duplex style and triangle zone formation insights from physical modeling duplexes are a common feature in thrust belts at many scales their geometries vary significantly from antiformal stacks with significant forethrusting in the cover e g southern pyrennes spain to triangle zones e g foreland canadian rockies to low displacement individually spaced ramp anticlines e g sub andean thrust belt bolivia we present a series of physical experiments demonstrating that the strength of the decollements relative to that of the intervening and overlying rock layers plays a significant role in controlling the duplex style the models comprise brittle layers made of dry quartz sand and decollements made of two types of viscous silicone polymers the strength of the decollements in the models is a function of the shortening rate applied to the model the relative strength of the decollements and surrounding rocks affects the development of active or passive roof duplexes triangle zones it also affects the amount of translation of individual thrust blocks and the spacing of thrust ramps which in turn determine if a duplex evolves into an antiformal stack or into individually spaced ramp anticlines model results indicate that specific associations of structural features form systematically under similar rheological and boundary conditions the presence of relatively strong decollements promotes local underthrusting of the cover individual ramp anticlines internal deformation of thrust sheets low early layer parallel shortening and sequential towards the foreland propagation of structures weak decollements promote forethrusting of the cover antiformal stacks coeval growth of structures and low internal strain with the exception of significant early layer parallel shortening no underthrusting at a regional scale occurred in any model

surface rupture of the 2005 kashmir pakistan earthquake and its active tectonic implications to provide a detailed record of a relatively rare thrust surface rupture and examine its active tectonic implications we have conducted field mapping of the surface rupture associated with the 2005 m w 7 6 kashmir earthquake despite the difficulty arising from massive earthquake induced landslides along the surface rupture we found that typical pressure ridges and warps extend northwestward for a distance of 70 km with a northeast side up vertical separation of up to 7 m neither the main frontal thrust nor the main boundary thrust is responsible for the earthquake but three active faults or fault segments within the sub himalaya collectively called the balakot bagh fault compose the causative fault although the fault exhibits substantial geomorphic expression of repeated similar surface ruptures only a part of it had been mapped as active before the earthquake the location of the hypocenter suggests that the rupture was initiated at a deep portion of the northern central segment boundary and propagated bilaterally to eventually break all three segments our obtained surface rupture traces and the along strike slip distribution are both in good agreement with results of prompt analyses of satellite images indicating that space geodesy can greatly aid in time consuming field mapping of surface ruptures assuming that the extensive fill terrace in the meizoseismal area was abandoned during 10 30 ka we tentatively estimate the earthquake recurrence interval and shortening rate on the balakot bagh fault to be 1000 3300 yr and 1 4 4 1 mm yr respectively these estimates indicate that the balakot bagh fault is not a main player of himalayan contraction accommodation graphic 1 selected field photographs and arcgis files of the mapped surface rupture traces and measured vertical separations are available in the electronic supplement to this article 1 embed inline graphic 1 gif

kinematics of eastern salt range and south potwar basin pakistan a new scenario the salt range of northern pakistan represents an emergent thrust front along which the potwar plateau has been translated southward based on the analysis of subsurface data we have constructed a balanced cross section exhibiting a frontal fault bend fold and a set of detachment folds below the potwar plateau from the restored section we are able to propose a forward kinematic modelling using the thrustpack software the main characteristics of the model are the alternation of periods during which deformation was concentrated on the frontal thrust between 10 and 5 ma and since 1 9 ma and an intervening episode during which deformation was distributed along the whole section between 5 and 1 9 ma the latter phase is marked by development of out of sequence structures the episodes of frontal thrust activation are characterised by high denudation rates on the contrary out of sequence folding occurred during periods of important sedimentary accumulation the consequences for petroleum exploration are also discussed however timing of the petroleum system is strongly dependent on hypotheses made on basal heat flow

assessment and compensation of inconsistent coupling conditions in point receiver land seismic data we introduce a method to detect and compensate for inconsistent coupling conditions that arise during onshore seismic data acquisitions the reflected seismic signals the surface waves or the ambient noise records can be used for the evaluation of the different coupling conditions of closely spaced geophones we derive frequency dependent correction operators using a parametric approach based upon a simple model of the interaction between geophone and soil the redundancy of the measurements available permits verification of the assumptions made on the input signals in order to derive the method and to assess the validity of the model used the method requires point receiver data in which the signals recorded by the individual geophones are digitized we have verified the accuracy of the method by applying it to multicomponent ambient noise records acquired during a field experiment in which the coupling conditions were controlled and modified during different phases of the experiment we also applied the method to field data which were acquired without the coupling conditions being controlled and found that only a few geophones showed an anomalous behaviour it was also found that the length of the noise records routinely acquired during commercial surveys is too short to provide enough statistics for the application of our method

deformation metamorphism and imbrication of the indian plate south of the main mantle thrust north pakistan south of the main mantle thrust in north pakistan rocks of the northern edge of the indian plate were deformed and metamorphosed during the main southward thrusting phase of the himalayan orogeny in the hazara region between the indus and kaghan valleys metamorphic grade increases northwards from chlorite zone to sillimanite zone rocks in a typically barrovian sequence metamorphism was largely synchronous with early phases of the deformation the metamorphic rocks were subsequently imbricated by late north dipping thrusts each with higher grade rocks in the hanging wall than in the footwall such that the metamorphic profile shows an overall tectonic inversion the rocks of the hazara region form one of a number of internally imbricated metamorphic blocks stacked after the metamorphic peak on top of each other during the late thrusting this imbrication and stacking represents an early period of post himalayan uplift

late cambrian furongian to mid ordovician euconodont events on baltica invasions and immigrations abstract the stratigraphic distributions taxonomy diversity evolutionary lineages and events of late cambrian to middle ordovician euconodonts of baltica are briefly reviewed and re evaluated the euconodonts of the late furongian stage 10 late cambrian to middle ordovician successions of baltica record innovation immigration and two invasions of short duration and one major extinction the innovation event with an origin on baltica is the rise of the proconodontus serratus lineage in the late furongian stage 10 the immigration events comprise the cordylodus immigration to baltoscandia in latest cambrian and this phylogenetic lineage persisted to mid tremadocian early ordovician and vanished at the global mid tremadocian extinction event the late floian basal dapingian transition is a significant event on baltica it is characterized by the immigration of the important genera baltoniodus and microzarkodina and upon their arrival these taxa remained on the baltica palaeocontinent and stayed for a long period forming evolutionary lineages the basal darriwilian immigration event by the genus lenodus and coeval prominent sea level lowstand were caused by a short global icehouse stage related to the expansion of the polar ice sheets the extinction event caused the disappearance of the characteristic cordylodus fauna most events are related to changes in the palaeoclimate resulting from the movement of the baltica palaecontinent and associated eustatic sea level changes however the cause of the global early tremadocian extinction event is not yet completely clear and remains unsolved perhaps abrupt and significant palaeoceanographic changes on a global scale i e plate tectonic movements causing sudden change of ocean currents and climate from warm to cold were the cause of this significant extinction in the early ordovician

the usefulness of geophone ground coupling experiments to seismic data ground coupling devices measure local conditions around a geophone and are therefore useful for geophone design for purposes of gathering seismic data the data from local ground coupling experiments must be related to seismic data in particular the geophysicist wants to know whether a local measurement could help in detecting a ground coupling problem or in correcting the seismic data for it two sets of field experiments have been carried out to investigate these effects our experimental data of coupling measurement devices show that the behavior of well planted spiked geophones is determined by shear along the spike while the behavior of poorly planted geophones is determined by its weight however when a link is established between the data from a coupling measurement device to seismic data it becomes clear that the usefulness of this device for predicting problematic ground coupling phenomena in seismic data is very limited

global seismicity of 2001 centroid moment tensor solutions for 961 earthquakes abstract centroid moment tensor cmt solutions are presented for 961 earthquakes occurring during 2001 the solutions are obtained using corrections for aspherical earth structure represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward a m dziewonski r l woodward acoustic imaging at the planetary scale in h emert h p harjes eds acoustical imaging vol 19 plenum press new york 1992 pp 785 797 the model of anelastic attenuation of durek and ekstrom bull seism soc am 86 1996 144 is used to predict the decay of the waveforms

the role of extension during brittle deformation within the nw indian himalaya 1 synorogenic extension has been recognized as an integral structural constituent of mountain belts and high elevation plateaus during their evolution in the himalaya both orogen parallel and orogen normal extension has been recognized however the underlying driving forces for extension and their timing are still a matter of debate here we present new fault kinematic data based on systematic measurements of hundreds of outcrop scale brittle fault planes in the nw indian himalaya this new data set as well as field observations including crosscutting relationships mineral fibers on fault planes and correlations with deformation structures in lake sediments allows us to distinguish different deformation styles the overall strain pattern derived from our data reflects the large regional contractional deformation pattern very well but also reveals significant extensional deformation in a region which is dominated by shortening in total we were able to identify six deformation styles most of which are temporally and spatially linked representing protracted shortening our observations also furnish the basis for a detailed overview of the younger deformation history in the nw himalaya which has been characterized by extension overprinting previously generated structures related to shortening the four dominant deformation styles are 1 shortening parallel to the regional convergence direction 2 arc normal extension 3 arc parallel extension and finally 4 e w extension this is the first data set where a succession of both arc normal and e w extension has been documented in the himalaya importantly our observations help differentiate e w extension triggered by processes within the tibetan plateau from arc parallel and arc normal extension originating from the curvature of the himalayan orogen

stress field evolution in the northwest himalayan syntaxis northern pakistan 1 we have conducted a systematic inversion of striated fault planes throughout northern pakistan in order to better depict the temporal and spatial variations in stress patterns two domains are evidenced at a regional scale separated by the active raikhot fault the western boundary of the nanga parbat spur west of this fault a wrench type stress field with 1 axis oriented around n s predominates in the karakorum and in kohistan it predates pliocene quaternary exhumation of nanga parbat and corresponds to the miocene or earlier regional stress field related to indian asian convergence east of the raikhot fault compression parallel to the belt accounts for initiation of the nanga parbat anticlinorium after 5 ma it is followed by predominant post 2 ma extension both parallel to the belt and nne ssw oriented thus in the n w himalayan syntaxis multidirectional extension is juxtaposed on short timescales to shortening either parallel or perpendicular to the belt such juxtaposition could be characteristic of strain and stress partitioning during oblique convergence

paleo depth of fossil faults estimated from paleostress state applications from the alps and the apennines italy abstract estimating the paleo depth of a fossil fault usually requires the application of complex and highly specialized techniques we propose a new method that is based mainly on field data and simplifies the process calculation of the reduced stress tensor with four variables through inversion of fault slip data calculation of the complete stress tensor i e the two remaining unknowns using the friction and the rupture laws estimation of the paleo depth the friction law is defined by the lower boundary of the cloud of points in the mohr space represented by inherited faults this operation fixes the abscissa origin of the mohr diagram to calculate the rupture law we estimate both intact rock and outcrop quality parameters and need pairs of conjugate faults their dihedral angle fixes a point on the mohr circle where the rupture law has to be tangent thus defining the scale of the axes and the values of the principal stresses to define the paleo depth we estimate the average density of overlying rocks and the hydraulic conditions i e the pore pressure testing of this workflow in three well constrained geological case studies proved its promising reliability showing a good agreement with independent stratigraphic and structural evidence

geophone ground coupling for frequencies much lower than the coupling resonant frequency the geophone accurately follows the ground motion but for higher frequencies the coupling can alter both the amplitude and phase of the seismic signal the normal planting of vertical geophones in the field results in coupling adequate for conventional recording that uses frequencies less than 100 hz however for very loose soils or for high frequency seismic recording i recommend that the geophones be buried to place the geophones in firmer soil the coupling resonant frequency for vertical geophones is determined by the firmness of the soil and i have measured resonant frequency ranging from 100 to 500 hz at different locations because the firmness of the soil increases with depth the coupling resonant frequency can be increased by burial of the geophones or by the use of longer spikes the rocking of horizontal geophones causes a low frequency coupling resonance it is crucial that horizontal geophones be planted with their bases firmly contacting the soil geophones so planted have a resonance around 130 hz whereas those 1 cm off the ground can have a resonance of 30 hz or lower soil conditions have little effect on the resonant frequency horizontal geophones with 1 inch spikes are as well coupled as those with longer spikes but the best coupling is achieved by burial of the geophones modified journal abstract

paleozoic and mesozoic stratigraphy of the peshawar basin pakistan correlations and implications the most complete paleozoic sequence described from pakistan is exposed in bedrock inliers and in ranges fringing the eastern peshawar basin interbedded quartzite and argillite of the precambrian and cambrian tanawal formation is overlain unconformably by the cambrian ambar formation the misri banda quartzite unconformably overlies the ambar and contains ordovician cruziana ichnofossils new conodont discoveries restrict the ages of overlying formations as follows panjpir formation llandoverian to pridolian nowshera formation lochkovian to frasnian and jafar kandao formation kinderhookian to westphalian the karapa greenschist consisting of metamorphosed lava flows separates the jafar kandao from upper triassic carnian marbles of the kashala formation the upper triassic and jurassic nikanai ghar formation forms the top of the section correlatives to the peshawar basin stratigraphy are present locally in the sherwan synclinorium of hazara and in the khyber pass region the sequence contrasts markedly with the paleozoic and mesozoic section exposed south of the khairabad thrust in the attock cherat range this thrust and its northeastern continuation in hazara north of abbottabad thus form the boundary in pakistan between the lesser himalayan and tethyan himalayan sections a function performed by the main central thrust mct in the central himalaya of india and nepal the newly dated carboniferous to triassic horizons provide the first firm age constraints on the protoliths of the high grade swat metasediments the dating of the metasediments has in turn provided age constraints on pre himalayan tectonism and associated intrusions two major tectonic episodes during the late cambrian and carboniferous produced positive areas north of the peshawar basin that provided coarse detritus to the misri banda quartzite and jafar kandao formation

unravelling polyphase brittle tectonics through multi software fault slip analysis the case of the voltri unit western alps italy abstract we have analyzed the brittle structures in a key area of the alps apennines transition zone nw italy here two orogens have interfered with each other since oligocene times producing a complex structural evolution and a heterogeneous fault population only relative chronologies can be reconstructed as stratigraphic constraints are lacking we have performed the inversion of fault slip data with two softwares for paleostress calculations combined with field observations at selected structural stations and photo interpretation the resulting incompatible stress tensors can be grouped in this sequence i a strike slip tensor with nnw sse trending 1 event a ii a strike slip tensor with ne sw trending 1 event b and iii an extensional transtensional tensor with nw se or ne sw trending 3 event c we correlated our results with structures of known age from adjacent areas event a is possibly rupelian early chattian linked to far field incipient rifting in the future ligurian provencal basin event b fits oligo miocene shortening the faults may belong to a sinistral strike slip zone that accommodated the oblique component of deformation during the rotation of the corsica sardinia block event c is attributed to a pliocene quaternary neotectonic event therefore combining different inversion procedures with a detailed structural analysis has successfully unravelled the polyphase brittle tectonics

signatures of the existence of frontal and lateral ramp structures near the kishtwar window of the jammu and kashmir himalaya evidence from microseismicity and source mechanisms

wrench faulting in the northern pakistan foreland the acquisition processing and interpretation of reflection seismic gravity and magnetic data in conjunction with detailed geological mapping throughout the kohat plateau have resulted in a reinterpretation of the structural style of this portion of the northern pakistan foreland our interpretation of the recently acquired geologic and geophysical data as well as a critical reevaluation of previously acquired data and regional geology indicates that the kohat plateau has undergone major episodes of strike slip faulting basement involved reverse faulting and minor thrust faulting consistent with transpressional tectonics our interpretation contrasts with previous models that invoked only southward directed thrust faulting the principal key to the reinterpretation of seismic data was depth migration before stack mbs seismic processing which was performed on five seismic lines to resolve the structural geology mbs processed seismic data show complex deformation and steep dips more accurately than other methods and allowed us to identify the high amplitude structures in the kohat plateau surface geological mapping in the kohat plateau and adjacent areas indicates tight anticlines consistent steep dips horizontal motion fabrics and a conspicuous lack of low angle thrust faults aeromagnetic and gravity data indicate that precambrian basement is involved in the deformation modern seismicity indicates that faults mapped at the surface and subsurface are dominated by strike slip displacement the kohat plateau is located near the intersection of the transcurrent chaman fault system a 1000 km long system of north south striking sinistral strike slip faults and east west striking contractual structures that form the grain of the himalayan mountain chain in this area of northwest pakistan surface and subsurface structures fit the expected regional patterns that result from transpressional deformation in this complex zone of intersection our reinterpretation has applicability to other deformed belts worldwide that exhibit analogous characteristics and criteria of transpressional tectonics but are interpreted as being dominated by low angle thrust tectonics

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

tempo of earliest ordovician graptolite faunal succession conodont based correlations from the tremadocian of quebec successive tremadocian planktic dendroid graptolite assemblages from continental slope sequences in quebec can be correlated with north american platform biozonations on the basis of conodonts anisograptid bearing assemblage 2 middle tremadocian matane faunas are associated with early ordovician rossodus manitouensis zone new designation conodonts younger middle tremadocian faunas with adelograptids assemblage 3 are no younger than the rossodus manitouensis zone key dendroid evolutionary immigration events take place within the lower conodont fauna b interval rooted dendroids near cap des rosiers quebec and in eastern new york state occur with lower fauna b conodonts and the trilobites pareuloma and borthaspidella however the earliest tremadocian and earliest ordovician dendroid immigration event represented by the local lowest occurrence of faunas with dictyonema flabelliforme s l at localities in western newfoundland eastern new york state norway and eastern china also lies with

wrenching in the external zone of the betic cordilleras southern spain abstract regional structural trends in the caravaca huescar area forming the central part of the external zone in the betic cordilleras indicate that deformation of the area results from right lateral wrenching subparallel to the paleogeographic zonation the structural trends do not fit the nappe interpretation generally used elsewhere in the external zone arguments for wrenching in the area are the structural inverse symmetry with respect to a central transcurrent fault zone the crevillente fault zone the distributional pattern of stratigraphic anomalies and types of deformation and the outcrop pattern of the paleogeographic zones it is argued that certain tectonic units in the area formerly interpreted as klippes in a nappe configuration form centers of flower structures and are vertically squeezed out blocks a theoretical model is sketched illustrating the evolution of a wrench zone under the stratigraphic conditions of the studied area and resulting in its present characteristics many of the features of the caravaca huescar area are also present elsewhere in the external zone and support the idea that wrenching was a major deformational mechanism it is therefore suggested that the external zone should in general not be described in terms of a nappe structure as has been done so far but in terms of a strike slip orogen or a wrenched continental margin

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

stress distribution at the transition from subduction to continental collision northwestern and central betic cordillera 1 we analyze focal mechanisms of shallow intermediate earthquakes in a nw se transect along the western betic cordillera and alboran sea and deep earthquakes located in the central betics to constrain the state of stress at the gibraltar arc slow convergence area shallow earthquakes 620 km show very similar focal mechanisms fitting the general slab behavior of resistance to further descent at the 660 km discontinuity seismicity features evidence the present day stress distribution in a context of transition from subduction to continental collision

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

long lasting transcurrent tectonics in sw alps evidenced by neogene to present day stress fields abstract the sw alps are an active orogen undergoing intra mountainous extension and peripheral compression we discuss the significance of syn orogenic extension based on a comparison of paleo stress derived from fault slip data inversion reflecting the long term

sinistral transpression along the main boundary thrust in amritpur area southeastern kumaun himalaya india abstract outcrop mapping and structural analyses in a 100 m thick fault damage zone elucidate geometry and kinematics of the main boundary thrust in the study area the north dipping fault damage zone is sandwiched between the proterozoic amritpur granite in the hangingwall and the neogene siwalik sediments in the footwall the amritpur granite is overlain by the volcanic sedimentary sequence along a top to the south thrust the footwall sediments are deformed into gentle upright and steeply plunging folds by contrast the hangingwall granite is generally massive the km scale folds in the sub himalayan sediments are geometrically discordant to the folds in the lesser himalayan volcanic sedimentary sequence the damage zone contains both the sub himalayan sediments and the lesser himalayan amphibolite it consists of an imbricate structure tectonic wedges and pressure solution bands the imbricate structure is made up of seven fault bounded lithotectonic domains that record the imprints of coaxial refolding and subsequent modification of the folds into sheath like structures the geometry and kinematics of mesoscopic structures and the results of paleostress analysis reveal a sinistral wrench accompanied n s to nne ssw directed subhorizontal shortening in the damage zone the aforesaid evidences also help distinguish between pure contractional pure wrench contraction dominated and wrench dominated deformation in the different domains and the tectonic wedges the sinistral transpression in the damage zone is ascribed to the occurrence of an oblique lateral ramp along the main boundary thrust in the study area

shallow and intermediate depth earthquakes in the hindu kush region across the afghan pakistan border abstract we investigated the spatio temporal seismicity parameters of shallow 0 70 km and intermediate 70 300 km depth earthquakes in the hindu kush region which is characterized by the occurrence of large earthquakes in a small zone of intense activity by way of comparison intermediate depth earthquakes dominate the hindu kush seismicity using a catalogue of 3820 earthquakes we determined the various earthquake histograms time series plots variations of frequency magnitude distribution b value and seismicity rate changes z value both time periods encompassing pre and post 1964 subsets of earthquakes differ significantly in terms of reporting earthquakes b and z value for shallow and intermediate seismicity the b values appear to be lower 1 07 and 0 90 for intermediate depth earthquakes than do the b values produced by shallow earthquakes 1 32 and 1 06 using the pre and post 1964 data sets the three low b value

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

the inverse problem in microtectonics and the separation of tectonic phases abstract the algorithm of inverse problems is applied to three cases in microtectonics a collection of striations measured on pre existing faults may be processed automatically and interpreted in terms of tectonic stress a comparison is made between two different methods formerly proposed by the authors both methods are tested with field data the theoretical results agree with independent field criteria for a separation of tectonic phases

paleostresses associated with faults of large offset abstract in order to test empirically the limitations of paleostress analysis we used etchecopar s computer program to compute the orientations and relative magnitudes of paleostress principal values in two southern appalachian u s a thrust zones from minor fault and slickenside attitudes in both thrust zones faults are closely spaced many faults have offsets whose magnitudes exceed the distance to adjacent faults of comparable size and deformation was strongly non coaxial while even in the less deformed thrust zone bulk strains due to fault movement have axial ratios as high as 10 1 nearly 75 of the fault slickenside pairs in each thrust zone conform with paleostress tensors that indicate 1 sequential transport parallel compression transport parallel extension and extension oblique to transport and 2 low resolved shear stresses on the thrusts finite strains measured in one thrust zone share a principal plane with the first two tensors and the inclinations of the paleostress and finite strain principal directions in that plane are consistent with thrust parallel shearing relative magnitudes of paleostress and strain principal values do not correlate well moreover the locations and inferred origins of fault slickenside pairs inconsistent with paleostress tensors suggest that stresses in rocks between faults were not as is assumed in paleostress analyses uniform this complexity may also occur in faulted rocks where bulk strains are small paleostress tensors from rocks with large bulk strains may be viable but they must be interpreted cautiously

an early to middle ordovician succession of conodont faunas at maekalda northern estonia the maekalda section presents a c 12 m thick succession of mainly limestones dolomites and siltstones of late tremadoc to late llanvirn age exposed on the eastern outskirts of tallinn northern estonia the condensed sequence is rich in well preserved conodont elements that provide the basis for detailed biozonation in the baltoscandian zonation beds from the upper varangu paltodus deltifer zone up to the lower aseri eoplacognathus foliaceus subzone have been identified in all the conodont faunas exhibit a close resemblance to swedish faunas many intervals can also be compared with coeval strata in western russia the presence at some levels of representatives of laurentian conodont lineages provides an unusual opportunity for correlating baltoscandian sequences with sequences in north america especially in the lower arenig part of the succession the middle volkhov upper middle arenig paroistodus originalis zone at maekalda is remarkably complete bearing in mind the highly condensed nature of the section as a whole the details of this zone can be correlated with the equivalent intervals in swedish sections in the upper volkhov lower kunda beds there is a considerable stratigraphic gap in the section but the upper kunda has provided an excellent series of successive populations of eoplacognathus indicating that in this part the section is virtually complete

thrust tectonics and the deep structure of the pakistan himalaya the systematic restoration of thrust systems provides a powerful constraint on the deep structure of orogenic belts a balanced cross section through the imbricated upper crust of the indian plate in the footwall to the main mantle thrust of the western himalaya restores to a minimum width of 730 km the implicit shortening being in excess of 470 km this requires the himalaya and southern tibetan region to be underlain by a wedge of indian crust however a full appraisal of gross crustal structure awaits deep seismic control

llanvirnian ord iron ooids in baltoscandia element mobility ree distribution patterns and origin of the ree abstract the chemical and mineralogical compositions of llanvimian ordovician iron and associated phosphate ooids from sweden estonia and russia have been examined the oolites are generally thin and lean mud supported and dominated by fe oxyhydroxide goethite limonite ooids one swedish oolite contains a mixture of chamosite goethite and hematite ooids and it is suggested that the two latter types were derived from chamosite ooids by early diagenetic alteration the ree distribution patterns were unaffected by these reactions all ooids in the area show a typical negative eu anomaly inherited from the source material major and minor element contents in limonite and chamosite ooids are similar whereas their ree patterns are different limonite ooids have a lree hree ratio from 1 to 2 4 and chamosite ooids from 3 to 5 the amounts of ree in the ooids are strongly dependent on the amount of phosphate

geo tectonic framework of the himalaya of n pakistan in the karakorum range there is a structurally complicated cretaceous are comprising the kohistan sequence on its northern side the northern suture consists of a mega melange and is bounded to the s by tightly folded pillow bearing volcanics and sediments to the s the kohistan plutonic belt consists of southwards a early foliated and late post tectonic tonalites and diorites b aplites and pegmatites up to 30 of rock volume c basic dykes up to 10 m thick d the chilas complex a stratiform cumulate body over 300 km long and 8 km thick chromite layered dunites gabbros and norites with a low pressure granulite facies mineral fabric of tectonic origin e an amphibolite belt with a complex mixture of other rocks and f the jijal complex a 200 km 2 tectonic wedge of high pressure granulites and chromite layered dunites cumulate graded units in the chilas complex show that it is folded by an isoclinal anticline f 1 the mid upper crust of the are is folded by a 50 km half wavelength f 2 syncline the whole kohistan sequence with its two phases of isoclinal folds was tilted during himalayan collision so that the structures are now subvertical the southern suture main mantle thrust has a wedge of glaucophane schists the indian plate contains a basement of psammites and schists intruded by cambrian granites and overlain by isoclinally folded and metamorphosed carbonates and shales

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

tectonic regime and slip orientation of reactivated faults the slip orientation of reactivated faults is predicted by assuming that one principal stress direction is vertical that faulting occurs on pre existing planes of weakness with a slip direction along the applied shear stress and by extending the original concept of tectonic regime so as to include the stress tensor aspect ratio the predicted rake of slip is then analysed so as to reveal the respective influence of the fault plane orientation strike and dip and of the tectonic regime the analysis of this direct problem allows one to describe the geometry of the slip directions within any given tectonic regime its evolution as the tectonic regime varies and the constraints provided by slip direction data on the tectonic regime however the question of what fault orientations would satisfy a failure criterion and thus be preferentially reactivated is not addressed in any tectonic regime pure strike slip occurs on vertical planes and only on them except in wrench regimes where it also occurs on all fault planes along four strikes that are determined by the tectonic regime pure dip slip occurs on planes striking along one of the horizontal principal stress directions and only on them except in radial compression and radial extension regimes where it occurs on all planes except vertical ones at fixed strike but varying dip the slip direction is closest to dip slip for zero dip and pure strike slip for vertical dip at fixed dip and varying strike the slip direction is pure dip slip for strikes along one of the horizontal principal stress directions and closest to strike slip for four strikes that are determined by the tectonic regime the horizontal principal stress directions separate four quadrants two where the slip direction is dextral and two where it is sinistral the slip directions of all fault planes of the same dip can be easily deduced from those of subhorizontal planes and can be constructed geometrically as the tectonic regime varies continuously from radial compression to radial extension the domain of fault plane orientations where steep reverse slip directions are possible shrinks and disappears when the extensional regime is entered conversely the domain where steep normal slip directions are possible appears when the wrench regime is entered and grows thereafter the strike slip domain first grows towards shallow dip until the wrench regime is entered and then shrinks after the extensional regime is entered whereas in the model of failure in isotropic rocks dip slip or strike slip data fully determine the original tectonic regime in the model of failure on pre existing planes of weakness constraints on the extended tectonic regime require additional information the sense of shallow slip direction data which are to be found on steeply dipping planes constrains the horizontal principal stress directions and the steepness of slip direction data on shallow dipping planes striking away from the principal stress directions constraints the extended tectonic regime in the case of wrench regimes an extra constraint arises from the fact that the extended tectonic regime also controls the strike at which the dip component of slip changes from normal to reverse these constraints can be quantified by superposing a simple plot of the data rake versus strike with an abacus that is called breddin s graph for tectonic regimes while this graph does not replace inverse techniques it may help in detecting tectonic phases in complex data sets without using this graph or resorting to inverse techniques the transition from wrench to either compressional or extensional regime is difficult to infer from data that display a limited range of fault plane strikes and the same sense of dip component of the slip direction

magnetic polarity stratigraphy and ages of siwalik group rocks of the potwar plateau pakistan abstract six magnetic polarity sections have been established over the potwar plateau region of pakistan including the major stratotypes of the siwalik group in all six sections the dominant feature of the magnetic polarity stratigraphy is a long normal polarity zone which is contained within the nagri formation this conspicuous normal polarity zone has been radiometrically dated at 9 5 0 6 m y which identifies it as magnetic chron 9 radiometric dates from the upper siwalik formation have also been used to identify the chron 2 3 boundary in two of the sections the magnetic polarity stratigraphy of three of the sections has been correlated securely with the accepted magnetic polarity time scale so that the ages of the local stratigraphy are indexed accordingly based exclusively on data from stratotype sections the chinji nagri and dhok pathan formations have nominal age ranges of 10 1 13 1 7 9 10 1 and 5 1 7 9 m y age fluctuations on the order of 105 years may be anticipated for these formational boundaries within radius of some 20 km of the designated stratotype mean sediment accumulation rates during the chinji nagri and dhok pathan interval range from 13 to 52 cm 103 yr essentially linear sediment accumulations are locally maintained over time intervals of several million years the chinji nagri lithofacies boundary marks a transition from slow to faster sediment accumulation over much of the potwar plateau indicating a fundamental sedimentary tectonic change at this time

how much does slip on a reactivated fault plane constrain the stress tensor given a fault plane and its slip vector the stress tensor which caused the displacement is sought two constraints are considered first a geometrical constraint that the shear stress applied to the fault plane is parallel to the slip wallace 1951 bott 1959 second a frictional constraint that the shear to normal stress ratio equals tan 0 coulomb 1776 in a first step the stress tensors that satisfy the geometrical constraint are sought for tensors belonging to the vectorial space of solutions shear and normal stress magnitudes become a function of the orientation of the principal stresses and are mapped extending a study by mckenzie 1969 in a second step it is investigated which of these tensors also satisfy the frictional constraint within this more restricted vectorial space there is a relationship between the magnitudes 1 2 1 3 and s 1 3 1 and the orientations of the principal stresses both the range of s and the spatial distribution of are more restricted than when the geometrical constraint alone is considered as when the geometrical constraint is solely considered mckenzie 1969 the orientations of the principal stresses may lie significantly away from and up to right angle to the p b t axes however this can happen only in two cases 1 either the effective stress difference s has reached a high value which is unlikely to happen if enough preexisting fractures are available to release the stress or 2 2 becomes close to either 1 or 3 and therefore barely distinguishable from it in that case the delocalization of the orientations of the principal stresses is best described by a tendency for to exchange role with either or when the stress difference remains small and 2 reasonably away from 1 and 3 approach positions that we define as the pf b tf axes and that are obtained from the p b t axes by a rotation of angle 0 2 around b and toward the slip vector this explains why the p b t axes gives reasonable estimates of the orientations of the principal stresses scheidegger 1964 despite objections mckenzie 1969 however whenever the fault plane can be distinguished from the auxiliary plane pf b tf should give a better estimate raleigh et al 1972 in an area where many fault planes are available and a uniform tensor is assumed the scatter in the plane orientations contains information about both the relative position of 2 represented by and the relative stress difference s the higher s or the closer to either 0 or 1 the more scatter this information could then be extracted by inverse methods because a friction law would constrain these inverse method more tightly it may show the necessity of nonuniform tensor to explain scattered fault plane

the tectonic history of kohistan and its implications for himalayan structure the tectonic history of kohistan northern pakistan involves two collisional events cleavage and folding developed at 90 100 ma along the northern suture between the kohistan island arc and the asian plate at the same time there was major folding and shearing of the lower part of the kohistan arc approximately 100 km south of the suture this deformation was followed by ocean subduction south of the kohistan arc generating the kohistan calc alkaline batholith with subsequent ocean closure during the eocene and obduction of the kohistan arc together with the adjacent part of the asian plate over the indian continental crust the construction of balanced cross sections through the imbricated upper part of the indian continental crust in the footwall to this southern suture indicates a minimum displacement of 470 km requiring the western himalayan hinterland to be underlain by a large wedge of indian middle to lower crust there is some shortening of the overriding kohistan and asian plates by thrusts and shear zones but it is insufficient to satisfy the palaeomagnetic data there must be major crustal shortening involving thrusts in the hindu kush and pamirs north of kohistan the post eocene thrust direction which for most of pakistan is towards 160 is almost perpendicular to that immediately to the east in the himalayan belt generating complex refolded thrust patterns in the hazara syntaxis and large scale folding and rapid uplift with associated brittle faulting and seismic activity adjacent to the nanga parbat syntaxis these different thrust trends indicate that major thrust movement as well as the folds and deformation fabrics cannot always be related to plate movement vectors but are modified by or develop from complex rotations during place collision or from the gravitational spreading of a thickened crust a regional approach is required to recognize and correctly attribute the various components in thrust displacements

fault analysis and paleostress evolution in large strain regions methodological and geological discussion of the southeastern himalayan fold and thrust belt in pakistan abstract we document the structure and kinematics of the southeastern part of the fold and thrust belt of the pakistani himalaya field analysis documents the importance of strike slip faulting associated with folding accordingly a transpression regime is inferred to be responsible for variable amounts of shortening from fault block to fault block the analysis of fault populations that affect the mesozoic to early miocene sediments allows distinguishing two paleostress tensor directions a dominant nw se compression and a minor e w compression are compatible with buckling around the n s axis of the near by hazara kashmir syntaxis from the lack of both systematic overprinting relationships and spatial trend the two tensors were obtained at different locations we conclude that in each location any of these two shortening directions can dominate the distribution of the paleostress tensors substantiates a transpressional regime due to far field himalayan compression and a lateral escape component of the allochthonous fold and thrust belt away from the growing hazara kashmir anticline

intermontane basin development in the past 4 myr in the north west himalaya the through the combined use of magnetic polarity stratigraphy with fission track dating of volcanic ashes a new chronology spanning 4 myr has been developed for the intermontane basin of kashmir in the northwestern himalaya

fault systems and paleo stress tensors in the indus suture zone nw pakistan abstract analysis of fault striations measured in the kohistan part of the indus suture zone nw himalaya pakistan has been carried out to document dynamic evolution during the brittle stage of the collision of india and asia processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as sse nnw compression e w compression radial extension and ssw nne compression the last corresponds to the present day stress field defined from seismic activity the earlier stress fields are related to times during the miocene when convergence related stresses were disturbed by the formation of the nearby nanga parbat and indus syntaxes

long recurrence interval of faulting beyond the 2005 kashmir earthquake around the northwestern margin of the indo asian collision zone the 2005 kashmir earthquake in pakistan occurred on a previously mapped active fault around the northwest margin of the indo asian collision zone to address the quantitative contribution of the earthquake to plate convergence we performed paleoseismological trench excavations at nisar camp site near muzaffarabad across the middle section of the 2005 surface rupture the fault strands exposed in the trench cut late holocene fluvial deposits and record evidence of both the 2005 and a penultimate event supported by the presence of colluvial deposits and a downdip increase in displacement along the fault strands the 2005 event produced a net slip of 5 4 m and the penultimate earthquake exhibits a similar amount of slip radiocarbon ages and historical accounts loosely constrain the timing of the penultimate event between 500 and 2200 yr b p however the exposed section encompasses 4 k y of stratigraphy suggesting an average interevent interval of 2 k y for the 2005 type events we thus conclude that the 2005 event did not occur on the plate boundary megathrusts but on intraplate active faults within the sub himalaya consequently the accumulated elastic strain around the complex northwestern margin of the indo asian collision zone has not been significantly released by the 2005 earthquake

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

present day deformation of the pyrenees revealed by gps surveying and earthquake focal mechanisms until 2011 the pyrenean mountain range is a slowly deforming belt with continuous and moderate seismic activity to quantify its deformation field we present the velocity field estimated from a gps survey of the pyrenees spanning 18 yr the potsis and respyr networks including a total of 85 gps sites were installed and first measured in 1992 and 1995 1997 respectively and remeasured in 2008 and 2010 we obtain a deformation field with velocities less than 1 mm yr 1 across the range the estimated velocities for individual stations do not differ significantly from zero with 95 per cent confidence even so we estimate a maximum extensional horizontal strain rate of 2 0 1 7 nanostrain per year in a n s direction in the western part of the range we do not interpret the vertical displacements due to their large uncertainties in order to compare the horizontal strain rates with the seismic activity we analyse a set of 194 focal mechanisms using three methods i the r factor relating their p and t axes ii the stress tensors obtained by fault slip inversion and iii the strain rate tensors stress and strain rate tensors are estimated for i the whole data set ii the eastern and western parts of the range separately and iii eight zones which are defined based on the seismicity and the tectonic patterns of the pyrenees each of these analyses reveals a lateral variation of the deformation style from compression and extension in the east to extension and strike slip in the west of the range although the horizontal components of the strain rate tensors estimated from the seismic data are slightly smaller in magnitude than those computed from the gps velocity field they are consistent within the 2 uncertainties furthermore the orientations of their principal axes agree with the mapped active faults

paleostress regimes from brittle structures of the karakoram kohistan suture zone and surrounding areas of nw pakistan paleostress orientations were calculated from fault populations at 24 sites along the sw ne segment and five sites along the e w yasin segment of the karakoram kohistan suture zone in nw pakistan they demonstrate the importance of combined thrusting and strike slip faulting however several paleostress tensor directions are distinguished a dominant nw se compression and a minor e w compression are compatible with the recent evolution of this part of the hindu kush from the lack of both systematic overprinting relationships and spatial trend the two tensors were obtained at different locations we conclude that in each location any of these two shortening directions can dominate heterogeneously distributed extension is found in some places and is likely due to local conditions these paleostress tensors substantiate a transpressional regime due to far field himalayan compression and document the long term background of the seismogenic deformation in this region