accelerated pacific plate subduction following interplate thrust earthquakes at the japan trench interplate thrust earthquakes are usually followed by afterslips and they let the fore arc move slowly trenchward however we do not know if the subducting oceanic plate is accelerated landward after such earthquakes the westward velocity of global positioning system gps stations in ne japan show gradient decreasing from east to west reflecting the e w contractional strain built up by the inter plate coupling here we show that such coupling significantly enhanced 1 5 times after the 2003 tokachi oki earthquake mw 8 0 hokkaido in the segments adjacent to the ruptured fault the coupling seems to be further enhanced 3 times after the 2011 tohoku oki earthquake mw 9 0 it is unlikely that interplate friction suddenly increased over such a large region and relatively strong pre 2003 coupling there would not allow such enhancements even if full coupling is attained hence they are attributable to the temporary acceleration of the pacific plate subduction we propose a simple 2 dimensional model in which down dip acceleration of the slab let the force balance rapidly recover promoted by a thin low viscosity layer on the slab surface the accelerated subduction would account for temporary activations of regional interplate seismicity after megathrust earthquakes

pull apart formation and strike slip partitioning in an obliquely divergent setting leka ophiolite norway abstract the leka ophiolite complex loc is located on the island of leka norway and belongs to the uppermost allochthon of the scandinavian caledonides the rocks of the adjacent mainland and most of the surrounding islands are basement gneisses and supracrustal rocks not related to the ophiolite complex paleostress analysis gravity inversion and regional geology support a fault bounded rhombochasm geometry for the loc the paleostress inversions revealed two types of tensors interpreted as small strains 1 horizontal extension generally e w to ne sw and 2 horizontal extension in the same direction with an added component of perpendicular horizontal contraction a strong positive gravity anomaly 25 mgal is centered on leka and gravity inversion indicates that the loc lies directly below its surface exposures with steep sided walls and a flat bottom located at 7 km depth the faults bounding the loc probably initiated during postorogenic extension in the scandinavian caledonides the faults are regional in scale and are parallel to other ne sw trending en echelon faults along the norwegian coastline and on the adjacent mainland a pull apart structure explains the down dropping and subsequent preservation of the loc as it is surrounded by rocks from lower structural positions within the nappe stack the paleostress directions from leka support a sinistral component of shear along these faults the gravity inversion is consistent with a fault bounded geometry this pull apart structure as uniquely recorded by the dense ophiolitic rocks suggests that strike slip partitioning was active in an obliquely divergent setting

fault reactivation and structural inversion backarc and intraplate compressive deformations example of the eastern sunda shelf indonesia the tectonic evolution of the eastern sunda platform in indonesia is revealed by the study of seismic profiles and comprises three general tectonic periods during the cenozoic extension with graben infill from the paleogene to the early miocene a tectonically quiet period with only broad subsidence and a middle miocene recent period of folding inversion and thrusting these structures reveal changes in the intraplate stress field which was controlled by the changes in the boundary conditions of the plates collisions on the northern and eastern sides and interplate coupling southward along the java subduction zone inversions often occurred without reactivation of pre existing normal fault planes at the upper levels of these faults the factors controlling these deformations are discussed with special interest placed on the conditions for the potential reactivation of cohesionless normal faults inversion and reactivations were mostly controlled by the orientation of the pre existing fault planes in relation with the regional stress field and by the tectonic stress regime in a strike slip regime effective principal stresses 1 and 3 horizontal with 1 2 3 the optimum conditions for reactivation in isotropic rocks are pre existing faults that strike close to the potential two vertical conjugate failure planes the same mechanical properties as for pre existing fault prevail in such conditions strike slip movements and reverse strike slip movements and associated en echelon folds were generally observed in a compressive regime 1 and 2 horizontal with 1 2 3 typical steeply dipping normal faults are difficult to reactivate by slip movements we suggest that reverse slip movements occurred in the deeper levels of faults and were accommodated by flexure above the pre existing fault planes and the inversion of grabens the strongly inverted grabens are those whose orientation is perpendicular to the regional compression nevertheless with strong regional shortening large uplifts and thrust faults were observed with reactivation in the form of reverse or reverse strike slip movements along pre existing steeply dipping normal fault planes

seven years of postseismic deformation following the 1999 m 7 4 and m 7 2 izmit duzce turkey earthquake sequence 1 we report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode gps observations for the 1999 izmit duzce earthquake sequence resolvable time dependent postseismic changes to the preearthquake interseismic velocity field extend at least as far as the continuous gps station in ankara 200 km southeast of the izmit rupture seven years after the earthquake sequence the relative postseismic velocity across the north anatolian fault naf reaches 10 12 mm a roughly 50 of the steady state interseismic rate with the highest postseismic velocities within 40 km of the coseismic ruptures we use a sequence of logarithmic time functions to fit gps site motions up to three logarithmic terms with decay constants of 1 150 and 3500 days are necessary to fit all the transient motion observed at the continuous gps stations the first term is required for the component of site motion parallel to the naf at near field sites strongly implicating rapid shallow afterslip the intermediate and longer term postseismic velocity components reflect more broadly distributed strain with a symmetric double couple pattern suggestive of either localized deep afterslip or viscoelastic relaxation of the upper mantle and or lower crust in two areas including the marmara sea this pattern is superimposed on north south extension centered on the naf we speculate that this extension may result from aseismic dip slip along coseismically weakened faults driven by the background tectonic stress

fogo volcano cape verde islands seismicity derived constraints on the mechanism of the 1995 eruption seismic data recorded in the vicinity of the active vent of the 1995 fogo eruption global volcanism network bulletin 1995 20 3 2 4 is used to constrain the associated stress field and deformation using the frequency content of the seismograms to distinguish between brittle fracture of cold host rock and deformation in the vicinity of the intruding magma a sub vertical dyke with 060 strike is identified as the feeder of the eruption and delineated down to a depth of about 4 km the local stress field during the eruption is estimated from composite focal mechanisms besides the expected 3 direction normal to the dyke a group of focal solutions point to a stress field with nearly dyke parallel 3 which is interpreted as a re adjustment of the edifice following the eruption maybe partially controlled by gravity this effect may have increased the instability of the steep eastern flank of the island since the deformation detected during the magma drainback is compatible with predominantly dip slip motion on east dipping surfaces

characterizing afterslip and ground displacement rate increase following the 2014 iquique pisagua mw 8 1 earthquake northern chile proyecto fondecyt conicyt chile 11140904 german science foundation dfg 2310 3 1

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

seismicity induced by gas production ii lithology correlated events induced stresses and deformation a 3d relocation technique permits precise locations of induced earthquakes geostatistical processing using the data of 87 boreholes provides the basis of a precise 3d structure with a dome geometry conventional laboratory mechanical tests performed on deep rock samples 1000 m to 5000 m define the rock properties at depths similar to those of the seismic events 1 ml 4 2 that range from 1 to 7 km

paleostress analysis of cenozoic faulting in the kraishte area sw bulgaria abstract paleostress calculations from fault planes in paleogene sediments and in the underlying basement were used to determine the orientation and the chronology of the principal stresses during the cenozoic tectonic evolution of the kraishte area southwest bulgaria the results show that middle eocene early oligocene wsw ene extension led to the formation of grabens and half grabens filled with thick continental to marine deposits in the hanging wall of extensional detachments the paleogene sediments and their basement were then intruded by subvolcanic bodies and dykes during sw ne extension between 32 and 29 ma these wsw ene and sw ne extensional stages are related to the general rollback of the hellenic slab from the late oligocene to the earliest miocene sse nnw transtension generated coal bearing sedimentary basins the anticlockwise rotation of the main tensile axis by almost 50 with respect to the previous tectonic stage was probably related to a switch from the aegean back arc extension to crustal stretching and extrusion of continental fragments around the moesian platform since the middle miocene extension in the kraishte area accommodated by faults with relatively small displacement led to the formation of restricted basins filled with alluvial to lacustrine deposits

supercycle at the ecuadorian subduction zone revealed after the 2016 pedernales earthquake large earthquakes are usually assumed to release all of the strain accumulated since the previous event implying a reduced seismic hazard after them however long records of seismic history at several subduction zones suggest supercycle behaviour where centuries long accumulated strain is released through clustered large earthquakes resulting in an extended period of enhanced seismic hazard here we combine historical seismology results present day geodesy data and dense local observations of the recent mw 7 8 2016 pedernales earthquake to reconstruct the strain budget at the ecuador subduction zone since the great 1906 earthquake we show that the pedernales earthquake involved the successive rupture of two patches on the plate interface that were locked prior to the earthquake and most probably overlaps the area already ruptured in 1942 by a similar earthquake however we find that coseismic slip in 2016 exceeds the deficit accumulated since 1942 the seismic moment of every large earthquake during the twentieth century further exceeds the moment deficit accumulated since 1906 these results together with the seismic quiescence before 1906 highlighted by historical records and marine palaeoseismology argue for an earthquake supercycle at the ecuador colombia margin this behaviour which has led to an enhanced seismic hazard for 110 years is possibly still going on and may apply to other subduction zones that recently experienced a great earthquake large earthquakes are often assumed to reset the seismic hazard of a region analysis of recent and historical seismicity in ecuador suggests that this region may experience clusters of large earthquakes and extended periods of high seismic hazard

on the relationship between offshore geodetic coverage and slip model uncertainty analog megathrust earthquake case studies we apply a geodetic slip inversion technique to analog subduction megathrust earthquakes to demonstrate how limited offshore geodetic coverage affects coseismic slip models we analyzed two archetypical megathrust earthquakes trench breaking and non trench breaking earthquakes slip inversion models of analog earthquakes show quantitative and qualitative changes as a function of offshore coverage shallow slip cannot be resolved if the observation coverage of the offshore segment is 50 moreover the slip pattern of shallow event flips from landward to trenchward skewed as offshore coverage reduces to 40 the estimated slip for both event types converges to a similar unimodal pattern when there is no offshore coverage we infer 5 20 slip overestimation when the observations are above the high slipping zone during trench breaking events versus 5 10 underestimation during non trench breaking events if observations are land limited the moment magnitude derived for trench breaking ruptures might be significantly affected m w 0 5

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

breddin s graph for tectonic regimes abstract a simple graphical method is proposed to infer the tectonic regime from a fault and slip data set an abacus is overlaid on a plot of the rake versus strike of the data this yields the horizontal principal stress directions and a constraint on the stress tensor aspect ratio in a manner similar to breddin s graph for two dimensional strain analysis the main requirement is that one of the principal stress directions is close to the vertical this method is illustrated on monophase synthetic and natural data but is also expected to help sort out multiphase data sets

neotectonic deformation within an extensional stepover in el salvador magmatic arc central america implication for the interaction of arc magmatism and deformation abstract dominantly westward movement of the el salvador forearc at rates of 11 mm yr is accommodated by a series of e w to wnw oriented dextral strike slip fault zones herein referred to as the el salvador fault system esfs the geometry of the esfs defines a series of extensional step overs along the arc basaltic volcanism in the stepovers is associated with nnw oriented normal faults whereas rhyolitic volcanism is associated with strike slip fault zones of the esfs on the esfs the san salvador extensional stepover sses is bound to the south by the san vicente fault zone where the rhyolitic ilopango caldera is located in the sses tephras from ilopango the tierra blanca tb sequence track long term elongation older tb units tb5 8 contain abundant normal faults lying unconformably above these older tb units younger tb members tbj tb2 4 are generally unfaulted analyses of faults in tb5 8 indicate ne to ene oriented elongation in the sses deformation occurred between deposition of the tb4 and tb5 units during quiescence of the ilopango eruptive center using this temporal constraint minimum elongation rates of 3 50 10 15 s 1 2 06 10 14 s 1 and 4 42 10 14 s 1 were calculated for three traverses from regional geodetic data and fault kinematics throughout el salvador we interpret the sses as part of a series of pull apart structures along the arc axis the calculated paleostress orientations are consistent with a pull apart geometry resulting from forearc movement the extensional deformation occurs during a 50 k y lull in rhyolitic activity suggesting an interplay between magmatism and deformation within the arc during significant rhyolitic volcanic activity only minor elongation is observed in the sses despite ongoing translation of the salvadoran forearc we speculate that rhyolitic magmatism along upper crustal faults may facilitate strike slip movement on the esfs rather than distributing deformation throughout the extensional stepover

earthquake supercycles inferred from sea level changes recorded in the corals of west sumatra records of relative sea level change extracted from corals of the mentawai islands sumatra imply that this 700 kilometer long section of the sunda megathrust has generated broadly similar sequences of great earthquakes about every two centuries for at least the past 700 years the moment magnitude 8 4 earthquake of september 2007 represents the first in a series of large partial failures of the mentawai section that will probably be completed within the next several decades

stress and timing relationships of a fault related paleohydrothermal system in central new hampshire record of a mesozoic stress change in new england a mineral assemblage comprised of chalcedony drusy quartz and very fine grained iron hydroxide limonite with or without blocky calcite qfc coats joint surfaces fills fractures and commonly occurs as pressure shadow encrustations on brittle fault surfaces in central new hampshire but only occurs sporadically in other areas of new england locally qfc includes silicified breccias of highly altered host and euhedral quartz crystal fragments suspended in a matrix of chalcedony and limonite one hundred and four brittle faults from central new hampshire mineralized with qfc can be separated into two families set n is composed of primarily north northeast to northeast trending steeply dipping normal faults n 61 and set s is composed of north northwest to north northeast trending steeply dipping primarily right lateral strike to normal oblique slip faults n 43 these two sets of faults are thought to record two paleostress conditions the extension direction for both tensors plunges gently east southeast but the compression direction is near vertical for set n and trends roughly northeast plunging 30 for set s fault slip inversion suggests that set n faults are best fit with 1 most deviatoric 2 3 set s is best fit with 3 most deviatoric 1 2 and low values for fault plane coefficient of friction and or high fluid pressure qfc occurs in the 158 ma belknap mountain complex of the white mountain magma series and is thought to have developed at relatively shallow crustal levels based on the assemblage nature of fluid inclusions and association of qfc as brittle fault and fracture filling mineralization occurrence of qfc in the 158 ma belknap mountain complex paleostress implications of qfc mineralized brittle faults and range and character of fault fabrics in the belknap units suggests that qfc developed around the time of belknap intrusion and cooling and that late jurassic to early cretaceous is the approximate time at which a regional change in paleostress conditions occurred in new england this age and nature of the paleostress change is in accord with a change postulated by de boer et al 1988

inversion of field data in fault tectonics to obtain the regional stress i single phase fault populations a new method of computing the stress tensor summary we attempt a general definition of the inverse problem of computing the components of the regional stress tensor from a set of field data including the measurements of the strike and dip of several faults and the directions and senses of relative motion along these faults as indicated by slickenslides in previous treatments of this problem no experimental errors could be taken into account except those in measuring the pitch of slickenslides thus errors in the orientation of the fault strike and dip which have considerable practical importance were neglected in our work all experimental errors in the field measurements are taken into account so that the agreement between the computed stress tensor and the set of field measurements can be rigorously checked

unravelling polyphase brittle tectonics through multi software fault slip analysis the case of the voltri unit western alps italy abstract we have analyzed the brittle structures in a key area of the alps apennines transition zone nw italy here two orogens have interfered with each other since oligocene times producing a complex structural evolution and a heterogeneous fault population only relative chronologies can be reconstructed as stratigraphic constraints are lacking we have performed the inversion of fault slip data with two softwares for paleostress calculations combined with field observations at selected structural stations and photo interpretation the resulting incompatible stress tensors can be grouped in this sequence i a strike slip tensor with nnw sse trending 1 event a ii a strike slip tensor with ne sw trending 1 event b and iii an extensional transtensional tensor with nw se or ne sw trending 3 event c we correlated our results with structures of known age from adjacent areas event a is possibly rupelian early chattian linked to far field incipient rifting in the future ligurian provencal basin event b fits oligo miocene shortening the faults may belong to a sinistral strike slip zone that accommodated the oblique component of deformation during the rotation of the corsica sardinia block event c is attributed to a pliocene quaternary neotectonic event therefore combining different inversion procedures with a detailed structural analysis has successfully unravelled the polyphase brittle tectonics

time varying interseismic strain rates and similar seismic ruptures on the nias simeulue patch of the sunda megathrust fossil coral microatolls from fringing reefs above the great m w 8 6 megathrust rupture of 2005 record uplift during the historically reported great earthquake of 1861 such evidence spans nearly the entire 400 km strike length of the 2005 rupture which was previously shown to be bounded by two persistent barriers to seismic rupture moreover at sites where we have constrained the 1861 uplift amplitude it is comparable to uplift in 2005 thus the 1861 and 2005 ruptures appear to be similar in both extent and magnitude at one site an uplift around ad 1422 also appears to mimic the amount of uplift in 2005 the high degree of similarity among certain ruptures of this nias simeulue section of the sunda megathrust contrasts with the substantial disparities amongst ruptures along other sections of the sumatran portion of the sunda megathrust at a site on the northwestern tip of nias reefs also rose during an earthquake in ad 1843 known historically for its damaging tsunami along the eastern coast of the island the coral microatolls also record interseismic vertical deformation at annual to decadal resolution spanning decades to more than a century before each earthquake the corals demonstrate significant changes over time in the rates of interseismic deformation on southern simeulue interseismic subsidence rates were low between 1740 and 1820 but abruptly increased by a factor of 4 10 two to four decades before the 1861 rupture this may indicate that full coupling or deep locking of the megathrust began only a few decades before the great earthquake in the banyak islands near the pivot line separating coseismic uplift from subsidence in 2005 ongoing interseismic subsidence switched to steady uplift from 1966 until 1981 suggesting a 15 year long slow slip event with slip velocities at more than 120 of the plate convergence rate

superposed local and regional paleostresses fault slip analysis of neogene extensional faulting near coeval caldera complexes yucca flat nevada numerous reduced stress tensors are computed by multiple inversions of 906 temporally and spatially partitioned fault slip data from the yucca flat region in the southwest nevada volcanic field to constrain the neogene paleostress and faulting history and to investigate how the regional tectonic stress field was affected by local caldera magmatism perturbed shallow 400 m pre 11 ma paleostress configurations determined west and northwest of present post 11 ma yucca flat basin existed during mild extensional faulting and are attributed to superposition of transient caldera magmatic stresses on the regional stress field northwest of yucca flat a progressive shift in least principal stress 3 directions near known calderas located 5 15 km to the west occurred under a normal slip stress state during caldera development between about 15 and 13 ma a brief 0 5 m y change to a strike slip stress state occurred at about 13 ma and was accompanied by small offset quasi conjugate strike slip faulting this stress state was most distinct relative to a normal slip state near calderas where stress solutions and fault relations indicate closer affinities to a reverse slip state inferred 11 6 11 45 ma paleostress tensors indicate radial tension associated with either initial caldera collapse or local post collapse topographic modification of the stress field post 11 ma normal slip stress tensors are associated with normal and oblique slip faults that accommodated subsidence and eastward extension of yucca flat basin away from the caldera complexes these tensors do not indicate stress modifications due to residual caldera related effects and thus were used to infer post 11 ma regional stress changes the stress field has rotated as much as 65 clockwise since 11 ma during extensional development of yucca flat basin with most of the rotation and extension occurring before about 8 5 ma results suggest that shallow magmatism and caldera development can strongly alter extensional tectonic stress fields fault patterns and slip directions in the uppermost crust out to distances of roughly two magma chamber radii away from a magma body

the cardston earthquake swarm and hydraulic fracturing of the exshaw formation alberta bakken play more than 60 small earthquakes m l 0 7 3 0 were detected from december 2011 to march 2012 north of cardston alberta an area with little evidence for previous seismic activity the timing of these events closely correlates 99 7 confidence with hydraulic fracturing completions of the devonian mississippian age exshaw formation at a nearby horizontal well unanimous waveform multiplicity within the swarm suggests that the events share a similar origin and source mechanism this observation is corroborated by the point like collocation of hypocenters within the crystalline basement during robust double difference relocations furthermore the presence of a pre existing fault is confirmed via formation top offset mapping and interpreted to be a late cretaceous extensional fault the confirmation of this fault at depth provides a plausible pathway for rapid hydraulic communication from the fracturing interval into the crystalline basement consistent with structural interpretations and available stress information moment tensor inversion of the largest magnitude event m w 3 0 indicates reactivation of a basement fault with normal slip we conclude that the genesis of this earthquake swarm was likely caused by increased pore pressure within the basement fault as a result of fracturing stimulation online material figure showing frequency magnitude distribution of earthquakes and table of the velocity models used in the study

reawakening of large earthquakes in south central chile the 2016 mw 7 6 chiloe event on 25 december 2016 the mw 7 6 chiloe earthquake broke a plate boundary asperity in south central chile near the center of the rupture zone of the mw 9 5 valdivia earthquake of 1960 to gain insight on decadal scale deformation trends and their relation with the chiloe earthquake we combine geodetic teleseismic and regional seismological data gps velocities increased at continental scale after the 2010 maule earthquake probably due to a readjustment in the mantle flow and an apparently abrupt end of the viscoelastic mantle relaxation following the 1960 valdivia earthquake it also produced an increase in the degree of plate locking the chiloe earthquake occurred within the region of increased locking breaking a circular patch of 15 km radius at 30 km depth located near the bottom of the seismogenic zone we propose that the chiloe earthquake is a first sign of the seismic reawakening of the valdivia segment in response to the interaction between postseismic viscoelastic relaxation and changes of interseismic locking between nazca and south america

small scale faulting in the upper cretaceous of the groningen block the netherlands 3d seismic interpretation fault plane analysis and regional paleostress abstract over the last years field based studies have shown that fault surfaces can exhibit a considerable self affine topography it is reasonable to assume that similar undulations are also present in fault interpretations from 3d reflection seismic data however both the interpretation uncertainty and geophysical resolution limits hinder their analysis this study analyses a set of small scale non reactivated faults in the upper cretaceous chalk group upper ommelanden formation of the nw part of the groningen block the netherlands in a high quality pre stack depth migrated 3d seismic data set the studied faults are fully contained inside the chalk group in an area located between the major tectonic bounding faults of the nw groningen block over 200 faults with offsets in the order of 30 50 m were interpreted across an area of ca 150 km 2 showing a clear preferential orientation for strike dip and dip direction detailed interpretations and 3d fault plane analyses show undulations on the fault plane we show that these undulations are not an interpretation or gridding artefact and interpret these to indicate direction of fault slip these results were used to calculate a paleostress tensor using all faults to calculate a single stress tensor for the entire study area by numerical dynamic analysis based on the orientation position and a thickness analysis it is interpreted that these faults formed due to the tectonic reactivation of salt structures in the latest cretaceous the calculated paleostress state shows a general nw se extension with a vertical maximum principle stress and a stress ratio of about 0 3 indicating that the studied faults are not the result of dewatering this interpretation agrees both with a nearby salt tectonic reconstruction as well as field based paleostress results from the uk belgium and france a first look at other surveys from the dutch sector indicates that similar faults are present in other areas with different orientations we propose that a dedicated analysis of these faults across on and offshore europe would allow extending the stress map of the late cretaceous into areas where the chalk is not outcropping

paleostress states at the south western margin of the central european basin system application of fault slip analysis to unravel a polyphase deformation pattern abstract we analyse the deformation pattern along the south western margin of the central european basin system cebs where upper carboniferous mesozoic rocks are uplifted due to the late cretaceous basin inversion the geometry of mesoscale faults and associated striae are used to calculate the stress state s responsible for the observed deformation each reduced stress tensor obtained comprises i the directions of the principal stress axes 1 2 and 3 1 2 3 and ii the ratio of principal stress differences r 2 3 1 3 we present a stress inversion technique that allows each stress state inherent in a heterogeneous fault population to be identified by integrating the results of the pbt method turner f j 1953 nature and dynamic interpretation of deformation lamellae in calcite of three marbles american journal of sciences 251 4 276 298 sperner b ratschbacher l and ott r 1993 fault striae analysis a turbo pascal program package for graphical presentation and reduced stress tensor calculation computers geosciences 19 1361 1388 and the multiple inverse method yamaji a 2000 the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data journal of structural geology 22 4 441 452 this comprehensive approach not only facilitates the separation of complex data sets into homogeneous subsets but also guarantees that each stress state derived fulfils both the criteria of low misfit angles wallace bott hypothesis and high shear to normal stress ratios mohr coulomb criterion the reliability of our technique is confirmed by the fact that irrespective of i the number of fault slip data from an outcrop ii the number of subsets they represent and iii the proportion of newly formed and reactivated faults we obtain consistent results from outcrops of variously aged rocks this consistency concerns both calculated stress states as well as locally observed deformation sequences such local chronologies are derived from cross cutting relationships and superimposition of different fault slip data which individually are assigned to a consistent stress state a synthesis of results from different locations of the study area argues for the superposition of two main deformation events most prominently the area was affected by a stress state with a horizontal n s to ne sw directed maximum compression 1 and a low stress ratio which induced reverse and strike slip faulting a pure strike slip regime of e w to nw se directed compression with moderate stress ratios is less prevalent and probably younger the age of the youngest rocks documenting these two phases proves the stress fields to correspond to the polyphase late cretaceous tertiary basin inversion of the cebs during post cenomanian times the youngest tectonic imprints detected in the study area correspond to locally appearing extensional stress states with varying directions of 3 at many sites the youngest derived paleostress state coincides with the present day stress field in terms of the direction of the maximum horizontal stress axis s hmax the only stress state detected which pre dates the basin inversion corresponds to an extensional regime with an wnw ese to nw se directed 3 axis observed only locally in the n s striking leine graben and its prolongation to the north the fact that the majority of variously aged rocks exhibit only the traces of the latest deformation phases indicates a high degree of fault plane reactivation in the study area

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

paleostress inversion a multi parametric geomechanical evaluation of the wallace bott assumptions wallace 1951 and bott 1959 were the first to introduce the idea that the slip on each fault surface has the same direction and sense as the maximum shear stress resolved on that surface however this simplified hypothesis is questionable since fault mechanical interactions may induce slip reorientations earlier numerical geomechanical models confirmed that the slickenlines slip vectors are not necessarily parallel to the maximum resolved shear stress but are consistent with local stress perturbations this leads us to ask as to what extent the wallace and bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data here a geomechanical multi parametric study using a 3d boundary element method covering i fault geometries such as intersected faults or corrugated fault surfaces ii the full range of andersonian state of stress iii fault friction iv fault fluid pressure v half space effect and vi rock properties is performed in order to understand the effect of each parameter on the misfit angle between geomechanical slip vectors and the resolved shear stresses it is shown that significant misfit angles can be found under specific configurations invalidating the wallace and bott assumptions even though fault friction tends to minimize the misfit we therefore conclude that in such cases stress inversions based on fault slip data should be interpreted with care

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

spatial heterogeneity of tectonic stress and friction in the crust the complex geometry of faults seismicity and diversity of earthquake mechanisms suggest that the stress and strength in earth s crust are spatially heterogeneous we investigated the degree of heterogeneity using the following two end member models in one end member model we assumed that the orientation of stress is uniform in the crust as is assumed in many stress inversion studies in this model the variability of earthquake mechanisms means that friction during faulting must vary for each event we computed friction from the ratio of the resolved shear stress to the effective normal stress on the fault plane with the assumption of hydrostatic pore pressure the values of vary over a large range from 0 to 1 5 in the other extreme model we assumed optimally oriented slip and a constant 0 6 as is suggested by byerlee s law for all the earthquakes and determined the local stress orientation for each earthquake the orientation of the stress changes drastically from one earthquake to another and the assumption of uniform stress field commonly used in stress inversion is not warranted an important conclusion is that a regionally uniform stress field and constant friction on optimally oriented faults are mutually exclusive the actual situation in the crust is most likely to be intermediate between these two end member models from the existing data alone we cannot determine the degree of heterogeneity uniquely but both and the local stress field near earthquake faults are likely to vary substantially and studies on earthquake rupture dynamics must take these heterogeneities into consideration

forty years of paleostress analysis has it attained maturity abstract powerful methods of paleostress analysis from fault slip data have been used since the 1970 s and have demonstrated their capacity for reconstructing stress fields with tectonic significance however in some cases these methods have been applied to samples that do not fulfill basic requirements or developed on the basis of unsound conceptual models most methods of fault slip are based on the wallace bott principle dynamic paradigm while others invoke the necessity of remaining within the alternative kinematic paradigm therefore inferring only finite strain or strain rate axes the scientific community shares neither standard procedures for applying these methods nor standard parameters for assessing the quality of results this indicates that paleostress analysis has not attained maturity it is necessary to see back to the conceptual and methological bases following accurate procedures of data collection using additional field observations and critically assessing the results within the tectonic setting spatial and temporal heterogeneity of stress fields over all scales makes the mean stress tensor obtained from site analysis just an abstract notion though indispensable for understanding lithosphere dynamics

stress and the direction of slip on fault planes the shear stress direction on a fault plane depends only on four of the six components of the stress tensor assuming only that the slip direction marks the shear stress direction on any fault plane and that stress is homogeneous it is possible to estimate these four stress parameters from populations of fault planes with known slip directions as several workers have observed different formulations of the problem may yield varying best fitting stresses and estimates of uncertainty in the simplest case no assumptions are made regarding the orientations of fault planes relative to the stress tensor thus the technique allows for the possibility that the fault planes may be very weak here we present simple analytical and graphical descriptions of the field of admissible fault geometries relative to any four parameter stress model which can be used to illustrate the significance of various inverse strategies in particular this paper explores the effects of using two alternative measures of misfit between an observed fault datum and stress model 1 the pole rotation the angle between the observed and predicted slip direction on the observed fault plane and 2 the minimum rotation the smallest angle between the observed fault geometry and any fault geometry which is consistent with the model by allowing for variation of the fault plane as well as the slip vector the minimum rotation procedure generally achieves a more stable and presumably realistic estimate of the actual discrepancy between a fault observation and stress model than the pole rotation procedure in a test case using 17 earthquake focal mechanisms from the yuii region of eastern taiwan separate inversions based on the two misfit criteria yield different optimum stress models and uncertainty estimates additional constraints on the stress tensor such as the effect of friction can be superimposed on the ones used here

san andreas fault rupture scenarios from multiple paleoseismic records stringing pearls we present a new method to objectively combine paleoseismic event data from multiple sites into rupture scenarios and apply it to the southern san andreas fault ssaf of california first a pool is constructed of all ruptures between sites allowed by fault geometry and available event age probability distribution functions pdfs scenarios constructed by drawing from this pool are evaluated by the average quality of agreement event dating evidence by the degree of misfit of cumulative displacement over all ruptures compared to a prediction from the fault slip rate and elapsed time and by the number of events in the scenario three slip rate models from the 2008 working group on california earthquake probabilities wgcep were considered scenarios with full fault length ruptures tend to be inconsistent with low slip rates through the san bernardino and san gorgonio sections of the ssaf favorable scenarios tend to include 1857 like ruptures for three of the most recent five prehistoric ruptures in the northern half of the ssaf from carrizo to approximately wrightwood they also include one to two ruptures that involve the southern half of the ssaf but most earthquakes there appear shorter and exhibit less consistency from event to event by combining paleoseismic data into ensembles of scenarios and selecting viable scenarios using external constraints our method provides rupture histories useful for seismic hazard assessment without having to first settle which event at a site correlates with those at adjoining sites this opens a way for paleoseismic data to be used with greater power to understand the seismic hazard posed by faults like the southern san andreas

comparison of orientations of stress and strain tensors based on fault plane solutions in kaoiki hawaii the stress tensor orientation was estimated based on inversion from 238 first motion fault plane solutions of earthquakes with mostly m 3 5 0 6 located in the 10 km radius kaoiki crustal volume separate inversions for subvolumes containing 20 50 events yielded the same results in several adjacent volumes suggesting that the stress tensor is homogeneous in those parts of the kaoiki area and that the inversion results are stable and meaningful five spatial subsets of the data were found for which the orientation of at least one of the principal axes was different from that in the other sets by 20 80 and at confidence levels exceeding 95 the volcano summits of kilauea and mauna loa and their rift systems are identified as the source of stress in the kaoiki crust because the greatest principal stress points to kilauea and mauna loa in addition the strain tensor due to energy released by these 238 earthquakes was computed for the kaoiki area and several subvolumes of it by summing the moment tensors the moment tensor of each earthquake was constructed from the individual fault plane solutions and from an estimate of the scalar moment derived from the moment magnitude relationship a comparison of the directions of strain and stress tensors showed close agreement for subvolumes with predominantly strike slip faulting in these volumes the inversion process for stress directions led to misfits of approximately equal size for the conjugate near vertical nodal planes these observations are interpreted to show that in the strike slip regime of the upper part of the crust neither of the nodal planes is preferred for faulting rupture probably occurs along the nw and along the nh striking nodal planes in separate earthquakes subvolumes with more decollement faulting showed significant differences of 30 40 between the principal strain and stress directions in these volumes the near horizontal nodal planes showed noticeably smaller misfits in the inversion for the stress directions these facts are interpreted to indicate that the decollement plane is weak allowing slip on it even if the principal stresses are inclined at a large angle to it it is proposed that comparison of strain and stress tensor calculations may be able to differentiate between tectonic regimes uniform in strength no well developed fault plane and regimes in which a fault with low frictional strength dominates as a function of time significant rotations of the strain tensor by approximately 45 can be observed which seem to be related to the occurrences of kaoiki mainshocks during three background periods of about 7 years each the average strain tensor showed an orientation typical for predominant decollement faulting while two premainshock periods of 2 5 years each showed an orientation closer to strike slip faulting it is proposed that this pattern may be repeated before the next kaoiki mainshock the strain released seismically is less than the geodetically observed strain by approximately an order of magnitude stress strain fault plane solutions hawaii

nicoya earthquake rupture anticipated by geodetic measurement of the locked plate interface part of the subduction zone plate interface beneath costa rica was previously locked which allowed strain to accumulate analyses using gps and geomorphic data show that almost the entire locked region ruptured during a megathrust quake in 2012 implying that plate interface mapping towards the end of the earthquake cycle can aid seismic hazard assessments

spatial correlation of interseismic coupling and coseismic rupture extent of the 2011 mw 9 0 tohoku oki earthquake 1 imaging the extent to which the rupture areas of great earthquakes coincide with regions of pre seismic interplate coupling is central to understanding patterns of strain accumulation and release through the earthquake cycle both geodetic and seismic estimates of the coseismic rupture extent for the march 11 2011 mw 8 9 9 0 earthquake tohoku oki earthquake may be spatially correlated 0 26 0 05 to 0 82 0 05 with a region estimated to be partially to fully coupled in the interseismic period preceding the earthquake though there is substantial variation in the estimated distribution and magnitude of coseismic slip the 400 km long region estimated to have slipped 4 m corresponds to an area of the subduction zone interface that was coupled at 30 of long term plate convergence rate with peak slip near a region coupled 80 the northern termination of rupture is collocated with a region of relatively low 20 interseismic coupling near the epicenter of the 1994 mw 7 6 sanriku oki earthquake and near a region of potential long term low coupling or ongoing slow slip slip on the subduction interface beneath the coastline 40 50 km depth is best constrained by the land based gps data and least constrained on the shallowest portion of the plate interface due to the 230 km distance between geodetic observations and the japan trench

modes of reverse reactivation of domino type normal faults experimental and theoretical approach experiments with sand cement models show that reverse reactivation of a set of parallel faults bounding domino blocks takes place in two principal modes in mode i reactivation the domino blocks undergo counter rotation during contraction while normal faults are reactivated as reverse faults mode ii reactivation occurs by fault block translation we present a theoretical analysis of the two modes which considers forces and their rotational moments in a domino block and show that low angle normal faults are commonly reactivated in mode ii by contrast steep faults are reactivated in mode i furthermore fault reactivation depends on the initial fault spacing a large initial fault spacing opposes fault reactivation especially in mode i instead the system deforms along new thrusts dipping opposite to the normal faults we generate reactivation parameters for the conditions of the two modes as functions of the ratio r between fault spacing and effective thickness of fault horizon the fault dip the coefficient of friction and the ratio of principal stresses sr during late contraction

critical stress difference fault orientation and slip direction in anisotropic rocks under non andersonian stress systems abstract the coulomb navier failure criterion is applied to geological faulting in the general three dimensional case of rocks containing arbitrarily oriented strength anisotropies and subject to non andersonian stress systems i e with none of the principal stresses acting in a vertical direction general expressions for the critical stress difference necessary to cause failure as a function of depth are given in terms of material parameters pore fluid pressure orientation of the stress field and orientation of the strength anisotropy the range of angles between a plane of anisotropy and the maximum principal stress direction for which slip occurs along the pre existing anisotropy rather than along a new fault is calculated as a function of depth for different stress regimes when the stress field is non andersonian and or strength anisotropies not containing the intermediate stress direction occur in the rock faulting generally is oblique slip a kinematic classification of faulting is given on the basis of the angle between the strike direction and the slip direction on the fault plane triangular diagrams analogous to those used in petrology are introduced to describe i faulting in isotropic rock subject to arbitrarily oriented stress fields and ii faulting in anisotropic rock when one principal stress direction is vertical the type of faulting as a function of stress field and anisotropy orientation can be read off directly from these diagrams

the super interseismic phase of the megathrust earthquake cycle in chile along a subduction zone great megathrust earthquakes recur either after long seismic gaps lasting several decades to centuries or over much shorter periods lasting hours to a few years when cascading successions of earthquakes rupture nearby segments of the fault we analyze a decade of continuous global positioning system observations along the south american continent to estimate changes in deformation rates between the 2010 maule m8 8 and 2015 illapel m8 3 chilean earthquakes we find that surface velocities increased after the 2010 earthquake in response to continental scale viscoelastic mantle relaxation and to regional scale increased degree of interplate locking we propose that increased locking occurs transiently during a super interseismic phase in segments adjacent to a megathrust rupture responding to bending of both plates caused by coseismic slip and subsequent afterslip enhanced strain rates during a super interseismic phase may therefore bring a megathrust segment closer to failure and possibly triggered the 2015 event

possible focal mechanism change during reactivation of a previously ruptured subduction zone and stress tensor implications summary body waveform inversion methods usually assume a constant double couple source or a combination of such subevents previous studies suggest that the source rupture of mature sources in terms of coupling along smooth subduction zones are usually resolved on this assumption however for events where the source area overlaps previously ruptured zones the conventional inversion methods fail to resolve the source process for such events the subduction coupling may vary between the mature source area and the previously ruptured zone causing a variation in the focal mechanism too we study the implications on the stress tensor of the coexistence of two such focal mechanisms using a major aftershock of the 1985 chilean earthquake m 6 0 the 1978 kurile m 7 6 and 1980 santa cruz islands m 7 7 earthquakes for the first event we use the two different sets of focal parameters obtained by a study which describes a focal mechanism change during the process the epicentres of the latter two large events are located in the spots which had remained unbroken in the preceding large events e g the 1963 and 1969 kurile earthquakes and the 1966 santa cruz is earthquake respectively for each event one of the focal mechanism solutions shows a substantial strike slip component the stress tensors are examined under the constraints that the shear stress is parallel to the slip vector and a friction law is satisfied two particular families of stress tensors examined are 1 the tensors that are optimally orientated with respect to the mature source area and 2 the tensors that have a vertical principal stress direction the first type of tensors can fully account for the observed slip orientation only for the chile aftershock but it comes close to the observed one in the case of the kurile island event and would indeed reactivate the decoupled area at a reasonably low stress level the second type of tensors can be compatible with the two observed slip orientations in all cases however for the santa cruz is and kurile is earthquakes the friction law which should be satisfied on each plane requires too high a stress deviation

stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle

a closing ligurian sea two earthquakes occurred in the ligurian sea in december 1989 and april 1990 both were widely felt along the french and italian rivieras thus reminding us of the seismic risk in this region the significant increase in the number of seismic stations in the area facilitated the study of these two shocks and their related aftershocks using different techniques absolute and relative hypocentral locations doublet analysis and waveform modeling we computed accurate hypocentral locations and estimated the location error range for earthquakes in this area we also computed the focal mechanisms for both mainshocks and we present here a synthesis that integrates previous data the reactivation in compression of the ligurian sea sphenochasm is confirmed which would eventually result in the closing of an aborted oceanic domain as the seismic activity is clearly restricted to the northern margin we suggest it locally results from the lateral expulsion of the south western alps along the apulian indenter

estimation of the frictional strength of faults from inversion of fault slip data a new method abstract the conventional stress inversion methods estimate only four of the six independent parameters of the tectonic stress tensor using the coulomb navier failure criterion as an additional constraint it is possible to estimate the fifth parameter characterized by the normalized critical stress difference i e the critical stress difference divided by the effective overburden pressure this parameter is related to the average friction coefficient of faults if the stress field is uniform faults with different orientations and at different depths have the same normalized critical stress difference on this basis a new method is proposed to estimate the average friction coefficient and the normalized critical stress difference from inversion of a population of faults of measured orientations and slip directions this method is applicable both to newly formed faults and to reactivated faults this method is applied to four data sets in three cases an average friction coefficient gm 0 0 64 0 70 and 0 88 is obtained one case shows a relatively low average friction coefficient gm 0 0 22 but this value is of poor quality due to the effect of a possibly nonuniform stress field these results are in agreement with the average value of friction coefficient gm 0 0 75 derived from laboratory experiments

eocene oligocene tectonics and kinematics of the rhine saone continental transform zone eastern france a tectonic analysis of brittle deformaton was performed in the rhine saone transform in order to decipher and understand the deformation processes in a typical continental hansfer zone cenozoic major and minor fault patterns are described and brittle structures are interpreted in terms of paleostress orientations the eocene n s compression related to africa eurasia convergence is marked mainly by strike slip faults it was followed by a major phase of crustal extension mainly oligocene in age related to the west european rifting this extensional phase is expressed by normal faults tension gashes and extensional strike slip faults which are especially abundant in the transform zone these two events are found to be quite different in terms of distribution of horizontal shess trajectories the trend of ol axes is very homogeneous for the n s compression whereas o3 orientations associated with the major extension vary from e w in most of the rift system to i v se within the transform zone finally the mio pliocene tectonic emplacement of the jura fold and thrust belt is marked in the field by strike slip faults associated with a well defined trend of ol oriented w iiw e se to nw se the preexisting basement fracture pattern between the grabens was also considered in order to estimate which faults were likely to have been reactivated during the oligocene transform kinematics and the theoretical shear motion on these inherited fault surfaces when submitted to e w extension was calculated left laterauextensional reactivation of a preexisting 60 n trending fault system in the brittle upper crust is likely to have accommodated the shear strain arising between the rift segments in response to crustal stretching two independent numerical modelings based on distinct element and finite element analyses respectively enabled us to verify and to refine the hypothesis of transform kinematics related to e w extension and inducing regional perturbations of extensional stress trajectories the overall mechanism and the transtensional kinematics of the rhine saone transform zone are thus tightly conshained the inherited crustal anisotropy the large scale perturbations of extensional stress trajectories and the development of distributed brittle deformation within the sedimentary cover are found to play a major role in the tectonic evolution of continental rift transform systems

paleostress analysis of the yesilyurt elazig fault zone and its importance for the tectonic evolution east turkey abstract the yesilyurt elazig fault zone yefz located in eastern anatolia is a morphologically distinct ne sw trending left lateral strike slip fault about 150 km long in this study inversion of fault slip data collected from the yefz and tectonic locations of the stratigraphic units are used in order to reveal the tectonic evolution and chronology of faulting from early paleocene to today based on the inversion of about 250 fault slip data four successive deformation phases are defined in the study area since early paleocene the first deformation phase is characterized by n s compression during the early paleocene the second deformation phase is nw se extension related to slab steepening and breakoff in late paleocene early miocene the third deformation phase is a nne ssw compressional one in the middle miocene early pliocene a strike slip phase with nne ssw compression is the fourth and youngest deformation phase in the study area dip slip striations are overprinted by strike slip striations we hence interpret that these faults were reactivated under the later stress field our results are consistent with other published regional studies

super interseismic periods redefining earthquake recurrence precise geodetic measurements made over broad swaths of tectonically active regions record patterns of interseismic strain accumulation providing key insights into the locus and timing of pending earthquakes recent studies of geodetic position time series including that of melnick et al 2017 illustrate temporal variation in the pattern of interseismic deformation these authors propose that the 2010 mw 8 8 maule chile earthquake enhanced coupling on the andean subduction zone adjacent to the rupture including on the portion of the megathrust that broke 5 years later in the mw 8 3 illapel event

stress space striated faults deformation twins and their constraints on paleostress abstract stress space is used to illustrate a discussion of the range of stress tensors theoretically compatible with striated faults and with deformation twinning other than friction laws each of the main constraints placed on stress by such data specifies the magnitude of a component of traction being linear in elements of the stress tensor such a constraint by each datum is represented in stress space by a hyperplane comparison at each level of constraint orientation sense of shear assumption of critical ratio or value of shear stress for faulting twinning is made for a single datum followed by consideration of sets of data and stress tensor reduction at no level of constraint are striated faults and deformation twins equivalent fault data cannot constrain absolute values of stress components data for untwinned crystals within twinned untwinned sets provide the fullest limit to values of deviatoric stresses paleostress estimates from twinned untwinned data are generally preferable to those from striated faults

strain budget of the ecuador colombia subduction zone a stochastic view the 2016 pedernales earthquake m w 7 8 ruptured a portion of the colombia ecuador subduction interface where several large historical earthquakes have been documented since the great 1906 earthquake m 8 6 considering all significant ruptures that occurred in the region it has been suggested that the cumulative moment generated co seismically along this part of the subduction over the last century exceeds the moment deficit accumulated inter seismically since 1906 such an excess challenges simple models with earthquakes resetting the elastic strain accumulated inter seismically in locked asperities these inferences are however associated with large uncertainties that are generally unknown the impact of spatial smoothing constraints on co seismic and inter seismic models also prevents any robust assessment of the strain budget we propose a bayesian kinematic slip model of the 2016 pedernales earthquake using the most comprehensive dataset to date including insar and gps offsets tsunami waveforms and kinematic records from high rate gps and strong motions in addition we use inter seismic geodetic velocities to produce a probabilistic inter seismic coupling model of the subduction interface our stochastic co seismic and inter seismic solutions include the ensemble of all plausible models consistent with our prior information and that fit the observations within uncertainties the analysis of these model ensembles indicates that an excess of co seismic moment during the 1906 2016 period is likely in central ecuador only if we assume that 1942 and 2016 earthquakes are colocated if this assumption is relaxed we show that this conclusion no longer holds given uncertainties in co and inter seismic processes the comparison of 1942 and 2016 teleseismic records reveals large uncertainties in the location of the 1942 event hampering our ability to draw strong conclusions on the unbalanced moment budget in the region our results also show a heterogeneous coupling of the subduction interface that coincides with two slip asperities in our co seismic model for the 2016 pedernales earthquake and with the location of historical ruptures in 1958 1979 and 1998 the spatial variability in coupling and complexity in earthquake history suggest strong heterogeneities in frictional properties of the subduction megathrust

dynamic rupture simulations of the 1920 ms 8 5 haiyuan earthquake in chinadynamic rupture simulations of the 1920 ms 8 5 haiyuan earthquake in china

the strain pattern in the western hellenic arc deduced from a microearthquake survey summary than loo0 earthquakes recorded during 7 weeks in 1986 in the peloponnese and surrounding areas show shallow seismicity spread over a wide area bounded by the hellenic trench the highest level in the energy release is for clusters located along the hellenic trench where changes in the morphology are seen a few clusters are also observed as at the intersection between the gulf of corinth and the gulf of patras near the lake trikhonis or between kythira and crete in the peloponnese the shallow earthquakes do not define single faults but are diffusely distributed a higher concentration and a deepening of the foci within the whole crust towards the west seem to reflect a higher strain rate there fault plane solutions exhibit a scattered pattern for earthquakes shallower than 11 km but for earthquakes deeper than 11 km they show some consistency in the orientation of p t and b axes gently dipping nodal planes are seen all over the peloponnese with the conjugate vertical plane striking in various directions and with no consistency in the sense of motion these earthquakes are located between 8 and 18 km deep and could reflect a decoupling between the lower and the upper crust reverse faulting is seen in the gulf of kefallinia and the western peloponnese the p axes trend ne sw to e w normal faulting is seen in the gulf of corinth and in central peloponnese with the t axes trending n s and in the southern peloponnese where the t axes trend nw se the deformation over the western hellenic arc revealed by fault plane solutions of earthquakes with depth between 11 and 40 km appears to be the superposition of two phenomena first throughout the aegean crustal extension with orientation roughly parallel to the trench dominates with crustal shortening and subduction along the aegean arc superimposed on this is a more local effect of the collision between the aegea and apulia which seems to induce horizontal compression roughly perpendicular to the aegean arc west of the peloponnese and epirus the compression due to this decays eastward at a distance comparable with the width of the collision zone the deepening of the brittleductile transition is likely to be due to an increase of the strain field towards the ionian islands

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

triggered slip on a back reverse fault in the mw6 8 2013 lushan china earthquake revealed by joint inversion of local strong motion accelerograms and geodetic measurements abstract the 2013 mw6 8 lushan china earthquake occurred in the southwestern end of the longmenshan fault zone we jointly invert local strong motion data and geodetic measurements of coseismic surface deformation including gps and insar to obtain a robust model of the rupture process of the 2013 lushan earthquake our joint inversion best model involves the rupture of two opposing faults during the lushan earthquake a main fault and a secondary fault it is only when the secondary fault is included that both the gps and insar measurements are fit along with the near field strong motion over 75 of the computed moment was released in slip on the main fault segment a northwest dipping listric thrust fault with buried thrust and dextral strike slip at hypocenter depths and with only minor slip closer to the surface the secondary fault mainly involved oblique thrust slip or pure dextral strike slip at shallower depths and accounts for just under 24 of the moment released in the lushan earthquake coulomb stress changes of about 0 5 mpa on the secondary fault segment at the time coseismic slip initiated on that fault indicate that slip was likely triggered by the coseismic slip on the main blind thrust fault our coseismic slip model is consistent with a sub horizontal and east west to southeast northwest trending most compressive stress our inferred coseismic slip model is also consistent with previous gps derived models of strain accumulation on the longmenshan fault system

an effective noise suppression technique for surface microseismic data abstractthe presence of strong surface wave noise in surface microseismic data may decrease the utility of these data we implement a technique based on the distinct characteristics that microseismic signal and noise show in the p domain to suppress surface wave noise in microseismic data because most microseismic source mechanisms are deviatoric preprocessing is necessary to correct for the nonuniform radiation pattern prior to transforming the data to the p domain we employ a scanning approach similar to semblance analysis to test all possible double couple orientations to determine an estimated orientation that best accounts for the polarity pattern of any microseismic events we then correct the polarity of the data traces according to this pattern prior to conducting signal noise separation in the p domain we apply our noise suppression technique to two surface passive seismic data sets from different acquisition surveys the first data set includes a synthetic microseismic event added

accuracy evaluation of both wallace bott and bem based paleostress inversion methods abstract four decades after their introduction the validity of fault slip inversion methods based on wallace 1951 and bott 1959 hypothesis which states that the slip on each fault surface has the same direction and sense as the maximum resolved shear stress is still a subject of debate according to some authors this hypothesis is questionable since fault mechanical interactions induce slip reorientations as confirmed by geomechanical models this leads us to ask as to what extent the wallace bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data in this paper we compare two inversion methods the first is based on the wallace bott hypothesis and the second relies on geomechanics and mechanical effects on fault heterogeneous slip distribution in that context a multi parametric stress inversion study covering i the friction coefficients ii the full range of andersonian state of stress and iii slip data sampling along the faults is performed for each tested parameter the results of the mechanical stress inversion and the wallace bott wb based stress inversion for slip are compared in order to understand their respective effects the predicted discrepancy between the solutions of both stress inversion methods based on wb and mechanics will then be used to explain the stress inversions results for the chimney rock case study it is shown that a high solution discrepancy is not always correlated with the misfit angle and can be found under specific configurations r geometry invalidating the wb solutions we conclude that in most cases the mechanical stress inversion and the wb based stress inversion are both valid and complementary depending on the fault friction some exceptions i e low fault friction simple fault geometry and pure regimes that may lead to wrong wb based stress inversion solutions are highlighted

depth dependency of stress ratios during the sedimentation of nw gyeongsang basin cretaceous southeast korea estimate of stress parameters and timing of tectonic episodes abstract the natural stress state in the lithosphere consists of the vertical load and poisson ratio and then additional horizontal compression and extension denoted by h and t respectively are assumed to be superimposed upon this gravitational stress field the resulting stress state is composed of the maximum medium and minimum stresses denoted by 1 2 and 3 respectively the stress ratio is given as 2 3 1 3 a linear relation is found between or 1 and the vertical load in wrench faulting and extensional stress regimes respectively the slope and intercept of the linear relation result in the additional horizontal stresses and level of average paleo surface respectively stress ratio is also determinable by the stress tensor inversion of fault slip data the earliest tectonic event t 1 event in the cretaceous gyeongsang basin consists of coexisting e w compression and n s extensional faulting episodes plots of or 1 against the burial depth or vertical load display several linear trends two clusters in extensional episodes and two or three clusters in wrench faulting episodes because h is assumed to be null or negligible in the extensional regime t is determinable from the slopes of two linear clusters as being 2 5 to 4 0 mpa in wrench faulting episodes the values of h are given to be 61 6 101 4 mpa by applying determined additional horizontal extensions determined levels of average paleo surfaces and those of syndepostional structures illustrate that more than five wrench faulting or extensional episodes have occurred during the t 1 event whose active age consequently ranges from the barremian to the coniacian this supports that the coexisting coaxial faulting episodes with the same extension may correspond to the alternation of wrench faulting and extensional episodes

earthquakes along the ryukyu kyushu arc strain segmentation lateral compression and the thermomechanical state of the plate interface we systematically determined the focal depths and mechanisms of 49 large to moderate sized earthquakes mb 5 4 that occurred along the ryukyu kyushu arc since 1963 by inverting the waveforms and amplitudes of p and sh wave trains at teleseismic distances the results are sufficiently precise to delineate seismogenic structures near the plate interface in detail revealing features not predicted by plate kinematics in contrast to previous studies of this arc and those along other subduction zones shallow seismicity along the plate interface is systematic showing two distinct layers of activities the second layer of seismicity is delineated by a few earthquakes that occurred at depths between 50 and 65 km some 10 20 km directly beneath the seismogenic portion of the interplate thrust zone these earthquakes indicate lateral compressional strain within the subducted slab as their p axes are subparallel to the local strike of the arc not perpendicular to the arc as one would expect from the direction of plate convergence the occurrence of these events cannot be accounted for by membrane stress due to the geometry of the subducted slab to our knowledge similar earthquakes occurred only beneath the northern indoburman ranges and along the banda arc where subducted slabs as part of the indian plate are being dragged northward with their northern edges bumping into east west trending collision zones nearby by drawing an analogy between the tectonic settings of these three regions we interpret events beneath the plate interface along the ryukyu kyushu arc as a consequence of ongoing collision between the philippine sea plate and eurasia near taiwan the interplate thrust zone is largely aseismic down to a depth of approximately 30 km a large number of earthquakes showing low angle thrust faulting commence at this depth and are accompanied by two events that show antithetic thrust faulting at a slightly shallower depth of 20 25 km these observations suggest that the strength of the plate interface increases significantly below the depth of proximately 25 5 km based upon available heat flow measurements between the trench axis and the volcanic arc we estimated the temperature field and magnitude of shear traction along the interplate thrust zone the deepest interplate earthquakes 40 50 km correspond to temperatures of approximately 730 980 c comparable to the limiting temperature of intraplate mantle earthquakes 800 c and that of intermediate and deep focus earthquakes at wadati benioff zones potential temperature 900 k therefore the cessation of seismicity in general is probably controlled by similar temperature conditions regardless of the tectonic settings of source regions the magnitude of shear traction along the seismogenic portion 40 50 km depth of the interplate thrust zone seems to be of the order of 100 mpa which in turn implies a low average coefficient of friction of only 0 10 0 05 considerably less than those observed for laboratory specimens the inception of intermediate focus earthquakes within the subducted slab is at a depth of about 100 km whereas shallow earthquakes show no apparent variations along the entire arc intermediate depth earthquakes indicate downdip extension along the northern end of the arc near kyushu but abruptly change to downdip compression along the rest of the arc all available evidence indicates that this is a spatial pattern unrelated to earthquake cycles at the moment tectonic interpretation of such a distinct strain segmentation along the arc is enigmatic without the presence of clear discontinuities in the age of the subducted slab the sudden switch in the strain field of the slab is difficult to explain by the continuously varying rate of subduction along the arc in any case this pattern of strain segmentation requires the presence of a major accommodation structure such as a tear fault in the subducted slab near the tokara channel appendix is available with entire article on microfiche order from american geophysical union 2000 florida ave n w washington dc 20009 document b91 004 2 50 payment must accompany order

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

the inverse problem in microtectonics and the separation of tectonic phases abstract the algorithm of inverse problems is applied to three cases in microtectonics a collection of striations measured on pre existing faults may be processed automatically and interpreted in terms of tectonic stress a comparison is made between two different methods formerly proposed by the authors both methods are tested with field data the theoretical results agree with independent field criteria for a separation of tectonic phases

microseismicity and focal mechanisms at the western termination of the north anatolian fault and their implications for continental tectonics summary for seven weeks a temporary network of 68 seismological stations was operated in central greece in the region of thessaly and evia located at the western termination of the north anatolian fault system we recorded 510 earthquakes and computed 80 focal mechanisms seismic activity is associated with the ne sw dextral north aegean fault or with very young e w striking normal faults that are located around the gulf of volos and the gulf of lamia the important nw se striking faults bounding the pilion or the basins of larissa and karditsa are not seismically active suggesting that it is easier to break continental crust creating new faults perpendicular to the principal stresses than to reactivate faults that strike obliquely to the principal stress axes

two decades of spatiotemporal variations in subduction zone coupling offshore japan spatial patterns of interplate coupling on global subduction zones can be used to guide seismic hazard assessment but estimates of coupling are often constrained using a limited temporal range of geodetic data here we analyze 19 years of geodetic observations from the geonet network to assess time dependent variations in the spatial distribution of coupling on the subduction zones offshore japan we divide the position time series into five 3 75 year epochs each decomposed into best fit velocity annual periodic signals coseismic offsets and postseismic effects following seven major earthquakes nominally interseismic velocities are interpreted in terms of a combination of tectonic block motions and earthquake cycle activity the duration of the inferred postseismic activity covaries with the linear velocity to address this trade off we assume that the nominally interseismic velocity at each station varies minimally from epoch to epoch this approach is distinct from prior time series analysis across the earthquake cycle in that position data are not detrended using preseismic velocity which inherently assumes that interseismic processes are spatially stable through time but rather the best fit velocity at each station may vary between epochs these velocities reveal significant consistency since 1996 in the spatial distribution of coupling on the nankai subduction zone with variation limited primarily to the tokai and bungo channel regions where long term slow slip events have occurred and persistently coupled regions coincident with areas that slipped during historic great earthquakes on the sagami subduction zone south of tokyo we also estimate relatively stable coupling through time on the japan kuril trench we image significant coupling variations owing to effects of the 1994 mw 7 7 sanriku oki 2003 mw 8 2 tokachi oki and 2011 mw 9 0 tohoku oki earthquakes in particular strong coupling becomes more spatially extensive following the 1994 event until 2011 coseismic sense slip precedes the tohoku oki event and coupling offshore northern honshu is reduced after the 2011 earthquake despite the occurrence of the 2003 tokachi oki earthquake persistent coupling offshore hokkaido suggests ongoing seismic hazard possibly similar to past mw 9 class earthquakes interpreted from coastal paleoseismic records this time dependent analysis of interseismic deformation illuminates rich diversity in the distribution of subduction zone coupling including spatiotemporal stability in coupling effective reduction in strongly coupled regions due to aseismic thrust sense slip events and broad changes in the distribution of coupling following major earthquakes

tectonic regime and slip orientation of reactivated faults the slip orientation of reactivated faults is predicted by assuming that one principal stress direction is vertical that faulting occurs on pre existing planes of weakness with a slip direction along the applied shear stress and by extending the original concept of tectonic regime so as to include the stress tensor aspect ratio the predicted rake of slip is then analysed so as to reveal the respective influence of the fault plane orientation strike and dip and of the tectonic regime the analysis of this direct problem allows one to describe the geometry of the slip directions within any given tectonic regime its evolution as the tectonic regime varies and the constraints provided by slip direction data on the tectonic regime however the question of what fault orientations would satisfy a failure criterion and thus be preferentially reactivated is not addressed in any tectonic regime pure strike slip occurs on vertical planes and only on them except in wrench regimes where it also occurs on all fault planes along four strikes that are determined by the tectonic regime pure dip slip occurs on planes striking along one of the horizontal principal stress directions and only on them except in radial compression and radial extension regimes where it occurs on all planes except vertical ones at fixed strike but varying dip the slip direction is closest to dip slip for zero dip and pure strike slip for vertical dip at fixed dip and varying strike the slip direction is pure dip slip for strikes along one of the horizontal principal stress directions and closest to strike slip for four strikes that are determined by the tectonic regime the horizontal principal stress directions separate four quadrants two where the slip direction is dextral and two where it is sinistral the slip directions of all fault planes of the same dip can be easily deduced from those of subhorizontal planes and can be constructed geometrically as the tectonic regime varies continuously from radial compression to radial extension the domain of fault plane orientations where steep reverse slip directions are possible shrinks and disappears when the extensional regime is entered conversely the domain where steep normal slip directions are possible appears when the wrench regime is entered and grows thereafter the strike slip domain first grows towards shallow dip until the wrench regime is entered and then shrinks after the extensional regime is entered whereas in the model of failure in isotropic rocks dip slip or strike slip data fully determine the original tectonic regime in the model of failure on pre existing planes of weakness constraints on the extended tectonic regime require additional information the sense of shallow slip direction data which are to be found on steeply dipping planes constrains the horizontal principal stress directions and the steepness of slip direction data on shallow dipping planes striking away from the principal stress directions constraints the extended tectonic regime in the case of wrench regimes an extra constraint arises from the fact that the extended tectonic regime also controls the strike at which the dip component of slip changes from normal to reverse these constraints can be quantified by superposing a simple plot of the data rake versus strike with an abacus that is called breddin s graph for tectonic regimes while this graph does not replace inverse techniques it may help in detecting tectonic phases in complex data sets without using this graph or resorting to inverse techniques the transition from wrench to either compressional or extensional regime is difficult to infer from data that display a limited range of fault plane strikes and the same sense of dip component of the slip direction

earthquake supercycles on the mentawai segment of the sunda megathrust in the seventeenth century and earlier over at least the past millennium the mentawai segment of the sunda megathrust has failed in sequences of closely timed events rather than in single end to end ruptures each the culmination of an earthquake supercycle here we synthesize the sixteenth and seventeenth century coral microatoll records into a chronology of interseismic and coseismic vertical deformation we identify at least five discrete uplift events in about 1597 1613 1631 1658 and 1703 that likely correspond to large megathrust ruptures this sequence contrasts with the following supercycle culmination which involved only two large ruptures in 1797 and 1833 fault slip modeling suggests that together the five cascading ruptures involved failure of the entire mentawai segment interseismic deformation rates also changed after the onset of the rupture sequence as they did after the 1797 earthquake we model this change as an altered distribution of fault coupling presumably triggered by the 1597 rupture we also analyze the far less continuous microatoll record between a d 1 and 1500 while we cannot confidently delineate the extent of any megathrust rupture during that period all evidence suggests that individual major ruptures involve only part of the mentawai segment often overlap below the central mentawai islands often trigger coupling changes and occur in clusters that cumulatively cover the entire mentawai segment at the culmination of each supercycle it is clear that each mentawai rupture sequence evolves uniquely in terms of the order and grouping of asperities that rupture suggesting heterogeneities in fault frictional properties at the 100 km scale

how much does slip on a reactivated fault plane constrain the stress tensor given a fault plane and its slip vector the stress tensor which caused the displacement is sought two constraints are considered first a geometrical constraint that the shear stress applied to the fault plane is parallel to the slip wallace 1951 bott 1959 second a frictional constraint that the shear to normal stress ratio equals tan 0 coulomb 1776 in a first step the stress tensors that satisfy the geometrical constraint are sought for tensors belonging to the vectorial space of solutions shear and normal stress magnitudes become a function of the orientation of the principal stresses and are mapped extending a study by mckenzie 1969 in a second step it is investigated which of these tensors also satisfy the frictional constraint within this more restricted vectorial space there is a relationship between the magnitudes 1 2 1 3 and s 1 3 1 and the orientations of the principal stresses both the range of s and the spatial distribution of are more restricted than when the geometrical constraint alone is considered as when the geometrical constraint is solely considered mckenzie 1969 the orientations of the principal stresses may lie significantly away from and up to right angle to the p b t axes however this can happen only in two cases 1 either the effective stress difference s has reached a high value which is unlikely to happen if enough preexisting fractures are available to release the stress or 2 2 becomes close to either 1 or 3 and therefore barely distinguishable from it in that case the delocalization of the orientations of the principal stresses is best described by a tendency for to exchange role with either or when the stress difference remains small and 2 reasonably away from 1 and 3 approach positions that we define as the pf b tf axes and that are obtained from the p b t axes by a rotation of angle 0 2 around b and toward the slip vector this explains why the p b t axes gives reasonable estimates of the orientations of the principal stresses scheidegger 1964 despite objections mckenzie 1969 however whenever the fault plane can be distinguished from the auxiliary plane pf b tf should give a better estimate raleigh et al 1972 in an area where many fault planes are available and a uniform tensor is assumed the scatter in the plane orientations contains information about both the relative position of 2 represented by and the relative stress difference s the higher s or the closer to either 0 or 1 the more scatter this information could then be extracted by inverse methods because a friction law would constrain these inverse method more tightly it may show the necessity of nonuniform tensor to explain scattered fault plane

an estimate of the stress tensor in sweden using earthquake focal mechanisms abstract an estimate of the state of stress in sweden is made by inversion of the fault plane solutions of naturally occurring earthquakes it is shown that the stress state in southern sweden is significantly different from that in northern sweden in southern sweden the principal compression is in a roughly nw se direction similar to that prevailing in northwest europe as a whole this stress direction is is consistent with the stresses expected on the basis of motions of the major tectonic plates in northern sweden however there is no strongly dominant stress direction this latter observation is consistent with a situation in which processes other than first order plate motions are important the most likely explanation in this case is the effect of the deglaciation of fennoscandia which is producing rates of rebound as high as 9 mm year in northern sweden

tectonic analysis and paleo stress determination of the upper lava section at odp iodp site 1256 east pacific ocean abstract research on the deep sea is of great importance for a better understanding of the mechanism of magma emplacement and the tectonic evolution of oceanic crust however details of the internal structure in the upper levels of the oceanic crust are much less complete than that of the more fully studied sub aerial areas for the first time this study proposes a dynamic analysis using the inversion method on core data derived from the drilled basement of the present day intact oceanic crust at odp iodp site 1256 in the cocos plate the research is based on an innovative core reorientation process and combines different stress hypothesis approaches for the analysis of heterogeneous failure slip data via exploitation of two distinct techniques from the analysis of the failure slip data both techniques produce 5 distinct subsystem datasets all calculated subsystems are mechanically and geometrically admissible interpretation of the results allows the researchers to note a complex local and regional tectonic evolution deriving from the interplay of 1 the ridge push and rotation of both the east pacific rise and the cocos nazca spreading center 2 the effect of the slab pull of the middle america trench 3 the influence of lava emplacement mechanisms and 4 intra plate deformation

fault analysis and paleostress evolution in large strain regions methodological and geological discussion of the southeastern himalayan fold and thrust belt in pakistan abstract we document the structure and kinematics of the southeastern part of the fold and thrust belt of the pakistani himalaya field analysis documents the importance of strike slip faulting associated with folding accordingly a transpression regime is inferred to be responsible for variable amounts of shortening from fault block to fault block the analysis of fault populations that affect the mesozoic to early miocene sediments allows distinguishing two paleostress tensor directions a dominant nw se compression and a minor e w compression are compatible with buckling around the n s axis of the near by hazara kashmir syntaxis from the lack of both systematic overprinting relationships and spatial trend the two tensors were obtained at different locations we conclude that in each location any of these two shortening directions can dominate the distribution of the paleostress tensors substantiates a transpressional regime due to far field himalayan compression and a lateral escape component of the allochthonous fold and thrust belt away from the growing hazara kashmir anticline

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

fault systems and paleo stress tensors in the indus suture zone nw pakistan abstract analysis of fault striations measured in the kohistan part of the indus suture zone nw himalaya pakistan has been carried out to document dynamic evolution during the brittle stage of the collision of india and asia processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as sse nnw compression e w compression radial extension and ssw nne compression the last corresponds to the present day stress field defined from seismic activity the earlier stress fields are related to times during the miocene when convergence related stresses were disturbed by the formation of the nearby nanga parbat and indus syntaxes

extreme multi millennial slip rate variations on the garlock fault california strain super cycles potentially time variable fault strength and implications for system level earthquake occurrence abstract pronounced variations in fault slip rate revealed by new measurements along the garlock fault have basic implications for understanding how faults store and release strain energy in large earthquakes specifically dating of a series of 26 0 3 5 2 5 m fault offsets with a newly developed infrared stimulated luminescence method shows that the fault was slipping at 14 0 2 2 1 8 mm yr approximately twice as fast as the long term average rate during a previously documented cluster of four earthquakes 0 5 2 0 ka this elevated late holocene rate must be balanced by periods of slow or no slip such as that during the ca 3300 yr long seismic lull preceding the cluster moreover whereas a comparison of paleoseismic data and stress modeling results suggests that individual garlock earthquakes may be triggered by periods of rapid san andreas fault slip or very large slip events the on off behavior of the garlock suggests a longer term mechanism that may involve changes in the rate of elastic strain accumulation on the fault over millennial time scales this inference is consistent with most models of the geodetic velocity field which yield slip deficit rates that are much slower than the average latest pleistocene early holocene post 8 13 ka garlock slip rate of 6 5 1 5 mm yr these observations indicate the occurrence of millennia long strain super cycles on the garlock fault that may be associated with temporal changes in elastic strain accumulation rate which may in turn be controlled by variations in relative strength of the various faults in the garlock san andreas eastern california shear zone fault system and or changes in relative plate motion rates

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them

paleostress regimes from brittle structures of the karakoram kohistan suture zone and surrounding areas of nw pakistan paleostress orientations were calculated from fault populations at 24 sites along the sw ne segment and five sites along the e w yasin segment of the karakoram kohistan suture zone in nw pakistan they demonstrate the importance of combined thrusting and strike slip faulting however several paleostress tensor directions are distinguished a dominant nw se compression and a minor e w compression are compatible with the recent evolution of this part of the hindu kush from the lack of both systematic overprinting relationships and spatial trend the two tensors were obtained at different locations we conclude that in each location any of these two shortening directions can dominate heterogeneously distributed extension is found in some places and is likely due to local conditions these paleostress tensors substantiate a transpressional regime due to far field himalayan compression and document the long term background of the seismogenic deformation in this region

stress ratio determinations from striated faults a spherical plot for cases of near vertical principal stress for stress regimes with one principal axis z vertical the stress ratio is best represented by an angular function f arctan 3 z x1 x2 z 3 x1 x2 or if the larger of the horizontal principal stresses x1 and x2 is designated y by f arctan 3 z x y z 3 y x traditional palaeostress regimes normal wrench reverse represent equal angular sectors of f or f and may be subdivided on a spherical projection of f against 2y where y is the bearing of maximum horizontal stress the locus of all combinations of stress orientation and stress ratio capable of generating one datum known slip direction on a known fault plane is a great circle since tanf cos 2y 2s b 3 cosb where tanb tan cosd and s d and are the fault strike dip and striation pitch respectively stereographic construction is simple using pencil and paper and gives a visual appreciation of the definition of palaeostress states which could have generated the fault motions it facilitates better than previous methods 1 the identification of radially symmetrical stress states 2 recognition of suspect or incompatible data and 3 delimiting the palaeostress state according to sense of shear where this is known great circle and pole representations are suited to different purposes and data types for which examples are given

remarks on the relationship between the tectonic regime the rake of the slip vectors the dip of the nodal planes and the plunges of the p b and t axes of earthquake focal mechanisms abstract we use a triangular representation of the plunges of p b and t axes to compare the different ways tectonic regime is inferred from earthquake focal mechanisms in recent works we argue that p b and t axes provide a reasonable estimate of principal stress directions when faulting is close to andersonian conditions and that this can be estimated from the location on a triangular diagram we analyze the geometrical relationship between the plunges of p b and t axes on one hand and the rake of slip and dip of nodal planes on the other hand we show that the rake and dip level curves correspond to trajectories of the vertical direction along great and small circles with respect to the frame of the p b and t axes this shows that dip slip faulting is compatible with vertical p or t axes but does not require it and instead requires horizontal b axes it also shows that strike slip faulting does not require vertical b axes but p and t axes with equal plunges this also reveals that focal mechanisms where p b and t axes all have moderate plunge correspond to two very different types of nodal planes a steeply dipping one with oblique slip and a moderately dipping one with strike slip seismically active and moderately dipping strike slip faults are to be found among these events