the characteristics of movable fluid in the triassic lacustrine tight oil reservoir a case study of the chang 7 member of xin anbian block ordos basin china abstract the micropore throat structure of a tight oil reservoir is complex and its movable fluid distribution differs from that of a conventional reservoir by using nuclear magnetic resonance nmr and centrifugation the movable fluid distribution in the chang 7 tight reservoir in the xin anbian block of the ordos basin was quantitatively evaluated combined with the results of the physical property and high pressure mercury intrusion experiments the effects of the porosity permeability pore size distribution and micropore throat structure on the movable fluid distribution in the chang 7 tight reservoir were analyzed the nmr results show that the t2 spectral morphology of the chang 7 tight oil reservoir in the xin anbian block can be characterized by three main patterns with different amplitudes of front and post peaks the front peak corresponds to the scale of small pores and the post peak corresponds to the scale of large pores based on the three t2 spectrum patterns the chang 7 tight reservoir can be divided into three types type 1 reservoir with more small pores and fewer large pores type 2 reservoir with similar amounts of small and large pores and type 3 reservoir with fewer small pores and more large pores thus the characteristics of these three types of reservoirs can be determined the movable fluid parameters were calculated by nmr and centrifugation the movable fluid saturation of the type 1 reservoir is low with an average of 20 38 and the average movable fluid porosity is 1 47 the type 2 and type 3 reservoirs have higher movable fluid contents of 40 79 and 47 04 respectively the average movable fluid porosities of the type 2 and type 3 reservoirs are 3 37 and 3 48 respectively the greater number of small pores and smaller number of large pores in the type 1 reservoir result in weak correlations of the movable fluid with the physical properties and pore throat structure parameters the movable fluid saturation is negatively correlated with the maximum pore radius mainstream throat radius and maximum mercury saturation and is strongly positively correlated only with the porosity of the large pores as the number of large pores increases the movable fluid saturation strongly correlates with the property parameters pore size distribution and pore throat structure parameters in the type 2 and type 3 reservoirs the movable fluid saturations are positively affected by the maximum pore radius median radius mainstream throat radius and effective porosity but are strongly negatively correlated only with the radius mean value these results indicate that the fluid mobility of these two types of reservoirs can be promoted by the pore throat system to obtain favorable seepage characteristics

coseismic and postseismic slip from the 2003 san simeon earthquake and their effects on backthrust slip and the 2004 parkfield earthquake 1 the 2003 m6 5 san simeon earthquake occurred less than a year before and 50 km west of the long awaited parkfield earthquake of 2004 aftershocks of the san simeon event occurred not only on the presumptive rupture plane but also delineated subconjugate structures to the east backthrusts insar data show a complex pattern of deformation during the postseismic time interval and suggest that shallow postseismic slip may have occurred on the backthrust structures in this paper we present a model inversion for slip during and after the earthquake from four interferograms and gps data we find that the data are well fit when coseismic slip is allowed on two planes the main rupture plane and a backthrust structure to the south the backthrust structure accommodates slip amounting to about one third of the coseismic moment release shallow postseismic slip also occurred on the main rupture plane updip from the coseismic slip and on the southern backthrust postseismic slip on the more northern backthrust structure is not well constrained and the data is fit nearly as well without including it the areas of postseismic slip on the backthrusts correspond well with areas that experienced unclamping and little slip is found in regions of clamping no value for the coefficient of friction below 1 0 results in a coulomb failure stress field that matches the aseismic slip distributions better than the normal stress alone we also investigate whether static stress changes from the san simeon earthquake acted to encourage right lateral strike slip on the parkfield segment of the san andreas fault we find that the san simeon earthquake s rupture planes were oriented in such a way that the maximum increase in coulomb failure stress on the san andreas fault occurred on the parkfield segment the 2004 parkfield earthquake differed from its expected behavior by nucleating in the southern portion of the parkfield segment an area that experienced increased shear stress of 0 1 0 14 bars from coseismic slip in the san simeon earthquake postseismic slip from san simeon further loaded the southern portion of the parkfield segment preferentially over the northern portion though the size of the stress changes was small 0 03 0 04 bars

postseismic relaxation following the 1992 m7 3 landers and 1999 m7 1 hector mine earthquakes southern california 1 postseismic relaxation measured postseismic deformation less the deformation that would have occurred at the preseismic rate has been monitored at the same 10 monuments over 6 years following both the 1992 landers and the 1999 hector mine earthquakes for both earthquakes the displacement components of the observed relaxation are well described by i if1 t where i and i are constants peculiar to each component at each monument t is the time after the earthquake and f1 t is a temporal function common to all components and all monuments for that earthquake the temporal function f1 t can be approximated by bt c loge 1 t where 38 7 15 2 days and 25 6 7 7 days for the landers and hector mine relaxations respectively because the estimated values of do not differ significantly the transient term loge 1 t in the temporal function may be the same for both earthquakes the asymptotic t relaxation rates ib are only a few mm a and do not appear to be significantly different following the two earthquakes the asymptotic deformation rates appear to be slightly greater than the preseismic deformation rates but the preseismic rates were not measured directly thus the deformations of the landers array measured over the first 5 6 years following the landers earthquake and over the first 6 4 years following the hector mine earthquake are generally consistent with a simple model in which the transient postearthquake relaxation depends upon time as loge 1 t with 28 5 days and the asymptotic postseismic speeds of the monuments exceed the preseismic speeds by at most only a few millimeters per annum

on the effects of thermally weakened ductile shear zones on postseismic deformation 1 we present three dimensional 3 d numerical models of postseismic deformation following repeated earthquakes on a vertical strike slip fault our models use linear maxwell burgers and temperature dependent power law rheology for the lower crust and upper mantle we consider effects of viscous shear zones that result from thermomechanical coupling and investigate potential kinematic similarities between viscoelastic models incorporating shear zones and elastic models incorporating rate strengthening friction on a deep aseismic fault root we find that the thermally activated shear zones have little effect on postseismic relaxation in particular the presence of shear zones does not change the polarity of vertical displacements in cases of rheologies that are able to generate robust postseismic transients stronger rheologies can give rise to an opposite polarity of vertical displacements but the amplitude of the predicted transient deformation is generally negligible we conclude that additional to thermomechanical coupling mechanisms of strain localization are required for a viscoelastic model to produce a vertical deformation pattern similar to that due to afterslip on a deep extension of a fault we also investigate the discriminating power of models incorporating burgers and power law rheology these rheologies were proposed to explain postseismic transients following large m7 earthquakes in the mojave desert eastern california numerical simulations indicate that it may be difficult to distinguish between these rheologies even with high quality geodetic observations for observation periods less than a decade longer observations however may potentially allow discrimination between the competing models as illustrated by the model comparisons with available gps and interferometric synthetic aperture radar data

steady state laboratory flow laws alone fail to explain postseismic observations abstract we test whether laboratory derived steady state flow laws for wet olivine can be used to explain postseismic relaxation in the upper mantle following the 1999 hector mine earthquake this is accomplished using rate changes in gps observed displacement time series at far field stations as constraints on the parameters associated with laboratory derived temperature and stress dependent flow laws for diffusion and dislocation creep of olivine we primarily concentrate on the influences of temperature grain size and background strain rate to explain observed fast early displacement rates that slow rapidly in the 7 years of postseismic observations we find that a reasonable fit to the observed time series cannot be achieved by any combination of flow law parameters and plausible assumptions for the tectonic environment of the mantle beneath the mojave desert we conclude that postseismic relaxation within the mantle following the hector mine earthquake likely includes an initial transient weakening phase suggesting that steady state flow laws by themselves are insufficient to characterize the flow of mantle rocks when stress conditions evolve

introduction to unconventional petroleum systems ben law is a consultant and sole proprietor of pangea hydrocarbon exploration llc his research interests include basin centered gas and coalbed methane systems prior to his consulting position he was a member and chief of the u s geological survey western tight gas sand project and regional coordinator of south asia for the u s geological survey world energy project he received b s and m s degrees from san diego state university california john b curtis is associate professor and director petroleum exploration and production center potential gas agency at the colorado school of mines he is an associate editor for the aapg bulletin and the mountain geologist as director of the potential gas agency he works with a team of 145 geologists geophysicists and petroleum engineers in their biennial assessment of remaining united states natural gas resources the collection of articles included in this theme issue of the aapg bulletin originated in the aapg

stress dependent power law flow in the upper mantle following the 2002 denali alaska earthquake abstract far field continuous global positioning system gps time series data following the 2002 m7 9 denali alaska earthquake imply that mantle viscoelastic rheology is stress dependent a linear viscous mantle cannot explain fast early displacement rates at the surface that rapidly decay with time whereas a power law rheology where strain rate is proportional to stress raised to the power of 3 5 0 5 provides decay rates and spatial patterns in agreement with observations this is consistent with laboratory measurements for hot wet olivine implying a hydrated mantle and a relatively thin 60 km thick lithosphere beneath south central alaska these results suggest that the viscous strength of the lithosphere varies both spatially and temporally and that effective viscosities inferred from different loading events or observational time periods can differ by up to several orders of magnitude thus the very conditions that enable the inference of rheologic strength transient loading and unloading events significantly alter the effective viscosity

petrophysical characterization of oil bearing shales by low field nuclear magnetic resonance nmr abstract shales are important components of petroleum systems and it is necessary to reveal their petrophysical properties as reservoirs low field nuclear magnetic resonance nmr has proven to be a non invasive and effective technique for petrophysical characterization of sandstone carbonate and coal however little study has been done using this technique to systematically investigate the petrophysical properties of oil bearing shales which is essential for characterizing shale oil reservoirs in this study two sets of nmr measurements were performed to reveal the porosity permeability movable fluid volume and pore size distribution psd of oil bearing shales the results show the following 1 the nmr t2 spectrum strongly relates to the content of quartz and the amount of dissolution pores within shale three t2 spectrum peaks were identified by the relaxation times at 0 03 1 ms 1 20 ms and 20 ms corresponding to micropores 1000 nm respectively 2 by combining nmr with centrifugation both nmr porosity and movable porosity mp were calculated nmr porosity is well consistent with helium porosity and the mp values strongly relate to the development of mesopores in shales 3 based on the t2 spectrum an effective permeability model was proposed which can conveniently estimate the permeability of shales moreover two classical permeability models coates and sdr were also used to estimate shale permeability and the permeability values determined by these models agrees well with helium permeability 4 in combination with sem images analyses an nmr based psd was constructed that agrees well with the psd determined by sem the results demonstrate the applicability of nmr relaxation in a systematic investigation of the petrophysical properties of shales which has potential applications for geophysical logging in shale oil exploration

coseismic displacements 1992 landers california earthquake the rupture associated with the 1992 landers earthquake ms 7 5 extended along the west edge of a 60 50 km trilateration network that had been surveyed two months before the earthquake and was resurveyed a month after it the coseismic displacement field within the network was calculated from the changes observed in the trilateration network supplemented by the displacements measured at four gps stations and other less timely trilateration measurements stations near the rupture were displaced by as much as 3 m the observed changes are reproduced reasonably well by dislocation modeling in which the landers rupture is represented by 8 vertical fault segments each extending from the surface to 9 km depth two additional segments represent the big bear and eureka peak faults the average modeled right lateral slip on the landers rupture is about 5 m however the residuals for the best fit slip distribution are about four times greater than expected from measurement error given that uncertainty a broad range of slip models furnish acceptable fits to the data the large residuals are attributed to inelastic deformation principally sympathetic slip on numerous unmodeled faults within the fault blocks assumed to be elastic in the model

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

creep and strain dependent microstructures of synthetic anorthite diopside aggregates abstract we investigated plastic deformation of fine grained synthetic diopside and two phase anorthite diopside aggregates in triaxial compression and torsion up to 5 temperature confining pressure and stress ranged between 950 1180 c 200 400 mpa and 5 500 mpa respectively water content of samples ranged between 0 005 0 002 and 0 075 0 025 wt h 2 o all samples deformed in linear viscous creep with a stress exponent of 1 0 0 2 the activation energy ranged between 571 53 and 290 28 kj mol depending on mineralogy and water content sample strength depended on water fugacity with an exponent of 1 55 0 25 samples deformed in torsion and coaxial compression gave similar flow laws in spite of significant differences in the corresponding microstructures scanning and transmission electron microscopy of two phase samples deformed in torsion showed phase mixing cavitation and dislocation processes we suggest that linear viscous creep of fine grained two phase aggregates involved grain boundary sliding accommodated by grain boundary diffusion and significant dislocation accommodation at high strains we also observed that cavity coalescence and microcracking led to sample failure hence dynamic instabilities may exist in high strain shear zones accommodating viscous deformation in the lower continental crust

postearthquake relaxation evidence for laterally variable viscoelastic structure and water content in the southern california mantle i reexamine the lower crust and mantle relaxation following two large events in the mojave desert the 1992 m7 3 landers and 1999 m7 1 hector mine california earthquakes time series from continuous gps sites out to 300 km from the ruptures are used to constrain models of postseismic relaxation crustal motions in the mojave desert region are elevated above background for several years following each event to account for broadscale relaxation of the lower crust and mantle the burgers body model is employed involving transient and steady state viscosities joint afterslip postseismic relaxation modeling of the gps time series up to one decade following the hector mine earthquake reveals a significant rheological contrast between a northwest trending southwest domain that envelopes the san andreas fault system and western mojave desert and an adjacent northeast domain that envelopes the landers and hector mine rupture areas in the central mojave desert the steady state viscosity of the northeast domain mantle asthenosphere is inferred to be 4 times greater than that of the southwest domain this pattern is counter to that expected for regional heat flow which is higher in the northeast domain but it is explicable by means of a nonlinear rheology that includes dependence on both strain rate and water concentration i infer that the southwest domain mantle has a relatively low steady state viscosity because of its high strain rate and water content the relatively low mantle water content of the northeast domain is interpreted to result from the continual extraction of water through igneous and volcanic activity over the past 20 myr

strain accumulation near yucca mountain nevada 1993 1998 a 50 km aperture geodetic network centered on the proposed high level radioactive waste disposal site at yucca mountain nevada was surveyed with gps in 1993 and 1998 the average deformation rate across the area is described by the principal strain rates 22 8 8 8 nstrain yr 1 n77 6 w 13 5 and 8 8 11 9 nstrain yr 1 n12 5 e 13 5 extension reckoned positive and a clockwise rotation rate about a vertical axis of 9 6 7 4 nrad yr 1 relative to fixed north america quoted uncertainties are standard deviations those strain rates are consistent with the geodetic strain rates 2 12 nstrain yr 1 n87 12 w and 22 12 nstrain yr 1 n03 12 e previously reported by savage et al 1999 for the 1983 1998 interval and with the low extension rate 5 20 nstrain yr 1 marrett et al 1998 inferred from the geologic record none of those strain rates is consistent with the 50 9 nstrain yr 1 n65 w extension rate for the area reported by wernicke et al 1998

pore throat structure and fractal characteristics of tight sandstones in yanchang formation ordos basin abstract pore throat structure is a key factor that influences the storage and fluid flow capacity of tight sandstone reservoirs by performing petro physical characteristic tests scanning electron microscopy and casting thin sections the main pore types of tight sandstone reservoir samples collected from the upper triassic yanchang formation in the baibao area of the southwest ordos basin in china were identified to be dissolved pores intergranular pores intercrystalline pores and micro cracks meanwhile the size of the pore throat was widely distributed whereas its shape varied given the advantages and disadvantages of various technical methods high pressure mercury injection hpmi and nuclear magnetic resonance nmr technology were used to study the distribution characteristics of a full size pore throat all 10 samples showed bimodal and unimodal distribution characteristics and their distribution characteristics were consistent with the results of the petro physical characteristics high pressure mercury injection and movable fluid saturation tests the throat distribution characteristics of the reservoir were studied by applying constant rate mercury injection crmi and the throat radius ranged from 0 43 m to 9 76 m with an average of 3 34 m the fractal features of the pore throat and throat were quantitatively characterized by crmi the fractal curves of the pore throat showed self similarities and the fractal dimension d ranged between 2 6297 and 2 9529 with an average of 2 7865 the fractal curves of the throats were broken down into two segments and the fractal dimensions corresponded to two ranges namely the small dt1 and large throats dt2 fractal dimensions the average of fractal dimension dt1 was 2 9170 and the average of fractal dimension dt2 was higher than that of dt1 with an average of 2 9828 thereby indicating the complex structure and strong heterogeneity of the former the fractal dimensions d dt1 and dt2 were negatively correlated with permeability movable fluid saturation average throat radius clay mineral content and laumontite content positively correlated with quartz content and showed poor correlation with feldspar compared with dt2 the fractal dimension dt1 had a higher correlation with pore throat parameters and mineral content given the higher self similarity of small throats their distribution is considered highly homogeneous

implications of deformation following the 2002 denali alaska earthquake for postseismic relaxation processes and lithospheric rheology 1 during the first 2 years following the 2002 mw 7 9 denali alaska strike slip earthquake a large array of global positioning system gps receivers recorded rapid postseismic surface motions extending at least 300 km from the rupture and at rates of more than 100 mm yr in the near field here we use three dimensional 3 d viscoelastic finite element models to infer the mechanisms responsible for these postseismic observations we consider afterslip both from an inversion of gps displacements and from stress driven forward models poroelastic rebound and viscoelastic flow in the lower crust and upper mantle several conclusions can be drawn 1 no single mechanism can explain the postseismic observations 2 significant postseismic flow below a depth of 60 km is required to explain observed far field motions best explained by a weak upper mantle with a depth dependent effective viscosity that ranges from 1019 pa s at the moho 50 km depth to 3 4 1018 pa s at 100 km depth 3 shallow afterslip within the upper crust occurs adjacent to and beneath the regions of largest coseismic slip 4 there is a contribution from deformation in the middle and lower crust from either lower crustal flow or stress driven slip afterslip is preferred over broad viscoelastic flow owing to the existence of seismic velocity discontinuities across the fault at depth though our modeling does not favor either mechanism if the process is viscoelastic relaxation the viscosity is a factor of 3 greater than the inferred mantle viscosity 5 poroelastic rebound probably contributed to the observed postseismic deformation in the immediate vicinity of the denali totschunda junction these conclusions lead us to infer an alaskan mechanical lithosphere that is about 60 km thick overlying a weak asthenosphere and a denali fault that cuts through the entire lithosphere with shear accommodated by faulting in the top 20 km and time dependent aseismic shear below

application of nmr logging to reservoir characterization of low resistivity sands in the gulf of mexico1 nuclear magnetic resonance nmr technology from laboratory data and well logs is rapidly gaining acceptance as a petrophysical tool for evaluating reservoir quality the evaluation of laboratory nmr data as a core analysis technique shows that nmr relaxation time distributions match independent estimates of pore size distributions these other pore size estimates come from grain size analyses pore throat distributions from mercury porosimetry thin section petrography and permeability values irreducible water saturation estimates from nmr based pore size distributions also correspond well with independent measures of irreducible water from special core flood tests in this study we look at the relaxation time distributions extracted from laboratory and downhole nmr measurements to determine pore geometry and volumetrics within a reservoir this understanding leads to a better overall reservoir characterization both core and log nmr data are used to demonstrate that there is a direct connection between nmr relaxation time distributions and the fundamental property of pore size in sandstones this description of pore size distributions allows us to estimate permeability and irreducible water saturation additionally the nmr logs accurately characterize the nmr core lab measurements and provide important information that enhances the description of low resistivity pay

deep subduction of h2o and deflection of volcanic chain towards backarc near triple junction due to lower temperature in central japan near the triple junction of the pacific philippine sea and north american or ohotsuku plates the volcanic chain deflects towards backarc compared to the adjacent northeast japan and izu bonin arcs and lies 200 300 km above the wadati benioff zone numerical modeling shows that thermal recovery of the subducting pacific plate is slow due to the overlapping philippine sea plate which shifts the dehydration reactions to greater depths along the pacific plate and causes the magmatism above the deep wadati benioff zone the low geothermal gradient along the subducting pacific plate also implies that a considerable amount of h2o is carried further down by phase a which is formed just above the subducting plate without being released for magmatism central japan can be regarded as an entrance for h2o into the deep mantle

oil charging model and controlling factors revealed by an online nuclear magnetic resonance nmr system abstract it is very difficult to simulate the charging process of crude oil under experimental conditions due to the low porosity and permeability of tight sandstone however simulations are important for revealing the mechanism of formation of tight oil and the oil water distribution characteristics as well as for enhancing the oil recovery efficiency in this study we established a new method called nuclear magnetic resonance coupling displacement nmr dp to simulate the tight oil charging process online the nmr dp method has the advantages of high precision velocity recyclability and the ability to reflect the distribution of fluids in the micropores of a tight rock we conducted a simulation experiment involving the charging of crude oil into eight sandstone samples from gaotaizi in the qijia longhupao area of the songliao basin the results of this experiment were combined with those of microscopic measurements conducted on the pore structure i e nuclear magnetic resonance nitrogen adsorption high pressure and rate controlled mercury injections and micron computed tomography in this way we clarified the charging process and its controlling factors e g physical properties and wettability and established a tight oil charging model the results indicate that the oil charging saturation was controlled by several factors including the charging pressure physical properties pore throat structure and mineral composition of the rock a smaller radius of the pore throat corresponded to a lower oil charging saturation and higher starting pressure gradient the lower the content of clay and carbonate minerals and the higher the content of feldspar mineral the higher the oil saturation oil mainly occurred in the larger pores while residual water mainly occurred in the smaller pores the charging process was divided into four stages an exponential rapid growth stage a logarithmic slow growth stage a linear slow growth stage and a quasi stationary stage the method established in this paper is expected to be helpful for analyzing the distribution law of oil and water in tight sandstone areas thereby aiding in the prediction of sweet spots and development of tight oil

using short term postseismic displacements to infer the ambient deformation conditions of the upper mantle 1 to interpret short term postseismic surface displacements in the context of key ambient conditions e g temperature pressure background strain rate water content creep mechanism we combined steady state and transient flow into a single constitutive relation that can explain the response of a viscoelastic material to a change in stress the flow law is then used to investigate mantle deformation beneath the eastern california shear zone following the 1999 m7 1 hector mine earthquake the flow law parameters are determined using finite element models of relaxation processes constrained by surface displacement time series recorded by 55 continuous gps stations for 7 years following the earthquake results suggest that postseismic flow following the hector mine earthquake occurs below a depth of 50 km and is controlled by dislocation creep of wet olivine diffusion creep models can also explain the data but require a grain size 3 5 mm that is smaller than the inferred grain size 10 20 mm based on the mantle conditions at these depths in addition laboratory flow laws predict dislocation creep would dominate at the stress grain size conditions that provide the best fit to diffusion creep models model results suggest a transient creep phase that lasts 1 year and has a viscosity 10 times lower than subsequent steady state flow in general agreement with laboratory observations the postseismic response is best explained as occurring within a relatively hot upper mantle e g 1200 1300 c at 50 km depth with a long term background mantle strain rate of 0 1 0 2 mstrain yr consistent with the observed surface strain rate long term background shear stresses at the top of the mantle are 4 mpa then decrease with depth to a minimum of 0 1 0 2 mpa at 70 km depth before increasing slowly with depth due to the pressure dependence of viscosity these conditions correspond to a background viscosity of 10 21 pa s within a thin mantle lid that decreases to 5 10 19 pa s within the underlying asthenosphere this study shows the utility of using short term postseismic observations to infer long term mantle conditions that are not readily observable by other means

pore throat sizes in sandstones tight sandstones and shales pore throat sizes in siliciclastic rocks form a continuum from the submillimeter to the nanometer scale that continuum is documented in this article using previously published data on the pore and pore throat sizes of conventional reservoir rocks tight gas sandstones and shales for measures of central tendency mean mode median pore throatsizes diameters are generally greater than2 mm in conventionalreservoir rocks range from about 2 to 0 03 mm in tight gas sandstones and rangefrom0 1to0 005 mminshales hydrocarbonmolecules asphaltenes ring structures paraffins and methane form another continuum ranging from 100 a 0 01 mm for asphaltenes to 3 8 a 0 00038 mm for methane the pore throat size continuum provides a useful perspective for considering 1 the emplacement of petroleum in consolidated siliciclastics and 2 fluid flow through fine grained source rocks now being exploited as reservoirs

interseismic uplift at the nankai subduction zone southwest japan 1951 1990 uplift as a function of time from 1951 through 1990 has been deduced from annual mean sea level measured at 15 tide gages along the nankai subduction zone southwest japan the recurrence interval for rupture of the nankai subduction zone is about 100 years and the most recent rupture was in late 1946 thus the 1951 1990 uplift record covers most of the first half of the earthquake cycle the precision of the uplift record is better than could be obtained currently by annual global positioning system gps measurements the pre 1960 uplift record shows rapid deformation that appears to terminate in 1959 after 1959 the uplift record is remarkably linear in time significant curvature in the uplift versus time plots is detected at only three of the 15 tide gages the inferred uplift rates are not quantitatively consistent with the predictions of either the viscoelastic coupling or elastic half space models of subduction but the agreement is sufficient to suggest that the causative physical mechanisms have been identified the immediate postseismic response is controlled by the propagation of slip downward along the downdip extension of the coseismic rupture and the interseismic response is caused by the accumulation of a slip deficit on the main thrust zone asthenosphere relaxation is not required to explain the observations

a unified analysis of crustal motion in southern california 1970 2004 the scec crustal motion map 1 to determine crustal motions in and around southern california we have processed and combined trilateration data collected from 1970 to 1992 vlbi data from 1979 to 1992 and gps data from 1986 to 2004 a long temporal coverage required in part by the occurrence of several large earthquakes in this region from a series of solutions for station positions we have estimated interseismic velocities coseismic displacements and postseismic motions within the region from 31 n to 38 n and east to 114 w the final product includes estimated horizontal velocities for 1009 gps 190 trilateration and 16 vlbi points with ties between some of these used to stabilize the solution all motions are relative to the stable north american reference frame snarf as realized through the velocities of 20 gps stations this provides a relatively dense set of horizontal velocity estimates with well tested errors for the past quarter century over the plate boundary from 31 n to 36 5 n these velocities agree well with those from the plate boundary observatory which apply to a later time period we also estimated vertical velocities 533 of which have errors below 2 mm yr most of these velocities are less than 1 mm yr but they show 2 4 mm yr subsidence in the ventura and los angeles basins and in the salton trough our analysis also included estimates of coseismic and postseismic motions related to the 1992 landers 1994 northridge 1999 hector mine and 2003 san simeon earthquakes postseismic motions increase logarithmically over time with a time constant of about 10 days and generally mimic the direction and relative amplitude of the coseismic offsets

coseismic surface deformation from air photos the kickapoo step over in the 1992 landers rupture coseismic deformation of the ground can be measured from aerial views taken before and after an earthquake we chose the area of the kickapoo landers step over along the 1992 landers earthquake zone using air photos scale 1 40 000 scanned at 0 4 m resolution two photos acquired after the earthquake are used to assess the accuracy and to evaluate various sources of noise optical distortions film deformation scanning errors or errors in viewing parameters can yield metric bias at wavelength larger than 1 km offset field at shorter wavelength is more reliable and mainly affected by temporal decorrelation of the images induced by changes in radiometry with time temporal decorrelation and resulting uncertainty on offsets are estimated locally from the correlation degree between the images relative surface displacements are measured independently every about 15 m and with uncertainty typically below 10 cm rms the offset field reveals most of the surface ruptures mapped in the field the fault slip is accurate to about 7 cm rms and measured independently every 200 m from stacked profiles slip distribution compares well with field measurements at the kilometric scale but reveals local discrepancies suggesting that deformation is generally although not systematically localized on the major fault zone located in the field this type of data can provide useful insight into the fault zone s mechanical properties our measurements indicate that elastic coseismic strain near the fault zone can be as large as 0 5 10 3 while anelastic yielding was attained for strain in excess of about 1 2 10 3

porosity permeability and textural heterogeneity of reservoir sandstones from the lower cretaceous putaohua member of yaojia formation weixing oilfield songliao basin northeast china abstract with the granulometric analyses mineral composition x ray diffraction xrd analyses porosity and permeability measurements scanning electron microscopy sem observations and mercury porosimetry measurements of the reservoir sandstones from four wells in the weixing oilfield songliao basin ne china the porosity permeability and pore structural heterogeneity features of the putaohua member sandstone of the lower cretaceous yaojia formation have been investigated in this paper the sandstones are mostly characterized by a similar deposition in continental detrital environments with quartz and feldspar taking the majority 97 and argillaceous minerals illite kaolinite and chlorite the minority 3 however their granule size sorting index porosity and permeability vary significantly in contrast to the generality that high porosity permeability often corresponds to large grain sizes and sorting indexes the porosity and permeability here show no good correlations to the grain size and sorting index suggesting the presence of a remarkable textural heterogeneity in terms of sequential change in permeability along the well depth cyclic sedimentation modes have been identified in some sub layers despite the porosity data showing little response to those scenarios this may be ascribed to the sandstone s peculiar intergranular pore structures in which the cementation occurred in pore lining and filling manners to different extents depending on their depositional environments the distributary channel facies tends to have lowest detrital clay content and rather open packed texture in pore lining cementation manner whereas sand sheet facies has pore filling manner the hg porosimetry analytical data are in fairly good agreement with the heterogeneous pore structures observed by sem large sized pores and channels connecting them though only accounting for a low percentage of the total porosity are believed to contribute mostly to the effective permeability in the sandstone reservoir such textural heterogeneities should be closely associated with the dynamic changing sedimentary facies of sandstones in the continental environment

multiscale insar time series mints analysis of surface deformation 1 we present a new approach to extracting spatially and temporally continuous ground deformation fields from interferometric synthetic aperture radar insar data we focus on unwrapped interferograms from a single viewing geometry estimating ground deformation along the line of sight our approach is based on a wavelet decomposition in space and a general parametrization in time we refer to this approach as mints multiscale insar time series the wavelet decomposition efficiently deals with commonly seen spatial covariances in repeat pass insar measurements since the coefficients of the wavelets are essentially spatially uncorrelated our time dependent parametrization is capable of capturing both recognized and unrecognized processes and is not arbitrarily tied to the times of the sar acquisitions we estimate deformation in the wavelet domain using a cross validated regularized least squares inversion we include a model resolution based regularization in order to more heavily damp the model during periods of sparse sar acquisitions compared to during times of dense acquisitions to illustrate the application of mints we consider a catalog of 92 ers and envisat interferograms spanning 16 years in the long valley caldera ca region mints analysis captures the ground deformation with high spatial density over the long valley region

slip rate and locking depth from gps profiles across the southern dead sea transform 1 the dead sea transform is a major strike slip fault bounding the arabia plate and the sinai subplate on the basis of two gps campaign measurements 6 years apart at 17 sites distributed in israel and jordan complemented by israeli permanent stations we compute the present day deformation across the southern segment of the dead sea transform the wadi araba fault elastic locked fault modeling of fault parallel velocities provides a slip rate of 4 9 1 4 mm a and a best fit locking depth of 12 km this slip rate is slightly higher than previous results based only on israeli permanent gps stations data which are located west of the fault it is in good agreement with results based on offset geomorphologic and geologic features that average longer periods of time 10 ka to 1 ma projection in itrf2000 reference frame allows using our data combined with results published earlier to further study the kinematics between arabia nubia and sinai systematic combination of euler poles available in the literature in addition to our new set of data shows that a wide range of arabia sinai pole positions and angular velocities predict reasonable slip rate on the dead sea fault we highlight uncertainties of calculating such poles due to the small size of the blocks and their slow relative motion along a short and almost straight strand of the transform fault which lead to a large trade off between pole location and angular velocity

interseismic strain and rotation rates in the northeast mojave domain eastern california 1 the northeast mojave domain a type locality for bookshelf faulting is a region of east striking left lateral faults in the northeast corner of the mojave block a block otherwise dominated by n40 w striking right lateral faults paleomagnetic evidence suggests that blocks within the domain have rotated clockwise about a vertical axis as much as 60 since 12 8 ma schermer et al 1996 in 1994 and again in 2002 the u s geological survey surveyed an array of 14 geodetic monuments distributed across the northeast mojave domain the 2002 survey results were adjusted to remove the coseismic offsets imposed by the nearby hector mine earthquake 16 october 1999 mw 7 1 the adjusted deformation across the array appears to be uniform and can be approximated by the principal strain rates e1 28 9 9 1 n77 2 w 4 8 and e2 48 2 8 9 n12 8 e 4 8 nstrain yr 1 extension reckoned positive and quoted uncertainties are standard deviations that strain accumulation could be released by slip on faults striking n32 w but not by bookshelf faulting on the east striking faults alone the vertical axis rotation rate of the northeast mojave domain as a whole relative to fixed north america is 71 0 6 4 nrad yr 1 4 07 0 37 myr 1 clockwise about twice the maximum tensor shear strain rate the observed rotation rate acting over 12 8 myr would produce a clockwise rotation of 52 1 4 7 exclusive of possible coseismic rotations that rotation is in rough agreement with the paleomagnetic rotation accumulated in the individual fault blocks within the northeast mojave domain since 12 8 ma

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

deformation from 1973 through 1991 in the epicentral area of the 1992 landers california earthquake ms 7 5 deformation of a 50 60 km trilateration network that spans the epicenter of the 1992 landers earthquake ms 7 5 was measured by seven surveys over the 19 years preceding the earthquake three moderate earthquakes 1979 homestead valley ms 5 6 1986 north palm springs ms 6 0 and 1992 joshua tree ms 6 1 occurred within the network during those 19 years here we use geodetic and seismic data to construct a dislocation model for each of the three moderate earthquakes coseismic changes due to these three moderate earthquakes as predicted by the dislocation models are then removed from the trilateration data the residual geodetic changes appear to be uniform in time we take those changes to represent secular strain accumulation this strain accumulation clearly shows right lateral shear across the san andreas fault but also suggests a northwest southeast extension northeast of the eastern end of the big bend of the san andreas fault the landers earthquake ruptured along a north northwest trend across this region of northwest southeast extension

mobility of continental mantle evidence from postseismic geodetic observations following the 1992 landers earthquake the crust around the rupture zone of the 1992 landers earthquake has continued to deform in the years following the earthquake at rates 3 times greater than pre earthquake rates we use a combination of global positioning system gps and synthetic aperture radar insar data collected during a 3 year epoch following the earthquake in order to investigate postseismic mechanisms responsible for the high transient velocities in order to maximize the potential signal from viscoelastic relaxation we evaluate and model postseismic relaxation following the first few months of documented accelerated deformation the combination of gps and insar data allows us to establish viscoelastic relaxation of the lower crust and upper mantle as the dominant postseismic process and to discriminate among possible viscoelastic models the data particularly require the presence of a highly ductile uppermost mantle beneath the central mojave domain with temperature between the wet and dry basalt solidus this is consistent with independent seismic and geochemical inferences of a regionally warm uppermost mantle further consideration of seismic velocity variations in conjunction with faulting patterns within the mojave desert suggests that the primary faulting characteristics of the mojave desert namely the pervasive late cenozoic deformation within the eastern california shear zone versus the near absence of faults in the western mojave domain are controlled by the rheology of the uppermost mantle

continuous gps observations of postseismic deformation following the 16 october 1999 hector mine california earthquake mw 7 1 rapid field deployment of a new type of continuously operating global positioning system gps network and data from southern california integrated gps network scign stations that had recently begun operating in the area allow unique observations of the postseismic deformation associated with the 1999 hector mine earthquake innovative solutions in fieldcraft devised for the 11 new gps stations provide high quality observations with 1 year time histories on stable monuments at remote sites we report on our results from processing the postseismic gps data available from these sites as well as 8 other scign stations within 80 km of the event a total of 19 sites from these data we analyze the temporal character and spatial pattern of the postseismic transients data from some sites display statistically significant time variation in their velocities although this is less certain the spatial pattern of change in the postseismic velocity field also appears to have changed the pattern now is similar to the pre landers pre 1992 secular field but laterally shifted and locally at twice the rate we speculate that a 30 km 50 km portion of crust near twentynine palms which was moving at nearly the north american plate rate to within 3 5 mm yr of that rate prior to the 1992 landers sequence now is moving along with the crust to the west of it as though it has been entrained in flow along with the pacific plate as a result of the landers and hector mine earthquake sequence the inboard axis of right lateral shear deformation at lower crustal to upper mantle depth may have jumped 30 km farther into the continental crust at this fault junction that comprises the southern end of the eastern california shear zone

diagenesis porosity evolution and petroleum emplacement in tight gas reservoirs taranaki basin new zealand abstract tight gas reservoirs have become popular targets in petroleum exploration in recent years due largely to the increasing market demand for gas and also to technology advances used in extraction reservoir quality is typically poor due to deep burial diagenesis resulting in significant compaction cementation and illitization however analysis of tight reservoirs using integrated techniques can improve our understanding about the controls on reservoir quality and these results can potentially be used to help predict reservoir quality at other sites the use of integrated analysis of diagenetic and burial history is here shown for the eocene k3e kapuni group reservoir in cardiff 1 taranaki basin new zealand the k3e belongs to a deep gas play that was considered uncommercial in the early 1990 s due to poor reservoir quality associated with extensive authigenic illite potassium argon dating has shown that destruction of the reservoir through illitization occurred in the pliocene associated with a late stage heating and or fluid flow event timing of illite authigenesis in the k3e reservoir postdates the likely circulation of co2 rich fluids that caused reaction of feldspar to form kaolinite and quartz homogenization temperatures from two phase aqueous fluid inclusions within quartz cements together with 1d basin models of co2 expulsion from coaly source rocks indicate that feldspar reactions may have started in the mid miocene the co2 rich fluids are thought to have been generated by thermal decarboxylation of intraformational paleocene eocene coals at the same time oil was being expelled from older cretaceous coals and migrated into the mid late eocene reservoirs evidence for oil migration is demonstrated by the presence of residual oil and by the local occurrence of abundant oil bearing fluid inclusions the products of feldspar dissolution appear to be in reasonable balance with the amount of dissolved feldspar suggesting a relatively closed diagenetic system with little improvement in reservoir quality despite the large volume of feldspar dissolved petrographic evidence of reservoir sandstones at cardiff 1 demonstrates the presence of some illite free secondary macropores lined by residual oil this local preservation of porosity may be replicating the original distribution of oil saturated pores in the pliocene at the time when authigenic kaolinite underwent reaction to form illite remobilization of the oil probably occurred by gas flushing after the main phase of illitization at c 5 ma the data presented in this study are consistent with redistributed liquid petroleum into up dip traps and represent the potential for a new exploration play the eocene reservoir at cardiff 1 is currently gas charged with the pore system composed of approximately one third large macropores connected by a tortuous microporous network however it is possible that with the currently buoyant gas market and modern hydraulic fracturing techniques it may now be economic to flow gas from the locally large pores identified in the k3e reservoir

postseismic deformation associated with the 1992 m ω 7 3 landers earthquake southern california following the 1992 m 7 3 landers earthquake a linear array of 10 geodetic monuments at roughly 5 km spacing was established across the emerson fault segment of the landers rupture the array trends perpendicular to the local strike of the fault segment and extends about 30 km on either side of it the array was surveyed by global positioning system 0 034 0 048 0 381 1 27 1 88 2 60 and 3 42 years after the landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation the temporal behavior is described roughly by a short term decay time 84 23 days exponential relaxation superimposed upon an apparently linear trend because the linear trend represents motions much more rapid than the observed preseismic motions we attribute that trend to a slower decay time greater than 5 years postseismic relaxation the curvature of which cannot be resolved in the short run 3 4 years of postseismic data about 100 mm of right lateral displacement and 50 mm of fault normal displacement accumulated across the geodetic array in the 3 4 year interval covered by the postseismic surveys those displacements are attributed to postseismic right lateral slip in the depth interval 10 to 30 km on the downward extension of the rupture trace the right lateral slip amounted to about 1 m directly beneath the geodetic array and the fault normal displacement is apparently primarily a consequence of the curvature of the rupture these conclusions are based upon dislocation models fit to the observed deformation however no dislocation model was found with rms residuals as small as the expected observational error

postseismic relaxation and aftershocks 1 perfettini et al 2005 suggested that the temporal dependence of surface displacements u t measured in the epicentral area following an earthquake is related to n t the cumulative number of aftershocks by the equation u t a bt cn t d 1 e t where a b c d and are constants chosen to fit the data and t is the postearthquake time n t appears in the expression for u t because both the aftershocks and a portion of u t are thought to be driven by the same source postseismic fault creep at subseismogenic depths on the downdip extension of the coseismic rupture we show that this equation with the actually observed n t fits the postseismic displacements recorded on several baselines following each of five earthquakes 1999 m7 6 chi chi taiwan 1999 m7 1 hector mine southern california 2002 m7 9 denali central alaska 2003 m6 5 san simeon central california and 2004 m6 0 parkfield central california earthquakes although there are plausible physical interpretations for each of the terms in the expression for u t the large number of adjustable constants a b c d and involved in fitting the rather simple postseismic displacements diminishes the significance of the fit because the observed n t is well fit by the modified omori s law fault creep at depth presumably exhibits the same temporal dependence that dependence could be explained if the rheology of the fault downdip from the coseismic rupture is consistent with ordinary transient creep montesi 2004 demonstrated that power law creep across a shear zone at depth would also produce that temporal signal

qualitative and quantitative characterization of multiple factors that influence movable fluid saturation in lacustrine deep water gravity flow tight sandstones from the yanchang formation southern ordos basin china abstract fluid mobility is one of the most important factors in evaluating the potential for recovering tight oil however quantitative effects of multiple factors that influence movable fluid saturation in different pore throat combinations and their relationships with lithofacies in tight sandstones especially for lacustrine deep water gravity flow deposits remain controversial due to the strong heterogeneity and complex pore structure of tight reservoirs core samples obtained from the upper triassic yanchang formation in southern ordos basin were evaluated by using a variety of techniques including nuclear magnetic resonance nmr scanning electron microscopy sem x ray diffraction xrd pressure controlled porosimetry pcp rate controlled porosimetry rcp impregnated thin sections and helium porosity and nitrogen permeability measurements based on nmr t2 distributions under water saturated and centrifugal conditions four types of pore throat combinations are identified by using the relaxation time thresholds ts1 and ts2 from nmr large intergranular pore dominated pore throat combinations lip small intergranular pore dominated pore throat combinations sip intragranular pore dominated pore throat combinations iap and micropore dominated pore throat combinations mp among them sip is the dominant pore space favorable for fluid flow movable fluid saturation in sip pore space varies among different lithofacies the best fluid mobility commonly occurs in fine grained cross bedded sandstones sc whereas the worst fluid mobility usually appears in siltstones to very fine grained sandstones ss the quantitative effects of a total of 41 factors that influence movable fluid saturation of different pore throat combinations were investigated through the analysis of the pearson correlation matrix the results demonstrate that porosity and permeability mainly affect the movable fluid saturation in the pore space of sip and mp in addition maximum mercury intrusion saturation from pcp smax and tortuosity are the critical pore structure parameters affecting the movable fluid saturation in the pore space of sip and mp whereas the average pore throat radius ratio is the critical factor affecting the movable fluid saturation in lip pore space overall movable fluid saturation in different pore throat combinations is characterized mainly by different microscopic pore structure parameters a general pore network model for different lithofacies with different fluid mobility is established to facilitate assessment of the heterogeneity of tight sandstones and to further guide hydrocarbon exploration and development in similar lacustrine deep water depositional settings

near field postseismic deformation associated with the 1992 landers and 1999 hector mine california earthquakes after the landers earthquake m w 7 3 1992 489 a linear array of 10 monuments extending about 30 km n50 e on either side of the earthquake rupture plus a nearby off trend reference monument were surveyed frequently by gps until 2003 2 the array also spans the rupture of the subsequent hector mine earthquake m w 7 1 1999 792 the pre landers velocities of monuments in the array relative to interior north america were estimated from earlier trilateration and very long baseline interferometry measurements except at the reference monument the post landers velocities of the individual monuments in the array relaxed to their preseismic values within 4 years following the hector mine earthquake the velocities of the monuments relaxed to steady rates within 1 year those steady rates for the east components are about equal to the pre landers rates as is the steady rate for the north component of the one monument east of the hector mine rupture however the steady rates for the north components of the 10 monuments west of the rupture are systematically 10 mm yr 1 larger than the pre landers rates the relaxation to a steady rate is approximately exponential with decay times of 0 50 0 10 year following the landers earthquake and 0 32 0 18 year following the hector mine earthquake the postearthquake motions of the landers array following the landers earthquake are not well approximated by the viscoelastic coupling model of pollitz et al 2000 a similar viscoelastic coupling model pollitz et al 2001 is more successful in representing the deformation after the hector mine earthquake

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

modeling afterslip and aftershocks following the 1992 landers earthquake one way to probe the rheology of the lithosphere and fault zones is to analyze the temporal evolution of deformation following a large earthquake in such a case the lithosphere responds to a known stress change that can be assessed from earthquake slip models constrained from seismology and geodesy here we model the postseismic response of a fault zone that is assumed to obey a rate strengthening rheology where the frictional stress varies as a ln e e being the deformation rate and a 0 a rheological parameter the model is simple enough that these parameters can be estimated by inversion of postseismic geodetic data we apply this approach to the analysis of geodetic displacements following the m w 7 3 1992 landers earthquake the model adjusts well the measured displacements and implies a 0 47 0 53 mpa in addition we show that aftershocks and afterslip follow the same temporal evolution and that the spatiotemporal distribution of aftershocks is consistent with the idea that they are driven by reloading of the seismogenic zone resulting from frictional afterslip

deformation and seismicity associated with continental rift zones propagating toward continental margins 1 we study the propagation of a continental rift and its interaction with a continental margin utilizing a 3 d lithospheric model with a seismogenic crust governed by a damage rheology a long standing problem in rift mechanics known as thetectonic force paradox is that the magnitude of the tectonic forces required for rifting are not large enough in the absence of basaltic magmatism our modeling results demonstrate that under moderate rift driving tectonic forces the rift propagation is feasible even in the absence of magmatism this is due to gradual weakening and long term memory of fractured rocks that lead to a significantly lower yielding stress than that of the surrounding intact rocks we show that the style rate and the associated seismicity pattern of the rift zone formation in the continental lithosphere depend not only on the applied tectonic forces but also on the rate of healing accounting for the memory effect provides a feasible solution for thetectonic force paradox our modeling results also demonstrate how the lithosphere structure affects the geometry of the propagating rift system toward a continental margin thinning of the crystalline crust leads to a decrease in the propagation rate and possibly to rift termination across the margin in such a case a new fault system is created perpendicular to the direction of the rift propagation these results reveal that the local lithosphere structure is one of the key factors controlling the geometry of the evolving rift system and seismicity pattern

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