toward a global model for correction of bottomhole temperature data progress and limitations static formation temperature sft can be estimated from temperatures measured during wire line logging tm a large number of correction models for obtaining sft from tm have been suggested several studies have shown that sfts yielded by such models are off by an average of 6 c 10 c 43 f 50 f at burial depths of 1 5 3 5 km 0 9 2 2 mi and thus have the potential to cause serious issues in thermal and hydrocarbon generation models this paper explores the causes for erroneous sft predictions generated from tm measurements and identifies factors that should be addressed to generate a globally applicable correction model we also present an improved empirical correction model for tm data from eight oil and gas fields located on the norwegian continental shelf the new empirical model was designed to give correct average sft predictions and is applicable to single tm measurements it has been validated against temperatures recorded during drill stem testing which closely represent local sfts the expression yields improved results compared with other correction models applied to the data set however the average error in computed sft values varies by up to 10 c 18 f between the investigated hydrocarbon fields we conclude that these variations result from differences in operational practices such as fluid circulation and drilling velocities therefore current empirical and physical models for sft prediction from tm require local calibration it is also suggested that more accurate compilations and analyses of operational data could lead to improved and more globally applicable models

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

accelerated stress buildup on the southern san andreas fault and surrounding regions caused by mojave desert earthquakes a sequence of four mw 6 earthquakes including the 1992 mw 5 7 3 landers and mw 5 7 1 hector mine earthquakes occurred in the mojave desert in the 1990s in close proximity to the southern san andreas fault inducing stress changes on several of its segments we calculate that coseismic slip combined with postseismic relaxation of viscous lower crust and or upper mantle has led to a coulomb stress increase of 2 3 3 5 bar on the san bernardino mountain segment of the southern san andreas fault between 1992 and 2001 with a projected increase of 3 6 4 9 bar by the year 2020 in comparison the calculated coseismic stress increase is 1 8 bar for this segment this accelerated buildup of stresses is predicted to bring the san bernardino mountain segment which last ruptured more than 190 yr ago closer to a potentially major rupture meanwhile we project a net stress decrease of as much as 23 5 bar between 1992 and 2020 for the western coachella valley segment if the fault is governed by low effective friction or an increase of 1 5 bar if the fault is governed by high effective friction coulomb stresses are calculated to decrease on the mojave segment by as much as 21 bar between 1992 and 2020 accelerated stress buildup is also predicted to occur on parts of the san jacinto elsinore and calico faults the pattern of the observed post landers aftershock clustering and the calculated coulomb stress buildup on the calico fault is similar to that noted in the hector mine region prior to the 1999 mw 5 7 1 earthquake these results imply that the stress changes caused by an earthquake may still play a role in triggering future quakes in neighboring crust many years later through viscoelastic processes

heat flux through an old 175 ma passive margin offshore southeastern united states new heat flow data on the southeastern united states passive margin show that measured uncorrected flux averages 49 11 8 mw m 2 through old 175 ma oceanic crust nonuniform thermal gradients were measured at about half of the 114 penetrations that comprise the data set and over the full range of water depths 1900 m to 4250 m at which data were collected with the simplifying assumption that the nonuniform gradients were caused by a step function change in bottom water temperatures at some time before the heat flow cruises concave down decreasing dt dz with depth and concave up increasing dt dz sediment thermal gradients can be explained by respective average temperature decreases and increases of 0 1 0 2 k amplitude occurring 28 35 days before the measurements thermal gradients throughout the entire region are strongly influenced by oceanographic phenomena and locally by the presence of subsurface diapiric structures while sediment thickness variations and lateral differences in sedimentation rate and sediment lithology appear to exercise relatively little control over thermal regimes mean reduced heat flow in the study area is estimated at 49 mw m 2 by decompacting and back stripping the 5 8 km of sediment deposited on the margin since the formation of the underlying oceanic crust this value agrees with previous measurements made on younger crust in the blake ridge area but is significantly higher than the reduced heat flow value in a similar passive margin setting at the baltimore canyon trough we use the calculated average thermal gradient value and an assumption of constant conductivity to estimate temperatures of 19 5 c to 24 5 c at the bottom simulating reflector bsr on the blake ridge slope

consequences of viscous drag beneath a transform fault 1 a transform fault is modeled as a vertical cut through an elastic layer schizosphere of thickness h overlying a viscous substrate plastosphere we consider a steady transform motion accommodated in the schizosphere wholly by slip on the fault and in the plastosphere insofar as possible by viscous flow for the case where the viscosity in the plastosphere is strain rate dependent but independent of temperature the velocity solution in the plastosphere is v where v is the slip rate on the fault in the schizosphere and r and are the cylindrical coordinates with the origin at the bottom of the fault the viscous stress is singular at the bottom of the fault r 0 and exceeds the brittle frictional strength for r r0 equating the brittle strength to the viscous stress defines the brittle ductile boundary r0 in the plastosphere as a function of h and viscosity the additional condition that r0 must be small allows the viscosity to be estimated from h for small r the temperature independent solution is a valid approximation to the temperature dependent solution and the relation between viscosity and h should remain valid from the temperature independent model we estimate that self heating due to dissipation in the plastosphere for reasonable earth parameters is less than 20 c

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

behavior of the southernmost san andreas fault during the past 300 years surficial creep occurs at low rates along the coachella valley segment of the san andreas fault which has not produced a large earthquake during the period of historical record geodetic data indicate however that the crust adjacent to this segment of the san andreas fault is accumulating strain at a high rate furthermore neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries in view of its long term behavior the occurrence of creep along the surficial trace of the fault in the coachella valley is of particular interest along two short reaches of the san andreas fault in the coachella valley measurements of offset geological deposits and man made structures and from alignment arrays and creep meters show that slip rates of 2 4 mm yr near indio and near the salton sea have persisted for the past three centuries this slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault we suggest that the coachella valley segment of the san andreas fault creeps in its upper few kilometers this behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault

holocene rate of slip and tentative recurrence interval for large earthquakes on the san andreas fault cajon pass southern california abstract detailed mapping of the san andreas fault zone where it crosses cajon creek southern california has revealed a number of late quaternary deposits and geomorphological features offset by the fault radiocarbon dates from alluvial and swamp deposits provide a detailed chronology with which to characterize the activity of the san andreas fault four independent determinations of the slip rate on the san andreas fault yield an average rate of 24 5 3 5 mm yr for the past 14 400 years the similarity of the four values which span different intervals of time from 5900 to 14 400 years ago suggest that the slip rate has been constant during this period the slip rate confirms that the san andreas fault is accumulating slip faster than any other fault in the plate boundary throughout california also the sum of the slip rates on the san andreas 24 5 mm yr and the san jacinto 10 mm yr faults south of their junction is the same as the san andreas north of their junction 35 mm yr an excavation provided evidence for at least two and up to four earthquakes that caused rupture on the fault between 1290 and 1805 a d and tentative evidence for six earthquakes in about the last 1000 years both lines of evidence imply an average recurrence interval for large earthquakes of about 1 to 2 centuries combined with the historic record this investigation indicates that the last major earthquake at cajon creek was probably at the beginning or middle of the 18th century while the record at cajon creek may suggest that the next major earthquake on the san andreas fault is overdue the data can be interpreted to indicate that the recurrence interval for earthquakes on the san andreas south of the 1857 rupture is 3 to 4 centuries and that the anticipated event should not be expected until the next century

viscoelastic coupling model for the earthquake cycle driven from below in a linear system the earthquake cycle can be represented as the sum of a solution which reproduces the earthquake cycle itself viscoelastic coupling model and a solution that provides the driving force we consider two cases one in which the earthquake cycle is driven by stresses transmitted along the schizosphere and a second in which the cycle is driven from below by stresses transmitted along the upper mantle i e the schizosphere and upper mantle respectively act as stress guides in the lithosphere in both cases the driving stress is attributed to steady motion of the stress guide and the upper crust is assumed to be elastic the surface deformation that accumulates during the interseismic interval depends solely upon the earthquake cycle solution viscoelastic coupling model not upon the driving source solution thus geodetic observations of interseismic deformation are insensitive to the source of the driving forces in a linear system in particular the suggestion of bourne et al 1998 that the deformation that accumulates across a transform fault system in the interseismic interval is a replica of the deformation that accumulates in the upper mantle during the same interval does not appear to be correct for linear systems

transient creep of a composite lower crust 1 constitutive theory a composite model is proposed to describe the time dependent response of the earth s lower crust the motivation for such a model is twofold first new observations of widespread postseismic deformation indicate that the deep continental crust responds viscoelastically having both long and short term decay times second by any number of observationally based rationales the lower crust is compositionally and structurally heterogeneous over many length scales for heterogeneities that have much smaller characteristic lengths than the minimum deformation wavelength of interest the aggregate rheology can be described by composite media theory for wavelengths of the order of the thickness of the lower crust 25 40 km and larger composite theory may be applied to heterogeneities that are smaller than about several hundred meters or equivalent to the vertical extent of a thick lower crustal mylonitic shear zone the composite media theory developed here is constructed using both eshelby mori tanaka theory for aligned generalized spheroidal inclusions and a generalized self consistent method the inclusions and matrix are considered to be maxwellian viscoelastic a rheology that is consistent with past homogeneous models of postseismic stress relaxation the composite theory presented here introduces a transient response to a suddenly imposed stress field which does not appear in homogeneous maxwell models analytic expressions for the amplitude and duration of the transient and for the effective long and short term viscosities of the composite are given which describe the sensitivity to inclusion concentration to shape and to ratio of inclusion to matrix viscosity r

geothermal model of the continental margins of eastern canada abstract deep temperature distributions on six seismic cross sections on the passive continental margins of eastern canada have been calculated each of the considered profiles of the crustal structure includes sections with continental and oceanic crusts and also a zone of ocean continent transition present calculations show that on each profile the crust and upper mantle beneath the ocean have temperatures considerably higher than those beneath the continent the difference between sub oceanic and sub continental temperatures at the same depth amounts to 100 150 k at the depth of 50 km the temperature in the continental and oceanic regions reaches 500 700 c and 700 900 c respectively in the region with continental crust the crustal radioactivity and the outflow of heat from the mantle constitute approximately equal heat sources in producing the crustal temperatures in the area with oceanic crust the mantle heat flow is the dominant source of heating on these sections of the profiles more than about 75 of the surface heat flow has its origin in the mantle the thickness of the lithosphere across the margins decreases seawards in the region with oceanic crust its thickness reduces to 70 75 km typical of the north atlantic

relative contributions of crustal temperature and composition to controlling the depth of earthquakes in southern california 1 control of the 13 km range of the maximum depth of earthquakes in southern california has been attributed previously to lateral variations in either crustal temperature or crustal rock composition here i compare heat flow a proxy for crustal temperature local maximum depths of earthquakes d95 and best guess crustal rock compositions plotting heat flow versus d95 produces distinct trends for each rock composition with each trend representing an isotherm marking the onset of plastic behavior offsets between the trends measure the differences in the plastic behavior temperatures of each rock composition these offsets are comparable to the d95 variations with heat flow thus crustal temperature and composition contribute about equally to the control of the maximum depths of earthquakes the observed isotherm slopes imply vertical variations in crustal composition in addition to the lateral variations

influence of the earthquake cycle and lithospheric rheology on the dynamics of the eastern california shear zone the eastern california shear zone is bounded by the high heat flow region of the basin and range province and the low heat flow region of the sierra nevada block this difference in thermal state influences the rheology of the lower crust upper mantle resulting in a viscosity contrast between the two regions we analyze the effect of such a contrast on the kinematics and dynamics of the shear zone with numerical models this viscosity contrast drives asymmetric strain accumulation in the upper crust producing an asymmetric surface velocity field an additional consequence of this strain pattern is the potential for asymmetric co seismic displacement during an earthquake

basin modeling meets rift analysis a numerical modeling study from the jeanne d arc basin offshore newfoundland canada abstract the jeanne d arc basin on the grand banks offshore newfoundland is a confined failed rift basin its initial development and burial history were controlled by crustal stretching and thinning this study provides a detailed analysis of the heat flow tectonic subsidence stretching factor maturation and temperature history based on 44 1d models and one full 4d space and time model in basin models the heat flow history is usually calculated from vitrinite reflectance vrr data however this causes uncertainties and reflects only the periods of sedimentation which where penetrated by wells therefore other methods should be used to reconstruct the early heat flow history not recorded by sediments in this study a discontinuous pure shear stretching model including radioactive heat production reflecting the timing and magnitude of stretching factors of crust and lithospheric mantle was applied to a 4d numerical model for the jeanne d arc basin it is the first time that this new technique is shown on a real case scenario and it gives new insights into the regional geodynamics results show that to understand the thermal evolution of the jeanne d arc sedimentary basin completely it is crucial to consider the triassic rift system this first rift generated the structural framework of the basin where most of the sediments were deposited the second extension in the cretaceous represents most likely an ultra slow extension phase with a heat impulse too weak to leave any thermal record this study demonstrates that the entire evolution of the jeanne d arc basin can be reconstructed assuming just one single triassic thermal rift additionally it shows the effects of a lateral heat transfer on the determination of stretching factors and thus on tectonic subsidence and the resulting heat flow history

what can gps data tell us about the dynamics of post seismic deformation summary this paper describes differences in time varying post seismic deformation due to after slip and viscoelastic relaxation following large strike slip earthquakes and how these differences may be exploited to characterize the configuration and rheology of aseismically deforming material in the subsurface the analysis involves two steps first near field time dependent post seismic deformation characteristics of a typical mw 7 4 strike slip earthquake is defined based on analysis of gps data from three recent earthquakes secondly this earthquake is modelled assuming uniform slip along a rectangular surface and several classes of after slip and viscoelastic relaxation models that can reproduce the evolution of early post seismic displacements with time at a near field reference point are developed postseismic displacements and velocities away from the reference point where the differences are greatest and thus most likely to be distinguished with gps are compared i find that displacements from a judiciously designed network of continuous or frequently occupied campaign mode gps sites are sufficiently precise to distinguish linear viscoelastic relaxation from after slip on a vertical surface extending the coseismic rupture furthermore both the thickness and viscosity of a relaxing linearly viscoelastic layer may be identified to maximize what post seismic gps surveys can tell us particularly concerning potential relaxation of low viscosity layers in the crust and or upper mantle some gps sites should be located along strike beyond the rupture tip also far field gps sites should be occupied as frequently as sites close to the rupture

heat flow of the eastern canadian rifted continental margin revisited continental shelves are regions where heat flow is not measured directly by conventional marine techniques but estimated from oil exploration data with possible bias in order to overcome this problem we recently proposed a method based on neural networks geophys j int 2006 166 115 that provides better constraints on thermal conductivity it allowed us to derive 161 heat flow estimates on the eastern margin of canada where previous studies had concluded to the existence of heat flow higher than that in the adjacent continent and ocean we conversely found rather homogeneous values 45 55 mw m 2 all along and across the margins from labrador to nova scotia the difference seems essentially related to the porosity of sediments that was not taken into account in previous studies our results support a high asymmetry for the conjugate iberian canadian margins and could indicate that mantle heat flow increases abruptly from the canadian shield to the margins

marine heat flow observations on the canadian arctic continental shelf and slope abstract we present 36 new heat flow measurements grouped within five separate sites on the canadian arctic continental shelf and slope between 95 115 w and 80 82 n observations consist of temperature gradients and in situ thermal conductivity using a modified marine type multiple penetration probe with a length of 4 6 m repeat measurements from nearby locations at different times of the year indicate that for depths deeper than 200 m the bottom water remains sufficiently stable to allow shallow measurements to characterize the deeper geothermal flux in this respect the cold ice covered deep water arctic margin is unique among the world s passive continental margins using these data we construct a preliminary geothermal transect between the continental sverdrup basin to the south and the oceanic canada basin to the north values of 35 45 mw m 2 exist on the axel heiberg headland nansen channel and on the continental slope and indicate a broad scale reduction from higher values of 55 60 mw m 2 within the canadian basin to values of 40 50 mw m 2 within the sverdrup basin in contrast there is a zone of high heat flow with well constrained values of 80 mw m 2 within peary channel low values in the northeastern sector of the margin suggest that the early tertiary eurekean orogen near ellesmere island has not thermally affected the margin based on calculations for pure shear extension the 15 mw m 2 reduction across the continental margin suggests that the canada basin proper may not have opened until late cretaceous unless the pre existing continental crust contains an extremely low amount of radiogenic material lithospheric models cannot account for the high values in peary channel which may indicate water movement within the sedimentary basin

salton trough regional deformation estimated from combined trilateration and survey mode gps data the salton trough in southeastern california united states has one of the highest seismicity and deformation rates in southern california including 20 earthquakes m 6 or larger since 1892 from 1972 through 1987 the u s geological survey usgs measured a 41 station trilateration network in this region we re measured 37 of the usgs baselines using survey mode global positioning system methods from 1995 through 1999 we estimate the salton trough deformation field over a nearly 30 year period through combined analysis of baseline length time series from these two datasets our primary result is that strain accumulation has been steady over our observation span at a resolution of about 0 05 strain yr at 95 confidence with no evidence for significant long term strain transients despite the occurrence of seven large regional earthquakes during our observation period similar to earlier studies we find that the regional strain field is consistent with 0 5 0 03 strain yr total engineering shear strain along an axis oriented 311 6 23 east of north approximately parallel to the strike of the major regional faults the san andreas and san jacinto all uncertainties in the text and tables are standard deviations unless otherwise noted we also find that 1 the shear strain rate near the san jacinto fault is at least as high as it is near the san andreas fault 2 the areal dilatation near the southeastern salton sea is significant and 3 one station near the southeastern salton sea moved anomalously during the period 1987 95 1995 11 online material tables of stations used in this study and of estimated strain fields manuscript received 8 january 2003

viscoelastic coupling model of the san andreas fault along the big bend southern california the big bend segment of the san andreas fault is the 300 km long segment in southern california that strikes about n65 w roughly 25 counterclockwise from the local tangent to the small circle about the pacific north america pole of rotation the broad distribution of deformation of trilateration networks along this segment implies a locking depth of at least 25 km as interpreted by the conventional model of strain accumulation continuous slip on the fault below the locking depth at the rate of relative plate motion whereas the observed seismicity and laboratory data on fault strength suggest that the locking depth should be no greater than 10 to 15 km the discrepancy is explained by the viscoelastic coupling model which accounts for the viscoelastic response of the lower crust thus the broad distribution of deformation observed across the big bend segment can be largely associated with the san andreas fault itself not subsidiary faults distributed throughout the region the working group on california earthquake probabilities 1995 in using geodetic data to estimate the seismic risk in southern california has assumed that strain accumulated off the san andreas fault is released by earthquakes located off the san andreas fault thus they count the san andreas contribution to total seismic moment accumulation more than once leading to an overestimate of the seismicity for magnitude 6 and greater earthquakes in their type c zones

deep sea drilling project heat flow and models of the rifted west rockall margin downhole thermal measurements for the southwest rockall bank rifted margin made on deep sea drilling project leg 81 plus those previously made on leg 48 give six reliable heat flow values in the narrow range 62 71 mw m 2 with an average of 66 5 mw m 2 the temperatures were obtained using a self contained downhole temperature recording device a long probe is inserted through the drill bit into the undisturbed sediments below the bottom of the hole at intervals during drilling the thermal disturbance from the penetration was extrapolated to equilibrium in situ temperatures using the cylindrical decay function the thermal conductivities have been measured on core samples using the needle probe method supplemented with porosity conductivity relations heat production in the sedimentary volcanic sequence above basement probably makes a negligible contribution to the heat flow there is no systematic heat flow trend with water depth which ranges from 1650 to 1900 m or with position and the mean value is not significantly different from that expected from pure oceanic crust of age equal to the approximately 50 ma time of rifting however the unloaded basement depth is over 1 km shallower than expected for normal oceanic crust of the 50 ma rifting age the heat flow combined with subsidence data fits a simple rifting model with crustal stretching and thinning by a factor of 3 or 4 over a zone at least 100 km wide occurring about 50 ma the heat production in the stretched crust is taken to contribute 4 mw m 2 based on a prerift structure comparable to once adjacent north america a major uncertainty in thermal and subsidence models for the margin is the effect of the earlier iceland hot spot which produced extensive margin volcanism on the northern british isles and greenland and shoaling of the oceanic crust at about the time of west rockall rifting

estimates of terrestrial heat flow in offshore eastern canada from available bottom hole temperatures and conductivities estimated from lithologic descriptions heat flow estimates are calculated for 72 sites on the canadian atlantic shelf the resulting data suggest a pattern of low heat flow 055 mw m2 within the paleozoic basins in proximity to land areas and generally intermediate heat flow 60 80 mw m2 along the outer half of the continental shelf higher heat flows 90 mw m2 are estimated along the shelf edge in some areas e g the southwestern scotian shelf and the eastern newfoundland and labrador shelves radioactive heat generation in sediments that thicken seawards probably does not account for the observed increase in heat flow the possibility that higher heat flows in some areas may arise because of fluid movement from depth is suggested various other causes for the high heat flows e g tectonic or magmatic activity are considered less likely

uncertainties in slip rate estimates for the mission creek strand of the southern san andreas fault at biskra palms oasis southern california this study focuses on uncertainties in estimates of the geologic slip rate along the mission creek strand of the southern san andreas fault where it offsets an alluvial fan t2 at biskra palms oasis in southern california we provide new estimates of the amount of fault offset of the t2 fan based on trench excavations and new cosmogenic 10be age determinations from the tops of 12 boulders on the fan surface we present three alternative fan offset models a minimum a maximum and a preferred offset of 660 m 980 m and 770 m respectively we assign an age of between 45 and 54 ka to the t2 fan from the 10be data which is significantly older than previously reported but is consistent with both the degree of soil development associated with this surface and with ages from u series geochronology on pedogenic carbonate from t2 described in a companion paper by fletcher et al this volume these new constraints suggest a range of slip rates between 12 and 22 mm yr with a preferred estimate of 14 17 mm yr for the mission creek strand of the southern san andreas fault previous studies suggested that the geologic and geodetic slip rate estimates at biskra palms differed we find however that considerable uncertainty affects both the geologic and geodetic slip rate estimates such that if a real discrepancy between these rates exists for the southern san andreas fault at biskra palms it cannot be demonstrated with available data

on steady rate coupling between an elastic upper crust and a viscous interior although it is commonly accepted that the upper seismogenic layer of the earth s crust deforms elastically except in localized zones faults where deformation is discontinuous the sub seismogenic layer is not as well understand possibilities for the rheology include viscous or viscoelastic behavior and localization of shear to relatively thin zones that can sometimes be 1 km in width if the sub seismogenic layer is viscous or viscoelastic then during interseismic periods a steady rate of deformation will be achieved after transients associated with viscoelastic relaxation have decayed away for sufficiently long earthquake cycles i find that in this situation the motion in the elastic layer is decoupled from that deep within the viscous layer and they may be very different from each other this implies that one can not use contemporary geodetic data to infer steady motion in a viscous sub seismogenic layer although it may be used to study viscoelastic relaxation

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

paleoseismology and global positioning system earthquake cycle effects and geodetic versus geologic fault slip rates in the eastern california shear zone published slip rates for the owens valley fault zone in eastern california based on geodetic data and elastic half space models 5 7 mm yr are faster than longer term geologic rates 2 3 mm yr we use global positioning system data spanning the central owens valley a more realistic rheological model with an elastic upper crust over a viscoelastic lower crust and upper mantle and paleoseismic data from adjacent faults to show that this difference could reflect earthquake cycle effects we estimate a long term rate 2 1 0 7 mm yr and earthquake recurrence interval 2750 350 1000 yr from the geodetic data both in agreement with independent geologic estimates

holocene paleoenvironmental reconstruction from deep ground temperatures a comparison with paleoclimate derived from the δ18o record in an ice core from the agassiz ice cap canadian arctic archipelago

mantle flow beneath a continental strike slip fault postseismic deformation after the 1999 hector mine earthquake two recent large earthquakes in the mojave desert california the magnitude 7 3 1992 landers and magnitude 7 1 1999 hector mine earthquakes have each been followed by elevated crustal strain rates over periods of months and years geodetic data collected after the hector mine earthquake exhibit a temporally decaying horizontal velocity field and a quadrant uplift pattern opposite to that expected for localized shear beneath the earthquake rupture we interpret the origin of this accelerated crustal deformation to be vigorous flow in the upper mantle in response to the stress changes generated by the earthquake our results suggest that transient flow in the upper mantle is a fundamental component of the earthquake cycle and that the lower crust is a coherent stress guide coupling the upper crust with the upper mantle

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

terrestrial heat flow density estimates for the jeanne d arc basin offshore eastern canada corrected bottom hole temperatures from 35 wells together with measured and assumed rock thermal conductivities are used to estimate linear geothermal gradients and effective thermal conductivities in the jeanne d arc basin in offshore eastern canada heat flow density values calculated for each well location indicate that heat flow density is slightly higher in the deeper northern part of the basin than in the southern part it appears that the heat flow density distribution is affected by fluid motion within the sediments and not by heat generation or basement topography dehydration is suggested as the mechanism that produces the fluid flow pattern that influences the heat flow density distribution in the basin and a simple fluid flow model of the jeanne d arc basin is presented

present day crustal deformation in southern california the effects of laterally homogeneous mantle electrical conductivity have been included in steady using an extensive set of precise geodetic measurements we have developed a detailed picture of present day deformation rates in southern california this large set of measurements amounting to nearly 2000 repeated distance measurements over the period 1973 to 1991 comes from the u s geological survey s geodolite trilateration program involving their combined anza joshua tree and salton networks building on previous results from these data we are able to present the deformation field as estimates of the rate of horizontal strain accumulation in small four station subnetworks of the overall 89 station network using this technique the spatial details of the 18 year average strain rate field can be determined by correlating these spatial details with the tectonics of the region we are able to understand better how deformation is partitioned across this highly complex margin between the pacific and north american tectonic plates some of the more interesting findings of this study are that 1 the vast majority of strain rate estimates show a pattern of nearly pure shear as would be expected in a transcurrent environment 2 the fastest accumulation of surface strain in southern california is along the san jacinto fault west of the salton sea not along the san andreas fault 3 strain accumulation rate along the length of the san jacinto fault increases toward the southeast as the fault enters the imperial valley 4 a large area near the southern end of the salton sea where the san andreas fault meets the brawley seismic zone is undergoing areal dilatation which is in part consistent with the formation of crust at a spreading center and 5 deformation at the transition zone between the san andreas fault and the eastern california shear zone also appears to be the result of crustal spreading

discrepancy between geological and geodetic deformation rates in the ventura basin space geodesy provides a new tool for measuring neotectonic deformation which when combined with geological and geophysical observations and models can be used to infer rates and styles of deformation in the ventnra basin region of southern california the geodetically measured convergence rates of 7 10 mm yr 1 ref 1 are significantly lower than the 20 25 mm yr 1 estimated from geological data2 3 here we investigate the possible implications of this discrepancy it might be for example that temporal variations cause the short and long term convergence rates to differ but if this were the case we would expect to observe the long term rate by extending the geodetic measurements over a broader region yet only 11 3 mm yr 1 of regional convergence is observed4 our preferred explanation of the discrepancy is that the geological models require revision and to this end we present two deformation models that satisfy both the geological and geodetic constraints our modelling suggests that the faults bounding the basin are locked at the surface but are slipping at depths below 2 5 km

new kinematic models for pacific north america motion from 3 ma to present i evidence for steady motion and biases in the nuvel 1a model we use velocities derived from 2 4 5 years of continuous gps observations at 21 sites on the pacific and north american plates along with a subset of the nuvel 1a data to examine the steadiness of pacific north america motion since 3 16 ma the transfer of baja california to the pacific plate and the magnitude of biases in the nuvel 1a estimate of pacific north america motion we find that pacific north america motion has remained steady since 3 16 ma but at rates significantly faster than predicted by nuvel 1a in the vicinity of baja california our gps derived model and recent seafloor spreading rates in the southern gulf of california both indicate that the nuvel 1a model underestimates pacific north america rates by 4 2 mm yr 1 steady pacific north america motion since 3 16 myr and increasing seafloor spreading rates since 3 58 myr in the gulf of california imply that pacific north america motion was partitioned between seafloor spreading in the gulf of california and decelerating slip along faults in or offshore from the baja peninsula

an accurate and efficient method for including the effects of topography in three dimensional elastic models of ground deformation with applications to radar interferometry topography has a large effect on the results predicted by elastic surface deformation models in regions of significant relief in some cases topography may have more influence on the predicted deformation field than do model source parameters we have developed an approximate analytical technique for including topographic effects that retains most of the computational simplicity of elastic half space models while providing an accurate representation of topographic effects we use a series expansion of the elastic half space solution with a small slope approximation yielding a set of higher order corrections the integrated effect of these corrections is evaluated using fourier methods we investigate the effectiveness of our method by comparing predicted results for a tilted triaxial ellipsoid with those predicted by finite element models the resulting displacements and displacement gradients are in good agreement with finite element results both for relatively smooth topography synthetically generated and for the greater relief in the vicinity of mount etna volcano we then compare the results of our method with those predicted by traditional elastic half space models using different reference elevations and with a previously proposed method of estimating topographic effects our new method provides a significantly better fit to the finite element results than do the other methods our method is able to accurately portray both the number and the horizontal pattern of fringes in a synthetic interferogram when compared with finite element results in particular the method accurately represents the broadening of fringes that is observed in regions of high relief as well as reproducing the location of the fringe center and the topographically induced deviation of the fringes from a regular pattern elastic half space models typically show a fringe center that is displaced with respect to the finite element results indicating that parameter inversions based on such a model would provide incorrect estimates of the horizontal source position the lack of topographically generated fringe distortions in elastic half space results would also likely lead to inaccuracies in the predicted magnitude and orientation of proposed deformation sources our new technique over comes these limitations and should be useful when evaluating either traditional geodetic results or the greater areal coverage provided by interferometric observations

relationships between pore pressure stresses and present day geodynamics in the scotian shelf offshore eastern canada a geomechanical study of the mesozoic and tertiary sediments beneath the scotian shelf shows that two major weak layers exist at depth the overpressured unit at 4000 m and the basal argo salt which is ductile and diapiric a consistent relationship is observed between the overpressures and the stress state in the basin first the smaller horizontal principal stress increases dramatically just above the onset of overpressuring and secondly borehole breakouts indicators of stress anisotropy decrease in abundance within the overpressured zone neither tectonic shear nor rapid burial can explain these observations however overpressuring by fluid generation will result in horizontal stress increase and eventually lead to an isotropic stress state compelling evidence is found for hydrocarbon generation being a key cause of overpressuring in the scotian shelf present day horizontal stress orientations in the sediments overlying the overpressured zone are aligned with contours of equal overpressure but not with the traces of tertiary listric normal faults or with the shelf edge this implies that contemporary stresses in these sediments are causally related to overpressuring the upward transmission of lithospheric plate movements and associated stress is unlikely because the ductile argo salt effectively detaches the sediments from basement instead the rocks of the scotian shelf are attempting to slide down the geomechanically weak overpressured zone in the directions indicated by the breakouts but they are prevented from doing so by the bowl shaped basement structure in the region

effects of rifting and subsidence on thermal evolution of sediments in canada s east coast basins regional maps of lithospheric deformation and thermal history have been derived for the eastern continental margin of canada subsidence associated with the rifting and cooling stages of rifted margin formation was calculated from gridded maps of sediment thickness and bathymetry along the labrador grand banks and nova scotian margins a two layer lithospheric extension model was used to compute the deformation and thermal evolution of each region deformation results show that the crust and lower lithosphere have generally stretched by different amounts and that either crustal or subcrustal lithospheric stretching dominates beneath the various basins thermal modelling results for the older nova scotian and grand banks margins show a strong correlation between thermal gradient crustal stretching and sediment thickness and the predicted thermal gradient pattern for the younger labrador margin correlates extremely well with predicted stretching of the still cooling subcrustal lithosphere predictions

new evidence on the slip rate renewal time and late holocene surface displacement southernmost san andreas fault mecca hills california we estimate a renewal time for large earthquakes on the southernmost san andreas fault saf of 260 100 years based on new paleoseismological data and a 34 millennia slip rate of 5 8 mm yr our mean recurrence interval 260 100 is longer and its variance is smaller than the 160 240 93 estimate for a m 7 earthquake used by the working group on california earthquake probabilities wgcep 1995 a smaller creep rate than on contiguous 12 km fault segments is explained by global positioning system data that reveals 2 4 mm yr of creep on the recently discovered witbaard fault that bypasses the 12 km long north shore strand of the saf geomorphic features near an archaeological site that cross the fault allow us to measure displacements of 155 25 cm based on right lateral gully offsets by the most recent earthquake e g 1690 an indian stone ring straddling the fault trace is currently offset 142 12 cm the ring lies on the 12 km long north shore segment of the saf that has accumulated a minimum of 30 mm of triggered slip and aseismic creep since 1969 contrasting slip rates of 23 35 mm yr near indio and 5 14 mm yr on the southernmost saf suggest that the coachella valley strand may be comprised of two distinct segments smaller long term strain accumulation along the southernmost segment probably reduces earthquake potential for that area

present day kinematics of the eastern california shear zone from a geodetically constrained block model we use global positioning system gps data from 1993 2000 to determine horizontal velocities of 65 stations in eastern california and western nevada between 35 and 37 n we relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km the velocity of the sierra nevada block with respect to nevada is 11 1 0 3 mm yr with slip partitioned across the death valley 2 8 0 5 mm yr panamint valley 2 5 0 8 mm yr and airport lake owens valley 5 3 0 7 4 6 0 5 mm yr faults the western mojave block rotates at 2 1 0 8 my clockwise with 3 7 0 7 mm yr of left lateral motion across the western garlock fault we infer 11 2 mm yr of right lateral motion across the mojave region of the eastern california shear zone

mantle heterogeneities and the scec reference three dimensional seismic velocity model version 3 we determine upper mantle seismic velocity heterogeneities below southern california from the inversion of teleseismic travel time residuals teleseismic p wave arrival times are obtained from three temporary passive experiments and southern california seismic network scsn stations producing good raypath coverage the inversion is performed using a damped least squares conjugate gradient method lsqr the inversion model element spacing is 20 km before the inversion the effects of crustal velocity heterogeneities represented by the southern california earthquake center scec seismic velocity model version 2 are removed from the teleseismic travel times the p wave inversion produces a variance reduction of 43 s wave velocities are determined from laboratory vp vs ratios the most prominent features imaged in the results are high p wave velocities 3 in the uppermost mantle beneath the northern los angeles basin and the previously reported tabular high velocity anomaly 3 to depths of 200 km beneath the transverse ranges crosscutting the san andreas fault we incorporate the upper mantle seismic velocity heterogeneities into the scec southern california reference seismic velocity model the prior accounting for the crustal velocity heterogeneity demonstrates the utility of the top down method of the scec seismic velocity model development

change of apparent segmentation of the san andreas fault around parkfield from space geodetic observations across multiple periods sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by coseismic and postseismic phases of stress release because the recurrence time of large earthquakes is often greater than the available span of space geodetic data it has been challenging to monitor the evolution of interseismic loading in its entire duration here we analyze large data sets of surface deformation at different key episodes around the cholame parkfield and creeping segments of the san andreas fault that show evidence of significant deceleration of fault slip during the interseismic period we compare the average fault slip rates before and after the 2004 mw6 parkfield earthquake in the 1986 2004 and 2006 2012 periods respectively avoiding 2 years of postseismic deformation after 2004 using a combination of gps data from the plate boundary observatory the southern california earthquake center crustal motion map and the bay area velocity unification networks and interferometric synthetic aperture radar from the advanced land observing satellite alos and envisat satellites we show that the area of coupling at the transition between the parkfield and cholame segments appears larger later in the interseismic period than it does earlier on while strong plate coupling is uniform across the parkfield and cholame segments in the 1986 2004 period creep occurs south of the 2004 epicenter after 2006 making segmentation of the san andreas fault south of parkfield more clearly apparent these observations indicate that analyses of surface deformation late in the earthquake cycle may overestimate the area of plate coupling a fault surface creeping much below plate rate may in some case be a region that does not promote earthquake nucleation but rather just be at a slower stage of its evolution our analysis also shows signs of large variation of slip velocity above and below plate rate in the creeping segment indicating that cycles of weakening and hardening can also be at play in dominantly aseismic areas

asymmetry in elastic properties and the evolution of large continental strike slip faults 1 we use geodetic studies to quantify several cases of significant asymmetry in interseismic and coseismic effects along large continental strike slip faults using simple two dimensional edge dislocation models we first show that asymmetric elastic loading characterizes the present main marmara fault a portion of the north anatolian fault along the northern margin of the sea of marmara the ratio of asymmetry there is about 10 this ratio is even larger about 30 along the northern sumatra fault near lake toba caldera we then examine two profiles near point reyes and point arena across the northern san andreas fault that have been previously proposed as affected by asymmetry both in interseismic and coseismic effects we show that an asymmetry ratio of 1 6 in interseismic loading exists near point arena with the southwest side of the fault being more rigid than the northeast one on the other hand we do not find significant asymmetry for the point reyes profile that was previously described as highly asymmetric we examine coseismic motion during the 1906 earthquake along the same two profiles ratios of 1 2 and 1 7 are found for the point arena and point reyes profiles respectively we discuss the possible causes of asymmetry contrasts in seismic velocity in the brittle portion suggest ratios generally not exceeding 2 5 for the dynamic rigidity in the upper brittle section larger ratios may involve other complex causes such as differences between static and dynamic rigidities contrasts in rheology in the deeper creeping sections and postseismic transients we conclude that asymmetry should be systematically included within the parameters to be inverted when dealing with the mechanics of large scale strike slip faults

timing of large earthquakes since a d 800 on the mission creek strand of the san andreas fault zone at thousand palms oasis near palm springs california paleoseismic investigations across the mission creek strand of the san andreas fault at thousand palms oasis indicate that four and probably five surface rupturing earthquakes occurred during the past 1200 years calendar age estimates for these earthquakes are based on a chronological model that incorporates radiocarbon dates from 18 in situ burn layers and stratigraphic ordering constraints these five earthquakes occurred in about a d 825 770 890 mean 95 range a d 982 840 1150 a d 1231 1170 1290 a d 1502 1450 1555 and after a date in the range of a d 1520 1680 the most recent surface rupturing earthquake at thousand palms is likely the same as the a d 1676 35 event at indio reported by sieh and williams 1990 each of the past five earthquakes recorded on the san andreas fault in the coachella valley strongly overlaps in time with an event at the wrightwood paleoseismic site about 120 km northwest of thousand palms oasis correlation of events between these two sites suggests that at least the southernmost 200 km of the san andreas fault zone may have ruptured in each earthquake the average repeat time for surface rupturing earthquakes on the san andreas fault in the coachella valley is 215 25 years whereas the elapsed time since the most recent event is 326 35 years this suggests the southernmost san andreas fault zone likely is very near failure the thousand palms oasis site is underlain by a series of six channels cut and filled since about a d 800 that cross the fault at high angles a channel margin about 900 years old is offset right laterally 2 0 0 5 m indicating a slip rate of 4 2 mm yr this slip rate is low relative to geodetic and other geologic slip rate estimates 26 2 mm yr and about 23 35 mm yr respectively on the southernmost san andreas fault zone possibly because 1 the site is located in a small step over in the fault trace and so the rate is not be representative of the mission creek fault 2 slip is partitioned northward from the san andreas fault and into the eastern california shear zone and or 3 slip is partitioned onto the banning strand of the san andreas fault zone

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

transient rheology of the uppermost mantle beneath the mojave desert california abstract geodetic data indicate that the m7 1 hector mine california earthquake was followed by a brief period a few weeks of rapid deformation preceding a prolonged phase of slower deformation we find that the signal contained in continuous and campaign global positioning system data for 2 5 years after the earthquake may be explained with a transient rheology quantitative modeling of these data with allowance for transient linear biviscous rheology in the lower crust and upper mantle demonstrates that transient rheology in the upper mantle is dominant its material properties being typified by two characteristic relaxation times 0 07 and 2 years the inferred mantle rheology is a jeffreys solid in which the transient and steady state shear moduli are equal consideration of a simpler viscoelastic model with a linear univiscous rheology 2 fewer parameters than a biviscous model shows that it consistently underpredicts the amplitude of the first 3 months signal and allowance for a biviscous rheology is significant at the 99 0 confidence level another alternative model deep postseismic afterslip beneath the coseismic rupture predicts a vertical velocity pattern opposite to the observed pattern at all time periods considered despite its plausibility the advocated biviscous rheology model is non unique and should be regarded as a viable alternative to the non linear mantle rheology model for governing postseismic flow beneath the mojave desert

estimates of terrestrial heat flow in northern chihuahua mexico based upon petroleum bottom hole temperatures bottom hole temperature data from deep petroleum tests are used in conjunction with estimated and measured thermal conductivity values to estimate heat flows at 12 sites in northern chihuahua the errors and uncertainties associated with these estimates and measurements are discussed from these heat flow estimates several geothermal regions are proposed which appear reasonable in terms of data statistics and the geologic environments in northeastern chihuahua an area of considerable tectonic activity with no cenozoic volcanic activity the heat flow mean is 73 mw m 2 westward in north central chihuahua the heat flow values become 85 mw m 2 farther westward in northwestern chihuahua heat flows 105 mw m 2 are estimated however there is only a modest probability that mean heat flow values for northwestern and north central chihuahua differ very high heat flows 250 mw m 2 and low heat flows 2 are not observed in north central or in northwestern chihuahua the deep temperature data may be removed from the effects of hydrothermal activity in sediments and along faults which can cause very high or low values it may also be possible that potential magma sources in the crust of the study area are not as young and hot as the sources associated with the volcanics along the rio grande rift in new mexico although heat flows of 105 mw m 2 do suggest crustal magmatic sources additional geophysical data will be needed to consider these possibilities

calculation of organic maturation levels for offshore eastern canada implications for general application of lopatin s method recorded maximum bottom hole temperatures may vary significantly from true formation temperatures because of the effects of drilling fluid circulation a theoretical temperature correction technique was applied to log heading data to compute 191 static temperatures for 64 wells on the scotian shelf a linear regression performed on 140 computed temperatures produced an average geothermal gradient of 2 66 c 100 m correlation coefficient 0 97 a geothermal gradient map constructed from the corrected data shows that areas of thicker sediment accumulation are marked by high geothermal gradients e g abenaki sable subbasins whereas areas of shallow basement coincide with low gradients e g lahave platform canso ridge it is proposed that the major control on the distribution of scotian shelf geothermal gradients is the thermal conductivity of the sediments radiogenic heat production within the sediments and subsurface fluid movement probably contribute to a lesser extent within the basins higher

thermal constraints on earthquake depths in california the high quality databases for california seismicity from the southern and northern california earthquake centers and an extensive compilation of thermal measurements in california are used to quantify the concept of temperature as a fundamental parameter for determining the thickness of the seismogenic zone the base of this zone below which only a small percentage of crustal earthquakes occur is termed the cutout depth and it is at or near the brittle ductile transition in the crust based on laboratory deformation studies this transition should be temperature strain rate lithology and stress state dependent in this study qualitative comparisons between the heat flow in california and earthquake hypocentral distributions show first that as expected earthquake cutout depths are inversely related to heat flow second the epicentral distributions tend to parallel thermal transitions this correlation is probably related to stress concentrations in these locations an ancillary observation is that the cooler western mojave block in southern california appears to be behaving similarly to the tibetan indenter block in asia as faults tend to go around it into areas of higher heat flow where the seismogenic zone is thinner and the crust may be weaker and it is pushed toward and under the southern cold sierra nevada block third to quantitatively compare the data sets temperatures for the seismicity cutout depth in california were calculated using the steady state 1d heat conduction equation with the variables based on published values for heat flow heat generation and thermal conductivity the analysis was restricted to profiles along which the heat flow and earthquake databases were constrained which allowed the error in the temperature calculation to be determined using monte carlo simulations the results show that two distinct ranges of temperatures dependent upon location describe the cutout depth d 99 of seismicity for california 450 50 c and 260 40 c the 450 50 c cutout depth temperature is most widespread geographically occurs within many provinces and is higher than the frequently referenced temperature of 300 50 c for the brittle ductile transition the lower temperature 260 c seems to be restricted to provinces where the heat flow is near or below 50 mw m 2 such as the mojave block and sierra nevada the differences in these cutout temperatures suggest that additional factors such as strain rate stress regime and or lithology may contribute to the seismicity cutout depth fourth along a profile with significant seismic activity and a 450 c cutout temperature the envelope for the maximum energy released by earthquakes falls at or below the 300 c isotherm detailed characterization of the heat flow and earthquake synergy in this manner furthers the understanding of the earthquake process and can aid in the estimation of the maximum depth of rupture for great earthquakes particularly in areas of low seismicity thus reducing uncertainties in hazard calculations manuscript received 26 february 2003

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

transient creep of a composite lower crust 2 a polymineralic basis for rapidly evolving postseismic deformation modes postseismic horizontal strain and displacement following the june 28 1992 landers california earthquake mw 7 3 is broad scale and cannot be explained solely by delayed afterslip located at the rupturing fault trace both the observed strain at pinon flat observatory pfo and observed global positioning system receiver velocities evolve rapidly after the landers big bear earthquake sequence the observed exponential decay of these motions with timescales of 4 34 days may reflect a soft creep rheology in the lower crust and brittle ductile transition zone or even within the seismogenic crust itself here a simple model of a two dimensional screw dislocation in a layered maxwell viscoelastic earth is employed in conjunction with a composite rheology to demonstrate that the short timescale transient response modes 4 34 days are consistent with the behavior of a biviscous lower crust the lowest viscosity of this system is derivable from laboratory experimental data on the long term creep of natural quarztites and the highest viscosity is consistent with isostasy related lower crustal flow in a continental extensional tectonic environment the model predicts significant stress relaxation at the base of the seismogenic crust near the base of the seismogenic zone and about 4 km away from the mainshock the rate of predicted relaxation is of the order of 0 01 mpa d 1 during the first 20 days of postseismic flow oblate spheroidal inclusions at 5 concentration levels that are both aligned and fairly flat in shape and that have a viscosity of 3 4 1015 pa s are consistent with both the amplitude and decay time of horizontal crustal strain observed at pfo after the landers mainshock it is speculated that the structures exposed in cross sections and in seismic reflection profiles of the lower crust that have mylonitic associations are in part the cause of such rapid postseismic evolution in southeastern california unmylonitized quartz rich rock at sufficiently elevated temperatures could also contribute to the rapid decay modes

relationship of geodetic velocities to velocities in the mantle 1 we examine the relationship of the velocities at the surface i e geodetic velocities to the velocities in the upper most mantle throughout a seismic cycle we model the rheology of the lower crust and mantle as linear viscoelastic and vary the relative viscosities between the lower crust and mantle as well as the distribution of viscosities and secular velocities in the mantle we find that the geodetic velocities are related to the transient velocities at depth the strength of the relationship decreases as the contrast between the lower crust and mantle viscosity increases in these models we find that the geodetic velocities are not related to the secular velocities at depth

paleo heat flow of eastern canada s passive margins abstract tectonic subsidence rates derived from several wells in the labrador sea and offshore nova scotia and newfoundland were used to estimate the paleo heat flow along the margins of eastern canada if tectonic subsidence is caused by the cooling of the lithosphere only the transient component of the heat flow i e the heat flow in excess of background heat flow can be estimated directly from subsidence data for the nova scotia and the labrador sea margins the analysis shows that the transient component of the heat flow decreased markedly from 28 56 mw m 2 immediately after rifting to a present value between 7 and 14 mw m 2 depending on boundary conditions the analysis shows a distinctive difference between the evolution of the labrador sea and that of the northeastern newfoundland margin where it is estimated that the transient component of the heat flow exceeded 100 mw m 2 after rifting and dropped rapidly to very low values the study suggests that the subsidence of the newfoundland margin was not caused by cooling only but required an additional mechanism such as lower crustal phase transformations or continuing extension after continental breakup with ductile deformation in the lower crust and upper mantle the estimated transient heat flow was used to calculate the average present surface heat flow in eastern canada s margins which is the sum of heat flow from the mantle crustal heat production and the transient cooling of the lithosphere the calculated heat flow compares well with heat flow density data obtained from bottom hole temperature measurements

a seismotectonic analysis of the anza seismic gap san jacinto fault zone southern california small earthquake epicenters near the anza seismic gap define a 20 km quiescent segment of fault bounded to the northwest and southeast by areas of relatively high seismicity recent moderate earthquakes on and near the san jacinto fault in the gap and their relatively depressed aftershock activity indicate that the fault is seismogenic and highly stressed but locked by some mechanism the locked nature of the fault may be due to relatively high compressive stress normal to the fault resulting from the convergent geometries of the local active discontinuous faults and the oblique orientation of the regional maximum compressive stress strain is not being relieved by aseismic fault creep a swarm of small earthquakes in the crustal block 13 km southwest of the anza gap beneath the cahuilla valley recently released stress in an area which was previously highly active before the 1918 m 6 8 and 1937 m l 6 0 earthquakes the occurrence of these periods of increased seismicity near cahuilla in the years immediately before the nearby closer than 35 km large earthquakes and the recent swarm suggest that the ground beneath cahuilla may be acting as a stress meter signaling the presence of high stresses before large local earthquakes the length of the quiescent fault segment suggests potential for about an m 6 5 earthquake if the entire segment ruptures at once

mechanics of graben formation in crustal rocks a finite element analysis small 1 10 km wide grabens are ubiquitous tectonic structures that have been observed on the surfaces of all the terrestrial planets and satellites in spite of their frequent occurrence there is no fundamental understanding of how they form other than that they are characteristic of extensional terranes this paper examines the mechanics of the initial stages of graben formation and demonstrates that the configuration of a pair of antithetically dipping normal faults a graben is the energetically most favorable fault configuration in elastic brittle rocks subjected to pure extension a corollary to this hypothesis is that the occurrence of synthetic normal faults is indicative of a stress field other than purely extensional or of nonhomogeneous characteristics of the rock the analysis proceeds by computing the stress field in the vicinity of a single initial normal fault using a two dimensional finite element model it is shown that slip on this fault substantially lowers the proximity to failure of the surrounding rocks except for two small regions one near the surface of the downthrown block and the other near the fault tip the region on the downthrown block is located a horizontal distance from the initial fault slightly less than the fault s depth the proximity to failure actually increases here and a secondary fault develops an antithetic secondary fault would link this region with the other failure zone near the fault tip to demonstrate the preference for antithetic secondary faults more rigorously we show that this fault configuration results in a smaller total strain energy than the synthetic configuration in addition a two layer model is used to show that the graben s width is only weakly dependent upon the presence of mechanically distinct layers in the crust both weak over strong and strong over weak configurations are investigated the depth of the initial fault and the thickness of the top layer are varied and the width of the resulting graben is evaluated by computing the distance between the initial fault and the region of highest proximity to failure near the surface this analysis indicates that the depth of the initial fault is the major factor controlling graben width

viscoelastic shear zone model of a strike slip earthquake cycle i examine the behavior of a two dimensional 2 d strike slip fault system embedded in a 1 d elastic layer schizosphere overlying a uniform viscoelastic half space plastosphere and within the boundaries of a finite width shear zone the viscoelastic coupling model of savage and prescott 1978 considers the viscoelastic response of this system in the absence of the shear zone boundaries to an earthquake occurring within the upper elastic layer steady slip beneath a prescribed depth and the superposition of the responses of multiple earthquakes with characteristic slip occurring at regular intervals so formulated the viscoelastic coupling model predicts that sufficiently long after initiation of the system 1 average fault parallel velocity at any point is the average slip rate of that side of the fault and 2 far field velocities equal the same constant rate because of the sensitivity to the mechanical properties of the schizosphere plastosphere system i e elastic layer thickness plastosphere viscosity this model has been used to infer such properties from measurements of interseismic velocity such inferences exploit the predicted behavior at a known time within the earthquake cycle by modifying the viscoelastic coupling model to satisfy the additional constraint that the absolute velocity at prescribed shear zone boundaries is constant i find that even though the time averaged behavior remains the same the spatiotemporal pattern of surface deformation particularly its temporal variation within an earthquake cycle is markedly different from that predicted by the conventional viscoelastic coupling model these differences are magnified as plastosphere viscosity is reduced or as the recurrence interval of periodic earthquakes is lengthened application to the interseismic velocity field along the mojave section of the san andreas fault suggests that the region behaves mechanically like a 600 km wide shear zone accommodating 50 mrn yr fault parallel motion distributed between the san andreas fault system and eastern california shear zone in the viscoelastic coupling model savage and prescott 1978 time dependent deformation around a strike slip fault zone is realized by loading subsequent rupture and relaxation of a fault present in a schizosphere elastic upper crust overlying a ductile plastosphere assuming a two dimensional 2 d geometry periodic rupture of the fault and identical slip interseismic deformation is obtained as the superposition of viscoelastic relaxation of the plastosphere summed over the infinity of past periodic earthquakes this model yields far field interseismic motions equal to 1 2 of the average slip rate v0 imposed on the fault thus even when no external mechanism is invoked to load the fault i e when the locked portion of the fault penetrates the entire schizosphere the model satisfies the expectation of rigid plate like behavior in the far field in addition when periodic coseismic offsets are factored in the model predicts that the time averaged fault parallel velocity of each point is vol2 depending on location

reservoir induced deformation and continental rheology in vicinity of lake mead nevada lake mead is a large reservoir in nevada formed by the construction of the 221 m high hoover dam in the black canyon of the colorado river the lake encompasses an area of 635 km2 and the total volume of the reservoir is 35 5 km3 filling started in february 1935 on the basis of a first order leveling in 1935 several levelings were carried out to measure the deformation induced by the load of the reservoir subsidence in the central parts of the lake relative to the first leveling was around 120 mm 1941 218 mm 1950 and 200 mm 1963 the subsidence pattern clearly shows relaxation of the underlying basement due to the water load of the lake which ceased after 1950 modeling of the relaxation process by means of layered viscoelastic compressible flat earth models with a detailed representation of the spatial and temporal distribution of the water load shows that the thickness of the elastic crust underneath lake mead is 30 3 km the data are also consistent with a 10 km thick elastic upper crust and a 20 km thick viscoelastic lower crust with 1020 pa s as a lower bound for its viscosity the subcrust has an average viscosity of 1018 0 2 pa s a surprisingly low value the leveling data constrain the viscosity profile down to 200 km depth

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

temperature and the seismic aseismic transition observations from the 1992 landers earthquake an important constraint on the size and destructive potential of earthquakes is the depth extent of rupture laboratory studies of the transition from unstable to stable sliding along with observed relationships between surface heat flow and the thickness of the seismogenic crust provide strong evidence for the significance of temperature in determining the maximum nucleation depth of large earthquakes the june 28 1992 mw 7 3 landers earthquake ruptured fault segments within 20 km of 11 pre existing heat flow measurements and shallowing of the base of aftershock seismicity along strike correlates with an increase in heat flow crustal geotherms estimated from these measurements place the base of seismicity along the 250 c isotherm this temperature is consistent with predictions from laboratory studies of the frictional stability of westerly granite but estimated temperatures for the seismic aseismic transition along other faults within the san andreas fault system are in the range of 350 to 400 c variations in country rock and fault gouge composition together with higher slip rates may account for this difference although part of the landers seismogenic crust might remain unruptured

chapter 5 extension and contraction within an evolving divergent strike slip fault complex the san andreas and san jacinto fault zones at their convergence in southern california

seismic tomography of the southern california plate boundary region from noise based rayleigh and love waves we use cross correlations of ambient seismic noise between pairs of 158 broadband and short period sensors to investigate velocity structure over the top 5 10 km of the crust in the southern california plate boundary region around the san jacinto fault zone sjfz from the 9 component correlation tensors associated with all station pairs we derive dispersion curves of rayleigh and love wave group velocities the dispersion results are inverted first for rayleigh and love waves group velocity maps on a 1 5 1 5 km2 grid that includes portions of the sjfz the san andreas fault saf and the elsinore fault we then invert these maps to 3d shear wave velocities in the top 7 km of the crust the distributions of the rayleigh and love group velocities exhibit 2 azimuthal anisotropy with fast directions parallel to the main faults and rotations in complex areas the reconstructed 3d shear velocity model reveals complex shallow structures correlated with the main geological units and strong velocity contrasts across various fault sections along with low velocity damage zones and basins the sjfz is marked by a clear velocity contrast with higher v s values on the ne block for the section se of the san jacinto basin and a reversed contrast across the section between the san jacinto basin and the saf velocity contrasts are also observed along the southern parts on the saf and the elsinore fault with a faster southwest block in both cases the region around the salton trough is associated with a significant low velocity zone strong velocity reductions following flower shape with depth are observed extensively around both the sjfz and the saf and are especially prominent in areas of geometrical complexity in particular the area between the sjfz and the saf is associated with an extensive low velocity zone correlated with diffuse seismicity at depth and a similar pattern including correlation with deep diffuse seismicity is observed on a smaller scale in the trifurcation area of the sjfz these results augment local earthquake tomography images that have low resolution in the top few km of the crust and provide important constraints for studies concerned with behavior of earthquake ruptures generation of rock damage and seismic shaking hazard in the region

evidence of power law flow in the mojave desert mantle studies of the earth s response to large earthquakes can be viewed as large rock deformation experiments in which sudden stress changes induce viscous flow in the lower crust and upper mantle that lead to observable postseismic surface deformation laboratory experiments suggest that viscous flow of deforming hot lithospheric rocks is characterized by a power law in which strain rate is proportional to stress raised to a power n refs 2 3 most geodynamic models of flow in the lower crust and upper mantle however resort to newtonian linear stress strain rate relations here we show that a power law model of viscous flow in the mantle with n 3 5 successfully explains the spatial and temporal evolution of transient surface deformation following the 1992 landers and 1999 hector mine earthquakes in southern california a power law rheology implies that viscosity varies spatially with stress causing localization of strain and varies temporally as stress evolves rendering newtonian models untenable our findings are consistent with laboratory derived flow law parameters for hot and wet olivine the most abundant mineral in the upper mantle and support the contention that at least beneath the mojave desert the upper mantle is weaker than the lower crust

measured radiogenic heat production in sediments from continental margin of eastern north america implications for petroleum generation measurements of radiogenic heat production are presented for most of the major sedimentary formations beneath the rifted continental margin off nova scotia canada the measurements were made on 32 samples from 14 deep exploratory wells drilled in the area the results show that heat production ranges from about 1 8 to 0 3 w m 3 and varies with lithology the effect of this radiogenic heat production is to increase the heat flow and the temperatures within the sediments by up to 15 and 30 6 f 17 c respectively these temperature changes will increase the rate of organic maturation so that for example oil generation should occur 10 to 30 ma earlier in jurassic sediments than if those sediments exhibited no heat production it is noted ho ever that other thermal properties of the sediments must be studied before predictions of organic maturation and the timing of oil generation can be considered reliable the results presented here show that radiogenic heat production in sediments is an important parameter in making reliable predictions of their thermal maturity and thus should be included in future studies of thermal models for sedimentary basins

nonlinear strain buildup and the earthquake cycle on the san andreas fault two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault accompanied by a progressive broadening of the zone of deformation adjacent to it in the thin lithosphere model transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere for an earth model with a thick elastic lithosphere plate thickness depth of seismic slip transient motions are due to postearthquake aseisrnic slip below the coseismic fault plane data from the san andreas fault indicate a long term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle observations support a cycle long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar if so the usually lower strain rates and broader deformation zone currently observed on the southern san andreas represent a later evolutionary stage of the northern locked section where a great earthquake is a more recent occurrence although the data allow some extreme models to be discarded no sufficiently strong constraints exist to decide between the thin and thick lithosphere models regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause significant departures from recurrence estimates based on linear strain accumulation and the time predictable model

heat flow in the utah wyoming thrust belt from analysis of bottom hole temperature data measured in oil and gas wells bottom hole temperature bht data from oil and gas wells represent a large albeit low quality data base for heat flow determinations a method for analyzing bht data sets that directly addresses the problem of noise in the data is presented and illustrated by application to 303 bhts from the anschutz ranch ar cave creek cc and anschutz ranch east are oil gas fields in the utah wyoming thrust belt located in the middle rocky mountain physiographic province of the western united states correction of raw bht data by means of a horner plot yields 81 corrected bhts an additional 90 bhts not suitable for a horner correction are corrected by means of a new bht correction which may be applied to any single bht for which a depth and time of measurement are known the average geothermal gradient at both ar cc and are is found to be 23 c km although an average gradient analysis fails to explain scatter in the data analysis of corrected bhts through inversion of a layered earth model yields estimates of formation thermal gradients and temperature fields at ar cc and are that are stable and unique with an average precision of 2 to 3 c thermal conductivity measurements were made on 360 drill cutting samples representing 14 thrust belt formations in situ conductivity is estimated using porosity from calibrated well logs heat flow is estimated by comparing temperature calculated by a two dimensional finite element model with temperature estimated from analysis of bht data analysis of bht data from the ar cc area yields an estimated regional heat flow of 60 mw m2 8 mw m2 a similar analysis at are results in an estimate of 58 mw m2 8 mw m2 these estimates are close to values determined for the wyoming basin and the central colorado plateau and imply that a thermal transition from the middle rocky mountains to elevated heat flow characteristic of the basin and range province 80 to 90 mw m2 must take place within 50 km

seasonal temperature variation below the thermocline detected by argo floats 1 strong seasonal temperature variation below the thermocline is detected by argo profiling floats the variation is associated with a long baroclinic rossby wave the results of this study show that seasonal signals can be captured at 1000 2000 dbar not only in basin boundary regions or deep convection regions but also in the interior ocean a clear westward propagation signal is observed the phase speed is of the same order as a theoretically derived speed below the thermocline the first mode of empirical orthogonal function analysis of potential density variations in the strong signal region shows a clear seasonal variation even in the middle layer the amplitude of the temperature anomaly is 0 05 0 12 c at 1200 dbar which is equivalent to the annual standard deviation from the woa01 these results are obtained using the dense spatial and temporal distributions provided by the argo observations

seismic cycle and rheological effects on estimation of present day slip rates for the agua blanca and san miguel vallecitos faults northern baja california mexico 1 geodesy can be used to infer long term fault slip rates assuming a model for crust and upper mantle rheology we examine the sensitivity of fault slip rate estimates to assumed rheology for the agua blanca and san miguel vallecitos faults in northern baja california mexico part of the pacific north america plate boundary zone the agua blanca fault is seismically quiet but offset alluvial fans indicate young activity current seismicity is confined to the nearby san miguel vallecitos fault a small offset fault better aligned with plate motion gps measurements between 1993 and 1998 suggest that both faults are active with a combined slip rate of 4 8 mm yr 1 regardless of rheological model however slip rate estimates for the individual faults are sensitive to assumed rheology elastic half space models yield 2 3 mm yr 1 for the agua blanca fault and somewhat faster rates for the san miguel vallecitos fault 2 4 mm yr 1 with uncertainties of about 1 mm yr 1 models incorporating viscoelastic rheology and seismic cycle effects suggest a faster slip rate for the agua blanca fault 6 1 mm yr 1 and a slower rate for the san miguel vallecitos fault 1 1 mm yr 1 in better agreement with geological data but these rates are sensitive to assumed rheology numerical simulations with a finite element model suggest that for similar rheological and friction conditions slip on the san miguel vallecitos fault should be favored due to better alignment with plate motion long term faulting processes in the larger offset agua blanca fault may have lowered slip resistance allowing accommodation of motion despite misalignment with plate motion index terms 1206 geodesy and gravity crustal movements interplate 8155 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 8107 tectonophysics continental neotectonics keywords fault slip rates and the seismic cycle northern baja california

kinematics of the pacific north america plate boundary zone northern california we measured motions of 54 sites in an east west transect across northern california at 38 40 north by global positioning system gps observations over a 4 year we estimate the total slip rate on the san andreas fault system to be 39 6 0 6 1 5 mm yr 68 6 upper and lower confidence intervals from a nonlinear inversion are indicated by superscripts and subscripts slip rates on the individual faults are determined less precisely due to the high correlations between the estimated parameters our best fitting model fits the fault parallel velocities with a mean square error of 1 04 and the following estimated fault slip rates all in mm yr san andreas 17 4 3 1 2 5 ma acama 13 9 2 8 4 1 and bartlett springs 8 2 1 9 2 1 the data are fit best by models in which the san andreas fault is locked to 14 9 7 1 12 5 km the ma acama fault locked to 13 4 4 8 7 4 km except for shallow creep in the upper 5 km and the bartlett springs fault creeping at all depths the ma acama fault most likely poses a significant seismic hazard as it has a high slip rate and has accumulated a slip deficit large enough to generate a magnitude 7 earthquake we find little evidence for contraction across coast ranges except at western edge of great valley where 1 3 mm yr of shortening is permitted by the data no strain is observed within the great valley or sierra nevada except that associated with right lateral strike slip on the san andreas fault system this is consistent with models of the pacific north america plate boundary zone in which the relative plate motion is partitioned into two domains one strike slip and one dominantly extensional separated by the elastically deforming sierra nevada great valley block

holocene slip rate of the wasatch fault zone utah from geodetic data earthquake cycle effects 1 gps data define a broad zone of present day deformation in the eastern basin and range province western us using finite element models with elastic upper crust over viscoelastic lower crust upper mantle and incorporating earthquake cycle effects we show that these data are consistent with a model whereby most contemporary fault slip is focused on the wasatch fault zone modeled rates of horizontal extension are 3 0 4 5 mm yr in agreement with holocene geologic data the models are non unique in part because much of the wasatch fault is in the late stages of the earthquake cycle when surface velocity gradients across the fault are low

depth time correction of petroleum bottom hole temperatures in the po plain italy we have analyzed a wide set of time temperature data from petroleum wells in two areas of the po plain italy and propose empirical temperature corrections for mud circulation formation thermal parameters and the temperature dependence of thermal conductivity are taken into account analyses show that formation equilibrium temperatures computed with the horner method compare well with those obtained by the cooper and jones method which gives on average temperatures lower by only 2 c for shut in times less than 10 hours the corrected temperatures compared with temperatures measured during drillstem tests show that the proposed corrections are relatively accurate the two data sets give coherent results and the inferred average geothermal gradient is 21 5 mk m in the apenninic buried arc area and 25 2 mk m in the south piedmont basin pedealpine homocline area the horner slope data as a function of depth are then fitted with a second order polynomial and depthtime correction equations are calibrated for the two areas finally we propose an empirical function for the estimate of the mud circulation time which is often unavailable

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

deformation across the western united states a local estimate of pacific north america transform deformation we obtain a locally based estimate of pacific north america relative motion and an uncertainty in this estimate by integrating deformation rate along three different paths leading west across southwestern north america from east of the rio grande rift to near the continental escarpment data are primarily quaternary geologic slip rate estimates and resulting deformation determinations therefore are instantaneous in a geologic sense but long term with respect to earthquake cycles we deduce a rate of motion of the pacific plate relative to north america that is 48 2 mm yr a rate indistinguishable from that predicted by the global kinematic models rm2 and nuvel 1 however we obtain an orientation that is 5 9 counterclockwise of these models a more westerly motion of the pacific plate with respect to north america is calculated from all three paths the relatively westerly motion of the pacific plate is accommodated by deformation in the north american continent that includes slip on relatively counterclockwise oriented strike slip faults including the san andreas fault which is especially relevant in and south of the transverse ranges and a margin normal component of net extension across the continent which is especially relevant north of the transverse ranges deformation of the sw united states occurs in regionally coherent domains within which the style of deformation is approximately uniform in the vicinity of the transverse ranges two important shear systems splay from the san andreas fault the eastern california shear zone trending nnw from the eastern transverse ranges and the trans peninsular faults trending sse from the western and central transverse ranges within the transverse ranges the right lateral san andreas fault steps left seemingly requiring large amounts of convergence there however most of this convergence is avoided through a funneling flow of the crust toward the western transverse ranges and into the relatively narrow central california coast ranges and the northern motion of the mojave the former process involves an alternation of rotation direction from counterclockwise in and south of the central transverse ranges to clockwise in the western transverse ranges

latest pleistocene and holocene slip rate for the san bernardino strand of the san andreas fault plunge creek southern california implications for strain partitioning within the southern san andreas fault system for the last 35 k y an alluvial succession on the northeast side of the san bernardino strand of the san andreas fault includes distinctive aggradational and degradational features that can be matched with correlative features on the southwest side of the fault key among these are 1 a terrace riser on the northeast side of the fault that correlates with an offset channel wall on the southwest side of the fault and forms a basis for slip estimates for the period ca 35 ka to the present and 2 a small alluvial fan on the southwest side of the fault that has been matched with its most likely source gullies on the northeast side of the fault and forms a basis for slip estimates for the last 10 5 k y slip rate estimates for these two separate intervals are nearly identical the rate for the older feature is most likely between 8 3 and 14 5 mm yr with a 95 confidence interval of 7 0 15 7 mm yr the rate for the younger feature is most likely between 6 8 and 16 3 mm yr with a 95 confidence interval of 6 3 18 5 mm yr these rates are only half the previously published slip rate for the san andreas fault 35 km to the northwest in cajon pass a rate that traditionally is extrapolated southeastward along the san bernardino section of the fault results from plunge creek suggest that about half of the 25 mm yr rate at cajon pass transfers southeastward to the san jacinto fault as proposed by other workers on the basis of regional geologic relations these results indicate that the discrepancy between latest quaternary slip rates and present day rates of strain accumulation across the san bernardino section of the san andreas fault from geodesy can be largely explained by slip transfer between faults leading to spatial variation in rate along the san andreas fault nonetheless the latest pleistocene and holocene slip rate at plunge creek is still somewhat faster than rates inferred for the san bernardino section of the san andreas fault based on elastic block modeling of geodetic data and may be more appropriate than those rates for hazard estimation

tectonic geomorphology of the san andreas fault zone in the southern indio hills coachella valley california geomorphic investigation of the san andreas fault zone in the indio hills indicates many tectonically produced landforms including beheaded streams right lateral deflected and offset streams sags shutter ridges pressure ridges and fault scarps near biskra palms an alluvial fan pediment complex has an apparent cumulative offset of about 0 7 km along the mission creek fault zone north branch san andreas fault many of the tectonic landforms as well as the fracture pattern that has developed during the pleistocene are explainable by simple shear or uplift associated with a small left bend in the main trace of the mission creek fault the ratio of vertical to horizontal displacement in the vicinity of the bend is about 0 04 exposed in pushawalla canyon 5 km northwest of the alluvial fan pediment complex are 1 a sequence of stream terraces 2 folded plio pleistocene fanglomerates and 3 an example of stream capture following a right lateral deflection or offset of several hundred metres a left step of the mission creek fault in pushawalla canyon is a probably cause of folds and sporadic uplift that produced the stream terraces possible cause of recent stream capture are 1 juxtaposition of pushawalla canyon with a relict canyon moving northwestward along the mission creek fault or 2 right lateral deflection or offset of pushawalla canyon along the fault with simultaneous headward erosion of a shorter steep stream flowing toward the coachella valley estimation of a slip rate and identification of paleoseismicity for the san andreas fault in the indio hills is difficult however degree of topographic dissection formation and preservation of desert pavement and relative soil profile development suggest that the age of the offset fan may be as old as 70 000 yr but that most likely it is on the order of 20 000 to 30 000 yr these age estimates for the offset fan indicate a minimum slip rate for the san andreas fault of 10 to 35 mm yr with about 23 to 35 mm yr the most likely the pattern of observed offset drainages is complex but suggests that during the past few thousand years creep events or moderately large earthquakes have periodically produced several metres of right lateral displacement

interaction of the san jacinto and san andreas fault zones southern california triggered earthquake migration and coupled recurrence intervals two lines of evidence suggest that large earthquakes that occur on either the san jacinto fault zone sjfz or the san andreas fault zone safz may be triggered by large earthquakes that occur on the other first the great 1857 fort tejon earthquake in the safz seems to have triggered a progressive sequence of earthquakes in the sjfz these earthquakes occurred at times and locations that are consistent with triggering by a strain pulse that propagated southeastward at a rate of 1 7 kilometers per year along the sjfz after the 1857 earthquake second the similarity in average recurrence intervals in the sjfz about 150 years and in the mojave segment of the safz 132 years suggests that large earthquakes in the northern sjfz may stimulate the relatively frequent major earthquakes on the mojave segment analysis of historic earthquake occurrence in the sjfz suggests little likelihood of extended quiescence between earthquake sequences

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

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

geothermal gradients and heat flow in the beaufort mackenzie basin arctic canada thermal gradients have been calculated and heat flow estimates made for 34 petroleum exploration wells along four regional profiles crossing the mesozoic cenozoic beaufort mackenzie basin of northern canada the geothermal gradients vary from 22 mkm 1 to 44 mkm 1 four sets of possible thermal conductivity values were used to calculate a range of heat flow values for each well generally low heat flow is observed in wells within the deeper portions of the basin and higher heat flow values occur in wells along the aklavik arch complex which forms the southeastern margin of the basin

reconciling rapid strain accumulation with deep seismogenic fault planes in the ventura basin california global positioning system measurements across the east central ventura basin transverse ranges southern california before the nearby 1994 northridge earthquake show high strain rates interpreting this rapid strain accumulation using the usual model of deep slip on a dislocation in a uniform elastic half space requires slip to extend to within 5 km of the surface such shallow slip is difficult to reconcile with the substantial coseismic displacement at depths from 7 to 19 km during the northridge earthquake here we model the displacement and velocity fields throughout the earthquake cycle using a two dimensional finite element model with a viscoelastic rheology displacements are driven by far field and basal velocity boundary conditions and by imposed periodic earthquakes on the thrust faults bounding the basin the thrust faults rupture through an elastic upper crust to a depth of 15 km after a transient stage during which stresses and strains build up to quasi equilibrium values the behavior of the model becomes periodic the sum of the coseismic displacement divided by the repeat interval plus the average interseismic velocity is equal to the geologic velocity the temporal variation in surface velocity depends mainly on the elsasser relaxation time proportional to the product of the maxwell time of the lower crust and the ratio of the thicknesses of the entire crust and viscoelastic lower crust we are able to match the observed high strain rate only if we include the observed variations in elastic modulus associated with the deep basin sediments the model reconciles geologic geodetic and seismological observations of deformation there are trade offs among the far field convergence rate the elsasser time the earthquake repeat time and the time into the earthquake cycle acceptable convergence rates range from 8 mm yr for a relaxation time of the lower crust of 300 years to 12 mm yr for a 30 year relaxation time