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

effects of prestress state and rupture velocity on dynamic fault branching 1 we consider a mode ii rupture which propagates along a planar main fault and encounters an intersection with a branching fault using an elastodynamic boundary integral equation formulation allowing the failure path to be dynamically self chosen we study the following questions does the rupture initiate along the branch does it continue is the extensional or compressional side most favored for branching does rupture continue on the main fault too failure is described by a slip weakening law for which the strength at any amount of slip is proportional to normal stress our results show that dynamic stresses around the rupture tip which increase with rupture velocity at locations off the main fault plane relative to those on it could initiate rupture on a branching fault as suggested by prior work whether branched rupture can be continued to a larger scale depends on principal stress directions in the prestress state and on rupture velocity the most favored side for branching rupture switches from the extensional to the compressional side as we consider progressively shallower angles of the direction of maximum compressive prestress with the main fault simultaneous rupturing on both faults can be activated when the branching angle is wide but is usually difficult for a narrow branching angle due to strong stress interactions between faults however it can be also be activated by enhanced dynamic stressing when the rupture velocity is very near the rayleigh velocity natural examples seem consistent with the simulations that we present

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

paleoseismic evidence from trench investigation along hajipur fault himalayan frontal thrust nw himalaya implications of the faulting pattern on landscape evolution and seismic hazard abstract the study area falls within the mesoseismal zone of 1905 kangra earthquake mw 7 8 two parallel nnw sse striking active fault scarps named as hajipur faults hf1 and hf2 along the northwestern end of the janauri anticline in the foothill zone have displaced floodplain sediments of the beas river the hf1 and hf2 represent the imbricate faults of the himalayan frontal thrust hft and are the result of lateral propagation of deformation from two fold segments i e jf1 and jf2 respectively in northwest direction along the strike ground penetrating radar gpr profiles and trenching across the hf2 reveal two low angle thrust fault strands f1 and f2 displacements of 7 5 m on f2 and 1 5 m on the associated branching faults f a f b and f c were observed total four stratigraphic units unit a gravel with a lens of medium sand unit a is the oldest overlain by units b medium to coarse sand unit c with fine to medium sand and unit d fine to medium sand with scattered gravel were observed in trench radiocarbon ages of the charcoal samples from unit b and unit d optical ages of sediments from units a b and c gpr data and trench log suggest two major events along f1 and f2 strands event i along f1 occurred during 2600 800 yr bp and event ii along f2 around 400 yr bp and before 300 yr bp given the uncertainty in dates it is suggested that the latest event occurred during 1500 1600 ad considering the oldest unit unit a exposed in trench with vertical displacement of 7 5 8 m age of 2600 500 yr bp and net displacement of 9 m during single event along low angle fault 25 implies slip rate 7 6 1 7 mm yr uplift rate 3 2 0 6 mm yr shortening rate 6 9 1 4 mm yr and recurrence interval 1160 250 yr for large magnitude event with mw 7 0 with the recurrence of 1100 yr the penultimate event probably occurred at around 1400 1500 yr bp given the recent gps based slip rate of 14 1 mm yr in kangra reentrant baneerjee and burgman 2002 the present study suggests that about half of this slip is consumed along the hft and that this fault is more active compared to those in the hinterland

seismically active fold and thrust belt in the san joaquin valley central california structural analysis of late cenozoic folds along the western and southern margins of the san joaquin basin suggests that the folds are related to development of a fold and thrust belt rather than to wrench tectonics the folds have formed by the processes of fault bend folding and fault propagation folding which commonly occur in fold and thrust belts our structural interpretation attributes the seismically active coalinga and kettleman hills north dome anticlines to fault bend folding above a thrust fault s that steps up from a detachment within the franciscan assemblage to a detachment at the base of the great valley group this thrust does not reach the surface blind thrust and its slip is consumed in backthrusting and formation of subsurface folds under the san joaquin valley movement on the postulated thrust s would explain the cause of the may 2 1983 coalinga earthquake and the august 15 1985 avenal earthquake and would account for the lack of significant surface rupture or shallow subsurface faulting during both earthquakes well documented examples of fault bend and fault propagation folding also occur at wheeler ridge in the san emigdio mountains and at kettleman hills south dome deformation associated with fold and thrust belts can be extremely complicated considerable fault movement can occur without accompanying surface rupture or shallow level faulting conversely surface rupture can occur that has no direct relationship to fault slip at depth an example would be flexural slip folding wherein the slip planes reach the surface but do not root into any significant faults at depth consequently traditional geologic approaches to seismic risk evaluation which rely largely on surface data are subject to numerous pitfalls when applied to fold and thrust belts our interpretation of the structural style that developed in central california during the late cenozoic requires that the strain associated with the transpressive motion between the pacific and north american plates be resolved into normal and tangential components thrust faulting and folding normal to the plate boundary and strike slip faulting parallel to the plate boundary san andreas fault the thrust faults root in a deecollement at the brittle ductile transition zone above which shortening is associated with folding and thrust faulting and beneath which shortening in the lower crust is accommodated by ductile processes of tectonic thickening or incipient subduction

tertiary extension and contraction of lower plate rocks in the central mojave metamorphic core complex southern california several authors recently have proposed the rolling hinge model for the formation of extensional detachment faults in metamorphic core complexes in this model isostatic uplift of the denuded footwall of a major normal fault causes the near surface part of the fault to rotate from a higher to a lower dip for the rolling hinge model to be acceptable the footwalls of detachment faults must have undergone the strain pattern dictated by the rolling hinge in this paper the structural development of the footwall of the central mojave metamorphic core complex is used as a field test tertiary structures in the lower plate of the core complex record ne directed ductile extensional shear followed by cataclastic ne side up shear with a significant component of contraction along the previous extension direction this strain history agrees with the rolling hinge model and particularly with a version of the model in which footwall uplift occurs by a combination of elastic flexure and flexurally driven upper crustal failure similar late stage layer parallel contraction appears to be present in some other tectonically denuded terranes of the basin and range suggesting that the flexural failure rolling hinge model for extensional terranes may be widely applicable

an empirical relation between ocean surface wind direction and the bragg line ratio of hf radar sea echo spectra twelve days of tests with six u s air force oth b over the horizon radars produced a large surface wind direction data set covering much of the north atlantic and pacific oceans we compare wind directions derived from the sea echo bragg line ratio with concurrent in situ measurements made by ships and buoys and with the national meteorological center nmc global data assimilation system model using 1900 such comparisons we derive an empirical model for the dependence of surface wind direction on the bragg line ratio of hf radar sea echoes the rms difference between the empirical model and the combined nmc and in situ data is about 33 when only very high quality radar data are used the rms difference between the radar and buoy measurements alone is 24 the pattern of surface streamlines derived from 1 day s radar measurements over the northeastern pacific ocean closely matches that derived from the nmc model

role of fault branches in earthquake rupture dynamics 1 we analyze earthquake ruptures propagating along a straight main fault and encountering a finite length branch fault such intersections are often observed in natural fault systems the predicted effects of the interaction with the branch that we report can be remarkable they can strongly perturb the propagation velocity on the main fault and in some cases even arrest that propagation earlier work kame et al 2003 bhat et al 2004 emphasized the role of the fault pre stress state branch geometry i e branching angle and the incoming rupture velocity at the branching junction in determining whether the rupture would follow the branch or continue on the main fault or both through simulations which did not let a rupture on the branch encounter a barrier or a fault end called infinite branch cases henceforth in this study we look at finite branch cases and study the effect also of branch length with rupture being blocked from propagation beyond the branch end it is known that sudden stoppage of a dynamic rupture front leads to the propagation of large dynamic stress perturbations in the medium these have been known to nucleate or terminate ruptures on adjacent fault segments harris et al 1991 harris and day 1993 1999 harris et al 2002 fliss et al 2005 among others we thus anticipate interaction between the rupture on the main fault and the branched one at two stages when the rupture is propagating on the branch and when it is suddenly blocked at the branch end we show that in general rupture termination on a compressional branch little affects propagation on the main fault compared to the infinite branch cases for branches on the extensional side we show in some cases that whereas an infinite branch would have allowed or stopped rupture propagation on the main fault a finite branch stops or allows propagation on the main fault such results have a dependence on branch length that we document we also illustrate branch related complexities in rupture velocity evolution which could be one of the sources of the high frequency content of strong ground motion record complexities in the slip distribution often associated with a presumed heterogeneous strength distribution along the fault can also be observed when rupture is terminated on a branch

downdip segmentation of strike slip fault zones in the brittle crust outcrop scale field evidence from the southern san jacinto fault zone in southern california indicates that bedding parallel slip may be an important mechanism for transferring and accommodating slip within strike slip fault zones that cut across heterogeneous stratigraphy steeply dipping strike slip fault segments exposed in conglomeratic sandstones abruptly terminate at weaker shale layers where slip occurs on bedding parallel planes cross sections of fault related seismicity within the southern san jacinto fault zone reveal that events generally cluster within tabular steeply dipping fault parallel streaks that are limited in extent in the downdip direction the depths of the downdip terminations of shallow streaks tend to be roughly coincident with the depths of the updip terminations of deeper streaks these configurations define stepover geometries that range in character from sharp to diffuse the examples described herein provide evidence that downdip segmentation within strike slip fault zones may be common over a wide range of scales

dynamic slip transfer from the denali to totschunda faults alaska testing theory for fault branching we analyze the observed dynamic slip transfer from the denali to totschunda faults during the mw 7 9 3 november 2002 denali fault earthquake alaska this study adopts the theory and methodology of poliakov et al 2002 and kame et al 2003 in which it was shown that the propensity of the rupture path to follow a fault branch is determined by the preexisting stress state branch angle and incoming rupture velocity at the branch location here we check that theory on the denalitotschunda rupture process using 2d numerical simulations of processes in the vicinity of the branch junction the maximum compression direction with respect to the strike of the denali fault near the junction has been estimated to range from approximately 73 to 80 we use the values of 70 and 80 in our numerical simulations the rupture velocity at branching is not well constrained but has been estimated to average about 0 8 cs throughout the event we use 0 6 cs 0 8 cs 0 9 cs and even 1 4 cs as parameters in our simulations we simulate slip transfer by a 2d elastodynamic boundary integral equation model of mode ii slip weakening rupture with self chosen path along the branched fault system all our simulations except for 70 and 0 9 cs predict that the rupture path branches off along the totschunda fault without continuation along the denali fault in that exceptional case there is also continuation of rupture along the denali fault at a speed slower than that along the totschunda fault and with smaller slip

the deep crustal structure of the mojave desert california from cocorp seismic reflection data cocorp seismic reflection profiling in the western and northern mojave desert of southern california has revealed the presence of numerous major low angle reflecting horizons within the crust these complex though laterally continuous horizons are interpreted to represent major southwesterly dipping crustal fault zones and as such they place important constraints on the tectonic evolution of the region the upper most horizon is interpreted to be the rand thrust which where exposed places precambrian and late cretaceous crystalline rocks over possibly younger pelona rand orocopia schist this reflecting horizon extends for 25 km southwest of the rand mountains where it appears to be truncated at a depth of about 7 4 km by another horizon which may be a later low angle normal fault the other reflecting horizons are not traceable to the surface and so greater ambiguity remains in their interpretation the most prominent of these horizons occurs at midcrustal depths 15 6 km exhibits a ramp and flat geometry and extends over the northern area of the mojave survey into the basin and range province a lower horizon at depths of 20 30 km in the northern part of the survey area is antiformal and appears to terminate above a flat and relatively continuous moho depth horizon the crustmantle transition appears to be represented by a continuous series of reflections which occur at about 10 s 33 km in the north of the survey and at about 8 9 s 26 29 km in the south these reflections are offset in the vicinity of the town of mojave the deep intracrustal fault zones inferred from the cocorp survey may represent 1 the deep crustal continuation of the system of mesozoic thrusts which crops out in southern nevada and southeastern california 2 late cretaceous to early cenozoic northeast vergent thrusts related to the uplift of the pelona orocopia rand schist or 3 low angle normal faults related to early miocene northeast southwest directed crustal extension the cocorp survey also traversed the major strike slip faults that bound the mojave block the san andreas fault zone appears to truncate reflectors at depths of 6 8 and 20 km within the mojave basement suggesting that it is a major vertical feature which extends to at least 20 km depth conversely the garlock fault does not offset an underlying reflecting horizon which occurs at 9 km depth and therefore appears to be a relatively shallow crustal feature

role of subsurface loads and regional compensation in the isostatic balance of the transverse ranges california evidence for intracontinental subduction bouguer gravity anomalies in the transverse ranges of southern california show a pronounced asymmetry in north south profiles across the mountains and a characteristic shape which is largely insensitive to variations in the topographic load along strike while individual gravity topography profile pairs could be consistent with a number of isostatic compensation mechanisms the unusual relationship between gravity and topography in the san bernardino mountains severely limits the class of acceptable models if the bouguer gravity field is caused by flexure of the crust mantle boundary the simplest solution consistent with the data in the western transverse ranges the san gabriel mountains and the san bernardino mountains models the great valley and mojave provinces to the north as a 50 km thick elastic plate supporting the mountains which are underthrust by a much weaker plate to the south the best fit to the gravity data in the san bernardino mountains requires a terminal bending moment on the southern plate beneath the mountains the magnitude of the terminal bending moment decreases to the west in the san gabriel and western transverse ranges we equate the load responsible for this terminal moment with the high velocity slablike feature mapped in the upper mantle beneath the transverse ranges using seismic tomography the coupling between the subsurface load and the overlying lithosphere suggests that the slab represents lithospheric subduction with an extremely small density contrast rather than a small scale convective feature

aspects of the crustal structure of the western mojave desert california from seismic reflection and gravity data seismic and gravity data taken along line 1 of the 1982 consortium for continental reflection profiling cocorp mojave desert survey n s profile 30 km long have been used to characterize the upper crust north of the san andreas fault in the western mojave block of southern california consortium for continental reflection profiling seismic reflection data were reprocessed to emphasize the upper 5 seconds two way travel time the resultant common depth point cdp sections provided starting models for generating a refined geologic cross section using a combination of ray tracing forward modeling and gravity interpretation the forward modeling was used to validate the existence of faults and constrain their dips the gravity data were used to refine the overall model particularly in poor data areas on the cdp sections gravity data taken along three nearby profiles parallel to primary line of section were also used to determine the structural trend results from the first two seconds indicate the presence of a series of ene striking reverse faults beneath the late tertiary and quaternary sedimentary cover of the western mojave the faults dip northward and offset the sediment basement interface the largest such feature has an apparent throw of 1 8 km and exhibits a subtle scarp at the earth s surface suggesting holocene displacement the orientation of these faults although not an instantaneous representation of the present day stress field is consistent with nnw compression across the western mojave block and wnw striking san andreas fault as determined from nearby focal mechanisms and in situ stress measurements the faults also appear to be closing small sedimentary basins in the mojave block which may have formed during an earlier extensional phase similar to what is happening on a much larger scale in the los angeles basin to the south of the san andreas fault reflections between 2 and 5 s coupled with the local geology and gravity modeling are consistent with the presence of the pelona rand schist in the subsurface beneath the western mojave the upper surface of the schist i e vincent rand thrust equivalent rises southward toward the san andreas fault where it is displaced vertically up to the south at least 5 km along the e w trending hitchbrook fault such that the schist crops out between the hitchbrook and subparallel san andreas to the south the same structure may exist beneath the tehachapi mountains with the roles of the hitchbrook and san andreas faults played by the north and south branches of the garlock fault respectively the rising or arching of the basement toward the san andreas fault and toward the garlock is not only reflected in the geology and topography local to these faults in many places but is also generally observed on seismic reflection profiles in the vicinity of these faults in the western mojave furthermore the arching is also consistent with a strong component of fault normal compression

late quaternary alluvial fans and paleosols of the kangra basin nw himalaya tectonic and paleoclimatic implications abstract the paper describes late quaternary pedosedimentary sequences of the alluvial fans from the kangra basin of nw himalayas for tectonic and paleoclimatic implications in the proximal part of the kangra basin three coalescing alluvial fans namely rait rihlu fans 65 km2 kangra fans 200 km2 and palampur fans 170 km2 from west to east evolved due to reactivation of longitudinal and transverse faults and climatic changes during the late quaternary the fans are characterised by subsidence of rait rihlu fans uplift of kangra fans and tilting of palampur fans the thick 90 m pedosedimentary sequences exposed along the rivers characterise the dominant formative processes over the fans the stream flow sediments dominate the rait rihlu fans whereas the debris flow sediments dominate the kangra and palampur fans the fan sequences are also marked by the formation of strongly developed paleosols on loess l1 l3 loess paleosols and weakly developed paleosols on fluvial deposits in response to the tectonics and climate change in nw himalayas formation of the loess in proximal and distal settings of the alluvial fans is related to the cool dry climates during the advance of glaciers in the adjoining areas at 78 ka 44 ka 30 ka and 20 ka when climate was approaching towards the last glacial maxima field characters micromorphology grain size and clay minerals of these loessic deposits suggest strong pedogenesis of the loess during a warm humid climate after the retreat of glaciers in the nw himalayan region and are likely related to marine isotope stages mis4 5 in proximal and mis2 3 in distal the loess paleosols show some degree of syndepositional pedogenesis in upper horizons and are accretionary in nature weakly expressed pedogenic features in fluvial and debris flow deposits suggest rapid sedimentation over unstable surfaces related to the reactivation of main boundary thrust mbt and other regional faults

active fault fault growth and segment linkage along the janauri anticline frontal foreland fold nw himalaya india the 100 km long frontal foreland fold the janauri anticline in nw himalayan foothills represents a single segment formed due to inter linking of the southern js1 and the northern js2 janauri segments this anticline is a product of the fault related fold growth that facilitated lateral propagation by acquiring more length and linkage of smaller segments giving rise to a single large segment the linked portion marked by flat uplifted surface in the central portion represents the paleo water gap of the sutlej river this area is comparatively more active in terms of tectonic activity well justified by the occurrence of fault scarps along the forelimb and backlimb of the anticline occurrence of active fault scarps on either side of the anticline suggests that the slip accommodated in the frontal part is partitioned between the main frontal thrust i e the himalayan frontal thrust hft and associated back thrust the uplift in the piedmont zone along southern portion of janauri anticline marked by dissected younger hill range suggests fore landward propagation of tectonic activity along newly developed frontal piedmont thrust fpt an imbricated emergent thrust branching out from the hft system we suggests that this happened because the southern segment js1 does not linked up with the northwestern end of chandigarh anticline segment cs in the northwestern end of the janauri anticline due to no structural asperity the tectonic activity on hft was taken up by two hf1 in the frontal part and hf2 towards the hinterland side newly developed parallel active faults hajipur fault branched from the main js2 segment the lateral propagation and movements along hf1 and hf2 resulted in uplift of the floodplain as well as responsible for the northward shift of the beas river gpr and trench investigations suggest that earthquakes during the recent past were accompanied with surface rupture osl optical stimulated luminescence dates from the trench suggests occurrence of at least two events during the recent historic past with the latest event ii during 1500 ad

structure and shortening of the kangra and dehra dun reentrants sub himalaya india surface geology oil well seismic reflection and magnetostratigraphic data are integrated to evaluate the structural style and the shortening rate at the himalayan front sub himalaya of northwest india the sub himalaya between the main boundary thrust and the himalayan frontal fault is the primary surface expression of shortening between the himalaya and the indian plate at certain locations the himalayan frontal fault is a blind thrust beneath anticlines of siwalik tertiary molasse parallel to the himalayan orogen the main boundary thrust is sinuous so the width of the sub himalaya ranges from 30 to 80 km where the sub himalaya is narrow nahan salient tertiary rocks are exposed in imbricate thrust sheets where the sub himalaya is broad kangra and dehra dun reentrants alluvium fills wide synclinal valleys duns seismic reflection data reveal that surface anticlines form in association with south vergent thrusts that root in a decollement at the base of the tertiary section reflection profiles and well data also indicate that the basement lithology changes northward from precambrian crystalline rocks beneath the indo gangetic plains to precambrian and cambrian metasedimentary rocks beneath the sub himalaya the sub himalayan decollement dips 2 5 northward beneath the kangra reentrant but it is steeper 6 beneath the dehra dun reentrant the kangra and dehra dun reentrants display fault propagation folds having steep limbs in the north and fault propagation and fault bend folds that have gently north dipping limbs in the south a balanced cross section of the kangra reentrant shows that a minimum of 23 km shortening has occurred since 1 9 1 5 ma yielding a shortening rate of 14 2 mm yr shortening has occurred at a rate of 6 16 mm yr across the dehra dun reentrant these data are similar to other published shortening rates and indicate that approximately 25 of the total india eurasia convergence at this longitude is accommodated within the sub himalaya given continued convergence and the presence of overpressured wells in the kangra reentrant the region is likely at risk from moderate and or great earthquakes in the future

depth migration of imaged time sections none of the leading approaches to the migration of seismic sections the kirchhoff summation method the finite difference method or the frequency domain method readily migrates seismic reflections to their proper positions when overburden velocities vary laterally for inhomogeneous media the diffraction curve for a localized buried scatterer is no longer hyperbolic and its apex is displaced laterally from the position directly above the scatterer hubral observed that the kirchhoff summation method images seismic data at emergent image ray locations rather than at the desired positions vertically above scatterers in addition distortions in diffraction shapes lead to incorrect imaging i e incomplete diffraction collapse and hence to further displacement errors for dipping reflections the finite difference method has been believed to continue waves downward correctly through inhomogeneous media in conventional implementations however both the finite difference method and frequency domain a

crustal thickness variations in southern california from los angeles region seismic experiment passive phase teleseismic travel times the goal of the 1993 los angeles region seismic experiment larse93 passive phase was to collect waveform data from local and distant earthquakes to study lower crust and upper mantle structural features in southern california particularly under the san gabriel mountains and san andreas fault during larse93 approximately 88 stations were deployed in a 175 km long linear array across the los angeles basin san gabriel mountains and mojave desert northeast of los angeles during the four weeks of continuous recording teleseismic events recorded at each site provided a wide range of ray path backazimuths the teleseismic events included a number of intermediate magnitude earthquakes with epicenters in the aleutian island kamchatka kuril island mid atlantic ridge solomon island japan fiji island and chile regions this experiment was followed by larse94 which involved land refraction and deep crustal seismic reflection profiles from offshore and onshore explosion sources we have used the joint data sets in this study to distinguish upper crustal features from adjacent lower crustal and upper mantle structures p wave travel times were determined from 17 teleseisms and upper crustal residual signatures were removed by incorporating larse94 upper crustal velocity model results within each backazimuth range the resulting relative traveltime residuals increase from negative values 0 5 sec average recorded in the northern san gabriel valley southern san gabriel mountain foothills to positive values 0 2 sec average in the central and northern san gabriel mountains the residual patterns display variations for different backazimuths and incidence angles but show almost no lateral spatial shift of maximum or minimum residual along the array indicating that the dominant source of the residual pattern is shallow 50 km the patterns of residuals require a sharp lateral gradient in shallow velocities between the northern san gabriel valley located in the northernmost los angeles basin and the san gabriel mountains over a distance of less than 50 km most of the residual pattern can be explained by laterally varying crustal thickness and a high velocity anomaly in the upper mantle in our model of moho depth variations the northern san gabriel valley to the southwest of the array is underlain by thinned continental crust crustal thickness increases laterally by 12 km over a distance of less than 50 km into the san gabriel mountains this conclusion is supported by widespread surface evidence for rift style volcanism and crustal extension in southern california crustal rocks

morphology and facies of the alluvial fan sedimentation in the kangra valley himachal himalaya abstract a number of alluvial fans having an average width e w of 10 15 km and length n s of 8 15 km have been mapped using the landsat tm imageries on 1 250 000 scale in the kangra valley of himachal himalaya this important geomorphic zone of alluvial fans is confined between the foot of the dhauladhar range and the siwalik ridges these fans are gently sloping from north to south and are slightly dissected having distinct horizons of glacial glacio fluvial fluvial lacustrine and loessic sediments derived from the dhauladhar granitic complex dharamsala and siwalik formations during the glacial and interglacial climatic stages of the quaternary period the vertical lithological profiles of these fans show a dominance of gravelly nearly 60 facies along with other lithofacies associations representing a braided river depositional environment in general the thickness of fan sediments ranges between 90 and 120 m the vertical facies are subdivided into three main facies i e lower middle and upper fan facies showing distinct sediment characteristics the presence of glacial moraines and clay rich debris flow deposits is significant in the upper fan facies the middle fan facies is gravel dominated along with some interbedded sandy channel fill deposits whereas the lower fan facies is composed of sand silt and mud the genesis of these three fan facies is closely related with the uplift of the source area and climatic changes during the pleistocene period

oblique convergence and slip partitioning in the nw himalaya implications from gps measurements we report gps measurements of crustal deformation across the kashmir himalaya we combined these results with the published results of gps measurements from the karakoram fault system and suggest that in the kashmir himalaya the motion between the southern tibet and india plate is oblique with respect to the structural trend we estimated this almost north south oblique motion to be 17 2 mm yr which is partitioned between dextral motion of 5 2 mm yr on the karakoram fault system and oblique motion of 13 6 1 mm yr with an azimuth of n198 e in the northwest southeast trending kashmir himalayan frontal arc thus the partitioning of the india southern tibet oblique motion is partial in the kashmir himalayan frontal arc however in the neighboring nepal himalaya there is no partitioning the entire india southern tibet motion of 19 20 mm yr is arc normal and is accommodated entirely in the himalayan frontal arc the convergence rate in the kashmir frontal himalaya is about 25 less than that in the nepal himalayan region however here the karakoram fault system accommodates about 20 of the southern tibet and indian plate convergence and marks the northern extent of the nw himalayan arc sliver the kaurik chango rift a north south oriented seismically active cross wedge transtensional fault appears to divide the sliver in two parts causing varying translatory motion on the karakoram fault on either side of the kaurik chango rift

convergence across the northwest himalaya from gps measurements 1 horizontal velocities of 26 global positioning system gps stations in the northwest himalayan region provide new constraints on the partitioning of india eurasia convergence and elastic strain accumulation about the locked main frontal thrust mft the northwest striking karakorum fault slips at 11 4 mm yr and contributes to east west extension of southern tibet and westward motion of the northwest himalaya towards nanga parbat rather than playing a role in eastward extrusion of tibet crustal shortening across the himalaya occurs within a zone centered about 100 km north of the siwalik foothills and the mft model inversions of the gps data indicate that the mft is locked over a width of 100 km comparison with geologic mft slip rate estimates suggests that this zone is building up a slip deficit at a rate of 14 1 mm yr and will eventually fail in future great earthquakes

wind direction estimation using small aperture hf radar based on a circular array compact high frequency hf antenna arrays are convenient to deploy however using a small aperture hf surface wave radar for wind direction measurement is still a challenging problem since an unsatisfactory array pattern degrades the performance of bragg ratio estimation to address this issue a digital beamforming method based on a superdirective synthesis technique for an hf receiving array that consists of seven elements positioned on a 5 m diameter circle is proposed this superdirective beamforming method contains a sidelobe constraint subsequently a hybrid superdirective beamforming and direction finding method is adopted to estimate the wind direction using a multifrequency hf radar based on a circular array mhf c the superdirective beamforming approach as well as the wind direction estimation method is presented in detail the wind direction estimation method has been applied to the raw data sets that were collected with two mhf c radars installed along the coast of the east china sea in april 2015 and comparisons between radar derived and in situ wind directions have been made ship mounted anemometers were used to obtain in situ measurements at six sampling locations within the overlapping coverage of both radars another comparison between the radar derived and anemometer derived wind directions which were obtained from june 15 2015 to august 12 2015 has also been made the results indicate that the proposed method is effective for wind direction estimation with root mean square differences rmsds between 24 1 and 33 1 when wind speeds were higher than 5 m s the analysis encourages us to recommend a minimum wind speed of 5 m s for reasonably assessing wind direction measurement performance

seismotectonics of the kangra region northwest himalaya abstract the occurrence of major and moderate earthquakes having thrust and strike slip mechanism along the longitudinal and transverse feature within the same seismogenic zone requires us to study the area in detail to infer the seismotectonics the epicentral distribution of earthquakes 4 0 mb between chamba and sundernagar region shows the high rate of activity either north of chamba i e north of the main central thrust mct or north of dharamsala in between the panjal thrust pt and mct in the dhauladhar range it is however surprising that all the moderate earthquakes that have triggered in the kangra region have either been in the frontal belt along the transverse features or have followed the arcuate belt close to the main boundary thrust mbt the spatio temporal variation of the seismicity from 1973 to 2000 4 0 mb reveals a migration trend between chamba and sundernagar during the seventies and early eighties the seismicity was concentrated in the chamba region and in the late eighties and early nineties the seismicity shifted around dharamsala and later further north in this arcuate tectonic belt of the chamba sundernagar region the foreland region has a characteristic tectonic setting all the fault and fold structures in the oligocene miocene and neogene pliestocene sediments in the foreland region show relative movement in the area of transverse tectonics the surface structures i e thinning and thickening of the sediments are controlled by the basement cofiguration controlled by the subduction process the mbt and the pt are closely spaced and meet each other just northwest of dharamsala the width of the lesser himalaya in the chamba sundernagar region is also much narrower as compared to the region in the east in garhwal kumaun and western nepal this suggests that the convergence is taken up largely by underthrusting of the lesser himalayan formations along the pt the occurrence of a moderate earthquake of magnitude 6 5 in 1978 and the 1986 dharamsala earthquake along the se dipping and sw dipping nodal planes within the ne dipping thrust regime and displacement of the mbt and pt from 4 to 12 km reflects the active involvement of the ne sw trending fault system in controlling the seismic behavior of the kangra region the microearthquake migration in time and space in the chamba sundernagar region also reflects the time differential segmental collision behavior of the basement

seismic exploration of continental strike slip zones abstract seismic exploration of both palaeozoic and active strike slip zones shows strike slip faults that penetrate all or most of the crust offsets on the moho are evident particularly at young and active zones with a component of compression such as the alpine fault of new zealand where a change in crustal thickness of about 20 km is observed moho offsets for the old palaeozoic strike slip zones are usually much less prominent careful migration of crustal seismic reflection data from some of these zones shows that instead of sharp offsets the moho structure consists of a localized keel type crustal thickening of a few kilometres in amplitude and occurs over a zone approximately 10 km wide the large moho offsets of young strike slip zones may in some cases partially decay with time active strike slip zones are becoming an important focus of study but seismic exploration is hampered by complex near surface geology 3d structure and the difficulty of imaging steeply dipping structure in the subsurface in order to meet this challenge a wide range of seismic techniques is now being deployed these include wide angle seismic reflection refraction p wave delays and the study of guided s waves results from california give geophysical images of vertical strike slip faults that penetrate to the moho in contrast the alpine fault of new zealand appears to be a surface manifestation of an inclined 40 ramp extending down to the lower crust and along which uplift and exhumation of the continental crust and possibly strike slip motion is taking place

interpretation of crustal seismic velocities in the san gabriel mojave region southern california the increased concern over seismic hazards in the los angeles region has created interest in the crustal structure and mechanical properties associated with faults like the sierra madre and san andreas this study presents the seismic properties of major lithologies found in the vicinity of the san andreas fault zone in order to correlate with the los angeles region seismic experiment lars e results scientists from the larse group have recently acquired high quality seismic data along three transects thirty nine rock samples were collected along the larse line i which trends ne sw across the central mojave desert and the san gabriel mountains these rock samples represent the following lithologies precambrian gneisses san gabriel anorthosite mesozoic granitic intrusives pelona schist mendenhall granulite gneisses and san andreas fault zone cataclasites the seismic properties were determined by measuring compressional and shear wave velocities as a function of confining pressure average compressional and shear wave velocities at 150 mpa show a wide range of values the mendenhall gneiss and the san gabriel anorthosite complex have high velocities 6 5 km s and 6 4 km s respectively the pelona schist the mojave granitic intrusives and the san andreas cataclasitic rocks have average velocities of 5 8 km s 5 2 km s and 5 1 km s respectively average densities range from 2320 kg m3 for fault zone cataclasites to 3100 kg m3 for a mendenhall granulite gneiss gneisses and schists show significant seismic anisotropy 5 20 due to preferred mineral orientation while most other rocks are nearly isotropic poisson s ratios range from a high of 0 29 in the san gabriel anorthosite to a low of 0 22 in the san gabriel gneiss comparison of the measured seismic properties with the larse velocity model allows interpretation of crustal structure in terms of rock compositions the upper crust southwest of the san andreas fault contains granitic intrusives gneisses and schists while under the mojave desert the upper crust is dominated by gneisses high velocities under the san gabriel mountains represent either lower crustal granulites or anorthosite the velocity decrease beneath the san andreas fault zone originates from minor amounts of cataclasite or the presence of low velocity lithologies such as pelona schist 1998 elsevier science b v all rights reserved

hf radar wave and wind measurement over the eastern china sea high frequency hf radar can be employed to measure sea surface state parameters such as waveheight wind field and surface current velocity this paper describes the application of the hf ground wave radar in remote sensing the surface conditions over the eastern china sea in october 2000 the radar referred to as the osmar2000 was developed by wuhan university preliminary wave spectra waveheights and wind fields estimated from the collected data are presented and compared with ship recorded measurements where such are available the range for wind direction sensing is up to 200 km wave information and wind speed can be provided up to a range of 120 km the mean difference between radar and ship measured significant waveheight is 0 323 m wind direction is measured within 20 spl deg and wind speed to within 0 6 m s with such agreement being fairly reasonable the feasibility of the inversion algorithm and the ocean state real time sensing capability of osmar2000 are demonstrated

active tectonic influence on the evolution of drainage and landscape geomorphic signatures from frontal and hinterland areas along the northwestern himalaya india abstract the kangra re entrant in the nw himalaya is one of the most seismically active regions falling into seismic zone v along the himalaya in 1905 the area experienced one of the great himalayan earthquakes with magnitude 7 8 the frontal fault system the himalayan frontal thrust hft associated with the foreland fold janauri anticline along with other major as well as secondary hinterland thrust faults provides an ideal site to study the ongoing tectonic activity which has influenced the evolution of drainage and landscape in the region the present study suggests that the flat uplifted surface in the central portion of the janauri anticline represents the paleo exit of the sutlej river it is suggested that initially when the tectonic activity propagated southward along the hft the janauri anticline grew along two separate fault segments north and south faults the gap between these two fault and the related folds allowed the sutlej river to flow across this area later the radial propagation of the faults towards each other resulted in an interaction of the fault tips which caused the rapid uplift of the area rapid uplift resulted in the disruption and longitudinal deflection of the sutlej river channel fluvial deposits on the flat surface suggest that an earlier fluvial system flowed across this area in the recent past geomorphic signatures like the sharp mountain fronts along the hft in some places as well as along various hinterland subordinate faults like the nalagarh thrust nat the barsar thrust bat and the jawalamukhi thrust jmt the change in the channel pattern marked by a tight incised meander of the beas channel upstream of the jmt indicate active tectonic movements in the area the prominent v shaped valleys of the beas and sutlej rivers flowing across the thrust fronts with vf values ranging from

paleomagnetic and geologic data indicating 2500 km of northward displacement for the salinian and related terranes california results of a pair of paleomagnetic studies of sedimentary rocks in the salinian terrane of westernmost california indicate a northward displacement of about 2500 km since cretaceous time stratigraphic relations suggest that the salinian terrane became amalgamated with several others by the late cretaceous and all underwent the same northward translation this composite terrane allochthon became sutured to cratonal north america by early tertiary time one paleomagnetic study involved upper cretaceous turbidites of the pigeon point formation fine grained thin bedded turbidites yielded the most reliable results whereas medium to coarse grained sandstones are not always stably magnetized contorted layers resulting from soft sediment deformation usually gave directional results parallel to those of undeformed sedimentary layers thereby implying a postdepositional remanence process there is no indication of inclination error or other processes affecting the fidelity of the remanent magnetization paleomagnetic results from four separate locations in the pigeon point formation gave positive fold tests and mean inclination values near 36 a mean geomagnetic latitude calculated from these results is 21 2 5 3 much more southerly than the value of 46 5 2 3 calculated for pigeon point using paleomagnetic pole data from late cretaceous rocks from cratonic north america declination values are not antipodal for normal and reversed polarity sites analysis of depositional current directions from sandstone beds of the same outcrops shows that the difference is the result of neogene rotations of small crustal blocks adjacent to the san gregorio fault in a sequence of paleocene turbidites that crop out at point san pedro four sample localities yielded positive fold tests with mean inclination values near 40 declination values however were spread over a range between 230 and 320 comparison with depositional current directions from the same outcrops indicates clockwise rotations related to neogene right slip on the pilarcitos fault the mean geomagnetic latitude calculated for the point san pedro sediments is 24 5 4 0 and is more southerly than the 43 3 2 5 latitude expected for that location for the salinian terrane and the west coast of cratonic north america absolute rates of latitudinal motion were 8 5 cm yr northward and 3 cm yr southward respectively

role of extrusion of the rand and sierra de salinas schists in late cretaceous extension and rotation of the southern sierra nevada and vicinity the rand and sierra de salinas schists of southern california were underplated beneath the southern sierra nevada batholith and adjacent mojave salinia region along a shallow segment of the subducting farallon plate in late cretaceous time various mechanisms including return flow isostatically driven uplift upper plate normal faulting erosion or some combination thereof have been proposed for the exhumation of the schist we supplement existing kinematic data with new vorticity and strain analysis to characterize deformation in the rand and sierra de salinas schists these data indicate that the schist was transported to the ssw from deep to shallow crustal levels along a mylonitic contact the rand fault and salinas shear zone with upper plate assemblages crystallographic preferred orientation patterns in deformed quartzites reveal a decreasing simple shear component with increasing structural depth suggesting a pure shear dominated westward flow within the subduction channel and localized simple shear along the upper channel boundary the resulting flow type within the channel is that of general shear extrusion integration of these observations with published geochronologic thermochronometric thermobarometric and paleomagnetic studies reveals a temporal relationship between schist unroofing and upper crustal extension and rotation we present a model whereby trench directed channelized extrusion of the underplated schist triggered gravitational collapse and clockwise rotation of the upper plate

tidal currents in the northwestern adriatic high frequency radio observations and numerical model predictions the results of a two year long deployment of high frequency radars along the italian coast of the northern adriatic are analyzed to characterize the surface tidal currents m2 and k1 ellipses are aligned with the basin axis and exhibit large eccentricities in the middle of the basin decreasing toward the italian coast comparisons are made with a 3d finite element non linear numerical model of the tides complex correlations between modeled and observed tidal currents show a remarkable agreement in the middle of the basin with magnitudes reaching 0 985 and average phases of 6 4 deg however the magnitudes drop to 0 5 within 20 30 km from the italian coast where the modeled currents amplitudes are underestimated by 2cm s and the phases lag the observed phases by 60 deg this shallow region less than 30 m deep is characterized by low salinity water originating at the po river and laterally sheared coastal flows the radars may have captured the influence of stratification or mean sheared flows both absent from the model the model parameterization of bottom friction may also inadequately represent the effects of real bottom friction on the vertical current shear

active fault and paleoseismic studies in kangra valley evidence of surface rupture of a great himalayan 1905 kangra earthquake mw 7 8 northwest himalaya india our findings suggest that interseismic strain accumulated south of the fault ramp under the higher himalayas was not only released periodically along the himalayan frontal thrust hft during large magnitude earthquakes but also along the active faults in the hinterland the 4 april 1905 kangra earthquake m w 7 8 killed more than 20 000 people and destroyed the towns of kangra and dharamsala in northwest himalaya in spite of its large magnitude with a maximum intensity x on the rossi forel intensity scale recorded in the epicentral area no surface rupture was reported and no focal mechanism is available this article uses satellite imagery and field mapping to identify an active right lateral strike slip fault named the kangra valley fault kvf we infer that the kvf represents the surface rupture of the 1905 kangra earthquake extending west northwest east southeast and east west for 60 km it cuts through the kangra and sihunta valleys and is capable of producing m w 7 2 earthquakes existence of the kvf in the kangra re entrant is indicative of oblique convergence and slip partitioning between the main boundary thrust in the north the jawalamukhi thrust in the south and a strike slip fault in the northwest himalaya paleoseismic investigations revealed evidence of at least four earthquakes on the kvf event i oldest occurred before 900 b c or between 900 b c and 2500 b c event ii occurred between 100 b c and 80 b c penultimate event iii occurred around a d 800 and a d 1000 and the most recent event event iv occurred after a d 1620 and before a d 1940 and is likely the 1905 kangra earthquake m w 7 8 a longer recurrence along the kvf is inferred between older paleoearthquake events i and ii and a shorter interval of 1050 150 years is inferred between younger events ii iii and iv because the strain during the 1905 kangra earthquake was released along the kvf potential for large magnitude earthquakes in northwest himalaya along the hft still remains online material figures of quartz response curves growth curves and histograms of sample numbers and trench photomosaics

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

active fault topography along kangra valley fault in the epicentral zone of 1905 mw7 8 earthquake nw himalaya india the 1905 ce kangra earthquake mw7 8 was one of the most damaging earthquakes in himalaya malik et al 2015 suggested that the kangra valley fault kvf from the epicentral zone was the source of the 1905 kangra earthquake in this article we discuss the active fault topography along kvf marked by distinct right lateral strike slip movement extends for about 60 km between patka village in nw and tanda village in se the prominent offset of streams ranging from 10 m to 340 m have been identified along the fault trace the lateral offset of 10 m may be indicative of displacement during a single event lateral as well as the vertical offset of alluvial fan surfaces and fluvial terraces resulted in formation of the north as well as south facing fault scarps ranging in height from 1 2 to 14 m kvf between two major thrust systems i e main boundary thrust mbt and jawalamukhi thrust jmt suggest that slip partitioning is taking place between the thrust and strike slip faults and is a net result of oblique convergence in nw himalaya the end points of the fault traces exhibit typical y shape because of stepping and branching out of rupture from the main fault considering the pre stress axis from the gps velocity vectors from banerjee and burgman 2002 the branching scenario we obtained for kvf is not consistent with the simulated models by kame et al 2003 and poliakov et al 2002 for other faults this could be attributed to the ongoing oblique convergence in nw himalaya based on the y shape pattern and the upthrown and downthrown sides mapped along the fault trace we suggest two possibilities for surface rupture 1 the fault rupture initiated from pathiyar malan side and propagated unilaterally towards west 2 taking into account the y shape on both the end sections of the fault trace it can be inferred that the rupture during most recent event probably started in the center at miniana and propagates bilaterally in e w

fault branching and rupture directivity 1 could the directivity of a complex earthquake be inferred from the ruptured fault branches it created typically branches develop in forward orientation making acute angles relative to the propagation direction direct backward branching of the same style as the main rupture e g both right lateral is disallowed by the stress field at the rupture front here we propose another mechanism of backward branching in that mechanism rupture stops along one fault strand radiates stress to a neighboring strand nucleates there and develops bilaterally generating a backward branch such makes diagnosing directivity of a past earthquake difficult without detailed knowledge of the branching process as a field example in the landers 1992 earthquake rupture stopped at the northern end of the kickapoo fault jumped onto the homestead valley fault and developed bilaterally there nnw to continue the main rupture but also sse for 4 km forming a backward branch we develop theoretical principles underlying such rupture transitions partly from elastostatic stress analysis and then simulate the landers example numerically using a two dimensional elastodynamic boundary integral equation formulation incorporating slip weakening rupture this reproduces the proposed backward branching mechanism based on realistic if simplified fault geometries prestress orientation corresponding to the region standard lab friction values for peak strength and fracture energies characteristic of the landers event we also show that the seismic s ratio controls the jumpable distance and that curving of a fault toward its compressional side like locally along the southeastern homestead valley fault induces near tip increase of compressive normal stress that slows rupture propagation

granulometry and mineralogy of some northeastern florida placers a consequence of heavy mineral concentration in nearshore bars abstract heavy mineral placer deposits of pleistocene age in northeastern florida were examined sedimentologically neither general setting nor granulometric or mineralogic results are in agreement with a concentration of the heavy minerals in a beach eolian or fluvial environment granulometric moment parameters of the ore sands seem to be distinctive they include moderate sorting high positive skewness high kurtosis and a distinctive fine tail similarities of grain size curves of the placer sands with nearshore offshore sands exist mineralogically the samples are more variable but always impoverished in epidote this scarcity of epidote is atypical for eolian sediments in the study area and the lack of garnet and the fineness of ore sands are uncommon for beach placers of northeast florida underlain by dune ridges which acted as obstacles on the shallow sea floor during the penholoway transgression 1 3 0 1 ma b p heavy minerals in the boulogne and green cove springs main ore body must have been concentrated in bars by the interplay of longshore and transverse bottom currents lighter heavy minerals were deposited in smaller nearshore bars closer to the former coast green cove springs small ore body or in dunes of barrier islands green cove springs western ore body as is true today layers of noteworthy concentrations of economic minerals in the swash zone of florida beaches were formed only rarely during storms contrary to the coasts of australia or india where higher energetic conditions prevail the proposed model of concentration of heavy minerals in certain outer nearshore bars has long been assumed but never been proven

u pb zircon strontium and oxygen isotopic and geochronological study of the southernmost sierra nevada batholith california the southernmost sierra nevada offers a view into the deep levels of the mesozoic batholithic belt which constitutes much of the range to the north and represents one of the major tectonic features of western north america the main crystalline rocks of the study area are 1 the intrusive suite of bear valley a middle cretaceous tonalite batholith complex with coeval gabbroic intrusives and 2 the gneiss complex of the tehachapi mountains which consists of early cretaceous orthogneiss and subordinate paragneiss with local domains having granulite facies metamorphic assemblages the orthogneisses are dominantly tonalitic in composition with significant layers of granodioritic to granitic and lesser dioritic to gabbroic gneiss quartz rich and psammitic metasedimentary rocks with subordinate marble constitute the main framework assemblage into which the plutonic rocks were emplaced field relations demonstrate assimilation of metasedimentary material into the orthogneiss and tonalite batholith magmas and magma mixing between mafic tonalitic and granitic materials significant domains of both homogenization and inhomogenization are recognized isotopically within the mixed rocks u pb zircon studies have resolved two major igneous suites and a third suite of postdeformational intrusives all lying between 90 and 120 ma the first suite gneiss complex of the tehachapi mountains was emplaced at 115 ma and exhibits penetrative high temperature deformation developed at or near solidus conditions a number of discordance patterns along with the physical properties of the zircon suggest minor inheritance of proterozoic zircon and limited open system behavior in response to a major 100 ma plutonic event the 100 3 ma intrusive suite of bear valley crosscuts the older suite but also exhibits significant synplutonic deformation mainly concordant zircon ages indicate the igneous crystallization age but some discordances occur due to inheritance or entrainment of proterozoic zircon the high temperature deformation fabrics in these suites and within the metasedimentary framework rocks were crosscut by the granodiorite of claraville 90 ma and pegmatite dikes 95 ma the granodiorite of claraville shows strong inheritance of proterozoic zircon and high initial 87 sr 86 sr and 18 o zircon populations from paragneiss and quartzite samples are dominated by proterozoic detrital grains strontium and oxygen isotopic data on the zircon geochronology sample suite suggest simple twocomponent mixing of mantle derived gabbroic to tonalitic magmas with partial to complete melt products from the metasedimentary framework rocks sedimentary admixtures for some granitic rocks may be as high as 45 but for the tonalitic batholithic complex are no higher than about 15 modeled values of 10 20 metasediment are typical for the orthogneisses initial 87 sr 86 sr correlates directly with 18 o and generally correlates inversely with sr content some subtle complexities in the sr and o isotopic data suggest the involvement of a third cryptic component such a component could be early phanerozoic ensimatic accretionary terranes that were structurally beneath the observed metasedimentary sequence or altered oceanic crust and sediments introduced into the mantle magma source area by subduction one of the initial aims of this study was to seek out remnants of proterozoic sialic crystalline rocks within the gneiss complex of the tehachapi mountains no such remnants were found and our studies strongly suggest that sialic components within this link of the mesozoic batholithic belt were introduced into mantle derived magraatic systems by anatexis of continent derived sedimentary rocks

seismic refraction evidence for steep faults cutting highly attenuated continental basement in the central transverse ranges california a 2 d upper crustal structural profile with seven steeply dipping faults was constructed from the los angeles region seismic experiment phase ii larse ii seismic refraction data recorded over the north central transverse ranges and adjacent mojave desert in southern california the profile extends to a depth of approximately 4 km the faults were identified from distinctive features in the seismic first arrival data while the velocity structure was determined from travel times and refined by forward modelling the resulting seismic velocity structure is correlative to the geological structure along the profile and is used to help constrain a geological cross section six of the seven faults detected from the seismic data correspond directly to geologically mapped faults in the central transverse ranges and adjacent mojave desert from south to north they are the pelona fault the san francisquito fault the clearwater fault the san andreas fault and two faults that cut the portal ridge the seventh fault is buried beneath quaternary deposits of the western mojave desert and appears to correlate with an additional fault that cuts portal ridge out of the section line the southernmost fault the pelona fault separates the younger vasquez formation in the south from the pelona schist in the north and is determined to be an intermediate 40 60 south dipping normal fault this coupled with field observations indicate that the pelona fault was instrumental in the late oligocene early miocene formation of the soledad basin and the structural ascent and exhumation of the pelona schist along the proto sierra pelona intrabasin ridge analogous neogene extensional deformation is found to have affected the western mojave desert region where faults 6 and 7 appear to have had north side down normal displacement and to have been instrumental in forming the western antelope basin a 6 0 km s 1 basal layer to our shallow seismic structure is correlated with the pelona schist south of the san andreas fault and with the tectonically related rand schist beneath the western mojave desert granitic and gneissic crystalline rocks which form regional upper plate complexes along the vincent thrust above the pelona schist and along the rand thrust above the rand schist yield consistently low seismic velocities as compared with the expected velocities for the constituent rock types these anomalous velocities are reconciled by the degraded structural and textural state of the upper plate crystalline rocks that resulted from extreme shearing brittle fracturing and related retrogressive hydration reactions starting during or shortly after the latest cretaceous early palaeocene underthrusting of the schists extension translation along the san andreas transform system and compressional faulting with the uplift of the transverse ranges further accentuated the basement deformations the integrated result is that the survival of the precambrian through mesozoic granitic crust of the region became a rootless and highly attenuated upper crustal layer

observation and intercomparison of wave motion and wave measurement using shore based coherent microwave radar and hf radar shore based coherent microwave radar and high frequency hf surface wave radar are two components of a rapidly emerging set of technologies suitable for ocean wave remote sensing to investigate their differences this paper describes and analyzes the relationship between the water particle velocity and the wave height spectrum based on linear wave theory which underpins the algorithms developed for the analysis of data collected by coherent microwave radar the backscatter mechanism which addresses the interaction of the hf radio waves with the ocean surface waves as well as the empirical method adopted in our hf radar is also presented the wave characteristics observed by the shore based coherent s band radar microwave ocean remote sensor morse are analyzed a multifrequency hf mhf radar based on a circular receiving array which is capable of sensing waves up to 100 km offshore is also introduced an intercomparison of the wave height measurements obtained from the morse mhf radar and wave buoy is made the comparison indicates that the wave heights measured by the morse and the mhf radar are consistent with the buoy derived wave heights with the root mean square differences rmsds of 0 27 and 0 37 m respectively

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

dynamic shear rupture interactions with fault bends and off axis secondary faulting 1 on the basis of elastodynamic stress fields for singular crack and nonsingular slip weakening models of propagating rupture we develop preliminary answers to such questions as follows if a rupturing fault is intersected by another providing a possible bend in the failure path when will stressing be consistent with rupture along the bend what secondary fault locations and orientations in a damaged region bordering a major fault will be stressed to failure by the main rupture stresses that could initiate rupture on a bend are shown to increase dramatically with crack speed especially near the limiting speed rayleigh for mode ii shear for mode iii whether a bend path once begun can be continued to larger scales depends on principal stress directions and ratios in the prestress field conditions should often be met in mode ii for which bend paths encouraged by stressing very near the rupture tip are discouraged by the larger scale stressing a basis for intermittent rupture propagation and spontaneous arrest secondary failure in the damage zone likewise increases markedly as the limiting speed is approached such may make the fracture energy much greater than for slip on a single surface the extent of secondary faulting is strongly affected by prestress directions and the ratio of residual to peak strength for mode ii prestress controls whether activation occurs primarily on the extensional side which we show to be the typical case or on the compressional side too natural examples are consistent with the concepts developed

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

crustal structure near palmdale california from borehole determined ray parameters abstract seismic refraction profiles across and along the san andreas fault zone near palmadale california were used to establish propagation paths for several phases whose travel times are being monitored for earthquake precursors the profiles were generated using an airgun submerged in bouquet reservoir together with surface and borehole geophone receivers source signal stacking coupled with the noise reduction provided by the downhole receivers provided data of sufficient quality to measure the ray parameters of the phases using the ray parameters and surface travel time curves velocity structures parallel and transverse to the fault zone have been constructed two of the observed phases are confined to the upper portions of the crustal structure which was found to differ across the fault a third phase is consistent with a reflection from a depth of approximately 10 km two later arrivals are suggestive of reflections from depths of 21 and 27 km

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

a hybrid beam forming and direction finding method for wind direction sensing based on hf radar recent studies indicate that the poor antenna sidelobe level of phased array high frequency hf radars degrades the performance of bragg ratio estimation for wind direction measurements to explore this issue this paper improves the previous model of wind direction estimation for phased array hf radars and the effect of unsatisfactory array patterns on bragg ratio estimation is theoretically analyzed moreover a hybrid beam forming and direction finding method in which wind direction is measured by reducing the influence of unsatisfactory array patterns on bragg ratio estimation is proposed for multifrequency hf radars installed along the coast of zhejiang province in china the procedure for implementing this scheme is also presented in detail wind directions derived from 8 05 10 7 16 8 and 19 2 mhz radar data are compared with measurements collected with anemometers at three sampling locations to verify the proposed method and the measurements with root mean square errors from 19 5 to 26 6 show that this strategy is effective for wind direction measurements we recommend adopting the proposed method or using similar approaches to estimate wind direction based on hf radars especially in situations where the array pattern is not sufficiently narrow

magnitude calibration of north indian earthquakes this article is concerned primarily with the evaluation of the size and location of northern indian and southern tibetan earthquakes during the last 200 yr it draws attention to the problems of assessing intensity of early and more recent earthquakes in a built environment which is different from that for which the intensity scale has been constructed and to the way in which isoseismals are drawn through a re evaluation of intensities and a reassessment of isoseismals a formula for the estimation of surface wave magnitude using isoseismal radii is derived this formula is used to estimate the surface wave magnitudes of 16 earthquakes that occurred in the region between 1803 and 1900 this study shows that it is possible to calculate accurate surface wave magnitudes for earthquakes that occurred before the advent of the scale and that there is no need to resort to empirical formulae for the assessment of the size and seismic moment release of pre 20th century earthquakes also derived are formulae for the conversion of ms to m0 in total locations surface wave magnitudes and m0 estimates are presented for 43 important events that occurred in the region between 1803 and 1974 eight of which were in the lower crust or were subcrustal we find that the m0 ms scaling for india yields smaller ms than the global relation and that the methodology used can help to evaluate more realistic slip rates as well as to address other issues related to earthquake hazard in northern india

a three dimensional magnetotelluric investigation of the california basin and range band limited magnetotelluric measurements were collected at several sites across a wide area in the california basin and range and northern mojave desert from early 1988 until march 1989 due to the large spacing between sites and the limited frequency range of the data there are limits to what the data can resolve however a three dimensional 3 d magnetotelluric modeling study and sensitivity analysis of a subset of the data support the following conclusions 1 electrical currents from the pacific ocean are channelled across the western mojave desert and into the southern basin and range 2 the 3 d geometry of the basins significantly influences the fit to the data mode aligned along the strike of the basins transverse electric mode 3 the lower crust in the california basin and range is more conductive than the lower crust under the mojave desert and pacific ocean the resistivity values we modeled for the lower crust in the california basin and range though inconsistent with mineral semiconduction can be explained by electrical conduction through small amounts of saline fluids

a new light on arresting mechanism of dynamic earthquake faulting classic analyses have shown that dynamic growth of a shear crack cannot be arrested in a uniformly stressed elastic medium with homogeneously distributed fracture strengths this leads to a general supposition that earthquake rupture growth is arrested by inhomogeneities in the distributions of strengths or stresses we propose a novel idea for arresting mechanism of dynamic crack growth in the simulation with no constraints on the crack geometry our analysis shows that the arresting occurs spontaneously soon after crack bending even in the homogeneous medium and that inhomogeneities are indispensable not for stopping crack growth but for its promotion