observing earthquakes triggered in the near field by dynamic deformations we examine the hypothesis that dynamic deformations associated with seismic waves trigger earthquakes in many tectonic environments our analysis focuses on seismicity at close range within the aftershock zone complementing published studies of long range triggering our results suggest that dynamic triggering is not confined to remote distances or to geothermal and volcanic regions long unilaterally propagating ruptures may focus radiated dynamic deformations in the propagation direction therefore we expect seismicity triggered dynamically by a directive rupture to occur asymmetrically with a majority of triggered earthquakes in the direction of rupture propagation bilaterally propagating ruptures also may be directive and we propose simple criteria for assessing their directivity we compare the inferred rupture direction and observed seismicity rate change following 15 earthquakes m 5 7 to m 8 1 that occurred in california and idaho in the united states the gulf of aqaba syria guatemala china new guinea turkey japan mexico and antarctica nine of these mainshocks had clearly directive unilateral ruptures of these nine seven apparently induced an asymmetric increase in seismicity rate that correlates with the rupture direction the two exceptions include an earthquake preceded by a comparable magnitude event on a conjugate fault and another for which data limitations prohibited conclusive results similar but weaker correlations were found for the bilaterally rupturing earthquakes we studied although the static stress change also may trigger seismicity it and the seismicity it triggers are expected to be similarly asymmetric only if the final slip is skewed toward the rupture terminus for several of the directive earthquakes we suggest that the seismicity rate change correlates better with the dynamic stress field than the static stress change manuscript received 1 march 2002

southern san andreas fault seismicity is consistent with the gutenberg richter magnitude frequency distribution the magnitudes of any collection of earthquakes nucleating in a region are generally observed to follow the gutenberg richter gr distribution on some major faults however paleoseismic rates are higher than a gr extrapolation from the modern rate of small earthquakes would predict this along with other observations led to the formulation of the characteristic earthquake hypothesis which holds that the rate of small to moderate earthquakes is permanently low on large faults relative to the large earthquake rate wesnousky et al 1983 schwartz and coppersmith 1984 we examine the rate difference between recent small to moderate earthquakes on the southern san andreas fault ssaf and the paleoseismic record hypothesizing that the discrepancy can be explained as a rate change in time rather than a deviation from gr statistics we find that with reasonable assumptions the rate changes necessary to bring the small and large earthquake rates into alignment agree with the size of rate changes seen in epidemic type aftershock sequence modeling where aftershock triggering of large earthquakes drives strong fluctuations in the seismicity rates for earthquakes of all magnitudes the necessary rate changes are also comparable to rate changes observed for other faults worldwide these results are consistent with paleoseismic observations of temporally clustered bursts of large earthquakes on the ssaf and the absence of m 7 earthquakes on the ssaf since 1857

the role of a keystone fault in triggering the complex el mayor cucapah earthquake rupture large earthquakes can rupture several faults analysis of seismic data from the 2010 el mayor cucapah earthquake in california suggests that multiple faults were pinned to a keystone fault whose rupture triggered cascading slip the 2010 mw 7 2 el mayor cucapah earthquake in baja california mexico activated slip on multiple faults of diverse orientations1 2 which is commonly the case for large earthquakes3 4 5 6 the critical stress level for fault failure depends on fault orientation and is lowest for optimally oriented faults positioned approximately 30 to the greatest principal compressive stress7 yet misoriented faults whose positioning is not conducive to rupture are also common8 9 here we use stress inversions of surface displacement and seismic data to show that the el mayor cucapah earthquake initiated on a fault that owing to its orientation was among those that required the greatest stress for failure although other optimally oriented faults must have reached critical stress earlier in the interseismic period coulomb stress modelling shows that slip on these faults was initially muted because they were pinned held in place by misoriented faults that helped regulate their slip in this way faults of diverse orientations could be maintained at critical stress without destabilizing the network we propose that regional stress build up continues until a misoriented keystone fault reaches its threshold and its failure then spreads spontaneously across the network in a large earthquake our keystone fault hypothesis explains seismogenic failure of severely misoriented faults such as the san andreas fault and the entire class of low angle normal faults

the evolution of a thrust fault system processes of rupture initiation propagation and termination in the 1980 el asnam algeria earthquake summary we discuss work completed to date on the 1980 algerian earthquake and introduce a description of the earthquake in terms of rupture propagation using the nomenclature of fracture mechanics field and teleseismic studies have shown the earthquake fault to be divided into three major thrust segments rupture began at the sw end of the system and propagated along successive segments geological sections reveal that different fault segments have suffered different amounts of displacement in the past the amount of geological displacement increases systematically from almost zero at the sw end of the fault to several hundred metres further ne faulting at the sw end is very young and appears to be extending the thrust system along strike the aftershock data of ouyed et al reveal that strike slip aftershocks occur beyond the sw end of the thrust fault these are accommodating compression by conjugate strike slip faulting on north and west trending planes this network of conjugate faults plays a crucial role in the initiation of major eathquakes on the thrust system and may be regarded as a plastic zone beyond the end of the thrust fault increasing horizontal stress causes the strike slip system to evolve into a zig zag network of thrusts which is partly controlled by the pre existing strike slip faults finally a through going thrust can develop and leads to catastrophic rupture along the main fault plane to describe the propagation of the main shock we extend aki s concept of geometric barriers and divide these into two types in conservative barriers the slip vector is common to both fault planes whereas in non conservative barriers the slip vectors are different on the two fault planes that meet at the barrier although both types of barrier arrest dynamic rupture only nonconservative barriers need produce aftershocks as off fault deformation is required to accommodate the difference in slip vectors by considering the aftershock zones as areas of distributed deformation we show that fracture toughness in the earth is not a material constant but is related to fault geometry and therefore changes as fault systems evolve the current south westwards growth of the el asnam thrust system can be seen as the latest phase in an evolution consisting of periods of along strike extension alternating with periods of increasing net displacement during which no fault growth occurs these two types of behaviour allow a segmented fault system to be produced

the 1999 mw 7 1 hector mine california earthquake sequence complex conjugate strike slip faulting the 1999 m w 7 1 hector mine mainshock showed right lateral strike slip faulting with an initial strike of n6 w and vertical dip the mainshock was preceded within 20 hours by 18 recorded foreshocks of 1 5 m 3 8 within a few kilometers distance of the mainshock hypocenter the aftershocks delineate how the hector mine earthquake ruptured with strike n6 w to the south for a distance of 15 km and possibly to the north for a distance of several kilometers the two largest aftershocks of m 5 9 and m 5 7 occurred near the north and south ends of the first mainshock rupture segment the second segment of rupture starting 15 km to the south away from the mainshock hypocenter delineated by strike slip and thrust faulting aftershocks extends 10 km farther away with a strike of s140 e along the bullion fault the aftershocks also outline an unusual third rupture segment extending from about 5 km south of the hypocenter with a strike of n30 w to n35 w for a distance of 20 km approximately 10 to 25 km farther to the north and west of the mainshock epicenter several clusters form a complex aftershock distribution three dimensional vp and vp vs models of the region exhibit only small regional changes as is typical for the mojave region nonetheless the mainshock rupture started within a region of rapidly varying vp and at least three regions of low vp vs are imaged within the aftershock zone the rate of decay for the hector mine earthquake sequence has been slightly above the mean for both p values and b values in southern california the focal mechanisms of the aftershocks and the state of stress are consistent with strike slip faulting including a component of normal faulting most prominent to the north the orientation of the regional maximum horizontal stress the variation in orientation of the mainshock fault segments by 30 and scattered distribution of aftershocks suggest that the mainshock and aftershock deformation field exhibit volumetric shear deformation accommodated by complex conjugate sets of strike slip faults

the gutenberg richter or characteristic earthquake distribution which is it abstract paleoearthquake and fault slip rate data are combined with the cit usgs catalog for the period 1944 to 1992 to examine the shape of the magnitude frequency distribution along the major strike slip faults of southern california the resulting distributions for the newport inglewood elsinore garlock and san andreas faults are in accord with the characteristic earthquake model of fault behavior the distribution observed along the san jacinto fault satisfies the gutenberg richter relationship if attention is limited to segments of the san jacinto that are marked by the rupture zones of large historical earthquakes or distinct steps in fault trace the observed distribution along each segment is consistent with the characteristic earthquake model the gutenberg richter distribution observed for the entirety of the san jacinto may reflect the sum of seismicity along a number of distinct fault segments each of which displays a characteristic earthquake distribution the limited period of instrumental recording is insufficient to disprove the hypothesis that all faults will display a gutenberg richter distribution when averaged over the course of a complete earthquake cycle but given that 1 the last 5 decades of seismicity are the best indicators of the expected level of small to moderate size earthquakes in the next 50 years and 2 it is generally about this period of time that is of interest in seismic hazard and engineering analysis the answer to the question posed in the title of the article at least when concerned with practical implementation of seismic hazard analysis at sites along these major faults appears to be the characteristic earthquake distribution

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

hypocenter locations in finite source rupture models we use a database of more than 80 finite source rupture models for more than 50 earthquakes m w 4 1 8 1 with different faulting styles occurring in both tectonic and subduction environments to analyze the location of the hypocenter within the fault and to consider the correlation between hypocenter location and regions of large slip rupture in strike slip and crustal dip slip earthquakes tends to nucleate in the deeper sections of the fault subduction earthquakes do not show this tendency ratios of the hypocentral slip to either the average or the maximum slip show that rupture can nucleate at locations with any level of relative displacement rupture nucleates in regions of very large slip d 2 3 d max in only 16 of the events in regions of large slip 1 3 d max d d max in 35 of the events and in regions of low slip d 1 3 d max in 48 of the events these percentages significantly exceed the percentages of fault area with very large 7 and large 28 slip ruptures that nucleate in regions of low slip however tend to nucleate close to regions of large slip and encounter a zone of very large slip within half the total rupture length applying several statistical tests we conclude that hypocenters are not randomly located on a fault but are located either within or close to regions of large slip

dynamic slip transfer from the denali to totschunda faults alaska testing theory for fault branching we analyze the observed dynamic slip transfer from the denali to totschunda faults during the mw 7 9 3 november 2002 denali fault earthquake alaska this study adopts the theory and methodology of poliakov et al 2002 and kame et al 2003 in which it was shown that the propensity of the rupture path to follow a fault branch is determined by the preexisting stress state branch angle and incoming rupture velocity at the branch location here we check that theory on the denalitotschunda rupture process using 2d numerical simulations of processes in the vicinity of the branch junction the maximum compression direction with respect to the strike of the denali fault near the junction has been estimated to range from approximately 73 to 80 we use the values of 70 and 80 in our numerical simulations the rupture velocity at branching is not well constrained but has been estimated to average about 0 8 cs throughout the event we use 0 6 cs 0 8 cs 0 9 cs and even 1 4 cs as parameters in our simulations we simulate slip transfer by a 2d elastodynamic boundary integral equation model of mode ii slip weakening rupture with self chosen path along the branched fault system all our simulations except for 70 and 0 9 cs predict that the rupture path branches off along the totschunda fault without continuation along the denali fault in that exceptional case there is also continuation of rupture along the denali fault at a speed slower than that along the totschunda fault and with smaller slip

surface rupture during the 2010 mw 7 1 darfield canterbury earthquake implications for fault rupture dynamics and seismic hazard analysis the september 2010 m w 7 1 darfield canterbury earthquake in new zealand is one of the best recorded earthquakes of this magnitude the earthquake occurred on a previously unidentified fault system and generated a 29 5 0 5 km long surface rupture across a low relief agricultural landscape high accuracy measurements of coseismic displacements were obtained at over 100 localities along the greendale fault maximum net displacement d max 5 3 0 5 m and average net displacement d avg 2 5 0 1 m are anomalously large for an earthquake of this m w d max surface rupture length srl and d avg srl ratios are among the largest ever recorded for a continental strike slip earthquake geologically derived estimates of moment magnitude m w g are less than the seismologically derived m w derived using widely employed srl m w scaling regressions m w g is greater than m w using d max and d avg m w regressions the geologically derived static stress drop of 13 9 3 7 mpa provides a context with which to compare this earthquake rupture to interplate and intraplate ruptures of similar m w this data set provides fundamental information on fault rupture processes relevant to seismic hazard modeling in this region and analogous settings globally

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

the 2010 2011 canterbury new zealand seismic sequence multiple source analysis from insar data and modeling 1 the 2010 2011 canterbury sequence is a complex system of seismic events that started with a mw7 1 earthquake and continued with large aftershocks with dramatic consequences particularly for the city of christchurch we model the main earthquakes using insar data providing displacement maps and the respective modeling for the september 4th 2010 february 22nd 2011 and june 13th 2011 events relocated aftershocks field and gps surveys are used to constrain models obtained by inversion of insar data the fault slip distribution is retrieved with a variable patch size approach aimed at maximizing the spatial resolution on the fault plane for the september 2010 earthquake we estimated significant slip values below 10 km depth the calamitous february 2011 event in christchurch is modeled with a double fault source with slip values less than 2 m down to 7 km depth for the second june 13th event in christchurch we identified a nw se striking fault as responsible for the earthquake last we introduce the use of insar coherence maps to quickly detect the areas subject to soil liquefaction in christchurch as shown for the two main events

high resolution relocation of aftershocks of the mw 7 1 darfield new zealand earthquake and implications for fault activity 1 low slip rate regions often represent under recognized hazards and understanding the progression of seismicity when faults in such areas rupture will help us to better understand earthquake rupture patterns the 3 september 2010 utc mw 7 1 darfield earthquake revealed a formerly unrecognized set of faults in the canterbury region of new zealand an area that had previously been mapped as one of the lower hazard areas in the country in this study we analyze the first four months of its aftershock sequence to identify active faults and temporal changes in seismicity along them we jointly invert for three dimensional p wave and s wave velocities and hypocentral locations using data for 2840 aftershocks recorded at 36 temporary and permanent seismic stations within 70 km of the main shock epicenter these relocations delineate eight individual faults active prior to the 22 february 2011 mw 6 3 christchurch earthquake the largest aftershock of the darfield earthquake two of these faults are in the christchurch region one of which corresponds to geodetically determined rupture planes of the christchurch earthquake using focal mechanisms calculated from first motion polarities we find mainly strike slip faulting events with some reverse and normal faulting events as well we compare the orientations of these faults to the prevailing regional stress directions to identify which faults may have been active prior to the darfield earthquake and which may be newly developed

new insights into the tectonic inversion of north canterbury and the regional structural context of the 2010 2011 canterbury earthquake sequence new zealand the 2010 2011 canterbury earthquake sequence highlighted the existence of previously unknown active faults beneath the north canterbury plains and pegasus bay south island new zealand we provide new insights into the geometry and kinematics of ongoing deformation by analyzing marine seismic data to produce new maps of regional faults and cross sectional reconstructions of deformation history active faulting and folding extends up to 30 km offshore and involves reactivation of sets of late cretaceous paleogene normal faults under nw se tectonic compression the active faults consist predominantly of ne sw striking se dipping reverse faults and less commonly e w to nw se faults suitably oriented for strike slip reactivation additionally newly developing reverse faults obliquely segment and overprint the inherited basement fabric and impose geometric and kinematic complexities revealed by mapping and reverse displacement profiles of markers the quaternary reverse slip rates decrease from 0 1 0 3 mm yr beneath northern pegasus bay to 0 05 mm yr approaching banks peninsula fault growth modeling involving trishear fault propagation folding mechanisms successfully restores an evolutionary sequence of progressive fault inversion revealing a history of reactivated individual faults tectonic inversion and overprinting processes beneath pegasus bay are immature and 1 2 0 4 ma old with no evidence of systematic spatial migration of deformation our marine data analyses give insights into the structural context of the 2010 2011 canterbury earthquake sequence while the combined onshore to offshore data provide an excellent illustration of fault growth associated with immature inversion tectonics in which selective fault reactivation results from compressive stress imposed across a complex network of inherited faults

fault damage zones of the m7 1 darfield and m6 3 christchurch earthquakes characterized by fault zone trapped waves abstract to characterize the subsurface structure of the damage zones caused by the 2010 2011 canterbury earthquake sequence in new zealand s south island we installed two short linear seismic arrays array 1 across the greendale fault gf surface rupture and array 2 over the surface projection of the blind port hills fault phf that ruptured in the 2010 m7 1 darfield and 2011 m6 3 christchurch earthquakes respectively we recorded 853 aftershocks for 4 months after the christchurch earthquake fault zone trapped waves fztws identified at array 1 for aftershocks occurring on both the gf and the phf show that the post s durations of these fztws increase as focal depths and epicentral distances from the array increase suggesting an effective low velocity waveguide formed by severely damaged rocks existing along the gf and phf at seismogenic depths locations of aftershocks generating prominent fztws delineates the subsurface gf rupture extending eastward as bifurcating blind fault segments an additional 5 8 km beyond the mapped 30 km surface rupture into a zone with comparably lower seismic moment release west of the phf rupture which extends westward to within 5 3 1 km of the subsurface gf the propagation of fztw through the intervening gap indicates moderate gf phf structural connectivity we interpret this zone as a fracture mesh reflecting the interplay between basement faults and stress aligned microcracks that enable the propagation of phf sourced fztws into the gf damage zone simulations of observed fztws suggest that the gf rupture zone is 200 250 m wide consistent with the surface deformation width velocities within the zone are reduced by 35 55 with the maximum reduction in the 100 m wide damage core zone corresponding with surface and shallow subsurface evidence for discrete fracturing the damage zone extends down to depths of 8 km or deeper consistent with hypocentral locations and geodetically derived fault models

from orientation to magnitudes in paleostress determinations using fault slip data abstract determinations of reduced stress tensors using fault slip data yield the orientation of principal stress axes and the ratio of the differences between principal stress magnitudes the use of rupture and friction laws allows determination of the two remaining unknowns that is the reconstruction of the complete stress tensor taking into account the depth of overburden brings an additional constraint the method is applied and discussed in the case of the hoover dam site western u s a where large data sets and rock mechanics information are available differences between intact sample and rock mass properties account for apparent disagreements between paleostress levels determined in similar tectonic environments pore pressure plays an important role where information about pore pressure is absent zero and hydrostatic pore pressure cases should be considered as limits

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

geometric incompatibility in a fault system abstract interdependence between geometry of a fault system its kinematics and seismicity is investigated quantitative measure is introduced for inconsistency between a fixed configuration of faults and the slip rates on each fault this measure named geometric incompatibility g depicts summarily the instability near the fault junctions their divergence or convergence unlocking or locking up and accumulation of stress and deformations accordingly the changes in g are connected with dynamics of seismicity apart from geometric incompatibility we consider deviation k from well known saint venant condition of kinematic compatibility this deviation depicts summarily unaccounted stress and strain accumulation in the region and or internal inconsistencies in a reconstruction of block and fault system its geometry and movements the estimates of g and k provide a useful tool for bringing together the data on different types of movement in a fault system an analog of stokes formula is found that allows determination of the total values of g and k in a region from the data on its boundary the phenomenon of geometric incompatibility implies that nucleation of strong earthquakes is to large extent controlled by processes near fault junctions the junctions that have been locked up may act as transient asperities and unlocked junctions may act as transient weakest links tentative estimates of k and g are made for each end of the big bend of the san andreas fault system in southern california recent strong earthquakes landers 1992 m 7 3 and northridge 1994 m 6 7 both reduced k but had opposite impact on g landers unlocked the area whereas northridge locked it up again

understanding heavy mineral enrichment using a three dimensional numerical model layered deposits of relatively light and heavy minerals can be found in many aquatic environments quantification of the physical processes which lead to the fine scale layering of these deposits is often limited with flumes or in situ field experiments therefore the following research questions were addressed i how can selective grain entrainment be numerically simulated and quantified ii how does a mixed bed turn into a fully layered bed and iii is there any relation between heavy mineral content and bed stability herein a three dimensional numerical model was used as an alternative measurement to study the fine scale process of density segregation during transport the three dimensional model simulates particle transport in water by combining a turbulence resolving large eddy simulation with a discrete element model prescribing the motion of individual grains the granular bed of 0 004 m in height consisted of 200 000 spherical particles d50 500 m five suites of experiments were designed in which the concentration ratio of heavy 5000 kg m to light particles i e 2560 kg m was increased from 6 15 35 60 to 80 all beds were tested for 10 s at a predefined flow speed of 0 3 m s analysis of the particle behaviour in the interior of the beds showed that the lighter particles segregated from the heavy particles with increasing time the latter accumulated at the bottom of the domain forming a layer whereas the lighter particles were transported over the layer forming sweeps particles below the heavy particle layers indicated that the layer was able to armour the particles below consequentially enrichment of heavy minerals in a layer is controlled by the segregation of a heavy mineral fraction from the light counterpart which enhances current understanding of heavy mineral placer formation this article is protected by copyright all rights reserved

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

using regional moment tensors to constrain the kinematics and stress evolution of the 2010 2013 canterbury earthquake sequence south island new zealand abstract on september 3 2010 a m w 7 0 u s geological survey moment magnitude earthquake ruptured across the canterbury plains in south island new zealand since then new zealand gns science has recorded over 10 000 aftershocks m l 2 0 and larger including three destructive m w 6 0 earthquakes near christchurch we treat the canterbury earthquake sequence as an intraplate earthquake sequence and compare its kinematics to an andersonian model for fault slip in a uniform stress field we determined moment magnitudes and double couple solutions for 150 earthquakes having m w 3 7 and larger through the use of a waveform inversion technique using data from broadband seismic stations on south island new zealand the majority 126 of these double couple solutions have strike slip focal mechanisms with right lateral slip on ene fault planes or equivalently left lateral slip on sse fault planes the remaining focal mechanisms indicate reverse faulting except for two normal faulting events the strike slip segments have compatible orientations for slip in a stress field with a horizontal 1 oriented n115 e and horizontal 3 the preference for right lateral strike slip earthquakes suggests that these structures are inherited from previous stages of deformation reverse slip is interpreted to have occurred on previously existing structures in regions with an absence of existing structures optimally oriented for strike slip deformation despite the variations in slip direction and faulting style most aftershocks had nearly the same p axis orientation consistent with the regional 1 there is no evidence for significant changes in these stress orientations throughout the canterbury earthquake sequence

complex rupture during the 12 january 2010 haiti earthquake initially the devastating mw 7 0 12 january 2010 haiti earthquake seemed to involve straightforward accommodation of oblique relative motion between the caribbean and north american plates along the enriquillo plantain garden fault zone here we combine seismological observations geologic field data and space geodetic measurements to show that instead the rupture process involved slip on multiple faults primary surface deformation was driven by rupture on blind thrust faults with only minor deep lateral slip along or near the main enriquillo plantain garden fault zone thus the event only partially relieved centuries of accumulated left lateral strain on a small part of the plate boundary system together with the predominance of shallow off fault thrusting the lack of surface deformation implies that remaining shallow shear strain will be released in future surface rupturing earthquakes on the enriquillo plantain garden fault zone as occurred in inferred holocene and probable historic events we suggest that the geological signature of this earthquake broad warping and coastal deformation rather than surface rupture along the main fault zone will not be easily recognized by standard palaeoseismic studies we conclude that similarly complex earthquakes in tectonic environments that accommodate both translation and convergence such as the san andreas fault through the transverse ranges of california may be missing from the prehistoric earthquake record

complex multifault rupture during the 2016 mw 7 8 kaikōura earthquake new zealand the 2016 moment magnitude m w 7 8 kaik ura earthquake was one of the largest ever to hit new zealand hamling et al show with a new slip model that it was an incredibly complex event unlike most earthquakes multiple faults ruptured to generate the ground shaking a remarkable 12 faults ruptured overall with the rupture jumping between faults located up to 15 km away from each other the earthquake should motivate rethinking of certain seismic hazard models which do not presently allow for this unusual complex rupture pattern science this issue p eaam7194 1 1 lookup doi 10 1126 science aam7194

relation between continental strike slip earthquake segmentation and thickness of the crust 1 high resolution maps of large continental strike slip earthquake surface ruptures show that they are formed of fault segments these segments are bounded by fault bends step overs or combinations of the two the lowest limit in size for such segments may not be relevant in the understanding of earthquake mechanics as it pertains to the granular properties of fault zones the maximum limit in segment length however is important as it is directly relates to the maximum extent of seismic rupture to measure the length of the segments a new quantitative method based on piecewise linear fitting is developed and is used to automatically retrieve segments from earthquake rupture maps next this approach is tested against a set of ten continental strike slip earthquake ruptures derived from similar high quality maps the test suggests that segments have a maximum length of 18 km independent of regional tectonic setting slip inversions for earthquakes based on seismological and or geodetic data most often are not unique and can show some variability even for one particular event some basic characteristics however such as total moment release or general source geometry seem to persist that are relevant to earthquake mechanics measurements of the maximum horizontal extent of individual slip patches derived from seismic source inversion for strike slip ruptures show that their strike dimension does not increase infinitely with magnitude but instead reaches a maximum value of 25 km these two independent lines of observations complemented by earlier data and analog experiments suggest that it is the thickness of the seismogenic crust that controls the structural scaling of the length of seismic segments and that it is independent of the ultimate size of individual earthquakes

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

generic dependence of the frequency size distribution of earthquakes on depth and its relation to the strength profile of the crust 1 we explore the idea that the relative size distribution of earthquakes quantified using the so called b value is negatively correlated with differential stress because the maximum possible differential stress increases linearly in the brittle upper crust we expect to find a decrease of b with depth we test this expectation for seven continental areas around the world each of which is described by a regional earthquake catalog we find a monotonic decrease in b value between 5 and 15 km depth the decrease stops near the brittle ductile transition we specifically focus on the high quality catalogs of earthquakes in california to perform a sensitivity test with respect to depth uncertainty we also estimate the probability depth gradient for the occurrence of a target magnitude event and study the behavior of b with depth in near and off fault zones we also translate the observed b depth gradients into b differential stress gradients our findings suggest that b values are negatively correlated with differential stress and hus have the potential to act as stress meters in the earth s crust

finite element simulations of dynamic shear rupture experiments and dynamic path selection along kinked and branched faults we analyze the nucleation and propagation of shear cracks along nonplanar kinked and branched fault paths corresponding to the configurations used in recent laboratory fracture studies by rousseau and rosakis 2003 2009 the aim is to reproduce numerically those shear rupture experiments and from that provide an insight into processes which are active when a crack initially propagating in mode ii along a straight path interacts with a bend in the fault or a branching junction the experiments involved impact loading of thin homalite 100 a photoelastic polymer plates which had been cut along bent or branched paths and weakly glued back together everywhere except along a starter notch near the impact site strain gage recordings and high speed photography of isochromatic lines provided characterization of the transient deformation fields associated with the impact and fracture propagation we found that dynamic explicit 2 d plane stress finite element analyses with a simple linear slip weakening description of cohesive and frictional strength of the bonded interfaces can reproduce the qualitative rupture behavior past the bend and branch junctions in most cases and reproduce the principal features revealed by the photographs of dynamic isochromatic line patterns the presence of a kink or branch can cause an abrupt change in rupture propagation velocity additionally the finite element results allow comparison between total slip accumulated along the main and inclined fault segments we found that slip along inclined faults can be substantially less than slip along the main fault and the amount depends on the branch angle and kink or branch configuration

possible earthquake rupture connections on mapped california faults ranked by calculated coulomb linking stresses probabilistic seismic hazard assessment is requiring an increasingly broad compilation of earthquake sources fault systems are often divided into char acteristic ruptures based on geometric features such as bends or steps though events such as the 2002 m 7 9 denali and 2011 m 9 0 tohoku oki earthquakes raise the possibility that earthquakes can involve subsidiary faults and or rupture through iden tified geometric barriers here we introduce a method to discriminate among a wide range of possible earthquakes within a large fault system and to quantify the prob ability of a rupture passing through a bend or step we note that many of the conditions favoring earthquake rupture propagation can be simulated using a static coulomb stress change approximation such an approach lacks inertial effects inherent in a full dynamic simulation but does capture many of the empirical observations drawn from examining past ruptures such as continuity of rake and strike as well as distance across gaps or stepovers we make calculations for a test region in northern california and find that the method provides a quantitative basis for ranking possible ruptures within localized fault systems

stress release and source scaling of the 2010 2011 canterbury new zealand earthquake sequence from spectral inversion of ground motion data the canterbury earthquake sequence beginning with the 2010 m w 7 2 darfield earthquake is one of the most notable and well recorded crustal earthquake sequences in a low strain rate region worldwide and as such provides a unique opportunity to better understand earthquake source physics and ground motion generation in such a tectonic setting ground motions during this sequence ranged up to extreme values of 2 2 g recorded during the february 2011 m w 6 2 event beneath the city of christchurch a better understanding of the seismic source signature of this sequence in particular the stress release and its scaling with earthquake size is crucial for future ground motion prediction and hazard assessment in canterbury but also of high interest for other low to moderate seismicity regions where high quality records of large earthquakes are lacking here we present a source parameter study of more than 200 events of the canterbury sequence covering the magnitude range m w 3 7 2 source spectra were derived using a generalized spectral inversion technique and found to be well characterized by the 2 source model we find that stress drops range between 1 and 20 mpa with a median value of 5 mpa which is a factor of 5 larger than the median stress drop previously estimated with the same method for crustal earthquakes in much more seismically active japan stress drop scaling with earthquake size is nearly self similar and we identify lateral variations throughout canterbury in particular high stress drops at the fault edges of the two major events the m w 7 2 darfield and m w 6 2 christchurch earthquakes

three dimensional dynamic rupture simulations across interacting faults the m w 7 0 2010 haiti earthquake the mechanisms controlling rupture propagation between fault segments during a large earthquake are key to the hazard posed by fault systems rupture initiation on a smaller fault sometimes transfers to a larger fault resulting in a significant event e g 2002 m7 9 denali usa and 2010 m7 1 darfield new zealand earthquakes in other cases rupture is constrained to the initial fault and does not transfer to nearby faults resulting in events of more moderate magnitude this was the case of the 1989 m6 9 loma prieta and 2010 m7 0 haiti earthquakes which initiated on reverse faults abutting against a major strike slip plate boundary fault but did not propagate onto it here we investigate the rupture dynamics of the haiti earthquake seeking to understand why rupture propagated across two segments of the leog ne fault but did not propagate to the adjacent enriquillo plantain garden fault the major 200 km long plate boundary fault cutting through southern haiti we use a finite element model to simulate propagation of rupture on the leog ne fault varying friction and background stress to determine the parameter set that best explains the observed earthquake sequence in particular the ground displacement the two slip patches inferred from finite fault inversions are explained by the successive rupture of two fault segments oriented favorably with respect to the rupture propagation while the geometry of the enriquillo fault did not allow shear stress to reach failure

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

evidence for different scaling of earthquake source parameters for large earthquakes depending on faulting mechanism scaling relationships between seismic moment rupture length and rupture width have been examined for this purpose the data from several previous studies have been merged into a database containing more than 550 events for large earthquakes a dependence of scaling on faulting mechanism has been found whereas small and large dip slip earthquakes scale in the same way the self similarity of earthquakes breaks down for large strike slip events furthermore no significant differences in scaling could be found between normal and reverse earthquakes and between earthquakes from different regions since the thickness of the seismogenic layer limits fault widths most strike slip earthquakes are limited to rupture widths of between 15 and 30 km while the rupture length is not limited the aspect ratio of dip slip earthquakes is similar for all earthquake sizes hence the limitation in rupture width seems to control the maximum possible rupture length for these events the different behaviour of strike slip and dip slip earthquakes can be explained by rupture dynamics and geological fault growth if faults are segmented with the thickness of the seismogenic layer controlling the length of each segment strike slip earthquakes might rupture connected segments more easily than dip slip events and thus could produce longer ruptures than dip slip events of the same width

predominance of unilateral rupture for a global catalog of large earthquakes the manner in which an earthquake rupture propagates across a fault reflects both the initial properties of the fault and the dynamical stresses produced by the rupture we quantify the propagation of an earthquake rupture using the second moments of the earthquake space time distribution in particular the second moments provide a simple way to differentiate between approximately bilateral and predominantly unilateral ruptures we determined the second moments for a catalog of m w 7 earthquakes that have occurred since 1994 the results show that approximately 80 of large shallow ruptures are predominantly unilateral our result agrees well with strong motion inversions from previous studies on moderate and large earthquakes the predominance of unilateral propagation in large earthquakes is explained by a simple characteristic earthquake model in which large events rupture an entire structurally defined fault segment and nucleation points are uniformly distributed along the fault the predominance of unilateral rupture may also be enhanced by the dynamic stress field produced by contrasts in the elastic properties between the two sides of plate boundary faults manuscript received 16 november 2001

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

plio pleistocene transpressional reactivation of paleozoic and paleogene structures in the rhine bresse transform zone northern switzerland and eastern france pliocene to recent uplift and shortening in the southern rhinegraben is documented by deformation of pliocene fluvial gravels deposited on a nearly planar surface as well as by progressive deflection and capture of rivers this deformation is suggested to result from thick skinned tectonic movements as evidenced by ob servations on seismic records which demonstrate a spatial coincidence between en chelon anticlines at the surface and faults located in the crystalline basement these findings contradict the often invoked thin skinned tectonism in the recent tectonic history of the rhine graben in particular the transfer zone between the rhinegraben and the bressegraben is very suitable for reactivation under the present day stress field thick skinned reactivation of faults in the basement is also expressed by focal plane mechanisms of recent earth quakes showing strike slip rather than reverse faulting characteristics this is of importance for the densely populated and industrialised southern rhinegraben pre viously affected by large earthquakes in historical times e g basel 1356

statistical evaluation of characteristic earthquakes in the frequency magnitude distributions of sumatra and other subduction zone regions 1 if subduction zone earthquakes conform to a characteristic model in which persistent segments fail at predictable stress levels due to the steady accumulation of tectonic loading historical seismicity may constrain the occurrence of future events we test this model for earthquakes on the sumatra andaman megathrust and other subduction zones using frequency magnitude distributions using simulations we show that poisson confidence intervals correctly account for the counting errors of histogram data these confidence intervals demonstrate that we cannot reject the gutenberg richter distribution in favor of a characteristic model in any of the real catalogues tested a visual bias in power law count data at high magnitudes combined with a sample bias for large earthquakes is sufficient to explain candidate characteristic events this result implies that historical earthquakes are likely poor models for future events and that monte carlo simulations will provide a better assessment of earthquake and associated hazards

slip in the 2010 2011 canterbury earthquakes new zealand the 3rd september 2010 mw 7 1 darfield and 21st february 2011 mw 6 3 christchurch new zealand earthquakes occurred on previously unknown faults we use insar ground displacements sar amplitude offsets field mapping aerial photographs satellite optical imagery a lidar dem and teleseismic body wave modeling to constrain the pattern of faulting in these earthquakes the insar measurements reveal slip on multiple strike slip segments and secondary reverse faults associated with the darfield main shock fault orientations are consistent with those expected from the gps derived strain field the insar line of sight displacement field indicates the main fault rupture is about 45 km long and is confined largely to the upper 10 km of the crust slip on the individual fault segments of up to 8 m at 4 km depth indicate stress drops of 6 10 mpa in each event rupture initiated on a reverse fault segment before continuing onto a strike slip segment the non double couple seismological moment tensors for each event are matched well by the sum of double couple equivalent moment tensors for fault slip determined by insar the slip distributions derived from insar observations of both the darfield and christchurch events show a 15 km long gap in fault slip south west of christchurch which may present a continuing seismic hazard if a further unknown fault structure of significant size should exist there

paleoseismology of the 2010 mw 7 1 darfield canterbury earthquake source greendale fault new zealand abstract the previously unknown greendale fault ruptured in the september 2010 moment magnitude mw 7 1 darfield earthquake surface rupture fracture patterns and displacements along the fault were measured with high precision using real time kinematic rtk gps tape and compass airborne light detection and ranging lidar and aerial photos no geomorphic evidence of a penultimate surface rupture was revealed from pre 2010 imagery the fault zone is up to 300 m wide and comprises both distributed folding and discrete faulting deformation dominated by right lateral displacement surface fracturing accommodates 30 of the total right lateral displacement in the central fault zone the remainder is accommodated by distributed deformation ground penetrating radar and trenching investigations conducted across the central greendale fault reveal that most surface fractures are undetectable at depths exceeding 1 m however large discrete riedel shears continue to depths exceeding 3 m and displace interbedded gravels and sand filled paleochannels at one trench site a riedel shear displaces surface agricultural markers e g fences and plow lines and a subsurface 0 6 m deep paleo channel by 60 cm right laterally and 10 cm vertically indicating the paleochannel has been displaced only in the darfield earthquake optically stimulated luminescence osl dating of the displaced paleochannel yields an age of 21 6 1 5 ka two additional paleochannels at 2 5 m depth with osl ages of 28 4 2 4 ka and 33 2 ka have been displaced 120 cm right laterally and 20 cm vertically the doubling of displacement at depth is interpreted to indicate that in the central section of the greendale fault the penultimate surface rupturing event occurred between ca 20 and 30 ka the greendale fault remained undetected prior to the darfield earthquake because the penultimate fault scarp was eroded and buried during late pleistocene alluvial activity similar active faults with low slip rates i e lower than sedimentation erosion rates are likely to be concealed in alluvial settings globally

properties of the seismic nucleation phase abstract near source observations show that earthquakes begin abruptly at the p wave arrival but that this beginning is weak with a low moment rate relative to the rest of the main shock we term this initial phase of low moment rate the seismic nucleation phase we have observed the seismic nucleation phase for a set of 48 earthquakes ranging in magnitude from 1 1 8 1 the size and duration of the seismic nucleation phase scale with the total seismic moment of the earthquake suggesting that the process responsible for the seismic nucleation phase carries information about the eventual size of the earthquake the seismic nucleation phase is characteristically followed by quadratic growth in the moment rate consistent with self similar rupture at constant stress drop in this paper we quantify the properties of the seismic nucleation phase and offer several possible explanations for it

the 1997 may 10 zirkuh qa enat earthquake mw 7 2 faulting along the sistan suture zone of eastern iran summary the destructive zirkuh e qa enat earthquake of 1997 may 10 mw 7 2 ms 7 3 mb 6 3 produced 125 km of nnw sse right lateral strike slip surface faulting on the abiz fault in the sistan suture zone of eastern iran the longest known surface rupture associated with an iranian earthquake analysis of the body wave seismograms from the main shock shows that rupture occurred in four main subevents propagating in a sequence from north to south although predominantly strike slip the orientation of the faulting in each subevent varies with appreciable reverse components in the north central part and at the southern end of the abiz fault this change in fault style along the abiz fault inferred from the seismograms is also seen in the coseismic surface ruptures and the geomorphology average coseismic surface displacements were approximately 2 m implying a static stress drop of only 5 bar 0 5 mpa the 1997 surface ruptures followed clear traces of late quaternary slip on the abiz fault and for its northern 50 km re ruptured fault segments that had slipped in previous earthquakes of ms 6 0 6 6 in 1936 and 1979 the 1997 earthquake ruptured the northern end of the n s right lateral strike slip system of the sistan suture zone ending where it abuts a system of e w left lateral strike slip faults which have also slipped in large earthquakes during the last 30 years the earthquakes on this conjugate system of strike slip faults form a sequence that may have been triggered by the enhancement of stress on one fault as a result of slip on a neighbouring fault together these faults achieve n s right lateral shear of deforming iran against stable western afghanistan by n s slip on the right lateral faults and clockwise rotation of the e w left lateral faults

dynamic models of earthquakes on the north anatolian fault zone under the sea of marmara effect of hypocenter location 1 we perform three dimensional spontaneous dynamic rupture models of potential earthquakes on the geometrically complex north anatolian fault zone nafz under the marmara sea turkey the nafz south of the city of istanbul consists of a large scale extensional stepover with right lateral strike slip segments linked by an oblique normal segment we find that earthquakes nucleating near the stepover do not propagate across the entire fault system due to the statically unfavorable stress field on the oblique fault and lead to moderate size events only however earthquakes initiating a significant distance from the stepover cause significant dynamic unclamping of the oblique fault and thus generate large through going ruptures dynamic unclamping also produces supershear rupture propagation in the vicinity of fault discontinuities the results emphasize that estimations of earthquake size rupture propagation and slip distribution cannot be decoupled from the location of the hypocenter and the orientation of the geometrically complex fault system within the tectonic stress field

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

changes in frequency size relationship from small to large earthquakes the constant b value observed in frequency magnitude distributions of earthquakes has been taken as an indication of self similarity at all magnitudes hence earthquake properties should scale uniformly in the same way from small to large earthquakes it has often been observed however that the seismic moment released in small earthquakes scales differently with rupture length than it does for large events1 2 where the crossover between small and large events is defined at a rupture dimension equal to the down dip width of the seismogenic zone a possible explanation for this contradiction is that frequency size distributions are biased by small earthquakes small events dominate most global earthquake catalogues because of the short time period covered another source of bias in size distributions is the saturation of earthquake magnitudes for large events here we correct biases in calculations of b values and present evidence for a change in b value in frequency size distributions we find that a break in self similarity from small to large earthquakes occurs at a point where the dimension of the event equals the down dip width of the seismogenic layer

mineralogy of gold in the elshitsa massive sulphide deposit sredna gora zone bulgaria the elshitsa volcanic hosted massive sulphide deposit occurs in the central part of the srena gora metallogenic zone in bulgaria the gold bearing massive sulphide mineralization is considered to be the product of an island arc volcano plutonic process and hydrothermal activity that took place during the late cretaceous in addition to the major gold hosted opaque minerals such as pyrite chalcopyrite sphalerite and galena there are minor phases of tennantite goldfieldite se bearing aikinite native silver and bornite in the massive sulphide lenses and stringer zones most of the sulphide minerals are se bearing all of the six mineral assemblages that were deposited during the pyrite and copper pyrite stages of mineralization are gold bearing the gold tenor as a rule is less than 1 g t native gold and electrum occur as blebs or intergranular particles in the sulphide minerals gold in the early massive pyrite is of submicroscopic type 100 m in the late gold sulphide assemblages the electrum fineness in 41 individually studied grains varies between 780 and 992 with a mean of 895 native silver was found in association with bornite cu te sb and bi are the most common trace elements in gold and electrum the cu zn pb association is most important as a au ag carrier a model for gold behaviour during sulphide deformation is proposed involving coarsening of gold grain size from the earlier to the later sulphide mineral assemblages

shape of the magnitude frequency distribution for the canterbury earthquake sequence from integration of seismological and geological data abstract we combine geological and seismological data to describe the shape of the magnitude frequency distribution for the canterbury earthquake sequence in doing so we take the opportunity of the new datasets to address a long standing debate in the literature as to whether the seismicity of individual faults or fault zones is best described by the gutenberg richter gr relationship or the characteristic earthquake ce model we find that the magnitude frequency distribution for the entire composite fault zone of the canterbury earthquake sequence is adequately described by the gr relationship when uncertainties in the gr curve fitted to the instrumental catalog data and the range of paleoseismically derived recurrence intervals for large mainshock earthquakes on the greendale fault are collectively considered in contrast the magnitude frequency distribution for the smaller area of the greendale fault is better described by the ce model the difference is one of scale in that the composite fault zone represented by the canterbury earthquake sequence shows a gr distribution whereas individual faults within the zone show ce distributions definition of magnitude frequency distributions for seismic hazard modeling must therefore take scaling considerations into account rather than simply assuming that a single magnitude frequency distribution shape is applicable to all fault definitions

coseismic slip propagation on the tohoku plate boundary fault facilitated by slip dependent weakening during slow fault slip slow slip phenomena including earthquake afterslip and discrete slow slip events sse may have a major effect on megathrust earthquakes in subduction zones however the nature of this effect is still incompletely understood here we report that in friction experiments using samples from the plate boundary fault zone in the 2011 tohoku oki earthquake an increase in sliding velocity can induce a change from steady state frictional strength or slip strengthening friction to slip weakening frictional behavior specifically significant slip weakening is caused by velocity steps with initial slip rates consistent with afterslip observed after the largest tohoku earthquake foreshock on march 9th 2011 this suggests that the foreshock afterslip which is slightly faster than discrete sses is favorable for fault weakening that may have contributed to the large coseismic slip during the mainshock on the shallow plate boundary fault during the tohoku oki earthquake

earthquake centroid locations using calibration from ambient seismic noise earthquakes occur in complex geology making it difficult to determine their source parameters and locations because of uncertainty in path effects we can avoid some of these problems by applying the cut and paste cap method which allows for timing shifts between phases assuming a 1d model and determines source parameters if the travel times or lags of the phases due to path effects are known relative to a reference model we can locate the events centroid with surface waves without knowledge of the 3d velocity structure here we use ambient seismic noise for such a calibration we cross correlate the seismic stations near the earthquake with stations 100 300 km away to obtain the 10 100 s surface wave green s functions the new method is tested in southern california to locate the 2008 chino hills earthquake which proves consistent with the epicenter location from p waves it appears possible to use the location offset between the high frequency p wave onset relative to the centroid to provide a fast estimate of directivity

long term b value variations of shallow earthquakes in new zealand a hmm based analysis the magnitude frequency relationship is a fundamental statistic in seismology customarily the temporal variations of b values in the magnitude frequency distribution are demonstrated via sliding window approach however the window size is often only tuned empirically which may cause difficulties in interpretation of b value variability in this study a continuous time hidden markov model hmm is applied to characterize b value variations of new zealand shallow earthquakes over decades hmm based approach to the b value estimation has some appealing properties over the popular sliding window approach the estimation of b value is stable over a range of magnitude thresholds which is ideal for the interpretation of b value variability the overall b values of medium and large earthquakes across north island and northern south island in new zealand vary roughly at a decade scale it is noteworthy that periods of low b values are typically associated with the occurrences of major large earthquakes the overall temporal variations of b values seem prevailing over many grids in space as evidenced by a comparison of spatial b values in many grids made between two periods with low or high b values respectively we also carry out a pre seismic b value analysis for recent darfield earthquake and cook strait swarm it is suggested that the mainshock rupture is nucleated at the margin of or right at low b value asperities in addition short period of pre seismic b value decrease is observed in both cases the overall time varying behavior of b values over decades is an indication of broad scale of time varying behavior associated with subduction process probably related to the convergence rate of the plates the advance in the method of b value estimation will enhance our understanding of earthquake occurrence and may lead to improved risk forecasting

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

size distributions for large and small earthquakes small and large earthquakes obey different scaling laws and inhabit distinct populations both characterized by power laws with different exponents when considering earthquakes on a single fault or fault segment the one large earthquake that occurs during a seismic cycle is discontinuous with the population of small earthquakes here it is shown that these two observations together with the scaling laws are self consistent when proper account is taken of the size distribution of faults

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

statistics of characteristic earthquakes statistical methods are used to test the characteristic earthquake hypothesis several distributions of earthquake size seismic moment frequency relations are described based on the results of other researchers as well as my own tests evidence of the characteristic earthquake hypothesis can be explained either by statistical bias or statistical artifact since other distributions of earthquake size provide a simpler explanation for available information the hypothesis cannot be regarded as proven

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

dynamic rupture through a branched fault configuration at yucca mountain and resulting ground motions we seek to characterize the likelihood of multiple fault activation along a branched normal fault system during earthquake rupture using dynamic finite element analyses this is motivated by the normal faults in the vicinity of yucca mountain nevada a potential site for a high level radioactive waste repository the solitario canyon fault scf a north south trending fault located approximately 1 km west of the crest of yucca mountain is the most active of these faults based on the results of previous branching work by kame et al 2003 branch activation in the hanging wall of a normal fault such as the scf may be possible for fast ruptures propagating near the rayleigh wave speed at the branch junction dynamic branch activation along a splay of the scf during a seismic event could have important effects on the rupture velocity and resulting ground motions at the proposed repository site we consider elastic as well as a pressure dependent elastic plastic response of the off fault material we find that based on the regional stress state in the area the only likely candidates for branch activation in the hanging wall of the scf are more steeply westward dipping intrablock splay faults we also find that the rupture velocity for an earthquake propagating updip along the scf must reach supershear speeds in order for dynamic branch activation to occur branch activation can have significant effects on the ground motions at the proposed repository site 1 km away from the scf beneath the crest of yucca mountain causing the repository site to experience a second peak in large vertical particle velocities elastic plastic response near the branch junction reduces peak ground velocities and accelerations at the proposed repository site

frequency of occurrence of moderate to great earthquakes in intracontinental regions implications for changes in stress earthquake prediction and hazards assessments we investigate the departure of shallow intracontinental earthquakes from the frequency magnitude relationship log n m a bm we consider seven large continental regions but exclude subduction zones in each active and stable areas are differentiated within active areas we separately categorize earthquakes on faults with high slip rates we use data sets from 1978 1994 and 1900 1994 which are complete for moment magnitudes mw 5 3 and 7 0 to calculate changes in b value with mw for all active intracontinental regions combined except asia b changes at 98 confidence from 0 90 to 2 1 at a corner magnitude mc of 6 9 to 7 0 the distribution for stable regions indicates a similar change values of mc are associated with downdip widths of rupture of about 23 to 27 km which are smaller than those for subduction zones in each case mc marks a transition from unbounded to bounded earthquakes in asia events from 1958 to 1994 also delineate a similar change near mc 7 0 earthquakes in asia of 7 0 mw 8 1 from 1900 to 1957 however define a b value of 1 0 and a moment release rate 5 6 times higher than that from 1958 to 1994 those anomalous values indicate that a large region of asia was close to failure i e near a self organized critical state during the earlier period we associate those changes with the giant himalayan earthquake in 1950 of mw 8 6 regional variations in seismic strain release rates correlate with the types of processes at adjacent plate boundaries extrapolating rates of activity of the past 95 years to mw 8 0 indicates that such events should be very rare in stable areas

the magnitude distribution of earthquakes near southern california faults we investigate seismicity near faults in the southern california earthquake center community fault model we search for anomalously large events that might be signs of a characteristic earthquake distribution we find that seismicity near major fault zones in southern california is well modeled by a gutenberg richter distribution with no evidence of characteristic earthquakes within the resolution limits of the modern instrumental catalog however the b value of the locally observed magnitude distribution is found to depend on distance to the nearest mapped fault segment which suggests that earthquakes nucleating near major faults are likely to have larger magnitudes relative to earthquakes nucleating far from major faults

rates of deformation uplift and landscape development associated with active folding in the waipara area of north canterbury new zealand analysis of the geometry and ages of faulted and tilted late quaternary fluvial terraces and their associated cover beds provide evidence of active folding at three locali ties in the waipara area of north canterbury new zealand terrace survey data the occurrence of the approximately 22 6 kyr old aokautere ash and examination of soil profiles indi cate that folding has continued into the late holocene but that the amounts and rates of deformation are locally variable rates of uplift in the waipara area are compared with those de rived from marine terraces preserved at the pacific coast east of the study area results indicate that rates of measurable de formation reach a maximum along the waipara range front where bedrock deformation is most intense and shortening rates of up to 5 57 0 69 100 kyr occur across the coastal ranges the average rate of shortening is 0 8 0 4 100 kyr which corresponds with an absolute shortening rate of 1 4 0 6 m kyr and represents only a small proportion of the pre dicted plate motion vector in this region uplift rates range from 0 1 83 m kyr for a late last glacial fluvial terrace and from 1 36 2 16 m kyr for three marine terraces fluvial and marine terrace uplift rates vary in accord with the geometries of the folds in bedrock and the spatial pattern of uplift di rectly reflects fold growth the structure contour pattern of folded surfaces provides a first approximation to the spatial pattern of uplift differential uplift due to folding accounts for up to approximately 55 75 of the total uplift and has produced folds with structural relief of about 1300 m i e amplitudes of 600 700 m these folds have formed over the

reliability of coulomb stress changes inferred from correlated uncertainties of finite fault source models 1 static stress transfer is one physical mechanism to explain triggered seismicity coseismic stress change calculations strongly depend on the parameterization of the causative finite fault source model these models are uncertain due to uncertainties in input data model assumptions and modeling procedures however fault model uncertainties have usually been ignored in stress triggering studies and have not been propagated to assess the reliability of coulomb failure stress change cfs calculations we show how these uncertainties can be used to provide confidence intervals for co seismic cfs values we demonstrate this for the mw 5 9 june 2000 kleifarvatn earthquake in southwest iceland and systematically map these uncertainties a set of 2500 candidate source models from the full posterior fault parameter distribution was used to compute 2500 cfs maps we assess the reliability of the cfs values from the coefficient of variation cv and deem cfs values to be reliable where they are at least twice as large as the standard deviation cv 0 5 unreliable cfs values are found near the causative fault and between lobes of positive and negative stress change where a small change in fault strike causes cfs values to change sign the most reliable cfs values are found away from the source fault in the middle of positive and negative cfs lobes a likely general pattern using the reliability criterion our results support the static stress triggering hypothesis nevertheless our analysis also suggests that results from previous stress triggering studies not considering source model uncertainties may have lead to a biased interpretation of the importance of static stress triggering

the 2010 2011 canterbury earthquake sequence environmental effects seismic triggering thresholds and geologic legacy abstract seismic shaking and tectonic deformation during strong earthquakes can trigger widespread environmental effects the severity and extent of a given effect relates to the characteristics of the causative earthquake and the intrinsic properties of the affected media documentation of earthquake environmental effects in well instrumented historical earthquakes can enable seismologic triggering thresholds to be estimated across a spectrum of geologic topographic and hydrologic site conditions and implemented into seismic hazard assessments geotechnical engineering designs palaeoseismic interpretations and forecasts of the impacts of future earthquakes the 2010 2011 canterbury earthquake sequence ces including the moment magnitude m w 7 1 darfield earthquake and m w 6 2 6 0 5 9 and 5 8 aftershocks occurred on a suite of previously unidentified primarily blind active faults in the eastern south island of new zealand the ces is one of earth s best recorded historical earthquake sequences the location of the ces proximal to and beneath a major urban centre enabled rapid and detailed collection of vast amounts of field geospatial geotechnical hydrologic biologic and seismologic data and allowed incremental and cumulative environmental responses to seismic forcing to be documented throughout a protracted earthquake sequence the ces caused multiple instances of tectonic surface deformation 3 events surface manifestations of liquefaction 11 events lateral spreading 6 events rockfall 6 events cliff collapse 3 events subsidence 4 events and hydrological 10s of events and biological shifts 3 events the terrestrial area affected by strong shaking e g peak ground acceleration pga 0 1 0 3 g and the maximum distances between earthquake rupture and environmental response r rup both generally increased with increased earthquake m w but were also influenced by earthquake location and source characteristics however the severity of a given environmental response at any given site related predominantly to ground shaking characteristics pga peak ground velocities and site conditions water table depth soil type geomorphic and topographic setting rather than earthquake m w in most cases the most severe liquefaction rockfall cliff collapse subsidence flooding tree damage and biologic habitat changes were triggered by proximal moderate magnitude m w 6 2 earthquakes on blind faults ces environmental effects will be incompletely preserved in the geologic record and variably diagnostic of spatial and temporal earthquake clustering liquefaction feeder dikes in areas of severe and recurrent liquefaction will provide the best preserved and potentially most diagnostic ces features rockfall talus deposits and boulders will be well preserved and potentially diagnostic of the strong intensity of ces shaking but challenging to decipher in terms of single versus multiple events most other phenomena will be transient e g distal groundwater responses not uniquely diagnostic of earthquakes e g flooding or more ambiguous e g biologic changes preliminary palaeoseismic investigations in the ces region indicate recurrence of liquefaction in susceptible sediments of 100 to 300 yr recurrence of severe rockfall event s of ca 6000 to 8000 yr and recurrence of surface rupturing on the largest ces source fault of ca 20 000 to 30 000 yr these data highlight the importance of utilising multiple proxy datasets in palaeoearthquake studies the severity of environmental effects triggered during the strongest ces earthquakes was as great as or equivalent to any historic or prehistoric effects recorded in the geologic record we suggest that the shaking caused by rupture of local blind faults in the ces comprised a worst case seismic shaking scenario for parts of the christchurch urban area moderate m w blind fault earthquakes may contribute the highest proportion of seismic hazard be the most important drivers of landscape evolution and dominate the palaeoseismic record in some locations on earth including locations distal from any identified active faults a high scientific priority should be placed on improving the spatial extent and quality of off fault shaking records of strong earthquakes particularly near major urban centres