the use of stress tensor discriminator faults in separating heterogeneous fault slip data with best fit stress inversion methods ii compressional stress regimes abstract synthetic heterogeneous fault slip data as driven by andersonian compressional stress tensors were used to examine the efficiency of best fit stress inversion methods in separating them heterogeneous fault slip data are separated only if a they have been driven by stress tensors defining hybrid compression r 1 axes differ in trend more than 30 r 0 or 50 r 0 25 separation is not feasible if they have been driven by b real r 0 375 and hybrid compressional tensors having their 1 axes in similar trend or c real compressional tensors in case a the stress tensor discriminator faults stdf exist in more than 50 of the activated fault slip data while in cases b and c they exist in percentages of much less than 50 or not at all they constitute a necessary discriminatory tool for the establishment and comparison of two compressional stress tensors determined by a best fit stress inversion method the best fit stress inversion methods are not able to determine more than one real compressional stress tensor as far as the thrust stacking in an orogeny is concerned they can only possibly discern stress differences in the late orogenic faulting processes but not between the main and late orogenic stages

faulting of lemnos island a mirror of faulting of the north aegean trough northern greece abstract a detailed analysis of the faulting on lemnos island since the miocene was achieved by grouping the recorded meso scale faults and their slickenlines into different groups replacing them with mean representative fault planes mrfp and lineations mrfl and finding the stress tensors driven to the activation of the different mrfp mrfl pairs the oldest recognized fault activity followed the late oligocene n s contraction and uplift d1 event as the latter is implied by e w to ene wsw buckle folds in the upper eocene lower oligocene molasse type sediments it was an early middle miocene strike slip to transpression deformation d2 event associated with n s contraction that also affected the lower miocene volcanogenic rocks the next fault activity was dated in middle late miocene and caused a wnw ese extension d3 event this deformation suggests that a during the late eocene oligocene the north aegean trough was developed as a fore arc basin between the rhodopian magmatic arc and its subduction accretion complex to the south and b during the late oligocene middle miocene the north aegean trough as the whole hellenic hinterland was subjected to the transpression s l deformation and lateral extrusion because of the late collisional processes between apulia and eurasia plates and the retreating of the hellenic orogen from late miocene to pliocene a ne sw extension to right lateral transtension d4 event dominated the north aegean trough indicating that the retreating of the hellenic orogen was completely balanced by a back arc extension the deformation facilitates the westward propagation of the north anatolian fault into the north aegean sea since the early pleistocene the deformation of the north aegean trough is related to a nne ssw back arc extension d5 of the present day hellenic subduction zone and the dominant ene wsw to e w faults along the north aegean trough function as normal to oblique right lateral normal faults

the tr method the use of slip preference to separate heterogeneous fault slip data in compressional stress regimes the surface rupture of the 1999 chi chi taiwan earthquake as a case study abstract synthetic contractional fault slip data have been considered in order to examine the validity of widely applied criteria such as the slip preference slip tendency kinematic p and t axes transport orientation and strain compatibility in different andersonian compressional stress regimes radial compression rc radial pure compression rc pc pure compression pc pure compression transpression pc trp and transpression trp are examined with the aid of the win tensor stress inversion software furthermore the validity of the recently proposed graphical tr method which uses the concept of slip preference for the separation of heterogeneous fault slip data is also examined for compressional stress regimes in these regimes only contractional faults can be activated and their slip preferences imply the distinction between real i e rc rc pc and pc and hybrid i e pc trp and trp stress regimes for slip tendency values larger than 0 6 the activated faults dip at angles from 10 to 50 but in the hybrid regimes faults can dip with even higher angles the application of the tr method is here refined by introducing two controlling parameters the coefficient of determination r2 of the final tensor ratio line ftrl and the normal or inverse distribution of the faults plotted within the final tensor ratio belt ftrb the application of the tr method on fault slip data of the 1999 chi chi earthquake taiwan allowed the meaningful separation of complex heterogeneous contractional fault slip data into homogeneous groups in turn this allowed the identification of different compressional stress regimes and the determination of local stress perturbations of the regional or far stress field generated by the 1999 chi chi earthquake this includes clear examples of stress permutation and stress partitioning caused by pre existing fault structures such as the n s trending chelungpu thrust and the ne sw trending shihkang shangchi fault zone

the multiple inverse method a new technique to separate stresses from heterogeneous fault slip data abstract a new inverse technique is presented here to separate stresses from heterogeneous fault slip data without a priori information on the stresses or on the classification of faults according to the stresses four parameters are determined by the inversion one for the shape of the stress ellipsoid and three for the direction of the stress axes accordingly the inversion is equivalent to the projection of the fault slip data to a point in four dimensional parameter space the data are divided into k element subsets to which the inverse technique is applied where k 4 or 5 is the optimal choice for the stability of solutions and for the reduction of computation significant solutions are identified as clusters in parameter space the technique is demonstrated first by simulated fault slip data as an example field data obtained from miocene fore arc sediments in western japan were processed by the method

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

reconstruction of the stress regime in the jiaolai basin east asian margin as decoded from fault slip analysis abstract the east asian margin has experienced a complex tectonic history since the mesozoic and has developed a complex basin mountain system the jiaolai basin which is located on the east asian margin is a typical mesozoic rift basin that has undergone multiple tectonic episodes here using field geological surveys effective stress inversions and accurate chronological data we recognize six tectonic episodes that have occurred in the jiaolai basin since the cretaceous e w extension 135 121 ma which controlled the early deposition of the laiyang group nw se extension 120 93 ma which controlled the late deposition of the laiyang group and the eruption of the volcanic rocks in the qingshan group ne sw compression 92 86 ma which produced folding of the qingshan group and its underlying strata and the formation of the unconformity surface between the wangshi and the qingshan groups n s extension 85 60 ma which controlled the deposition of the wangshi group nw se compression 60 55 ma which produced the unconformity between the wangshi group and the wutu group and ne sw extension ca

possible paleostress tensor configurations derived from fault slip data in eastern vermont and western new hampshire the configuration of six possible paleostress tensors have been derived from 152 faults measured in eastern vermont and western new hampshire populations of potentially genetically related faults were separated using two techniques tensor configurations for each population were derived using a linear least squares inversion method based in part on the work of reches 1987 and a grid search inversion method which tests over 100 000 possible tensors for compatibility with all or portions of the data faults belonging to the oldest population set r n 24 occur primarily in high grade rocks this set is composed of semiductile northeast trending reverse and west northwest trending left lateral faults fault fabrics of quartz rods and thin mylonite layers suggest that the host rocks were at crustal levels of 8 10 km during faulting the derived tensor indicates a roughly east west 1 and near vertical 3 set r faults are offset by normal faults sets n1 and n2 and are interpreted to be pre mesozoic in age perhaps related to late paleozoic alleghanian compression normal and normal oblique faults mineralized with chlorite calcite and strained quartz n 73 have been separated into two populations sets n1 n 49 and n2 n 24 even though these faults are likely of similar age host rocks were probably at moderate crustal depths of perhaps 5 km during faulting faults of both sets are most likely related to mesozoic rifting tensor configurations indicate that 1 plunges steeply northwest n1 and southeast n2 and 3 plunges gently roughly east west these faults cut presumably mesozoic age dikes and are themselves offset by normal oblique faults set t and right lateral faults set rl strongly deviatoric near vertical 1 suggests a thermally driven tectonic regime during the development of normal faulting in new england set t n 25 is composed of normal oblique slip faults mineralized similarly as sets n1 and n2 the plunge of 1 is 50 n and 3 plunges gently east field relations indicate set t faults document the transition from normal sets n1 and n2 to strike slip faulting regimes set rl a compatible sequence of mesozoic stress fields is suggested de boer et al 1988 north northeast trending right lateral faults of set rl n 7 are mineralized with quartz limonite calcite chlorite calcite twins are bent and fractured and quartz grains show minor internal strain suggesting that these faults developed while host rocks were at relatively shallow crustal levels the plunge of 1 is gently northeast and 3 plunges gently east southeast seven distinctly mineralized feldspar siderite quartzoalcite 1imonite chlorite gently northwest dipping thrust faults of set f define the sixth tensor these faults are cut by essentially vertical east side up faults and are assumed to be mesozoic in age by analogy with similar faults in western massachusetts

from orientation to magnitudes in paleostress determinations using fault slip data abstract determinations of reduced stress tensors using fault slip data yield the orientation of principal stress axes and the ratio of the differences between principal stress magnitudes the use of rupture and friction laws allows determination of the two remaining unknowns that is the reconstruction of the complete stress tensor taking into account the depth of overburden brings an additional constraint the method is applied and discussed in the case of the hoover dam site western u s a where large data sets and rock mechanics information are available differences between intact sample and rock mass properties account for apparent disagreements between paleostress levels determined in similar tectonic environments pore pressure plays an important role where information about pore pressure is absent zero and hydrostatic pore pressure cases should be considered as limits

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

favoured states of palaeostress in the earth s crust evidence from fault slip data abstract in a major survey of published palaeostress estimates obtained by the use of fault slip data over 2000 stress tensors from shallow crustal levels have been compiled the results are derived from regions where deformation is dominated by brittle processes and consist of incomplete stress tensors in which the orientations of the principal stresses 1 2 3 are known together with the stress ratio 2 3 1 3 the orientations of the stress axes display a preferred orientation with a tendency for one of the axes to be vertical this accords with anderson s assumed standard state stress configuration near to the earth s free surface although the tendency is strong there are frequent deviations from the arrangement in 25 of cases the steepest stress axis deviates by more than 25 from the vertical in undertaking studies of palaeostress it would be therefore unwise to use methods that assume a priori one vertical stress axis unless previous local results indicate this to be the case normal strike slip and thrust stress arrangements with 1 2 and 3 as the steepest stress respectively occur in the database with frequencies approximately in the ratio 2 2 1 in the compiled results the raw stress ratios which have a theoretical range from 0 to 1 show a lack of very high values and to a lesser extent very low values this suggests that triaxial stress states are more common than axial compression deviatoric stress and axial tension deviatoric stress however this relative abundance of triaxial stress states is considered to be a natural feature of a uniform distribution of stress tensors in addition there is a marked bias in the collated ratios towards values less than 0 5 and this is expressed by an overall mean of 0 39 several possible explanations for the distribution of stress ratios are discussed these explanations are related to the tendency for tectonic deformation to be of plane strain type coupled with volume change and to the fact that gravitational loading makes an important contribution to the state of stress in the crust

structural controls on granitoid hosted gold mineralization and paleostress history of the edikan gold deposits kumasi basin southwestern ghana the 9 moz total aggregate gold endowment at the edikan mine kumasi basin ghana is contained within a cluster of orogenic gold deposits located along the akropong fault zone the granitoid hosted orebodies at edikan e g ag2 ag3 fobinso esuajah essentially an interconnected mesh of gold bearing quartz veins formed during deformation event d3edk which postdates the penetrative regional d2edk deformation the gold bearing quartz veins developed in and adjacent to n s and nw se trending low angle thrust faults that crosscut lithological contacts and earlier formed steeply dipping d2edk faults our paleostress analysis shows that the d3edk deformation during which the mineralized fault system developed was characterized by a wnw ese hybrid compression that evolved to a strike slip regime this progressive deformation is best described with the following stress regimes wnw ese transpression pure compression t1 associated with low angle thrusting subsequent transpression strike slip t2 and later strike slip transtension t3 associated with steeply dipping strike slip faulting the bulk of the granitoid hosted gold mineralization at edikan is associated with two principal sets of gold bearing quartz veins including low angle fault fill veins controlled by thrusts and shallow dipping oblique extension veins that developed during t1 the activation of the reverse and sinistral strike slip faults led to the development of restraining jogs characterized by abundant shallow and steeply dipping gold quartz veins with moderately ne plunging ore shoots the geometry of the mineralized fault fracture meshes is consistent with fault valve behavior in a horizontal compressive stress regime under sustained conditions of supralithostatic fluid pressures at low differential stress

a stress inversion procedure for polyphase fault slip data sets palaeostress estimation from striated fault data is frequently frustrated by the fact that natural fault data are heterogeneous in the sense that they cannot satisfactorily be explained by reactivation brought about by a single stress tensor in many instances there is clear evidence to show that striation data can record the effects of multiple stress events any attempt to find the tensor which best fits or explains such dynamically mixed data sets risks determining a spurious stress state which is some form of compromise between the real stress states corresponding to different tectonic phases to avoid this problem a strategy is proposed here which involves an initial separation of the raw data into coherent sub sets prior to formal stress inversion this separation is performed by assigning attributes to each fault which describe the fault s compatibility with trial stress tensors using these attributes faults can be grouped into dynamically homogeneous families using the statistical techniques of cluster analysis

slip preference on pre existing faults a guide tool for the separation of heterogeneous fault slip data in extensional stress regimes abstract synthetic fault slip data have been considered in the present paper in order to examine through a simple graphical manner the validity and use of the widely mentioned and applied criteria such as the slip preference slip tendency kinematic p and t axes transport orientation and strain compatibility the examination and description concern extensional stress regimes whose greatest principal stress axis 1 always remains in vertical position as in andersonian stress states in particular radial extension re radial pure extension re pe pure extension pe pure extension transtension pe trn and transtension trn are examined with the aid of the win tensor stress inversion software in all of these extensional stress regimes only extensional faults can be activated the lower dip angle of the reactivated faults is about 40 assuming that the coefficient of friction is no smaller than 0 6 the increase of the stress ratio and or the fault dip angle up to 70 results in the increase of the slip deviation from the normal activation based on the present examination of the slip preference and slip tendency in different extensional stress regimes a new simple and practical method is proposed herein in order to separate originally heterogeneous fault slip data into homogeneous fault groups by which different extensional stress regimes could be determined the application of the method on the already published fault slip data of lemnos island supports its validity since over 90 the resulted fault groups and stress regimes coincide to the already published ones

influence of measurement errors on stress estimated from single phase fault slip data abstract the influence of measurement errors on estimated stress is investigated in reduced sigma space on the basis of numerous sets of homogeneous fault slip data generated under different extensional stress and then modified by varying measurement errors for the striation pitch for a given measurement error error propagation to a datum vector depends upon the controlling stress and fault orientation with respect to the controlling stress for a given stress ratio both the dispersion of datum vectors i e root mean square cosine and the misfit between estimated and controlling stresses i e similarity and stress difference increase with the increase in measurement error the two measures appear generally smaller at small measurement error than at large error and have a strong tendency to increase with stress ratio for a given measurement error the measurement error has an apparent effect in estimated stress only if it is greater than 10 implying a limited effect on homogeneous fault slip data that is carefully measured at outcrop in which a smaller error can be guaranteed in a majority of cases

numerical simulations of the atmospheric response to a sea surface temperature anomaly over the equatorial eastern pacific ocean abstract the atmospheric response to a sea surface temperature anomaly over the equatorial eastern pacific ocean ssta is investigated using the ucla general circulation model the ssta used is an idealization of that compiled by rasmusson and carpenter for the mature phase of el nino two simulations over seasons one without and the other with the ssta are performed and their results are compared for the northern hemisphere winter season in the tropics the ssta enhances precipitation over the central and eastern equatorial pacific while it decreases precipitation over the adjacent regions the anomalous precipitation is predominantly balanced by the anomalous moisture flux convergence which has comparable magnitude in the planetary boundary layer pbl and in the free atmosphere with quite different geographical distribution this suggests that the anomalous precipitation and hence the anomalous tropical cumulus heating cannot be related exclusively to either flow anomalies in the pbl or in the

in situ measurements of tropospheric volcanic plumes in ecuador and colombia during tc4 a nasa dc 8 research aircraft penetrated tropospheric gas and aerosol plumes sourced from active volcanoes in ecuador and colombia during the tropical composition cloud and climate coupling tc 4 mission in july august 2007 the likely source volcanoes were tungurahua ecuador and nevado del huila colombia the tc 4 data provide rare insight into the chemistry of volcanic plumes in the tropical troposphere and permit a comparison of so 2 column amounts measured by the ozone monitoring instrument omi on the aura satellite with in situ so 2 measurements elevated concentrations of so 2 sulfate aerosol and particles were measured by dc 8 instrumentation in volcanic outflow at altitudes of 3 6 km estimated plume ages range from 2 h at huila to 22 48 h downwind of ecuador the plumes contained sulfate rich accumulation mode particles that were variably neutralized and often highly acidic a significant fraction of supermicron volcanic ash was evident in one plume in plume o 3 concentrations were 70 80 of ambient levels downwind of ecuador but data are insufficient to ascribe this to o 3 depletion via reactive halogen chemistry the tc 4 data record rapid cloud processing of the huila volcanic plume involving aqueous phase oxidation of so 2 by h 2o 2 but overall the data suggest average in plume so 2 to sulfate conversion rates of 1 2 h 1 so 2 column amounts measured in the tungurahua plume 0 1 0 2 dobson units are commensurate with average so 2 columns retrieved from omi measurements in the volcanic outflow region in july 2007 the tc 4 data set provides further evidence of the impact of volcanic emissions on tropospheric acidity and oxidizing capacity

the use of stress tensor discriminator faults in separating heterogeneous fault slip data with best fit stress inversion methods abstract a widely accepted best fit stress inversion method is applied on synthetic extensional heterogeneous fault slip data generated by two driving andersonian stress tensors having similar stress ratios and 3 axes with different trends in order to examine whether the misfit angle ma minimization criterion can be used for separating heterogeneous fault slip data the examination shows that the resolved best fit stress tensors have 3 axes that tend to the bisector of the 3 axes of the driving stress tensors and stress ratios smaller than those of the latter moreover there is a tendency towards determining radial extension stress regimes although such regimes are rare in the earth s crust more importantly the best fit stress inversion methods that use solely the ma minimization criterion cannot be used for the separation of heterogeneous fault slip data especially when the extensional driving stress tensors have stress ratios smaller than r 0 5 i e as are the favored paleostresses in the earth s crust in contrast the percentage of the stress tensor discriminator faults stdf can be a very useful discriminator tool for the establishment and comparison between two resolved stress tensors as the latter have been determined by a best fit stress inversion method moreover the existence of fault slip data that can been considered as possible stdfs during the recording stage advocate for the heterogeneous origin of the fault slip dataset

transtensional origin of the ne sw simitli basin along the strouma strymon lineament sw bulgaria several depocentres have developed along the nnw sse striking strouma strymon lineament since the miocene forming the strouma strymon graben system some of these basins including the dzherman and simitli strike at high angles to the lineament the rhomboid shaped simitli basin is limited in the south by the ne sw striking seismically active kroupnik fault and contains terrestrial clastic sediments which have been deposited since the sarmatian its formation is attributed to wrench dominated transtension d b event which activated the basin9s ne sw striking boundary faults as left lateral strike slip structures during the early middle miocene this deformation was associated with nne ssw contraction and wnw ese extension and succeeded the nne ssw contraction caused by pure shear dominated transpression d a event which governed the region in late oligocene early miocene times during the middle late miocene the d b event was followed by wnw ese pure shear dominated extension d 1 event which caused further widening of the basin the transtensional origin of the simitli basin is explained by lateral extrusion of the crustal mass squeezed between the apulian adriatic microplate and the european foreland towards the north aegean sea the subduction retreat of the hellenic orogen possibly enhanced this lateral extrusion and from the late miocene onwards the ne sw oriented back arc extension balanced the continuing retreat

impacts of sst anomalies on the north atlantic atmospheric circulation a case study for the northern winter 1995 1996 the present paper selects the northern winter of december 1995 february 1996 for a case study on the impact of sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic and western europe in the atlantic the selected winter was characterized by positive sst anomalies over the northern subtropics and east of newfoundland and negative anomalies along the us coast a weak la nina event developed in the pacific the north atlantic oscillation nao index was low precipitation over the iberian peninsula and northern africa was anomalously high and precipitation over northern europe was anomalously low the method of study consists of assessing the sensitivity of ensemble simulations by the ucla atmospheric general circulation model ucla agcm to sst anomalies from the observation which are prescribed either in the world oceans the atlantic ocean only or the subtropical north atlantic only the results obtained are compared with a control run that uses global time varying climatological sst the ensemble simulations with global and atlantic only sst anomalies both produce results that resemble the observations over the north atlantic and western europe it is suggested that the anomalous behavior of the atmosphere in the selected winter over those regions therefore was primarily determined by conditions within the atlantic basin the simulated fields in the tropical north atlantic show anomalous upward motion and lower upper level convergence divergence in the atmosphere overlying the positive sst anomalies consistently the subtropical jet intensifies and its core moves equatorward and precipitation increases over northern africa and southern europe the results also suggest that the sst anomalies in the tropical north atlantic only do not suffice to produce the atmospheric anomalies observed in the basin during the selected winter the extratropical sst anomalies would provide a key contribution through increased transient eddy activity which causes an extension of the subtropical jet eastward from the coast of north america

tectonic evolution of the intra uplift vigodi gugriana khirasra netra fault system in the seismically active kachchh rift basin india implications for the western continental margin of the indian plate abstract the e w striking kachchh rift basin krb at the western continental margin of indian plate is located in the northern part of gujarat state india krb has undergone polyphase deformation owing to changing stress field since late triassic we establish the kinematic framework along the nw striking intra uplift vigodi gugriana khirasra netra fault system vgknfs located at the western part of the krb the vgknfs consists of 0 25 50 km long sub parallel striated reactivated dip slip faults a total of 1150 fault slip data consisting of fault planes and striations attitude were recorded from 66 sites including a single site with systematic joints slip sense of faults was determined by documenting kinematic indicators paleostress analysis was carried out using win tensor t tecto faultkin and sg2ps to compare and validate the results the chi square statistical analysis was undertaken to evaluate how relevant are paleostress analysis results to the present day compressional stress field geophysical investigations were conducted at selected sites using ground penetrating radar gpr to understand the shallow subsurface geometry and trace the continuity of faults buried below patchy alluvial cover 15 17 m long 2d gpr cross sections were recorded across faults using monostatic antenna of 200 mhz frequency two major deformation events d1 and d2 are determined in the present study the extension event d1 shows w and nw nnw extension during late triassic to late cretaceous it occurred during the rift phase of krb in response of the break up of gondwanaland the latest event d2 shows nne ne compression from late cretaceous up to the present it is interpreted to have developed during post rift inversion phase induced by collision of the indian plate with the eurasian plate at 55 ma

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

the kinematics of the dasht e bayaz earthquake fault during pliocene quaternary implications for the geodynamics of eastern central iran the arabia eurasia convergence is accommodated across the iranian plateau and surrounding mountain ranges strike slip faults play significant roles in the current deformation of the iranian plateau and were responsible for several moderate to large earthquakes especially in east of iran the sinistral dasht e bayaz fault shows conspicuous seismic and geological activities while the role of the fault in the accommodation of active convergence is still debated this paper focuses on the pliocene quaternary to present day states of stress in the region affected by the dasht e bayaz fault we applied the fault slip inversion technique to both kinds of seismologic and geological fault slip data the inversion results indicate a mean n045 5 e trending 1 in the modern stress field which agrees with the present day tectonic regime regional n050 05 e trending 1 deduced from the inversion of earthquake focal mechanism data the paleostress state is characterized by a n135 15 e trending regional mean 1 with a transpressional stress regime e w faults of the region such as the dasht e bayaz fault were reverse dextral in this paleostress field we show that the shift in fault kinematics during the pliocene quaternary times has not been restricted to northeastern parts of the iranian plateau the cross cutting relationship between active n s dextral and e w sinistral faults indicates a crosswise to conjugate fault arrangement in the middle and the eastern end of the dasht e bayaz fault integrating our results at a larger regional scale we present a kinematic model in which the region between lut and kopeh dagh is divided by the doruneh fault into two tectonic domains in the northern domain active convergence is taken up by the extrusion of fault bounded crustal blocks while in the southern domain the convergence is accommodated through crosswise strike slip faulting accompanied by reverse thrust faulting in confining wedges

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them

recent temporal change in the stress state and modern stress field along the north anatolian fault zone turkey summary the north anatolian fault naf is a dextral strike slip fault which runs about 1400 km from east to west from the karliova triple junction to the aegean domain it was active during the plio quaternary as a consequence of the collision between the eurasian and arabian plates the naf intracontinental deformation zone contributes with the sinistral east anatolian fault to the westward extrusion of anatolia as a consequence of the northward drift of arabia the central naf zone forms a northward convex bend where the eastern naf n110 e trending segment extending from karliova is connected to the western naf n75 e trending segment running to aegea analysing the slip occurring in major earthquakes around the naf we show that the present day stress pattern along the naf agrees with stress magnitude and strike variations from east to west the stress regime along the naf is nnw trending hmax 1 transpression in eastern naf this progressively changes westwards to nw trending 1 transtension in central anatolia this lateral variation means a relative decrease of the hmax magnitude which evolves progressively to an extensional regime 1 vertical around the westernmost naf characterized by a nne trending hmin 3 the drastic change in the tendency of the regional stress state in the north anatolian block from compressional to extensional is effective within the central naf bend the stress regime determined by inversion of slip vectors measured on fault planes of various scales confirms the present day transtensional regime in the central part of the naf bend however the fault kinematic analysis of quaternary stress states within the central naf indicates that this stress state was not continuous throughout the quaternary indeed chronologies of fault slip vectors provide evidence for two distinct quaternary regional strike slip stress states within this zone both states have consistent ne and nw trending 3 and 1 axes respectively but have significantly different r values the change in the strike slip stress regime probably occurred in the middle pleistocene the older mean stress state is characterized by a n142 8 e trending 1 a n52 13 e trending 3 and a mean arithmetic rm value of 0 75 which indicates that the regional stress regime is transpressional the younger strike slip regime is characterized by a n142 14 e 1 axis a n52 10 e 3 axis and a mean rm of 0 24 which indicates the transtensional character for this regime the low r values of the stress deviators related to the recent stress state reflect normal component slips these temporal and spatial stress changes along the naf result from the coeval influence of forces due to the aegean subduction in the west and to the northward drift of arabia in the east over these boundary forces shear is superimposed along the naf which accommodates the anatolia extrusion however the timing of the temporal stress change permits the suggestion that the quaternary stress regime variation in north anatolia is mainly due to the influence of the aegean domain

recent state of stress change in the walker lane zone western basin and range province united states the nw to north trending walker lane zone wlz is located along the western boundary of the northern basin and range province with the sierra nevada this zone is distinguished from the surrounding basin and range province on the basis of irregular topography and evidence for both normal and strike slip holocene faulting inversion of slip vectors from active faults historic fault offsets and earthquake focal mechanisms indicate two distinct quaternary stress regimes within the wlz both of which are characterized by a consistent wnw 3 axis these are a normal faulting regime with a mean 3 axis of n85 9 w and a mean stress ratio r value r 2 1 3 1 of 0 63 0 74 and a younger strike slip faulting regime with a similar mean 3 axis n65 70 w and r values ranging between 0 1 and 0 2 this younger regime is compatible with historic fault offsets and earthquake focal mechanisms both the extensional and strike slip stress regimes reactivated inherited mesozoic and cenozoic structures and also produced new faults the present day strike slip stress regime has produced strike slip normal oblique slip and normal dip slip historic faulting previous workers have explained the complex interaction of active strike slip oblique and normal faulting in the wlz as a simple consequence of a single stress state with a consistent wnw 3 axis and transitional between strike slip and normal faulting maximum horizontal stress approximately equal to vertical stress or r 0 in both regimes with minor local fluctuations the slip data reported here support previous results from owens valley that suggest deformation within temporally distinct normal and strike slip faulting stress regimes with a roughly constant wnw trending 3 axis zoback 1989 a recent change from a normal faulting to a strike slip faulting stress regime is indicated by the crosscutting striae on faults in basalts 300 000 years old and is consistent with the dominantly strike slip earthquake focal mechanisms and the youngest striae observed on faults in plio quaternary deposits geologic control on the timing of the change is poor it is impossible to determine if there has been a single recent absolute change or if there is rather an alternating or cyclical variation in stress magnitudes our slip data in particular the cross cutting normal and strike slip striae on the same fault plane are inconsistent with postulated simple strain partitioning of deformation within a single regional stress field suggested for the wlz by wesnousky and jones 1994 the location of the wlz between the deep seated regional extension of the basin and range and the right lateral strike slip regional tectonics of the san andreas fault zone is probably responsible for the complex interaction of tectonic regimes in this transition zone in early to mid tertiary time the wlz appears to have had a similarly complex deformational history in this case as a back arc or intra arc region accommodating at least part of the right lateral component of oblique convergence as well as a component of extension

separation of polyphase fault slip data an objective function algorithm based on hard division the objective function algorithm ofa on the basis of hard division is presented in the paper to separate polyphase fault slip data the separation is made by detection of linear structures existing in the data in fry s 1999 sigma space different from other exhaustive search methods the ofa is direct and robust in theory without any arbitrary assumptions polyphase fault slip data are simulated under prescribed tensors in order to validate the method the results show its efficiency in stress estimation the accuracy of stress estimation is controlled by random errors in the orientation of fault striations and by similarity between prescribed stress vectors related to different tectonic phases the similarity between controlling stress vectors has an obvious effect on the estimation either when random errors are sufficiently large or when some similarity coefficients between the vectors are large enough the accuracy of stress inversion tends to decrease as the range in errors increases the ofa makes a very good approach to recognition of similar controlling stress vectors from polyphase fault slip data which are often associated with spatial and temporal variation of the tectonic stress field in a region thus critical to understanding of the formation of geological structures