block models of crustal motion in southern california constrained by gps measurements 1 we estimate slip rates on major active faults in southern california using a block model constrained by global positioning system measurements of interseismic deformation the block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle our estimates of the right lateral strike slip rate on the san andreas fault vary by at least a factor of 5 from a high of 35 9 0 5 mm yr in the carrizo plain to a low of 5 1 1 5 mm yr through the san bernadino segment shortening across the puente hills thrust and left lateral slip on the raymond hill fault are consistent with both thickening and escape tectonics in the los angeles basin discrepancies between geodetic and geologic slip rate estimates along the san andreas and san jacinto faults as well as in the eastern california shear zone may be explained by a temporal change in fault system behavior we find no substantial evidence for long term postseismic relaxation and infer that the viscosity of the lower crust upper mantle may be relatively high 1019 pa s

accelerated stress buildup on the southern san andreas fault and surrounding regions caused by mojave desert earthquakes a sequence of four mw 6 earthquakes including the 1992 mw 5 7 3 landers and mw 5 7 1 hector mine earthquakes occurred in the mojave desert in the 1990s in close proximity to the southern san andreas fault inducing stress changes on several of its segments we calculate that coseismic slip combined with postseismic relaxation of viscous lower crust and or upper mantle has led to a coulomb stress increase of 2 3 3 5 bar on the san bernardino mountain segment of the southern san andreas fault between 1992 and 2001 with a projected increase of 3 6 4 9 bar by the year 2020 in comparison the calculated coseismic stress increase is 1 8 bar for this segment this accelerated buildup of stresses is predicted to bring the san bernardino mountain segment which last ruptured more than 190 yr ago closer to a potentially major rupture meanwhile we project a net stress decrease of as much as 23 5 bar between 1992 and 2020 for the western coachella valley segment if the fault is governed by low effective friction or an increase of 1 5 bar if the fault is governed by high effective friction coulomb stresses are calculated to decrease on the mojave segment by as much as 21 bar between 1992 and 2020 accelerated stress buildup is also predicted to occur on parts of the san jacinto elsinore and calico faults the pattern of the observed post landers aftershock clustering and the calculated coulomb stress buildup on the calico fault is similar to that noted in the hector mine region prior to the 1999 mw 5 7 1 earthquake these results imply that the stress changes caused by an earthquake may still play a role in triggering future quakes in neighboring crust many years later through viscoelastic processes

nonlinear dynamical triggering of slow slip on simulated earthquake faults with implications to earth 1 among the most fascinating recent discoveries in seismology are the phenomena of dynamically triggered fault slip including earthquakes tremor slow and silent slip during which little seismic energy is radiated and low frequency earthquakes dynamic triggering refers to the initiation of fault slip by a transient deformation perturbation most often in the form of passing seismic waves determining the frictional constitutive laws and the physical mechanism s governing triggered faulting is extremely challenging because slip nucleation depths for tectonic faults cannot be probed directly of the spectrum of slip behaviors triggered slow slip is particularly difficult to characterize due to the absence of significant seismic radiation implying mechanical conditions different from triggered earthquakes slow slip is often accompanied by nonvolcanic tremor in close spatial and temporal proximity the causal relationship between them has implications for the properties and physics governing the fault slip behavior we are characterizing the physical controls of triggered slow slip via laboratory experiments using sheared granular media to simulate fault gouge granular rock and glass beads are sheared under constant normal stress while subjected to transient stress perturbation by acoustic waves here we describe experiments with glass beads showing that slow and silent slip can be dynamically triggered on laboratory faults by ultrasonic waves the laboratory triggering may take place during stable sliding constant friction and slip velocity and or early in the slip cycle during unstable sliding stick slip experimental evidence indicates that the nonlinear dynamical response of the gouge material is responsible for the triggered slow slip

stress changes modelled for the sequence of strong earthquakes in the south iceland seismic zone since 1706 the south iceland seismic zone is roughly speaking situated between two sections of the mid atlantic ridge i e the reykjanes ridge southwest of iceland and the eastern volcanic zone on the island it is a transform zone where earthquakes are expected to occur on e w trending left lateral shear faults equivalent to conjugate n s oriented right lateral rupture planes in fact earthquakes take place on en echelon n s oriented faults which is indicated by the distribution of main shock intensities aftershocks as well as by surface fault traces the stress field continuously generated in the fault zone by opening of the adjacent ridges is computed and superimposed on the stress field changes induced by a series of 13 earthquakes m 6 between 1706 and 2000 the level of the pre seismic stress field is analysed as well as the size of the area under high stress finally the post seismic stress field of june 2000 is analysed to see where high stresses might have accumulated the modelling indicates that the rupture planes located on separated parallel n s striking zones are dense enough to lead to an area wide stress release by the series of events the obtained pre seismic stress level for most events is high and stable with the exception of situations when several strong shocks occur over a time span of several days i e display typical main shock aftershock patterns the size of areas under high stress aside from of the rupture plane i e where no event occurs at the specific time is of medium to small size

holocene turbidites record earthquake supercycles at a slow rate plate boundary ongoing evidence for earthquake clustering calls for records of numerous earthquake cycles to improve seismic hazard assessment especially where recurrence times overstep historical records we show that most turbidites emplaced at the africa eurasia plate boundary off west algeria over the past 8 k y correlate across sites fed by independent sedimentary sources requiring a regional trigger correlation with paleoseismic data inland and ground motion predictions support that m 7 earthquakes have triggered the turbidites the bimodal distribution of paleo events supports the concepts of earthquake supercycles and rupture synchronization between nearby faults 13 paleo earthquakes underpin clusters of 3 6 events with recurrence intervals of 300 600 yr separated by periods of quiescence of 1 6 k y without major events on other faults over the study area this implies broad phases of strain loading alternating with phases of strain release our results suggest that fault slip rates are time dependent and call for revising conventional seismic hazard models

pulsed strain release on the altyn tagh fault northwest china abstract earthquake recurrence models assume that major surface rupturing earthquakes are followed by periods of reduced rupture probability as stress rebuilds although purely periodic time or slip predictable rupture models are known to be oversimplifications a paucity of long records of fault slip clouds understanding of fault behavior and earthquake recurrence over multiple ruptures here we report a 16 kyr history of fault slip including a pulse of accelerated slip from 6 4 to 6 0 ka determined using a monte carlo analysis of well dated offset landforms along the central altyn tagh strike slip fault atf in northwest china this pulse punctuates a median rate of 8 1 1 2 0 9 mm a and likely resulted from either a flurry of temporally clustered mw 7 5 ground rupturing earthquakes or a single large mw 8 2 earthquake the clustered earthquake scenario implies rapid re rupture of a fault reach 195 km long and indicates decoupled rates of elastic strain energy accumulation versus dissipation conceptualized as a crustal stress battery if the pulse reflects a single event slip magnitude scaling implies that it ruptured much of the atf with slip similar to or exceeding the largest documented historical ruptures both scenarios indicate fault rupture behavior that deviates from classic time or slip predictable models

fault slip distribution of two june 2000 m w 6 5 earthquakes in south iceland estimated from joint inversion of insar and gps measurements abstract we present the first detailed estimates of co seismic slip distribution on faults in the south iceland seismic zone sisz an area of bookshelf tectonics we have estimated source parameters for two m w 6 5 earthquakes in the sisz on june 17 and 21 2000 through a joint inversion of insar and gps measurements our preferred model indicates two simple 15 km long near vertical faults extending from the surface to approximately 10 km depth the geometry is in good agreement with the aftershock distribution the dislocations experienced pure right lateral strike slip reaching maxima of 2 6 m and 2 9 m for the june 17 and 21 events respectively we find that the distribution of slip with depth may be correlated to crustal layering with more than 80 of the total geometric moment release occurring in the uppermost 6 km according to the distributed slip model the middle and upper crust appears to be more apt to generate large displacements than the lower crust the geodetic estimates of seismic moments are 4 4 10 18 nm m w 6 4 and 5 0 10 18 nm m w 6 5 the total moment released by the two events equals that generated by several decades of plate motion in the area but is only a fraction of the moment accumulated in the area since the last major earthquake in 1912

evidence for paleoseismic slip on a continental low angle normal fault tectonic pseudotachylyte from the west salton detachment fault ca usa abstract the potential of continental low angle normal faults lanf to nucleate large 6 0 m w earthquakes at low angles remains unclear despite much focused research we document evidence for ancient seismicity along a continental lanf detachment fault that formed and slipped at low angles and produced tectonic pseudotachylyte these thick and laterally persistent pseudotachylyte accumulations along the west salton detachment fault wsdf salton trough usa preserve convincing evidence for a frictional melt origin including spherulitic microlites ductile flow structures preservation of high temperature phases as clasts and injection veins cumulative thickness of pseudotachylyte along the fault ranges from 0 1 to 1 5 m and pseudotachylyte cataclasite in the fault core and damage zone are exposed along 2 6 km length of the fault reworked fragments of pseudotachylyte in cataclasites and multiple generations of cataclasites provide evidence for the preservation of multiple earthquake cycles the limited exposure

determining the present day kinematics of the idrija fault slovenia from airborne lidar topography abstract located in central europe at the junction of the southern alps and the dinarides the 100 km long idrija fault striking n310 and dipping 80 ne is often considered as the potential source of the historical 1511 earthquake estimated macroseismic magnitude mm 6 8 using 1 25 000 to 1 5000 topographical maps satellite images spot5 12 5 m illuminated dem and airborne lidar data derived 1 m dem we examined in detail the idrija fault trace along a 20 km long swath in the central portion of the fault combining topographic and remote sensing data allows characterizing the recent activity along the idrija fault and estimating its cumulative displacement along strike between tolmin and godovic the fault trace is mostly linear but appears divided into three disconnected segments of 11 20 km long morphological evidences such as offset streams and ridges and major drainage abandonments suggest ongoing movement at three sites field observations and lidar dem analysis allow measuring cumulative dextral offsets comprised between 35 and 65 m we found two larger offsets of 140 m and 360 m at the southeasternmost site the vertical component is significant and revealed by a rake ranging from 0 to 33 the derived n303 n310 striking slip vector is in agreement with the motion along this fault as suggested by the geodesy assuming that the smallest measured offsets have been recorded after the last glacial maximum lgm about 20 ka ago the minimum slip rate for the idrija fault is about 1 5 mm yr over this period of time

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

slip rate of the calico fault implications for geologic versus geodetic rate discrepancy in the eastern california shear zone 1 long term 10 5 years fault slip rates test the scale of discrepancy between infrequent paleoseismicity and relatively rapid geodetic rates of dextral shear in the eastern california shear zone ecsz the calico fault is one of a family of dextral faults that traverse the mojave desert portion of the ecsz its slip rate is determined from matching and dating incised pleistocene alluvial fan deposits and surfaces displaced by fault slip a high resolution topographic base acquired via airborne laser swath mapping aids in identification and mapping of deformed geomorphic features the oldest geomorphically preserved alluvial fan unit b is displaced 900 200 m from its source at sheep springs wash in the northern rodman mountains this fan deposit contains the first preserved occurrence of basalt clasts derived from the pipkin lava field and overlies quaternary conglomerate deposits lacking these clasts the 40 ar 39 ar dating of two flows from this field yields consistent ages of 770 40 ka and 735 9 ka an age of 650 100 ka is assigned to this fan deposit based on these ages and on the oldest cosmogenic 3 he exposure date of 653 20 ka on a basalt boulder from the surface of unit b this assigned age and offset together yield a mid pleistocene to present average slip rate of 1 4 0 4 mm yr ayounger fan surface unit k records 100 10 m of dextral displacement and preserves original depositional morphology of its surface granitic boulders and pavement samples from this surface yield an average age of 56 4 7 7 ka after taking into account minimal cosmogenic inheritance of granitic clasts the displaced and dated k fans yield a slip rate of 1 8 0 3 mm yr distributed deformation of the region surrounding the fault trace if active could increase the overall displacement rate to 2 1 0 5 mm yr acceleration of slip rate from an average of 1 4 mm yr prior to 50 ka to 1 8 mm yr since 50 ka is possible though a single time averaged slip rate of 1 6 0 2 mm yr satisfies the data these rates are faster than any other paleoseismic or long term slip rate yet determined for other dextral faults in the mojave desert and imply that fault slip rates and earthquake productivity are heterogeneous across this portion of the ecsz total displacement across the calico fault diminishes northward as shear is distributed into folding and sinistral faults in the calico mountains this pattern is consistent with an approximately threefold drop in geologic slip rate as the calico fault steps over onto the blackwater fault and demonstrates the significance of fault interaction for understanding the pattern of present day strain accumulation in the ecsz

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

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

the dinaric fault system large scale structure rates of slip and plio pleistocene evolution of the transpressive northeastern boundary of the adria microplate located at the northeastern corner of the adria microplate the alps dinarides junction represents a key region for understanding how the adria microplate interacts with stable europe however little is known on how the present day deformation imposed by the rotation of the adria microplate is absorbed across the dinarides using morphotectonic analysis based on satellite and aerial images accurate topographical maps and digital elevation models combined with field investigations we mapped in detail the three main active faults of the northern dinarides geomorphic and geological cumulative displacements ranging from a few meters to several kilometers have been identified on those faults and dated for the most recent ones using 36 cl exposure dating those results yielded a total right lateral motion of 3 8 0 7 mm yr oriented n317 comparing our results with the motion expected from adria rotation models suggests that the northern dinarides absorbs most of the predicted adria eurasia motion thus representing the eastern boundary of the microplate however a significant e w component is lacking suggesting that part of the stress imposed by the microplate rotation is transferred farther to the east finally bounds placed on the plio pleistocene kinematics confirm that faulting onset occurred during the early pliocene and evidence a significant kinematic change at the early middle pleistocene boundary

surface ruptures of the iranian earthquakes 1900 2014 insights for earthquake fault rupture hazards and empirical relationships abstract a database of iranian earthquakes during the instrumental period 1900 2014 is used to analyze geometric and kinematic aspects of the surface ruptures in different seismotectonic regions of the country majority of the ruptures have occurred along or associated with known geological or active faults thrust and strike slip faults show a maximum surface rupture length of 85 and 125 km respectively excluding the distributed displacements on bedding thrusts during the 1979 tabas earthquake which was summed up differently to 1 5 and 3 0 m maximum displacement on individual faults of thrust mechanism is 1 5 m while strike slip faults show a maximum horizontal displacement of 4 5 m surface rupture zone width of 3 km is observed in an strike slip event and a 4 km distance between the known active fault and the surface rupture of an event suggests that care should be taken in evaluation of setback zone for rupture hazards of some faults with complex geometry kinematics partitioning in space and time of ruptures in earthquakes requires a better understanding of exact kinematics of active fault zones while rerupturing of a fault segment in alternating events complicates the rupture history of the segment simultaneous rupture of several fault segments and sympathetic faulting should be taken into account for evaluation of earthquake hazard in specific regions with such possible seismotectonic setting secondary ruptures and fractures either in the presence or absence of primary surface ruptures develop via different mechanisms and complicate the surface deformations while surface ruptures are frequently associated with earthquakes in eastern iran these features are very rare in zagros and makran regions empirical relations are suggested among surface rupture length maximum displacement and moment magnitude for different earthquake fault mechanisms in iran which may be more compatible to the events within iran using these relations the maximum surface rupture length maximum surface displacement and the associated maximum credible earthquakes are suggested for different regions in iran the suggested values may also be used for estimation of earthquake magnitudes in paleoseismological studies

large earthquake triggering clustering and the synchronization of faults large earthquakes are sometimes observed to trigger other large earthquakes on nearby faults the magnitudes of the calculated coulomb stress transfers presumed to cause the triggering are 10 2 10 3 of the earthquake stress drops the earthquake stress drops and the triggering delay times are similarly small with respect to the natural recurrence time of the earthquakes this requires that both faults be simultaneously very close to the ends of their seismic cycles paleoseismological data show that for the same regions prior earthquakes have occurred in clusters of ruptures of several faults separated by long quiescent periods both observations suggest that synchronization is occurring between faults theory and observations indicate that synchronization can occur between nearby faults with positive stress coupling and intrinsic slip velocities within an entrainment threshold in the south iceland seismic zone the central nevada seismic belt and the eastern california shear zone several synchronous clusters that apparently act independently can be recognized this behavior is the 3d equivalent of the phase locking that results in the seismic cycle of individual faults being dominated by large characteristic earthquakes and for synchronization of fault segments along a given fault rupture patterns of repeated individual earthquakes or earthquake clusters are not identical in either the 2d or 3d cases the state of this system which exhibits strong indications of synchrony without exact repetition may be called fuzzy synchrony

a 2500 yr long paleoseismologic record of large infrequent earthquakes on the north anatolian fault at cukurcimen turkey paleoseismologic trenches excavated across the north anatolian fault near the village of cukurcimen in north central turkey yield a complete record of surface ruptures for the past 2500 yr the trenches provide mutually consistent evidence for the timing of the five most recent surface ruptures at the site as well as at least two older events these are interpreted as 1 the historic 1939 m w 7 9 earthquake 2 the historic 1254 a d earthquake 3 the historic 1045 a d earthquake 4 an earthquake that probably occurred late in the interval between 250 and 540 a d possibly the historic 499 a d earthquake and 5 an earthquake that occurred sometime between 770 and 50 b c and probably between 230 and 50 b c one additional earthquake occurred sometime between 1450 and 800 b c and at least one other surface rupture occurred between 2880 and 200 b c but the stratigraphic section at the site was not completely exposed for sediments older than 2500 yr as a result it is unclear whether the oldest event horizons represent a single earthquake or multiple events our findings when coupled with other published results and the historical record enable us to construct a space time history of earthquakes along the north anatolian fault the most striking aspects of this analysis are 1 the rarity of earthquakes at any given place along the fault suggesting that the fault typically ruptures in large infrequent events 2 earthquake occurrence is relatively temporally regular with inter event times that range from 200 to 900 yr and vary by a factor of only 3 4 and 3 almost the entire length of the north anatolian fault ruptured in short lived clusters of activity in the seventeenth to eighteenth centuries and in the tenth to twelfth centuries similar to the twentieth century sequence the magnitude and sequence of the individual ruptures however have varied considerably between clusters moreover the paleoseismologic and historical data indicate that the north anatolian fault does not always rupture in sequences similar to the twentieth century cluster these results suggest that the relatively regular recurrence of rare large magnitude earthquakes may be the expected mode of earthquake occurrence on mature strike slip faults in settings where such faults are structurally isolated from other major seismic sources

geomorphic evidence for plio quaternary compression in the andean foothills of the southern neuquen basin argentina the southern central andes foothills are made of imbricate thick and thin skinned fold and thrust belts they were formed during cretaceous and miocene compressive periods by successive eastward propagation episodes of the orogenic front we analyze remnant terraces and alluvial deposits of the neuqun river and its tributaries to study the plio quaternary tectonic regime in the southern neuqun basin topographic profiles of remnant terraces show a crustal scale tens of kilometers anomaly above the chihuido south anticline this anomaly is accompanied by sedimentary aggradations downstream and upstream of the anticline another anomaly in the terrace profiles correlated with a knickpoint in the current neuqun river is observed farther east near aelo we interpret these anomalies to be the consequence of a plio quaternary uplift of the chihuidos and aelo anticlines folding and surface faulting of plio quaternary alluvial deposits show that this uplift is concomitant with the reactivation of the miocene orogenic front and of the predominantly thin skinned agrio fold and thrust belt from these data we infer that the southern neuqun basin is still shortening under a compressive stress regime and that the andean orogenic front is migrating farther to the east extensional features in the study area correspond mainly to thin skinned gravitational gliding resulting from crustal uplift thus we argue that the tectonic compressive regime is preserved in the southern neuqun basin throughout the plio quaternary though the slab may have steepened during this period

multimillennial incremental slip rate variability of the clarence fault at the tophouse road site marlborough fault system new zealand incremental slip rates of the clarence fault a dextral fault in the marlborough fault system of south island new zealand varied by a factor of 4 5 during holocene latest pleistocene time as revealed by geomorphic mapping and luminescence dating of faulted fluvial landforms at the tophouse road site we used high resolution lidar microtopographic data and field surveys to map the fine scale geomorphology and precisely restore the offset features we dated the offsets using a stratigraphically informed protocol for infrared stimulated luminescence dating these data show that incremental slip rates varied from 2 0 to 9 6 mm year averaged over multiple earthquakes and millennial timescales comparison to incremental slip rates of the nearby awatere fault suggests that these faults may behave in coordinated and anticorrelated fashion this study adds to a growing body of evidence suggesting that incremental slip rate variation spanning multiple earthquake cycles may be more common than previously recognized

earthquake synchrony and clustering on fucino faults central italy as revealed from in situ cl 36 exposure dating we recover the holocene earthquake history of seven seismogenic normal faults in the fucino system central italy we collected 800 samples from the well preserved limestone scarps of the faults and modeled their 36cl concentrations to derive their seismic exhumation history we found that 30 large earthquakes broke the faults in synchrony over the last 12 ka the seven faults released strain at the same periods of time 12 9 ka 5 3 ka and 1 5 1 ka on all faults the strain accumulation and release occurred in 3 6 ka supercycles each included a 3 5 ka phase of slow 0 5 2 mm yr strain accumulation in relative quiescence followed by a cluster of three to four large earthquakes or earthquake sequences that released most of the strain in 1 2 ka the large earthquakes repeated every 0 5 0 3 ka during the paroxysmal phases and every 4 3 0 9 ka between those phases earthquakes on the northern faults produced twice larger surface slips 2 m and had larger magnitudes mw 6 2 6 7 than those on the southern faults on most faults the relative strain level was found to control the amount of slip and the time of occurrence of the next large earthquake faults entered a phase of clustered activity once they had reached a specific relative strain threshold the tre monti fault is identified as the most prone to break over the next century our data document earthquake synchrony and clustering at a broader space and time scale than has been reported to date

the dynamic history of the trans mexican volcanic belt and the mexico subduction zone abstract the trans mexican volcanic belt tmvb is a 1000 km long neogene continental arc showing a large variation in composition and volcanic style and an intra arc extensional tectonics it overlies the rivera and cocos slabs which display marked changes in geometry geophysical studies indicate that lithospheric mantle is very thin or absent beneath the forearc and arc the fluids from the slab are released in a 40 to 100 km wide belt beneath the frontal part of the arc and the lower crust beneath the arc is partially molten east of 101 w the tmvb is built on a precambrian to paleozoic crust with thickness of 50 55 km west of 101 w the tmvb is underlain by jurassic to cenozoic marine and continental arcs with a 35 40 km thick crust the evolution of the tmvb occurred in four stages 1 from 20 to 10 ma the initial andesitic arc moved inland showing progressively drier melting and eventually slab melting suggesting flattening of the subducted slab 2 since 11 ma a pulse of mafic volcanism migrated from west to east reaching the gulf of mexico by 7 ma this mafic lavas marks the lateral propagation of a slab tear triggered by cessation of subduction beneath baja california 3 thereafter the volcanic front started moving trenchward with a marked phase of silicic volcanism between 7 5 and 3 ma local emplacement of small volume intraplate like basalts since 5 ma and development of extensional faulting these features are related to slab rollback enhancing asthenophere flux into the mantle wedge and promoting partial melting of the crust 4 the modern arc consists of a frontal belt dominated by flux and slab melting and a rear belt characterized by more differentiated rocks or by mafic lavas with little or no evidence of subduction fluids but higher asthenosphere fingerprint

delayed triggering of the 1999 hector mine earthquake by viscoelastic stress transfer stress changes in the crust due to an earthquake can hasten the failure of neighbouring faults and induce earthquake sequences in some cases1 2 3 4 5 the 1999 hector mine earthquake in southern california magnitude 7 1 occurred only 20 km from and 7 years after the 1992 landers earthquake magnitude 7 3 this suggests that the hector mine earthquake was triggered in some fashion by the earlier event but uncertainties in the slip distribution and rock friction properties associated with the landers earthquake have led to widely varying estimates of both the magnitude and sign of the resulting stress change that would be induced at the location of the hector mine hypocentre with estimates varying from 1 4 bar ref 6 to 0 5 bar ref 7 more importantly coseismic stress changes alone cannot satisfactorily explain the delay of 7 years between the two events here we present the results of a three dimensional viscoelastic model that simulates stress transfer from the ductile lower crust and upper mantle to the brittle upper crust in the 7 years following the landers earthquake using viscoelastic parameters that can reproduce the observed horizontal surface deformation following the landers earthquake our calculations suggest that lower crustal or upper mantle flow can lead to postseismic stress increases of up to 1 2 bar at the location of the hector mine hypocentre during this time period contributing to the eventual occurrence of the 1999 hector mine earthquake these results attest to the importance of considering viscoelastic processes in the assessment of seismic hazard8 9 10 11

stress triggering of the great indian ocean strike slip earthquakes in a diffuse plate boundary zone 1 on april 11 2012 two great magnitude 8 earthquakes occurred within a two hour period off the west coast of northern sumatra indonesia in the broadly distributed india australia plate boundary zone the magnitude 8 6 mainshock holds the distinction of being both the largest instrumentally recorded strike slip earthquake and the largest earthquake away from a recognized plate boundary fault the mainshock involved sequential ruptures of multiple fault planes oriented nearly perpendicular to each other the adjacent 2004 megathrust earthquake statically loaded the northern wharton basin oceanic lithosphere on both of the 2012 mainshock fault plane orientations and greatly enhanced the rate of earthquake activity in the region for a year viscoelastic relaxation of the asthenosphere following the 2004 and 2005 megathrust earthquakes continued to positively stress the offshore region correlating with the locations of later strike slip earthquakes including two magnitude 7 and the 2012 magnitude 8 earthquakes

effects of source model variations on coulomb stress analyses of a multi fault intraplate earthquake sequence abstract fault models are quickly produced and iteratively improved over weeks to years following a major earthquake to characterise the dynamics of rupture evaluate the role of stress transfer and contribute to earthquake forecasting we model coulomb stress transfer cfs between the largest foreshock mw 5 4 1 year prior to first mainshock and three mw 6 1 to 6 5 earthquakes that occurred in a 12 hour period on january 22 1988 in central australia tennant creek earthquake sequence to investigate the role of static stress transfer in earthquake triggering relative to progressive source model development the effects of fault model variance are studied using cfs modelling of five different fault source model sequences 27 total models using different inputs from seismic and geospatial data some initial models do not yield positive cfs changes proximal to hypocentres but in all models preceding earthquakes generate positive cfs 0 1 bar on 10 to 30 of the forthcoming receiver fault rupture areas the most refined and data integrative model reveals cfs 0 7 to 13 bars within 2 km of impending hypocentres and large 30 to 99 areas of positive cfs when compared to global compilations of threshold cfs prior to impending ruptures average 3 71 bar median 1 bar this suggests that coulomb stress change theory adequately explains the tennant creek rupture sequence in the most refined model earthquake inter event times decrease as cfs increases suggesting that higher stress magnitudes may have more rapidly within hours triggered successive events thus accounting for some temporal aspects of this sequence cfs analyses provide a useful framework for understanding the spatiotemporal aspects of some intraplate earthquakes the progressive refinement of source models using emergent data may reduce epistemic uncertainties in the role of stress transfer that result from different model inputs approaches and results

holocene and latest pleistocene activity on the mesquite lake fault near twentynine palms eastern california shear zone implications for fault interaction paleoseismic data from the mesquite lake fault reveal evidence for up to four prehistoric earthquakes since the latest pleistocene with three large surface rupturing events in about the past 10 2 ka three events were recorded in trenches excavated for this investigation on mesquite lake playa a buried fault scarp brack eted by accelerator mass spectrometer radiocarbon ages of detrital charcoal indicate that a mid to late holocene event occurred between about 2 7 and 7 4 ka most likely between about 3 9 and 4 6 ka an early holocene rupture defined by a subtle buried scarp and upward terminating fissures is bracketed between about 7 7 and 10 2 ka evidence for an inferred late pleistocene event prior to about 10 2 ka includes a subtle scarp upward termination of faults folding and in filled craters and fissures a previous paleoseismic investigation just south 2 km of the playa identified at least one event in the past 1 3 ka although this event was not identified in this study at the playa site apparent vertical offsets of about 1 0 m and 1 2 m for the last two events at the playa site suggest a sequence of similar serial ruptures these separa tions are comparable to the height of surficial scarps just south of the playa because the vertical separations produced by each event are similar the mesquite lake fault at least locally experiences similar slip per event since the initiation of holocene playa development just over 10 2 ka ago we estimate a horizontal slip rate of 0 7 0 9 mm yr 1 that is consistent with slip rates for other faults in the eastern california shear zone despite large uncertainties event stratigraphy at the playa site shows that periods of quiescence up to thousands of years separated large ruptures similar to other faults in the eastern california shear zone comparison of paleoseismic studies in the eastern california shear zone suggest that the mesquite lake and possibly the bullion and lavic lake faults in the eastern part of the shear zone may have failed during periods of seismic quiescence in the western part of the zone at about 1 5 ka this suggests that seismic strain release may vary spatially across the shear zone and that temporal clusters of earthquakes are not necessarily spatially limited to specific regions

the fate of olivine in the lower crust pseudomorphs after olivine in coronitic metagabbro from the grenville orogen ontario abstract orthopyroxene oxide symplectites after olivine are among the most enigmatic features of corona assemblages in metagabbros two coronitic metagabbro bodies from the algonquin suite in the grenville orogen ontario contain exceptionally well preserved orthopyroxene fe ti oxide symplectite formed during prograde ottawan ca 1060 ma granulite facies metamorphism based on textural evidence we propose a new hypothesis for the formation of these symplectites under oxidising conditions associated with fluid infiltration magmatic olivine and ilmenite underwent a coupled reaction whereby magnetite produced by oxidation of olivine replaced adjacent igneous ilmenite ilmenite was re precipitated as a fine grained intergrowth with orthopyroxene and some magnetite in the former olivine sites this hypothesis is supported by textural evidence showing partial replacement of magmatic ilmenite by magnetite and a close spatial association between magmatic oxides and orthopyroxene fe ti oxide symplectite which locally radiates from ilmenite into olivine measured orthopyroxene oxide ratios in the symplectite 20 35 oxides agree with the ratio predicted from the proposed reaction ca 30 coronas and pseudomorphs formed during high grade metamorphism with increasing fo2 interpreted to result from fluid infiltration at near peak conditions of ca 13 kbar 800 c the same samples contain red brown fine grained aggregates interpreted as iddingsite pseudomorphs after olivine raman spectroscopy suggests that the iddingsite consists largely of amorphous silica and fe hydroxide textural evidence indicates that it formed by late stage oxidation and hydration of olivine that survived earlier metamorphism the unusual co occurrence of granulite facies pseudomorphs after olivine with an alteration product formed at near surface conditions indicates that some olivine may survive protracted high grade metamorphism in environments where fluid access is limited

coulomb stress evolution in a diffuse plate boundary 1400 years of earthquakes in eastern california and western nevada usa diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults and by relatively low strain rates these characteristics make it difficult to understand the spatial and temporal distribution of seismicity the area east of the sierra nevada between longitudes 121 degrees w and 116 degrees w is part of a diffuse plate boundary at least 17 major surface rupturing earthquakes have happened here in the last 1400 years our purpose is to determine whether these events influence each other or whether they are randomly distributed in time and space we model the evolution of coseismic and postseismic coulomb failure stress changes delta cfs produced by these earthquakes and we also model interseismic stresses on the entire fault network our results show that 80 of the earthquake ruptures are located in areas of combined coseismic and postseismic delta cfs 0 2 bar this relationship is robust as shown by the control tests that we carried out using random earthquake sequences we also show that the fish lake valley pyramid lake and honey lake faults have accumulated 45 37 and 27 bars respectively of total delta cfs i e coseismic postseismic interseismic in the last 1400 years such values are comparable to the average stress drop in a major earthquake and these three faults may be therefore close to failure

coulomb stress changes in the south iceland seismic zone due to two large earthquakes in june 2000 1 the south iceland seismic zone experienced the largest earthquakes for 88 years in june 2000 with a ms 6 6 event on june 17 followed by another ms 6 6 earthquake on june 21 these events occurred on two parallel n s striking right lateral strike slip faults separated by about 17 km we calculate the static coulomb stress change for the june 17 and 21 earthquakes using a distributed slip model derived from joint inversion of insar and gps data we find that the static stress change caused by the june 17 event is about 0 1 mpa at the location of the june 21 hypocenter promoting failure on the second fault locations of aftershocks agree well with areas of increased coulomb failure stress our calculations indicate that positive stress changes due to the two earthquakes make the area west of the june 21 rupture the most likely site of the next large earthquake in south iceland

modeling earthquake moment magnitudes on imbricate reverse faults from paleoseismic data fox peak and forest creek faults south island new zealand coeval rupture of imbricate reverse faults increases the moment magnitude m w of the resulting earthquake detailed mapping and paleoseismic data can yield useful insights into the probability and m w potential of multifault ruptures we present a paleoseismic study of two active imbricate reverse faults the fox peak and forest creek faults in the central south island of new zealand both faults have recurrence intervals of 3000 years most recent events with overlapping age distributions and sole into the same structure at depth surface and subsurface data indicate average single event displacements of 2 m for the fox peak fault and 1 m for the forest creek fault monte carlo simulations provide m w estimates for a range of rupture scenarios independent and combined fault geometries and coseismic displacements the exponential fault to fault jump probability depends on the shortest distance between two faults which is allowed to vary in the model based on regional hypocentral depths and the modeled fault geometries coulomb stress modeling is used to analyze stresses induced on the receiver fault plane the forest creek fault as a semiquantitative test of triggered rupture feasibility and to determine credible m w distributions the results suggest a maximum credible event mce of m w 7 5 7 6 for listric geometries on the fox peak and forest creek faults these estimates represent a 0 2 0 5 magnitude increase over most models which show averages of m w 7 1 7 3 for rupture scenarios on planar faults the monte carlo approach employed herein is an improvement over simple empirical relationships for estimating m w for surface rupturing earthquakes and mces for reverse fault systems because it provides realistic uncertainty estimates and can be readily applied to other fault systems around the world online material digital elevation model and sedimentation model of the trench 1 area color trench logs with photomosaics and detailed trench unit descriptions

renewal models and coseismic stress transfer in the corinth gulf greece fault system 1 we model interevent times and coulomb static stress transfer on the rupture segments along the corinth gulf extension zone a region with a wealth of observations on strong earthquake recurrence behavior from the available information on past seismic activity we have identified eight segments without significant overlapping that are aligned along the southern boundary of the corinth rift we aim to test if strong earthquakes on these segments are characterized by some kind of time predictable behavior rather than by complete randomness the rationale for time predictable behavior is based on the characteristic earthquake hypothesis the necessary ingredients of which are a known faulting geometry and slip rate the tectonic loading rate is characterized by slip of 6 mm yr on the westernmost fault segment diminishing to 4 mm yr on the easternmost segment based on the most reliable geodetic data in this study we employ statistical and physical modeling to account for stress transfer among these fault segments the statistical modeling is based on the definition of a probability density distribution of the interevent times for each segment both the brownian passage time bpt and weibull distributions are tested the time dependent hazard rate thus obtained is then modified by the inclusion of a permanent physical effect due to the coulomb static stress change caused by failure of neighboring faults since the latest characteristic earthquake on the fault of interest the validity of the renewal model is assessed retrospectively using the data of the last 300 years by comparison with a plain time independent poisson model by means of statistical tools including the relative operating characteristic diagram the r score the probability gain and the log likelihood ratio we treat the uncertainties in the parameters of each examined fault source such as linear dimensions depth of the fault center focal mechanism recurrence time coseismic slip and aperiodicity of the statistical distribution by a monte carlo technique the monte carlo samples for all these parameters are drawn from a uniform distribution within their uncertainty limits we find that the bpt and the weibull renewal models yield comparable results and both of them perform significantly better than the poisson hypothesis no clear performance enhancement is achieved by the introduction of the coulomb static stress change into the renewal model

relationship of the 1999 hector mine and 1992 landers fault ruptures to offsets on neogene faults and distribution of late cenozoic basins in the eastern california shear zone this report examines the hector mine and landers earthquakes in the broader context of faults and fault related basins of the eastern california shear zone ecsz we compile new estimates of total strike slip offset horizontal separation at nearly 30 fault sites based on offset magnetic anomaly pairs we also present a map of the depth to pre cenozoic basement rock thickness of basin filling late cenozoic deposits for the region based on an inversion of gravity and geologic data our estimates of total long term strike slip offsets on faults that slipped during the 1999 hector mine 3 4 km and the 1992 landers earthquakes 3 1 to 4 6 km fall within the 3 to 5 km range of total strike slip offset proposed for most faults of the western ecsz faults having offsets as great as 20 km are present in the eastern part of the ecsz although the landers rupture followed sections of a number of faults that had been mapped as independent structures the similarity in total strike slip offset associated with these faults is compatible with one of the following hypotheses 1 the landers multistrand rupture is a typical event for this linked fault system or 2 this complex rupture path has acted as a coherent entity when viewed over some characteristic multiearthquake cycle the second hypothesis implies that for each cycle slip associated with smaller earthquakes on individual fault segments integrates to a uniform slip over the length of the linked faults with one exception the region surrounding the hector mine and landers ruptures is devoid of deep late cenozoic basins in particular no deep basins are found immediately north of the pinto mountain fault a place where a number of kinematic models for development of the ecsz have predicted basins in contrast some basins exist near barstow and along the eastern part of the ecsz where the model of dokka et al 1998 predicts basins

viscoelastic earthquake cycle models with deep stress driven creep along the san andreas fault system 1 we develop a two dimensional boundary element earthquake cycle model including deep interseismic creep on vertical strike slip faults in an elastic lithosphere coupled to a viscoelastic asthenosphere uniform slip on the upper part of the fault is prescribed periodically to represent great strike slip earthquakes below the coseismic rupture the fault creeps in response to lithospheric shear stresses within a narrow linear viscous fault zone the model is applied to the gps contemporary velocity field across the carrizo plain and northern san francisco bay segments of the san andreas fault as well as triangulation measurements of postseismic strain following the 1906 san francisco earthquake previous analysis of these data using conventional viscoelastic coupling models without stress driven creep segall 2002 shows that it is necessary to invoke different lithosphere asthenosphere rheology in northern and southern california in order to explain the data we show that with deep stress driven interseismic creep on the san andreas fault the data can be explained with the same rheology for northern and southern california we estimate elastic thickness in the range 44 100 km 95 confidence level fault zone viscosity per unit width of 0 5 8 2 1017 pa s m and asthenosphere relaxation time of 24 622 years 0 1 2 9 1020 pa s for northern and southern california we estimate a slip rate of 21 27 mm yr and recurrence time of 188 315 years for the northern san francisco bay san andreas fault and slip rate of 32 42 mm yr with recurrence time of 247 536 years for the carrizo plain

sedimentary evidence of historical and prehistorical earthquakes along the venta de bravo fault system acambay graben central mexico abstract the venta de bravo normal fault is one of the longest structures in the intra arc fault system of the trans mexican volcanic belt it defines together with the pastores fault the 80 km long southern margin of the acambay graben we focus on the westernmost segment of the venta de bravo fault and provide new paleoseismological information evaluate its earthquake history and assess the related seismic hazard we analyzed five trenches distributed at three different sites in which holocene surface faulting offsets interbedded volcanoclastic fluvio lacustrine and colluvial deposits despite the lack of known historical destructive earthquakes along this fault we found evidence of at least eight earthquakes during the late quaternary our results indicate that this is one of the major seismic sources of the acambay graben capable of producing by itself earthquakes with magnitudes mw up to 6 9 with a slip rate of 0 22 0 24 mm yr 1 and a recurrence interval between 1940 and 2390 years in addition a possible multi fault rupture of the venta de bravo fault together with other faults of the acambay graben could result in a mw 7 earthquake these new slip rates earthquake recurrence rates and estimation of slips per event help advance our understanding of the seismic hazard posed by the venta de bravo fault and provide new parameters for further hazard assessment

crustal earthquake triggering by pre historic great earthquakes on subduction zone thrusts triggering of earthquakes on upper plate faults during and shortly after recent great m 8 0 subduction thrust earthquakes raises concerns about earthquake triggering following cascadia subduction zone earthquakes of particular regard to cascadia was the previously noted but only qualitatively identified clustering of m 6 5 crustal earthquakes in the puget sound region between about 1200 900 cal years b p and the possibility that this was triggered by a great cascadia thrust subduction thrust earthquake and therefore portends future such clusters we confirm quantitatively the extraordinary nature of the puget sound region crustal earthquake clustering between 1200 900 cal years b p at least over the last 16 000 we conclude that this cluster was not triggered by the penultimate and possibly full margin great cascadia subduction thrust earthquake however we also show that the paleoseismic record for cascadia is consistent with conclusions of our companion study of the global modern record outside cascadia that m 8 6 subduction thrust events have a high probability of triggering at least one or more m 6 5 crustal earthquakes

synchronization of great subduction megathrust earthquakes insights from scale model analysis the magnitude of great subduction megathrust earthquakes is controlled mainly by the number of adjacent asperities failing synchronously and the resulting rupture length here we investigate experimentally the long term recurrence behavior of a pair of asperities coupled by static stress transfer over hundreds of seismic cycles we statistically analyze long c 500 ka time series of m8 9 analogue earthquakes simulated using a seismotectonic scale model approach with two aims first to constrain probabilistic measures frequency size distribution variability useful for hazard assessment and second to relate them with geometric observables coseismic slip pattern locking pattern we find that the number of synchronized asperity failures relative to the number of individual asperity failures as well as the coefficients of variation of recurrence intervals and seismic moment scale with the logarithm of stress coupling between the asperities accordingly tighter packed asperities tend to recur more periodically and with a more characteristic magnitude while more distant asperities show clustering of more variable sized events the probability of synchronized failures seems to be controlled to first order by geometrical relations i e spacing and offset of asperities the effects of rheological properties are evident but it remains to be explored to which extent they vary in nature and how sensitive the system is to those

the seismic coupling of subduction zones revisited 1 the nature of seismic coupling for many of the world s subduction zones has been reevaluated geodetic estimates of seismic coupling obtained from gps measurements of upper plate deformation during the interseismic period are summarized we compared those with new estimates of seismic coupling obtained from seismological data the results show that with a few notable exceptions the two methods agree to within about 10 the seismological estimates have been greatly improved over those made 20 30 years ago because of an abundance of paleoseismological data that greatly extend the temporal record of great subduction earthquakes and by the occurrence in the intervening years of an unusual number of great and giant earthquakes that have filled in some of the most critical holes in the seismic record the data also again with a few notable exceptions support the frictional instability theory of seismic coupling and in particular the test of that theory made by scholz and campos 1995 overall the results support their prediction that high coupling occurs for subduction zones subjected to high normal forces with a switch to low coupling occurring fairly abruptly as the normal force decreases below a critical value there is also considerable variation of coupling within individual subduction zones earthquake asperities correlate with areas of high coupling and hence have a semblance of permanence but the rupture zones and asperity distributions of great earthquakes may differ greatly between seismic cycles because of differences in the phase of seismic flux accumulation

paleoseismology of the 1912 acambay earthquake and the acambay tixmadeje fault trans mexican volcanic belt the acambay graben is a major intra arc basin of the trans mexican volcanic belt trenching studies at four sites along the acambay tixmadeje fault reveal evidence for the 1912 acambay earthquake and at least four late pleistocene and holocene ground rupturing earthquakes with similar displacements to the 1912 event evidence for multiple events was recognized by a combination of upward terminating faults fissure fills erosionally truncated fissures colluvial wedge fills and downward increasing separation of stratigraphic units sites along the central part of the ese wnw trending rangefront fault indicates large dip slip separations across a multi event scarp in holocene colluvium with a penultimate event that occurred since 5230 calibrated years before present cal yr b p on the huapango plain near the eastern end of the 1912 rupture where slip was oblique the penultimate earthquake occurred after 4700 cal yr b p and there is evidence for at least four more earthquakes in the last 34 000 cal yr b p three dimensional excavation of lacustrine and channel deposits at las lomas yields a left normal slip vector of s40 5 e with 105 10 cm of slip for the last three events there this slip vector is consistent with nne oriented extension across the graben the amount and style of slip documented for prehistoric ruptures are also consistent with the 1912 rupture with a mean of 60 cm event of dip slip on the rangefront and a mean of 35 cm event of oblique slip on the n48 w trending huapango plain assuming these values represent a characteristic behavior yields an average recurrence interval of 3600 years for the last four large earthquakes since 11 570 cal yr b p and a slip rate of 0 17 mm yr across the rangefront empirical earthquake parameters calculated from our paleoseismic data support instrumental measures indicating that the 1912 acambay earthquake was of m 6 8 7 0 the 1912 event is representative of ground rupturing earthquakes on the acambay tixmadeje fault and demonstrates that large seismic events m 7 can be generated by faults in the trans mexican volcanic belt and in other intra arc settings

pattern and rates of faulting in the central nevada seismic belt and paleoseismic evidence for prior beltlike behavior the central nevada seismic belt cnsb is a concentration of historical 1915 1932 1954 surface faulting in the western basin and range province forming a linear nearly continuous 300 km long rupture zone previous results are integrated in this study with new paleoseismic and exploratory trenching data from the historical zones to look for evidence of older similar beltlike patterns or elevated slip rates that could indicate whether the cnsb is a zone of focused long term crustal strain the data show that the continuous rupture belt produced by the seven earthquakes occurring between 1915 and 1954 is unique in the available paleoseismic record at the 1954 fairview peak fault the lack of prehistorical faulting in deposits containing the wilson creek bed 19 tephra eliminates the possibility of an identical seismic belt in the past 35 4 ka our studies also show that the faults have net slip rates ranging from a low of 0 09 mm yr on the fairview peak fault to a high of 0 7 mm yr on the 1932 cedar mountain fault these are considered moderate to low rates that are similar to most late quaternary faults in the western basin and range province a space time comparison shows that the paleoseismic histories for these multiple rupture zones are diverse and the number and timing of events in each of the zones indicate that there is little evidence for older contemporaneous ruptures of these same faults based on these results we reach several conclusions regarding the longer term holocene behavior of the cnsb although paleoseismic data preclude an older identical rupture belt among the historical zones consideration of associated holocene faults within the greater cnsb region indicates that several similar but not identical beltlike rupture patterns are plausible during the past 13 ka although each requires seismic gaps in the along strike pattern although long term strain represented by density of young faults does appear to increase from east to west into the cnsb the slip rate data demonstrate that the cnsb is not a belt of concentrated or elevated crustal strain compared with areas that extend west to the sierra nevada the increase in the distribution of holocene fault activity from east to west into the cnsb is consistent with a marked increase in the 1992 2002 gps velocity field at the latitude of the 1954 rupture sequence however a comparison of the geologic rates across the belt at this same latitude indicates that the extension rates 0 59 1 37 mm yr are systematically lower than both the campaign and continuous gps rates 2 20 3 13 mm yr by factors of 2 5 these discrepancies may be due to postseismic strain or to some form of off fault deformation we conclude that the results of our study of fault behavior in the cnsb best support the belt migration model proposed by wallace 1987 for the western basin and range province in which temporal tectonic pulses are believed to migrate regionally activating different beltlike combinations of late quaternary faults in an as yet unknown pattern of migration

do weak global stresses synchronize earthquakes insofar as slip in an earthquake is related to the strain accumulated near a fault since a previous earthquake and this process repeats many times the earthquake cycle approximates an autonomous oscillator its asymmetric slow accumulation of strain and rapid release is quite unlike the harmonic motion of a pendulum and need not be time predictable but still resembles a class of repeating systems known as integrate and fire oscillators whose behavior has been shown to demonstrate a remarkable ability to synchronize to either external or self organized forcing given sufficient time and even very weak physical coupling the phases of sets of such oscillators with similar though not necessarily identical period approach each other topological and time series analyses presented here demonstrate that earthquakes worldwide show evidence of such synchronization though numerous studies demonstrate that the composite temporal distribution of major earthquakes in the instrumental record is indistinguishable from random the additional consideration of event renewal interval serves to identify earthquake groupings suggestive of synchronization that are absent in synthetic catalogs we envisage the weak forces responsible for clustering originate from lithospheric strain induced by seismicity itself by finite strains over teleseismic distances or by other sources of lithospheric loading such as earth s variable rotation for example quasi periodic maxima in rotational deceleration are accompanied by increased global seismicity at multidecadal intervals

static stress interactions in extensional earthquake sequences an example from the south lunggar rift tibet 1 an extensional earthquake sequence occurred in 2004 8 across a graben in the south lunggar rift on the tibetan plateau we use insar data to determine the location fault geometry and slip distribution of these earthquakes and to test whether the sequence is compatible with static stress triggering the mw 6 2 and 6 3 earthquakes in 2004 and 2005 both ruptured west dipping faults on the east side of a graben in 2008 a mw 6 7 earthquake ruptured a pair of east dipping fault segments on the other side of the graben offset from the earlier ruptures we compute first order dislocation models of stress change and demonstrate that the order and spatial configuration of this sequence of events is compatible with triggering by static stress transfer a continuation of the sequence would be most likely to occur on the northern extension of the 2008 rupture although variable slip rate along the rift may mean that the sequence has run its course the insar data for the 2008 earthquake also reveal slip on a fault that cuts the graben at a highly oblique angle we suggest that this is a release fault accommodating differential throw in the hanging wall and associate the deformation with a mw 6 0 aftershock activity on such a release fault has not been directly imaged before the zhongba sequence is one of several examples of recent clustered normal fault earthquakes on the plateau and may be an example of phase locking of similar faults

holocene coastal notches in the mediterranean region indicators of palaeoseismic clustering abstract marine tidal notches are developed by bioerosion in the intertidal zones of rocky coasts but a combination of sea level change and crustal movements can result in them being raised above or submerged below the water line for that reason the present day elevation of these former shorelines relative to the mean sea level has long been used to quantify relative coastal uplift and subsidence in tectonically active areas assuming that the sea level eustatic change component is known along the microtidal mediterranean littoral it is generally assumed that notches develop during relative stillstands of sea level when tectonic and eustatic trends are in unison and that discrete notch levels record abrupt shoreline changes caused by local seismic displacements recently however a climatic model for notch formation has been proposed in which stable periods of holocene climate favour enhanced erosion in this competing model the rate of sea level rise is lower than the tectonic uplift rate and individual notches are not specific seismic indicators because marine notches are widely used as geomorphic markers of tectonic and in some cases palaeoseismic movements a reappraisal of the geological significance of these strandlines is warranted in this paper we explore the two conflicting notch models using a database of eastern mediterranean palaeoshorelines although we conclude that the spatial and temporal distribution of the notches supports a dominantly tectonic control on notch genesis as a result of earthquake clustering we highlight how the diachronous timing of notch development tempers their value as tectonic markers

a simplified spring block model of earthquakes the time interval between earthquakes is much larger than the actual time involved during slip in an individual event the authors have used this fact to construct a cellular automaton model of earthquakes this model describes the time evolution of a 2 d system of coupled masses and springs sliding on a frictional surface the model exhibits power law frequency size relations and can exhibit large earthquakes with the same scatter in the recurrence time observed for actual earthquakes

strain release and strain build up in the south iceland seismic zone abstract the south iceland seismic zone is a 70 km long and 10 20 km broad area of land in southern iceland where historically the most destructive earthquakes in iceland have occurred the zone is part of the e w bridge between the mid atlantic ridge and the neovolcanic zone which is an eastward offset of the ridge through iceland the basis for the present study is a historical and an instrumental earthquake catalogue the nature of strain release in earthquakes and as it is revealed in earthquake cracks and observations of aseismic strain release and source propagation the strain build up is modelled as an interplay between the general e w drift across the mid atlantic ridge and stresses caused by the horizontal outflow of upwelling mantle material a complex model of strain release is outlined including seismic as well as aseismic components while seismic strain release plays the dominant role in the eastern and central part of the zone to a depth even below 15 km aseismic slip takes up most of the motion in the western part of the zone and in its continuation in the reykjanes peninsula towards the reykjanes rid e

dynamic friction in sheared fault gouge implications of acoustic vibration on triggering and slow slip friction and deformation in granular fault gouge are among various dynamic interactions associated with seismic phenomena that have important implications for slip mechanisms on earthquake faults to this end we propose a mechanistic model of granular fault gouge subject to acoustic vibrations and shear deformation the grain scale dynamics is described by the shear transformation zone theory of granular flow which accounts for irreversible plastic deformation in terms of flow defects whose density is governed by an effective temperature our model accounts for stick slip instabilities observed at seismic slip rates in addition as the vibration intensity increases we observe an increase in the temporal advancement of large slip events followed by a plateau and gradual decrease furthermore slip becomes progressively slower upon increasing the vibration intensity the results shed important light on the physical mechanisms of earthquake triggering and slow slip and provide essential elements for the multiscale modeling of earthquake ruptures in particular the results suggest that slow slip may be triggered by tremors

paleoseismology of the johnson valley kickapoo and homestead valley faults clustering of earthquakes in the eastern california shear zone paleoseismic data from 11 trenches at seven sites excavated across the southern johnson valley kickapoo and homestead valley faults that ruptured in the 1992 landers earthquake as well as the northern johnson valley fault which did not fail in 1992 indicate that the return period for large surface rupturing events in this part of the eastern california shear zone is in the range of 5 15 ka the inferred slip rates based on their respective recurrence intervals are in the range of 0 2 0 6 mm yr for each of the faults studied a previous large earthquake ruptured the southern johnson valley and kickapoo faults about 5 ka b p the northern johnson valley fault also failed at about this time at 5 8 ka b p and may have been part of the same rupture in contrast the penultimate large earthquake that we identify on the homestead valley fault occurred about 15 ka b p much earlier than other faults involved in the 1992 rupture from these observations combined with paleoseismic work by others after the 1992 earth quake it appears that previous events along the southern johnson valley and kick apoo faults were different than those of 1992 and may have involved other fault segments it has been over 5 ka since the most recent rupture on the northern johnson valley fault therefore it is surprising that it did not fail in the 1992 rupture from our observations dextral shear appears to be distributed across the entire eastern california shear zone with individual faults taking only a small proportion of the overall slip release of this regional strain appears to occur in temporal clusters of large earthquakes with the 1992 event apparently the most recent of a sequence of late holocene 0 1 ka earthquakes that have ruptured the nine faults we have trenched in the southwestern mojave desert previous clusters of earthquake activity occurred in the early 8 9 ka and middle 5 6 ka holocene and possibly the latest pleistocene 15 ka

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

recovering paleoearthquake slip record in a highly dynamic alluvial and tectonic region hope fault new zealand from airborne lidar knowing the slip amplitudes that large earthquakes produced in prehistorical times is one key to anticipate the magnitude of large forthcoming events it is long known that the morphology is preserving remnants of paleoearthquake slips in the form of fault offset landforms however the measured offsets that can be attributed to the most recent paleoearthquakes are generally few along a fault so that they rarely allow recovering the slip distributions and largest slips of these earthquakes we acquired 1 m resolution airborne lidar data on a 30 km stretch of a fast slipping strike slip fault eastern hope fault new zealand located in a region of high alluvial dynamics where landforms are rapidly evolving data analysis reveals 200 offset landforms only 30 allow a good to moderate quality offset measurement from these good to moderate quality measures we recover the slip length distributions and largest slips of the four most recent large paleoearthquakes and find evidence of 4 6 prior events the record suggests that large earthquake slip recurred in multiples of about 4 m along the 30 km stretch although they have larger uncertainties the more numerous lower quality offsets that we also measured reveal a similar earthquake slip record this shows that although offset landforms are partly degraded in dynamically active landscapes they store valuable information on paleoearthquake slips this information might be recovered provided that the morphology is analyzed at high resolution and continuously over a significant fault length remote lidar data are powerful to perform such analyses

triggered tremor phase locking and the global clustering of great earthquakes abstract a system of non linear coupled relaxation oscillators is used to show how the communication between large earthquakes on a global scale can align their seismic cycles to produce a worldwide clustering of large events our model builds on recent observations that the seismic waves from a large earthquake can trigger an episode of non volcanic tremor at the base of a distant fault we assume that tremor is indicative of creep on the ductile extension of the fault zone that loads its overlying seismogenic layer thus advancing the fault toward failure if this advance is larger toward the end of the seismic cycle we show that two or more interacting faults will align their cycles even if their recurrence intervals are not identical

postseismic deformation following the 1906 san francisco earthquake we have reevaluated triangulation data from northern california following the 1906 san francisco earthquake thereby increasing the temporal and spatial resolution of postseismic deformation following that event we have calculated uniform shear strain rates and average station velocities at point arena using data from 1906 1907 1929 1930 and 1973 1975 and for the point reyes petaluma arc using data from 1929 1930 1938 1939 and 1960 1961 with the addition of recent geodetic data we infer an effective relaxation time for long term postseismic deformation following the 1906 earthquake of 36 16 years the point arena data are satisfactorily fit with accelerated afterslip at depth along the san andreas fault plane for a 10 km deep 25 km wide afterslip zone the average slip rate between 1906 and 1930 is 11 2 cm yr between 1929 and 1975 it is 4 6 cm yr deformation in the point reyes petaluma arc is clearly asymmetric with respect to the trace of the san andreas fault especially between 1929 and 1939 after inverting for the range of acceptable accelerated deep afterslip and horizontal detachment models a detailed analysis using geologically reasonable geometries revealed that both model types have trouble explaining the spatial variations in the deformation field through time in particular accelerated deep afterslip models cannot reproduce the breadth of the observed deformation field to the northeast of the san andreas fault as a result more complex time varying deformation mechanisms are required to explain the point reyes petaluma arc observations

elevated shear zone loading rate during an earthquake cluster in eastern california we compare geodetic velocity to geologic fault slip rates to show that tectonic loading was doubled across the eastern california shear zone ecsz during a cluster of major earthquake activity new slip rates are presented for six dextral faults that compose the ecsz in the central mojave desert these rates were determined from displaced alluvial fans dated with cosmogenic 10 be and from a displaced lava flow dated with 40 ar 39 ar we find that the sum geologic mojave ecsz slip rate 6 2 1 9 mm yr is only half the present day geodetically measured velocity of 12 2 mm yr these rates account for cumulative fault slip and geodetic observations that span the 60 km wide shear zone therefore this difference cannot be attributed to postseismic relaxation redistribution of tectonic loading over the earthquake cycle at a regional scale suggests that earthquake clustering may be enhanced via feedback with weakening of ductile shear zones

temporal clustering of major earthquakes along individual faults due to post seismic reloading palaeoseismic evidence suggests that earthquake recurrence intervals in some regions can be highly variable with clusters of multiple large events separated by much longer periods of quiescence because post seismic processes have a significant effect on the reloading rate of the coseismic fault we hypothesize that temporal variations in the amount of stress concentrated in the non seismogenic lithosphere can modulate large earthquake recurrence times we explore this hypothesis using simple analogue spring dashpot slider models we find that in the presence of small amounts of environmental noise post seismic stress transfer over timescales much longer than an earthquake cycle may be an important factor in generating clustering behaviour the propensity for the system to be clustered is a function of a non dimensional number that we call the wallace number w w is defined as the average earthquake stress drop divided by the product of the long term geologic strain rate across the fault and the effective viscosity of the system our results indicate that environments with relatively low strain rates and a relatively weak non seismogenic lithosphere are most susceptible to clustering driven by post seismic stress recycling mechanisms

the role of viscoelastic stress transfer in long term earthquake cascades insights after the central italy 2016 2017 seismic sequence central italy is characterized by a network of active faults that interact in a complex manner coseismic coulomb stress changes have been invoked by several authors to explain the concentration of moderate to strong earthquakes in this region but none has considered the time dependent viscoelastic relaxation of the lower crust and upper mantle as a possible additional source of stress changes at a regional scale here starting from the 1915 m w 6 9 0 2 fucino earthquake we calculated the coseismic plus postseismic coulomb failure stress changes cfs due to eight moderate to strong earthquakes that have struck central italy in the last century and culminated with the 2016 2017 sequence results from this modeling coupled with some synthetic tests simulating normal fault earthquakes with different magnitudes allowed us to highlight the importance of postseismic processes in particular the viscoelastic stress transfer due to events of m w 6 5 can modify the spatial distribution of cfs on a centennial timescale and therefore trigger events at larger distances in addition using these results we identified other earthquake clusters in the historical catalogue last 618 years which like the 1915 2017 series were potentially modulated by both coseismic and postseismic processes finally considering our calculations combined with historical and paleoseismological data we suggest that several faults in central italy may be at present close to failure

insights into the mechanism of intermediate depth earthquakes from source properties as imaged by back projection of multiple seismic phases 1 this study investigates the spatial and temporal distribution of energy release of large intermediate depth earthquakes using a modified back projection technique first used to study the 2004 sumatra andaman megathrust event multiple seismic phases are included in the back projection analysis which provides the capability to determine the energy distribution with respect to depth and time a total of 22 intermediate depth earthquakes with moment magnitudes greater than or equal to 6 5 are investigated with hypocentral depths between 100 and 300 km for most of these events the vertical extent of energy release is either below the resolution of this study 5 km or slightly above 15 km this observation agrees with previous studies that find large intermediate depth earthquakes have subhorizontal rupture planes the results also show a significant portion of the events have multiple rupture planes that are well separated in depth the closeness in time of the ruptures on separate planes and the distance between the planes suggest dynamic triggering where the p waves from the first rupture initiate rupture on the second plane we propose that a dehydration embrittlement mechanism combined with preferentially hydrated subhorizontal faults can explain the observations of dominant subhorizontal rupture planes and the frequent occurrence of rupture complexity involving multiple subevents

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

paleoseismology of the southern panamint valley fault implications for regional earthquake occurrence and seismic hazard in southern california 1 paleoseismologic data from the southern panamint valley fault pvf reveal evidence of at least four surface ruptures during late holocene time 0 33 0 48 ka 0 9 3 0 ka 3 3 3 6 ka and 4 1 ka these paleo earthquake ages indicate that the southern pvf has ruptured at least once and possibly twice during the ongoing 1 5 ka seismic cluster in the mojave section of the eastern california shear zone ecsz the most recent event mre on the pvf is also similar in age to the 1872 owens valley earthquake and the geomorphically youthful mre on the death valley fault the timing of the three oldest events at our site shows that the pvf ruptured at least once and possibly thrice during the well defined 2 5 ka seismic lull in the mojave section of the ecsz interestingly the 3 3 3 6 ka age of event 3 overlaps with the 3 3 3 8 ka age of the penultimate i e pre 1872 rupture on the central owens valley fault these new pvf data support the notion that earthquake occurrence in the ecsz may be spatially and temporally complex with earthquake clusters occurring in different regions at different times coulomb failure function modeling of the panamint valley and garlock faults reveals significant stress interactions between these two faults that may influence future earthquake occurrence specifically our models suggest a possible rupture sequence whereby an event on the southern panamint valley fault can lead to the potential triggering of an event on the garlock fault which in turn could trigger the mojave section of the san andreas fault

evolution of the stress field in southern california and triggering of moderate size earthquakes a 200 year perspective changes in stress in southern california are modeled from 1812 to 2025 using as input 1 stress drops associated with six large 7 0 7 5 earthquakes through 1995 and 2 stress buildup associated with major faults with slip rates 3 mm yr as constrained by geodetic paleoseismic and seismic measurements evolution of stress and the triggering of moderate to large earthquakes are treated in a tensoffal rather than a scalar manner we present snapshots of the cumulative coulomb failure function acff as a function of time for faults of various strike dip and rake throughout southern california we take acff to be zero everywhere just prior to the great shock of 1812 we find that about 95 of those well located m 6 earthquakes whose mechanisms involve either strike slip or reverse faulting are consistent with the coulomb stress evolutionary model that is they occurred in areas of positive acff the interaction between slow moving faults and stresses generated by faster moving faults significantly advanced the occurrence of the 1933 long beach and 1992 landers events in their earthquake cycles coulomb stresses near major thrust faults of the western and central transverse ranges have been accumulating for a long time future great earthquakes along the san andreas fault especially if the san bernardino and coachella valley segments rupture together can trigger moderate to large earthquakes in the transverse ranges as appears to have happened in the santa barbara earthquake that occurred 13 days after the great san andreas shock of 1812 maps of current acff provide additional guides to long term earthquake prediction

postseismic deformation associated with the 1992 m ω 7 3 landers earthquake southern california following the 1992 m 7 3 landers earthquake a linear array of 10 geodetic monuments at roughly 5 km spacing was established across the emerson fault segment of the landers rupture the array trends perpendicular to the local strike of the fault segment and extends about 30 km on either side of it the array was surveyed by global positioning system 0 034 0 048 0 381 1 27 1 88 2 60 and 3 42 years after the landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation the temporal behavior is described roughly by a short term decay time 84 23 days exponential relaxation superimposed upon an apparently linear trend because the linear trend represents motions much more rapid than the observed preseismic motions we attribute that trend to a slower decay time greater than 5 years postseismic relaxation the curvature of which cannot be resolved in the short run 3 4 years of postseismic data about 100 mm of right lateral displacement and 50 mm of fault normal displacement accumulated across the geodetic array in the 3 4 year interval covered by the postseismic surveys those displacements are attributed to postseismic right lateral slip in the depth interval 10 to 30 km on the downward extension of the rupture trace the right lateral slip amounted to about 1 m directly beneath the geodetic array and the fault normal displacement is apparently primarily a consequence of the curvature of the rupture these conclusions are based upon dislocation models fit to the observed deformation however no dislocation model was found with rms residuals as small as the expected observational error

rupture planes of the gazli earthquakes deduced from local stress tensor calculation and geodetic data inversion geotectonic implications three major earthquakes with ms 7 were clustered in space and time 1976 1984 near gazli uzbekistan without reported evidence for fault scarps to constrain the kinematics of the seismic sequence we invert both focal mechanism solutions of the mainshocks and major aftershocks and vertical surface displacements associated with the three major shocks for seven m 4 earthquakes that occurred in the 1976 1984 period we find that all the focal mechanisms agree with a single stress tensor one of the mechanical implications of this mathematical solution is the choice of the seismic fault plane the 1976 earthquake fracture planes are well constrained by the stress tensor to be striking e w and ene wsw and dipping to the south and the nnw respectively from stress tensor inversion alone it is impossible to determine if the fracture plane of the 1984 event dips to the se or to the nw coseismic vertical surface displacements allow us to infer possible fault plane orientations of the 1976 and 1984 events the best fit to the surface displacement for the 1976 earthquakes is obtained from the geometries that are derived from the homogeneous stress tensor inversion the inversion of vertical surface displacements for the 1984 event constrains the associated fault plane to correspond to a ne ws striking and se dipping plane the inversions of complementary geophysical data argue for the complexity of the orientations of the faults activated by the 1976 1984 seismic sequence the 1984 earthquake fault plane is well orientated to allow failure to be activated by a horizontal 1 under a mohr coulomb failure criterion under the same failure criterion and stress conditions unlike the 1984 fracture plane the 1976 fault planes are misorientated and likely to correspond to preexisting discontinuities concerning the principle stress orientations the gazli region seems to be under control of the regional tectonic setting from a regional point of view the wnw ese strike of 1 and the nne ssw strike of 2 deduced from this study for the kyzylkum desert can be explained at once by the interaction of the regional plate boundary motions

seismic slip history of the pizzalto fault central apennines italy using in situ produced 36cl cosmic ray exposure dating and rare earth element concentrations morphological and geological observations reveal that most apenninic faults are highly segmented and that the majority of the fault segments are less than 10 km long although these faults have undergone numerous paleoseismological investigations quantitative data remain crucially lacking for a large number of fault segments because such data are essential to understanding how these faults have ruptured and interacted in the past and how they might behave in the future we investigated the holocene seismic history of the pizzalto normal fault a 13 km long fault segment belonging to the pizzalto rotella aremogna fault system in the apennines we collected 44 samples from the pizzalto fault plane exhumed during the holocene and analyzed the 36cl and rare earth element ree contents together the 36cl and ree concentrations show that at least six events have exhumed 4 4 m of the fault scarp between 3 and 1 ka with slip per event values ranging from 0 3 to 1 2 m no major events have been detected over the last 1 kyr the rotella aremogna pizzalto fault system has a clustered earthquake behavior with a mean recurrence time of 1 2 kyr and a low to moderate probability ranging from 4 to 26 of earthquake occurrence over the next 50 years

long range and long term fault interactions in southern california paleoseismological data suggest the occurrence of four bursts of seismic moment release in the los angeles region during the past 12 000 yr the historic period appears to be part of an ongoing lull that has persisted for about the past 1000 yr these periods of rapid seismic displacement in the los angeles region have occurred during the lulls between similar bursts of activity observed on the eastern california shear zone in the mojave desert which is now seismically active a kinematic model in which the faults of the greater san andreas system suppress activity on faults in the eastern california shear zone and vice versa can explain the apparent switching of activity between the two fault networks combined with the observation that short term geodetic and longer term geologic rates co vary on major southern california fault systems this suggests that either 1 a temporal cluster of seismic displacements on upper crustal faults increases ductile deformation on their downward extensions or 2 rapid ductile slip in the lower crust beneath faults loads the upper crust driving a seismic cluster we suggest that alternating periods of rapid seismic displacement may be the expected mode of seismicity when two fault systems accommodate the same plate boundary motion and slip on one system suppresses slip on the other

fault segmentation as constraint to the occurrence of the main shocks of the 2016 central italy seismic sequence we perform the finite extent fault inversion of the three main events of the 2016 central italy seismic sequence using near source strong motion records we demonstrate that both earthquakes nucleation and rupture propagation were controlled by segmentation of the n nw s se trending quaternary normal faults the first shock of the sequence august 24th mw 6 0 ruptured at the relay zone between the laga mts lf and the cordone del vettore cvf normal faults the second shock october 26th mw 5 9 nucleated at a minor relay zone within the mt vettore mt bove fault vbf while the third and largest one october 30th mw 6 5 initiated at the relay zone between the vbf and cvf triggering the multiple rupture of the vbf cvf and probably lf we show that this latter relay zone corresponds to the deeper high angle fault zone of the sibillini mts cross structure a thrust ramp inherited from the miocene pliocene contractional phase of the apennines this structure acted as a barrier to rupture propagation of the first two events thus defining an area of large stress concentration until it acted as the initiator of the rupture originating the largest mw 6 5 event that crossed the barrier itself we suggest that the young cvf have started to cut through the barrier acting as a soft linkage between the two long lived lf and vbf the evidence that coseismic cumulative slip shows a maximum at the cvf provided by both slip inversion and original surface rupture data suggests that the cvf is growing faster than the adjacent faults

a physical basis for time clustering of large earthquakes we develop a theory that links stress interaction between earthquakes and the occurrence of temporal clustering coseismic static stress change in the vicinity 50 km of large earthquakes suggests that perturbations of 0 1 to 1 bars may affect the occurrence of other earthquakes at larger distances interactions also seem to exist four m 8 earthquakes have occurred in mongolia on distant faults 400 km during the last century also paleoseismic observations documenting much longer time periods display a time clustering of major events we demonstrate with simple mechanical concepts that postseismic stress relaxation magnifies the coseismic stress change and has a major effect on fault interaction during the seismic cycle in the simple case where two distant faults are coupled the probabilistic occurrence of triggered earthquakes may increase dramatically due to long range postseismic coupling

paleoseismologic investigation of the fault rupture of the 14 april 1928 chirpan earthquake m 6 8 southern bulgaria 1 seventy five years after the destructive chirpan earthquake of 14 april 1928 we conducted a paleoseismologic study of the causative fault combining a review of contemporary literature geomorphology geophysical prospecting and trenching we reidentified the fault scarp in the field and mapped it over a distance of 12 5 km geophysical profiles and boreholes demonstrate that chirpan scarp is the surface expression of a normal fault that was active throughout the pleistocene and holocene in 2002 we excavated a paleoseismologic trench to study the faulting history a narrow fault zone separates plio pleistocene alluvial sand in the footwall from holocene alluvial and colluvial silt in the hanging wall the 1928 earthquake is recorded by 0 45 m vertical offset of the topsoil in accordance with contemporary descriptions we identified three colluvial wedge like units in the hanging wall sediments next to the fault evidencing at least three surface rupturing paleoearthquakes since the atlantic their timing could only be loosely constrained using pollen the penultimate event had an offset of 0 40 0 45 m and occurred after circa 2600 calibrated years before present cal years b p event 3 displaced a subboreal semiarid calcic soil 0 55 0 70 m between circa 5750 and 2600 cal years b p the fourth event had a minimal offset of 0 50 0 70 m and occurred between circa 8900 cal years b p and 4900 b c when the region was first settled we obtain a holocene fault slip rate of 0 22 0 12 mm yr and an average recurrence interval of 2350 643 years for earthquakes comparable to or larger than the 1928 event

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

changes in state of stress on the southern san andreas fault resulting from the california earthquake sequence of april to june 1992 the april to june 1992 landers earthquake sequence in southern california modified the state of stress along nearby segments of the san andreas fault causing a 50 kilometer segment of the fault to move significantly closer to failure where it passes through a compressional bend near san gorgonio pass the decrease in compressive normal stress may also have reduced fluid pressures along that fault segment as pressures are reequilibrated by diffusion that fault segment should move closer to failure with time that fault segment and another to the southeast probably have not ruptured in a great earthquake in about 300 years

time dependent recurrence of strong earthquake shaking near plate boundaries a lake sediment perspective abstract accurate probabilistic seismic hazard analysis requires a good knowledge of the recurrence parameters of the strongest earthquakes in a region due to the typical short temporal span of instrumental and historical data it is often unclear whether one should adopt a time dependent or time independent poissonian recurrence model the choice of which has large repercussions on the probability estimates for new strong events the rapidly growing discipline of lacustrine paleoseismology aims at producing long continuous records of strong seismic shaking which integrate the activity of all significant seismic sources in a region and allow a reliable determination of recurrence patterns the typical continuous sedimentation regime in lakes can lead to complete sensitive paleoseismic records and a reduced temporal uncertainty in recurrence intervals here i present a worldwide compilation of published long lacustrine paleoseismic records grouped per tectonic domain and statistically explore the variability of their recurrence intervals expressed by the coefficient of variation cov a cov 1 indicates a time independent process whereas cov 1 may be related to changes in the sensitivity of the lacustrine paleoseismograph or to real earthquake clustering due to e g stress transfer between neighboring faults the most useful lacustrine paleoseismic records can be retrieved in high seismicity settings where many paleoseismic events can be recorded in a relatively short time span i e

elastic and visco elastic stress triggering in the south iceland seismic zone due to large earthquakes since 1706 abstract damaging earthquakes in the south iceland seismic zone sisz occur fairly regularly and often as a series of events with a few days only between individual events tolerably reliable information on epicentre locations and mechanisms are available for 13 m 6 events between 1706 and 2000 for these events we computed the co and post seismic stress fields hereby approximating the sisz by a mixed elastic visco elastic layered half space the horizontal shear stress and the coulomb stress changes were analysed to detect possible trigger mechanisms which may aid future earthquake mitigation efforts we tested several criteria but must conclude that the start of an earthquake series in the sisz cannot be explained by triggering through previous events inside an individual series however one may infer triggering our results are in contradiction with the findings in other regions of the world the reason might be related to the fact that the sisz is not a mature fault zone in which old faults are re activated if a certain stress level threshold is passed in addition uncertainties in the model parameters as well as the neglect of horizontal variations in the model and of possible stress transfer due to volcanic activity further complicate the evaluation of our results and need to be taken into account in future studies