the importance of considering a broader group of neighboring large earthquakes for coulomb stress analysis

sensitivity of static stress calculations to the earthquake slip distribution 1 the apparent strong correlation between coulomb stress changes and the spatial distribution of aftershocks suggests the possibility of making near real time estimations of areas at risk of experiencing off fault aftershocks in order to do this in practice a number of issues must first be addressed including the extent to which the main shock slip must be known in detail before a meaningful stress map can be constructed here we investigate this issue by constructing a time ordered sequence of slip solutions for the landers earthquake computing coulomb stress changes for each solution and quantitatively comparing the stress field with the observed aftershocks by 1 resolving the coulomb stress change onto the aftershock nodal planes and calculating the percentage of events consistent with triggering and 2 constructing a two dimensional map of coulomb stress and computing the correlation coefficient between the positive and negative areas and the locations of the aftershocks we find that slip solutions based on empirical relations and either focal mechanism or moment tensor data produce stress fields inconsistent with the observed spatial distribution of aftershocks whereas slip solutions incorporating the correct rupture geometry but greatly simplified slip produce stress fields consistent with the aftershock distribution when very near fault events are excluded we further find that resolving stress perturbations onto earthquake nodal planes and computing the percentage of events experiencing positive coulomb stress provides a poor measure of success because of the limited range of structures on which events occur and the compatibility of the main shock stress field with these structures our results support the hypothesis that coulomb stress changes affect the spatial distribution of aftershocks and suggest that meaningful calculations of coulomb stress can be made as soon as an earthquake s rupture geometry is well constrained

assessing elastic coulomb stress transfer models using seismicity rates in southern california and southwestern japan 1 we investigated whether observed changes in seismicity rate following the 1992 landers and 1995 kobe earthquakes correspond with predictions from coulomb stress transfer models to quantify the relationship between coulomb stress change and seismicity rate change we compared spatial changes in observed seismicity rates to the modeled changes in coulomb failure stress cfs for the two subject earthquakes we begin with the simplest and most common cfs model which assumes that regional stress orientations are uniform and the stress change is resolved on optimally oriented strike slip planes we then extended the cfs models to include the more geophysically realistic assumptions of spatially varying regional stress orientations and optimally oriented planes in three dimensions for all the tested cfs models we found that virtually everywhere seismicity rate changes could be resolved the rate increased regardless of whether the cfs theoretically promoted or inhibited failure and that we were not able to reliably resolve seismicity rate decreases an improvement in the correlation between the sign of the cfs and where rate increases occur when estimating the cfs on optimally oriented planes in three dimensions rather than two dimensions is a consequence of using optimally oriented planes and the ability to primarily observe rate increases the region of positive cfs increases by allowing more degrees of freedom so the correlation with positive rate change appears to increase the areas of highest seismicity rate following the main shock did not correlate with the sign or the magnitude of the cfs rather the areas most active after the main shock were also the most active before the main shock

electrical conductivity images of quaternary faults and tertiary detachments in the california basin and range comparison of an electrical resistivity section derived from magnetotelluric mt data to a geologic section extending eastward from the sierra nevada near latitude 36 20 n shows that the crust is dominated by steeply dipping conductive features that correlate with active strike slip faults while there is a subhorizontal conductor at a depth 20 km beneath some of the profile it is broken by vertical structures associated with the active strike slip faults the continuous subhorizontal anomalies in the lower crust typically observed in extensional regions are therefore absent in the resistivity section the present day strike slip tectonic regime as indicated by geodetic data in this part of the basin and range is not producing features that could be inferred to indicate subhorizontal shear zones resulting from lateral crustal flow during extension because the miocene tectonic regime resulted in the formation of metamorphic core complexes and thus was accompanied by such flow the present regime appears to represent a fundamental transition in the mode of crustal deformation in the region a serendipitous result of our study was the identification on resistivity sections of carbonate aquifers in the upper crust comparison of resistivities from the mt section to measured fluid resistivities from springs and boreholes suggests that the aquifers must be heterogeneous with more saline brines occupying the deepest portions of the carbonates

seismotectonics of the antalya basin and surrounding regions in eastern mediterranean from 8 to 28 december 2013 mw 5 0 5 8 earthquake sequence abstract the 8 28 december 2013 mw 5 0 5 8 antalya basin earthquake sequence in eastern mediterranean is examined centroid moment tensors for 16 earthquakes with moment magnitudes mw between 3 6 and 5 8 are determined by applying a waveform inversion method all earthquakes are shallow focus thrust events at a depth of 40 45 km the seismic moments mo of the earthquakes are estimated as 4 10 1016 5 54 1017 n m and rupture durations of the mainshocks are 20 22 s the focal mechanisms of the aftershocks are mainly thrust faulting with a strike slip component and reveal nw se trending direction of t axis in the entire activated region according to high resolution hypocenter relocation of the antalya earthquake sequence seven main clusters are revealed the aftershock activity in the observation period between 1 december 2013 and 23 january 2015 extends in an n to s direction a seismic cross section indicates that a complex pattern of the hypocenter distribution with the activation of seven segments the westernmost cluster cluster 1 is associated with a fault plane trending mainly wnw ese and dipping vertical while the cluster 5 is related to a fault plane trending nne ssw and dipping towards sse the best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust depth

uraniferous bitumen nodules in the talvivaara ni zn cu co deposit finland influence of metamorphism on uranium mineralization in black shales in the central part of the fennoscandian shield the talvivaara ni zn cu co deposit hosted by palaeoproterozoic metamorphosed black schists contains low uranium concentrations ranging from 10 to 30 ppm the talvivaara black schists were deposited 2 0 1 9 ga ago and underwent subsequent metamorphism during the 1 9 1 79 ga svecofennian orogeny anhedral uraninite crystals rimmed by bitumen constitute the main host of uranium u pb secondary ion mass spectrometry dating indicates that uraninite crystals were formed between 1 878 17 and 1 871 43 ma during peak metamorphism rare earth element patterns and high th content average 6 38 wt in disseminated uraninite crystals indicate that u was concentrated during high temperature metamorphism 400 c the formation of bitumen rims around uraninite may be explained by two distinct scenarios a a transport of u coincident with the migration of hydrocarbons or b post metamorphic formation of bitumen rims through radiolytic polymerization of gaseous hydrocarbons at the contact with uraninite

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

stress history controls the spatial pattern of aftershocks case studies from strike slip earthquakes earthquake ruptures perturb stress within the surrounding crustal volume and as it is widely accepted now these stress perturbations strongly correlates with the following seismicity here we have documented five cases of the mainshock aftershock sequences generated by the strike slip faults from different tectonic environments of world in order to demonstrate that the stress changes resulting from large preceding earthquakes decades before effect spatial distribution of the aftershocks of the current mainshocks the studied mainshock aftershock sequences are the 15 october 1979 imperial valley earthquake mw 6 4 in southern california the 27 november 1979 khuli boniabad mw 7 1 the 10 may 1997 qa enat mw 7 2 and the 31 march 2006 silakhor mw 6 1 earthquakes in iran and the 13 march 1992 erzincan earthquake mw 6 7 in turkey in the literature we have been able to find only these mainshocks that are mainly characterized by dense and strong aftershock activities along and beyond the one end of their ruptures while rare aftershock occurrences with relatively lower magnitude reported for the other end of their ruptures it is shown that the stress changes resulted from earlier mainshock s that are close in both time and space might be the reason behind the observed aftershock patterns the largest aftershocks of the mainshocks studied tend to occur inside the stress increased lobes that were also stressed by the background earthquakes and not to occur inside the stress increased lobes that fall into the stress shadow of the background earthquakes we suggest that the stress shadows of the previous mainshocks may persist in the crust for decades to suppress aftershock distribution of the current mainshocks considering active researches about use of the coulomb stress change maps as a practical tool to forecast spatial distribution of the upcoming aftershocks for earthquake risk mitigation purposes in near real time it is further suggested that the background mainshocks along the neighbouring faults should be taken into account in producing the stress change maps for commenting on aftershock occurrences

stress triggering and the canterbury earthquake sequence the canterbury earthquake sequence which includes the devastating christchurch event of 2011 february has to date led to losses of around 40 billion nz dollars the location and severity of the earthquakes was a surprise to most inhabitants as the seismic hazard model was dominated by an expected mw 8 earthquake on the alpine fault and an mw 7 5 earthquake on the porters pass fault 150 and 80 km to the west of christchurch the sequence to date has included an mw 7 1 earthquake and 3 mw 5 9 events which migrated from west to east here we investigate whether the later events are consistent with stress triggering and whether a simple stress map produced shortly after the first earthquake would have accurately indicated the regions where the subsequent activity occurred we find that 100 per cent of m 5 5 earthquakes occurred in positive stress areas computed using a slip model for the first event that was available within 10 d of its occurrence we further find that the stress changes at the starting points of major slip patches of post darfield main events are consistent with triggering although this is not always true at the hypocentral locations our results suggest that coulomb stress changes contributed to the evolution of the canterbury sequence and we note additional areas of increased stress in the christchurch region and on the porters pass fault

stress change and effective friction coefficient along the sumatra andaman sagaing fault system after the 26 december 2004 m w 9 2 and the 28 march 2005 m w 8 7 earthquakes the 2004 aceh and 2005 nias events are the two greatest earthquakes of the past 40 years with a total rupture of 1700 km long and a coseismic slip reaching up to 25 m these two earthquakes have caused large stress perturbations which significantly altered seismic activity in the sumatra andaman region using both detailed mapping of failure planes and various slip distributions we calculate this stress change along the sumatra andaman sagaing fault system from central sumatra to southern myanmar the static coulomb stress change delta cff and the observed seismic activity are in very good agreement with a coulomb index similar to 20 greater than the one obtained for random events compared to previous studies this high coulomb index confirms two important issues on the use of static stress change criterion unsuited to study near field aftershocks and only relevant for aftershocks analysis on large and mature faults at a time scale of several months the calculated delta cff distribution suggests that the 2004 and 2005 earthquakes inhibit failure on the north andaman rift and on the sagaing fault while failure is encouraged along the transform andaman zone the central andaman rift the west andaman fault the sumatra fault system and the offshore thrust faults west of sumatra island the maximum value of similar to 15 20 bar 1 5 2 mpa for delta cff is reached in the northern part of the sumatra fault system this high value together with the lack of major earthquake in the last 170 years result in a high seismic hazard for this region our results are also consistent with temporal evolution of both earthquakes location and focal mechanism prior to and after the events in particular we explain the occurrence and the mechanism of seismic swarms observed in the central andaman rift and along the west andaman fault finally our calculations reveal that the seismicity in the andaman rift zone can only be explained if mu 0 5 this result leads to two end member models one with a constant and high fault friction and one with spatial variations for which friction may depend on either the nature of the lithosphere oceanic versus continental or the fault type

impact of the receiver fault distribution on aftershock activity 1 aftershock models are usually based either on purely empirical relations ignoring the physical mechanism or on deterministic calculations of stress changes on a predefined receiver fault orientation here we investigate the effect of considering more realistic fault systems in models based on static coulomb stress changes for that purpose we perform earthquake simulations with elastic half space stress interactions rate and state dependent frictional earthquake nucleation and extended ruptures with heterogeneous fractal slip distributions we find that the consideration of earthquake nucleation on multiple receiver fault orientations does not influence the shape of the temporal omori type aftershock decay but changes significantly the predicted spatial patterns and the total number of triggered events so called stress shadows with decreased activity almost vanish and activation decays continuously with increasing distance from the main shock rupture the total aftershock productivity which is shown to be almost independent of the assumed background rate increases significantly if multiple receiver fault planes exist the application to the 1992 m7 3 landers california aftershock sequence indicates a good agreement with the locations and the total productivity of the observed directly triggered aftershocks

structural constraints on the spatial distribution of aftershocks 1 calculations of static stress changes due to large earthquakes have shown that the spatial distribution of aftershocks is predictable to first order with aftershocks primarily occurring in areas experiencing positive stress changes delineation of these areas relies on resolving the stress perturbation onto planes with known orientations common practice is to use poorly constrained regional stress information to compute optimally oriented failure planes assuming that they exist everywhere here we show that this assumption is not supported by observation but rather that aftershock failure planes are controlled by geological structure we argue that useful aftershock hazard estimates are better made by replacing information on regional stress with statistical measures of structural orientations

interpretation and tectonic implications of cooling histories an example from the black mountains death valley extended terrane california abstract in the death valley extended terrane of california the black mountains have long been considered unique because they largely lack the miogeoclinal cover rocks characteristic of the surrounding ranges fission track ages presented here are combined with published40ar 39ar ages and used to construct cooling path envelopes for samples of precambrian crystalline basement and miocene plutonic rocks collected across the entire range the cooling history reconstructions are used to differentiate between contrasting miocene unroofing histories proposed for this range apatite and zircon fission track ages from the southeastern portion of the range suggest unroofing occurred there at 13 8 5 ma from temperatures well below 300 c cooling age data from the central black mountains indicate major unroofing at 8 5 6 0 ma from temperatures greater than 300 c old cooling ages from directly beneath the highly extended amargosa chaos rocks are consistent with the chaos rocks being part of an allochthonous slice that was tectonically transported from high crustal levels onto deeper crustal levels scenarios for the miocene unroofing history of this range rely heavily on interpretations of the depth of emplacement of miocene plutons in the core of the range thermochronologic and geobarometric data and thermal modeling of intrusion cooling suggest emplacement of an 11 6 ma pluton into the crystalline core at a depth of 10 15 km both the cooling age data and considerations of the local geology seem to preclude an unroofing history dominated by erosion of the overlying miogeoclinal section the morphology of the cooling path envelopes constructed here are similar to those constructed for detachment fault terranes the data are most consistent with unroofing involving tectonic denudation 10 15 km along a single westerly dipping detachment zone diachronous rapid cooling from southeast to northwest within the range is interpreted as a result of the lower plate undergoing flexural deformation as it pulls out from underneath a relatively rigid scoop shaped hanging wall block the rolling hinge model migration of unroofing and tilting within the range mimics the overall east to west sequential tilting and unroofing of range blocks in the death valley extended terrane similar thermochronologic evidence for sequential range scale tilting has been obtained from the lake mead extended region suggesting that this style of extension might provide an explanation for strongly extended domains in the basin and range province

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

static stress impact of the 1992 landers earthquake sequence on nucleation and slip at the site of the 1999 m 7 1 hector mine earthquake southern california the proximity in time 7 years and space 20 km between the 1992 m 7 3 landers earthquake and the 1999 m 7 1 hector mine event suggests a possible link between the quakes we thus calculated the static stress changes following the 1992 joshua tree landers big bear earthquake sequence on the 1999 m 7 1 hector mine rupture plane in southern california resolving the stress tensor into rake parallel and fault normal components and comparing with changes in the post landers seismicity rate allows us to estimate a coefficient of friction on the hector mine plane seismicity following the 1992 sequence increased at hector mine where the fault was unclamped this increase occurred despite a calculated reduction in right lateral shear stress the dependence of seismicity change primarily on normal stress change implies a high coefficient of static friction 0 8 we calculated the coulomb stress change using 0 8 and found that the hector mine hypocenter was mildly encouraged 0 5 bars by the 1992 earthquake sequence in addition the region of peak slip during the hector mine quake occurred where coulomb stress is calculated to have increased by 0 5 1 5 bars in general slip was more limited where coulomb stress was reduced though there was some slip where the strongest stress decrease was calculated interestingly many smaller earthquakes nucleated at or near the 1999 hector mine hypocenter after 1992 but only in 1999 did an event spread to become a m 7 1 earthquake

onto what planes should coulomb stress perturbations be resolved 1 coulomb stress maps are produced by computing the tensorial stress perturbation due to an earthquake rupture and resolving this tensor onto planes of a particular orientation it is often assumed that aftershock fault planes are optimally oriented in other words the regional stress and coseismic stress change are used to compute the orientation of planes most likely to fail and the coseismic stress is resolved onto these orientations this practice assumes that faults capable of sustaining aftershocks exist at all orientations an assumption contradicted by the observation that aftershock focal mechanisms have strong preferred orientations consistent with mapped structural trends here we systematically investigate the best planes onto which stress should be resolved for the landers hector mine loma prieta and northridge earthquakes by quantitatively comparing observed aftershock distributions with stress maps based on optimally oriented planes two and three dimensional main shock orientation and regional structural trend we find that the best model differs between different tectonic regions but that in all cases models that incorporate the regional stress field tend to produce stress maps that best fit the observed aftershock distributions although not all such models do so equally well our results suggest that when the regional stress field is poorly defined or in structurally complex areas the best model may be to fix the strike of the planes upon which the stress is to be resolved to that of the main shock but allow the dip and rake to vary

response of the san jacinto fault zone to static stress changes from the 1992 landers earthquake we perform an analysis of the seismicity response of the san jacinto fault zone to static coulomb stress changes from the 1992 landers earthquake sequence results show that in general stress changes forecast rate changes well we find a significant positive correlation between the change in rate and the magnitude of the coulomb stress change with a correlation coefficient of 0 76 equivalent to 5 6 when compared to a 0 null hypothesis furthermore although the correlations are less clear over negative than positive stress changes there is evidence of some coulomb stress dependent quiescence on stress shadows models that account for heterogeneity in reference seismicity show clear improvements in their predictions of spatial variability of aftershock rates compared to those that assume uniform reference we find also that better performance is obtained 1 using a time dependent coulomb rate state model compared to a time independent exponential model and 2 using structurally constrained rather than optimal target fault orientations these results are an important step in the validation of coulomb stress based methods for quantitative seismicity forecasting we conclude that the correspondence between the predictions of coulomb stress models for aftershock seismicity may be sensitive to strong heterogeneity in aftershock locations and orientations associated with the presence of large scale structure in aftershock study areas in these cases we suggest that where the regional structure is mapped incorporating it explicitly into coulomb stress models may improve the performance of quantitative coulomb stress based forecasts

estimating rate and state friction parameters using a two node stochastic model for aftershocks abstract the well known omori and modified omori omori utsu empirical formulae describe the decay in the rate of occurrence of aftershocks dieterich s rate and state dependent constitutive law for aftershock production produces a similar temporal formula with physically interpretable parameters such as the shear stressing rates the normal stress and a fault constitutive parameter this naturally leads to an interest in estimating these parameters from earthquake catalogs which requires a simpler stochastic model an alternative to the epidemic type aftershock sequence etas model is the two node seismic transfer and release model where one node represents the mainshock process and a secondary node represents the aftershock zone the aftershock decay rate in the two node model equals that derived from dieterich s rate and state dependent constitutive law and the inclusion of aseismic slip in the aftershock zone allows for values of p 1 in the best matching modified omori law the two node model can be easily fitted to aftershock data and has an application to aftershock stacking for estimating p values the equivalence between the rate and state and two node aftershock rates forms a bridge between a formula derived from physical considerations and a phenomenological stochastic model we show how this can be exploited by identifying physical units for the parameters in the latter to estimate the fault constitutive parameters and the stressing rates in dieterich s formula through a best fit inversion on real aftershock sequences the procedure is illustrated using data from four japanese earthquakes

static stress changes induced by the magmatic intrusions during the 2002 2003 etna eruption 1 the shallow intrusive processes that occurred during 2002 2003 etna eruption as well as the complex interaction between the magma intrusive events and the tectonic response of the volcano s eastern flank are investigated with numerical deformation modeling and the estimation of changes in the static coulomb stress ground deformation and volcanologic evidence clearly indicate a composite mechanism of intrusion on both the southern and northeastern flanks of the volcano geodetic data inversions have been based on a homogeneous elastic half space model although geological data and seismic tomography indicate that mt etna is elastically inhomogeneous and that rigidity layering and heterogeneities are likely to affect the magnitude and pattern of the deformation field to account for topographic effects as well as a complicated distribution of material properties we use the finite element method fem to provide a more realistic model the presence of medium heterogeneity strongly affects the amplitudes of the static stress changes seismicity matches well the areas of positive increase in the static stress caused by the intrusive events along the southern and northeastern flanks the changes in the state of stress generated by the southern dike produce an extensional stress field that favors magma propagation along the north east rift the highest seismic releases were associated with the activation of two fault systems the timpe fault system and the pernicana fault the static stress changes resolved onto these faults indicate that the magma intrusions on the southern and northeastern flanks encouraged these seismogenic structures to slip

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

stress accumulation and increased seismic risk in eastern turkey abstract unlike the north anatolian fault zone which has produced 11 large earthquakes since 1939 the east anatolian fault zone eafz has been relatively quiescent in the last century when compared to historical records and has therefore accumulated significant stresses along its length determination of the location and likely magnitude of a future probable earthquake along the eafz is of interest both because of this history of large earthquakes m 8 and the density of population in the area here we calculate stress evolution along the fault zone due to both seismic and tectonic loading since 1822 a sequence of 10 well constrained historical earthquakes is selected and the resulting stresses are calculated summed with tectonic loading stresses and resolved onto the mapped active faults we identify two areas of particular seismic risk one of which might be expected to yield a large event our results are sensitive to the previous history of large earthquakes in the region and indicate a need for detailed investigations to constrain the exact rupture geometries of previous earthquakes on these segments

widespread seismicity excitation throughout central japan following the 2011 m 9 0 tohoku earthquake and its interpretation by coulomb stress transfer 1 we report on a broad and unprecedented increase in seismicity rate following the m 9 0 tohoku mainshock for m 2 earthquakes over inland japan parts of the japan sea and izu islands at distances of up to 425 km from the locus of high 15 m seismic slip on the megathrust such an increase was not seen for the 2004 m 9 1 sumatra or 2010 m 8 8 chile earthquakes but they lacked the seismic networks necessary to detect such small events here we explore the possibility that the rate changes are the product of static coulomb stress transfer to small faults we use the nodal planes of m 3 5 earthquakes as proxies for such small active faults and find that of fifteen regions averaging 80 by 80 km in size 11 show a positive association between calculated stress changes and the observed seismicity rate change 3 show a negative correlation and for one the changes are too small to assess this work demonstrates that seismicity can turn on in the nominal stress shadow of a mainshock as long as small geometrically diverse active faults exist there which is likely quite common