inverse kinematic and forward dynamic models of the 2002 denali fault earthquake alaska we perform inverse kinematic and forward dynamic models of the m 7 9 2002 denali fault alaska earthquake to shed light on the rupture process and dynamics of this event which took place on a geometrically complex fault system in central alaska we use a combination of local seismic and global positioning system gps data for our kinematic inversion and find that the slip distribution of this event is characterized by three major asperities on the denali fault the rupture nucleated on the susitna glacier thrust fault and after a pause propagated onto the strike slip denali fault approximately 216 km to the east the rupture abandoned the denali fault in favor of the more southwesterly directed totschunda fault three dimensional dynamic models of this event indicate that the abandonment of the denali fault for the totschunda fault can be explained by the totschunda fault s more favorable orientation with respect to the local stress field however a uniform tectonic stress field cannot explain the complex slip pattern in this event we also find that our dynamic models predict discontinuous rupture from the denali to totschunda fault segments such discontinuous rupture helps to qualitatively improve our kinematic inverse models two principal implications of our study are 1 a combination of inverse and forward modeling can bring insight into earthquake processes that are not possible with either technique alone and 2 the stress field on geometrically complex fault systems is most likely not due to a uniform tectonic stress field that is resolved onto fault segments of different orientations rather other forms of stress heterogeneity must be invoked to explain the observed slip patterns

heat flow strong near fault seismic waves and near fault tectonics on the central san andreas fault the main san andreas fault strikes subparallel to compressional folds and thrust faults its fault normal traction is on average a factor of 1 2 thr 1 thr2 thr where thr is the coefficient of friction for thrust faults times the effective lithostatic pressure a useful upper limit for thr of 0 6 where is 3 12 is obtained from the lack of heat flow anomalies by considering off fault convergence at a rate of 1 mm yr for 10 km across strike if the fault normal traction is in fact this high the well known heat flow constraint of average stresses of 10 20 mpa during strike slip on the main fault becomes more severe only a few percent of the total slip during earthquakes can occur at the peak stress before dynamic mechanisms weaken the fault the spatial dimension of the high stress rupture tip zone is 10 m for 3 12 and for comparison 100 m for 1 high dynamic stresses during shaking occur within these distances of the fault plane in terms of scalars fine scale tectonic stresses cannot exceed the difference between failure stress and dynamic stress plate scale slip causes stresses to build up near geometrical irregularities of the fault plane strong dynamic stresses near the rupture tip facilitate anelastic deformation with the net effects of relaxing the local deviatoric tectonic stress and accommodating deformation around the irregularities there also is a mild tendency for near fault material to extrude upward slip on minor thrust faults causes the normal traction on the main fault to be spatially variable

effects of prestress state and rupture velocity on dynamic fault branching 1 we consider a mode ii rupture which propagates along a planar main fault and encounters an intersection with a branching fault using an elastodynamic boundary integral equation formulation allowing the failure path to be dynamically self chosen we study the following questions does the rupture initiate along the branch does it continue is the extensional or compressional side most favored for branching does rupture continue on the main fault too failure is described by a slip weakening law for which the strength at any amount of slip is proportional to normal stress our results show that dynamic stresses around the rupture tip which increase with rupture velocity at locations off the main fault plane relative to those on it could initiate rupture on a branching fault as suggested by prior work whether branched rupture can be continued to a larger scale depends on principal stress directions in the prestress state and on rupture velocity the most favored side for branching rupture switches from the extensional to the compressional side as we consider progressively shallower angles of the direction of maximum compressive prestress with the main fault simultaneous rupturing on both faults can be activated when the branching angle is wide but is usually difficult for a narrow branching angle due to strong stress interactions between faults however it can be also be activated by enhanced dynamic stressing when the rupture velocity is very near the rayleigh velocity natural examples seem consistent with the simulations that we present

geologic investigations of a slip gap in the surficial ruptures of the 1992 landers earthquake southern california a 3 km long gap in the dextral surficial rupture of the 1992 mw 7 3 landers earthquake occurs at the north end of a major fault stepover between the johnson valley and homestead valley faults this gap is situated along a segment of the landers rupture that has been modeled geophysically as having a deficit in average slip at depth to better evaluate the nature of the slip gap we document in detail the character and distribution of surficial rupture within it along the gap is a northwest trending thrust fault rupture with an average of less than 1 rn of northeast directed reverse slip and nearly no oblique right slip we interpret this rupture to be limited to the shallow crust of the northern end of the stepover and to have been the secondary result of dextral shear rather than a mechanism of rigid block slip transfer from the landers kickapoo fault a zone of en echelon extensional ruptures also occurs along the slip gap which we interpret as the secondary result of diffuse dextral shear that accommodated less than 0 5 rn of west northwest extension these secondary ruptures represent a discontinuity in the surficial dextral rupture of the landers earthquake which we propose resulted from the lack of a mature fault connection between the johnson valley and homestead valley faults the rupture pattern of the slip gap implies a significant deficit in net surficial slip which compares favorably with some geophysical models aspects of this rupture pattern also suggest a temporal sequence of rupture that compares favorably with geophysical interpretations of the dynamic rupture propagation

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

stress sensitivity of fault seismicity a comparison between limited offset oblique and major strike slip faults we present a new three dimensional inventory of the southern san francisco bay area faults and use it to calculate stress applied principally by the 1989 m 7 1 loma prieta earthquake and to compare fault seismicity rates before and after 1989 the major high angle right lateral faults exhibit a different response to the stress change than do minor oblique right lateral thrust faults seismicity on oblique slip faults in the southern santa clara valley thrust belt increased where the faults were unclamped the strong dependence of seismicity change on normal stress change implies a high coefficient of static friction in contrast we observe that faults with significant offset 50 100 km behave differently microseismicity on the hayward fault diminished where right lateral shear stress was reduced and where it was unclamped by the loma prieta earthquake we observe a similar response on the san andreas fault zone in southern california after the landers earthquake sequence additionally the offshore san gregorio fault shows a seismicity rate increase where right lateral oblique shear stress was increased by the loma prieta earthquake despite also being clamped by it these responses are consistent with either a low coefficient of static friction or high pore fluid pressures within the fault zones we can explain the different behavior of the two styles of faults if those with large cumulative offset become impermeable through gouge buildup coseismically pressurized pore fluids could be trapped and negate imposed normal stress changes whereas in more limited offset faults fluids could rapidly escape the difference in behavior between minor and major faults may explain why frictional failure criteria that apply intermediate coefficients of static friction can be effective in describing the broad distributions of aftershocks that follow large earthquakes since many of these events occur both inside and outside major fault zones

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

the continental margin of the mesozoic tethys in the western alps abstract most of the structural units of the western alps were derived from the european continental margin of the ligurian ocean a segment of the mesozoic tethys ocean their mesozoic palaeotectonic and stratigraphic evolution bears witness of the following main stages 1 deposition of the triassic platform carbonates essentially prerift but nevertheless bearing the imprint of some extensional movements 2 the liassic middle jurassic rifting corresponds to the creation of a horst and graben system with especially tilted blocks and hence a shoal and basin palaeogeography but without a preliminary doming event 3 the late jurassic early cretaceous opening and spreading of the ligurian ocean began with a general collapse of the continental margin thermal subsidence latest middle jurassic and earliest late jurassic in this paper emphasis is given to the refting derived structures more especially to the major tilted crustal blocks a few tens of kilometres wide which can be either reconstructed or directly observed the rifting stage lasted roughly 40 m y with the alternation of extensional tectonic phases and of relatively quiet periods during the extensional phases movements along fault planes and related episodes of tilting were followed by sudden and rapid episodes of subsidence the latter may be interpreted as resulting from the isostatic and thermal readjustment that follows a phase of stretching of the crust and of the lithosphere the tectonic evolution of the margin continued but decreased during the late jurassic early cretaceous oceanspreading stage tectonic activity resumed in the late cretaceous this probably resulting from the beginning of contraction of both the ocean and the continental margin leading progressively to the continental collision in the tertiary

fine structure of the landers fault zone segmentation and the rupture process observations and modeling of 3 to 6 hertz seismic shear waves trapped within the fault zone of the 1992 landers earthquake series allow the fine structure and continuity of the zone to be evaluated the fault to a depth of at least 12 kilometers is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent this zone forms a seismic waveguide that extends along the southern 30 kilometers of the landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter another fault plane waveguide disconnected from the first exists along the northern rupture surface these observations in conjunction with surface slip detailed seismicity patterns and the progression of rupture along the fault suggest that several simple rupture planes were involved in the landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane reduction in rupture velocity can tentatively be attributed to fault plane complexity and variations in moment release can be attributed to variations in available energy

a balanced section across the pyrenean orogenic belt evolutionary models that have been proposed for the pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central axial zone it has been suggested by previous workers that uplift is a result of alpine compression or long lived strike slip movement on the north pyrenean fault we critically assess these models and propose a new model based on the generation of a thin skinned linked thrust system due to alpine collision of iberia and europe pyrenean alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6 within hercynian basement northerly directed thrusts of the north pyrenean zone and northern folded foreland are backthrusts from this sole fault a total orogenic shortening of 106 km in the central pyrenees was achieved between the palaeocene and oligocene at a time averaged rate of 0 62 cm yr 1 a thin skinned model requires that the north pyrenean fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace

three dimensional nonplanar simulation of the 1992 landers earthquake 1 we have simulated the rupture process of the 1992 landers california earthquake using a realistic nonplanar fault geometry including fault bends and branches through a three dimensional boundary integral equation method considering an external loading system due to local tectonics as well as a nonplanar fault structure we could reproduce the characteristic features of this earthquake such as spontaneous rupture transfer between faults pattern of slip distribution and propagation of rupture front without assuming any laterally heterogeneous distribution of parameters we could also reproduce seismic waveforms near the faults especially in the forward direction of rupture propagation where rupture directivity controlled by rupture transfer between faults significantly affects ground motion

surge zones in the moine thrust zone of nw scotland abstract the caledonian thrust zones of assynt show several examples of large fault bounded structures surge zones up to 8 km 2 in extent which have moved further than adjacent rocks extensional faults can be traced into strike slip faults and then to contractional imbricate faults there are also zones of extensional and contractional flow as shown by strained bioturbation marks in the cambrian pipe rock several other low angle extensional fault zones have been recognized along the length of the moine thrust zone notably in the kinlochewe district recognition of these extensional faults and local surge zones has solved several local problems such as the lack of continuity of the glencoul thrust and the out of sequence character of some of the large low angle faults though the thrust propagation direction was generally from east to west in the transport direction several of the eastern faults have been reactivated later and locally cut down as extensional faults the so called moine thrust shows extensional fault movement at several localities along its length the extensional structures and the surge zones suggest that body forces have been important in driving the faults rather than just a push from the rear the moines and moine thrust zone were presumably driven to the wnw by gravity spreading and thinning of the main scottish caledonides

lateral heterogeneity in the upper mantle beneath the tibetan plateau and its surroundings from ss s travel time residuals 1 we use ss s differential travel times to map the upper mantle structure of the tibetan plateau and its surroundings new observations from analog stations in the former soviet union help to fill in gaps in the spatial coverage of previous studies providing new data for eastern tibet the kunlun range and the tarim basin the effects of crustal thickness variations anisotropy and global heterogeneity are evaluated and explicitly accounted for by incorporating results of previous studies and by ray tracing through a global 3d model the resulting residuals suggest that with the exception of the eastern part of the plateau tibet is underlain almost entirely by lithosphere of normal to greater than normal thickness in general there appear to be strong lateral gradients in wave speed between eastern and western tibet we find little evidence for low wave speeds under northern tibet to the west of about 87 e instead the average shear wave speeds in the upper 300 km of the mantle beneath this part of tibet are about 0 5 km s faster than those directly to the north beneath the tarim basin these results support models of tibetan dynamics in which the lithosphere underlying northern tibet underplates the crust as opposed to those in which large portions of this lithosphere disappear by convection subduction or detachment at the same time the dominant e w gradient in residuals implies that 2d models inadequately explain the dynamics of all of tibet

influence of fault geometry on the spatial distribution of long term slip with implications for determining representative fault slip rates determining representative slip rates of active faults is essential to seismic hazard assessment and tectonic analysis here we take a two pronged approach to determine how spatially variable slip over many earthquake cycles impacts the sliprate record at potential sites of geologic investigation near releasing stepovers first we use 2d parametric models to estimate the probability that a point measurement is representative of the average slip rate for continuous strike slip faults and those with a range of releasing stepover geometries and friction values all models result in skewed distributions for which a randomly selected site has a higher probability of sampling a slip rate that exceeds the mean for most configurations individual point measurements are unlikely p 0 5 to yield a slip rate within 1 mm yr of the mean the probability can be notably improved 15 300 by summing slip rates of overlapping segments second we use 3d mechanical models of a well studied releasing stepover along the san jacinto fault to investigate the impact of specific fault geometries on slip rate distribution and the implications for existing slip rate estimates the model calculated dextral slip rates are consistent with the abundant geologic slip rate data available for this system although summing the slip rates at geologic sites across the stepover may produce a nonrepresentative slip rate the summed slip rates from the model are compatible with the representative slip rate thus the complete along trace slip rate distribution produced from the geologically consistent models provides a way to select sites for determining slip rates or interpreting isolated geologic slip rate data the site specific models also illustrate how to assess the uncertainty of slip rate data due to the spatial variability of slip rates in geometrically complex fault systems

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

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

uniform california earthquake rupture forecast version 2 ucerf 2 the 2007 working group on california earthquake probabilities wgcep 2007 presents the uniform california earthquake rupture forecast version 2 ucerf 2 this model comprises a time independent poisson process earthquake rate model developed jointly with the national seismic hazard mapping program and a time dependent earthquake probability model based on recent earthquake rates and stress renewal statistics conditioned on the date of last event the models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular extensible open seismic hazard analysis framework the rate model satisfies integrating measures of deformation across the plate boundary zone and is consistent with historical seismicity data an overprediction of earthquake rates found at intermediate magnitudes 6 5 m 7 0 in previous models has been reduced to within the 95 confidence bounds of the historical earthquake catalog a logic tree with 480 branches represents the epistemic uncertainties of the full time dependent model the mean ucerf 2 time dependent probability of one or more m 6 7 earthquakes in the california region during the next 30 yr is 99 7 this probability decreases to 46 for m 7 5 and to 4 5 for m 8 0 these probabilities do not include the cascadia subduction zone largely north of california for which the estimated 30 yr m 8 0 time dependent probability is 10 the m 6 7 probabilities on major strike slip faults are consistent with the wgcep 2003 study in the san francisco bay area and the wgcep 1995 study in southern california except for significantly lower estimates along the san jacinto and elsinore faults owing to provisions for larger multisegment ruptures important model limitations are discussed

northern scotland as an atlantic north sea divide president9s anniversary address 1984 from the end of the caledonian orogeny until the present northern scotland has acted as a structural high separating the north sea and atlantic basins or their forerunners the geological history of this positive massif is discussed in relation to that of the adjacent cratonic basins with the objective of determining the extent to which it adapted to regional tectonic developments and the manner in which its responses were modified by the pre existing basement structure from devonian to early palaeocene times the massif was generally low lying and its behaviour with respect to vertical movements was essentially neutral the land surface carved in the crystalline basement during the devonian period was preserved with relatively small modifications and little metamorphic detritus was supplied to the adjacent basins tectonic events of major importance in the basins such as the formation of the north sea and hebridean rift systems produced little change of conditions in the intervening massif it is inferred that the underlying keel of lithospheric mantle was protected from the effects of lithospheric stretching the uneventful history of the massif was interrupted by two phases of mafic igneous activity in late carboniferous and palaeocene times which record responses to regional plate motions the formation of the palaeocene igneous province was followed by a unique phase of uplift as a result of which the ancient sub devonian land surface was elevated and dissected and abundant crystalline detritus was supplied to the north sea the style of these events and the anomalous character of the continental margin off nw britain may have been determined by the refractory nature of the precambrian basement which inhibited stretching prior to sea floor spreading

static stress change from the 8 october 2005 m 7 6 kashmir earthquake 1 we calculated static stress changes from the devastating m 7 6 earthquake that shook kashmir on 8 october 2005 we mapped coulomb stress change on target fault planes oriented by assuming a regional compressional stress regime with greatest principal stress directed orthogonally to the mainshock strike we tested calculation sensitivity by varying assumed stress orientations target fault friction and depth our results showed no impact on the active salt range thrust southwest of the rupture active faults north of the main boundary thrust near peshawar fall in a calculated stress decreased zone as does the raikot fault zone to the northeast we calculated increased stress near the rupture where most aftershocks occurred the greatest increase to seismic hazard is in the indus kohistan seismic zone near the indus river northwest of the rupture termination and southeast of the rupture termination near the kashmir basin

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

superficial simplicity of the 2010 el mayor cucapah earthquake of baja california in mexico the geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation propagation and arrest of seismic ruptures the fault system that runs from southern california into mexico is a simple strike slip boundary the west side of california and mexico moves northwards with respect to the east however the m w 7 2 2010 el mayor cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike slip fault here we use geodetic remote sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake we find that the earthquake produced a straight 120 km long fault trace that cut through the cucapah mountain range and across the colorado river delta however at depth the fault is made up of two different segments connected by a small extensional fault both segments strike n130 e but dip in opposite directions the earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike slip motion we show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves we conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone

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

frontal part of the northern apennines fold and thrust belt in the romagna marche area italy shallow and deep structural styles in this study surface geological data resulting from a detailed field survey including structural and biostratigraphic analysis have been integrated with subsurface seismic lines and well logs data in order to reconstruct the tectonic evolution of the external zones of the northern italian apennines in the romagna marche foothills and adriatic sea areas this integrated analysis shows 1 a late messinian to lower pleistocene progression of structural development from the hinterland to the foreland of the studied sector of the thrust belt 2 relatively limited 20 southward increasing amounts of shortening obtained by the construction of line length balanced and restored geological cross sections 3 a regional deformation style characterized by the presence of backthrusts associated with most foreland vergent thrust ramps leading to quasi symmetric uplift and a low critical taper for the wedge typical of foreland fold and thrust belts with a weak basal decollement triassic anhydrites in the present case 4 an important influence of basement faulting which despite a general basement cover decoupling appears to control stress localization in the latter producing linkage of basement and cover stuctures in a combination of thin and thick skinned tectonic styles and 5 contrasting structural styles characterizing deep features as imaged by seismic reflection profiles and shallow ones deep stuctures consist of growth anticlines bounded by major thrust ramps and back limb back thrusts separated by broader open synclines both involving a mesozoic paleogene mainly carbonate passive margin succession in the crestal zones of major anticlines shallow structures affecting neogene terrigenous foredeep sediments show a complex pattern of upright to recumbent folds of tens to hundreds of meters wavelength related to minor thrusts and backthrusts deformation of the mesozoic paleogene multilayer appears to be dominated by thrust propagation in the cores of early formed anticlines developed by buckling instabilities the overlying neogene deposits are detached from the carbonate substratum along the base of the foredeep succession bedding parallel slip occurring along this detachment level appears to be accommodated by the complex structures in the crests of major anticlines where the thrusts lramp to the surface cutting up section complex shallow structures interpreted to accommodate at shallow structural levels the deep deformation would therefore represent a geometrical requirement for maintaining strain compatibility across the shallow detachment level located at the base of the foredeep succession

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

strains and folds within thrust sheets an analysis of the heilam sheet northwest scotland abstract the changes of shape and orientation of fossil worm burrows have been used to carry out a detailed strain analysis of the heilam thrust sheet in the moine thrust zone northwest scotland the strains have been factorised into components of layer parallel shear 1 layer normal shear 2 and layer parallel shortening or elongation variations in the 1 shear are largely lithologically controlled some strain is due to flexural processes as the thrusts and overlying beds change dip over thrust ramps or are tightened by later deformation while there may also be a component of drag which increases towards the overlying thrust this predating the shear due to flexure a contoured map of the values suggests that major folds within the thrust sheet developed as a result of stick or drag on the floor thrust prior to ramp climb this led to differential movement in the transport direction causing layer parallel shortening accompanied or followed by buckling of the layers a map showing layer normal shear strains 2 suggests that the heilam sheet forms a major surge zone the central part having moved further wnw than the northern and southern parts this has led to components of lateral shear along parts of the sheet especially in the north producing curvature of the imbricate faults

mechanics of nonplanar faults at extensional steps with application to the 1992 m 7 3 landers california earthquake 1 earthquakes that rupture across steps between faults can be larger than those predicted from individual fault lengths making understanding multifault events critical to assessing earthquake hazard empirical data from earthquake surface ruptures suggest that the distances between faults that rupture together can range from 1 to 5 km dynamic and quasi static models of planar faults determine similar distances however studies of interactions between realistic 3 d nonplanar faults are few a general comparison of quasi static stress perturbations and triggering potentials with mechanical models incorporating either planar or nonplanar faults highlights the sensitivity of planar fault models to model parameters and reveals no clear relationship between mean fault slip and triggering potential more specifically planar fault models predict triggering across a 3 km extensional step while models incorporating nonplanar faults indicate that a connecting fault is necessary to transfer slip through a 3 km step along the 1992 landers california earthquake rupture the mechanical approach taken captures the stress changes as well as the total stress following fault slip improving the criterion used to determine triggered failure potential this underscores the need for additional constraint on fault strength and cohesion the focus on complex fault geometry restricts analyses to the quasi static realm limiting the results to fault interactions over the short distances and slow rupture velocities for which the quasi static stress field is relevant or approximates the dynamic stress field

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

dynamic modeling of the 1992 landers earthquake we have used observed band pass filtered accelerograms and a previously determined slip distribution to invert for the dynamic rupture propagation of the 1992 landers earthquake in our simulations dynamic rupture grows under the simultaneous control of initial stress and rupture resistance by friction which we modeled using a simple slip weakening law we used a simplified landers fault model where the fault segments were combined into a single vertical planar fault by trial and error we modified an initial stress field inferred from the kinematic slip distribution proposed by wald and heaton 1994 until dynamic rupture generated a rupture history and final slip distribution that approximately matched those determined by the kinematic inversion we found that rupture propagation was extremely sensitive to small changes in the distribution of prestress and that a delicate balance with energy release rate controls the average rupture speed for the inversion we generated synthetic 0 5 hz ground displacements using an efficient green s function propagator method axitra this method enables us to propagate the radiation generated by the dynamic rupture to distances greater than those feasible using the finite difference method the dynamic model built by trial and error inversion provides a very satisfactory fit between synthetics and strong motion data we validated this model using records from stations used in the slip inversion as well as some which were not included we also inverted for a complementary model that fits the data just as well but in which the initial stress was perfectly uniform while rupture resistance was heterogeneous this demonstrates that inversion of ground motion is nonunique

the 11 april 2012 east indian ocean earthquake triggered large aftershocks worldwide although strong remote aftershocks are exceedingly rare their rate increased fivefold during the six days following the 2012 east indian ocean earthquake perhaps as a result of the strike slip nature of the 2012 event or a build up of close to failure nucleation sites

inverting for slip on three dimensional fault surfaces using angular dislocations the increasing quality of geodetic data synthetic aperture radar interferometry insar dense global positioning system gps arrays now available to geophysicists and geologists are not fully exploited in slip inversion procedures most common methods of inversion use rectangular dislocation segments to model fault ruptures and therefore oversimplify fault geometries these geometric simplifications can lead to inconsistencies when inverting for slip on earthquake faults and they preclude a more complete understanding of the role of fault geometry in the earthquake process we have developed a new three dimensional slip inversion method based on the analytical solution for an angular dislocation in a linear elastic homogeneous isotropic half space the approach uses the boundary element code poly3d that employs a set of planar triangular elements of constant displacement discontinuity to model fault surfaces the use of triangulated surfaces as discontinuities permits one to construct fault models that better approximate curved three dimensional surfaces bounded by curved tiplines shapes that commonly are imaged by three dimensional reflection seismic data and inferred from relocated aftershock data we demonstrate the method s ability to model three dimensional rupture geometries by inverting for slip associated with the 1999 hector mine earthquake the resulting model avoids displacement anomalies associated with the overlapping rectangular dislocations used in previous models improving the fit to the geodetic data by 32 and honors the observed surface ruptures thereby allowing more direct comparisons between geologic and geodetic data on slip distributions online material hector mine input files and file format description

influence of releasing step overs on surface fault rupture and fault segmentation examples from the 17 august 1999 izmit earthquake on the north anatolian fault turkey the 17 august 1999 izmit earthquake broke four distinct structural segments of the north anatolian fault from east to west the karadere sakarya sapanca and golcuk fault segments these segments are separated from one another and the adjoining yalova and duzce fault segments to the west and east respectively by distinct right releasing step over and or gaps in the fault trace these include from east to west the eften lake step over 2 4 km wide akyazi gap 6 13 km long sapanca step over 1 2 km wide golcuk step over 1 2 km wide and karamursel step over 4 5 km wide the earthquake nucleated within or near the golcuk step over with bilateral rupture propagation to the west and east to the west about 4 5 5 m of surface rupture up to 7 m of subsurface rupture on the golcuk segment was mostly if not entirely arrested by the 4 to 5 km wide karamursel step over to the east about 3 4 m of surface rupture about 4 m of subsurface rupture propagated through the 1 to 2 km wide sapanca step over triggering up to 4 5 5 5 m of surface rupture up to 5 6 m of subsurface rupture on the sakarya segment rupture on the sakarya segment stepped across the akyazi gap triggering 1 1 5 m of rupture on the karadere segment rupture on the karadere segment was arrested by the 2 to 4 km wide eften lake step over modeling of the transient stress field associated with the rupture propagation agrees well with the field observations the modeled fault rupture of 5 m on the golcuk segment appears to decrease the transient stress on the eastern tip of the adjoining yalova segment across the 4 to 5 km wide karamursel step over even if we allow rupture on the golcuk segment to extend along the entire southern margin of the step over our model shows that regardless of the amount of slip in a generic sense it is difficult to increase stress on the tip of an adjoining fault segment across a 5 km wide step over on the other hand fault rupture of 3 m on the western tip of the sapanca fault segment significantly increases the transient stress on the adjoining sakarya segment across the 1 to 2 km wide sapanca step over allowing rupture propagation across the basin an evaluation of 30 historical strike slip earthquakes involving 59 step over basins supports our field observations and stress modeling of the izmit fault rupture historical strike slip events with small to large displacements usually propagate through step overs less than 1 2 km wide with increasing displacement larger and larger step overs can be ruptured through the empirical data generally show a ratio ranging from 2 1 to 1 1 between step over width in kilometers and strike slip displacement in meters for a through going rupture however step overs of 4 to 5 km width appear to always arrest fault rupture regardless of the amount of displacement these results therefore provide important constraints for evaluating the probability of multisegment ruptures on segmented strike slip faults manuscript received 20 august 2000

integration of surface slip and aftershocks to constrain the 3d structure of faults involved in the m 7 3 landers earthquake southern california investigation of the mechanics of complex earthquakes requires insight into fault geometry we use linear elastic quasi static mechanical models of faults involved in the m 7 3 landers earthquake to test the influence of fault continuity dip and strike on fault slip and the perturbed stress field in regions of complex surface deformation and dense aftershock activity subsurface fault structure is constrained with both geological and geophysical data by comparing observed right lateral surface slip with slip along model faults and by comparing focal mechanisms with model coulomb planes at the locations of large aftershocks the refined structure of major faults at landers includes a southward extension of the johnson valley fault jvf at depth beyond the mapped fault trace a 75 w dip along the central johnson valley fault and a near surface discontinuity along the southern homestead valley fault hvf the final model better captures observed slip deficits along the johnson valley and homestead valley faults improves quantitative fit to the observed offset data and captures the local stress state in 9 of 12 locations studied relating aftershock orientations to local stresses resulting from mainshock fault slip provides a mechanical basis for deciphering between the two nodal planes provided by each focal mechanism slip along nonplanar faults with friction of 0 6 produces model failure planes in a variety of orientations indicating that heterogeneous aftershocks do not necessarily result from low fault friction mechanical selection of nodal planes suggests that aftershocks do not consistently reflect the orientation of their cluster or the orientation and slip direction of mainshock faults

coseismic and postseismic fault slip for the 17 august 1999 m 7 5 izmit turkey earthquake we use global positioning system gps observations and elastic half space models to estimate the distribution of coseismic and postseismic slip along the izmit earthquake rupture our results indicate that large coseismic slip reaching 5 7 meters is confined to the upper 10 kilometers of the crust correlates with structurally distinct fault segments and is relatively low near the hypocenter continued surface deformation during the first 75 days after the earthquake indicates an aseismic fault slip of as much as 0 43 meters on and below the coseismic rupture these observations are consistent with a transition from unstable episodic large earthquakes to stable fault creep sliding at the base of the seismogenic zone

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

heterogeneous stretching simple shear and basin development abstract the models of basin development which involve either homogeneous stretching of the whole lithosphere or displacement on a lithospheric scale shear zone are but two end members of a range of possible extensional models the homogeneous extension model thins the lower lithosphere beneath the thinned upper crust and superimposes a thermal subsidence basin on the earlier fault bounded basin the shear zone model offsets the zone of lower lithospheric stretching and thermal subsidence it is more likely that the zones of upper and lower lithospheric stretching will be heterogeneous and patchy but will often overlap in plan view this will produce localised uplift and subsequent thermal subsidence within the faulted basin and may explain many of the anomalies between the various stretching estimates made using different structural stratigraphic and geophysical techniques the model which combines heterogeneous lithospheric stretching and associated simple shear may explain 1 variations in dip of the major detachment zones in the large basins 2 variations in types of strain on or beneath the detachment zones 3 regional uplift of part of a basin to erode the earlier fault blocks and 4 the development of volcanism in basins with only low values of upper crustal extension the zone of stretched lower crust and lithospheric mantle may lie beneath the centre of the zone of upper crustal stretching or to one side it may be linked to the upper crustal zone by faults which dip consistently in one direction or by extensional systems which change their dominant dip direction with depth pulling out the mid crust as one or more wedges possible examples are discussed from the basin and range province and northwest european continental shelf

probability of multifault rupture abstract earthquake hazard modelers often assume that earthquake ruptures will be confined to individual faults and that earthquakes magnitudes will not exceed values related to the mapped fault length however earthquakes have been observed to jump from one fault to another producing a rupture longer than the originating fault the magnitudes of these earthquakes can exceed the value based on the originating fault length we estimated the probability of jumping as a function of interfault distance based on retrospective observations from past earthquakes a simple model consistent with the few available observations suggests that an earthquake on one strike slip fault may jump to another with a probability that decreases exponentially with separation the scale distance is about 3 km the model implies a nonnegligible probability of jumping as much as 10 km many california faults are within 10 km of one another we identified those and wrote a simple program to calculate the interfault distance and thus the jump probabilities we also formulated a simple way to estimate the magnitude frequency distribution for a pair of nearby faults as a function of their independent magnitude distributions and their separation distance allowing for multifault rupture increases the estimated upper magnitude limits for faults relative to a model in which faults are independent if the magnitude frequency distribution is constrained to be consistent with a fixed moment rate from fault slip rates for example then increasing the upper magnitude limits will reduce the rate of intermediate and small events

thrust tectonics and crustal shortening in the external french alps based on a seismic cross section abstract duplex geometry has an important bearing on understanding the development of orogenic zones based on a published seismic section through the french alps the external massifs are considered to form a duplex structure as a result of basement thrusting the duplex is restored to a uniform basement thickness giving a model estimate of shortening of 45 km the interpretation of this figure in terms of early alpine crustal thinning is discussed

abundance and speciation of iron across a subtropical tidal marsh of the min river estuary in the east china sea abstract iron has profound influence on anaerobic organic matter oxidation and fe s c biogeochemical cycling in tidal marshes to examine the abundance and speciation of iron six iron species poor crystalline fe iii crystalline fe iii non sulfidic fe ii porewater fe2 fes and fes2 were investigated in a cross transect span 250 m depth 1 2 m in a tidal marsh of the min river estuary in the east china sea the results suggested that sediment characteristics ph redox condition conductivity chloride sulfate and organic matter create a highly heterogeneous geochemical framework in the cross transect correspondingly the zonation of iron species differed significantly across the tidal marsh poor crystalline fe iii 48 24 mol g 1 and crystalline fe iii 75 32 mol g 1 accumulated on the surface of the high tide zone and decreased with elevation the non sulfidic fe ii minerals 140 61 mol g 1 accounted for the largest proportion of the six iron species the porewater fe2 was enriched within the deep layer of the upland region ph 6 2 6 5 and exhibited a maximum of 11 49 mm the aqueous sulfide concentration was below detection fes 39 6 mol g 1 and fes2 57 25 mol g 1 accumulated closer to the lower extremity tidal water brought o2 and removed certain amounts of dissolved organic carbon dissolved inorganic carbon and fe iii bearing particles in an element budget during tidal inundation variations of topography tidal hydrology seawater intrusion and organic matter altered the dominant organic matter oxidation pathway and further affected iron mineralization

incorporating fault mechanics into inversions of aftershock data for the regional remote stress with application to the 1992 landers california earthquake abstract we present a new stress inversion algorithm that accounts for the physics relating the remote stress slip along complex faults and aftershock focal mechanisms in a linear elastic heterogeneous isotropic whole or half space for each new remote stress the solution of the simulation is obtained by the superposition of three pre calculated solutions leading to a constant time evaluation consequently the full three dimensional boundary element method model need not be recomputed and is independent of the structural complexity of the underlying model using a synthetic model we evaluate several different measures of fit or cost functions between aftershocks and model results cost functions that account for aftershock slip direction provide good constraint on the remote stress while functions that evaluate only nodal plane orientations do not inversion results are stable for values of friction 0 5 on mainshock faults we demonstrate the technique by recovering the remote stress regime at the time of the 1992 m 7 3 landers california earthquake from its aftershocks and find that the algorithm performs well relative to methods that invert earthquakes occurring prior to the landers mainshock in the mechanical inversion incorporating fault structures is necessary but small differences in fault geometries do not impact these inversion results each inversion provides a complete solution for an earthquake as output including fault slip and the stress and deformation fields around the fault s this allows for many additional datasets to be used as input including fault surface slip gps data insar data and or secondary fracture orientations

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

fault branching and rupture directivity 1 could the directivity of a complex earthquake be inferred from the ruptured fault branches it created typically branches develop in forward orientation making acute angles relative to the propagation direction direct backward branching of the same style as the main rupture e g both right lateral is disallowed by the stress field at the rupture front here we propose another mechanism of backward branching in that mechanism rupture stops along one fault strand radiates stress to a neighboring strand nucleates there and develops bilaterally generating a backward branch such makes diagnosing directivity of a past earthquake difficult without detailed knowledge of the branching process as a field example in the landers 1992 earthquake rupture stopped at the northern end of the kickapoo fault jumped onto the homestead valley fault and developed bilaterally there nnw to continue the main rupture but also sse for 4 km forming a backward branch we develop theoretical principles underlying such rupture transitions partly from elastostatic stress analysis and then simulate the landers example numerically using a two dimensional elastodynamic boundary integral equation formulation incorporating slip weakening rupture this reproduces the proposed backward branching mechanism based on realistic if simplified fault geometries prestress orientation corresponding to the region standard lab friction values for peak strength and fracture energies characteristic of the landers event we also show that the seismic s ratio controls the jumpable distance and that curving of a fault toward its compressional side like locally along the southeastern homestead valley fault induces near tip increase of compressive normal stress that slows rupture propagation

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

synthesis of salt tectonics in the southern north sea uk abstract a structural model encompassing the southern north sea basin west of the central graben has been developed this model consists of a rift system affecting the post salt section around the basin margin and a large area of detached compressional buckle folds within the basin this pattern is initially a response to gravity sliding of the post salt section on the salt within the basin during the late triassic to late jurassic a close relationship between the location and trend of the peripheral graben system and basement structures in the pre salt is noted pre jurassic extension across the peripheral graben systems was balanced by the sum of fault heaves at the pre salt rotliegend level and shortening across salt cored buckle folds in the post salt section salt pillows and swells passively infilled the cores of these gravity induced buckle folds cretaceous and tertiary inversion involved basin tilt and renewed movement on basin bounding basement faults notably reverse movements did not propagate from basement structures up into the peripheral graben systems the post salt sedimentary section experienced gravity spreading in response to inversion related uplift resulting in syn inversion extensional faulting in the sole pit high where the mesozoic section was thickest this extension combined with a loss of fault heave in the pre salt section was balanced by amplification of salt cored buckle folds in the centre of the basin in the context of the model described here salt pillows represent passive infill of thin skinned compressional buckle folds which later amplified during thick skinned basement shortening crestal collapse of such folds occurs via normal faulting accompanied by reactive diapirism such reactive diapirs establish conduits through which salt may leak leading to pillow deflation and ultimately conduit preservation as a salt wall flanked by rim synclines in areas where the buckle folds were emergent the salt structures described here are related to cover folds and faults which in turn reflect episodes of basin extension tilting and inversion hence individual salt structures can be said to be only remotely connected with regional intraplate stresses

slip distribution of the 1992 landers earthquake and its implications for earthquake source mechanics we use near source 10 to 164 km displacement seismograms to image the slip distribution and rupture history of the 28 june 1992 mw 7 3 landers california earthquake aftershock seismograms from similar distances are modeled to find the velocity model and frequency range 0 05 to 0 25 hz over which theoretical green s functions are most accurate and the measure of fit is used as an upper bound on theoretical error in the mainshock inversion we represent the rupture surface with three planar segments divided into 3 by 3 km elements extending from the surface to 18 km depth and solve for the slip distribution and the rupture time model that minimizes misfit to both recorded seismograms and mapped surface displacement in a least squares sense we investigate two faulting models one with a uniformly short 3 sec rise time everywhere on the fault surface and the other with a variable rise time 2 to 6 sec we perform sensitivity tests using synthetic data from a hypothetical earthquake to evaluate model resolution and solution stability in the sensitivity tests both fault models recover similar slip and rupture features but neither is capable of imaging details of the rise time for the landers earthquake we find an average rupture velocity of 2 5 km sec and use this average for a starting model in a linearized inversion for rupture time in our solutions of slip amplitude distribution the southernmost johnson valley fault segment has 20 of the total seismic moment 6 to 8 1019 n m with small displacements near the hypocenter the homestead valley segment contributes half of the moment with the largest slip amplitudes 25 to 35 km northwest of the hypocenter at 4 to 12 km depth and the camp rock emerson segment contributes the remaining moment with the largest slip amplitude 35 to 50 km northwest of the hypocenter in the shallow crust 9 km there is some evidence that the rupture front is delayed as it encounters high slip regions suggesting that prior to the mainshock these areas were further from failure owing either to greater strength or lower prestress

tectonic stratigraphy and structural continuity of the northernmost moine thrust zone and moine nappe scottish caledonides the moine thrust zone and overlying moine nappe represent classic ground in scottish geology in which neoproterozoic moine metasedimentary rocks were translated towards the wnw over the laurentian foreland comprising lewisian basement gneisses and a cambrian cover succession during caledonian orogenesis at c 430 ma systematic mapping of both the moine nappe and underlying moine thrust zone in the loch hope to whiten head region of sutherland extends the tectonic stratigraphy developed in other parts of the thrust zone to the little studied north coast section an apparent continuum of deformation is recognized from the moine nappe down into the underlying thrust zone with a consistent gently ese dipping foliation associated with down dip mineral and extension lineations the polyphase fold history present within the moine nappe and the thrust zone results from progressive deformation during thrusting thrust related fold axes and bedding cleavage intersections are typically subparallel to the transport direction in high strain zones whereas gently north or south plunging attitudes are common in lower strain portions of the thrust zone thrusts are commonly deformed by folds developed within their footwalls consistent with a foreland propagating sequence of deformation the newly defined lochan riabhach thrust is interpreted as an out of sequence structure that sliced at low angles across the thrust zone and toward the wnw after initial thrust stacking comparison with the downfaulted segment of the moine nappe and thrust zone exposed on the foreland at faraid head demonstrates cross strike continuity of the thrust sheet template and structural history for at least 15 km to the nw

dynamic shear rupture interactions with fault bends and off axis secondary faulting 1 on the basis of elastodynamic stress fields for singular crack and nonsingular slip weakening models of propagating rupture we develop preliminary answers to such questions as follows if a rupturing fault is intersected by another providing a possible bend in the failure path when will stressing be consistent with rupture along the bend what secondary fault locations and orientations in a damaged region bordering a major fault will be stressed to failure by the main rupture stresses that could initiate rupture on a bend are shown to increase dramatically with crack speed especially near the limiting speed rayleigh for mode ii shear for mode iii whether a bend path once begun can be continued to larger scales depends on principal stress directions and ratios in the prestress field conditions should often be met in mode ii for which bend paths encouraged by stressing very near the rupture tip are discouraged by the larger scale stressing a basis for intermittent rupture propagation and spontaneous arrest secondary failure in the damage zone likewise increases markedly as the limiting speed is approached such may make the fracture energy much greater than for slip on a single surface the extent of secondary faulting is strongly affected by prestress directions and the ratio of residual to peak strength for mode ii prestress controls whether activation occurs primarily on the extensional side which we show to be the typical case or on the compressional side too natural examples are consistent with the concepts developed

the 17 august 1999 izmit earthquake on 17 august 1999 an earthquake of magnitude 7 4 shook northwestern turkey details on the earthquake9s characteristics and effects across northwestern turkey are provided and are put in the historical context of previous earthquakes in the region the earthquake was the seventh in a series of earthquakes migrating westwards along the north anatolian fault since 1939 information on historical earthquakes modeling and estimates of the slip rate along the fault indicate that the location and severity of the earthquake should not have come as a surprise

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults

strike slip fault geometry in turkey and its influence on earthquake activity the geometry of turkish strike slip faults has been reviewed and described from this data set it appears that fault geometry the distribution of discontinuities such as bends and stepovers along the main fault trace plays an important role in controlling the location of large earthquake rupture segments along the fault zones large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 more important than the size of each discontinuity however is the total geometric pattern i e the distribution of adjacent bends and stepovers based not only on distance from one another but also on relative discontinuity size certain geometric patterns restraining single or double bends are particularly common and can be viewed as responsible for strain accumulation along portions of the fault zone fault geometry not only plays a role in the extent of earthquake rupture but also in characteristics of earthquake behavior for example large earthquake epicenters often occur near restraining bends or double bends furthermore aftershocks and swarm activity can often be associated with releasing areas areas along the strike slip fault that are undergoing a relatively large amount of extension

transtensional tectonics of the minto flats fault zone and nenana basin central alaska abstract central alaska is a broad zone of crustal deformation that is produced by collision and flat slab subduction within central alaska there are large scale right lateral strike slip faults such as the denali fault 2002 m w 7 9 as well as smaller scale fold and thrust belts and a set of left lateral strike slip fault zones one of which is the minto flats fault zone mffz we use seismological evidence to document a pair of overlapping left lateral faults that define the mffz microseismicity delineates this 180 km long fault zone using body waves and surface waves we perform moment tensor inversions for the 11 best recorded earthquakes in the fault zone moment tensors reveal consistent left lateral faulting throughout the fault zone a finite source model for the 1995 m w 6 0 earthquake is consistent with left lateral faulting and provides rupture details for the largest known event in the fault zone the two main faults are separated by 10 km and overlap by 67 km forming a releasing stepover geometry within a local transtensional setting between the faults is a 90 km long 12 km wide and 8 km deep sedimentary basin the nenana basin we interpret the transtensional faulting to be responsible for the development of the basin over the past 6 ma the distances of fault overlap and fault separation are key parameters for determining 1 the 3d morphology of the sedimentary basin and 2 the likelihood of earthquake ruptures jumping from one fault to the next the structure of the nenana basin is consistent with shear motion accommodated by the identified faults the 10 km fault separation suggests that ruptures are not likely to span the entire fault zone earthquakes as large as m w 7 0 7 5 could occur on the faults the transtensional fault zone provides an important constraint for understanding the larger scale intraplate tectonic setting of central alaska online material figures of waveform fits depth estimation for moment tensors variation in seismicity and fault plane identification

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

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex