review of magnetic and electric field effects near active faults and volcanoes in the u s a abstract synchronized measurements of geomagnetic field have been recorded along 800 km of the san andreas fault and in the long valley caldera since 1974 and during eruptions on mount st helens since 1980 for shorter periods of time continuous measurements of geoelectric field measurements have been made on mount st helens and near the san andreas fault where moderate seismicity and fault slip frequently occurs significant tectonic and volcanic events for which nearby magnetic and electric field data have been obtained include 1 two moderate earthquakes m l 5 8 for which magnetometers were close enough to expect observable signals about three source lengths 2 one moderate earthquake m s 7 3 for which magnetometers were installed as massive fluid outflow occurred during the post seismic phase 3 numerous fault creep events and moderate seismicity 4 a major explosive volcanic eruption and numerous minor extrusive eruptions and 5 an episode of aseismic uplift for one of the two earthquakes with m l 5 8 seismomagnetic effects of 1 3 and 0 3 nt were observed for this event magnetometers were optimally located near the epicenter and the observations obtained are consistent with simple seismomagnetic models of the event similar models for the other event indicate that the expected seismomagnetic effects are below the signal resolution of the nearest magnetometer precursive tectonomagnetic effects were recorded on two independent instruments at distances of 30 and 50 km from a m l 5 2 earthquake longer term changes were recorded in one region in southern california where a moderate m l 5 9 earthquake has since occurred surface observations of fault creep events have no associated magnetic or electrical signature above the present measurement precision 0 25 nt and 0 01 respectively and are consistent with near surface fault failure models of these events longer term creep is sometimes associated with corresponding longer term magnetic field perturbations correlated changes in gravity magnetic field areal strain and uplift occurred during episodes of aseismic deformation in southern california primarily between 1979 and 1983 because the relationships between these parameters agrees with those calculated from simple deformation and tectonomagnetic models the preferred explanation appeals to short term strain episodes independently detected in each data set an unknown source of meteorologically generated noise in the strain gravity and uplift data and an unknown but correlated disturbance in the absolute magnetic data might also explain the data no clear observations of seismoelectric or tectonoelectric effects have yet been reported the eruption of mount st helens generated large oscillatory fields and 9 2 nt offset on the only surviving magnetometer a large scale traveling magnetic disturbance passed through the san andreas array from 1 to 2 h after the eruption subsequent extrusive eruptions generated small precursory magnetic changes in some cases these data are consistent with a simple volcanomagnetic model magneto gas dynamic effects and a blast excited traveling ionospheric disturbance traveling ionospheric disturbances tids also generated by earthquake related atmospheric pressure waves may explain many electromagnetic disturbances apparently associated with earthquakes local near fault magnetic field transients rarely exceed a few nt at periods of a few minutes and longer

the state of stress on some faults of the san andreas system as inferred from near field strong motion data we present a simple method to calculate the stress produced on an earthquake fault during rupture this method allows the complete evaluation of the stress spatio temporal history over the fault we apply this approach to study the changes in shear stress produced during four of the largest earthquakes which occurred along the san andreas fault system over the last 20 years the imperial valley earthquake of 1979 the morgan hill earthquake of 1984 the loma prieta earthquake of 1989 and the northridge earthquake of 1994 we use for this study the tomographic models of the fault rupture obtained from the inversion of the near field seismic data recorded during these earthquakes the results obtained show that the static and the dynamic stress drops vary greatly over the fault the peak values obtained for the four earthquakes studied range from about 20 to 100 mpa these high values imply that the initial shear stress level on the fault at the onset of the earthquake was high on at least a significant portion of the fault the regions of the fault which break with a high stress drop are also the regions where slip is large this suggests that most of the slip produced in a large earthquake takes place over the strong areas of the fault low slip regions tend to break with low stress drops after the earthquake the shear stress is increased over a significant portion of the fault which corresponds to low slip regions aftershock activity tends to be concentrated in these areas of stress increase the apparent strength of the fault before the earthquake that is the local shear stress increase which is required for rupture is also extremely heterogeneous the rupture velocity seems to be inversely correlated with this apparent fault strength the rupture accelerating over the weak areas of the fault and slowing down over the high strength areas

tectonomagnetism and tectonoelectricity the last four years has seen a considerable waning of efforts in the u s to use the inherent stress sensitivity of the magnetization of rocks in tectonically active regions as a tool for understanding and perhaps predicting earthquake activity and volcanic eruptions the primary reasons for this decreased interest derive from accumulating evidence that the mean deviatoric stress release during earthquakes and the ambient shear stress near active faults is lower than than had been previously assumed and secondly the observational limits of magnetometers separated by about 10 km after application of a variety of noise reduction techniques appear to be no better than about 0 1 nt lower estimates of the average change in deviatoric stress associated with earthquake rupture correspondingly reduce the fields calculated from tectonomagnetic models at the same time some unexpected and exciting results have been obtained which indicate many aspects of magnetic field changes near active faults and volcanoes are still not completely understood the more important of these results are 1 the observation of correlated magnetic strain uplift and gravity changes during the latter stages of a remarkable deformation episode near the san andreas fault in southern california 2 indications of anomalous change in magnetic fields along the san andreas fault to the southeast of palm springs 3 an unambiguous observation of a volcanomagnetic effect at mt st helens prior to an extrusive eruption and 4 the first observations of coseismic seismomagnetic effects on two independent magnetometers during the july 8 1986 ml 5 9 north palm springs earthquake a resurgence of interest has occurred during the quadrennium in a related area concerning electrical phenomena and electromagnetic effects related to earthquakes and volcanoes mechanisms have been proposed to explain the occurrence of earthquakes lights and the possibility of electromagnetic emission prior to the 1960 chilean earthquake has been proposed self potential anomalies have been observed before and during several eruptions on kilauea volcano in hawaii

origins of hydrocarbon gas seeping out from offshore mud volcanoes in the nile delta abstract this paper discusses the origin of gas seepages free gas or dissolved gas in ground water or brine sampled with the nautile submarine during the nautinil cruise at the seafloor of the deep water area of the nile turbiditic system on different mud volcanoes and brine pools generally the gas is wet and includes c1 c2 c3 ic4 nc4 co 2 these gas samples show no evidence of biodegradation which is not the case of the gas present in the deep hydrocarbon accumulations at depth it indicates that the gas expelled by the mud volcanoes is not issued from direct leakages from deep gas fields the collected gas samples mainly have a thermogenic origin and show different maturities some samples show very high maturities indicating that these seepages are sourced from great depths below the messinian salt moreover the different chemical compositions of the gas samples reflect not only differences in maturity but also the fact that the gas finds its origin in different deep source rocks carbon dioxide has an organic signature and cannot result from carbonate decomposition or mantle fluids the crustal derived radiogenic isotopes show that the analyzed gas samples have suffered a fractionation processes after the production of the radiogenic isotopes due either to oil occurrence at depth interacting with the flux of gas and or fractionation during the fluid migration

modeling surface deformations at complex strike slip plate boundaries two new versions of the physical base traction model of li and rice 1987 have been developed to study the loading processes and surface deformation near plate boundaries with geometric complexities including a shallow creeping fault segment and two subparallel faults predictions of surface velocity and surface slip rate for the region between the san andreas fault and the pacific coast at the latitude of the parkfield cholame segment using model parameters based on geologic geodetic and seismic considerations were found to be in good agreement with contemporary geodetic field data not used in constraining model parameters also predicted surface velocity for the salton sea coachella valley area were fit to recently derived contemporary geodetic data and very large baseline interferometry data although here the model parameters are not well constrained

continuation of a deep borehole stress measurement profile near the san andreas fault 2 hydraulic fracturing stress measurements at black butte mojave desert california hydraulic fracturing stress measurements were obtained in the black butte drill hole 18 km northeast of the san andreas fault in the mojave desert at depths from 251 to 635 m in all tests the least and greatest horizontal principal stresses s h and s h respectively exceeded the vertical stress s indicating a thrust faulting stress regime a single good quality hydraulic fracture impression from 309 m depth indicates an s h direction of n41 e 10 this s h direction should be interpreted with caution because it is based on only one observation this orientation is fairly compatible with nearby surface stress measurements but is incompatible with most of the hydraulic fracturing stress orientations reported from comparable depths in the mojave desert and is not favorable for right lateral slip on either the san andreas fault or nw striking faults present farther to the east the stress regime measured in the black butte hole is comparable to that measured at nearby shallow depths but differs from the strike slip or transitional strike slip to thrust faulting stress regime present at similar depths in two nearby holes crystallaire 4 km northeast of fhe san andreas fault and hi vista 32 km northeast of the san andreas fault the s h direction measured in these holes is approximately 60 counterclockwise of that observed in the black butte hole the differences in stress magnitudes and orientation among these holes substantiate previous indications of local variations in stress in the upper kilometer of the crust in this area and cast doubt on the validity of linear elastic models in which the effects of the san andreas fault dominate the stress field in the western mojave desert

near surface stress and displacement in a layered elastic crust in situ stress measurements on the san andreas fault are modeled in terms of a solution to the equations of three dimensional elastic equilibrium in a layered medium crustal stresses are expressed in terms of surface deformations in particular vertical stress gradients are shown to be proportional to horizontal gradients of vertical surface deformation in light of constraints derived by this relation it is proposed to reinterpret the observed near surface in situ vertical stress gradients on the san andreas fault as partly a manifestation of a layered crust with vertically increasing rigidity extrapolation to depth of the revised stress gradients suggests that the san andreas fault can be regarded as a low stress phenomenon compatible with estimates of shear stress obtained from heat flow data

stress modeling in the andes constraints on the south american intraplate stress magnitudes regions of high topography which exhibit both compressional and extensional deformation provide a natural laboratory to place constraints on horizontal intraplate stress magnitudes an elastic finite element analysis of the lithospheric stress field in the cordillera bianca region of peru has been used to evaluate the lithospheric stress state and constrain the south american intraplate stress magnitudes the orthogonal orientation of the andean high topography to the east west regional stress field in conjunction with the well documented change in deformation style from compression to extension across the cordillera provides a unique setting for the stress modeling a two dimensional finite element grid consisting of an assembly of isotropic elastic quadrilateral elements in a state of plane strain was used to represent the lithosphere an isostatically balanced crustal density model was used to calculate the stresses associated with the lateral density variations between the andean topography and the brazilian shield in some models horizontal stress was concentrated at midcrustal depths by including vertical variation in young s modulus the modeling results indicate bounds of 10 and 75 mpa for the magnitude of the average horizontal stress averaged over a 100 km thick lithosphere a preferred value of 25 mpa is obtained on the basis of fitting all of the data for the rheological models considered and predicting a transition from extension to compression near the 3000 m elevation contour such a far field average stress is consistent with a ridge push origin because the modeling performed in this study assumes that the topographic load is entirely compensated by the buoyancy of the deflected moho these estimates represent upper bounds the effect of incorporating thermal support for the topographic load of the cordillera bianca would be to further reduce our estimate of the intraplate stress magnitudes analysis of the distribution of calculated stress with depth indicates that previous assumptions about the vertical plane shear stress within the lithosphere being negligible are acceptable for the geometry of the andes

natural gas formation in the western nile delta eastern mediterranean thermogenic versus microbial abstract the offshore part of the nile delta is an emerging gas and condensate province and one of the most promising areas for future petroleum exploration and supply in northern africa while the nile delta s hydrocarbon potential and its geological and stratigraphic pattern has been the focus of numerous studies the origin of its gas has been poorly studied in order to characterize the natural gas and to determine whether microbial or thermogenic processes are the dominant generation pathways of methane a regional geochemical study was performed on 38 test gases collected from 9 neogene western nile delta discoveries main constituents of the gases are methane 89 4 99 4 up to pentane with traces of carbon dioxide and nitrogen methane carbon isotopic composition ranges from 66 0 to 39 6 displaying a mixed microbial and thermogenic character for most of the gases microbial gas contributions range from 15 to 95 the mixed and the more thermogenic gases are frequently accompanied by light oils and condensates 41 59 api calculated maturities of the thermogenic gas proportions suggest source rock maturities between 0 8 and 1 4 ro which are actually present in the pre miocene section evidence for microbial alteration of petroleum accumulations in the nile delta is largely manifested in anomalously heavy isotopic compositions of both wet gas components propane and n butane and preferential removal of higher n alkanes from condensates the hydrocarbon accumulations affected by biodegradation are trapped within shallow pliocene reservoirs

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

contemporary block tectonics california and nevada well determined fault plane solution and the gross pattern of late cenozoic faulting in california and nevada show a systematic relation between the orientation of fault planes and slip directions in general normal faults have northerly strikes reverse faults have easterly strikes and dextral and sinstral strike slip faults have northwesterly and northeasterly strikes respectively kinematically this relation is consistent with the response of clusters of fault bounded crustal blocks to a regional stress field generated by the relative motion between the pacific and north american plates in this stress field the greatest and least principal compressive stresses are restricted to northerly and easterly striking vertical planes respectively clusters of crustal blocks bound by faults having the above attitudes form three basic regimes 1 a spreading regime with a combination of normal and conjugate strike slip faults 2 a converging regime with a combination of reverse and conjugate strike slip faults and 3 a wrench regime with sets of subparallel throughgoing northwest striking dextral faults or northeast striking sinstral faults these three regimes are typified by faulting patterns in the basin and range province spreading the transverse ranges converging and the san andreas garlock fault systems wrench respectively the gross deformation of each regime resulting from relative displacements between individual blocks is characterized by north south shortening and east west extension with the ratio of extensional to shortening strains and the areal dilitation decreasing systematically from spreading to wrench to compressional regimes the wrench regime involves a component of net rotational deformation clockwise for dextral slip and counter clockwise for sinstral slip while deformation of the spreading and converging regimes is irrotational local deviations from regional kinematic directions are concentrated along the boundaries between regimes reflecting the mismatch in gross deformation fields between regimes maximum principal and shear stress magnitudes will increase systematically from spreading to wrench to converging regimes provided that fault slip is controlled by frictional strength byerlee s law along preexisting fractures and that pore pressure in the brittle crust is laterally uniform a minimum strength difference between active block bounding faults and block interiors is 15 30 simple arrangements of such block clusters mimic the gross kinematic pattern of quaternary faulting in california and nevada some implications for contemporary tectonics emphasized by this model involve the westward displacement of the sierra nevada block with respect to the stable interior of the north american plates oblique thrusting of the salinian block over the pacific plate and a progressive increase in the offset of the san andreas fault represented by the big bend through the transverse ranges

implications of an elastic analysis of in situ stress measurements near the san andreas fault twenty nine measurements of in situ stress obtained with the hydraulic fracturing technique near palmdale california are the basis of an elastic analysis of the state of stress in the mojave desert adjacent to the san andreas fault the measurements were made at depths extending from 80 to 849 m and at distances from the fault between 2 and 34 km the elastic solution indicates a state of deviatoric stress typical for continents in that the inferred depth gradient of the maximum shear stress is about 7 9 mpa km extrapolation yields an average shear stress in the upper 14 km of the crust of about 56 mpa a result that is higher than estimates of the average shear stress on the san andreas fault based on the analysis of heat flow data this finding is consistent however with estimates of fault strength based on laboratory determinations of the coefficient of friction for samples of san andreas fault gouge if the regional state of deviatoric stress is limited by the strength of the fault zone if so then the coefficient of friction of the san andreas fault zone inferred from the stress field results is about 0 45 the state of stress does not appear to vary systematically with distance from the san andreas fault although considerable localized variation is observed the observations suggest an upper bound of about 0 1 mpa km for the horizontal gradient of the maximum shear stress in the direction perpendicular to the san andreas fault a result that implies a corresponding limit of about 1 4 mpa on the shear traction applied to the base of the seismogenic layer finally we demonstrate the potential application of in situ stress data to the direct assessment of accumulated slip which could be released in a large earthquake we show that on the basis of a model involving a locked fault extending to about 22 km the total fault slip below the locked portion is less than 13 m a more comprehensive set of stress data could permit the estimation of an even lower bound

impact of hot fluid advection on hydrocarbon gas production and seepage in mud volcano sediments of thick cenozoic deltas hydrocarbon seeps are ubiquitous at gas prone cenozoic deltas such as the nile deep sea fan ndsf2 where seepage into the bottom water has been observed at several mud volcanoes mvs3 including north alex mv namv4 here we investigated the sources of hydrocarbon gases and sedimentary organic matter together with biomarkers of microbial activity at four locations of namv to constrain how venting at the seafloor relates to the generation of hydrocarbon gases in deeper sediments at the centre high upward flux of hot 70 c hydrocarbon rich fluids is indicated by an absence of biomarkers of anaerobic oxidation of methane aom and nearly constant methane ch4 concentration depth profile the presence of lipids of incompatible thermal maturities points to mixing between early mature petroleum and immature organic matter indicating that shallow mud has been mobilized by the influx of deep sourced hydrocarbon rich fluids methane is enriched in the heavier isotopes with values of 13c 46 6 vpdb and d 228 vsmow and is associated with high amounts of heavier homologues c2 suggesting a co genetic origin with the petroleum on the contrary at the periphery a lower but sustained ch4 flux is indicated by deeper sulphate methane transition zones and the presence of 13c depleted biomarkers of aom consistent with predominantly immature organic matter values of 13c ch4 60 vpdb and decreased concentrations of 13c enriched c2 are typical of mixed microbial ch4 and biodegraded thermogenic gas from plio pleistocene reservoirs of the region the maturity of gas condensate migrated from pre miocene sources into miocene reservoirs of the western ndsf is higher than that of the gas vented at the centre of namv supporting the hypothesis that it is rather released from the degradation of oil in neogene reservoirs combined with the finding of hot pore water and petroleum at the centre our results suggest that clay mineral dehydration of neogene sediments which takes place posterior to reservoir filling may contribute to intense gas generation at high sedimentation rate deltas

the 2011 mw 6 8 burma earthquake fault constraints provided by multiple sar techniques we used two tracks of alos palsar images to investigate the focal mechanism and slip distribution of the 2011 march 24 m w 6 8 burma strike slip earthquake three different sar techniques namely conventional interferometry sar pixel offsets spo and multiple aperture insar mai were employed to obtain the coseismic surface deformation fields along the 30 km length of the fault rupture along track measurements from spo and mai techniques show a high correlation and were subsequently used to precisely determine the location and extent of the surface fault trace the best fitting fault model geometry derived from an iterative inversion technique suggests that the rupture occurred on a near vertical sinistral strike slip fault west of the nam ma fault with a strike of 70 a maximum slip of 4 2 m occurs at a depth of 2 5 km with significant slip constrained only to the upper 10 km of the crust

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

analysis of states of stress between provinces of constant stress recent studies have indicated the existence of crustal provinces or domains within which the state of stress shows little apparent horizontal variation between provinces the state of stress may undergo substantial changes often over remarkably short distances as analyzed here the transition in stress state between adjacent domains is caused by shear tractions acting on the base of the elastic brittle layer and is mediated by a stress field within a zone between the provinces that can be determined by solving the equations of force equilibrium and stress compatibility the component of horizontal stress oriented perpendicular to the provincial boundary changes smoothly across the transition zone from one province to the other whereas the horizontal stress oriented parallel to the boundary shows smaller but discontinuous changes the horizontal component of shear stress is unlikely to change from one province to another because of the implausible nature of the required basal traction thus in this regard states of stress in adjacent domains appear to be coupled the coincidence of a number of stress transition zones with boundaries defined by heat flow suggests that in many cases the basal tractions are the result of thermally induced mass transport below the elastic brittle layer in the direction of increasing horizontal compressive stress this analysis provides a quantitative relationship between changes in the stress field measured in the upper portion of the crust and shear stresses acting on the base of the elastic brittle layer

comments on near surface stress and displacement in a layered elastic crust and stress in a stratified crust overlying a buried screw dislocation by p c leary

interaction of the san andreas fault creeping segment with adjacent great rupture zones and earthquake recurrence at parkfield three dimensional finite element calculations are employed to study interactions in space and time between the creeping segment of the san andreas fault in central california and the adjacent currently locked zones of the 1857 and 1906 great earthquakes vertically the model consists of an elastic upper crust over a maxwell viscoelastic region representing the entire lower crust or a narrower horizontal detachment layer and a stiffer and more viscous upper mantle the crust has a single vertical fault extending to the top of the mantle at 25 km depth in zones along strike corresponding to the 1857 and 1906 events the top 12 5 km of the fault is locked against slip except in great earthquakes below the locked zones and everywhere along the creeping region between them the fault is freely slipping the model parameters are compatible with seismological and geological observations and with a ratio of maxwell relaxation time to the relaxing layer thickness in the range 1 to 2 yr km as established by li and rice 1987 and fares and rice 1988 based on fits to geodetic data along the san andreas fault an imposed constant far field shear motion and periodic 1857 and 1906 type earthquakes generate slip rates along the creeping fault segment that evolve in time throughout the entire earthquake cycle shortly after an adjacent great earthquake slip rates in the creeping zone are higher than the far field velocity while later in the cycle they are lower hence time dependency should be accounted for when measurements of fault slip are used to estimate the plate motion if parkfield earthquakes are a response to a time dependent loading of the type simulated here their recurrence interval would tend to lengthen with time since the 1857 event thus the hypothesis of characteristic periodic earthquakes at parkfield may not provide the best estimate of the occurrence time of the next event using for example the statistics of past events and assuming that parkfield earthquakes are a response to a slip deficit near middle mountain and that the elastic crustal layer is 17 5 km thick we find that the next event is predicted for about 1992 9 years if the lower crust is a 7 5 km thick layer having a material relaxation time of 15 years and 1995 11 years if the 7 5 km thick lower crust is characterized by a relaxation time of 7 5 years these values may be compared to the 1988 7 years estimate based on periodicity in time the modeling results also indicate that the interaction between the 1857 and 1906 rupture zones is small

stress in a stratified crust overlying a buried screw dislocation a haskell matrix solution to the equation of stress equilibrium is used to describe the crustal response to a screw dislocation source lying beneath a uniform elastic crust capped by a region of layered rigidity the solution is used to illustrate the effect a stratified crustal rigidity has on the near surface in situ stress field without accounting for this effect it is possible to overestimate the deep tectonic stress levels inferred from in situ vertical gradients measured in the uppermost crust

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

shear stress on a vertical strike slip fault in a layered medium due to tectonic loading san andreas fault system depth distribution of shear stress at a transform boundary induced by tectonic loading is analyzed the lithospheric plate is assumed to be made up of two elastic layers and is loaded by the far field shear stress the upper part of the plate boundary is locked the slipping region that underlies the locked part is modeled by a mode iii crack containing a breakdown zone owing to the existence of a breakdown zone the stress possesses a pronounced peak at the tip of the slipping region and the loading stress takes high values both in front of the slipping region and within the breakdown zone the stress in the upper part of earth s crust is little influenced by the form of the slipping region and is mainly affected by elastic properties of the medium the comparison of the present results with those based on observational data in particular the data pertaining to the 1979 imperial valley earthquake allow the formulation of two general suggestions related to the faulting process first the depth difference between the point of initiation and the point of deepest penetration of rupture associated with major earthquakes correlates with the size of the breakdown zone second the process of faulting in the top part of earth s crust is primarily controlled by medium rigidity which explains why faulting and seismicity are suppressed in sediments

reservoir zonation rock typing and compartmentalization of the tortonian serravallian sequence temsah gas field offshore nile delta egypt abstract the present study aims to evaluate the petrophysical properties and to discriminate the tortonian wakar and the serravallian sidi salem formations in the offshore temsah gas field north egypt into distinctive rock types the measured conventional core data includes helium and summation fluids porosities grain and bulk densities horizontal and vertical permeabilities as well as the water saturation also the reservoir quality index rqi flow zone indicator fzi and reservoir potentiality index rpi were calculated to establish a successful reservoir zonation in the temsah field the tortonian serravallian sequence has been discriminated into four reservoir rock types rrts which are described based on its lithologic composition as 1 sandy to argillaceous carbonates rrt1 2 siliceous pebbly sandstones rrt2 and 3 argillaceous to calcareous sandstones rrt3 and 4 calcareous to dolomitic sandstones rrt4 based on the petrophysical interpretation and ranking for the studied samples samples of rrt2 have very good rank due to presence of very good porosity excellent permeability and good to very good rqi and fzi values which are assigned as the best reservoir rock type in the tortonian serravallian sequence the petrophysical behavior of rrt4 shows the lowest reservoir quality impervious rqi and poor fzi the examined sequence has been sliced into reservoir zones each zone has its hydraulic flow unit range that represents the studied rock types in each zone based on the applied pressure tools including repeat formation tester rft and the modular formation dynamic tester mdt both the wakar and sidi salem reservoirs represent completely isolated compartments therefore ranking both reservoirs and estimating their hydrocarbon potential must be done separately for each reservoir

a crack model of afterslip events on shallow faults summary post seismic evolution of surface displacement on a strike slip fault is studied employing a linear viscous rheology for the shallow fault zone a mathematical model is built in which the singular integral equation governing the equilibrium of cracks is transformed in an infinite dimensional linear symmetric system whose positive eigenvalues define a sequence of characteristic relaxation times the model lends to model vertical heterogeneities in the rheological parameters and the equations can be efficiently solved by truncation several specific problems are then considered in order to assess which parameters may govern the fast early relaxation observed in afterslip events in california neither stress heterogeneities nor the spectral distribution of characteristic relaxation times have significant effects on surface displacement if a uniform effective viscosity is employed viscosity heterogeneities however can provide fast early afterslip and perhaps precursory events post seismic creep data following the 1966 parkfield the 1979 imperial valley and the 1987 superstition hill earthquakes can be fitted well with this model without resorting necessarily to non linear rheological relations

stress orientation profile to 3 5 km depth near the san andreas fault at cajon pass california a detailed profile of the orientation of the apparent maximum horizontal compressive stress was constructed over the depth interval 1 75 3 46 km in the cajon pass drill hole located 4 2 km from the san andreas fault in southern california the profile is based on the analysis of stress induced well bore breakouts and consists of 32 616 orientation determinations at a basic sampling interval of 4 cm the azimuth of the apparent maximum horizontal compressive stress around the borehole is 057 s d 19 depth dependent variations in breakout azimuths from a few degrees to as much as 100 occur over depth intervals of several centimeters to hundreds of meters in the borehole with wavelengths showing a self similar distribution over a range of depth intervals the variations in breakout orientation at depth seem to reflect stress fluctuations associated with active faults penetrated by the drill hole assuming linear elastic behavior perturbations in stress magnitude and orientation were computed for predrilling slip on these faults fault stress drops limited to the ambient shear stress i e up to total stress drop along with occasional local extreme stress drops and geometrical complications can explain the variations in breakout orientations in the drill hole the penetrative stress inhomogeneity may suggest that the average orientation of borehole breakouts in cajon pass which indicates left lateral shear on planes parallel to the san andreas fault may not be representative of the state of stress near the fault at depth in this region rather the stress orientation profile indicates the superposition of numerous local stress perturbations on an average stress field which is characterized by an absence of appreciable right lateral shear on planes parallel to the san andreas combining these observations with the highly variable stress state in shallow boreholes in the western mojave desert it is suggested that the heterogeneous stress field in this region representing a spectrum of seismic events may extend over substantial distances across and along the san andreas fault zone if the average measured breakout orientation in cajon pass is representative of the state of stress near the san andreas in this region then substantial left lateral shear stress is resolved on planes parallel to the fault in contradiction to the sense of its long term motion we use an elastic dislocation model to compute the net stress change near the cajon pass drill site since just prior to the large 1812 earthquake taking into account coseismic slip in major earthquakes and aseismic accumulation of slip on the san andreas and san jacinto faults the model suggests that the net change in fault parallel shear stress during the current earthquake cycle in the cajon pass area is nearly negligible the difference between the measured and computed results requires that additional left lateral shear stress be superimposed on a generally fault normal maximum horizontal compressive stress the results suggest that during the great fort tejon earthquake of 1857 left lateral shear stress parallel to the san andreas fault in the region of cajon pass may have played a role in terminating the southeastward extent of the rupture propagation

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

crustal deformation in great california earthquake cycles periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model a depth l h extending downward from the earth s surface at a transform boundary between uniform elastic lithospheric plates of thickness h is locked between earthquakes it slips an amount consistent with remote plate velocity vpl after each lapse of earthquake cycle time tcy lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress the plates are coupled at their base to a maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions compatible with plate velocity are transmitted to the surface plates the coupling is described approximately through a generalized elsasser model we argue that the model gives a more realistic physical description of tectonic loading including the time dependence of deep slip and crustal stress buildup throughout the earthquake cycle than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone parameters of the model are chosen to fit seismic and geologic constraints and the apparent time dependence of surface strain rates along presently locked traces of the 1857 and 1906 san andreas ruptures we fix vpl 35 mm yr tcy 160 years and l 9 11 km based on earthquake nucleation depths the geodetic data are then found to be described reasonably within the context of a model that is locally uniform along strike and symmetric about a single san andreas fault strand by lithosphere thickness h 20 30 km and elsasser relaxation time tr 10 16 years we therefore suggest that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps crust mantle transition zone and has an effective viscosity between about 2 1018 and 1019 pa s depending on the thickness assigned to the asthenospheric layer predictions based on the chosen set of parameters are also consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces although the fit is degraded by asymmetry relative to the fault and by slip on adjacent fault strands

a physical model of the effect of a shallow weak layer on strong ground motion for strike slip ruptures we report results of foam rubber modeling of the effect of a shallow weak layer on ground motion from strike slip ruptures computer modeling of strong ground motion from strike slip earthquakes has involved somewhat arbitrary assumptions about the nature of slip along the shallow part of the fault e g fixing the slip to be zero along the upper 2 kilometers of the fault plane in order to match certain strong motion accelerograms most modeling studies of earthquake strong ground motion have used what is termed kinematic dislocation modeling in kinematic modeling the time function for slip on the fault is prescribed and the response of the layered medium is calculated unfortunately there is no guarantee that the model and the prescribed slip are physically reasonable unless the true nature of the medium and its motions are known ahead of time there is good reason to believe that in many cases faults are weak along the upper few kilometers of the fault zone and may not be able to maintain high levels of shear strain required for high dynamic energy release during earthquakes physical models of faulting as distinct from numerical or mathematical models are guaranteed to obey static and dynamic mechanical laws foam rubber modeling studies have been reported in a number of publications the object of this paper is to present results of physical modeling using a shallow weak layer in order to verify the physical basis for assuming a long rise time and a reduced high frequency pulse for the slip on the shallow part of faults it appears a 2 kilometer deep weak zone along strike slip faults could indeed reduce the high frequency energy radiated from shallow slip and that this effect can best be represented by superimposing a small amplitude short rise time pulse at the onset of a much longer rise time slip a weak zone was modeled by inserting weak plastic layers of a few inches in thickness into the foam rubber model for the 15 cm weak zone the average pulse is reduced by a factor of 0 46 the factor for the 20 cm case reduction is 0 11 for the 30 cm case it is 0 045 from these results we can see that the thicker the weak layer the more difficult it is for a short rise time acceleration pulse to push its way through the weak layer to the surface this is thus an approximate justification for reducing the high frequency radiation from shallower parts of strike slip faults if it is known that the shallow part of the fault is weak or has not stored up shear stress

foreshocks 1966 1980 in the san andreas system california the spatial and temporal distributions of seismicity preceding moderate ml 5 0 main shocks in the san andreas fault system in california have been analyzed to recognize and characterize the patterns of foreshock occurrence of 20 main shocks in the san andreas system 7 or 35 per cent have been preceded by immediate foreshock sequences that included events within 1 day and 5 km of the main shocks a possible correlation of the rate of foreshock occurrence with type of faulting was found such that none of the four main shocks with reverse faulting had foreshocks while 44 per cent of the strike slip earthquakes had foreshocks some enhanced seismic activity was also observed at relatively large distances from the main shock 13 to 30 km 1 to 5 days before 40 per cent of the main shocks but this activity cannot be clearly distinguished from the background seismicity of the seven immediate foreshock sequences only two had the swarm like appearance of the class ii foreshocks defined by mogi the other foreshock sequences appear to be single events sometimes with their own aftershocks preceding the respective main shocks four of these sequences are spatially correlated with distinct physical discontinuities in their faults between the hypocenters of the foreshock and main shock and similar discontinuities may also be associated with the other sequences the durations of the foreshock sequences were found to decrease as the depths of the main shocks increase from 3 to 11 km which has been interpreted as a dependence on stress to account for this stress dependence of the duration and the presence of discontinuities a model for foreshocks occurrence is presented this model proposes that foreshocks may represent a process of delayed multiple rupture and that the delay between occurrence of foreshock and main shock might represent the time needed for static fatigue to break the stronger rock at the discontinuity in the fault

maturation history of neogene quaternary sediments nile delta basin egypt geologic note the present nile delta area covers approximately 60 000 sq km fields in this area provide two thirds of the gas production in egypt geological knowledge of the nile delta is still limited because of insufficient subsurface data gas is generated and accumulates at stratigraphic levels ranging from the lower miocene to the lower pliocene the highest levels of organic maturation in the neogene quaternary section are in the northern part of the onshore area such as in the abu madi well and in the eastern part of the offshore area such as in the el temsah well where gas reservoirs occur in the lower pliocene sandstones abu madi formation and in the underlying sidi salem formation and lower miocene rocks here the sidi salem formation is probably generative having n r o of approximately 0 65 lom levels of organic metamorphism of 9 5 to 9 7 and tti time temperature index of 9 7 to 15 2 by contrast a different thermal history clearly existed in the western and eastern parts of the onshore area such as in the monaga and damanhur wells where the organic maturities are significantly lower than maturities elsewhere in the basin r o 0 38 and 0 29 respectively the predicted maturities obtained by using the lom method seem to fit much closer to the observed maturities than the predicted maturities obtained by using the lopatin tti method

focal mechanisms and the state of stress on the san andreas fault in southern california focal mechanisms have been determined from p wave first motion polarities for 138 small to moderate 2 6 m 4 3 earthquakes that occurred within 10 km of the surface trace of the san andreas fault in southern california between 1978 and 1985 on the basis of these mechanisms the southern san andreas fault has been divided into five segments with different stress regimes earthquakes in the fort tejon segment show oblique reverse sup on east west and northwest striking faults the mojave segment has earthquakes with oblique reverse and right lateral strikesup motion on northwest strikes the san bernardino segment has normal faulting earthquakes on north south striking planes while the banning segment has reverse strike sup and normal faulting events all occurring in the same area the earthquakes in the indio segment show strike slip and oblique normal faulting on northwest to north south striking planes these focal mechanism data have been inverted to determine how the stresses acting on the san andreas fault in southern california vary with position along strike of the fault one of the principal stresses is vertical in all of the regions the vertical stress is the minimum principal stress in fort tejon and mojave the intermediate principal stress in banning and indio and the maximum principal stress in san bernardino the orientations of the horizontal principal stresses also vary between the regions the trend of the maximum horizontal stress rotates over 35 from n15 w at fort tejon to n20 at indio except for the san bernardino segment the trend of the maximum horizontal stress is at a constant angle of about 65 to the local strike of the san andreas fault implying a weak fault the largest change in the present stress state occurs at the end of the rupture zone of the 1857 fort tejon earthquake it appears that the 1857 rupture ended when it propagated into an area of low stress amplitude possibly caused by the 15 angle between the strikes of the san jacinto and san andreas faults the strong correlation between present state of stress and segmentation in previous earthquakes suggests that the stress state is important in controlling rupture propagation

role of temperature and time on organic metamorphism geologic notes organic metamorphism kerogen to hydrocarbon transformation is a function of both temperature and exposure time the effect of temperature is exponential of that of time linear at very low temperatures 266 f 130 c the reaction proceeds at such a high rate that time also plays no important role the effect of time is noticeable in the range of 158 to 212 f 70 to 100 c where intermediate conversion rates prevail stopping the heating process termination of burial freezes the rate constant of the reaction and allows organic metamorphism to continue at a linear rather than exponential rate this effect is demonstrated with the help of a simple geologic model for the first example a source rock was subjected to continuous linear heating whereas for the second the heating was terminated at a certain temperature level the model was analyzed by using the oleum scale a modified lopatin approach

nannoplankton calendar applications of nannoplankton biochronology in sequence stratigraphy and basin analysis in the subsurface offshore nile delta egypt abstract a comprehensive nannoplankton biozonation of the pliocene pleistocene succession of off shore nile delta has been recorded from two wells namely baltim 1 and ndob 1 in the present contribution the biozonation is relied the identification of 8 nannoplankton biozones and their associated bioevents these biozones are pseudoemiliania lacunosa zone nn19 discoaster brouweri zone nn18 discoaster pentaradiatus zone nn17 discoaster surculus zone nn16 reticulofenestra pseudoumbilicus zone nn15 discoaster asymmetricus zone nn14 ceratolithus rugosus zone nn13 and amaurolithus tricorniculatus zone nn12 as arranged from top to base the pliocene pleistocene boundary is placed near to the top of d surculus zone nn16 the lower boundary of the pliocene is placed within the a tricorniculatus nn12 the recognized bioevents are used to calculate the sedimentation rates srs and to delineate their relative variations versus the depth the relative variations of the sr values were interpreted in accordance with the history of fluvial fresh water supply in the delta region since the early pliocene the relationship between the values of the sr and the potential occurrences of hydrocarbon sources organic matter oxic preservation and reservoir coarser clastics accumulation rocks in the studied succession has been clarified likewise the possible relationships of the sr values history of fresh water input in the nile valley and the sapropel formation mechanism has been discussed the relative variations of srs versus the depth have been interpreted in a sequence stratigraphic framework which led to identification of three correlatable genetic sequences in the studied succession the nannoplankton bioevents are used instead of stage and epoch boundaries in plotting of the burial history models for the studied wells which greatly improved the precision of the maturation onset and hydrocarbon generation this collection of nannoplankton biochronology based applications is of large importance for the future petroleum exploration in the nile delta region

tsunamis and submarine landslides in suruga bay central japan caused by nankai suruga trough megathrust earthquakes during the last 5000 years abstract magnitude 8 megathrust earthquakes that have generated large tsunamis with wave heights of 5 m in coastal areas of southwestern japan have occurred every 100 150 years along the nankai suruga trough which marks the convergent boundary between the eurasian and philippine sea plates using sedimentological geochemical and paleontological analyses as well as 14c dating we examined tsunami deposits in 12 sediment cores collected from the hamatome lowland yaizu plain shizuoka which faces the suruga trough four sandy tsunami deposits sands 1 4 are identified in sediments deposited during the last 5000 years sand 1 was deposited between 805 and 405 bc suggesting that only one tsunami left a sedimentological imprint in the hamatome lowland lagoon during the period of 4000 years between 3090 and 2913 bc and the ad 1096 eicho tokai earthquake this very low frequency of tsunami inundation may suggest that this tsunami was larger than those typically associated with megathrust earthquakes sands 2 4 are correlated with tsunamis associated with the eicho tokai ad 1361 shohei koan and ad 1498 meio tokai earthquakes respectively our data indicate that a sand spit which had previously protected the lagoon from oceanic waves was abruptly destroyed following the ad 1096 eicho tokai earthquake and did not re form at the same location this disappearance of the sand spit is inferred to have involved an earthquake induced submarine landslide the data presented in this paper together with information obtained from historical documents indicates that m8 megathrust earthquakes in ad 1096 and ad 1498 caused submarine landslides in the study area resulting in coastal subsidence and damage to coastal areas additional to that caused by the tsunamis

gravity induced stresses near topography of small slope topographic modification of gravity induced near surface stresses results in significant departures from a lithostatic state a perturbation scheme provides approximate analytical solutions for plane strain of an elastic half space with an irregularly shaped free surface of small characteristic slope e the leading order effect of the topography is equivalent to that of a distributed normal load on a plane boundary and the correction at order e is due to a distributed shear traction on a plane boundary in the near surface region these two effects contribute at the same order to departures from the lithostatic stress field the contribution of the shearing has been neglected in most previous analyses we present explicit solutions for several particular geometries a symmetric ridge or valley an adjacent ridge and valley a shelf and a sharp crested ridge notable features include 1 for a sufficiently steep ridge the horizontal normal stress is compressive at the crest and decreases possibly becoming tensile with depth 2 large horizontal tension is induced in a valley bottom at greater depth these effects vanish and the stresses approach lithostatic similar analysis is applied to a half space under a far field tectonic compression or tension the result shows that the leading order effect of topography is equivalent to a distributed shear traction on a plane surface regional horizontal compression can be significantly reduced or even change to tension in the neighborhood of a topographic high

hydraulic fracturing stress measurements at yucca mountain nevada and relationship to the regional stress field hydraulic fracturing stress measurements and acoustic borehole televiewer logs were run in holes usw g 1 and usw g 2 at yucca mountain as part of the nevada nuclear waste storage investigations for the u s department of energy eight tests in the saturated zone at depths from 646 to 1288 m yielded values of the least horizontal stress s h that are considerably lower than the vertical principal stress s v in tests for which the greatest horizontal principal stress s h could be determined it was found to be less than s v indicating a normal faulting stress regime the borehole televiewer logs showed the presence of long in excess of 10 m vertical drilling induced fractures in the first 300 m below the water table these are believed to form by the propagation of small preexisting cracks under the excess downhole fluid pressures up to 5 2 mpa applied during drilling the presence of these drilling induced hydrofractures provides further confirmation of the low value of the least horizontal stresses a least horizontal principal stress direction of n60 w n65 w is indicated by the orientation of the drilling induced hydrofractures n25 e n30 e and the orientation of stress induced well bore breakouts in the lower part of usw g 2 n65 w this direction is in good agreement with indicators of stress direction from elsewhere at the nevada test site the observed stress magnitudes and directions were examined for the possibility of slip on preexisting faults using these data the coulomb criterion for frictional sliding suggests that for coefficients of friction close to 0 6 movement on favorably oriented faults could be expected for coefficients of friction of 1 0 preexisting faults of all orientations should be stable laboratory studies on the yucca mountain tuffs reported elsewhere yield coefficients of friction ranging from 0 6 to 0 9

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details

shear heating in continental strike slip shear zones model and field examples summary a two layer crust and upper mantle finite diverence steady state thermomechanical model of a long lived several million years lithospheric strike slip fault is presented and its predictions compared with field observations from various major fault zones in order to estimate the maximum amount of shear heating all mechanical energy is assumed to be dissipated in heat in ductile as well as in brittle layers deformation follows a friction law in the brittle layer s and a power flow law in the ductile one s variations of several independent parameters and their influence on the thermomechanical state of the fault zone and on shear heating are systematically explored shear heating is found to be more important in fault zones avecting an initially cold lithosphere and increases with slip rate friction coeycient and stivness of materials in extreme cases slip rate of 10 cm yr 1 stiv lithosphere shear heating could lead to temperature increases close to 590 c at the moho and 475 c at 20 km depth for more common cases shear heating leads to smaller temperature increases but can still explain high grade metamorphic conditions encountered in strike slip shear zones however modelled temperature conditions often fall short of those observed this could be due to heat transport by mechanisms more eycient than conduction common syntectonic emplacement of granitic melts in ductile strike slip shear zones can be explained by lower crust partial melting induced by shear heating in the upper mantle besides slip rate the possibility of such melting depends mostly on the upper mantle rheology and on the fertility of the lower crust for hard upper mantle and highly fertile lower crust partial melting could occur at rates of 1 cm yr 1 while in most cases it would result from the breakdown of micas for slip rates over 3 cm yr 1 as a result of shear heating partial melting of the upper mantle could occur in the presence of small amounts of fluids rise of magmas and or hot fluids in the shear zone will further enhance the temperature increase in shallower parts of the fault zone in nature shear heating would inevitably cause strain localization in the deeper parts of strike slip faults as is often observed in the field for crustal shear zones