shallow creep on the haiyuan fault gansu china revealed by sar interferometry interferometric synthetic aperture radar data are used to map the interseismic velocity field along the haiyuan fault system hfs at the north eastern boundary of the tibetan plateau two m 8 earthquakes ruptured the hfs in 1920 and 1927 but its 260 km long central section known as the tianzhu seismic gap remains unbroken since 1000 years the envisat sar data spanning the 2003 2009 period cover about 200 300 km2 along three descending and two ascending tracks interferograms are processed using an adapted version of roi pac the signal due to stratified atmospheric phase delay is empirically corrected together with orbital residuals mean line of sight velocity maps are computed using a constrained time series analysis after selection of interferograms with low atmospheric noise these maps show a dominant left lateral motion across the hfs and reveal a narrow 35 km long zone of high velocity gradient across the fault in between the tianzhu gap and the 1920 rupture we model the observed velocity field using a discretized fault creeping at shallow depth and a least squares inversion the inferred shallow slip rate distribution reveals aseismic slip in between two fully locked segments the average creep rate is 5 mm yr 1 comparable in magnitude with the estimated loading rate at depth suggesting no strain accumulation on this segment the modeled creep rate locally exceeds the long term rate reaching 8 mm yr 1 suggesting transient creep episodes the present study emphasizes the need for continuous monitoring of the surface velocity in the vicinity of major seismic gaps in terms of seismic hazard assessment

kinematics and dynamics of the pamir central asia quantifying surface deformation and force balance in an intracontinental subduction zone kinematic and dynamic models quantify deformation and force balance in the pamir a region undergoing the rare and poorly understood process of intracontinental subduction we constrain a detailed kinematic model with 506 recent gps velocities and quaternary fault slip rates and show that the pamir is organized like the himalaya and tibet with regions of 1 localized strain rate 100e 9 yr along the pamir frontal thrust system the subduction interface similar to the himalaya and 2 distributed north south compression and east west extension similar to tibet through standard thin viscous sheet methods we demonstrate that the lithospheric force balance in the pamir is a combination of stresses caused by gravitational potential energy and india eurasia convergence accommodated at a subduction interface in this case the pamir frontal thrust system we find that strain rate and deviatoric stress patterns near the pamir frontal thrust system are characteristic of a mature subduction zone despite its initiation in continental lithosphere although the pamir and tibet are kinematically and dynamically similar the pamir is stiffer overall than tibet perhaps due to the presence of the highly arcuate geometrically stiffened continental slab at depth

crustal structure of the western new england appalachians and the adirondack mountains we present an interpretation of the crustal velocity structure of the new england appalachians and the adirondack mountains based on a seismic refraction wide angle reflection experiment in eastern north america extending from the adirondacks in new york state through the northern appalachians in vermont and new hampshire to central maine modeling of the eastern portion of the profile within the new england appalachians shows a subhorizontal layered crust with upper crustal velocities ranging from 5 5 to 6 2 km s a midcrustal velocity of 6 4 km s and a lower crustal velocity of approximately 6 8 km s crustal thickness increases from 36 km beneath maine to 40 km in vermont little evidence is seen for structures at depth directly related to the white mountains or the green mountains a major lateral velocity change in the upper and mid crust occurs between the appalachians and the adirondacks this boundary projecting to the surface beneath the champlain valley dips to the east beneath the green mountains and extends to a depth of 25 km below the eastern edge of the connecticut valley synclinorium in vermont the tahawus complex a series of strong horizontal reflections at 18 24 km depth beneath the adirondack highlands is seen to dip eastward beneath vermont upper crustal rocks in the adirondack mountains have poisson s ratios of 0 28 0 01 that can be correlated with the marcy anorthosite pois son s ratios of 0 24 0 01 calculated for rocks of the connecticut valley synclinorium indicate a siliceous upper crust in vermont the lower crust is considered to be best represented by intermediate to mafic granulites a high poisson s ratio 0 26 0 27 tends to support a mafic lower crust in the new england appalachians this seismic refraction wide angle reflection experiment provides further evidence for the obduction of the allochthonous western appalachian units onto grenvillian crust above a zone of detachment that penetrates at least to midcrustal depths and was the locus of successive paleozoic thrusting

shallow creep along the 1999 izmit earthquake rupture turkey from gps and high temporal resolution interferometric synthetic aperture radar data 2011 2017 characterizing the spatiotemporal evolution of creep is essential to constrain fault slip budget and understand creep mechanism studies based on interferometric synthetic aperture radar and global positioning system gps satellite observations until 2012 have shown that the central segment of the 17 august 1999 mw 7 4 izmit earthquake on the north anatolian fault began slipping aseismically following the event in the present study we combine new interferometric synthetic aperture radar time series based on terrasar x and sentinel 1a b radar images acquired over the period 2011 2017 with near field gps measurement campaigns performed every 6 months from 2014 to 2016 the mean velocity fields reveal that creep on the central segment of the 1999 izmit fault rupture continues to decay more than 19 years after the earthquake in overall agreement with models of postseismic afterslip decaying logarithmically with time for a long period of time along the fault section that experienced supershear velocity rupture during the izmit earthquake creep continues with a rate up to 8 mm year a significant transient accelerating creep is detected in december 2016 on the sentinel 1 time series near the maximum creep rate location associated with a total surface slip of 10 mm released in 1 month only additional analyses of the vertical velocity fields show a persistent subsidence on the hanging wall block of the golcuk normal fault that also ruptured during the izmit earthquake our results demonstrate that afterslip processes along the north anatolian fault east southeast of istanbul are more complex than previously proposed as they vary spatiotemporally along the fault

interseismic strain accumulation along the western boundary of the indian subcontinent 1 despite an overall sinistral slip rate of 3 cm yr few major earthquakes have occurred in the past 200 years along the chaman fault system the western boundary of the india plate with the eurasia plate gps and insar data reported here indicate sinistral shear velocities of 8 17 mm yr across the westernmost branches of the fault system suggesting that a significant fraction of the plate boundary slip is distributed in the fold and fault belt to the east at its southernmost on land segment 26 n near the triple junction between the arabia eurasia and india plates we find the velocity across the ornach nal fault is 15 1 13 4 16 9 mm yr with a locking depth probably less than 3 km at latitude 30 n near the town of chaman pakistan where a m6 5 earthquake occurred in 1892 the velocity is 8 5 6 8 10 3mm yr and the fault is locked at approximately 3 4 km depth at latitude 33 n and further north insar data indicate a velocity across the chaman fault of 16 8 2 7 mm yr the width of the plate boundary varies from several km in the south where we observe 2 mm yr of convergence near the westernmost strike slip faults to a few hundreds of km in the north where we observe 6 9 mm yr of convergence and where the faulting becomes distinctly transpressional the shallow locking depth along much of the transform system suggests that earthquakes larger than those that have occurred in the historical record would be unexpected and that the recurrence interval of those earthquakes that have occurred is of the order of one or two centuries similar in length to the known historical record

the 2013 mw 7 7 balochistan earthquake seismic potential of an accretionary wedge great earthquakes rarely occur within active accretionary prisms despite the intense long term deformation associated with the formation of these geologic structures this paucity of earthquakes is often attributed to partitioning of deformation across multiple structures as well as aseismic deformation within and at the base of the prism davis et al 1983 we use teleseismic data and satellite optical and radar imaging of the 2013 m w 7 7 earthquake that occurred on the southeastern edge of the makran plate boundary zone to study this unexpected earthquake we first compute a multiple point source solution from w phase waveforms to estimate fault geometry and rupture duration and timing we then derive the distribution of subsurface fault slip from geodetic coseismic offsets we sample for the slip posterior probability density function using a bayesian approach including a full description of the data covariance and accounting for errors in the elastic structure of the crust the rupture nucleated on a subvertical segment branching out of the chaman fault system and grew into a major earthquake along a 50 north dipping thrust fault with significant along strike curvature fault slip propagated at an average speed of 3 0 km s for about 180 km and is concentrated in the top 10 km with no displacement on the underlying decollement this earthquake does not exhibit significant slip deficit near the surface nor is there significant segmentation of the rupture we propose that complex interaction between the subduction accommodating the arabia eurasia convergence to the south and the ornach nal fault plate boundary between india and eurasia resulted in the significant strain gradient observed prior to this earthquake convergence in this region is accommodated both along the subduction megathrust and as internal deformation of the accretionary wedge

cocorp seismic profiling of the appalachian orogen beneath the coastal plain of georgia a southeastward extension onto the coastal plain of an earlier cocorp traverse which confirmed large scale thin skinned thrusting of crystalline rocks of the southern appalachians has provided some of the most spectacular reflections yet seen in crustal seismic data most of the reflectors can be interpreted as either fault surfaces or as metamorphosed strata of late precambrian early paleozoic age they are consistent with the hypothesis that a major detachment extends eastward beneath this part of the orogen although other interpretations with a more complex pattern of detachments or sutures are also possible large scale overthrusting provides a mechanism for incorporating sedimentary rocks into the lower crust and may help to explain many of the layered features on crustal seismic data reflections from deep beneath the coastal plain indicate that the structural configuration of the rocks is complex and that the remains of a collision zone are being observed several east dipping horizons which bear strong similarities to thrust faults in valley and ridge sedimentary rocks are seen in the basement at shallow and mid crustal levels beneath the coastal plain the augusta fault for example displays a reflection which extends at a low angle some 80 km or more southeast of its surface position in conjunction with surface geologic information these new data demonstrate that late paleozoic compressive deformation was pervasive and resulted in lateral movements in the upper crust extending from the valley and ridge to the crystalline rocks beneath the coastal plain a distance of 400 km or more a large antiform cresting at about 2 3 sec or about 6 km below the surface and other structures beneath the coastal plain of georgia deserve further consideration for petroleum exploration although metamorphism may have eliminated petroleum from these rocks refracted arrivals and fault geometries indicate two triassic rift basins beneath coastal plain sedimentary rocks one of which has apparently not been recognized previously

ball and socket tectonic rotation during the 2013 mw7 7 balochistan earthquake abstract the september 2013 m w 7 7 balochistan earthquake ruptured a 200 km long segment of the curved hoshab fault in southern pakistan with 10 0 2 m of peak sinistral and 1 7 0 8 m of dip slip this rupture is unusual because the fault dips 60 15 towards the focus of a small circle centered in northwest pakistan and despite a 30 increase in obliquity along strike the ratios of strike and dip slip remain relatively uniform surface displacements and geodetic and teleseismic source inversions quantify a bilateral rupture that propagated rapidly at shallow depths from a transtensional jog near the northern end of the rupture static friction prior to rupture was unusually weak 0 05 and friction may have approached zero during dynamic rupture here we show that the inward dipping hoshab fault defines the northern rim of a structural unit in southeast makran that rotates akin to a 2 d ball and socket joint counter clockwise in response to india s penetration into the eurasian plate this rotation accounts for complexity in the chaman fault system and in principle reduces seismic potential near karachi nonetheless these findings highlight deficiencies in strong ground motion equations and tectonic models that invoke anderson byerlee faulting predictions

distribution of aseismic slip rate on the hayward fault inferred from seismic and geodetic data 1 we solve for the slip rate distribution on the hayward fault by performing a least squares inversion of geodetic and seismic data sets our analysis focuses on the northern 60 km of the fault interferometric synthetic aperture radar insar data from 13 independent ers interferograms are stacked to obtain range change rates from 1992 to 2000 horizontal surface displacement rates at 141 bench marks are measured using gps from 1994 to 2003 surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion the fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface south of the city of hayward a steeply east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth the inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of 5 mm yr to a depth of 4 6 km the interferometric synthetic aperture radar insar data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath point pinole although the insar data might be complicated by a small dip slip component at this location a low slip rate patch of 1 mm yr is inferred beneath san leandro consistent with the source location of the 1868 earthquake we calculate that the entire fault is accumulating a slip rate deficit equivalent to a mw 6 77 0 05 per century however this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip

characterizing and estimating noise in insar and insar time series with modis 1 insar time series analysis is increasingly used to image subcentimeter displacement rates of the ground surface the precision of insar observations is often affected by several noise sources including spatially correlated noise from the turbulent atmosphere under ideal scenarios insar time series techniques can substantially mitigate these effects however in practice the temporal distribution of insar acquisitions over much of the world exhibit seasonal biases long temporal gaps and insufficient acquisitions to confidently obtain the precisions desired for tectonic research here we introduce a technique for constraining the magnitude of errors expected from atmospheric phase delays on the ground displacement rates inferred from an insar time series using independent observations of precipitable water vapor from modis we implement a monte carlo error estimation technique based on multiple 100 modis based time series that sample date ranges close to the acquisitions times of the available sar imagery this stochastic approach allows evaluation of the significance of signals present in the final time series product in particular their correlation with topography and seasonality we find that topographically correlated noise in individual interferograms is not spatially stationary even over short spatial scales 10 km overall modis inferred displacements and velocities exhibit errors of similar magnitude to the variability within an insar time series we examine the modis based confidence bounds in regions with a range of inferred displacement rates and find we are capable of resolving velocities as low as 1 5 mm yr with uncertainties increasing to 6 mm yr in regions with higher topographic relief

structure of the crust and upper mantle beneath the great valley and allegheny plateau of eastern pennsylvania 1 comparison of linear inversion methods for sparse wide angle reflection data we use p data extracted from a small number of wide angle recordings of quarry blasts to construct averaged one dimensional velocity models of the crust beneath portions of the great valley newark basin valley and ridge and allegheny plateau of the central appalachians of pennsylvania using the linear form of the equations for p in terms of slowness depth structure we compare inversion results for the extremal backus gilbert and generalized least squares methods although the uncertainties are large the models do show a well constrained increase in midcrustal velocities and crustal thickness beneath the allegheny plateau inversion of precritical reflections from the moho suggests bounds of 7 1 7 6 km s on p wave velocity and 3 9 4 2 km s on s wave velocity near the base of the crust p wave velocity models for the great valley show a crustal thickness between 40 and 45 km with an average velocity between 6 4 and 6 6 km s models for the allegheny plateau show a larger crustal thickness 47 52 km and a much higher average velocity 6 8 6 9 km s estimates of average shear wave velocities for the great valley range from 3 6 to 3 8 km s with crustal thickness estimates between 37 and 44 km for the relatively small number of singular values retained standard errors in depth for models derived by generalized least squares range from 1 to 2 km for the p wave slowness models and from 2 to 4 km for the s wave models extremal depth bounds in general are 2 to 3 times as wide corresponding uncertainties in interval velocity estimated from resolving kernels in slowness range from 0 15 to 0 45 km s for p wave models and from 0 15 to 0 40 km s for s wave models t2 x2 inversion of pmp data gives similar estimates for total crustal thickness and average velocity after correction for refraction effects t2 x2 inversion of pmp data for a fourth profile suggests the possibility of a slight thickening of the crust 47 48 km directly beneath the axis of the great valley gravity low estimates of average vp vs for the crust based on average velocities for models derived by generalized least squares inversion range from 1 73 to 1 77 estimates based on travel time ratios for events interpreted as p wave and s wave reflections from the moho lie between 1 75 and 1 79 for a crust in which the effects of velocity anisotropy can be neglected these estimates correspond to crustal averages between 0 25 and 0 27 for poisson s ratio the one dimensional velocity models derived here provide estimates of the long wavelength component of velocity structure besides demonstrating the maximum resolving power inherent in a limited p data set these averaged models can be used for migrating reflection data and as starting models for determining two dimensional velocity structure

fault creep rates of the chaman fault afghanistan and pakistan inferred from insar the chaman fault is the major strike slip structural boundary between the india and eurasia plates despite sinistral slip rates similar to the north america pacific plate boundary no major m7 earthquakes have been documented along the chaman fault indicating that the fault either creeps aseismically or is at a late stage in its seismic cycle recent work with remotely sensed interferometric synthetic aperture radar insar time series documented a heterogeneous distribution of fault creep and interseismic coupling along the entire length of the chaman fault including an 125 km long creeping segment and an 95 km long locked segment within the region documented in this study here i present additional insar time series results from the envisat and alos radar missions spanning the southern and central chaman fault in an effort to constrain the locking depth dip and slip direction of the chaman fault i find that the fault deviates little from a vertical geometry and accommodates little to no fault normal displacements peak documented creep rates on the fault are 9 12 mm yr accounting for 25 33 of the total motion between india and eurasia and locking depths in creeping segments are commonly shallower than 500 m the magnitude of the 1892 chaman earthquake is well predicted by the total area of the 95 km long coupled segment to a first order the heterogeneous distribution of aseismic creep combined with consistently shallow locking depths suggests that the southern and central chaman fault may only produce small to moderate earthquakes m7

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

creep and quakes on the northern transition zone of the san andreas fault from gps and insar data 1 the san juan bautista sjb segment forms the northern transition zone of the creeping section of the san andreas fault it is an area of moderate seismicity the largest instrumentally recorded earthquakes have been m5 5 however historic records suggest six m 6 earthquakes occurred near the sjb segment between 1840 and 1899 it is also an area that has experienced several slow earthquakes we perform a joint inversion of gps and insar data to determine the current rate and distribution of interseismic creep we find two low slip locked segments at mid seismogenic depths that may represent source regions for the 19th century earthquakes we find that the sjb segment is currently accumulating strain energy at the rate of one m6 3 6 7 earthquake per century at this rate the 1840 1899 sequence released 135 510 years of accumulated moment deficit

seismic signature and tectonic cross section of the variscan crust in western france deep seismic reflection profiling ecors program vertical and wide angle survey coupled with field and subsurface geology are used to propose a complete nne ssw section of the variscan belt in western france from belgium to southern brittany on this 800 km long profile which probably crosses two paleozoic sutures the variscan belt appears as a broad fanlike orogen characterized by large 100 km northward and southward overthrusts with polyphase deformation and metamorphism the central part of the belt central armorican zone suffered a simpler dextral shearing parallel to the strike of the belt with only green schist metamorphism deep reflection profiling shows that all the large thrusts visible at the surface root deeply in the lower crust or even crosscut the moho in the same way all the large strike slip faults parallel to the belt appear at depth as narrow discontinuities which crosscut the whole crust and in some cases the moho the seismically well layered crust develops essentially at depth in the most deformed and metamorphic internal parts of the belt in contrast with the relatively transparent brabant foreland basement which escaped the variscan deformation the moho appears as a relatively flat boundary at an average depth of 35 km with different characters it is sharp and strongly reflective both by wide angle and vertical seismics below the internal thrust zones much less distinct in the central armorican zone and only defined by low frequency signals at wide angle below the brabant foreland all these characteristics led us to consider the layering of the lower crust and the moho itself as initially tectonometamorphic features essentially produced by shearing and crust mantle decollement during the variscan stacking of the crust by intracontinental lithospheric subduction

earthquake potential along the northern hayward fault california the hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace dislocation models of the surface deformation adjacent to the hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at 7 millimeters per year to the bottom of the seismogenic zone along a 20 kilometer long northern fault segment microearthquakes with the same waveform repeatedly occur at 4 to 10 kilometer depths and indicate deep creep at 5 to 7 millimeters per year the difference between current creep rates and the long term slip rate of 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern hayward fault adjacent to the locked 1868 earthquake rupture which broke the southern 40 to 50 kilometers of the fault the potential for a major independent earthquake of the northern hayward fault might be less than previously thought

measurement of interseismic strain across the haiyuan fault gansu china by insar the haiyuan fault is part of a major left lateral fault system at the northeastern edge of the tibet qinghai plateau two m8 earthquakes 1920 and 1927 occurred along the fault bracketing an unbroken section of the fault identified as the tianzhu seismic gap we use interferometric synthetic aperture radar data from descending orbits of the ers satellites acquired between 1993 and 1998 along two adjacent tracks covering the gap to measure the current surface movements and better understand the present day mechanical behavior of this fault section the analysis of the radar data involves first the combined correction of orbital errors and errors associated with the phase delay through the troposphere a subset of the data is then selected based on the analysis of the residual noise spectra for each pair of data the selected interferograms are stacked and the average phase change rate is converted in fault parallel velocity assuming that the ground movement is horizontal and parallel to the fault velocity maps from both tracks show a zone of high velocity gradient across the fault a few kilometers wide consistent with left lateral slip on the haiyuan fault the average velocity field from the two tracks in their overlapping area is well fit with a single screw dislocation model in an elastic half space the derived fault slip rate at depth 4 2 8 mm yr is consistent with recent gps results the corresponding shallow apparent locking depth 0 4 2 km can be explained by a current low stress accumulation on the fault due to creep almost on the entire fault plane however unless it is transient this creep would be paradoxical with the occurrence of past large earthquakes along this fault section as revealed by paleoseismology an alternative model implying both shallow creep in the brittle upper crust and deep aseismic slip beneath the seismogenic layer separated by a locked section would be consistent with insar observations and with the potential for large earthquakes on the fault as well a two dislocation model with slip at 5 mm yr beneath 15 km and a transient creep rate of 11 mm yr between 2 and 7 km fits the insar data however the width and creep rate of the shallow creeping zone and their possible along strike variations are still poorly resolved with the present data set

processing and inversion of refraction and wide angle reflection data from the 1986 nevada passcal experiment we derive averaged one dimensional velocity models for the crust beneath the basin and range in western nevada by inverting p composites extracted from slant stacks of refraction and wide angle reflection data a combination of high cut filtering in the frequency domain with coherency filtering in the p domain has proved effective in smoothing severe static shifts due to lateral heterogeneities and suppressing artifacts due to spatial aliasing we supplement the low frequency information provided by the refraction records with higher frequency arrivals picked from the normal incidence and wide angle reflection sections generalized least squares inversion of data from eight shots for p and s wave velocity structure beneath two perpendicular profiles yields consistent estimates for total crustal thickness p wave 30 31 km s wave 30 32 km and average crustal velocity 6 2 km s 3 4 3 5 km s average poisson s ratio beneath the n s profile is 0 27 0 28 p wave velocities near the base of the crust 7 4 0 3 km s are estimated by inverting precritical reflections from the moho standard errors in depth for these models range from 1 to 3 km extremal depth bounds in general are about twice as large uncertainties in velocity estimated from resolving kernels range from 0 1 to 0 3 km s estimates of poisson1s ratio as a function of depth are characterized by large standard errors reflecting the poor resolution of shear wave velocities the combination of low average p and s wave velocities with a high average poisson s ratio in the upper half of the crust however is consistent with the presence of fluid filled cracks these results highlight the need for three component recording to better resolve shear wave velocity structure

over 100 years of faults interaction stress accumulation and creeping implications on chaman fault system pakistan the curve shaped chaman transform fault between pakistan and afghanistan demarks the western boundary of the indian plate which is the locus of many catastrophic earthquakes and this is poorly studied region to understand the earthquake fault interaction and hazard assessment based on earthquake triggering theory we investigate a sequence of earthquakes comprising five earthquakes that occurred in the chaman fault system since 1892 our results elucidate that three out of four earthquakes are triggered by the preceding earthquakes the 1935 earthquake of magnitude mw 7 7 is somewhat an independent earthquake in this sequence slightly influenced by the 1892 event the 1935 earthquake significantly loaded either terminus of its rupture with positive stress which later triggered the 1975 earthquake with 35 of its rupture length where cfs is above triggering threshold value and 1990 earthquake with 44 of its rupture length in positive stress lobe on ghazaband fault in the south lobe since the 1935 earthquake significantly increased the cfs on either terminus of its rupture the 2013 earthquake with magnitude mw 7 7 occurred on hoshab fault in the positive stress zone with 23 of its rupture length where cfs is positive moreover the northern locked segment of cf the southern segment of gbf southeastern segment of hf and paf demonstrate a high value of cfs it could trigger seismicity in these regions thus requiring arrangements to mitigate any seismic hazards in future

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

interpretation of migrated seismic reflection profiles across the northern appalachians in maine summary a simple line migration technique has been developed and applied to deep crustal reflection data collected in the northern appalachians of quebec and central maine preliminary interpretation of these data combined with the results of gravity and refraction studies shows thinning of the crust in two distinct steps beneath the silurian devonian merrimack synclinorium and shows evidence for mesozoic crustal stretching and dike intrusion

multi interferogram method for measuring interseismic deformation denali fault alaska summary studies of interseismic strain accumulation are crucial to our understanding of continental deformation the earthquake cycle and seismic hazard by mapping small amounts of ground deformation over large spatial areas insar has the potential to produce continental scale maps of strain accumulation on active faults however most insar studies to date have focused on areas where the coherence is relatively good e g california tibet and turkey and most analysis techniques stacking small baseline subset algorithm permanent scatterers etc only include information from pixels which are coherent throughout the time span of the study in some areas such as alaska where the deformation rate is small and coherence very variable it is necessary to include information from pixels which are coherent in some but not all interferograms we use a three stage iterative algorithm based on distributed scatterer interferometry we validate our method using synthetic data created using realistic parameters from a test site on the denali fault alaska and present a preliminary result of 10 5 5 0 mm yr 1 for the slip rate on the denali fault based on a single track of radar data from ers1 2

insar observations of strain accumulation and fault creep along the chaman fault system pakistan and afghanistan we use 2004 2011 envisat synthetic aperture radar imagery and insar time series methods to estimate the contemporary rates of strain accumulation in the chaman fault system in pakistan and afghanistan at 29 n we find long term slip rates of 16 2 3 mm yr for the ghazaband fault and of 8 3 1 mm yr for the chaman fault this makes the ghazaband fault one of the most hazardous faults of the plate boundary zone we further identify a 340 km long segment displaying aseismic surface creep along the chaman fault with maximum surface creep rate of 8 1 2 mm yr the observation that the chaman fault accommodates only 30 of the relative plate motion between india and eurasia implies that the remainder is accommodated south and east of the katawaz block microplate

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

a multiscale approach to estimating topographically correlated propagation delays in radar interferograms when targeting small amplitude surface deformation using repeat orbit interferometric synthetic aperture radar insar observations can be plagued by propagation delays some of which correlate with topographic variations these topographically correlated delays result from temporal variations in vertical stratification of the troposphere an approximate model assuming a linear relationship between topography and interferometric phase has been used to correct observations with success in a few studies here we present a robust approach to estimating the transfer function k between topography and phase that is relatively insensitive to confounding processes earthquake deformation phase ramps from orbital errors tidal loading etc our approach takes advantage of a multiscale perspective by using a band pass decomposition of both topography and observed phase this decomposition into several spatial scales allows us to determine the bands wherein correlation between topography and phase is significant and stable when possible our approach also takes advantage of any inherent redundancy provided by multiple interferograms constructed with common scenes we define a unique set of component time intervals for a given suite of interferometric pairs we estimate an internally consistent transfer function for each component time interval which can then be recombined to correct any arbitrary interferometric pair we demonstrate our approach on a synthetic example and on data from two locations long valley caldera california which experienced prolonged periods of surface deformation from pressurization of a deep magma chamber and one coseismic interferogram from the 2007 mw 7 8 tocapilla earthquake in northern chile in both examples the corrected interferograms show improvements in regions of high relief independent of whether or not we pre correct the data for a source model we believe that most of the remaining signals are predominately due to heterogeneous water vapor distribution that requires more sophisticated correction methods than those described here

fold and thrust partitioning in a contracting fold belt insights from the 1931 mach earthquake in baluchistan 1 surface deformation associated with the 27 august 1931 earthquake near mach in baluchistan is quantified from spirit leveling data and from detailed structural sections of the region interpreted from seismic reflection data constrained by numerous well logs mean slip on the west dipping dezghat bannh fault system amounted to 1 2 m on a 42 km 72 km thrust plane with slip locally attaining 3 2 m up dip of an inferred locking line at 9 km depth slip also occurred at depths below the interseismic locking line in contrast negligible slip occurred in the 4 km near the interseismic locking line the absence of slip here in the 4 years following the earthquake suggests that elastic energy there must either dissipate slowly in the interseismic cycle or that a slip deficit remains pending its release in a large future earthquake elastic models of the earthquake cycle in this fold and thrust belt suggest that slip on the frontal thrust fault is reduced by a factor of 2 to 8 compared to that anticipated from convergence of the hinterland a partitioning process that is presumably responsible for thickening of the fold and thrust belt at the expense of slip on the frontal thrust near the latitude of quetta gps measurements indicate that convergence is 5 mm yr hence the minimum renewal time between earthquakes with 1 2 m mean displacement should be as little as 240 years however when the partitioning of fold belt convergence to frontal thrust slip is taken into account the minimum renewal time may exceed 2000 years

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

earthquakes and associated deformation in northern baluchistan 1892 2001 we examine a century of seismicity and earthquake related deformation on the western margin of the indian plate in the pakistan region of northern baluchistan several catalogs of earthquakes for this region currently exist but early catalogs in particular suffer from errors incompleteness inhomogeneity and location bias we form a new catalog of more than 1000 earthquakes using original sources to confirm macroseismic locations and assign m s magnitudes to earthquakes since 1892 in doing so we reveal a systematic east northeast bias in locations caused largely by the uneven global distribution of seismic stations used in their determination an appendix provides narrative accounts and historical references to 34 significant earthquakes in the region the pattern of seismicity in the past century shows activity over a 700 km long 200 km wide segment of the plate boundary with predominantly strike slip faulting to the west and thrust faulting to the east at its narrowest near 29 n transpression of the plate boundary is partitioned into reverse and strike slip components separated by approximately 100 km the m 7 3 1931 mach earthquake slip 1 1 m on a 40 east southeast dipping reverse fault released fault normal stresses that may have unclamped the subsequent m 7 7 left lateral quetta earthquake 4 years later the northern chaman fault system in the past century has been largely inactive suggesting that this time period is not representative of long term activity in the region and that up to 4 m of potential slip is currently available to drive one or more future m 7 earthquakes despite triangulation installed in the late nineteenth and early twentieth centuries no recent geodetic data are available to permit plate boundary velocities to be measured directly

the moho in the northern basin and range province nevada along the cocorp 40 n seismic reflection transect cocorp seismic reflection profiles across nevada at about 40 n image a prominent essentially continuous band of reflectors at a two way traveltime of 9 to 11 s the approximate correspondence of this reflection time with estimates of the two way traveltime to the moho in this area provided by seismic refraction data suggests that the prominent reflections are from the moho the relief on these reflectors the reflection moho beneath nevada across a latitudinal transect of

coseismic slip and early afterslip of the 2015 illapel chile earthquake implications for frictional heterogeneity and coastal uplift great subduction earthquakes are thought to rupture portions of the megathrust where interseismic coupling is high and velocity weakening frictional behavior is dominant releasing elastic deformation accrued over a seismic cycle conversely postseismic afterslip is assumed to occur primarily in regions of velocity strengthening frictional characteristics that may correlate with lower interseismic coupling however it remains unclear if fixed frictional properties of the subduction interface coseismic or aftershock induced stress redistribution or other factors control the spatial distribution of afterslip here we use interferometric synthetic aperture radar and global position system observations to map the distribution of coseismic slip of the 2015 mw 8 3 illapel chile earthquake and afterslip within the first 38 days following the earthquake we find that afterslip overlaps the coseismic slip area and propagates along strike into regions of both high and moderate interseismic coupling the significance of these observations however is tempered by the limited resolution of geodetic inversions for both slip and coupling additional afterslip imaged deeper on the fault surface bounds a discrete region of deep coseismic slip and both contribute to net uplift of the chilean coastal cordillera a simple partitioning of the subduction interface into regions of fixed frictional properties cannot reconcile our geodetic observations instead stress heterogeneities either preexisting or induced by the earthquake likely provide the primary control on the afterslip distribution for this subduction zone earthquake we also explore the occurrence of coseismic and postseismic coastal uplift in this sequence and its implications for recent hypotheses concerning the source of permanent coastal uplift along subduction zones

depths and focal mechanisms of crustal earthquakes in the central andes determined from teleseismic waveform analysis and insar 1 we investigate the depths of crustal earthquakes mw 5 5 earthquakes from the global cmt catalog and previous work spanning 1944 2007 for 38 well recorded events we use teleseismic p and sh waveforms to model the strike dip rake focal depth and source time function we use insar observations of surface deformation from 9 earthquakes to compare inferred fault parameters with the waveform inversions and global catalogs to assess their accuracies while the depths from the insar and waveform analyses generally agree within error horizontal and depth errors in global catalogs are 10 to 50 km as found elsewhere as noted in previous work the majority of crustal earthquakes occur in the eastern cordillera and foreland regions of the central andes although a few normal and strike slip earthquakes occur beneath the altiplano plateau and in the forearc in southern peru and northernmost chile we propose a new interpretation of one of the basement thrusts shira mountain peru as a pop up block on the basis of our new earthquake depths we confirm that earthquakes in the flat slab areas of peru and argentina are within the sometimes aseismic lower crust lower crustal earthquakes are globally found in all types of tectonic settings only when the thermal lithosphere is more than 80 km thick and the amount of recent shortening extension is 30

the crustal structure in central maine from coherency processed refraction data in 1984 the u s geological surcvey and the canadian department of energy mines and resources conducted an extensive seismic refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surface velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surf ace velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from the ne to the sw end of the profile surface rocks at the sw end of the profile have a metamorphic depth of burial of at least 15 km indicating that the crust below the central maine synclinorium may have been thickened to at least 55 km during paleozoic collisions

slant stacks of refraction data from maine effects of lateral variations in velocity structure abstract we discuss some of the advantages and pitfalls associated with p analysis of wide angle profiles recorded over terranes characterized by significant lateral heterogeneity we construct composite slant stacks for a pair of reversed shots recorded along the axis of the merrimack synclinorium in southwest maine and invert picks for bounds on averaged one dimensional slowness depth structure extremal bounds on total crustal thickness derived from shot point 12 are 40 to 43 km average crustal velocities for individual slowness models corresponding to the extremal depths range from 6 5 to 6 6 km sec predicted normal incidence two way travel times for the moho lie between 12 2 and 13 2 sec the utility of one dimensional inversion of p data is largely in estimating the maximum resolving power of the data set this is information that forward modeling approaches do not provide comparisons of slant stacks of reversed shot gathers with intercept times predicted for a two dimensional model derived by ray tracing highlight some of the pitfalls associated with interpretation of p data in terms of one dimensional structure in some cases the principal arrival may become multi valued resulting in misidentification of phases and compounding biases in estimates of average crustal parameters slant stacks can be highly useful however in refining two dimensional models derived from travel times because of the sensitivity of ray parameters to dip and lateral velocity gradients we use slant stacks in conjunction with the original shot gathers to refine our estimate of the configuration of the moho beneath southwest maine our final model shows a step in the moho that is consistent with variations in normal two way travel times inferred from analysis of postcritical fan shots this abrupt change in crustal thickness may mark the northeast extent of significant underthrusting of avalon crust beneath medial new england basement during the acadian orogeny the preservation of offsets in moho that were formed during paleozoic compression is consistent with the limited amount of rifting experienced by this portion of the orogen during the opening of the atlantic

mesozoic ophiolites sutures and arge scale tectonic movements in afghanistan abstract the tectonic history of afghanistan appears to be the result of successive accretion of fragments of gondwana to the active margin of laurasia since the end of the paleozoic the margin in afghanistan lies along the present herat and panjshir faults south of hindu kush swings around the central pamirs and can presumably be traced along the present western altyn tagh and kunlun faults in tibet north of this boundary paleozoic rocks have been deformed in the upper paleozoic whereas south of it there is no trace of the hercynian orogeny the first collision of gondwanian fragments with laurasia probably occurred in the early mesozoic along the hindu kush and kunlun to the south ophiolites along the panjao and pangong nu chiang sutures respectively in central afghanistan and central tibet testify for another suturing event in the upper jurassic or lower cretaceous the indus tsangpo suture between india and tibet corresponds in eastern afghanistan to two ophiolite subbelts near kabul and khost both ophiolite complexes have been emplaced between maestrichtian and lower eocene by choking of two northward dipping subduction zones after complete contact between the indian and asian continents was achieved presumably in the end of eocene the penetration of india into asia caused large scale intra continental shortening a large part of the shortening was accommodated by strike slip faulting along mesozoic and more ancient sutures central afghanistan in particular was extruded to the west along the herat suture by the protrusion of the pamir wedge it subsequently collided with the lut block

localized and distributed creep along the southern san andreas fault we investigate the spatial pattern of surface creep and off fault deformation along the southern segment of the san andreas fault using a combination of multiple interferometric synthetic aperture radar viewing geometries and survey mode gps occupations of a dense array crossing the fault radar observations from envisat during the period 2003 2010 were used to separate the pattern of horizontal and vertical motion providing a high resolution image of uplift and shallow creep along the fault trace the data reveal pervasive shallow creep along the southernmost 50 km of the fault creep is localized on a well defined fault trace only in the mecca hills and durmid hill areas while elsewhere creep appears to be distributed over a 1 2 km wide zone surrounding the fault the degree of strain localization is correlated with variations in the local fault strike using a two dimensional boundary element model we show that stresses resulting from slip on a curved fault can promote or inhibit inelastic failure within the fault zone in a pattern matching the observations the occurrence of shallow localized interseismic fault creep within mature fault zones may thus be partly controlled by the local fault geometry and normal stress with implications for models of fault zone evolution shallow coseismic slip deficit and geologic estimates of long term slip rates

the accommodation of arabia eurasia plate convergence in iran continental convergence between arabia and eurasia is taken up by distributed deformation in iran at wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field the only quantitative source of information on the spatial distribution of strain rates within iran is the record of earthquakes we find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the arabia eurasia plate motion between the defined shapes of iran s rigid borders when in addition we specify central iran azerbaijan and the southern caspian basin to be relatively rigid blocks within the deforming zone then the fit to the style of the observed strain rate distribution is even better we conclude that much of the pattern of deformation in iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it this is likely also to have been a common occurrence in older orogenic belts we confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part 10 20 of the total deformation required by the convergence between the arabia and eurasia plates we then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes there is therefore no requirement that the large proportion of aseismic deformation in iran is substantially different in style orientation or distribution from that released seismically in the earthquakes

deep seismic soundings in india and the origin of continental crust the present day continental crust beneath stable cratons is generally thought to be 30 50 km thick1 2 although there are divergent views as to its initial thickness and the associated thermal and tectonic regimes3 4 likewise the lithosphere is believed to have been thinner in the archaean but its relationship to the crust at that time has not been specified structural details regarding the archaean crust revealed by a deep seismic sounding dss study across the south indian craton5 supplemented by similar data from the ukrainian shield1 show a relationship between crust and mantle which apparently places important constraints on the thermo tectonic conditions prevailing at the time of formation of the crust we interpret these details as indicating that at one time the crust constituted the lithosphere the moho marking its base

large earthquakes and creeping faults faults are ubiquitous throughout the earth s crust the majority are silent for decades to centuries until they suddenly rupture and produce earthquakes with a focus on shallow continental active tectonic regions this paper reviews a subset of faults that have a different behavior these unusual faults slowly creep for long periods of time and produce many small earthquakes the presence of fault creep and the related microseismicity helps illuminate faults that might not otherwise be located in fine detail but there is also the question of how creeping faults contribute to seismic hazard it appears that well recorded creeping fault earthquakes of up to magnitude 6 6 that have occurred in shallow continental regions produce similar fault surface rupture areas and similar peak ground shaking as their locked fault counterparts of the same earthquake magnitude the behavior of much larger earthquakes on shallow creeping continental faults is less well known because there is a dearth of comprehensive observations computational simulations provide an opportunity to fill the gaps in our understanding particularly of the dynamic processes that occur during large earthquake rupture and arrest

the 2013 mw 7 7 balochistan earthquake energetic strike slip reactivation of a thrust fault we analyse the mw 7 7 balochistan earthquake of 09 24 2013 based on ground surface deformation measured from sub pixel correlation of landsat 8 images combined with back projection and finite source modeling of teleseismic waveforms the earthquake nucleated south of the chaman strike slip fault and propagated southwestward along the hoshab fault at the front of the kech band the rupture was mostly unilateral propagated at 3 km s on average and produced a 200 km surface fault trace with purely strike slip displacement peaking to 10 m and averaging around 6 m the finite source model shows that slip was maximum near the surface although the hoshab fault is dipping by 45 to the north in accordance with its origin as a thrust fault within the makran accretionary prism slip was nearly purely strike slip during that earthquake large seismic slip on such a non optimally oriented fault was enhanced possibly due to the influence of the free surface on dynamic stresses or to particular properties of the fault zone allowing for strong dynamic weakening strike slip faulting on thrust fault within the eastern makran is interpreted as due to eastward extrusion of the accretionary prism as it bulges out over the indian plate portions of the makran megathrust some thrust faults in the kirthar range and strike slip faults within the chaman fault system have been brought closer to failure by this earthquake aftershocks cluster within the chaman fault system north of the epicenter opposite to the direction of rupture propagation by contrast few aftershocks were detected in the area of maximum moment release in this example aftershocks cannot be used to infer earthquake characteristics

active accommodation of plate convergence in southern iran earthquake locations triggered aseismic slip and regional strain rates 1 we present a catalog of interferometric synthetic aperture radar insar constraints on deformation that occurred during earthquake sequences in southern iran between 1992 and 2011 and explore the implications on the accommodation of large scale continental convergence between saudi arabia and eurasia within the zagros mountains the zagros mountains a salt laden fold and thrust belt involving 10 km of sedimentary rocks overlying precambrian basement rocks have formed as a result of ongoing continental collision since 10 20 ma that is currently occurring at a rate of 3 cm yr we first demonstrate that there is a biased misfit in earthquake locations in global catalogs that likely results from neglect of 3 d velocity structure previous work involving two m 6 earthquakes with well recorded aftershocks has shown that the deformation observed with insar may represent triggered slip on faults much shallower than the primary earthquake which likely occurred within the basement rocks 10 km depth we explore the hypothesis that most of the deformation observed with insar spanning earthquake sequences is also due to shallow triggered slip above a deeper earthquake effectively doubling the moment release for each event we quantify the effects that this extra moment release would have on the discrepancy between seismically and geodetically constrained moment rates in the region finding that even with the extra triggered fault slip significant aseismic deformation during the interseismic period is necessary to fully explain the convergence between eurasia and saudi arabia