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

spatial and temporal constancy of seismic strain release along an evolving segment of the pacific north america plate boundary abstract three new slip rates from the death valley fish lake valley dvflv fault contribute to an exceptionally detailed record of lateral rate variations on this 300 km long system from south to north these three new sites are south mud canyon cucomongo canyon and indian creek slip rates were determined by combining offsets measured with 1 m resolution airborne lidar data with 10be cosmogenic nuclide surface exposure and optically stimulated luminescence ages from displaced alluvial fans the offset fans date to 17 4 2 3 ka at south mud canyon 39 3 ka at cucomongo canyon and 6 3 1 8 ka at indian creek yielding slip rates of 2 1 0 5 0 4 mm yr 6 1 1 3 1 0 mm yr and 2 2 0 8 0 6 mm yr respectively at indian creek the holocene 6 ka and late quaternary 70 ka slip rates are the same within uncertainty suggesting temporal constancy of seismic strain release along the northern dvflv fault zone over these time spans when combined with slip rates determined in earlier companion studies these results show that the late quaternary slip rate decreases northward and southward from the central part of the fault as slip is transferred onto north trending zones of distributed normal faulting towards the northeast and southwest of the central zone of rapid deformation this complex pattern of strain accommodation may reflect structural evolution towards a straighter structurally simpler zone of dextral shear that locally utilizes well established dextral faults that are linked where necessary by nascent zones of deformation summation of the rates of all major faults in the eastern california shear zone ecsz at the 37 n latitude of red wall canyon in northern death valley shows that the cumulative geologic rate of 8 5 10 mm yr is indistinguishable from the 9 mm yr geodetic rate although the cumulative rate on the major faults of the ecsz is slower to the north and south this probably reflects more distributed deformation in these areas rather than transient strain accumulation these results demonstrate the importance of obtaining multiple slip rates to effectively document the behavior of any fault system especially in studies of seismic hazard assessment and comparisons of geologic and geodetic rate data

spatial and temporal deformation along the northern san jacinto fault southern california implications for slip rates the san timoteo badlands is an area of uplift and erosional dissection that has formed as a result of late quaternary uplift along a restraining bend in the san jacinto fault of the san andreas fault system in southern california this bend currently is located in a region where late quaternary deposits and associated surfaces have formed in lower san timoteo canyon we have used morphometric analysis of these surfaces in conjunction with computer modeling of deformational patterns along the san jacinto fault to reconstruct spatial and temporal variations in uplift along the bend morphometric techniques used include envelope subenvelope map ping a gradient length index along channels and denudation values age control is determined using a combination of thermoluminescence tl and near infrared op tical simulation luminescence dating irosl and correlation of soil development indices these approaches are combined with an elastic half space model used to determine the deformation associated with the fault bend the region of modeled uplift has a similar distribution as that determined by morphometric techniques luminescence dates and soil correlation age estimates generally agree based on soil development surfaces within the study area were stabilized at approximately 300 700 ka for q3 43 67 ka for q2 and 27 5 67 ka for q1 luminescence ages both tl and irosl for the formation of the younger two surfaces are 58 to 94 ka for q2 and 37 to 62 ka for q1 ages reported to 1r uncertainty periods of uplift were determined for the surfaces in the study area resulting in approximate uplift rates of 0 34 to 0 84 m ka for the past 100 ka and 0 13 to 1 00 m ka for the past 66 ka comparison of these rates of uplift to those generated by the model support a higher rate of lateral slip along the san jacinto fault than commonly assumed greater than 20 mm yr as compared to 8 12 mm yr commonly cited this higher slip rate supports the proposal that a greater amount of slip has transferred from the san andreas fault to the san jacinto fault than generally held the san jacinto fault may have accommodated a significant portion of the plate boundary slip during the past 100 ka

present day strain accumulation and slip rates associated with southern san andreas and eastern california shear zone faults 1 we present the first results from a dense network of 36 campaign and 46 continuous gps stations located in the eastern transverse ranges province etr a transition zone between the southernmost san andreas fault ssaf and eastern california shear zone ecsz we analyzed the campaign data together with available data from continuous gps stations for the period 1994 2009 we used the gps velocity estimates to constrain elastic block models to investigate fault loading rates representing four hypotheses characterized by different fault block geometries fault block scenarios include blocks bounded by the east striking left lateral pinto mountain blue cut and chiriaco faults of the etr blocks bounded by a right lateral north northwest striking structure the landers mojave earthquake line that cuts obliquely across the etr and mapped mojave desert faults and combinations of these end member hypotheses each model implies significantly different active fault geometries block rotation rates and slip rates for etr and ecsz structures all models suggest that ssaf slip rate varies appreciably along strike generally consistent with rates derived from tectonic geomorphology and paleoseismology with a maximum of 23 mm yr right lateral along the southernmost coachella valley strand decreasing systematically to 10 mm yr right lateral through the san gorgonio pass region slip rate estimates for the san jacinto fault are 12 mm yr for all models tested all four models fit the data equally well in a statistical sense qualitative comparison among models and consideration of geologic slip rates and other independent data reveals strengths and weaknesses of each model

interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

interseismic strain localization in the san jacinto fault zone we investigate interseismic deformation across the san jacinto fault at anza california where previous geodetic observations have indicated an anomalously high shear strain rate we present an updated set of secular velocities from gps and insar observations that reveal a 2 3 km wide shear zone deforming at a rate that exceeds the background strain rate by more than a factor of two gps occupations of an alignment array installed in 1990 across the fault trace at anza allow us to rule out shallow creep as a possible contributor to the observed strain rate using a dislocation model in a heterogeneous elastic half space we show that a reduction in shear modulus within the fault zone by a factor of 1 2 1 6 as imaged tomographically by allam and ben zion geophys j int 190 1181 1196 2012 can explain about 50 of the observed anomalous strain rate however the best fitting locking depth in this case 10 4 1 3 km is significantly less than the local depth extent of seismicity 14 18 km we show that a deep fault zone with a shear modulus reduction of at least a factor of 2 4 would be required to explain fully the geodetic strain rate assuming the locking depth is 15 km two alternative possibilities include fault creep at a substantial fraction of the long term slip rate within the region of deep microseismicity or a reduced yield strength within the upper fault zone leading to distributed plastic failure during the interseismic period

slip rates and off fault deformation in southern california inferred from gps data and models 1 in southern california fault slip rate estimates along the san andreas fault saf and garlock fault from geodetically constrained kinematic models are systematically at the low end or lower than geologic slip rate estimates the sum of geodetic model slip rates across the eastern california shear zone is higher than the geologic sum however the ranges of reported model and geologic slip rate estimates in the literature are sufficiently large that it remains unclear whether these apparent discrepancies are real or attributable to epistemic uncertainties in the two types of estimates we further examine uncertainties in geodetically derived slip rate estimates on major faults in southern california by conducting a suite of inversions with four kinematic models long term rigid elastic block models constrained by the geologic slip rates cannot fit the present day gps derived velocity field deforming permanent off fault strain elastic block models and viscoelastic earthquake cycle block models constrained by geologic slip rates can fit the present day gps derived velocity field with 28 33 of the total geodetic moment rate occurring as distributed deformation off of the major faults models incorporating viscoelastic mantle flow predict systematically higher slip rates than purely elastic models on many of the major southern california faults with ranges of elastic viscoelastic 29 34 30 37 mm yr for the carrizo saf segment 20 24 20 32 mm yr for the mojave saf segment 14 17 18 22 mm yr for the coachella saf segment 13 19 14 22 mm yr for the san jacinto fault and 5 11 5 11 mm yr for the western garlock fault

block kinematics of the pacific north america plate boundary in the southwestern united states from inversion of gps seismological and geologic data 1 the active deformation of the southwestern united states 30 41 n is represented by a finite number of rotating elastic plastic spherical caps gps derived horizontal velocities geologic fault slip rates transform fault azimuths and earthquake derived fault slip vector azimuths are inverted for block angular velocities creep on block bounding faults permanent strain rates within the blocks and the rotations of 11 published gps velocity fields into to a common north american reference frame gps velocities are considered to be a combination of rigid block rotations recoverable elastic strain rates resulting from friction on block bounding faults and nonrecoverable strain rates resulting from slip on faults within the blocks the resulting pacific north america angular velocity is similar to some published estimates and satisfies transform azimuths and one spreading rate in the gulf of california earthquake slip vectors in the gulf of california and alaska and gps velocities along coastal california and within the pacific basin published fault slip rates are satisfied except in the southern mojave desert where the motion of the mohave block relative to north america is faster than can be explained by mapped faults the largest blocks the sierra nevada great valley and the eastern basin and range show permanent strain rates after removing elastic strain of only a few nanostrain per year demonstrating approximately rigid behavior observed horizontal strain rates correlate strongly with predicted strain rates from known faults suggesting that the short term strains evident in gps velocities are largely elastic in only about 20 of the region is distributed deformation needed to match the data indicating that a plate tectonic style description of the deformation of the western united states is plausible most blocks rotate about vertical axes at approximately the same rate as the pacific relative to north america suggesting that locally spin rates are communicated from block to block arguing against both floating block and ball bearing mechanisms of block rotation the similarities of the blocks spin rates to that of the pacific suggests that the pacific strongly influences their motions through edge tractions however it is shown that the blocks cannot rotate about the pacific north america pole without spinning counter to the sense of pacific north america shear unlike some other broad plate boundaries in the western united states vertical axis rotations take up very little of the slip rate budget across the region

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

stress modulation on the san andreas fault by interseismic fault system interactions during the interseismic phase of the earthquake cycle between large earthquakes stress on faults evolves in response to elastic strain accumulation driven by tectonic plate motions because earthquake cycle processes induce non local stress changes the interseismic stress accumulation rate on one fault is influenced by the behavior of all nearby faults using a geodetically constrained block model we show that the total interseismic elastic strain field generated by fault interactions within southern california may increase stressing rates on the mojave and san bernardino sections of the san andreas fault within the big bend region by as much as 38 relative to estimates from isolated san andreas models assuming steady fault system behavior since the c e 1857 fort tejon earthquake shear stress accumulated on these sections due only to interaction with faults other than the san andreas reaches 1 mpa 3 times larger than the coseismic and postseismic stress changes induced by recent southern california earthquakes stress increases along big bend sections coincide with the greatest earthquake frequency inferred from a 1500 yr long paleoseismic record and may affect earthquake recurrence intervals within geometrically complex fault systems including the sections of the san andreas fault closest to metropolitan los angeles

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

variable rates of late quaternary strike slip on the san jacinto fault zone southern california three strike slip displacements of strata with known approximate ages have been measured at two locations on the san jacinto fault zone minimum horizontal offset between 5 7 and 8 6 km in no more than 0 73 m y northeast of anza indicates 8 12 mm yr average slip rate since late pleistocene time two measures of more recent displacement are based on trenching studies of stratigraphic offsets on the coyote creek fault in western imperial valley horizontal slip of 1 7 m has been calculated for the youngest sediment of lake cahuilla since its deposition 275 510 yr b p the corresponding slip rate is 2 8 5 0 mm yr right lateral offset of 10 9 m measured on a buried stream channel older than 5060 yr b p but younger than 6820 yr b p yields average slip rates for the intermediate time periods 400 to 6000 yr b p of 1 2 mm yr the average rates of slip for these three time intervals suggest a relatively quiescent period for the san jacinto fault zone from about 4000 b c to about 1600 a d to the extent that long term variations in seismic activity of major strike slip faults elsewhere are known fluctuations in slip rate for the san jacinto fault would not appear to be abnormal if the san jacinto and adjacent segments of the san andreas fault alternately assume dominant roles in absorbing motion between the pacific and american plates perhaps even more recently than 400 yr ago the san andreas fault south of the transverse ranges expressed most of the motion but has since become relatively inactive

denali fault slip rates and holocene late pleistocene kinematics of central alaska the denali fault is the principal intracontinental strike slip fault accommodating deformation of interior alaska associated with the yakutat plate convergence we obtained the first quantitative late pleistocene holocene slip rates on the denali fault system from dating offset geomorphic features analysis of cosmogenic 10be concentrations in boulders n 27 and sediment n 13 collected at seven sites offset 25 170 m by the denali and totschunda faults gives average ages that range from 2 4 0 3 ka to 17 0 1 8 ka these offsets and ages yield late pleistocene holocene average slip rates of 9 4 1 6 12 1 1 7 and 8 4 2 2 mm yr 1 along the western central and eastern denali fault respectively and 6 0 1 2 mm yr 1 along the totschunda fault our results suggest a westward decrease in the mean pleistocene holocene slip rate this westward decrease likely results from partitioning of slip from the denali fault system to thrust faults to the north and west

bedding plane slip in initial stages of fault related folding abstract frictional slip along bedding planes contributes to fault related folding of layered rocks we use numerical experiments to investigate the deformation of frictional bedding planes near dipping faults under layerparallel contraction and extension within the numerical experiments contraction boundary conditions produce asymmetric anticlines and extension produces asymmetric synclines the fold shape may be used to infer dip of the underlying fault in situations where the fault may not be observable additionally sense of slip along bedding planes may indicate proximity to the fault tip under uniform remote tectonic strain fault slip induces deformation in both the hangingwall and the footwall at depths as shallow as 1 km there is no significant difference between fold amplitudes in the hangingwall and the footwall this result is contrary to many kinematic models currently in use kinematic models of fault related folds commonly include the development of flat ramp and flat ramp flat fault geometries which may be attributed to initial ramp thrusting and later flat development our mechanical models show that fault flats may be produced from fault ramps due to slip along frictional bedding planes near the thrust fault tips our numerical experiments also evaluate joint initiation joints perpendicular to bedding are promoted in extensional environments we compare the results of the mechanical model to kinematic models of fault propagation folds and conclude that mechanical models offer important insights to better understand the folding process

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 the southern san andreas fault system to tectonic boundary conditions and fault configurations the southern big bend of the san andreas fault saf accommodates transpression along numerous non vertical non planar and intersecting active surfaces using three dimensional boundary element method bem models we test the sensitivity of fault slip rates to a range of tectonic boundary conditions constrained by global positioning system gps studies of the region 45 50 mm yr and 320 325 using this approach our models provide a range of distributed fault slip rates associated with both spatial variations in geometry and present day uncertainties in plate motion model slip rates match most of the available geologic slip rates and discrepancies may owe to inaccurate fault geometries more northerly plate velocity 325 produces greater transpression along the saf system associated with greater uplift of the san bernardino mountains greater reverse slip rates along range bounding reverse thrust faults lower strike slip rates along the san andreas and san jacinto faults and greater strike slip rates along the eastern california shear zone ecsz and garlock fault these results suggest that the degree of regional transpression controls the partitioning of deformation between uplift and slip along both the saf system and the ecsz the insensitivity of modeled slip rates to applied velocity along the southern san andreas and san jacinto faults suggests that fault geometry greatly influences slip rates within the san bernardino mountains region a northerly shift in plate velocity orientation could account for the abandonment of the mill creek strand of the saf 95 ka and development of the present day active geometry which accommodates greater uplift

late quaternary rate of slip along the san jacinto fault zone near anza southern california the anza section of the san jacinto fault southern california has not experienced a groundbreaking earthquake since at least 1918 and probably since before 1899 leading previous workers to designate this 20 km long fault segment as a seismic gap study of displaced pleistocene and holocene alluvial fan and fluvial deposits across the san jacinto fault near anza california dated using 14c and soil development age control indicates a minimum right lateral slip rate of 9 2 2 mm yr since 9 5 ka and a slip rate of 11 9 5 mm yr since 14 ka 12 9 5 mm yr since 17 ka and 13 10 6 mm yr since 50 ka these estimates agree with a previously determined 700 ka to present minimum slip rate of 10 2 mm yr based on an estimated average slip rate of 12 mm yr from the longer term slip rate estimates about 0 8 m of potential slip has accumulated if the 1918 earthquake broke the anza segment over 1 1 m of potential slip has accumulated if the last earthquake occurred prior to 1899 these data attest to the potential for an earthquake m6 5 for this section of the fault

a spatial random field model to characterize complexity in earthquake slip 1 finite fault source inversions reveal the spatial complexity of earthquake slip over the fault plane we develop a stochastic characterization of earthquake slip complexity based on published finite source rupture models in which we model the distribution of slip as a spatial random field the model most consistent with the data follows a von karman autocorrelation function acf for which the correlation lengths a increase with source dimension for earthquakes with large fault aspect ratios we observe substantial differences of the correlation length in the along strike a x and downdip a z directions increasing correlation length with increasing magnitude can be understood using concepts of dynamic rupture propagation the power spectrum of the slip distribution can also be well described with a power law decay i e a fractal distribution in which the fractal dimension d remains scale invariant with a median value d 2 29 0 23 while the comer wave number k c which is inversely proportional to source size decreases with earthquake magnitude accounting for larger slip patches for large magnitude events our stochastic slip model can be used to generate realizations of scenario earthquakes for near source ground motion simulations

geodetic slip rates in the southern san andreas fault system effects of elastic heterogeneity and fault geometry 1 we use high resolution interferometric synthetic aperture radar and gps measurements of crustal motion across the southern san andreas fault system to investigate the effects of elastic heterogeneity and fault geometry on inferred slip rates and locking depths geodetically measured strain rates are asymmetric with respect to the mapped traces of both the southern san andreas and san jacinto faults two possibilities have been proposed to explain this observation large contrasts in crustal rigidity across the faults or an alternate fault geometry such as a dipping san andreas fault or a blind segment of the san jacinto fault we evaluate these possibilities using a two dimensional elastic model accounting for heterogeneous structure computed from the southern california earthquake center crustal velocity model cvm h 6 3 the results demonstrate that moderate variations in elastic properties of the crust do not produce a significant strain rate asymmetry and have only a minor effect on the inferred slip rates however we find that small changes in the location of faults at depth can strongly impact the results our preferred model includes a san andreas fault dipping northeast at 60 and two active branches of the san jacinto fault zone in this case we infer nearly equal slip rates of 18 1 and 19 2mm yr for the san andreas and san jacinto fault zones respectively these values are in good agreement with geologic measurements representing average slip rates over the last 10 10 years implying steady long term motion on these faults

stable rapid rate of slip since inception of the san jacinto fault california 1 in california where the san jacinto fault sjf and san andreas fault saf accommodate the majority of the dextral shear deformation between the pacific and north american plates initiation of the sjf led to an apparent decline in the slip rate of the saf previous studies suggest that since then slip rate has covaried between these faults possibly due to changes in fault strength variation in topographic loading along a fault or the development of new faults and that presently the sjf is the dominant plate boundary structure however we dated displaced sedimentary deposits and landforms over three distinct time intervals since 700 ka and our results imply a constant slip rate of 12 1 3 4 2 6 mm yr this rate is similar to the fault s lifetime rate and from rates derived from geodesy suggesting that since the sjf initiated its slip rate has remained relatively stable and does not exceed that of the saf

on and off fault deformation associated with the september 2013 mw 7 7 balochistan earthquake implications for geologic slip rate measurements abstract the 24 september 2013 mw7 7 balochistan pakistan earthquake ruptured a 200 km long stretch of the hoshab fault in southern pakistan and produced the second largest lateral surface displacement observed for a continental strike slip earthquake we remotely measured surface deformation associated with this event using high resolution 0 5 m pre and post event satellite optical imagery we document left lateral near field on fault offsets 10 m from fault using 309 laterally offset piercing points such as streams terrace risers and roads peak near field displacement is 13 6 2 5 3 4 m we characterize off fault deformation by measuring medium 350 m from fault displacement using manual 259 measurements and automated image cross correlation methods respectively off fault peak lateral displacement values are 15 m and exceed on fault displacement magnitudes for 85 of the rupture length our observations suggest that for this rupture coseismic surface displacement typically increases with distance away from the surface trace of the fault however nearly 100 of total surface displacement occurs within a few hundred meters of the primary fault trace furthermore off fault displacement accounts for on average 28 of the total displacement but exhibits a highly heterogeneous along strike pattern the best agreement between near field and far field displacements generally corresponds to the narrowest fault zone widths our analysis demonstrates significant and heterogeneous mismatches between on and off fault coseismic deformation and we conclude that this phenomenon should be considered in hazard models based on geologically determined on fault slip rates

high grade metamorphic processes which influence archaean gold deposits with particular reference to big bell australia mineralogical and geochemical evidence indicates that partial melting and desulphidation have occurred in the big bell gold deposit decarbonation may also have occurred to account for the lack of a carbonate alteration halo this is compatible with the present data but difficult to test the big bell deposit consists of auriferous sulphide bearing lode schists with muscovite and k feldspar and surrounding biotite schists all derived by intense premetamorphic alteration of rocks of mafic composition assemblages which include cordierite sillimanite k feldspar garnet biotite quartz suggest peak metamorphic conditions of 4 5 kbar and 650 700 c based on phase relations geobaro meters and garnet biotite fe mg exchange partitioning partial melting occurred at peak metamorphism particularly in the altered mafic rocks in and around the deposit and its occurrence may have been essential to the preservation of the deposit melting greatly limited the importance of devolatilization reactions resulting in negligible aqueous fluids and no means of removing appreciable gold minor gold loss may have accompanied desulphidation a diversity of complex metamorphic assemblages occurs around the mine compared to the assemblages developed regionally variable bulk rock composition influences this contrast but there is no evidence of higher metamorphic grades at the mine nor that this might have been the prime control on the different assemblages in this narrow belt it is suggested that the big bell and hemlo deposits are the higher metamorphic grade equivalents of the more abundant greenschist facies gold deposits within archaean greenstone belts this interpretation is favoured by the host rock setting and geochemical characteristics of big bell alternative models that suggest that this class of deposit is a new type must account for the absence of high grade equivalents of the greenschist facies deposits and also the lack of low grade equivalents of the big bell hemlo type archaean gold deposits in high grade metamorphic terrains have undergone a series of processes that are not recorded in the more typical gold deposits of the greenschist facies

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

geologic evolution of the late archean abitibi greenstone belt of canada the southern volcanic zone svz of the late archean abitibi belt of the superior province of canada is dominated by komatiitic to tholeiitic volcanic plateaus and large bimodal mafic felsic volcanic centers these volcanic rocks were erupted between about 2717 and 2700 ma in a series of rift basins that formed as a result of wrench fault tectonics they overlie and juxtapose a volcano plutonic assemblage characterized in the northern abitibi belt the age of the assemblage is about 2720 ma or older and it comprises basaltic to andesitic and dacitic subaqueous massive volcanics cored by comagmatic sills and layered anorthositic complexes and overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 2 ma a tectonic model is proposed in which the svz formed in a series of rift basins that dissected an earlier formed volcanic arc comparisons are made with rift environments that have been postulated for phanerozoic areas such as the hokuroko basin of japan the taupo volcanic zone of new zealand and the sumatra and nicaragua arcs

interseismic deformation associated with three dimensional faults in the greater los angeles region california 1 existing interseismic models are not well suited to simulate deformation within the network of finite intersecting nonplanar faults observed in the greater los angeles region instead of applying fault slip rates to a model a priori we allow three dimensional fault surfaces to interact and accumulate mechanically viable slip distributions and then use the deep nonseismogenic portion of slip to calculate interseismic deformation we apply this approach to the los angeles region and find that the geologic timescale model results match well geologic slip rate data and the interseismic timescale model results match well the heterogeneous gps velocity pattern in the los angeles region model results suggest that localized geodetic convergence in the san gabriel basin can be achieved with slip on multiple active fault surfaces in the los angeles region including relatively fast slip on the sierra madre fault and slow slip on the puente hills thrusts in agreement with geologic data the ability of the three dimensional model to reproduce well both geologic slip rates and interseismic geodetic velocity patterns suggests that current day contraction rates in the greater los angeles region are compatible with long term geologic deformation rates and disputes suggestions of significant temporal variations in fault slip rates inferred from existing investigations

archean terrane docking upper crust collision tectonics abitibi greenstone belt quebec canada abstract the northern nvz and southern volcanic zones svz of the abitibi greenstone belt are separated by the major e trending destor porcupine manneville fault zone dpmfz the dpmfz is interpreted to be the locus of archean terrane docking between the older diffuse volcanic arc of the nvz 2730 2710 ma and the younger arc segments of the svz 2705 2698 ma two distinct evolutionary phases can be documented along the dpmfz of the abitibi greenstone belt and include 1 arc arc collision occurring between 2697 and 2690 ma and 2 arc fragmentation between 2689 and 2680 ma identification of these two events along the dpmfz is based on detailed structural studies sedimentary basin analysis and precise u pb age determinations the thrusting event representative of the arc arc collision phase is characterized by shallow north dipping foliations 20 40 and dip parallel stretching lineations in the eastern manneville segment of the dpmfz local overturned mafic pillowed units suggest recumbent folding late strike slip or transcurrent movement displayed in the late orogenic sedimentary duparquet basin records the arc fragmentation phase basin geometry e trending en echelon folds shallow e plunging stretching lineations and a late ne striking cleavage cross cutting the folds support a dextral shear sense along the western destor porcupine segment of the dpmfz the sedimentary facies observed in the basin are consistent with those of modern strike slip basins located along the east anatolian fault turkey hazar lake and the hope fault new zealand hanmer basin precise u pb zircon age determinations from porphyry stocks located at the northern and southern limits of the duparquet basin yielded 2681 1 ma and 2689 3 2 2 9 ma respectively these ages constrain the rapid change from thrusting to transcurrent movement it is apparent that once thrusting ceased the response to oblique subduction continued in the form of strike slip displacement modern fold and thrust belts commonly show this evolution the deformation pattern is the result of oblique convergence the abitibi greenstone belt is considered to be an archean analogue of modern subducting oceanic plates such as those found in the western pacific

southern san andreas san jacinto fault system slip rates estimated from earthquake cycle models constrained by gps and interferometric synthetic aperture radar observations we use ground geodetic and interferometric synthetic aperture radar satellite observations across the southern san andreas saf san jacinto sjf fault systems to constrain their slip rates and the viscosity structure of the lower crust and upper mantle on the basis of periodic earthquake cycle maxwell viscoelastic finite element models key questions for this system are the saf and sjf slip rates the slip partitioning between the two main branches of the sjf and the dip of the saf the best fitting models generally have a high viscosity lower crust 10 21 pa s overlying a lower viscosity upper mantle 10 19 pa s we find considerable trade offs between the relative time into the current earthquake cycle of the san jacinto fault and the upper mantle viscosity with reasonable assumptions for the relative time in the earthquake cycle the partition of slip is fairly robust at around 24 26 mm a for the san jacinto fault system and 16 18 mm a for the san andreas fault models for two subprofiles across the saf sjf systems suggest that slip may transfer from the western coyote creek branch to the eastern clark superstition hills branch of the sjf from nw to se across the entire system our best fitting model gives slip rates of 2 3 12 9 12 9 and 17 3 mm a for the elsinore coyote creek clark and san andreas faults respectively where the large uncertainties in the slip rates for the sjf branches reflect the large uncertainty in the slip rate partitioning within the sjf system

indicators of relative completeness of the glacial record of the port askaig formation garvellach islands scotland abstract the port askaig formation paf is a diamictite bearing succession in the dalradian supergroup of scotland that provides an excellent archive of a cryogenian glaciation in the garvellach islands and islay argyll the formation is 1100 m thick comprises 5 members and includes 47 diamictite beds interbedded with siltstones dolostones and sandstones here we document seven features of the paf that indicate its relative stratigraphic completeness there are gradual progressive changes up section in the lithologies of the diamictites their interbeds and clast lithologies the sharp basal surfaces of the diamictites each show the same repeated pattern of environmental change from non glacial to glacial many of the top surfaces of the diamictites show evidence of periglacial conditions the succession in the paf records a total of 76 climatically related stratigraphic episodes 28 glacial episodes 25 periglacial episodes and 23 non glacial episodes parts of member 1 diamictites 1 12 and diamictites 16 18 and member 2 diamictite 31 to the base of member 3 are most compete on the east coast of garbh eileach the paf in the garvellach islands occurs within a succession that is several kilometres thick as newly revealed by sea floor mapping compared with other cryogenian and phanerozoic glacial successions the paf is exceptional in its combination of formation thickness the number of climatically related stratigraphic episodes and the considerable thickness of its host supergroup furthermore these indicators of relative stratigraphic completeness provide evidence that the base of the paf on the east coast of garbh eileach is a succession without a major break in deposition supporting the account of the strata at and below the base of the paf in the companion article by fairchild et al 2018

estimating surface rupture length and magnitude of paleoearthquakes from point measurements of rupture displacement we present a method to estimate paleomagnitude and rupture extent from measurements of displacement at a single point on a fault the variability of historic ruptures is summarized in a histogram of normalized slip then scaled to give the probability of finding a given displacement within a rupture for any magnitude considered the histogram can be inverted assuming any magnitude earthquake is as likely as another yielding probability density functions of magnitude and rupture length for any given displacement measurement to improve these distributions we include a term to account for the probability that the earthquake would cause ground rupture and two alternative distributions of earthquake magnitude the gutenberg richter magnitude distribution predicts shorter rupture lengths and smaller magnitudes than does a uniform distribution where any magnitude earthquake is considered equally likely longer ruptures and larger magnitudes than the uniform model are predicted by an alternative magnitude distribution designed to return site average displacement this model is a generalization of the characteristic earthquake model and reasonably describes paleoseismic findings on the southern san andreas fault where slip is accommodated by average displacements of a few meters and earthquake recurrence times of 100 250 years our results should increase the value of paleoseismic displacement measurements for hazard assessment in particular they quantify probability estimates of earthquake magnitude and rupture length where point observations of rupture displacement are available and so can contribute to probabilistic seismic hazard analyses online material rupture profiles used to sample rupture variability

influence of fault connectivity on slip rates in southern california potential impact on discrepancies between geodetic derived and geologic slip rates along the san bernardino strand of the san andreas fault saf and across the eastern california shear zone ecsz geologic slip rates differ from those inverted from geodetic measurements which may partly be due to inaccurate fault connectivity within geodetic models we employ three dimensional models that are mechanically compatible with long term plate motion to simulate both fault slip rates and interseismic surface deformation we compare results from fault networks that follow mapped geologic traces and resemble those used in block model inversions which connect the san jacinto fault to the saf near cajon pass and connect distinct faults within the ecsz the connection of the saf with the san jacinto fault decreases strike slip rates along the saf by up to 10 and increases strike slip rates along the san jacinto fault by up to 16 however slip rate changes are still within the large geologic ranges along the saf the insensitivity of interseismic surface velocities near cajon pass to fault connection suggests that inverse models may utilize both an incorrect fault geometry and slip rate and still provide an excellent fit to interseismic geodetic data similarly connection of faults within the ecsz produces 36 greater cumulative strike slip rates but less than 17 increase in interseismic velocity when using overconnected models to invert gps for slip rates the reduced off fault deformation within the models can lead to overprediction of slip rates while the nature of fault intersections at depth remains enigmatic fault geometries should be chosen with caution in crustal deformation models

mechanical models favor a ramp geometry for the ventura pitas point fault california recent investigations have provided new and significantly revised constraints on the subsurface structure of the ventura pitas point fault system in southern california however few data directly constrain fault surfaces below 6 km depth here we use geometrically complex three dimensional mechanical models driven by current geodetic strain rates to test two proposed subsurface models of the fault system we find that the model that incorporates a ramp geometry for the ventura pitas point fault better reproduces both the regional long term geologic slip rate data and interseismic gps observations of uplift in the santa ynez mountains the model calculated average reverse slip rate for the ventura pitas point fault is 3 5 0 3 mm yr although slip rates are spatially variable on the fault surface with 8 mm yr predicted on portions of the lower ramp section at depth

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

how much can off fault deformation contribute to the slip rate discrepancy within the eastern california shear zone kinematic assumptions of geodetic inversions for fault slip require that the slip sums to the plate boundary velocity this assumption neglects permanent off fault deformation which could account for discrepancies between geologic and geodetic estimates we use three dimensional mechanical models to assess if unaccounted permanent strain surrounding faults could contribute to slip rate discrepancies across disconnected faults within the mojave desert california usa portion of the eastern california shear zone ecsz we modified fault configurations derived from the southern california earthquake center community fault model to better represent the disconnected nature of active faults in the ecsz south of the garlock fault the models with revised fault geometry produce slip rates that better match geologic strike slip rates thus validating the revisions within these models off fault deformation accounts for 40 23 of the total strain across the ecsz this suggests that a significant portion of the discrepancy between the geologic and geodetically modeled slip rates in the ecsz could be due to the geodetic inversion model assumption of zero permanent off fault deformation

evolving efficiency of restraining bends within wet kaolin analog experiments restraining bends along strike slip fault systems evolve by both propagation of new faults and abandonment of fault segments scaled analog modeling using wet kaolin allows for qualitative and quantitative observations of this evolution to explore how bend geometry affects evolution we model bends with a variety of initial angles from 0 for a straight fault to 30 high angle restraining bends 20 overcome initial inefficiencies by abandoning unfavorably oriented restraining segments and propagating multiple new inwardly dipping oblique slip faults that are well oriented to accommodate convergence within the bend restraining bends with 0 15 maintain activity along the restraining bend segment and grow a single new oblique slip fault on one side of the bend in all restraining bends the first new fault propagates at 5 mm of accumulated convergence particle image velocimetry analysis provides a complete velocity field throughout the experiments from these data we quantify the strike slip efficiency of the system as the percentage of applied plate parallel velocity accommodated as slip in the direction of plate motion along faults within the restraining bend bends with small initially have higher strike slip efficiency compared to bends with large although they have different fault geometries all systems with a 5 cm bend width reach a steady strike slip efficiency of 80 after 50 mm of applied plate displacement these experimental restraining bends resemble crustal faults in their asymmetric fault growth asymmetric topographic gradient and strike slip efficiency

geodynamic evolution of the southern abitibi and pontiac terranes evidence from geochemistry of granitoid magma series 2700 2630 ma four distinct granitic series developed during the evolution of the archean abitibi southern volcanic zone svz 1 a minor synvolcanic tonalite trondhjemite granodiorite ttg series was emplaced at 2700 ma which has extremely low k2o 1 5 wt rb 50 ppm and sr 200 ppm higher nb y and sc flat rare earth element ree patterns and negative eu anomalies 2 a voluminous tonalite granodiorite granite quartz monzonite tggm series developed syntectonically at 2695 2685 ma and displays low k2o 1 3 wt rb 10 50 ppm ba 1000 ppm and u enhanced sr depletion of ta nb and ti and strongly fractionated ree patterns la ybn 49 21 3 a late tectonic quartz syenite quartz monzonite granite smg series was emplaced from 2685 to 2675 ma and is grossly similar to the tggm but has lower cao k2o na2o and greater concentrations of rb ba th and u 4 a late tectonic to posttectonic alkali feldspar syenite alkali feldspar quartz syenite ss series was emplaced

synmetamorphic lode gold deposits in high grade archean settings lode gold deposits that formed under conditions of the middle to upper amphibolite and granulite facies have been identified in the yilgarn block of western australia these deposits which form a continuum with lower metamorphic grade mesothermal gold depos its show that at least some of the fluids responsible for mesothermal gold deposits originated in or below the middle crust studies of 18 o suggest that fluid compositions were controlled by the wall rocks at least for some elements these more proximal gold deposits provide more information about deep fluid sources than do investigations of higher level mineralization deposited from fluids strongly modified by wall rock interaction during the early part of their ascent

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

reconciling geologic and geodetic model fault slip rate discrepancies in southern california consideration of nonsteady mantle flow and lower crustal fault creep in southern california slip rates derived from geodesy constrained elastic models are lower than geologic rates along the mojave and san bernardino segments of the san andreas fault and the garlock fault in contrast the summed geodetic rate across the mojave eastern california shear zone ecsz is significantly higher than the summed geologic rate we show that geodetic and geologic slip rates in southern california can be reconciled using a viscoelastic earthquake cycle model that explicitly incorporates time dependent deformation due to nonsteady interseismic fault creep in the lower crust and viscous flow in the upper mantle to reconcile geologic and geodetic model rates our model requires that the southern san andreas fault and the garlock fault are in the late stages of the earthquake cycle resulting in lower current deformation rates than the cycle averaged rate our model implies that the ecsz and the san jacinto faults are in the early stages of the earthquake cycle resulting in high current deformation rates

integrating 3 d seismic data field analogs and mechanical models in the analysis of segmented normal faults in the wytch farm oil field southern england united kingdom we propose a methodology for the analysis of normal fault geometries in three dimensional 3 d seismic data sets to provide insights into the evolution of segmented normal fault systems and to improve recovery efforts in fault controlled oil fields limited seismic resolution can obscure subtle fault characteristics such as segmentation and gaps in fault continuity that are significant for oil migration and thus accurate reservoir characterization detailed seismic data analyses that incorporate principles of normal fault mechanics however can reveal evidence of fault segmentation we integrate seismic attribute analyses outcrop analog observations and numerical models of fault slip and displacement fields to augment the use of 3 d seismic data for fault interpretation we applied these techniques to the wytch farm oil field in southern england resulting in the recognition of significant lateral and to a lesser extent vertical segmentation of reservoir scale faults slip maxima on fault surfaces indicate two unambiguous segment nucleation depths controlled by the lithological heterogeneity of the faulted section faults initiated preferentially in brittle sandstone and limestone units subsequent growth and linkage of segments predominantly in the lateral direction resulted in composite fault surfaces that have long lateral dimensions and multiple slip maxima reservoir compartmentalization is greatest at the level of prevalent segment linkages which corresponds at wytch farm with the predominant hydrocarbon producing unit the sherwood sandstone at relatively shallower depths fault segments are younger and less evolved resulting in a greater degree of segmentation with intact relay zones

persistent slip rate discrepancies in the eastern california usa shear zone understanding fault slip rates in the eastern california shear zone ecsz using gps geodesy is complicated by potentially overlapping strain signals due to many sub parallel strike slip faults and by inconsistencies with geologic slip rates the role of fault system geometry in describing ecsz deformation may be investigated with total variation regularization which algorithmically determines a best fitting geometry from an initial model with numerous faults constrained by a western united states gps velocity field the initial dense model 1 enables construction of the first geodetically constrained block model to include all ecsz faults with geologic slip rates allowing direct geologic geodetic slip rate comparisons and 2 permits fault system geometries with many active faults that are analogous to distributed interseismic deformation beginning with 58 ecsz blocks a model containing 10 ecsz blocks is most consistent with geologic slip rates reproducing five of 11 within their reported uncertainties the model fits gps observations with a mean residual velocity of 1 5 mm yr persistent geologic geodetic slip rate discrepancies occur on the calico and garlock faults on which we estimate slip rates of 7 6 mm yr and 2 mm yr respectively indicating that inconsistencies between geology and geodesy may be concentrated on or near these faults and are not due to pervasive distributed deformation in the region discrepancies may in part be due to postseismic relaxation following the a d 1992 mw 7 3 landers and 1999 mw 7 1 hector mine earthquakes otherwise resolving geologic geodetic discrepancies would require as much as 11 4 mm yr of off fault deformation within 10 km of the main ecsz faults with 5 mm yr concentrated near the calico fault

metamorphic history of the hemlo gold deposit from al2sio5 mineral assemblages with implications for the timing of mineralization textural relations between al2sio5 phases and deformation fabrics provide constraints on the metamorphic history of the hemlo gold deposit kyanite in the deposit is most common within and on the margins of boudinaged quartz realgar veins and less commonly as rotated porphyroblasts within the matrix of schistose rocks kyanite predates the main d2 schistosity sillimanite postdates kyanite occurring irregularly as discrete knots and foliae that run parallel to but sometimes cut across the principal d2 foliation indicating that sillimanite postdates the d2 foliation we regard kyanite to be part of the peak metamorphic assemblage with sillimanite representing a partial later overprint most likely related to fluid infiltration rare andalusite occurs in two associations as late stage clean idioblastic crystals and as large fractured grains locally overprinted by sillimanite in boudinaged quartz realgar veins we suggest two possible origins for this second form of andalusite one involving generally late growth the second involving early growth prior to the development of peak metamorphic kyanite although not unambiguous we prefer the second scenario p t conditions from petrogenetic grid constraints and new geothermobarometric estimates indicate 6 7 gpa 600 650 c for the peak kyanite grade metamorphism ca 2677 ma and 4 5 gpa 600 c for the later sillimanite overprint ca 2672 ma we see these two events as part of an evolving p t path in a single metamorphic event in our early andalusite scenario the andalusite may have formed from pyrophyllite breakdown at 2 4 gpa 450 c possibly associated with emplacement of the regional suite of granodiorite plutons ca 2686 ma late andalusite formed sporadically on the retrograde path the occurrence of deformed andalusite and aligned kyanite in and on the margins of boudinaged auriferous realgar stibnite quartz veins provides evidence in support of a premetamorphic mineralization event

effects of nonplanar fault topology and mechanical interaction on fault slip distributions in the ventura basin california to assess the control of fault geometry and mechanical interactions on fault slip distributions in a complex natural system we present results from three dimensional mechanical models incorporating both nonplanar and rectangular planar representations of active faults within the ventura basin region of southern california we find that the incorporation of geologically constrained nonplanar fault surfaces into numerical models of active deformation results in a better match to available geologic slip rate data than models utilizing rectangular planar fault surfaces the model results demonstrate that nonplanar fault geometry and mechanical interactions exert a strong control on resultant slip distributions additionally we find that slip rates at most locations along the surface trace of ventura faults are not likely to rep resent average values for the entire fault surface we propose that results from three dimensional mechanical models using realistic i e nonplanar fault geometry can be used to both predict slip rates at specific locations and determine whether existing site specific slip rate estimates are representative of average fault slip rates although geo metric irregularities along fault surfaces should resist slip planar faults can have lesser slip than nonplanar faults due to the differing mechanical interactions among nearby faults in the two representations this suggests that models using simplified or planar fault geometry are likely to inaccurately simulate regional deformation we assert that detailed knowledge of three dimensional fault shape as well as the geometry and con figuration of deep fault intersections is essential for accurate seismic hazard char acterization of regions of complex faulting such as the ventura basin of southern california

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

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

constraints on fault slip rates of the southern california plate boundary from gps velocity and stress inversions summary we use global positioning system gps velocities and stress orientations inferred from seismicity to invert for the distribution of slip on faults in the southern california plate boundary region of particular interest is how long term slip rates are partitioned between the indio segment of the san andreas fault saf the san jacinto fault sjf and the san bernardino segment of the saf we use two new sets of constraints to address this problem the first is geodetic velocities from the southern california earthquake center s scec crustal motion map version 3 by shen et al which includes significantly more data than previous models the second is a regional model of stress field orientations at seismogenic depths as determined from earthquake focal mechanisms while gps data have been used in similar studies before this is the first application of stress field observations to this problem we construct a simplified model of the southern california fault system and estimate the interseismic surface velocities using a backslip approach with purely elastic strain accumulation following meade et al in addition we model the stress orientations at seismogenic depths assuming that crustal stress results from the loading of active faults the geodetically derived stressing rates are found to be aligned with the stress orientations from seismicity we therefore proceed to invert simultaneously gps and stress observations for slip rates of the faults in our network we find that the regional patterns of crustal deformation as imaged by both data sets can be explained by our model and that joint inversions lead to better constrained slip rates in our preferred model the sjf accommodates 15 mm yr 1 and the indio segment of the saf 23 mm yr 1 of right lateral motion accompanied by a low slip rate on the san bernardino segment of the saf anomalous fault segments such as around the 1992 m w 7 3 landers surface rupture can be detected there observed stresses deviate strongly from the long term loading as predicted by our simple model evaluation of model misfits together with information from palaeoseismology may provide further insights into the time dependence of strain accumulation along the san andreas system

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

simulating the recent evolution of the southern big bend of the san andreas fault southern california 1 the southern big bend of the san andreas fault has been interpreted to have successively abandoned two strands the mission creek and mill creek strands of the san andreas fault during the past 1 ma before taking up activity along its present day configuration this evolution is simulated within three dimensional models to explore the hypothesis that fault systems evolve to increase mechanical efficiency the three dimensional boundary element method models are validated by comparison of modeled fault slip rates and uplift rates with geologic data the model results match well the geologic strike slip rates and uplift patterns overestimation of reverse slip rates along the northern san bernardino mountains may reflect model assumptions of fault geometry the partitioning of slip among active faults changes between the three phases of southern san andreas fault evolution revealing 1 a trade off in strike slip rates between the san jacinto and san andreas faults 2 a trade off between strike slip rates on the san andreas fault and reverse slip along faults associated with uplifting the san bernardino mountains and 3 a trade off in strike slip rates along the san andreas and strike slip rates along the eastern california shear zone mechanical efficiency of the entire model increases from the mission creek to mill creek fault configuration and decreases from the mill creek configuration to the present day configuration the decrease in mechanical efficiency with the transition to the present day fault geometry may reflect gaps in our understanding of tectonic loading and or fault geometry

persistent rupture terminations at a restraining bend from slip rates on the eastern altyn tagh fault abstract restraining double bends along strike slip faults inhibit or permit throughgoing ruptures depending on bend angle length and prior rupture history modeling predicts that for mature strike slip faults in a regional stress regime characterized by simple shear a restraining bend of 18 and 4 km length impedes propagating rupture indeed natural evidence shows that the most recent rupture s of the xorkoli section 90 93 e of the eastern altyn tagh fault atf ended at large restraining bends however when multiple seismic cycles are considered in numerical dynamic rupture modeling heterogeneous residual stresses enable some ruptures to propagate further modulating whether the bends persistently serve as barriers these models remain to be tested using observations of the cumulative effects of multiple earthquake ruptures here we investigate whether a large restraining double bend on the atf serves consistently as a barrier to rupture by measuring long term slip rates around the terminus of its most recent surface rupture at the aksay bend our results show a w e decline in slip as the satf enters the bend as would be predicted from repeated rupture terminations there prior work demonstrated no holocene slip on the central most misoriented portion of the bend while 19 79 m offsets suggest that multiple ruptures have occurred on the west side of the bend during the holocene thus we conclude the gradient in the satf s slip rate results from the repeated termination of earthquake ruptures there however a finite slip rate east of the bend represents the transmission of some slip suggesting that a small fraction of ruptures may fully traverse or jump the double bend this agreement between natural observations of slip accumulation and multi cycle models of fault rupture enables us to translate observed slip rates into insight about the dynamic rupture process of individual earthquakes as they encounter geometric complexities along faults

slip rate gradients along the eastern kunlun fault 1 whether strike slip fault systems in eurasia accomplish eastward extrusion of tibetan crust and lithosphere depends largely on the kinematics of deformation at the fault tip here we present new slip rate determinations using millennial scale geomorphic markers from sites along the easternmost segment of the kunlun fault in north central tibet this fault system represents one of the major strike slip faults within the indo asian collision zone has been argued to exhibit uniform slip rates along much of its length and plays a central role in models for eastward extrusion of tibetan lithosphere displaced fluvial terrace risers along tributaries of the yellow river coupled with 14c ages of terrace material provide constraints on slip rates over late pleistocene to holocene time results indicate that slip rates decrease systematically along the eastern 150 km of the fault from 10 to 2 mm yr these data challenge the view that slip along the kunlun fault remains uniform along the entire length of the fault and instead reveal gradients in displacement similar to those expected at fault tips moreover slip along the fault appears to terminate within the thickened crust of the plateau and therefore any extrusion of tibetan lithosphere accomplished by slip along the kunlun fault must be absorbed by internal deformation of the plateau surrounding the fault tip

plate tectonic analysis of shallow seismicity apparent boundary width beta corner magnitude coupled lithosphere thickness and coupling in seven tectonic settings a new plate model is used to analyze the mean seismicities of seven types of plate boundary crb continental rift boundary ctf continental transform fault ccb continental convergent boundary osr oceanic spreading ridge otf oceanic transform fault ocb oceanic convergent boundary sub subduction zone we compare the platelike nonorogen regions of model pb2002 bird 2003 with the centroid moment tensor cmt catalog to select apparent boundary half widths and then assign 95 of shallow earthquakes to one of these settings a tapered gutenberg richter model of the frequency moment relation is fit to the subcatalog for each setting by maximum likelihood best fitting values range from 0 53 to 0 92 but all 95 confidence ranges are consistent with a common value of 0 61 0 66 to better determine some corner magnitudes we expand the subcatalogs by 1 inclusion of orogens and 2 inclusion of years 1900 1975 from the catalog of pacheco and sykes 1992 combining both earthquake statistics and the plate tectonic constraint on moment rate corner magnitudes include the following crb graphic 1 ctf graphic 2 ccb graphic 3 ocb graphic 4 and sub graphic 5 coupled lithosphere thicknesses are found to be the following crb graphic 6 ctf graphic 7 ccb graphic 8 osr graphic 9 for normal faulting and graphic 10 for strike slip otf graphic 11 and graphic 12 at low medium and high velocities ocb graphic 13 and sub graphic 14 in general high coupling of subduction and continental plate boundaries suggests that here all seismic gaps are dangerous unless proven to be creeping in general low coupling within oceanic lithosphere suggests a different model of isolated seismic fault patches surrounded by large seismic gaps that may be permanent online material global seismic subcatalogs of shallow earthquakes 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif 5 embed inline graphic 5 gif 6 embed inline graphic 6 gif 7 embed inline graphic 7 gif 8 embed inline graphic 8 gif 9 embed inline graphic 9 gif 10 embed inline graphic 10 gif 11 embed inline graphic 11 gif 12 embed inline graphic 12 gif 13 embed inline graphic 13 gif 14 embed inline graphic 14 gif

high resolution interseismic velocity data along the san andreas fault from gps and insar 1 we compared four interseismic velocity models of the san andreas fault based on gps observations the standard deviations of the predicted secular velocity from the four models are larger north of the san francisco bay area near the creeping segment in central california and along the san jacinto fault and the east california shear zone in southern california a coherence spectrum analysis of the secular velocity fields indicates relatively high correlation among the four models at longer wavelengths 15 40 km with lower correlation at shorter wavelengths to improve the short wavelength accuracy of the interseismic velocity model we integrated interferometric synthetic aperture radar insar observations initially from advanced land observing satellite alos ascending data spanning from the middle of 2006 to the end of 2010 totaling more than 1100 interferograms with gps observations using a sum remove filter restore approach the final insar line of sight data match the point gps observations with a mean absolute deviation of 1 5 mm yr we systematically evaluated the fault creep rates along major faults of the san andreas fault and compared them with creepmeters and alignment array data compiled in uniform california earthquake rupture forecast version 2 ucerf2 moreover this insar line of sight dataset can constrain rapid velocity gradients near the faults which are critical for understanding the along strike variations in stress accumulation rate and associated earthquake hazard

late quaternary slip rate gradient defined using high resolution topography and 10be dating of offset landforms on the southern san jacinto fault zone california 1 recent studies suggest the san jacinto fault zone may be the dominant structure accommodating pa na relative plate motion however because the late quaternary slip history of the southern san andreas fault system is insufficiently understood it is difficult to evaluate the partitioning of deformation across the plate boundary and its evolution landforms displaced by the clark fault of the southern san jacinto fault zone were mapped using high resolution airborne laser swath topography and selected offset landforms were dated using cosmogenic 10be beheaded channels at rockhouse canyon displaced by 500 70 m and 220 70 m have been dated to 47 8 ka and 28 9 ka respectively farther south near the southern santa rosa mountains an alluvial deposit displaced by 51 9 m has been dated to 35 7 ka from these sites the slip rate of the clark fault is determined to diminish southward from 8 9 2 0 to 1 5 0 4 mm yr this implies a slip rate decrease along the clark fault from anza southeastward to its surface termination near the salton trough where slip is transferred to the coyote creek fault and additional deformation is compensated by folding and thrusting in the basin these data suggest that since 30 to 50 ka the slip rate along the southern san jacinto fault zone has been lower than or equivalent to the rate along the southernmost san andreas fault accordingly either the slip rate of the san jacinto fault has substantially decreased since fault initiation or fault slip began earlier than previously suggested

depositional gaps in abitibi greenstone belt stratigraphy a key to exploration for syngenetic mineralization models of greenstone belt development are crucial for exploration allochthonous models predict belts to be a collage of unrelated fragments whereas autochthonous models allow for prediction of syngenetic mineral deposits within specific stratigraphic intervals superior province greenstone belts consist of mainly volcanic units unconformably overlain by largely sedimentary timiskaming style assemblages and field and geochronological data indicate that the abitibi greenstone belt developed autochthonously we describe major revisions to stratigraphy of the abitibi greenstone belt and the implications of an autochthonous development of the volcanic stratigraphy for exploration for syngenetic mineralization the abitibi greenstone belt is subdivided into seven discrete volcanic stratigraphic episodes on the basis of groupings of numerous u pb zircon ages of pre 2750 2750 to 2735 2734 to 2724 2723 to 2720 2719 to 2711 2710 to 2704 and 2704 to 2695 ma we present revised lithotectonic and or stratigraphic nomenclature using these time intervals including 1 isotopic inheritance in younger episodes which indicates that the older episodes 2750 2735 and 2734 2724 ma had greater extent than is presently seen 2 dikes feeding younger volcanic episodes 2706 ma cutting older volcanic units 2734 2724 ma and 3 2710 to 2704 ma mafic to ultramafic sills intruding the 2719 to 2711 ma episode changes to the nomenclature include the identification of pre 2750 ma volcanic episode supracrustal fragments in the northern and southern abitibi greenstone belt and subdivision of the 2719 to 2711 ma 2710 to 2704 ma and 2704 to 2695 ma episodes into lower and upper parts we present the results of this lithostratigraphic subdivision as the first geochronologically constrained stratigraphic and or lithotectonic map of the abitibi greenstone belt many of the volcanic episodes are intercalated with and capped by a relatively thin sedimentary interface zone dominated by chemical sedimentary rocks stratigraphic and geochronological analysis of these zones indicates discontinuous deposition with localized gaps of 2 to 27 m y between volcanic episodes the zones consist of up to 200 m of iron formation chert breccia heterolithic debris flows of volcanic provenance sandstone and or argillite and conglomerate modeling of the time required for deposition of the volcanic units based on rates of magma production in modern arc and plume environments is on the order of 103 to 104 years whereas the time interval between basalt rhyolite cycles is 106 years the sedimentary interface zones are therefore interpreted as condensed sections zones with very low rates of sedimentation in a basinal setting or zones with negligible rates of sedimentation marked by silicification of existing rock types the sedimentary interface zones are therefore considered submarine correlative conformities disconformities or unconformities separating the equivalent of group level stratigraphic and lithotectonic units the unconformity bounded stratigraphic model provides a new regional to deposit scale interpretive model for use in exploration for syngenetic mineralization

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

invisible gold in ore and mineral concentrates from the hillgrove gold antimony deposits nsw australia vein hosted mesothermal stibnite gold mineralisation at the hillgrove au sb mine in northeastern new south wales has a halo of veinlet and disseminated auriferous arsenopyrite and arsenian pyrite in metasedimentary and granitic host rocks about 50 55 of the gold produced at hillgrove occurs invisibly in arsenopyrite and pyrite gold losses of 20 into tailings are due to this mineral chemical factor from pixe probe analyses it has been found that arsenopyrite contains 255 1500 ppm au and pyrite 24 223 ppm au with au contents of each mineral correlating moderately with as content arsenopyrite and pyrite also contain anomalous values of cu ag and sb whereas paragenetically later stibnite contains little invisible gold but minor fe as ag cu and pb the precipitation of invisible gold in arsenopyrite and pyrite by a possible fe au 3 as s 3 substitution mechanism may have been facilitated by rapid non equilibrium conditions involving pressure decreases and wall rock reaction sulphidation carbonatisation as a prelude to the main stage of stibnite and gold deposition

metamorphic evolution of the late archaean cadillac tectonic zone mcwatters abitibi belt quebec archaean greenstone belts are often cut by major shear zones for example the cadillac tectonic zone ctz of the southern abitibi region in north western quebec at mcwatters the ctz contains slices of metavolcanic units bounded by corridors of highly strained and altered rocks mineral assemblages of the metabasites record the metamorphic evolution of the ctz the mcwatters metabasalts and metagabbros have similar chemistry but different mineral assemblages consisting of variable amounts of actinolite hornblende chlorite albite epidote quartz carbonates titanite biotite rutile magnetite ilmenite and sulphides the different mineral assemblages which coexist in a single tectonic slice can be divided into three types characterized by a presence of hornblende and actinolite b presence of actinolite and epidote and c absence of amphibole and epidote partial replacements indicate that these mineral assemblages are not in equilibrium the hornblende of the least altered and deformed samples of the type a assemblage is a relict of a prograde metamorphic event contemporaneous with the development of the main schistosity the prograde conditions are estimated at p 5 kbar t 475 c with low pf the more altered and deformed samples of the type c assemblage record a later retrograde metamorphic event conditions of the later event are estimated at p 4 kbar t 400 c with higher pf widespread calcite precipitation occurred during a later episode the diversity of the mineral assemblages results from permeability variations along the high strain zones of the ctz

multistage gold mineralization at the lapa mine abitibi subprovince insights into auriferous hydrothermal and metasomatic processes in the cadillac larder lake fault zone the lapa gold deposit contains reserves of 2 4 mt at 6 5 g t au and is one of the few deposits located directly within the cadillac larder lake fault zone cllfz a first order crustal scale fault that separates the archean abitibi subprovince from the pontiac subprovince to the south gold mineralization is predominantly hosted in highly strained and altered upper greenschist lower amphibolite facies mafic to ultramafic rocks of the piche group auriferous ore zones consist of finely disseminated auriferous arsenopyrite pyrrhotite pyrite and native gold disseminated in biotite and carbonate altered wall rocks native gold which is also present in quartz dolomite calcite veinlets is locally associated with sb bearing minerals especially at depth 1 km from surface where the deposit is characterized by a au sb as association at vertical depth greater than 1 km gold is associated with arsenopyrite and pyrrhotite au as association the mineralogy and paragenesis of the lapa deposit metamorphosed ore and alteration assemblages record the superposition of three metamorphic episodes m1 m2 and m3 and three gold mineralizing events spatial association between biotitized wall rocks and auriferous arsenopyrite indicates that arsenopyrite precipitation is concomitant with potassic alteration the predominant au as association recognized across the deposit is related to gold in solid solution in arsenopyrite as part of a pre m2 low grade auriferous hydrothermal event however the occurrence of hornblende oligoclase porphyroblasts overprinting the biotite alteration and the presence of porous clusters and porphyroblasts of arsenopyrite with native gold and pyrrhotite indicate an auriferous metasomatic event associated with peak m2 prograde metamorphism late retrograde metamorphism m3 overprints the hornblende oligoclase m2 assemblage within the host rocks proximal to ore by an actinolite albite assemblage by precipitation of free gold and sb sulfosalts at lower p t the complex relationships between ore structural features and metamorphic assemblages at lapa are related to the tectonometamorphic evolution of the cadillac larder lake fault zone at different times and crustal levels and varying heat and fluid flow regimes the lapa deposit demonstrates that early low grade gold mineralization within the cadillac larder lake fault zone has benefited from late gold enrichment s during prograde and retrograde metamorphism suggesting that multi stage processes may be important to form gold rich orogenic deposits in first order crustal scale structures

fault slip rates effects of elastic heterogeneity on geodetic data and the strength of the lower crust in the salton trough region southern california 1 in southernmost california the salton trough sedimentary basin lies between the subparallel san jacinto and san andreas faults that together with the elsinore fault accommodate 80 of the 50 mm yr of pacific north american relative motion the slip rates on the san andreas and san jacinto faults have been a matter of recent debate and one source of uncertainty has been the influence of crustal strength heterogeneity due to elastically weak basin sediments on geodetic data to evaluate these effects we have modeled regional kinematics with elastic and viscoelastic finite element models that incorporate laterally and vertically varying crustal material properties we find that in general the effects of the sedimentary basin on surface deformation are relatively small and that to explain the geodetic velocity data the slip rate on the san andreas must be higher than that on the san jacinto fault consistent with traditional geologic estimates we also conclude that a relatively strong lower crust of viscosity 5 x 10 19 pa s exists in this region

estimating prehistoric earthquake magnitude from point measurements of surface rupture abstract we have developed a method for estimating the magnitude of prehistoric earthquakes using displacement data that usually can be collected from paleoseismic investigations this method is necessary because essentially all current magnitude estimates for prehistoric events rely on determining the total length of coseismic surface rupture which is rarely measurable or rely on segmentation scenarios for which uncertainties cannot be quantified although surface rupture length is a better predictor of magnitude than displacement for historic earthquakes paleoseismic investigations are better at providing measurements of the amount of displacement at a site along a fault the key to our method is to incorporate the variability in displacement observed in 14 modern events which allows a formal uncertainty in magnitude to be assigned to prehistoric ruptures we show how multiple measurements along a preserved fraction of a rupture can be combined to reduce the uncertainty in the estimate of magnitude our analysis shows that uncertainty asymptotically approaches the natural variability of ruptures so 5 to 10 displacement measurements are sufficient to characterize paleomagnitude we conclude that sampling of scarps with lengths of even 10 of the original rupture can provide magnitude values that reasonably estimate the earthquake tests of the method using randomly sampled data from the 1992 m w 7 3 landers and 1954 m s 6 8 dixie valley earthquakes provide close approximations of the actual magnitudes

shoshonitic lamprophyre dykes and their relation to mesothermal ausb veins at hillgrove new south wales australia abstract the hillgrove mineral field in the southern part of the new england orogen of northeastern new south wales australia contains numerous mesothermal au sb vein systems calc alkaline shoshonitic lamprophyre cal dykes are also associated with mineralisation with dilational lode structures acting as conduits for dyke intrusion which has occurred before and after major quartz stibnite veining dykes include minette and vogesite compositions and were emplaced in the late permian 247 255 ma at the same time as regionally extensive i type magmatism in the new england orogen least altered dykes are enriched in mg k ba rb sr zr th cr and ni relative to i type intrusives although chemical affinities are evident between lamprophyres and the more mafic members of the high k moonbi plutonic suite hillgrove lamprophyres are commonly enriched in sb as hg au w and bi with respect to average cal compositions evidence indicates this is most likely due to contamination of magma during intrusion through mineralised structures rather than a primary magmatic feature partially resorbed xenocrystic stibnite occurs in dykes which have intruded lode structures probably facilitated by the low melting point of stibnite 550 c and its incorporation into the magma carbon and oxygen isotopic data from carbonates in least altered post lode lamprophyres are indistinguishable from carbonate in altered dykes and veins implying that hydrothermal interaction continued after dyke intrusion although it is unlikely that lamprophyre dykes have been a direct source for mineralisation at hillgrove the close temporal and spatial relation of dykes mesothermal au sb veins and i type intrusions are interpreted to be manifestations of the post collisional setting and influx of mantle derived heat and partial melts into the new england orogen during the late permian

kinematic modeling of fault slip rates using new geodetic velocities from a transect across the pacific north america plate boundary through the san bernardino mountains california 2015 american geophysical union all rights reserved campaign gps data collected from 2002 to 2014 result in 41 new site velocities from the san bernardino mountains and vicinity we combined these velocities with 93 continuous gps velocities and 216 published velocities to obtain a velocity profile across the pacific north america plate boundary through the san bernardino mountains we modeled the plate boundary parallel horizontal deformation with 5 14 parallel and one obliquely oriented screw dislocations within an elastic half space our rate for the san bernardino strand of the san andreas fault 6 5 3 6mm yr is consistent with recently published latest quaternary rates at the 95 confidence level and is slower than our rate for the san jacinto fault 14 1 2 9mm yr our modeled rate for all faults of the eastern california shear zone ecsz combined 15 7 2 9mm yr is faster than the summed latest quaternary rates for these faults even when an estimate of permanent off fault deformation is included the rate discrepancy is concentrated on faults near the 1992 landers and 1999 hector mine earthquakes the geodetic and geologic rates agree within uncertainties for other faults within the ecsz coupled with the observation that postearthquake deformation is faster than the pre 1992 deformation this suggests that the ecsz geodetic geologic rate discrepancy is directly related to the timing and location of these earthquakes and is likely the result of viscoelastic deformation in the mantle that varies over the timescale of an earthquake cycle rather than a redistribution of plate boundary slip at a timescale of multiple earthquake cycles or longer