evidence for synchronous thin skinned and basement deformation in the cordilleran fold thrust belt the tendoy mountains southwestern montana the tendoy mountains contain the easternmost thin skinned thrust sheets in the cordilleran fold thrust belt of southwestern montana and are in the zone of tectonic overlap between the rocky mountain foreland and the cordilleran fold thrust belt the three frontal thrust sheets of the tendoy mountains are from north to south the armstead mckenzie and tendoy sheets near the southeastern terminus of the tendoy thrust sheet is a lateral ramp in which the tendoy thrust climbs along strike from the upper mississippian lombard limestone to lower cretaceous rocks this ramp coincides with the southeastern side of the paleozoic snowcrest trough and projection of the range flanking basement thrust of the blacktail snowcrest uplift suggesting either basement or stratigraphic control on location of the lateral ramp axes of major folds on the southern part of the tendoy thrust sheet are parallel to the direction of thrust transport and to the trend of the snowcrest range they are a result of 1 pre thrust folding above basement faults 2 passive transportation of the folds from a down plunge position 3 minor reactivation of basement faults and 4 emplacement of blind sub tendoy thin skinned thrust faults the tendoy sheet also contains a major out of sequence thrust fault that formed in thick upper mississippian shales and created large overturned foreland verging folds in upper mississippian to triassic rocks the out of sequence fault can be identified where stratigraphic section is omitted and by a stratigraphic separation diagram that shows it cutting down section in the direction of transport the prominent lateral ramp at the southern terminus of the tendoy thrust sheet is a result of fault propagation through strata folded over the edge of the blacktail snowcrest uplift

a numerical method for determining the state of stress using focal mechanisms of earthquake populations application to tibetan teleseisms and microseismicity of southern peru the numerical method described in this paper enables the study in terms of stress of the kinematics of seismic faults provided by focal mechanisms this method assumes a mean state of stress in the source region and is based on the simple mechanical model used for fault population analysis which supposes slip in the direction of the resolved shear stress acting on the fault plane the proposed algorithm first defines compressional and tensional zones resulting from superimposition of the compressional and tensional quadrants limited by the nodal planes this enables one to test the data homogeneity furthermore this restricts the space where the principal stress axes have to be searched then for each principal stress reference whose location is constrained by above confined zones the r value chosen equal to 2 1 3 1 is computed which fits the slip vector on each nodal plane this permits one to select a set of preferred seismic fault planes from a set of auxiliary planes finally a state of stress is computed from the preferred seismic fault plane set using the non linear simplex method already applied to fault populations this algorithm is constructed so as to avoid two major difficulties misleading estimation of the deviatoric stress tensor which may result from excessive emphasis by minimizing the residuals by a least squares method if some of the data are wrong and a lengthy prospection of the stress references over all the space of directions this calculation does not take into account possible changes of the strike and dip of the nodal planes however we use rotations of nodal planes in agreement with the first arrival data to test the compatibility of these data with the computed state of stress tibetan teleseisms and southern peruvian microseisms are analyzed and results are compared with kinematics of superficial recent and active faults measured in field in the same regions this suggests that major seismic events may give a good evaluation of the regional mean state of stress focal mechanisms of the small events are also modelled by a mean stress deviator but this differs significantly from the regional state of stress in southern peru deduced from quaternary faulting this may be due to imprecise location of the small events however some movements are strongly different from those predicted by the computed mean stress deviator this suggests that small fault kinematics surely depend on the regional state of stress but that local effects may control the small deformations

the mw 5 8 mineral virginia earthquake of august 2011 and aftershock sequence constraints on earthquake source parameters and fault geometry the mw 5 8 earthquake of 23 august 2011 17 51 04 utc moment m0 5 7 10 17 n m occurred near mineral virginia within the central virginia seis mic zone and was felt by more people than any other earthquake in united states history the u s geological survey usgs received 148 638 felt reports from 31 states and 4 canadian provinces the usgs pager system estimates as many as 120 000 people were exposed to shaking intensity levels of iv and greater with approximately 10 000 exposed to shaking as high as intensity viii both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast striking reverse fault that nucleated at a depth of approximately 7 2 km the distri bution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western united states horton and williams 2012 near source and far field damage reports which extend as far away as washington d c 135 km away and baltimore maryland 200 km away are consistent with an earthquake of this size and depth in the eastern united states eus within the first few days following the earthquake several government and aca demic institutions installed 36 portable seismograph stations in the epicentral region making this among the best recorded aftershock sequences in the eus based on modeling of these data we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry area of rupture and observations of the aftershock sequence mag nitude frequency and temporal distribution the observed slope of the magnitude frequency curve or b value for the aftershock sequence is consistent with previous eus studies b 0 75 suggesting that most of the accumulated strain was released by the mainshock the aftershocks define a rupture that extends between approxi mately 2 8 km in depth and 8 10 km along the strike of the fault plane best fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes n36 e and dips to the east southeast at 49 5 moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations both indicating reverse slip along a northeast southwest striking southeast dipping fault plane

high velocity anomaly adjacent to the western edge of the pacific low velocity province koki idehara 1 satoru tanaka2 and nozomu takeuchi3 1department of earth and planetary science university of tokyo 7 3 1 hongo bunkyo ku tokyo 113 0033 japan e mail idehara eps s u tokyo ac jp 2institute for research on earth evolution japan agency for marine earth science and technology 2 15 natsushima cho yokosuka 237 0061 japan 3earthquake research institute university of tokyo 1 1 1 yayoi bunkyo ku tokyo 113 0032 japan

paleogeographic reconstruction of the eocene idaho river north american cordillera eocene lake gosiute in southwestern wyo ming was progressively fi lled in by volcani clastic sediment between 49 6 and 47 0 ma the source of this material has long been thought to have been the absaroka volcanic province immediately north of the greater green river basin lead isotope compositions of sandstone from this interval however are consistent with derivation from the challis volcanic fi eld the 40 ar 39 ar ages of single de trital k feldspar crystals from greater green river basin sandstones are nearly identical to 40 ar 39 ar eruptive ages for volcanic rocks of the challis volcanic fi eld 49 8 45 5 ma but we also identify mesozoic and proterozoic crystals that are consistent with cooling ages for rocks that were likely exposed in the idaho segment of the north american cordillera during the eocene most of these rocks are traversed by or are up gradient of a major eocene paleovalley in central idaho the sud den appearance of challis derived sediment in the greater green river basin indicates that a major river here named the idaho river connected the interior of the north american cordillera to the greater green river basin this connection requires 500 km to reach from central idaho to the greater green river ba sin the idaho river probably carried detritus that was stripped from distant uplifted moun tains above the active challis volcanic fi eld as far south as the piceance creek basin suggest ing a total length of at least 1000 km middle eocene metamorphic core complexes in the northern cordillera likely produced a major highland in the headwaters of the idaho river which generated river systems that drained both eastward into the wyoming foreland and westward into the oregon coast ranges

folding of a detachment and fault modified detachment folding along a lateral ramp southwestern montana usa abstract the inversion of the middle proterozoic belt sedimentary basin during late cretaceous thrusting in montana produced a large eastwardly convex salient the southern boundary of which is a 200 km long oblique to lateral ramp subtended by a detachment between the belt rocks and archean basement a 10 km long lateral ramp segment exposes the upper levels of the detachment where hanging wall belt rocks have moved out over the paleozoic and mesozoic section the hanging wall structure consists of a train of high amplitude faulted asymmetrical detachment folds initial west east shortening produced layer parallel shortening fabrics and dominantly strike slip faulting followed by symmetrical detachment folding lock up of movement on the detachment surface produced regional simple shear and caused the detachment folds to become asymmetrical and faulted folding of the detachment surface after lock up modified the easternmost detachment folds further into a southeast verging overturned fold pair with a ramp related fault along the base of the stretched mutual limb

the binalud mountains a key piece for the geodynamic puzzle of ne iran 1 we applied a combined approach of morphotectonic analyzes of spot 5 satellite images and field surveys complemented by in situ produced10be exposure dating to determine the kinematics and rate of active faulting in the binalud mountains bounded by the neyshabur fault system to the southwest and the mashhad fault zone to the northeast three regional episodes of alluvial surface abandonment were dated at 4 8 ka q1 105 ka q3 and 255 ka s3 along the neyshabur fault system cumulative offsets recorded by q3fan surfaces yield slip rates of 2 4 0 5 and 2 8 0 6 mm yr for right lateral and reverse components of active faulting corresponding to an oblique slip rate of 3 6 1 0 mm yr respectively reconstructing the cumulative right lateral offset recorded by s3surfaces a maximum slip rate of 1 3 0 1 mm yr is suggested for the mashhad fault zone these imply an overall rate of 3 7 0 6 mm yr for the range parallel displacement and an uplift rate of 2 8 mm yr due to the range normal shortening 1 6 2 2 mm yr during late quaternary the binalud mountains are deformed as a soft linked restraining relay zone taking up the motion between central iran and eurasia at a rate of 4 0 1 3 mm yr this translates central iran in the n340 e direction our data favor localized faulting instead of distributed deformation at the northeastern boundary of the arabia eurasia collision zone

out of sequence thrusting in polycyclic thrust belts an example from the mesozoic yanshan belt north china craton the ew trending yanshan belt an intraplate fold thrust belt located in the northern north china craton that has experienced several episodes of deformation widely separated in time is characterized by out of sequence thrusts according to detailed mapping in the central yanshan belt five geometric and stratigraphic criteria used to aid in determining whether a thrust has an out of sequence geometry or not can be recognized they are 1 unconformable relationships 2 inclination of fault surfaces 3 irregular changes in apparent offset along strike 4 short fault length relative to apparent offset and 5 in sequence geometry with the help of these criteria two generations of out of sequence thrusts that postdate the original in sequence thrusting in the central yanshan belt are recognized the ancestral southward verging fold and thrust belt that formed prior to 180 ma was deformed and cut by two younger generations of faults that are probably more deeply rooted and are constrained to between 172 165 ma and 152 135 ma a series of thrusts with opposite vergence formed during the last period resulting in abundant abnormal field relationships such as younger on older thrust relations fold truncation and cutting down section the nature and occurrence of faults in the yanshan belt implies that superimposed deformation a common feature in polycyclic orogenic belts is a mechanism for the generation of out of sequence thrusting this adds to mechanisms already described in the literature such as maintaining constant critical taper at an orogenic scale inhibition of the deformation front and lateral changes in the nature of the decollement horizons

known and suggested quaternary faulting in the midcontinent united states abstract the midcontinent united states between the appalachian and rocky mountains contains 40 known faults or other potentially tectonic features for which published geologic information shows or suggests quaternary tectonic faulting we report results of a systematic evaluation of published and other publicly available geologic evidence of quaternary faulting these results benefit seismic hazard assessments by 1 providing some constraints on the recurrence intervals and magnitudes of large prehistoric earthquakes and 2 identifying features that warrant additional study for some features suggested quaternary tectonic faulting has been disproved whereas for others the suggested faulting remains questionable of the 40 features nine have clear geologic evidence of quaternary tectonic faulting associated with prehistoric earthquakes and another six features have evidence of nontectonic origins an additional 12 faults uplifts or historical seismic zones lack reported paleoseismological evidence of large quaternary earthquakes the remaining 13 features require further paleoseismological study to determine if they have had quaternary earthquakes that were larger than any known from local historical records seven of these 13 features are in or near urbanized areas where their study could affect urban hazard estimates these seven are 1 the belt of normal faults that rings the gulf of mexico from florida to texas 2 the northeast ohio seismic zone 3 the valmont and 4 goodpasture faults of colorado 5 the champlain lowlands normal faults of new york state and vermont and 6 the lexington and 7 kentucky river fault systems of eastern kentucky

active faulting and natural hazards in armenia eastern turkey and northwestern iran active fault zones of armenia se turkey and nw iran present a diverse set of interrelated natural hazards three regional case studies in this cross border zone are examined to show how earthquakes interact with other hazards to increase the risk of natural disaster in northern armenia a combination of several natural and man made phenomena earthquakes landslides and unstable dams with toxic wastes along the pambak sevan sunik fault pssf zone lowers from 0 4 to 0 2 0 3g the maximum permissible level mpl of seismic hazard that may induce disastrous destruction and loss of life in the adjacent vanadzor depression in the ararat depression a large active fault bounded pull apart basin at the junction of borders of armenia turkey iran and azerbaijan an earthquake in 1840 was accompanied by an eruption of ararat volcano lahars landslides floods soil subsidence and liquefaction the case study demonstrates that natural hazards that are secondary with respect to earthquakes may considerably increase the damage and the casualties and increase the risk associated with the seismic impact the north tabriz gailatu fault system poses a high seismic hazard to the border areas of nw iran eastern turkey nakhichevan azerbaijan and southern armenia right lateral strike slip motions along the north tabriz fault have given rise to strong earthquakes which threaten the city of tabriz with its population of 1 2 million the examples illustrate how the concentration of natural hazards in active fault zones increases the risk associated with strong earthquakes in armenia eastern turkey and nw iran this generally occurs across the junctions of international borders hence the transboundary character of active faults requires transboundary cooperation in the study and mitigation of the natural risk

state of stress and modern deformation of the northern basin and range province constraints on the current stress regime of the actively extending northern basin and range province are provided by deformation data focal mechanisms and fault slip studies hydraulic fracturing in situ stress measurements borehole elongation breakouts analyses and alignment of young volcanic vents the integrated data indicate significant variations both in principal stress orientations and magnitudes an approximately e w least principal stress direction appears to characterize both the eastern and western margins of the basin and range province whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented nw to n60 w the contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins active deformation along the southeastern and western province margins is characterized by a combination of strike slip and normal faulting focal mechanisms along northeastern province margin wasatch front and in central nevada indicate a combination of normal and oblique normal faulting temporal regional and depth dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles however some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated evidence for significant temporal variation or multiple cycles of variation in relative stress magnitude comes from the sierran front basin and range boundary region where recent earthquakes are predominantly strike slip whereas the profound relative vertical relief across the sierra frontal fault zone in the last 9 10 m y implies a normal faulting stress regime using the best data on stress orientation relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements analysis of well constrained slip vectors in the owens valley california area indicate that large temporal variations in the magnitude of the approximately n s oriented maximum horizontal stress are required to explain dominantly dip slip and strike slip offsets on subparallel faults similar faulting relations are observed throughout much of the boundary zone between the basin and range sierra nevada including the walker lane belt along the eastern province margin in the wasatch front area in utah available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of 4 5 km earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth furthermore superimposed sets of young fault striae along a segment of the wasatch fault also indicate temporal variations of relative stress magnitudes sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion thermally induced flow and the influence of the san andreas plate boundary although difficult to date accurately the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle 1000 5000 years and multiple earthquake cycles 10 000 years

the shuilikeng fault in the central taiwan mountain belt for over 200 km along strike the shuilikeng fault of taiwan separates miocene rocks of the western foothills from the largely eocene and oligocene rocks of the hsuehshan range to the east despite its importance in the taiwan mountain belt the structure and kinematics of the shuilikeng fault are not well known here we present results from new geological mapping along 100 km of its strike length at the surface the shuilikeng fault is a steeply east dipping brittle fault with a series of splays and bifurcations along its southern part it cuts an earlier fold and fault system outcrop kinematic data vary widely from thrusting to strike slip the surface data are integrated with a relocated and collapsed seismicity database to interpret the fault location at depth these data indicate that the shuilikeng fault can be traced to greater than 20 km depth some 260 focal mechanisms from this dataset indicate that its kinematics is overall transpressive from a regional perspective we interpret the shuilikeng fault to reactivate a pre existing rift related basin bounding fault to the east of which rocks in the hsuehshan range are being exhumed

structural analysis of the lombard thrust sheet and adjacent areas in the helena salient southwest montana usa abstract the helena salient is a prominent craton convex curve in the cordillera thrust belt of montana usa the lombard thrust sheet is the primary sheet in the salient structural analysis of fold trends cleavage attitudes and movement on minor faults is used to better understand both the geometry of the lombard thrust and the kinematic development of the salient early w e to wnw ene shortening directions in the lombard sheet are indicated by fold trends in the center of the thrust sheet the same narrow range of shortening directions is inferred from kinematic analysis of movement on minor faults and the orientations of unrotated cleavage planes along the southern lateral ramp boundary of the salient as the salient developed the amount and direction of shortening were locally modified as listric detachment faults rotated some tight folds to the nw and as right lateral simple shear caused by lock up and folding of the jefferson canyon fault above the lateral ramp rotated other folds northeastward where the lateral ramp and frontal oblique ramp intersect folds were rotated back to the nw our interpretation of dominant w e to wnw ese shortening in the lombard sheet later altered by local rotations supports a model of salient formation by primary parallel transport modified by interactions with a lateral ramp

possible effects of pre existing basement topography on thrust fault ramping finite element models show that one way in which thrust ramps may arise is through the mechanical interaction between basement and overlying sediments in the simplest case shear coupling between a planar basement sediment causes the differential stresses in the sediments to die out with depth and distance from the applied load for such cases curved thrust faults may result if the strength of the rock is exceeded basement topography may also affect the location and shape of ramps by acting as a stress concentrator by producing a stress shadow and by changing principal stress orientations modeling suggests that whether or not these basement topographic features cause ramping will depend on the height and angularity of the feature as well as the rock types that overlie it under the assumption of linear elasticity and for given boundary conditions the poisson s ratio plays an important role in determining the orientation and magnitude of the principal stresses calculations using experimentally measured poisson s ratios predict that the earliest maximum compressive stress directions should be nearly vertical in the more cratonward portions of thrust belts however the stress directions which are inferred to have occurred earliest in this part of thrust belts are nearly horizontal this suggests that non elastic or ductile processes have an effect on the propagation of thrust faults

basement influence on foreland thrust and fold belt development an example from the southern urals abstract the reactivation of two sets of pre existing basement faults provided strong control on the geometric and kinematic evolution of the paleozoic south urals foreland thrust and fold belt pre existing basement faults oriented subparallel to the uralide structural grain were related to several stages of precambrian deformation reactivation focused the deformation along these earlier faults resulting in the subsequent incorporation of crystalline basement thrust sheets in the thrust belt at an early stage of its evolution pre existing basement faults oriented subperpendicular to the developing thrust belt structural grain were related to aulacogens in the archean crystalline basement that were filled by variable thickness of riphean aged sediments these influenced the localisation and development of numerous structures in the thrust belt that caused along strike structural changes related to lateral ramps recognition of these features and their influence on the geometric and kinematic evolution of the south urals foreland thrust and fold belt are important for understanding seismic reflection fabrics in the south urals thrust belt and for potential field 3 d geological and kinematic modelling

the deep structure of south central taiwan illuminated by seismic tomography and earthquake hypocenter data abstract the taiwan mountain belt is generally thought to develop above a through going basal thrust confined to within the sedimentary cover of the eurasian continental margin surface geology magnetotelluric earthquake hypocenter and seismic tomography data suggest however that crustal levels below this basal thrust are also currently being involved in the deformation here we combine seismic tomography and earthquake hypocenter data to investigate the deformation that is taking place at depth beneath south central taiwan in this paper we define the basement as any pre eocene rifting rocks and use a p wave velocity of 5 2 km s as a reference for the interface between these rocks and their sedimentary cover we found that beneath the coastal plain and the western foothills clustering of hypocenters near the basement cover interface suggests that this interface is acting as a detachment this detachment is located below the basal thrust proposed from surface geology for this part of the mountain belt inherited basement faults appear to determine the geometry of this detachment and their inversion in the alishan area result in the development of a basement uplift and a lateral structure in the thrust system above them however across the shuilikeng and the chaochou faults earthquake hypocenters define steeply dipping clusters that extend to greater than 20 km depth above which higher velocity basement rocks are uplifted beneath the hsuehshan and central ranges we interpret these clusters to form a deeply penetrating east dipping ramp that joins westward with the detachment at the basement cover interface it is not possible to define a basal thrust to the east beneath the central range

the structure and kinematics of the central taiwan mountain belt derived from geological and seismicity data 1 the structure of the taiwan mountain belt is thought to be that of an imbricate thrust and fold belt developed in a forward breaking sequence above a shallowly dipping basal detachment in recent years however a growing amount of seismicity data from the internal part of the mountain belt indicates the existence of widespread fault activity in the middle and lower crust suggesting that deeper levels of the crust must be involved in the deformation than predicted by the shallow detachment imbricate thrust belt model to address this issue we present new geological mapping together with earthquake focal mechanism and seismic energy release data from the central part of taiwan we concur with the interpretation that the foreland basin part of the western foothills comprises an imbricate thrust system that is developing as a forward breaking sequence that is structurally and kinematically linked to a basal detachment at between 7 and 10 km depth to the east of the foreland basin however in the hsuehshan and central ranges our data show the presence of two fault systems an earlier inactive thrust system with a well developed cleavage is cut by a system of steeply dipping active faults that penetrate to a depth of 25 to 30 km or more in the hsuehshan range the second fault system is best represented by a structural and kinematic model in which this part of the mountain belt forms a zone of transpression with a structural architecture similar to that of a crustal scale positive flower structure eastward in the central range mesozoic basement rocks are over thrusting strongly folded and cleaved deep water sediments of the first now inactive thrust system the involvement of deep crustal levels and mesozoic basement in the second fault system is suggestive of the reactivation of preexisting basin bounding faults that were located on the eurasian continental margin

plio quaternary stress states in ne iran kopeh dagh and allah dagh binalud mountain ranges abstract ne iran including the kopeh dagh and allah dagh binalud deformation domains comprises the northeastern boundary of the arabia eurasia collision zone this study focuses on the evolution of the plio quaternary tectonic regimes of northeast iran we present evidence for drastic temporal changes in the stress state by inversion of both geologically and seismically determined fault slip vectors the inversions of fault kinematics data reveal distinct temporal changes in states of stress during the plio quaternary since 5 ma the paleostress state is characterized by a regional transpressional tectonic regime with a mean n140 10 e trending horizontal maximum stress axis 1 the youngest modern state of stress shows two distinct strike slip and compressional tectonic regimes with a regional mean of n030 15 e trending horizontal 1 the change from the paleostress to modern stress states has occurred through an intermediate stress field characterized by a mean regional n trending 1 the inversion analysis of earthquake focal mechanisms reveals a homogeneous transpressional tectonic regime with a regional n023 5 e trending 1 the modern stress state deduced from the youngest fault kinematics data is in close agreement with the present day stress state given by the inversions of earthquake focal mechanisms according to our data and the deduced results in northeast iran the arabia eurasia convergence is taken up by strike slip faulting along ne trending left lateral and nnw trending right lateral faults as well as reverse to oblique slip reverse faulting along nw trending faults such a structural assemblage is involved in a mechanically compatible and homogeneous modern stress field this implies that no strain and or stress partitioning or systematic block rotations have occurred in the kopeh dagh and allah dagh binalud deformation domains the plio quaternary stress changes documented in this paper call into question the extrapolation of the present day seismic and gps derived deformation rates over geological time intervals encompassing tens of millions of years

discovery of major basement cored uplifts in the northern galiuro mountains southeastern arizona implications for regional laramide deformation style and structural evolution lowell institute for mineral resources at the university of arizona arizona geological society j harold courtright scholarship

a new late cretaceous paleomagnetic pole from the adel mountains west central montana north america s apparent polar wander path has been poorly defined between the mid cretaceous and paleocene reference pole positions existing data allowed 13 of apparent polar motion over about 22 m y 87 65 ma roughly coinciding with the beginning of laramide deformation 80 ma we report on a paleomagnetic study of the adel mountain volcanic rocks to refine the north american apparent polar wander path for this interval the shonkinite rocks of the adel mountain volcanic field are on the eastern edge of the cretaceous paleocene fold and thrust belt some of these structures disturb the western edge of the volcanic pile we obtained two new k ar dates from the adel rocks one date on biotite from a shonkinite dike that crosscuts most of the volcanic rocks is 71 2 2 7 ma the other a whole rock date from a flow deep in the volcanic pile is 81 1 3 5 ma we collected six to nine paleomagnetic samples from each of 34 sites in roadcuts and natural outcrops of flows dikes and laccoliths positive fold and conglomerate tests along with alternating field and thermal demagnetization indicate that our characteristic remanent directions are primary magnetizations acquired before late cretaceous to paleocene thrust belt deformation averaging the virtual geomagnetic poles from 26 reliable sites all of normal polarity yields a paleopole at 82 2 n 209 9 e 95 6 80 k 18 38 this pole is concordant with the paleocene reference pole 82 0 n 170 2 e 95 3 5 k 18 6 diehl et al 1983 and is 11 6 from the globerman and irving 1988 mid cretaceous pole at 71 n 196 e the youngest information in the cretaceous stillstand pole is from the niobrara formation shive and frerichs 1974 at about 85 89 ma if we take the average age of the adel mountain volcanics to be 76 ma then 12 of apparent polar motion occurred between 87 ma and 76 ma thus rapid apparent polar motion correlates well with the onset of laramide deformation

the caucasus an actual example of the initial stages of continental collision abstract a field study of the neotectonics of the georgian caucasus is combined with geophysical geodetic and geological information in order to obtain a mechanical model of actual deformation the analysis of satellite photos together with topographical and geological maps shows that the great caucasus is bisected by a nne trending sinistral strike slip fault zone the western great caucasus is thrusted to the south over the rioni basin while on the other hand its northern flank is a monocline that descends gently into the russian platform active volcanism is present from elbruz to kazbeg the eastern great caucasus is limited by thrusts to the north and to the south and intermediate structures are disposed in a fan like shape no recent volcanism is observed the eastern limit of the chain is a nnw trending dextral strike slip fault zone seismicity from a local network illustrates the activity of the thrusts and gives evidence for the strike slip faults microtectonic data confirm the recent activity and the sinistral character of the borjomi kazbeg strike slip fault the strike slip faults bordering the eastern caucasus may be seen as the limits of a plastic wedge in front of the arabian plate at an early stage of continental collision

regional state of stress fault kinematics and adjustments of blocks in a fractured body of rock application to the microseismicity of the rhine graben a simple mechanical model of a homogeneous state of stress and independent fault motions is generally used to interpret fault kinematics in terms of stress however analysis of focal mechanisms of microearthquakes shows that as a result of incompatibilities of block motions in an assemblage of rigid or elastic blocks deformation of a fractured body of rocks is in general heterogeneous analyses of focal mechanism sets show that they are in general composed of a main group whose fault motions result from a mean state of stress tm in good agreement with the regional state of stress the remaining complex fault motions are explained by a compressional tc and or a tensional deviator te an important observation is that within the computed uncertainties these tc and te deviators are co axial with the mean state of stress tm these deviators statistically model the local fault slips probably due to the incompatibilities of block motions and cannot be considered as other mean states of stress thus if the regional state of stress is known for a fault plane whose strike and dip are given its kinematics cannot be surely predicted two types tc and te of motions different from that tm predicted by the regional state of stress may exist they are the kinematic instabilities as a consequence all the motions shown by focal mechanisms or by striated faults are not significant of the regional tectonic regime this is well illustrated by the microseismicity of the rhine graben where it is shown that the compressional fault motions are kinematic instabilities and the extensional fault motions are representative of a regional state of stress 1 vertical with a n45 trending 3 axis hence the simple mechanical model of homogeneous state of stress and independant fault motions is valid only if there are no incompatibilities of block motions possibly these incompatibilities may be accommodated by a pressure solution crystallization process for creep faulting or by internal cataclastic deformation of large blocks separated by major stick slip faults

the zandjan fault system morphological and tectonic evidences of a new active fault network in the nw of iran abstract the zandjan province is situated in the nw of iran at the junction between the southern termination of the tabriz right lateral strike slip fault and the western end of the alborz active mountain range despite this key location in terms of active tectonics there is no destructive earthquake reported in available historical seismicity catalogues even if a few low magnitude instrumental earthquakes have been recorded indicating that this area is actively deforming the zandjan region can be considered as a seismic gap based on detailed field investigations digital elevation models dems satellite image and aerial photo interpretations we have identified a major active fault network affecting this regions it is mainly constituted by several west and est verging thrust faults trending nw se to n s that clearly cut late quaternary to holocene deposits evidences in the morphology indicate also that they accommodate some right lateral slip component this fault network can be divided into four major fault zones affecting zandjan city present day population over 500 000 and part of the zandjan mianeh basin more to the west based on fault geometrical characteristics fault length segmentation and kinematics the zandjan fault system is certainly capable to produce moderate to large earthquakes mw 6 5 7 0 and serious damages in the zandjan city and surrounding areas the study of these faults is then of major interest for seismic hazard assessment in zandjan province where total population exceed 1 5 million but also to better understand present day geodynamic of nw iran

world map of active faults preliminary results of studies abstract the project world map of major active faults was confirmed in 1989 as a part of the international lithosphere program the objectives are to compile the world map in scale 1 10 000 000 the maps of continents in scale 1 5 000 000 and the maps of some seismic regions in scale of 1 1 000 000 or 1 5 000 000 with the explanatory notes and the catalogue of major active faults of continents the maps will show location age sense and rate of motion and reliability of identification of faults not older than 100 000 years as well as middle pleistocene faults contemporary folds flexures volcanoes and epicentres of strong earthquakes differentiated by magnitude depth and age the first results of the project are discussed one of them is predominance of the strike slip component of motion over the vertical one for the majority of continental active faults it has occurred because the strike slip motion is more efficient than the thrust the reverse and even the normal ones strike slip faults are differentiated into faults of translation rotation and squeezing the contribution of seismicity to faulting depends on the inpulse the creep and the inpulse creep regimes of recent motion in the fault zones different geological techniques for estimating the motion regime the magnitudes and the recurrence interval of strong holocene earthquakes are discussed

a tibetan model for the early tertiary western united states a comparative study of the geology of the early tertiary western united states and the modern tibetan and turkish iranian plateaux indicates that these three regions situated in the hinterland of major orogenic belts share a common taphrogenic evolutionary path both the tibetan and turkish iranian plateaux have high mean elevations above sea level 5 km and 2 0 2 5 km respectively have experienced fast uplift and widespread unroofing during the last 10 8 ma and are undergoing extension nearly perpendicular to the plate convergence direction successive accretionary and collisional events accompanied by significant shortening and underplating during the formation of these plateaux resulted in the generation of overthickened continental crust 50 km that is currently in the process of extending a two stage magmatism characterized by widespread calc alkaline volcanism followed and or overlapped by bimodal basaltic to rhyolitic volcanism occurs synchronously with crustal extension and thinning the plateaux in general have an internal closed drainage system and are drained by antecedent rivers near their edges the early tertiary western us cordillera displayed similar geological and geomorphic features to those observed in the tibetan and turkish iranian plateaux in the aftermath of a prolonged mesozoic orogeny and underwent an orogenic collapse starting around mid tertiary time a n trending crustal welt with a maximum thickness of 60 km and an elevation around 3 km formed a highland with alpine flora in the hinterland of the cordilleran orogenic belt and separated internal drainage basins and saline lakes on the east from major flood plains of antecedent river systems on the west this highland subsequently became the locus of crustal extension metamorphic core complex formation and wide spread calcalkaline volcanism 9ignimbrite flare up9 this early stage of orogenic collapse was followed by the basin and range extension characterized by block faulting and bimodal volcanism starting around 18 16 ma the basin and range extension and associated subsidence resulted in development of the great basin with a mean elevation of 1 5 km above sea level and a crustal thickness of 30 km similarities in the post orogenic evolutionary paths of these three regions indicate that continental lithosphere reacts to overthickening in a consistent way through large scale crustal remobilization and extensional collapse regardless of the mode and nature of its orogenic build up

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

isotopic dating of meso and neoproterozoic mafic magmatism in the southern tobacco root mountains southwestern montana abstract new isotopic dating of mafic dikes in the southern tobacco root mountains of southwestern montana provides evidence for two distinct episodes of subparallel proterozoic mafic magmatism separated by about 700 m y previously published geochemical data from dikes in the southern tobacco root mountains had identified three geochemical groups termed groups a b and c with apparent rb sr ages of 1455 ma group a and 1100 1120 ma groups b and c sm nd dating of a geochemical group a dike yields an age of 1448 49 ma that is interpreted to represent the emplacement age of the dikes this age is similar to published u pb dates from mafic sills that intrude the nearby mesoproterozoic belt supergroup and laramide basement cored uplifts of the archean wyoming province paleomagnetic results from groups a and b dikes are similar suggesting that the were emplaced at about the same time we suggest that the mafic magmatism recorded by the southern tobacco root mountains group a c dikes at about 1450 ma probably corresponds to continental extension that accompanied development of the mesoproterozoic belt basin u pb dating of baddeleyite from the group b dikes provides evidence for a younger magmatic event with an age of 782 4 4 9 ma 95 confidence 7 1 ma incorporating uranium decay constant errors this date is similar to isotopic dates from neoproterozoic mafic dikes and sills exposed elsewhere in uplifts of the rocky mountain foreland and that intrude the mesoproterozoic strata of the belt supergroup geochronologic data from elsewhere in the northern cordillera and canadian shield indicate that the group b dikes in the southern tobacco root mountains are part of a regional 780 ma magmatic event that extended for more than 2400 km along the western margin of laurentia the origin of the magmatic event is not clear but may be related to a mantle plume and crustal extension accompanying initial breakup of the supercontinent rodinia and development of the proto pacific ocean no evidence of ca 1100 ma mafic magmatism in this part of the northern cordillera was found

paleomagnetism of proterozoic mafic dikes from the tobacco root mountains southwest montana abstract paleomagnetic data from proterozoic mafic dikes in southwestern montana provides evidence for two distinct episodes of subparallel dike emplacement at ca 1450 and 780 ma published geochemical data from dikes in the southern tobacco root mountains has identified three distinct compositional groups termed groups a b and c geochronological data from the group a dikes yielded a sm nd age of 1448 49 ma emplacement of these dikes is thought to reflect mafic magmatism associated with extension accompanying development of the adjacent mesoproterozoic belt basin paleomagnetic results from these dikes and a group c dike yield antipodal magnetizations with a group mean direction of d 225 0 i 61 8 k 27 9 95 7 7 n 14 independent means 24 sites the average paleomagnetic pole 8 7 n 216 1 e a95 10 3 is considered to be primary on the basis of positive baked contact tests and similarity to poles of ca 1 45 1 4 ga from intrusions elsewhere in north america but is discordant with respect to poles from age equivalent sedimentary rocks of the meosoproterozoic belt supergroup 40ar 39ar dates from geochemical group b dikes are consistent with published u pb dates that demonstrate dike emplacement at 780 ma as part of the regional gunbarrel magmatic event hornblende concentrates from the group b dikes yield 40ar 39ar apparent ages of 778 772 ma whereas biotite from a baked contact zone yielded a plateau date of 788 ma paleomagnetic results from the group b dikes yield a mean direction of d 301 5 i 17 1 k 65 7 95 4 0 n 12 independent means 23 sites with a paleomagnetic pole at 14 6 n 127 0 e a95 3 2 the combination of geochronologic data results of a baked contact test and spatial agreement of the paleomagnetic poles with poles of similar age elsewhere in north america indicates that this is also a primary magnetization associated with dike emplacement paleomagnetic data from some of the tobacco root mountains dikes provide evidence that they were partially to completely remagnetized during latest cretaceous to early tertiary time perhaps due to thermal affects associated with emplacement of the late cretaceous tobacco root batholith the overall agreement of paleomagnetic poles from the proterozoic dikes with those of age equivalent rocks elsewhere in north america and agreement of the secondary magnetization with expected directions for the latest cretaceous early tertiary indicate that the rocks of the tobacco root mountains have not experienced significant tilting or vertical axis rotation since the mesoproterozoic the new paleomagnetic poles from this study thus provide key data for refining meso and neoproterozoic parts of the north american apw path

conjugate strike slip faulting along the bangong nujiang suture zone accommodates coeval east west extension and north south shortening in the interior of the tibetan plateau this is the published version copyright 2002 american geophysical union all rights reserved

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

nw iran eastern turkey present day kinematics results from the iranian permanent gps network abstract a network of continuous gps stations has been installed in nw iran since 2005 to complement the survey gps network already existing in the region we present the 1999 2009 gps derived velocity field for this region based on the continuous and survey mode observations the results confirm a right lateral slip of 7 1 mm yr for the north tabriz fault in agreement with previous studies this rate is consistent with earthquakes of magnitude 7 7 3 and recurrence times of 250 300 yr the higher spatial coverage of the new network shows that deformation is localized in the vicinity of the chalderan south gailatu siah cheshmeh khoy fault and the north tabriz fault however the eastern end of the north tabriz fault appears to cross mount bozgush rather than following its southern foothills this new velocity field does not indicate the 8 mm yr of nne ssw extension suggested earlier for the region but rather shows lower extension of 1 2 1 mm yr across the eastern segment of the north tabriz fault and the talesh to the west the chalderan and the western north tabriz fault segment act like pure strike slip faults without significant extension or compression the denser network in the rudbar earthquake region ms 7 3 1992 shows no significant motion across the fault suggesting that the recurrence time of earthquakes like the rudbar event must be very long the lack of substantial compressive strain and the sharp azimuth change of the velocity vectors in the transition zone from arabia to lesser caucasus motion imply that processes other than extrusion possibly related to old subduction or delamination contribute to active deformation

geochemical significance of the aromatic hydrocarbon distribution in the bitumens of the puertollano oil shales spain the bituminous series of the puertollano basin consists of three oil shale beds named pa pb and pc from top to bottom in this work results from the study of the aromatic fractions of the bitumens are presented the gas chromatographic traces are dominated by phenanthrene derivatives associated with variable contributions of arborane fernane derivatives and benzohopanes and overall small amounts of chrysene derivatives and secohopanes the compounds can be considered as part of two sub groups the first one consists of those compounds derived from regular hopanes such as secohopanes benzohopanes fully aromatized hopanes and degradation products of hopanes such as alkylated chrysenes and naphthalenes the second group is composed of arborane fernane derivatives and their degradation products such as alkylated phenanthrenes and tetrahydrophenanthrenes both groups of compounds appear to be indicative of a strong bacterial input to the sedimentary organic matter

paleoseismicity of two historically quiescent faults in australia implications for fault behavior in stable continental regions paleoseismic studies of two historically aseismic quaternary faults in australia confirm that cratonic faults in stable continental regions scr typically have a long term behavior characterized by episodes of activity separated by quiescent intervals of at least 10 000 and commonly 100 000 years or more studies of the approximately 30 km long roopena fault in south australia and the approximately 30 km long hyden fault in western australia document multiple quaternary surface faulting events that are unevenly spaced in time the episodic clustering of events on cratonic scr faults may be related to temporal fluctuations of fault zone fluid pore pressures in a volume of strained crust the long term slip rate on cratonic scr faults is extremely low so the geomorphic expression of many cratonic scr faults is subtle and scarps may be difficult to detect because they are poorly preserved both the roopena and hyden faults are in areas of limited or no significant seismicity these and other faults that we have studied indicate that many potentially hazardous scr faults cannot be recognized solely on the basis of instrumental data or historical earthquakes although cratonic scr faults may appear to be nonhazardous because they have been historically aseismic those that are favorably oriented for movement in the current stress field can and have produced unexpected damaging earthquakes paleoseismic studies of modern and prehistoric scr faulting events provide the basis for understanding of the long term behavior of these faults and ultimately contribute to better seismic hazard assessments

the 2012 august 11 ahar earthquakes consequences for tectonics and earthquake hazard in the turkish iranian plateau we have examined the faulting in the 2012 august 11 mw 6 4 and 6 3 ahar nw iran earthquakes using a combination of field mapping remote sensing observations of tectonic geomorphology the cross correlation of optical satellite images and the inversion of seismic waveforms the first event was close to pure strike slip and the second was an oblique combination of thrust and strike slip motion mapped surface ruptures indicate at least one of these events accommodated mostly right lateral strike slip motion on an e w striking plane the occurrence of these earthquakes highlights the spatially distributed deformation in nw iran which has implications for both hazard assessment the ahar events killed over 300 people and injured over 3000 and also tectonic models of the region furthermore these earthquakes demonstrate that the tectonics of the ahar area is characterized by strike slip faulting and a component of shortening and not the previously suggested extension

geometric and kinematic evolution of basement cored structures intraplate orogenesis within the yanshan orogen northern china abstract detailed surface mapping lithology facies analysis drillcore data and aeromagnetic interpretation reveal the geometries of the basement involved structures of laowopu nantan liudaohe xinglong and malanyu to have been generated by folding and thrusting the resulting basement cored anticlines are asymmetric with a shallowly dipping top and backlimb and a steep to overturned forelimb and or frontal fault linked with a gently dipping synclinal limb both the fold axes and frontal faults trend roughly east west suggesting north south shortening north to northeast trending faults behave as tear lateral or oblique ramp structures and formed coevally with their frontal faults their trends may have been inherited from proterozoic synsedimentary faults and archaean basement ductile shear zones foliations and mafic dikes thin skinned thrusts and their three dimensional geometry are locally controlled by detachment within mechanically incompetent layers four types of interrelationships between the thick and thin skinned structures occur including 1 lateral changes along the length of a fault 2 displacement transfer between thick and thin skinned structures 3 buttressing of thin skinned thrusts against the basement involved structures and 4 generation of an out of the syncline thrust under thick skinned shortening most of the deformation within the study area involved brittle behaviour but ductile shear zones developed where fluid access was possible both the basement involved structures and the thin skinned structures formed in the early mesozoic as constrained by cross cutting relationships isotopic ages of igneous rock and syntectonic basins the model of geometric and kinematic evolution of the basement involved structures and their relationship with the thin skinned structures defined in this paper provides an alternative to the current metamorphic core complex model used for the yanshan intraplate orogen

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

lateral ramps and thrust terminations an example from the moine thrust zone nw scotland detailed remapping within the assynt culmination in nw scotland shows that the ben more thrust joins the glencoul thrust along a lateral branch line positioned in loch glencoul this branch line marks the northern lateral termination of the glencoul thrust the thrust on the northern shore of loch glencoul the famous view is thus the ben more thrust the ben more thrust sheet is therefore much larger than previously thought the lateral terminations of the ben more thrust to the north and the south are of two distinct types this reinterpretation negates the existence of surge zones in assynt

the varzaghan ahar iran earthquake doublet mw 6 4 6 2 implications for the geodynamics of northwest iran on 2012 august 11 a pair of large damaging earthquakes struck the varzaghan ahar region in northwest iran in a region where there was no major mapped fault or any well documented historical seismicity to investigate the active tectonics of the source region we applied a combination of seismological methods local aftershock network calibrated multiple event relocation and focal mechanism studies field observations structural geology and geomorphological and inversions for the regional stress field the epicentral region is north of the north tabriz fault the first main shock is characterized by right lateral strike slip motion on an almost e w fault plane of about 23 km length extending from the surface to a depth of about 14 km the second main shock occurred on an ene striking fault that dips at 60 70a degrees to the nw independent inversions of focal mechanisms and geologically determined fault kinematic data for the active stress state yield a transpressional tectonic regime with sigma 1 oriented n132e for the region northeast of the north tabriz fault the presence of rigid lithosphere of the south caspian basin implies the kinematic adjustment by northward transferring of the contracted masses through both distributed deformation and structural deflections our results suggest that the kinematic adjustment inside a contracting wedge may occur along interacting crosswise or conjugate faults to accommodate low rates of internal deformation at a global scale our results indicate that despite the basic assumption of rigid blocks in geodetic plate modelling internal deformation of block like regions could control the kinematics of deformation and the level of seismic hazard within and around such regions of low deformation rate

keys and pitfalls in mesoscale fault analysis and paleostress reconstructions the use of angelier s methods whereas most of the stress inversion methods using fault slip data only minimize the angle between the measured striation and a computed shear stress to find the best fitting reduced stress tensor angelier 1990 proposed an alternative method named invd that also takes into account the relative shear stress magnitude which allows the fault to move using artificial datasets and particular fault geometries we compare this method with one of the classical methods based on the minimization of the shear slip angles r4dt angelier 1984 and we show that in most cases the new method has improved the quality of the results furthermore as proposed by angelier we point out that the quality of the stress inversion primarily depends on the quality of the field data we give advice and warn about some pitfalls concerning determination of sense of slip on fault planes recognition of successive faulting events and their chronology drawer or wedge faults stress permutations faults in vertical bedding we also argue that in case of tilted sequences fault diagrams should not be presented without bedding planes but we show that stress inversions when realized with caution and with the correct method can havemuch more applications than reconstructing stress fields like for determining the paleo horizontal the nature and the sense of motion of large faults the chronology and age of large structures

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

large earthquake doublets and fault plane heterogeneity in the northern solomon islands subduction zone in the solomon islands and new britain subduction zones the largest earthquakes commonly occur as pairs with small separation in time space and magnitude this doublet behavior has been attributed to a pattern of fault plane heterogeneity consisting of closely spaced asperities such that the failure of one asperity triggers slip in adjacent asperities we analyzed body waves of the january 31 1974 m w 7 3 february 1 1974 m w 7 4 july 20 1975 14 37 m w 7 6 and july 20 1975 19 45 m w 7 3 doublet events using an iterative multiple station inversion technique to determine the spatio temporal distribution of seismic moment release associated with these events although the 1974 doublet has smaller body wave moments than the 1975 events their source histories are more complicated lasting over 40 seconds and consisting of several subevents located near the epicentral regions the second 1975 event is well modeled by a simple point source initiating at a depth of 15 km and rupturing an approximate 20 km region about the epicenter the source history of the first 1975 event reveals a westerly propagating rupture extending about 50 km from its hypocenter at a depth of 25 km the asperities of the 1975 events are of comparable size and do not overlap one another consistent with the asperity triggering hypothesis the relatively large source areas and small seismic moments of the 1974 doublet events indicate failure of weaker portions of the fault plane in their epicentral regions variations in the roughness of the bathymetry of the subducting plate accompanying subduction of the woodlark rise may be responsible for changes in the mechanical properties of the plate interface