partitioning of convergence in northwest sub himalaya estimation of late quaternary uplift and convergence rates across the kangra reentrant north india the kangra reentrant constitutes a 80 km wide zone of fold thrust belt made of cenozoic strata of the foreland basin in nw sub himalaya earlier workers estimated the total long term shortening rate of 14 2 mm year by balanced cross section between the main boundary thrust and the himalayan frontal thrust geologically estimated rate is nearly consistent with the gps derived slip rate of 14 1 mm year there are active faults developed within 4 8 km depth of the sub himalayan fold thrust belt of the reentrant dating the strath surfaces of the abandoned fluvial terraces and fans above the thrust faults the uplift bedrock incision rates are computed the dips of thrust faults are measured in field and from available seismic depth profiles from the acquired data late quaternary shortening rates on the jawalamukhi thrust jt the soan thrust st and the himalayan frontal thrust hft are estimated the shortening rates on the jt are 3 5 4 2 mm year over a period 32 30 ka the st yields a shortening rate of 3 0 mm year for 29 ka the corresponding shortening and slip rates estimated on the hft are 6 0 and 6 9 mm year during a period 42 ka on the back thrust of janauri anticline the shortening and slip rates are 2 0 and 2 2 mm year respectively for the same period the results constrained the shortening to be distributed largely across a 50 km wide zone between the jt and the hft the emergence of surface rupture of a great and mega earthquakes recorded on the reactivated hft implies 100 km width of the rupture the ruptures of large earthquakes like the 1905 kangra and 2005 kashmir remained restricted to the hinterland the present study indicates that the high magnitude earthquakes can occur between the locking line and the active thrusts

new relationships between vs thickness of sediments and resonance frequency calculated by the h v ratio of seismic noise for the cologne area germany noise measurements were carried out in the cologne area germany and the resonance frequency of each site was estimated from the main peak in the spectral ratio between the horizontal and vertical component for 32 of these sites the thickness of the sedimentary cover was known from boreholes and a clear correlation between resonance frequency and sediment thickness was observed a formula that correlates cover thickness with frequency of the main peak in the horizontal to vertical spectral ratio was derived in addition a best fitting shear wave velocity distribution with depth vs z as well as a relationship between average shear wave velocity vs and thickness of the sedimentary cover was calculated by using all of the noise measurements and applying the derived relationships we obtained a subsoil classification for the cologne area

great earthquake surface ruptures along backthrust of the janauri anticline nw himalaya abstract results of a paleoseismic trenching investigation on a backthrust in the northern margin of janauri hill at mehandpur 31 18 11 37 n 76 18 31 47 e sub himalayan range of the himachal himalaya are presented the active backthrust revealed the last event took place after 0 8 0 03 ka ago i e post ce 1200 the age of the last earthquake with a minimum fault slip 1 m along f1 fault and presence of single colluvium on the back thrust nearly matches with an earthquake event previously documented on the bhatpur forethrust of the himalayan frontal thrust system uplifted and truncated fluvial terraces due to displacement on the backthrust are preserved along several north flowing river valley sections in the northern limb of janauri anticline the long term vertical uplift rate calculated through dividing difference between current elevation and elevation of current river grade is 1 08 0 08 mm yr field evidence shows fore and backthrusts are active and they form simultaneously but displacements are episodic suggesting the backthrust develops either due to locking of forethrust or to accommodate a large amount of fault slip due to magnitude of earthquake event along the forethrust further the backthrust may be used as an indirect method of inferring the age of the last event that took place along the forethrust

velocity contrast across the 1944 rupture zone of the north anatolian fault east of ismetpasa from analysis of teleseismic arrivals 1 we use differences between arrival times of teleseismic events at sets of stations crossing the north anatolian fault east of ismetpasa where shallow creep has been observed to detect and quantify a contrast of seismic velocities across the fault waveform cross correlations are utilized to calculate phase delays of p waves with respect to expected teleseismic arrivals with incident angles corresponding to the generating events compiled delay times associated with 121 teleseismic events indicate about 4 3 average p wave velocity contrast across the fault over the top 36 km with faster velocity on the north side the estimated contrast is about 8 3 if the velocity contrast is limited to the top 18 km the sense of velocity contrast is consistent with the overall tectonic setting and inference made for the examined fault section based on theoretical expectations for bimaterial ruptures and observed asymmetry of rock damage across the fault our data indicate lack of significant microseismicity near the fault suggesting that creep in the area is limited to the depth section above the seismogenic zone

distribution of aseismic slip rate on the hayward fault inferred from seismic and geodetic data 1 we solve for the slip rate distribution on the hayward fault by performing a least squares inversion of geodetic and seismic data sets our analysis focuses on the northern 60 km of the fault interferometric synthetic aperture radar insar data from 13 independent ers interferograms are stacked to obtain range change rates from 1992 to 2000 horizontal surface displacement rates at 141 bench marks are measured using gps from 1994 to 2003 surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion the fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface south of the city of hayward a steeply east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth the inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of 5 mm yr to a depth of 4 6 km the interferometric synthetic aperture radar insar data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath point pinole although the insar data might be complicated by a small dip slip component at this location a low slip rate patch of 1 mm yr is inferred beneath san leandro consistent with the source location of the 1868 earthquake we calculate that the entire fault is accumulating a slip rate deficit equivalent to a mw 6 77 0 05 per century however this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip

on the horizontal to vertical spectral ratio in sedimentary basins the horizontal to vertical spectral ratio hvsr has been used by many researchers to characterize local conditions in terms of the dynamic response of the soil one of its variants is that proposed by nakamura 1989 in which records of microtremors are used usually the analysis is aimed to obtain the predominant period of the site under study in this work we explore what can be achieved by using this method we study the response of different configurations under incident waves coming from an explosive source using the indirect boundary element method ibem we investigate two cases low and high velocity contrast holding constant the physical properties inside the basin and changing only the properties of the bedrock then we compute the seismic response using the horizontal sediment to bedrock spectral ratio sbsr at various locations on the free surface of the basins and compare it with the one calculated by the hvsr at the same locations the comparison shows that in general the predominant period computed with the hvsr is not the same as that obtained by the sbsr in all the locations on the other hand the hvsr approximation can reasonably well predict the fundamental local frequencies when the impedance contrast between the basin and the bedrock is low however hvsr cannot be used in sedimentary basins having a high impedance contrast with respect to the bedrock below

new empirical relationship between resonance frequency and thickness of sediment using ambient noise measurements and joint fit inversion of the rayleigh wave dispersion curve for kangra valley nw himalaya india

vs30 estimates using constrained h v measurements abstract most seismic codes adopt the average shear wave velocity as a key parameter in the first 30 m of subsoil v s 30 estimates of v s 30 are therefore required for both large and small scale seismic microzonation we propose a technique to measure the v s 30 based on the horizontal to vertical spectral ratio h v of microtremor recorded at a single station the h v is fitted with a synthetic curve using the independently known thickness of a superficial layer of the subsoil as a constraint the proposed procedure consists of three steps 1 identify the depth of a shallow stratigraphic horizon from independent geotechnical data 2 identify its corresponding h v marker and 3 use it as a constraint to fit the experimental h v curve with the theoretical one the synthetic h v curve is calculated by assuming a stratified one dimensional 1d soil model and a tremor wave field from distant random sources that are composed of rayleigh and love waves this technique has been validated on different geological settings following a triple check procedure 1 the theoretical rayleigh wave phase velocity dispersion curves calculated for the model derived from the h v fit were compared to the experimental curves measured with the 2d extended spatial autocorrelation esac method and the 1d refraction microtremor remi array surveys 2 the v s profiles and 3 the v s 30 estimates obtained by the proposed technique were compared to those obtained by using the latter array techniques finally the inferred stratigraphy was compared to the geological model the proposed technique is not meant to provide accurate v s profiles but has the potential to provide v s 30 estimates that are coherent with those measured through esac and remi and to satisfy law requirements furthermore the h v is found to be capable in detecting deviations from 1d subsoil geometry over the length of a few meters the correctness of which was confirmed by direct drilling

the use of hvsr measurements for investigating buried tectonic structures the mirandola anticline northern italy as a case study the mirandola anticline represents a buried fault propagation fold which has been growing during quaternary due to the seismogenic activity of a blind segment belonging to the broader ferrara arc the last reactivation occurred during the may 2012 emilia sequence in correspondence with this structure the thickness of the marine and continental deposits of the po plain foredeep is particularly reduced in order to better define the shallow geometry of this tectonic structure and hence its recent activity we investigated in a depth range which is intermediate between the surficial morphological observations and seismic profiles information in particular we carried out numerous passive seismic measurements single station microtremor for obtaining the horizontal to vertical spectral ratio the results of a combined analysis of the peak frequency and its amplitude nicely fit the available geological information suggesting that this low cost geophysical technique could be successfully applied in other sectors of wide morphologically flat alluvial plains to investigate blind and completely buried potential seismogenic structures

fault plane solutions for the 1984 morgan hill california earthquake sequence evidence for the state of stress on the calaveras fault fault plane solutions for 946 aftershocks of the april 24 1984 morgan hill california m6 2 earthquake reveal a pattern of complex faulting within a 10 km wide zone surrounding the calaveras fault the fault plane solutions fall into three groups strike slip mechanisms located along the calaveras fault with north northwest striking dextral slip planes nearly parallel to the fault strike slip mechanisms located northeast of the calaveras fault with north striking dextral slip planes and reverse mechanisms located southwest of the calaveras fault with northeast or southwest dipping slip planes the average azimuth of p axes for aftershocks located on the calaveras fault is n10 1 e in contrast the average azimuths of p axes for aftershocks northeast and southwest of the calaveras fault are n49 7 e and n37 3 e respectively by assuming that the earthquakes occur on preexisting cracks in response to a uniformly oriented regional stress field we are able to infer from the observed average slip directions an orientation for 1 the axis of maximum horizontal compression 63 80 from the local strike of the calaveras fault such a high angle orientation of 1 is incompatible with the classical andersonian model of strike slip faulting but is consistent with an alternate model in which a weak calaveras fault is driven by plate motion slightly convergent with respect to the san andreas fault system in central california if this inferred high angle uniform stress field is combined with the changes in the static stress field calculated with elastic dislocation theory for the 1984 morgan hill main shock the resulting stress field predicts most of the observed spatial pattern of the aftershocks and their fault plane solutions the orientations of the inferred aftershock slip planes are generally consstent with the fracture orientations predicted by the coulomb failure criterion areas with predicted increases in the coulomb failure function of only a few tenths of a megapascal correspond to areas of intense aftershock activity the invariance of focal mechanisms in the vicinity of the south end of the main shock rupture before and after the main shock suggests that the magnitude of compressive stress in this area is at least 10 mpa in addition to explaining a preponderance of the seismic observations of the aftershock sequence the presence of a predominantly fault normal compressive regional stress field accounts for the contemporary development of folds reverse faults and topographic relief observed throughout the central california coast ranges

dynamic rupture on a material interface with spontaneous generation of plastic strain in the bulk abstract we discuss 2d simulations of in plane ruptures on a fault between different solids in a model that includes dynamic generation of plastic strain off the fault the fault is governed by a regularized friction with a gradual response to abrupt changes of normal stress while plastic strain in the bulk is governed by a coulomb yielding criterion the occurrence of off fault damage stabilizes the slip velocity on the fault stable self sustaining ruptures propagate on the material interface as narrow unidirectional pulses in the direction of slip on the more compliant side of the fault plastic strain is generated only on the stiffer side of the fault the tensional quadrant in the direction of rupture propagation in a strip of approximately constant width that is correlated with the slip velocity on the fault simulations for various values of confining normal stress material contrast and cohesion in the bulk suggest that significant generation of off fault damage is limited to conditions that correspond to the top few kilometers of the crust the results are compatible with field observations of shallow asymmetric damage patterns in the structure of several large faults

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

site characterization through combined analysis of seismic and electrical resistivity data at a site of dhanbad jharkhand india we present the seismic site characterization study using joint modelling of horizontal to vertical spectral ratio hvsr and rayleigh wave phase velocity dispersion curves obtained from multi channel simulation with one receiver msor in a part of dhanbad jharkhand india the joint analysis of these two different but complementary datasets puts stronger constraints on the model parameter search space than one dataset and may help us in finding more unique shear wave velocity model the microtremor data from 12 observation points were utilized to iteratively search 1d shear wave velocity profiles in a predefined model search space these 1d shear wave velocity models were interpolated to generate a 2d shear wave velocity profile of the site using the cubic spline method our results show that the high peak amplitude value of hvsr is associated with low peak period values of hvsr at a distance of 60 m from the southern end of the profile which may indicate the presence of the basin edge effect we identified four layers based on significant changes in the shear wave velocities to a depth of 60 m the major impedance contrasts are located at average depths of 13 m 40 m and 55 m respectively these layers from the surface may indicate the presence of soil highly weathered rock mass moderately weathered rock and bedrock respectively the depth of engineering solid bedrock vs 600 m s is found at the depth of 55 m in the south which gradually decreases to a depth of 40 m in the northern end of the profile the shear wave velocity vs 30 for this area varies between 293 and 357 m s which can be classified as d type site for validation and comparison of our results the electrical resistivity tomography ert data were also recorded along the same traverse using wenner and schlumberger configurations our results show a significant amount of correlation between the 2d shear wave velocity and resistivity profiles obtained from joint analysis of tremor and ert data

the san andreas fault revisited through seismic noise and surface wave tomography 1 we present here surface wave tomography results for the san andreas fault in the parkfield area california usa that were extracted from microseismic noise in the 0 15 hz to 0 35 hz frequency band using passive seismic correlation techniques using directive noise incoming from the pacific ocean passive seismic noise tomography was performed using three component sensors from a dense seismic network a rotation algorithm was applied to the nine component noise correlation tensor that optimally forced each station pair to re align in the noise direction a necessary condition to extract unbiased travel times from passive seismic processing after the rotation was performed an optimal surface wave tensor is obtained from which love waves were extracted for tomography inversion dispersion curves were then inverted to obtain a three dimensional shear velocity map showing vertical geological structures and a 1 3 km wide low seismic velocity dip which are in agreement with previous tomography studies in the same area

evidence for a bimaterial interface along the mudurnu segment of the north anatolian fault zone from polarization analysis of p waves abstract we present results on imaging contrast of seismic velocities across the mudurnu segment of the north anatolian fault zone nafz in northwestern turkey with polarization analysis of early p waveforms generated by near fault seismicity and recorded by near fault stations the analysis uses changes in motion polarity from fault normal to source receiver directions to identify early arriving fault zone head waves on the slow side of the fault and measure the arrival times of the head and direct p waves the moveout between the head and direct waves with increasing source receiver distance along the fault provides an estimate of the average contrast of seismic velocities across the fault the results indicate that the average contrast of p wave velocities across the mudurnu segment of the nafz is at least 6 with the south block being the faster side the findings provide a basis for deriving improved event locations focal mechanisms and estimated shaking hazard associated with earthquakes on the fault the analysis technique can be used in other fault zones monitored with sparse seismic instrumentation

pulverized fault rocks and damage asymmetry along the arima takatsuki tectonic line japan abstract we present field and laboratory data on pulverized rocks at the hakusui kyo outcrop of the arima takatsuki tectonic line attl which is a dextral strike slip fault with 17 km displacement juxtaposing granite to the south against rhyolite to the north the majority of slip at the surface is localized to a clay rich gouge fault core 8 10 cm in width surrounded by a coarsening outwards fault breccias up to 3 m wide fault damage is highly asymmetric with respect to the slipping zone the granite south of the fault has a pulverized damage zone up to 200 m wide while the rhyolite to the north has only about 3 m wide non pulverized fault breccia the degree of pulverization in the granite decreases approximately logarithmically with normal distance from the slip zone the highly fractured pulverized rocks exhibit several distinct textural characteristics in thin section grains appear to be highly comminuted but the original grain shapes and margins are recognizable microfractures tend to be tensile in no preferred orientation grain fragments display little to no rotation and lack evidence of in situ shear consequently at macroscale the rocks appear to preserve original granitic textures despite being highly fractured and friable the observed pulverization and rock damage asymmetry are most consistent with generation mechanism involving ruptures on a bimaterial interface with statistically preferred propagation direction leading to damage primarily on the side with higher seismic velocity at depth this is supported by laboratory measurements of p wave ultrasonic velocities on intact samples which indicate that the granites have consistently higher velocity than the rhyolite with increasing confining pressure

holocene internal shortening within the northwest sub himalaya out of sequence faulting of the jwalamukhi thrust india the southernmost thrust of the himalayan orogenic wedge that separates the foreland from the orogen the main frontal thrust mft is thought to accommodate most of the ongoing crustal shortening in the sub himalaya steepened longitudinal river profile segments terrace offsets and back tilted fluvial terraces within the kangra re entrant of the nw sub himalaya suggest holocene activity of the jwalamukhi thrust jmt and other thrust faults that may be associated with strain partitioning along the toe of the himalayan wedge to assess the shortening accommodated by the jmt we combine morphometric terrain analyses with in situ 10be based surface exposure dating of the deformed terraces incision into upper pleistocene sediments within the kangra basin created two late pleistocene terrace levels t1 and t2 subsequent early holocene aggradation shortly before 10 ka was followed by episodic re incision which created four cut and fill terrace levels the oldest of which t3 was formed at 10 1 0 9 ka a vertical offset of 44 5 m of terrace t3 across the jmt indicates a shortening rate of 5 6 0 8 to 7 5 1 1 mm a 1 over the last 10 ka this result suggests that thrusting along the jmt accommodates 40 60 of the total sub himalayan shortening in the kangra re entrant over the holocene we speculate that this out of sequence shortening may have been triggered or at least enhanced by late pleistocene and holocene erosion of sediments from the kangra basin

evolving geometrical and material properties of fault zones in a damage rheology model we discuss numerical simulations of evolving fault zone structures in a 3 d lithospheric model with a seismogenic crust governed by a damage rheology that accounts for large strain associated with permanent brittle deformation results for the initial propagation of an existing narrow damage zone subjected to oblique loading exhibit strong asymmetry of the evolving damage with respect to the initial fault orientation and predict out of plane directions of the propagating damage zones the orientations of the simulated damage zones agree with analytical expectations based on fracture mechanics for the directions of wing cracks generated at the tips of a crack under mixed mode loading lithosphere scale numerical simulations for the long term evolution of a large strike slip fault zone produce initially a system of stepping en echelon segments associated with the asymmetric generation of new damage zones the simulated fault zone segments evolve with continuing deformation to a throughgoing localized structure large scale perturbation in the geometry of the moho interface together with the regional heat regime can reduce considerably the degree of localization of the fault zone structure and the associated deformation fields

nehrp soil classification and estimation of 1 d site effect of dehradun fan deposits using shear wave velocity abstract shear wave velocity of the near surface soil at nearly 50 sites in the sub himalayan mountain exit covering doon fan deposits was determined using multi channel analysis of surface waves masw a seismic reflection technique based on the average shear wave velocity of the upper 30 m soil column sites in the dehradun fan are predominantly classified as class d 180 360 m s similarly sites located on the northwestern eastern and southeastern sides of the fan deposit have shear wave velocities in the upper 30 m soil greater than 360 m s thereby classifying them as class c 360 760 m s in accordance with nehrp provisions some of the sites towards the southwestern side of the fan deposits had average shear wave velocities less than 180 m s and could be classified as soil class e one dimensional site effects including amplification and dynamic period were calculated for the majority of the sites however some of the representative suite of sites across the north south profile of dehradun fan has been discussed here although the attenuation is greater on the southwestern side of the dehradun fan deposits i e thicker low velocity sediments and the sites had been classified as class d and e but the site amplification tends to be greater in the northern and northwestern part of the city due to large impedance contrast with in the near surface soils

love wave group velocity maps of turkey and surrounding regions summary we present the analysis of a love wave dispersion study performed across turkey and the surroundings group velocity dispersion curves were obtained from the local and regional earthquakes recorded at both permanent and temporary stations operated in the region lovewave group velocity maps in the period range of 10 50 s were computed using a tomographic inversion method the study shows the existence of significantly different crustal types in the area the group velocity anomalies are associated with the major geological structures in the region low group velocities at shorter periods 10 20 s are observed in the local sedimentary basins the eastern mediterranean and the black sea the eastern anatolia region is also characterized by low group velocities while pontides and bitlis p ot urge massif display higher group velocities the central anatolia exhibits uniform velocity distribution indicating more homogenous crust the isparta angle is marked by a wedge shaped low group velocity anomaly the low velocities observed in the isparta angle are related to crustal thickening and subduction related complex high velocities observed on the maps are associated with metamorphics magmatic arcs along the orogenic belts of pontides p

rupture directivity of microearthquake sequences near parkfield california 1 the direction of propagation is an important factor that affects the pattern of ground motion generated by an earthquake characterizing factors favoring a potential rupture propagation direction is thus an important task here we analyze the earthquake directivity of repeating earthquake sequences located on the san andreas fault near parkfield california all earthquakes of a sequence have very similar waveforms and have overlapping surface ruptures we show that subtle variations of the transfer function between earthquakes of a common sequence can be interpreted as a change of apparent rupture duration relative apparent rupture durations are computed for all pairs of events at all available stations and for each sequence we invert these measurements to obtain an estimation of the apparent rupture duration for each individual event of the sequence relative to a reference event variation of apparent rupture duration with azimuth attests for the rupture directivity we show that the majority of analyzed microearthquakes presents a rupture in the south east direction we also show that on a given repeating sequence most earthquakes tend to show the same rupture direction

sedimentary basins formed and carried piggyback on active thrust sheets small sedimentary basins that formed on the apennine southern margin of the po basin complex northern italy have been studied using borehole and seismic reflection information and their evolution can be dated using the largely marine biostratigraphy of the miocene to quaternary sediments these studies show that the basins formed and were filled while being carried on moving thrust sheets and they are therefore named piggyback basins each of these basins corresponds to the active phase of a different thrust front ramp on the pyrenean northern margin of the ebro basin complex northern spain similar piggyback basins formed between eocene and mid miocene time they have since been uplifted and eroded and may therefore be studied in outcrop in northern spain much of the basin fill sediment was deposited in nonmarine environments

joint inversion of fault zone head waves and direct p arrivals for crustal structure near major faults a newly recognized class of seismic phases namely fault zone head waves arising from refraction at a transfault velocity contrast provides additional constraints to direct p waves in inversions of near fault arrival time data for earthquake location and velocity structure incorporation of fault zone head waves in the inversion process increases the available data and broadens the spatial coverage of ray paths between sources and receivers equally important the explicit recognition of fault zone head waves eliminates a source of error resulting from misidentifying head wave first arrivals as direct p waves a simple algorithm for the joint inversion of fault zone head waves and direct p phases is illustrated with observed and synthetic data application to a small data set recorded by the borehole seismic network at parkfield california provides separate seismic velocity depth profiles for the crustal blocks on the two sides of the san andreas fault for depths less than 3 km the obtained velocity contrast is 10 20 for greater depths it decreases to 3 7 numerical tests with synthetic data show that for sources with known locations and for well located local earthquakes randomized mislocation errors of up to 600 m proper use of fault zone head waves can significantly improve the accuracy of the fitted velocity structure the results of this work motivate the inclusion of fault zone head waves in state of the art joint structure hypocenter inversions using high quality near fault data

basement topography of the kathmandu basin using microtremor observation abstract kathmandu valley an intermontane basin of the himalaya has experienced many destructive earthquakes in the past the observations of the damage pattern during the 1934 earthquake m w 8 1 in particular suggest that the spectral ground amplification due to fluvio lacustrine sediments plays a major role in intensifying the ground motion in the basin it is therefore imperative to conduct a detailed study about the floor variation of sediments in the basin in this paper a preliminary attempt was made to estimate the thickness of soft sediment in the kathmandu basin using microtremor observations the measurements of microtremors were carried out at 172 sites spaced at a grid interval of 1 km the results showed that the predominant frequency varies from 0 488 hz to 8 9 hz a non linear regression relationship between resonance frequency and sediment depth was proposed for the kathmandu basin the thickness of lacustrine sediments at various points in the basin was estimated using the proposed equation and then the estimated thickness was used to plot a digital elevation model of the basement topography and cross profiles of the sediment distribution in the basin the results were validated by correlating the estimated sediment thickness with geology and geomorphology of the study area

investigation of 3 d basin structures in the izmit bay area turkey by single station microtremor and gravimetric methods summary we investigate 3 d basin structures and site resonance frequencies in the izmit bay area of turkey by new geophysical surveys based on 239 single station microtremor and 405 point gravity measurements a fundamental resonance frequency map of the izmit bay was produced from the main peak in the horizontal to vertical component spectral ratio hvsr of microtremors the hvsr analysis of the microtremor data reveals single double broad peaked or no peak type hvsr curves varying in accordance with the surface geology and spatial extent of the three basins present in the izmit bay area in the deepest sections of the izmit golcuk and derince basins of the izmit bay the fundamental resonance frequencies are dominantly 0 24 0 30 hz these resonance frequencies should be taken into consideration along with higher mode frequencies to construct earthquake resistant structures in the izmit bay area the 3 d gravimetric bedrock depth map of the izmit basin shows that the basin has an asymmetric shape with its deepest section coinciding with the surface trace of the north anatolian fault the northern shoulder of the basin has a gentle dip on the kocaeli peneplain side and the southern shoulder is much steeper and it is bounded by the samanli mountains we derive a power law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the gravity and shear wave velocity data in the izmit bay we use this relationship to estimate bedrock depths beneath golcuk and derince basins our estimation of maximum basin depths is 1400 m for the izmit and is 800 m for the golcuk and derince basins finally we have analysed a converted sp phase from a local earthquake recording made at site cmp to calculate and verify the sediment thickness estimations obtained from our gravimetric and microtremor analyses this calculation shows close agreement with that of the gravimetric and microtremor results our results show that the basins in the izmit bay area have a very thick sedimentary cover with very low shear velocities underlined by hard bedrock forming a sharp impedance contrast we anticipate that these results will be a key contribution to the quantitative assessment of seismic hazard for the izmit bay area before the occurrence of strong earthquakes in the marmara region

spatiotemporal variations of crustal anisotropy from similar events in aftershocks of the 1999 m7 4 izmit and m7 1 duzce turkey earthquake sequences summary we analyse spatiotemporal variations of crustal anisotropy along the karadere duzce branch of the north anatolian fault from similar earthquakes in the aftershock regions of the 1999 mw7 4izmit and mw7 1 duzce earthquakes the similar earthquake clusters are identified by performing cross correlation on waveforms generated by 18 000 earthquakes depending on the applied similarity criterion about 4 60 per cent of the events belong to similar event clusters splitting parameters averaged within each cluster show significant variations for slightly different ray paths indicating strong spatial variations of crustal anisotropy in this area we also find clear changes in the spatiotemporal seismicity patterns following the duzce main shock large apparent co seismic changes up to 30 per cent of shear wave splitting delay times are observed across the time of the duzce main shock at stations near the epicentral region however the changes can be mostly explained by the spatial variations of ray paths due to the changing seismicity rather than changes in the properties of the anisotropic medium splitting parameters measured within similar earthquake clusters indicate at most 2 per cent changes in delay times associated with the occurrence of the duzce main shock the results do not show systematic precursory changes before the duzce main shock

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

enhanced stress and changes to regional seismicity due to the 2015 mw 7 8 gorkha nepal earthquake on the neighbouring segments of the main himalayan thrust abstract in this study we evaluate stress evolution and change in seismic hazard after the 2015 gorkha earthquake sequence we take a methodology usually used in areas with well established seismic monitoring and apply it to an area with a sparse dataset and a limited time observation window our goal is to validate this approach as a rapid response tool for seismic forecasting after large earthquakes we propose a long term seismic forecasting model of the main himalayan thrust using the historical earthquake catalogue and regional paleo seismicity through application of the rate and state friction model we evaluate short term rate evolution after the gorkha earthquake the long elapsed time since the last megathrust event and the mainshock coseismic stress increase on the main himalayan thrust suggest high seismic potential in the lalitpur and lamjung areas along the fault system we also calculate the stress change on optimally oriented planes in the region and model the regional seismicity rate using a smoothing kernel method and seismicity since 1921 the location of the consequent earthquakes coincides with areas of high background seismicity rate and areas where stress was enhanced by the mw 7 8 mainshock and mw 7 3 aftershock we model the change of seismic rate over time and project a fast decrease due to the short aftershock duration assumption we use

rheological constraints on quartz derived from scaling relationships and numerical models of sheared brittle ductile quartz veins central southern alps new zealand abstract the mechanical properties of quartz strongly influence the strength of continental crust but natural examples to constrain quartz rheology are rare here brittle ductile fault arrays in the southern alps new zealand provide a natural laboratory into the rheology of quartz rocks the faults formed in the hanging wall of the alpine fault during the late cenozoic at 21 km depth they are near vertical extend over tens of metres strike sub parallel to the alpine fault and displace quartzofeldspathic metagreywacke through predominantly brittle processes they also displace centimetre thick quartz veins that are discordant to the dominant schist foliation with variably ductile to brittle slip we use field observed geometrical scaling relationships related to the sheared quartz veins and interactions between brittle faults and ductilely deforming quartz veins that intersect them to produce a set of viable numerical models quartz rheology is modelled by linear or power law creep and the material parameters extracted for the quartz veins together with viscous and brittle strength ratios between vein quartz and schist the results indicate that under the prevailing deformation conditions the dominant deformation mechanism in the quartz veins was dislocation creep resulting in a non linear quartz rheology

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