salinization in coastal aquifers of arid zones an example from santo domingo baja california sur mexico groundwater quality in the santo domingo irrigation district area in baja california sur mexico indicates the presence of various salinization processes 1 the geological matter of marine origin comprising the aquifer material suffers diagenetic effects due to its interaction with groundwater of low salinity 2 the effects of intensive agriculture practices produce effluents that infiltrate to the saturated zone and 3 the extraction of groundwater causes modifications in the natural flow system induces lateral flow of seawater from the coast line however groundwater management has been carried out with the belief that the latter is the main source of salinization this has resulted in a policy of installing wells increasingly far from the coast which is not solving the problem irrigation return and seawater that remains in the geological units have been identified as major sources of salinization controls should be imposed when installing wells in contact with clayey units that form the base of the aquifer extracted groundwater consists of a mixture of 1 groundwater of relatively low salinity that circulates in the aquifer and 2 an extreme member with salinity different to seawater contained mainly in formations that have low permeability which limits the aquifer underneath the geochemistry of carbonates and cation exchange reactions both direct and reverse control the concentration of ca mg na and hco3 as well as ph values the concentrations of dissolved trace elements f li ba sr suggest that the extreme saline member is different from the average seawater composition a distinction between the salinization caused by farming practices and that blamed on seawater is defined by the use of no3

the morphology of thrust faulting in the 21 september 1999 chichi taiwan earthquake abstract the 80 km long surface rupture of the chelungpu fault in the 21 september 1999 chichi taiwan mw 7 6 earthquake resulted in a surface scarp with vertical throws of 2 9 m and horizontal heaves of 4 8 m few major thrust faults have broken the surface in the past century and the chelungpu surface rupture is of interest in that it provides a morphological template for the identification of paleo surface thrusts in similar neotectonic environments such as the himalaya the toe of the thrust is found emplaced gently over underlying hanging wall materials partly by prograde hanging wall rotation and partly by simple shear leaving few overt clues as to the total amount or sense of slip despite the large surface slip near the toe of the chelungpu thrust its emplacement appears to have been relatively slow msk the medvedev sponheuer karnik 1981 revision of the seismic intensity scale msk81 supersedes the mercalli intensity scale for the description of acceleration induced damage to modern buildings intensity viii accelerations were imposed on buildings on the hanging wall and intensity vii on the footwall decaying in both directions by perhaps one intensity unit a few hundred meters from the rupture the somewhat moderate amplitude of these accelerations for a rupture with several meters of slip is attributed to non linear dissipative deformation near the toe of the rupture the partitioning of thrusting into basal slip and hillside steepening in some locations on the chelungpu fault suggests that the estimation of paleoseismic slip from the offset of piercing points crossing historic thrust faults elsewhere may result in underestimates of fault slip

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

eddy forcing of the mean flow in the southern ocean we examine the force or acceleration exerted by eddies on the mean flow of the southern ocean using mapped sea surface height anomalies derived from satellite altimeter measurements we compare this with the position of jets in the mean flow indicated by regions of increased gradient in the mean sea surface temperature the eddy force itself is not of primary importance rather the curl of that force affects the mean flow so the irrotational force due to the gradient of eddy kinetic energy can be ignored leaving a remainder that can be interpreted in terms of the eddy vorticity flux unlike previous modeling and altimetric studies we find that the eddies act to decelerate some of the strongest jets and act as vorticity sources for others the strongest jets are clearly not accelerated by eddies a problem of interpretation does remain however since it is not clear how sea surface temperatures are related to the mean flow this ambiguity can only be completely resolved by measurement of the mean flow requiring a geoid that is accurate at length scales of order 100 km

structure of the 1999 chi chi earthquake rupture and interaction of thrust faults in the active fold belt of western taiwan abstract we summarize the structural characteristics of the surface ruptures of the 1999 mw 7 6 chi chi earthquake in western taiwan and discuss the geological interaction of the chelungpu fault with adjacent faults based on geological investigations seismological analyses and gps measurements of surface co seismic displacements we describe the regional 3 d fault plane and slip distribution of the chi chi earthquake and compare these to the geological features of the chelungpu fault we find that one key feature of the chelungpu fault is the stratigraphy controlled slip surface at the level of the uppermost few kilometers the chelungpu fault slip plane generally follows the bedding plane of the pliocene chinshui shale the second key feature of the chelungpu fault is the difference in structurally geometric configuration between its northern and southern segments the northern fengyuan segment shows a bedding parallel thrust fault within east dipping strata in both footwall and hanging wall in contrast the southern tsaotun segment exhibits east dipping strata are overthrust onto flat lying recent alluvial deposits these two features not only explain a hinterland imbricate thrusting on the hanging wall of the fengyuan segment but also explain the change in strike of the chi chi surface ruptures at the northern end the southern end of the 1999 chi chi rupture is interpreted to be linked to a series of nw trending strike slip faults in particular we propose that the luliao strike slip fault served as the lateral ramp of the chelungpu fault and the gukeng strike slip fault acted as a barrier to end the southern propagation of the 1999 rupture geomorphic features and paleoseismological data indicate that the range front chelungpu fault has generated large earthquakes during the last several thousand years alternatively in the miaoli area to the north and the chiayi area to south historical earthquakes as well as active geomorphic features are not restricted on the range front thrust faults instead more complicated structures including tightly spaced folds duplex structures and strike slip faults are involved in seismogenic processes a more detailed investigation of regional structural characteristics is needed for mitigation against the seismic hazards in the 300 km long active fold belt in western taiwan where several damaging large earthquakes have been documented during the last century

time intervals to assess active and capable faults for engineering practices in italy abstract the time span necessary to define a fault as active and capable can mainly be derived from the framework of the regulations and the literature produced since the 1970s on risk estimation in engineering planning of strategic buildings within this framework two different lines of thought can be determined which have mainly developed in the usa on the one side there is a tendency to produce narrow chronological definitions this is particularly evident in the regulatory acts for the planning of nuclear reactors the much more effective second line of thought anchors the chronological definitions of the terms active and therefore capable to the concept of seismotectonic domain as the domains are different in different regions of the world the chronological definition cannot be univocal i e different criteria are needed to define fault activity which will depend on the characteristics of the local tectonic domain and of the related recurrence times of fault activation current research on active tectonics indicates that methodological aspects can also condition the chronological choice to define fault activity indeed this practice implies the use of earth science methods the applications of which can be inherently limited for example limits and constraints might be related to the availability of datable sediments and landforms that can be used to define the recent fault kinematic history for the italian territory we consider two main tectonic domains a the compressive domain along the southern margin of the alpine chain and the northern and northeastern margins of the apennines which is characterised by the activity of blind thrusts and reverse faults and b the extensional domain of the apennines and the calabria region which is often manifest through the activity of seismogenic normal and normal oblique faults in case a the general geomorphic and subsurficial evidence of recent activity suggests that a reverse blind fault or a blind thrust should be considered active and potentially capable if showing evidence of activity during the quaternary i e over the last 2 6 myr unless information is available that documents its inactivity since at least the last glacial maximum lgm ca 20 ka the choice of the lgm period as the minimum age necessary to define fault inactivity is related to practical aspects the diffusion of the lgm deposits and landforms and to the evidence that ca 20 kyr to assess fault inactivity precautionarily includes a number of seismic cycles in the extensional domains of the apennines and calabria region the general geological setting suggests that the present tectonic regime has been active since the beginning of the middle pleistocene therefore we propose that a normal fault in the italian extensional domain should be considered active and capable if it displays evidence of activation in the last 0 8 myr unless it is sealed by deposits or landforms not younger than the lgm the choice of the lgm as the minimum age to ascertain fault inactivity follows the same criteria described for the compressive tectonic domain

the armenian earthquake of 1988 december 7 faulting and folding neotectonics and palaeoseismicity summary the spitak earthquake of 1988 december 7 is the first well documented event directly associated with surface breaks in the transcaucasian regions of the ussr the earthquake was located within the ese wnw oriented pambak sevan thrust and fold zone corresponding to the southern front of the lesser caucasus the mechanism of the earthquake is consistent with the nearly ns compressive tectonics due to the active continental collision between the arabian block and the russian platform the rupture is composed by several branches two of which reach the surface the first branch oriented n140 begins near the village of alavar has a length of 11 km and disappears at about 4 km se of spitak it consists of a right lateral en echelon system of strike slip faults with a maximum offset of 50 cm the second branch is the main one and breaks for about 8 km between spitak and gekhasar with a general orientation n120 showing reverse faulting dipping to the north with a right lateral component surface ruptures between gekhasar and spitak show either a narrow band of pressure ridges in alluvial deposits and soil or a fault scarp in the bed rocks when soil is absent maximum displacements observed between spitak and gekhasar attain 160 cm of vertical motion and 90 cm of horizontal dextral offset the displacement also varies within this branch showing finer segmentation few secondary deformations are observed some normal faults near gekhasar correspond to the collapse of the uplifted block an anticline fold oriented parallel to the fault scarp and situated along its northwestern prolongation emphasizes the regional compressive tectonics landslides were activated on its flanks a 200 m long reverse fault break observed along the hinge of a secondary fold suggests the occurrence of a blind thrust at depth and that the hidden branches which continue the main central segment towards the nw are associated to surface folding therefore the total length of the fault and fold zone is about 40 km in agreement with the rupture length and seismic moment obtained on the basis of surface wave modelling well developed uplifted terraces in the northern block and subsiding valleys in the southern block indicate past quaternary activity in the fault region palaeoseismological evidence of ancient earthquakes has been recognized in trenches across the spitak fault one old event occurred between 17 000 years bp and the beginning of the formation of present day soil

reply to comment on a vertical exposure of the 1999 surface rupture of the chelungpu fault at wufeng western taiwan structural and paleoseismic implications for an active thrust fault by jian cheng lee yue gau chen kerry sieh karl mueller wen shan chen hao tsu chu yu chang chan charles rubin and robert yeats by yuan hsi lee shih ting lu tung sheng shih and wei yu wu we welcome y h lee et al s interest in our article lee et al 2001 we thank them for their comment which provides a further opportunity for discussing the quantification of the slip amounts including horizontal and vertical components and the fault geometry for an earthquake thrust scarp in wufeng western taiwan during the 1999 m 7 6 earthquake in their comment y h lee et al used restoration of deformed concrete fence across the 1999 scarp to estimate the slip vector of the main fault the estimated slip amount especially the horizontal component is different significantly less from our results presented in the 2001 bssa article they then applied an area balance technique to compare their results with ours they showed that their area balance method favored their estimates including the slip amounts and the fault dip angle they concluded that their estimated slip amounts are more reasonable than ours the fundamental questions in this issue in our opinions include the actual amounts of deformation slip and the associated deformation processes as well as the limitation and uncertainty of the applied techniques on an earthquake formed thrust scarp hereafter we attempt to answer these questions and clarify the related problems

rupture process of the 1964 prince william sound alaska earthquake from the combined inversion of seismic tsunami and geodetic data 1 four great earthquakes 1952 1960 1964 and 2004 have occurred since seismic monitoring began and only two since the installation of a global seismic network a reexamination of the 1964 m 9 2 prince william sound pws alaska earthquake is timely due to the 2004 sumatra earthquake because it adds constraints to the potential range of source parameters for these types of infrequent events and aids in the ability to predict the ground motions for other subduction zone including cascadia we first measured the durations of high frequency energy radiation from teleseismic p wave codas recorded by short period world wide standardized seismographic network wwssn sp instruments to put constraints on the earthquake rupture length the durations ranged between 250 and 600 s and are shorter in time between azimuths of 190 and 260 the fault length is estimated to range from 540 to 740 km rupturing at average speeds of 1 4 2 km s in a 220 238 direction we developed a multiple time window kinematic rupture model for the pws earthquake from the least squares inversion of teleseismic p waves tsunami tide gauge records and geodetic leveling survey observations based on the green s function technique we assume three major fault segments for the subduction zone dipping 6 12 based on geologic data the subfault size on the megathrust was set to 50 50 km the patton bay fault pbf imbricate thrust was assigned a 60 dip with a subfault size of 20 20 km we estimated a seismic moment of 5 52 1022 n m mw9 12 we identified three areas of major moment release on the pws segment near montague and middleton islands extending out to the trench beneath the portlock anticline on the cook segment between 58 n fracture zone and the kodiak bowie seamount chain and finally on the katmai segment off the coast of kodiak island extending to the trench our preferred rupture model has a peak slip of 14 9 m along the megathrust and 17 4 m along the pbf the addition of the pbf resulted in an 8 improvement in residuals and also had a significant effect on the overall slip distribution moment release occurred as deep as 50 km depth slab contour near the 350 c isotherm and mantle fore arc wedge which is about 10 20 km deeper than previous coupling depths

numerical investigation of dip slip fault propagation effects on offshore seabed sediments abstract an enhanced understanding of the phenomenon of dip slip fault propagation through young unconsolidated offshore sediments is essential for the evaluation of the response of shallow offshore structures and subsea oil gas pipelines substantial and permanent seafloor deformation constitutes a severe geohazard for these marine structures and associated offshore elements components this paper addresses the response of seabed sand deposits subjected to underlying dip slip fault movement the resulting propagation of the faulting offset in seabed sediments is explored using 2d finite element modeling in abaqus while accounting for nonlinear soil behavior with strain softening a 2d plain strain fem seabed model is adopted to investigate the effect of different seabed soil properties and layer thicknesses on the extent and magnitude of seabed surface deformation induced by normal and reverse faults with different dip angles the results indicate that 1 the adoption of sand properties that depend on depth is necessary to realistically model the fault propagation mechanism particularly for fault propagation through thick and dense sand deposits 2 the presentation of fault propagation results in a normalized manner with respect to sand cover thickness does not eliminate the dependency on the actual layer thickness and 3 the deformation of the beds in the cover as a result of basement faulting can be modeled realistically using trishear kinematic approaches

the deformation of overburden soil induced by thrust faulting and its impact on underground tunnels overburden soil beds situated above a fault are often deformed by propagation of bedrock thrusting from the fault during large earthquake the deformed beds formed a triangular shear zone this coseismic faulting often causes damage to underground tunnels located in the shear zone the present research studies the deformation behavior of the overburden soil beds and the tunnel the associated mechanism and the impact on the safety of tunnel linings induced by a large blind thrust slip based on sandbox experimental and numerical studies it is found that results from numerical analysis are in agreement with the sandbox model tests with regard to growths of the shear zones within the soil beds location of the tunnel in this shear zone and deformations of the tunnel the potential major shear zone may be bent or bifurcated into two sub shear zones owing to existence of a tunnel inside the shear zone furthermore the occurrence of back thrust faulting will threaten the safety of nearby structures it was also identified that stiffness of the soil and the fault dip angles are among the major factors controlling the configuration of shear zones the stresses within the soil and the loads on tunnel linings based on the identified mechanisms the strategies for hazard prevention are accordingly suggested and discussed

trench investigations through the trace of the 1980 el asnam thrust fault evidence for paleoseismicity during the ei asnam earthquake of 10 october 1980 ms 7 3 a clear active thrust fault with left lateral offset was observed three trenches have been excavated across this fault in order to determine slip rate and recurrence intervals between large earthquakes and thus reconstruct its past activity exposure i was excavated in the flood area created in 1980 by a pressure ridge across the cheliff and fodda rivers six flood deposits silty sandy and muddy horizons alternating with paleosoils appear in this exposure they are affected by normal faults associated with the main thrust fault assuming that every flood deposit results from a tectonic event of magnitude greater than 7 we can correlate previous flood deposits with these events exposures ii and iii display thrust faults displacing different paleosoils we propose a sequence of reconstructions based on the thickness of the various deposits and the dip slip of each tectonic event the late holocene slip rate is 0 65 mm yr for the dip slip and 0 46 mm yr for each of the horizontal and the vertical movements radiocarbon dates of coseismic movements indicate a rather irregular seismic activity during the past 7000 yr two sequences of large earthquakes around 4000 yr b p and around the modern age are separated with a period of quiescence the average late holocene recurrence interval of large earthquakes is 1061 yr however during the active faulting episodes the recurrence time varies from approximately 300 to 500 yr

defining fault avoidance zones and associated geotechnical properties using masw a case study on the springfield fault new zealand abstract the springfield thrust fault at dalethorpe west canterbury new zealand provides a test case to explore the correlation between shear wave velocities at a range of scales and direct field observations of distributed deformation and outcrop properties the springfield fault ruptures to the surface through hard torlesse greywacke overlain on a flight of late quaternary glacio fluvial terraces by 5 m of gravel fault slip has displaced all but the lowest terraces revealing the geometry and location of faulting we used multi channel analysis of surface waves and meter scale cross hole measurements to map shear wave velocities below the lowest apparently undisplaced terrace we correlated these surveys with geotechnical parameters measured at outcrops and investigated relationships in the laboratory both field and laboratory results indicate that the shear wave velocity of torlesse greywacke declines sharply with increasing fracture density field surveys further indicate that relatively unweathered high velocity greywacke is being exhumed in a bivergent wedge between two opposite facing thrusts the fracturing and low shear wave velocities are focused in a wide low velocity damage zone that has developed in the hanging wall of the main thrust and a smaller but similar feature in the hanging wall of the backthrust this is consistent with the geomorphology of the site our correlations of geomorphic indicators of deformation with fault zone velocity structure provide a useful method with which to characterize the distribution of cumulative strain this type of analysis has utility for land use planning on or close to active faults especially where they are obscured by fluvial deposits

quaternary active thrusts scarps tested as deformation markers by trishear models in the southern precordillera of argentina abstract scarps related to quaternary active thrust splays propagating in alluvial bajadas of the southern precordillera of argentina 32 20 were studied through detailed topographic surveys in order to understand the reliability of these landforms as deformation markers at an outcrop scale geometric parameters of causative structures were used to constrain balanced cross sections through trishear modelling for shortening estimation and also with the aim of comparing the predicted geometry of these models with the scarp profile shortening estimation through retro deformation of scarps contours was also conducted as an alternative approach for calculating deformation affecting these alluvial surfaces results indicate that fold geometries predicted by trishear modelling do not fit with the present scarp shapes suggesting modifications and slope angle decrease of the front limb in order to match the modelled folds with the scarp profiles it is necessary to place constraints to fault parameters such as ramp angle and tip point position not compatible with field observations trishear models predict shortening values 8 to 15 times larger than those obtained through line retrodeformation of scarp profiles therefore scarp shapes at a mesoscopic scale in the study area are not considered a reliable deformation marker for shortening estimation of propagating thrusts through an unconsolidated cover

coseismic slip resolution and post seismic relaxation time of the 1999 chi chi taiwan earthquake as constrained by geological observations geodetic measurements and seismicity summary we analysed the surface displacements estimated by global positioning system gps mea surements and systeme probatoire d observation de la terre spot image correlation and the seismicity change induced by the mw 7 6 1999 september 20 chi chi earthquake we first modelled the seismogenic zone for which we introduced a realistic geologically constrained ramp and flat geometry and estimated by joint inversion of the gps and spot data the co seismic slip distribution stressing the resolution of the model parameters the fair adjustment indicates that the ramp and flat geometry is consistent with the geodetic measurement the cal culated coseismic slip increases both towards the surface and northwards with maximum slip of approximately 15 m in good agreement with the observed surface rupture and previously ob tained slip models based on seismic waveforms this distribution may be represented to a good approximation by a linear increase of slip with a constant azimuth in the plate convergence direction special emphasis is given to the analysis of the model resolution which sharply decreases with depth in spite of the exceptionally well distributed and high quality inverted data this resolution decrease expected for any slip distribution based on surface observations only led us then to examine the seismicity as independent data to test our model following the static stress triggering hypothesis the model is accurately defined in terms of coulomb stress change in the central part of the rupture where the fault geometry is well constrained by seismic profile in contrast at the southern and northern ends it is less appropriate however the static stress triggering approach is not precise enough to determine whether fault geometry or slip distribution is less suitable we thus conclude that the analysis of seismicity in terms of coulomb stress change might not allow us to examine small scale features of seismogenic zones finally we discuss post seismic relaxation from the temporal variation of seismicity rate in contrast to the relaxation time of 0 23 0 90 yr inferred from post seismic permanent gps measurements we found that the decay of aftershock sequence follows omori s law with an 8 14 yr relaxation time we suggest that this discrepancy results from the coexistence of several different processes not all associated with the production of aftershocks

centrifuge modeling of reverse fault rupture propagation through single layered and stratified soil abstract many buildings have been built over active faults surface faulting as a main effect of earthquakes can cause damage such buildings properties of material over bedrock affect the pattern of rupture propagation through deposits and the width of the rupture zone on ground surface several researchers have primarily studied fault rupture propagation patterns on single layered granular soil however natural geologic deposits are rarely homogeneous and uniform but mostly consist of different layers in this study centrifuge model tests were conducted to investigate the patterns of reverse fault rupture propagation through single and double layered soil stratum it was observed that the soil type and sequence of layers affected the fault rupture propagation pattern as well as the surface rupture zone the results show that the width of deformation zone tends to decrease in stiffer soil in compare to softer soil these findings may help to produce a framework for predicting the occurrence and geometry of surface fault rupture zone that can help us to define a setback zone which is a major concern in building codes

complexity of the coseismic rupture for 1999 chi chi earthquake taiwan from inversion of gps observations abstract based on the elastic half space model and the layered earth model we use global position system observations to invert the distribution of coseismic slip along the chi chi earthquake rupture bending fault planes are introduced in our models the results indicate that the shear slip model can not fit horizontal and vertical coseismic displacements simultaneously unless the fault normal motion tensile component is considered in the inversion we interpret that the fault normal motion reflects the roughness of fault planes demonstrating the complexity of the rupture in property and geometry the distribution of the fault normal motion appropriately fits with the complexity of surface coseismic rupture from the field investigation and the distribution of the strike dip slip of coseismic rupture is similar to the results from inversion of the teleseismic data

caisson foundations subjected to reverse fault rupture centrifuge testing and numerical analysis recent large magnitude m 7 earthquakes have caused numerous failures induced by surface faulting demonstrating the need to account for tectonic deformation in seismic design thanks to their usually high rigidity embedded e g caisson foundations may divert the fault rupture and lead to favorable performance whereas surface or piled foundations may fail we present a series of centrifuge model tests to investigate the response of caisson foundations embedded in a cohesionless soil stratum the base of which is subjected to reverse faulting we elucidate the interplay between the propagating fault rupture and the caisson focusing on the role of the location of the outcropping rupture relative to the caisson the rigid body of the caisson causes diversion and or bifurcation of the shear localization which is forced to develop preferentially around the edges of the caisson the observed failure pattern and the consequent caisson response depend strongly on the exact caisson position relative to the

style of the surface deformation by the 1999 chichi earthquake at the central segment of chelungpu fault taiwan with special reference to the presence of the main and subsidiary faults and their progressive deformation in the tsauton area abstract we describe the style of surface deformation in the 1999 chichi earthquake in the central segment of the chelungpu fault the study covers the kung fu village north of han river to the south of tsauton area a characteristic style of the surface deformation is a convex scarp in profile and sinuous plan view due to the low angle thrust fault two subparallel faults including the west facing tsauton west fault and the east facing tsauton east fault limit the western and eastern margin of the tsauton terraced area the tsauton west fault is the continuation of the main chelungpu fault and the tsauton east fault is located about 2 km apart both faults record larger amounts of vertical displacement on the older terraces the 1999 surface rupture occurred exactly on a pre existing fault scarp of the tsauton west and east faults thus repeated activities of these two faults during the holocene possibly since the late quaternary are confirmed the amount of vertical offset of the tsauton east fault is smaller and about 40 50 of that of the tsauton west fault for the pre existing fault this indicates that the tsauton east fault is a subsidiary fault and moved together with the main fault but accommodated less amount

paleoseismology and kinematic characteristics of the xiaoyudong rupture a short but significant strange segment characterized by the may 12 2008 mw 7 9 earthquake in sichuan china abstract three faults were involved in the rupture process of the may 12 2008 mw7 9 wenchuan earthquake representing a rarely documented case of multiple faults rupturing simultaneously distinct from the other two major ne trending surface ruptures the 7 km long xiaoyudong surface rupture is oriented nw340 and shows thrust and left slip faulting in order to understand what role xiaoyudong rupture played in the tectonic evolution of longmenshan thrust system we conducted a detailed investigation including geomorphic feature observation coseismic displacement measurement paleo rupture event trenching and fault kinematic estimation of the xiaoyudong area our results not only document an in situ paleoearthquake occurring at 3 2 2 3 ka bp but also present the xiaoyudong rupturing event as an oblique thrust with minor components of left lateral slip we also found vertical and sinistral slip rates estimated as 1 1 1 5 mm yr and 0 5 0 7 mm yr respectively finally we suggest that the xiaoyudong rupture is not a passive tear fault but an active participator of slip partitioning on multiple faults within the longmenshan thrust system and moreover it gave strong response to both the 2008 and the penultimate earthquake while it kept silence with the antepenultimate event

locating distributed faulting contributions from insar imaging to probabilistic fault displacement hazard analysis pfdha abstract prediction of location and amount of slip for distributed faulting associated to strong earthquakes is a recently explored issue with major implications in terms of hazard assessment currently the best practice involves the applications of probabilistic fault displacement hazard analysis pfdha whose results fit sufficiently well real data in the near range of the primary fault but show considerable inaccuracies in the far range we believe that this inaccuracy descends from the biased earthquake databases used for regression analysis whose data relative to old earthquakes were largely collected only by field surveys focused close to the primary fault i e near range remotely sensed data i e interferometric radar imaging insar offer the opportunity to precisely measure the surface deformation induced by strong earthquakes and thus to explore its possible relation with distributed faulting we analyze the l aquila earthquake case study 29th april 2009 mw 6 3 and explore the correlation between location and slip on distributed faulting and insar derived deformation field we find a significant correlation between occurrence of distributed faulting and profile curvature of the dislocation field in spite of the distance from the primary fault moreover distributed faults tend to occur within the area deformed by the earthquake as imaged by insar data and whose extent is directly proportional to the earthquake magnitude mw according to a dataset of 30 recent earthquakes we then propose that these observations have to be incorporated into the present pfdha practice as limit boundaries to possible scenarios of probabilistic analysis and that an integrated use of field based and remotely data collection have to be implemented following strong earthquakes

fault scarp features and cascading rupture model for the mw 7 9 wenchuan earthquake eastern tibetan plateau china on 12 may 2008 the m w 7 9 wenchuan earthquake ruptured two northeast striking imbricated reverse faults and one northwest striking reverse fault along the middle longmen shan thrust belt at the eastern margin of the tibetan plateau the morphology of the coseismic scarp varies drastically along strike we distinguish eight different categories 1 simple thrust scarp 2 hanging wall collapse scarp 3 simple pressure ridge 4 dextral pressure ridge 5 fault related fold scarp 6 backthrust pressure ridge 7 local normal fault scarp and 8 pavement suprathrust scarp the coseismic surface ruptures confirm that the wenchuan earthquake is dominated by reverse faulting with some right lateral component that varies from site to site the surface rupture can be divided into two parts the yingxiu segment and the beichuan segment when the earthquake is split into two subevents accordingly they correspond to an m w 7 8 event and an m w 7 6 event respectively these two segments can in turn be divided into four second order subsegments which are equivalent to four subevents of m w 7 5 m w 7 7 m w 7 0 and m w 7 5 respectively the segmentation of the rupture is consistent with a cascading rupture pattern responsible for the total 110 s of the earthquake rupture in addition to surface ruptures the focal mechanisms determined for the aftershocks recorded by the local seismic network are used to constrain the fault geometry of the subsegments they show that the dip of the fault responsible for the earthquake varies along strike and the fault tends to flatten at depth in addition the fault plane gets steeper northward enabling the fault to accommodate a larger strike slip component along a lateral ramp this major earthquake confirms that crustal shortening could be the main driving force for the growth of high topography along the eastern margin of the tibetan plateau and that lower crustal flow is not required

representative styles of deformation along the chelungpu fault from the 1999 chi chi taiwan earthquake geomorphic characteristics and responses of man made structures the chi chi earthquake provides dramatic evidence of the damaging effects of surface ground deformation to buildings lifelines and other facilities much of the building damage is associated with surface faulting and folding along the chelungpu thrust fault our detailed surveying at representative sites along the fault shows that the rupture commonly is a relatively simple 1 to 4 m high scarp with minor hanging wall deformation and localized but severe uplift folding and graben formation along the scarp crest for individual scarps the width of deformation is about 10 to 20 times the net vertical displacement distributed secondary faulting and folding on the hanging wall occurred as much as 350 m from the primary fault near the northern end of the rupture growth of a pre existing 1 km wide late quaternary anticline produced severe ground rupture along multiple thrusts and backthrusts but only minor tilting between fault strands the pattern of building damage coincides with the pattern of geologic deformation with severe damage along large fault scarps and lesser but still significant damage attributable to distributed secondary surface deformation on the hanging wall rupture related building damage on the footwall occurred next to the prerupture fault trace where the hanging wall bulldozed onto the footwall the width of this damage zone is related to the local horizontal shortening along the fault and generally is less than 10 m building zonation along reverse faults should account for this pattern of surface deformation in addition buildings with massive foundations locally influenced the style and location of near surface deformation producing variations in fault strike or accentuated secondary deformation on the hanging wall manuscript received 15 january 2001

detailed surface co seismic displacement of the 1999 chi chi earthquake in western taiwan and implication of fault geometry in the shallow subsurface the northern segment of the chelungpu fault shows an unusually large co seismic displacement from the event of the mw 7 6 chi chi earthquake in western taiwan part of the northern segment near the fengyuan city provides an excellent opportunity for characterizing active thrust related structures due to a dense geodetic benchmark network we reproduced co seismic deformation patterns of a small segment of this chelungpu fault using 924 geodetic benchmarks according to the estimated displacement vectors we identified secondary deformations such as local rigid block rotation and significant shortening within the hanging wall the data set also allows us to determine accurately a 3d model of the thrust fault geometry in the shallow subsurface by assuming simple relations between the fault slip and the horizontal and vertical displacements at the surface the predicted thrust geometry is in good agreement with borehole data derived from two drilling sites close to the study area the successful prediction supports our assumptions of rigid displacement and control of displacement in the hanging wall by the fault geometry being useful first approximations

active folding in the algerian earthquake of 10 october 1980 a fold controlling the form of the local topography near el asnam algeria increased in amplitude at the time of the earthquake of 10 october 1980 the deformation occurred rapidly in an elastic brittle manner and not in the gradual ductile fashion in which folds are normally thought to develop

quantitative analysis of movement along an earthquake thrust scarp a case study of a vertical exposure of the 1999 surface rupture of the chelungpu fault at wufeng western taiwan a vertical exposure across the principal thrust scarp of the 1999 mw 7 6 earthquake allows quantification offault slip the exposure is located on the active chelungpu fault near wufeng along the range front of the fold and thrust belt in western taiwan the 1999 surface ruptures at the wufeng site are characterized by a west facing 2 to 3 m high principal thrust scarp and an east facing lesser backthrust scarp we mapped a 15 mlong 5 m deep exposure across the principal thrust scarp and characterized complex deformation structures which include a main basal thrust fault a wedge thrust and a pop up anticlinal fold with two secondary opposing thrust faults the vertical displacement across the principal thrust scarp is measured directly from the offsets of the same sedimentary horizons between the hangingwall and the footwall the average vertical displacement is 2 2 0 1 m and the maximum displacement is 2 5 m at the crest of the small pop up fold horizontal displacement estimates were determined using line and area balancing methods with line length methods we estimated a horizontal displacement of 3 3 0 3 m across the principal scarp for four sedimentary horizons for area balancing first we selected three horizontal soil sand deposits with a total thickness of about 0 5 m the estimate yields an average horizontal displacement of 4 8 1 0 m using these individual and relatively thin stratigraphic layers yielded significant standard deviations in displacement estimates as a result of thickness variations second we used the 3 mthick overbank soil sand and the lower part offluvial pebble cobble to calculate a horizontal displacement of 2 6 0 2 m with the area balancing technique according to the geometry of the dip angle 35 408 of the basal thrust the line length measurement and the 3 m thick package area balancing both providedreasonable results of horizontal displacement by comparing thedifferent deposits applied to theline and area balancing methods we interpret that decoupling of deformation occurred between the lower fluvial gravels and the upper overbank sand and mud deposits due to lesser confining pressure at the surface additional deformation occurred in the upper 1 2 m thick overbank deposits this additional deformation yielded further vertical uplift of 0 3 0 5 m and horizontal displacement of 0 2 0 8 m around the core of the pop up fold our work suggests that determination of slip across surface thrust ruptures varies as a function of the mechanical behavior of young late quaternary deposits q 2003 elsevier ltd all rights reserved

surface ruptures of large himalayan earthquakes in western nepal evidence along a reactivated strand of the main boundary thrust the chronology of the seismic ruptures along the active faults of western nepal remains almost unconstrained despite their high seismogenic potential we present here a slip history of one of these structures a 120 km long reactivated segment of the main boundary thrust named the surkhet gorahi fault this slip history is based on geomorphologic and neotectonic mapping of active faults deduced from the analysis of a high resolution total station digital elevation model and 15 detrital charcoals radiocarbon ages constraining the age of deposition or abandonment of 4 alluvial terraces of the bheri river in botechaur our results show that the last two earthquakes occurred on this fault after 1860 and 640 bp respectively and accommodated slip greater than 8 m each a value corresponding to the incremental vertical offset of the terraces such events released a significant part of the slip deficit accumulated on the main himalayan thrust fault however given the geometry of this fault system as well as the date of occurrence of the last events the ruptures could be associated with major earthquakes also rupturing the main frontal thrust such as the great 1505 earthquake

multiple late holocene earthquakes along the reelfoot fault central new madrid seismic zone the reelfoot fault is an east vergent reverse fault underlying the lake county uplift a low amplitude late holocene anticline bordered on the east by the 32 km long reelfoot scarp fluvial deposits across the scarp define an 8 m high east facing monocline most near surface deformation along the scarp is accommodated via folding rather than faulting we interpret the scarp as a fault propagation fold developed over a wcst dipping reverse fault interpreted from shallow seismic reflection data trench exposurcs provide evidence for three episodes of deformation along the reelfoot fault within thc past approximately 2400 years between a d 780 and 1000 between a d 1260 and 1650 and during a d 1812 our best estimate of the average recurrence interval for deformation along the scarp is 400 500 years each episode of deformation had a slightly different style the third most recent event produced a small graben a few tens of centimeters deep in the hanging wall of the reverse fault the second most recent earthquake produced about 1 3 m of throw in the graben as well as folding along the updip projection of the reverse fault and development of the scarp thesc relations suggest that graben development increased through time concomitant with growth of the monocline or that the events are of different magnitude the 1811 1812 episode of deformation produced abundant liquefaction prominent folding of fluvial strata along the scarp and minor faulting in the graben

late holocene earthquakes on the toe jam hill fault seattle fault zone bainbridge island washington five trenches across a holocene fault scarp yield the first radiocarbon measured earthquake recurrence intervals for a crustal fault in western washington the scarp the first to be revealed by laser imagery marks the toe jam hill fault a north dipping backthrust to the seattle fault folded and faulted strata liquefaction features and forest soil a horizons buried by hanging wall collapse colluvium record three or possibly four earthquakes between 2500 and 1000 yr ago the most recent earthquake is probably the 1050 1020 cal calibrated yr b p a d 900 930 earthquake that raised marine terraces and triggered a tsunami in puget sound vertical deformation estimated from stratigraphic and surface offsets at trench sites suggests late holocene earthquake magnitudes near m7 corresponding to surface ruptures 36 km long deformation features recording poorly understood latest pleistocene earthquakes suggest that they were smaller than late holocene earthquakes postglacial earthquake recurrence intervals based on 97 radiocarbon ages most on detrital charcoal range from 12 000 yr to as little as a century or less corresponding fault slip rates are 0 2 mm yr for the past 16 000 yr and 2 mm yr for the past 2500 yr because the toe jam hill fault is a backthrust to the seattle fault it may not have ruptured during every earthquake on the seattle fault but the earthquake history of the toe jam hill fault is at least a partial proxy for the history of the rest of the seattle fault zone

two post glacial earthquakes on the saddle mountain west fault southeastern olympic peninsula washington abstract two earthquakes ruptured the western strand of the saddle mountain fault after the cordilleran ice sheet began its retreat from the puget sound lowland about 17 ka the fault system includes multiple northeast trending thrust faults on the southeastern olympic peninsula delineated on light detection and ranging topography by prominent east side up scarps that deform vashon till and extend over 6 7 km the cargill creek trench on the saddle mountain west fault exposed faulted drift and postglacial colluvium below a 1 2 m high scarp steeply dipping northeast striking faults form a 10 m wide zone beneath the scarp structural relations in the trench indicate that two earthquakes produced at least 1 m of vertical separation additional folding or faulting beyond the trench raised the scarp to a total height of 1 7 m aligned cobbles dipping approximately 40 to the north attest to earthquake related tilting a cobble firmly lodged in till and split by a secondary fault indicates that hanging wall deformation involved a dextral component of slip however slip on the master fault may have involved a left lateral component based on slip indicators at adjacent trench sites in the region a single charcoal age and estimates of the onset of ice retreat limit the time of the oldest earthquake to 17 7 7 ka the most recent event occurred after 1 7 ka and may be the same earthquake that dammed price lake about 1100 yr ago known from related studies empirical relations suggest that the most recent earthquake was about m 7 0 2 and produced an estimated total slip of 1 3 1 7 m the total postglacial slip rate ranges from 0 1 to 0 3 m k yr these results support the hypothesis that the saddle mountain fault is part of a larger fault system that accommodates transpressive strain as the puget lowland crust migrates around the eastern flank of the olympic mountains