seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

cenozoic tectonics in the urumgi korla region of the chinese tien shan cenozoic deformation within the tien shan of central asia has accommodated part of the post collisional indentation of the indian plate into asia within the urumgi korla region of the chinese tien shan this occurred dominantly on thrusts with secondary strike slip faulting the gross pattern of deformation is of moderate to steeply dipping thrusts that have overthrust foreland basins to the north and south of the range the junggar and tarim basins respectively smaller foreland basins lie within the margins of the range itself turfan chai wo pu korla and qumishi basins these lie in the footwalls of local thrust systems both the turfan and the korla basins contain major thrusts within them they are complex foreland basins deformation has progressively affected regions further into the interior of the junggar basin and propagated into the interiors of the intermontane basins no unidirectional deformation front has passed across the tien shan in the neogene and quaternary an oligocene unconformity may indicate the time of the onset of the cenozoic deformation but most of the cenozoic molasse has been deposited after the palaeogene the rate of deposition in basins next to the uplifted ranges has increased since the onset of deformation there has been at least about 80 km of cenozoic shortening across this part of the tien shan cenozoic shortening is greater in sections of the range further west these are nearer to the northern margin of the indian indenter cenozoic compression has reactivated structures created by the two late palaeozoic collisions that created the ancestral tien shan these palaeozoic structures have exerted a strong control over the style and location of the cenozoic deformation

basin evolution within and adjacent to the tien shan range nw china two late palaeozoic collisions produced the ancestral tien shan range extension following the younger collision preceded a phase of thermal subsidence associated with fluvial and lacustrine sedimentation throughout the jurassic cretaceous and early tertiary this thermal subsidence was interrupted by renewed movement on palaeozoic reverse faults caused by the mesozoic collisions at the southern margin of asia the india asia collision in the early tertiary has produced widespread thrusting in the tien shan which in turn is responsible for the formation of active foreland basins at the southern and northern margins of the range and similar basins within the range itself this compression produced uplift and relief and consequent erosion gave rise to alluvial fans braidplains and ephemeral lakes in an extremely arid environment

the influence of surface ruptures on building damage in the 1999 chi chi earthquake a case study in fengyuan city abstract in addition to the main surface rupture along the chelungpu fault associated with the 1999 chi chi taiwan earthquake numerous secondary or branch ruptures on hangingwall were also observed these secondary surface ruptures are parallel or sub parallel to the main rupture within a distance of a few meters to 1 2 km the rupture length of these secondary ruptures varies from a few tens of meters up to 5 km the surface deformation resulted in serious damages of buildings the present work studied the features of surface deformation on the hangingwall around the chung cheng park fengyuan taichung three distinct surface ruptures minor ruptures and tension cracks were observed in this area the observed distribution and types of building damage on the hangingwall are demonstrated due to the difference in geological condition and complex pattern of surface deformation the resulted building damages on the hangingwall vary a series of site investigation including field survey drilling seismic prospecting p s logging tests and laboratory tests were carried out in the interested area a geological structure model was proposed on the basis of the results of site investigation numerical simulation was carried out to model the surface deformation as well as subsurface potential damage zone of an active fault it reasonably explains the observed pattern of surface deformation and indicates that the surface deformation zone during a catastrophic earthquake is predictable

source parameters for 11 earthquakes in the tien shan central asia determined by p and sh waveform inversion the tien shan mountain belt of central asia was formed in late paleozoic time and reactivated in tertiary time following the collision of india with eurasia more than 1500 km to the south to study the style and distribution of faulting occurring today in the tien shan we digitized long period world wide standard seismograph network p and sh waveforms of 11 of the largest tien shan earthquakes between 1965 and 1982 and then used a least squares inversion routine to constrain their fault plane solutions and depths four of the earthquakes occurred near the southern edge of the tien shan and two occurred in the intermontane fergana basin these earthquakes occurred at depths of 10 20 km and are associated with thrust faulting on east west to southwest northeast striking fault planes that dip moderately 35 55 the other five earthquakes in the northern tien shan were mostly deeper 15 44 km and the fault plane solutions of four of them are similar to the events farther south the exception an event on june 2 1973 probably occurred on a gently northward dipping east west striking fault plane all events occur within the basement at depths of 10 km or greater waveforms for earthquakes near the edges of the dzungarian fergana and kucha basins are fit best using velocity structures with thick sediment layers implying that sediments from these basins have been and are being underthrust beneath the neighboring mountains we examined only the relatively small mb 5 5 6 2 events after 1965 and did not study any of the largest events ms 8 that occurred in the tien shan earlier in this century still we can conclude that north south shortening is presently occurring in the tien shan with the formation of basement uplifts flanked by moderately dipping thrust faults the present day tectonics of the tien shan seem to be analogous to those of the rocky mountains in colorado wyoming and utah during the laramide orogeny in late cretaceous and early tertiary time

fault chronology and uplift history of the southern wind river range wyoming implications for laramide and post laramide deformation in the rocky mountain foreland the stratigraphy provenance and structural involvement of tectogenic sedimentary rocks along the southern and western margins of the wind river range in western wyoming record a complex laramide and later uplift history and identify the timing and position of individual faulting events the chronology of these events is 1 main uplift of the range by displacement on the wind river fault between 90 and 49 to 50 ma 2 the formation of reverse faults in the hanging wall of the wind river fault ca 50 to 51 ma 3 sagging of the toe of the wind river fault into sedimentary fill of the green river basin between 46 and 23 ma 4 uplift of the core of the range along reactivated precambrian shear zones between 30 and 23 ma and 5 collapse of the southern part of the range along normal faults beginning at 13 ma the sedimentary record of uplift and erosion indicates that erosion and basin fill kept pace or caught up with uplift so that by the end of the laramide there was little topographic relief between the crest of the range and the adjacent green river basin the present topography of the range characterized by a high level erosion surface and distinct crestal ridge derives from uplift of the erosion surface by the late laramide reverse faulting post laramide uplift of the crest of the range and neogene exhumation initial uplift of the range as early as 110 ma and prior to displacement on the wind river fault suggests either a pre laramide event of unknown origin or that laramide crustal shortening began nearly 35 m y earlier than commonly assumed

suppression of baroclinic instabilities in buoyancy driven flow over sloping bathymetry abstractbaroclinic instabilities are ubiquitous in many types of geostrophic flow however they are seldom observed in river plumes despite strong lateral density gradients within the plume front supported by results from a realistic numerical simulation of the mississippi atchafalaya river plume idealized numerical simulations of buoyancy driven flow are used to investigate baroclinic instabilities in buoyancy driven flow over a sloping bottom the parameter space is defined by the slope burger number s nf 1 where n is the buoyancy frequency f is the coriolis parameter and is the bottom slope and the richardson number ri n2f2m 4 where m2 hb is the magnitude of the lateral buoyancy gradients instabilities only form in a subset of the simulations with the criterion that sh sri 1 2 uf 1w 1 m2f 2 0 2 where u is a horizontal velocity scale and sh is a new parameter named the horizontal slope burger number suppression of instability formation for certain flow conditions contrasts

late quaternary right lateral displacement along active faults in the yanqi basin southeastern tian shan northwest china abstract late quaternary right lateral displacement and slip rates have been determined along wnw ese trending active faults in the intermontane yanqi basin on the southeastern flank of the chinese tian shan detailed analyses of satellite images and field investigation have revealed that the active kaidu river fault zone on the southern margin of the basin is a strike slip fault zone drainage systems incising late pleistocene holocene alluvial fans record between 3 and 250 m dextral offsets and show progressive displacement along the fault zone fault scarps developed in the alluvial fans range in height from 1 to 25 m and alternate along the strike of the fault zone from northeast to southwest facing in a left stepping en echelon pattern based on the offset of stream channels 14c dates of alluvial deposits and fabrics within fault rocks we infer that 1 the average right lateral slip rate is about 8 mm year with a vertical component of 1 mm year 2 the offset produced by individual seismic faulting event is typically 3 7 m 3 the average recurrence interval of large seismic events m 7 is ca 500 years and 4 the most recent movement occurred during the past 2 5 ky in the kaidu river fault zone these strike slip faults represent partitioning of horizontal slip within an otherwise thrust dominated orogen related to the india eurasia collision within the tian shan during late quaternary

spatial scale analysis of hydrographic data over the texas louisiana continental shelf on the basis of hydrographic data collected by the texas louisiana shelf circulation and transport processes study latex a and on earlier cruises we examined the energetic scales of spatial variability over the texas louisiana continental shelf shelf scale spatial reference fields were sought to represent the general distributions of circulation and water properties over the shelf at the time of the observations various methods were explored for determining such reference fields of potential temperature salinity and geopotential anomaly at the sea surface relative to 70 db spatial reference fields obtained from mean may fields and from polynomials fitted to individual may cruise data were compared on the basis of those comparisons quadratics were selected to fit property distributions from individual cruises and so to yield reference fields smaller scale anomaly fields were obtained by removing the reference fields from the observed distributions calculation of correlation versus separation distance based on these anomaly fields then allowed estimation of spatial scales of anomaly fields for cross shelf and along shelf transects the zero crossing scale and the gaussian decay scale are shown to be essentially the same and the zero crossing scale is used the principal results for the anomaly scales are 1 cross shelf scales over the western shelf are shorter order 15 km than those in the eastern and central regions order 20 km 2 along shelf spatial scales are of the order of 35 km 3 there is no significant difference in cross shelf scales at the surface middepth and bottom and 4 along shelf scales are essentially the same over the western and eastern regions of the shelf over the midshelf 50 m isobath and along the shelf break 200 m isobath and at different depths along the 200 m isobath the same spatial scales are found when using data with spatial resolution of 1 10 km cross shelf and 10 20 along shelf to obtain the anomaly fields so the data resolution used is adequate to represent the scales the variances of the observed shelf wide salinity temperature and geopotential anomaly are greater cross shelf than along shelf the variance of the cross shelf anomaly fields is around 10 of the shelf wide fields that of the along shelf anomaly fields is about 35 of that in the shelf wide fields the analysis of scales when grouped by season did not show persuasive evidence of seasonal variation

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

blending hf radar and model velocities in monterey bay through normal mode analysis nowcasts of the surface velocity field in monterey bay are made for the period august 1 9 1994 using hf radar observations blended with results from a primitive equation model a spectral method called normal mode analysis was used objective spatial and temporal filtering were performed and stream function velocity potential relative vorticity and horizontal divergence were calculated over the domain this type of nowcasting permits global spectral analysis of mode amplitudes calculation of enstrophy and additional analyses using tools like empirical orthogonal functions the nowcasts reported here include open boundary flow information from the numerical model nowcasts using no open boundary flow information however still provide excellent results for locations within the observation footprint this method then is useful for filtering high resolution data like hf radar observations even when open boundary flow information is unavailable also since the nowcast velocity gradient fields were much less noisy than the observations this may be an effective method for preconditioning high resolution observation sets for assimilation into a numerical model

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

circulation over the continental shelf in the northern gulf of mexico abstract more than 750 surface drifters were deployed over the northern continental shelf in the gulf of mexico gulf from 1993 through 1998 drifters were mostly air deployed on a schedule giving continuous data over much of the texas louisiana and west florida shelves for an entire year the drifter data are analyzed to give descriptive statistical and dynamical views of the northern gulf circulation on synoptic to seasonal scales circulation on both the texas louisiana and west florida shelves is characterized by coherent along shore and across shore modes which explain more than 50 of the variance a pronounced seasonal cycle exists on the texas louisiana shelf but not the west florida shelf both shelves display synoptic signals due to local wind forcing strong connectivity between the shelves occurs during isolated period of strong winds associated with the passage of tropical storms eddies impinging upon the shelf are responsible for moving drifters cross shore offshore flows generally occur prior to reversals in the along shore direction regions with near zero mean velocities but large total energy exist drifters leave these areas and move thorough much of the gulf and into the atlantic within 90 days despite negligible annual mean eulerian velocities

centrifuge modeling of fault propagation through alluvial soils the behavior of alluvial deposits subjected to fault movements in the underlying bedrock is of major concern for critical structures located within fault zones an understanding of fault propagation through soils would assist in design of such structures but could also be utilized in geological interpretation of fault displacement history on the premise that alluvial fault morphology contains shear patterns characteristic of modes and rates of fault displacements a study was undertaken involving centrifugal and numerical models of reverse faulting this paper describes the centrifuge model testing performed to backup simultaneous numerical studies geognosis report 1980 which will be described elsewhere a comprehensive model test series under earth gravity conditions 1g involving reverse and normal faulting under different angles has recently been undertaken by cole 1979 however model tests performed under 1g conditions are limited to rather thin soil layers because of their inability to simulate realistic gravity stress conditions furthermore it is not possible to simulate faulting fast enough to include inertial effects with such models

origins of karenia brevis harmful algal blooms along the texas coast the dinoflagellate karenia brevis is the major harmful algal bloom hab species in the gulf of mexico given that the rapid appearance of k brevis cannot be explained by plankton growth alone advection is likely important in bloom initiation forward and backward moving numerical surface drifters were employed in a numerical model of the texas louisiana shelf to help determine the basic physical mechanisms explaining sporadic interannual occurrences of k brevis along the texas coastline results from data analysis from the area show that hab events occur in years in which there are weaker mean downcoast along shore wind speeds the drifter experiments suggest that southern waters play a role in hab event initiation providing an offshore source of cells at the end of summer as winds switch from upcoast to downcoast in early fall offshore populations of k brevis are swept southward by wind driven currents in years with strong downcoast winds however when the downshore wind is weak shoreward ekman transport creates a convergent flow near the coast that allows cells to concentrate and initiate a bloom

aspects of warm rings in the gulf of mexico various aspects of warm rings in the gulf of mexico were derived from satellite infrared data and ship of opportunity data after the warm rings separate from the loop current they move into the western gulf of mexico it was shown from 12 years of data 1973 through 1984 that there are three characteristic paths of movements of the rings a northern path a mid gulf path and a path that takes the rings into the southern extremities of the western gulf of mexico it was shown that all three paths eventually lead the ring to a region in the northwestern portion of the western gulf of mexico the area defined by 25 n to 28 n and 93 w to 96 w as the rings move from the eastern gulf to the western gulf the speed of the ring was observed to oscillate the oscillation is over a speed range from 1 to 8 km per day on the average and the period varies from 40 to 100 days the average speed of the ring was 5 km per day after the ring separates from the loop current the surface area of the ring decreases to about 55 percent of its initial size in approximately 150 days and to about 31 percent of its initial size in about 300 days

fault movement and its impact on ground deformations and engineering structures in many regions around the world engineering structures such as earth dams buildings pipelines landfills bridges roads and railroads are often built in areas very close to strike slip fault segments for the safe design of these structures earthquake and geotechnical engineers need a reliable estimate of the ground deformations that fault movements will induce at the sites of the proposed structures the estimation of the vertical ground deformations associated with the movement of strike slip fault segments is the focus of this proposed study these vertical ground deformations are the result of stresses concentrated by the ends of active fault segments in this study the stresses and the resulting tri dimensional vertical ground deformations that develop around moving fault segments were obtained using linear elastic fracture mechanics theory the theoretical analysis was used to estimate the amount of vertical deformation experienced by the ground surrounding a strike slip fault segment in china that mobilized during the 1970 tonghai earthquake the calculated vertical deformations and the ones measured in the field compared well

reconstructing basin scale eulerian velocity fields from simulated drifter data abstract a single layer reduced gravity double gyre primitive equation model in a 2000 km 2000 km square domain is used to test the accuracy and sensitivity of time dependent eulerian velocity fields reconstructed from numerically generated drifter trajectories and climatology the goal is to determine how much lagrangian data is needed to capture the eulerian velocity field within a specified accuracy the eulerian fields are found by projecting on an analytic set of divergence free basis functions drifter data launched in the active western half of the basin supplemented by climatology in the eastern domain the time dependent coefficients are evaluated by least squares minimization and the reconstructed fields are compared to the original model output the authors find that the accuracy of the reconstructed fields depends critically on the spatial coverage of the drifter observations with good spatial coverage the technique allows accurate eulerian reconstructions with under 200 drifters deploy

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

wind modulated buoyancy circulation over the texas louisiana shelf this numerical investigation examines buoyancy driven circulation on the texas louisiana shelf modulated by seasonal winds in wintertime with downcoast in the direction of kelvin wave propagation wind forcing the mississippi atchafalaya river plume exhibits a bottom advected pattern the plume is fairly wide and the horizontal density gradients span almost across the entire shelf inshore of 50 m within the plume vertical shear of alongshore flow is in thermal wind balance with the cross shore density gradient and the shear causes a slight reversal of alongshore flow near the bottom an alongshore flow estimated by the thermal wind relation along with an assumption of zero bottom velocity generally well agrees with the actual flow near the surface in regions deeper than 20 m in spring and summer the thermal wind balance derived flow deviates from the actual alongshore flow and an ekman flow driven by strong onshore wind makes the major contribution to the deviation besides the summertime upcoast wind component transforms the plume to a surface advected state resulting in reduced cross shore density gradients and increasing the relative importance of wind driven barotropic alongshore flow which contributes to the remaining deviation

objectively mapped stream function fields on the texas louisiana shelf based on 32 months of moored current meter data on the basis of current measurements observed at 31 moorings during april 1992 through november 1994 as part of the texas louisiana shelf circulation and transport processes study we describe the horizontally nondivergent part of the near surface shelf wide scale low frequency circulation and its variability on the texas louisiana continental shelf by means of objectively fitted stream function fields the 32 month mean velocity stream function patterns generally support the cochrane and kelly 1986 circulation schema for the shelf circulation in which an elongated cyclonic gyre exists during the nonsummer period september through may but with flow in the summer june to august directed upcoast toward the mississippi delta over the entire shelf there exists significant interannual variability of the stream function fields especially in the transition period from spring to summer to fall and along the shelf break strong upcoast downcoast currents dominate at the western shelf break associated with the presence of energetic anticyclones cyclones the dominant pattern of stream function variability deduced by empirical orthogonal function eof analysis of 32 individual monthly mean patterns contains about 89 of the variance and shows a simple shelf wide along shelf pattern of circulation the monthly evolution in amplitude of this dominant eof pattern clearly mimics the monthly evolution of the along shelf component of the wind with squared correlation of 0 83 this provides strong evidence that the seasonal variation of the shelf circulation is wind forced in support of cochrane and kelly the second and residual eofs show more complex features near the shelf break that are associated with loop current eddies known to impact the continental slope and shelf break

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

active alluvial systems in the korla basin tien shan northwest china sedimentation in a complex foreland basin the tien shan is a cenozoic orogenic belt in central asia caused by the post collisional convergence of india with asia that reactivated palaeozoic faults the korla basin is a complex foreland basin within the chinese tien shan elongate sub basins within it have received sediment from both the hangingwall and footwall blocks above and below reverse faults on their northern margins the footwall blocks are themselves uplifted by the next fault to the south the greater part of the sediment supply measured by area comes from the footwall block this sediment supply pattern is analogous to that of extensional half graben

shallow structure of the tangshan fault zone unveiled by dense seismic array and horizontal to vertical spectral ratio method abstract the tangshan fault zone has been considered to be a potential seismogenic fault from the devastating 1976 ms 7 8 tangshan earthquake based on the dense seismic array with interstation distance of 1 km and length of 40 km hvsr horizontal to vertical spectral ratio curves at 37 stations are obtained with the micro tremor seismic waveforms and the two dimensional quaternary sedimentary structures cross the tangshan fault zone are imaged by frequency to depth conversion results suggest that two significant seismic impedance interfaces at 100 m and 300 800 m depth are clearly revealed respectively the interface at 100 m depth can be attributed to the strong contrasts between the unconsolidated sand clay and semi consolidated silt which suggests very small variations and is well consistent with the seismic reflection interface from shallow seismic reflection exploration while the deeper interface at 300 800 m depth can be attributed to the quaternary sedimentary basement which increases from 300 to 800 m from the west to the east and is also consistent with the results in previous studies rapid variations 200 m of the quaternary sedimentary basement depth just beneath the fault zone well agrees with spatial characteristics of the fault revealed by deep seismic reflection profiling our work suggests that the tangshan fault zone has been significantly ruptured and modified by strong earthquake activities since quaternary this study also suggests that the hvsr method with dense seismic array is an efficient effective non invasive and low cost method for investigating active faults in shallow sediments it is useful for probing the active faults buried by thick sediments in the densely populated urban settings where seismic investigation with explosive sources are too hazardous to carry out

near inertial oscillations over the texas louisiana shelf wind induced near inertial oscillations over the texas louisiana shelf in spring and summer 1992 are described using the current and wind observations taken during the first year of the texas louisiana shelf circulation and transport processes study latex a rotary spectral analysis shows clockwise rotating energy peaks at near inertial frequencies for records from all current meter moorings after the suppression of principal tidal signals the vertical structure of near inertial oscillations is characterized by a first baroclinic mode with a near 180 phase difference between the upper mixed layer and the lower stratified layer the oscillations are intermittent with a modulation timescale of about 5 10 days they are surface intensified and have maximum values near the shelf break decaying gradually toward the coast but rapidly offshore near inertial oscillations appear to accompany a sudden change of the wind stress during frontal passages diagnostic analysis suggests that the large near inertial oscillations over the latex shelf are mainly generated by high frequency near inertial variation of the wind stress accompanying the passage of atmospheric fronts when the downward transfer of the near inertial energy to the deep stratified layer is small a simple mixed layer model forced by the observed wind stress provides a reasonable prediction of the near inertial currents in the mixed layer

processes controlling mid water column oxygen minima over the texas louisiana shelf we investigate distributions of dissolved oxygen over the texas louisiana shelf using spatially highly resolved observations in combination with a regional circulation model with simple oxygen dynamics the observations were collected using a towed undulating ctd during the mechanisms controlling hypoxia mch program mid water oxygen minimum layers dissolved oxygen lower than 3 2 ml l 1 were detected in many transects these oxygen minimum layers are connected with the bottom boundary layer and follow the pycnocline seaward as a tongue of low oxygen into the mid water column t s diagrams highlighting the low oxygen minima in both observations and simulations imply direct connections between low oxygen bottom water and the oxygen minimum layer the dynamics of these oxygen minimum layers in the mid water column are examined using a three dimensional hydrodynamic model based on the regional ocean modeling system roms convergence within the bottom boundary layer relative to density surfaces is calculated results show that there is a convergence in the bottom boundary layer at the location where the pycnocline intersects the bottom buoyancy advection forced by bottom ekman transport creates this convergent flow and the corresponding low oxygen intrusion similar intrusions of near bottom water into the pycnocline are observed in other regions the presence of hypoxia within the bottom boundary layer in the northern gulf of mexico creates a unique situation in which these intrusions are also associated with low dissolved oxygen

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

the role of bed parallel slip in the formation of blind thrust faults abstract a finite element code is used to model the mechanical behaviour of elastoplastic sedimentary layers that are deformed by the movement of a faulted deformable basement the propagation of the blind thrust fault is analysed in terms of the evolution of strain localization in the elastoplastic layers of strain softening and strain hardening materials the role of layer thickness bedding parallel slip and fault dip are also studied we found that if no interlayer slip is allowed blind thrusts tend to propagate with constant dip regardless of the rheological properties of the sediment layers however if bedding parallel slip is present a mechanical decoupling appears between layers allowing stress transfers along large distances and favouring the formation of backthrusts fault dip also has significant influence on the qualitative behaviour when interlayer slip is possible a steep fault will tend to split

deformation of overburden soil induced by thrust fault slip abstract when the blind thrust fault slips due to earthquakes overburden soil strata may deform and fail leading to a development of a coseismic fault zone how overburden soil strata will deform or be faulted is an essential issue in the evaluation on the safety of ground underground infrastructures located near the potential plastic zone on the basis of previous work by cole and lade cole d a lade p v 1984 influence zones in alluvium over dip slip faults journal of geotechnical engineering 110 599 615 this research further explores the processes of thrust faulting within overburden soil and examines the influences of corresponding factors or parameters under a range of boundary conditions using physical models and numerical analysis for both small scale and full scale configurations factors explored include uplifting rate fault dip angle dilation angle of plastic flow young s modulus poisson ratio cohesive strength frictional angle scaling as well as the location of ground loadings applied on ground surface the experimental results indicate that although one major fault slip surface can be developed subsidiary faults may also form which requires special attention when defining stain patterns young s modulus and the dilation angle are the most influential parameters in our models a stiffer e leads to early fault propagation and the occurrence of back thrusts and causes more significant discrepancies in the deformation behaviors of models with different scales a greater dilation angle of the overburden soil leads to a wider fault zone the above mentioned phenomena highlight that a careful consideration of the applicable young s modulus and the dilation angle is essential in a proper simulation or prediction of the fault zone development for small scale physical models used to simulate the fault development for a full scale problem the stiffness of model soil should be properly scaled down which still requires further study

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

mass wasting on the mississippi river subaqueous delta abstract the mississippi river delta front mrdf is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to seafloor failures the occurrence of seafloor landslides on the mrdf has been recognized since the 1950s but the bulk of research on the topic was conducted in the 1970s 80s after seafloor landslides triggered by hurricane camille damaged offshore infrastructure through these efforts it was recognized that seafloor instability features are present across the entire delta front that rapid sediment delivery from the mississippi river is a primary preconditioning factor for failures and that cyclic loading from hurricane waves is the main triggering mechanism for deep seated catastrophic events however mounting evidence shows that mrdf seafloor motion occurs even during periods of no hurricane activity which could be attributed to creep like motion of underconsolidated sediment or smaller episodic flows triggered by winter storms or mississippi river floods given the extensive spatial distribution of instabilities on the mrdf the multiple mechanisms of failure and variety of resulting morphology and the range of potential triggering mechanisms with short recurrence the mrdf is an exceptional location to assess the complex problem of seafloor landslides an improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling as they can evacuate large volumes of sediment into deep water over short time periods additionally seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments this paper presents a review and synthesis of geological and geotechnical research on the mrdf particularly with respect to seafloor landslides their occurrence geological and geotechnical controls triggering mechanisms and knowledge gaps related thereto this synthesis is conducted at times of rapidly developing technologies for studying seafloor instability and as the mrdf enters a stage of degradation characterized by reduced sediment delivery and accumulation

centrifuge modeling of pile sand interaction induced by normal faulting abstractmany forensic studies conducted after catastrophic earthquakes revealed severe damages to pile foundations caused by bedrock fault movement the mechanism behind these pile foundation failures is not yet fully understood in this study two centrifuge model tests are carried out on a single pile and on a group of three piles in sand subjected to normal faulting the surface settlement profile and additional internal forces of the piles are measured the surface settlement profile in sand could be well fitted and predicted with a profile function error function the single pile which is located in a differential settlement zone is displaced and the pile top rotates toward the hanging wall inducing an additional bending moment along the pile the pile group is then forced to rotate toward the hanging wall because the three piles are well connected to the pile cap driven by the movement of the two additional piles and a pile cap in place the pile on the footwall side experiences greater displ

eddy energy and shelf interactions in the gulf of mexico sea surface height anomaly data from satellite are continuously available for the entire gulf of mexico surface current velocities derived from these remotely sensed data are compared with surface velocities from drifting buoys the comparison shows that satellite altimetry does an excellent job resolving gulf eddies over the shelf rise depths between 200 and 2000 m if the proper length scale is used correlations between altimeter and drifter derived velocities are statistically significant r 0 5 when the surface slope is computed over 125 km indicating that remotely sensed sea surface height anomaly data can be used to aid the understanding of circulation over the shelf rise velocity variance over the shelf rise from the altimetry data shows regions of pronounced eddy energy south of the mississippi outflow south of the texas louisiana shelf and in the northwest and northeast corners of the gulf these are the same locations where surface drifters are most likely to cross the shelf rise suggesting gulf eddies promote cross shore flows this is clearly exemplified with both warm and cold eddies finally the contribution of gulf eddies and wind stress to changes in the mean circulation are compared results indicate that the eddy generated vorticity flux to the mean flow is greater than the contribution from the surface wind stress curl especially in the region of the loop current and along the shelf rise base in the western gulf future modeling efforts must not neglect the role of eddies in driving gulf circulation over the shelf rise

effects of the hanging wall and footwall on ground motions recorded during the northridge earthquake abstract systematic differences in ground motion on the hanging wall and footwall during the northridge earthquake are evaluated using empirical data an empirical model for the hanging wall effect is developed for the northridge earthquake this empirical model results in up to a 50 increase in peak horizontal accelerations on the hanging wall over the distance range of 10 to 20 km relative to the median attenuation for the northridge earthquake in contrast the peak accelerations on the footwall are not significantly different from the median attenuation over this distance range recordings from other reverse events show a similar trend of an increase in the peak accelerations on the hanging wall indicating that this systematic difference in hanging wall peak accelerations is likely to be observed in future reverse events

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

centrifuge and numerical modeling of normal fault rupture propagation in clay with and without a preexisting fracture abstractover the last few decades extensive research has been conducted to investigate fault rupture propagation induced by faulting through uncemented soil while it has long been realized that many natural soils are cemented relatively few publications have been devoted to investigating fault rupture propagation in cemented soil moreover preexisting fracture in soil may be reactivated during earthquakes and its influence on fault rupture propagation is not fully understood in this study three centrifuge model tests are reported on investigating fault rupture propagation induced by normal faulting in uncemented clay and cemented clay with and without a preexisting fracture preliminary numerical analyses of the centrifuge tests are also carried out to study the mechanism of fault rupture propagation in these three ground conditions ground deformation was dominated by a shear mechanism in uncemented clay and a shear zone along the projection of the bedrock fault plane was observed on the other h

quantitative description and analysis of earthquake induced deformation zones along strike slip and dip slip faults 1 deformation zones are belts of high strains that can occur at the ground surface centered or asymmetrical relative to the trace of an earthquake fault and can range in width from a meter or two up to hundreds of meters in order to minimize damage to engineering structures within deformation zones one needs to be able to determine the characteristics of the deformation zones we develop an elastic plastic model of fault slip propagation to explain formation of deformation zones and estimate certain parameters to characterize deformation zones our theory suggests the ratio of widths of deformation zones in hanging wall and footwall of dipping faults should be controlled by fault dip angle and the kind of fault the relations are different for strike slip and dip slip faults also the total width of the deformation zone normalized with fault slip during the earthquake should be determined by the dip angle the exponent of the yield condition and the kind of fault the theoretical parameters measured for deformation zones along the strike slip duzce bolu fault at kaynasli turkey and two deformation zones along the chi chi thrust fault taiwan agree well with parameters determined from geophysical and geological sources the theoretical model also indicates that the winnetka strain belts related to the 1994 northridge earthquake could have formed above a previously unknown blind fault at winnetka the analysis suggests that the winnetka fault is a normal dip slip fault dipping 54 s with a fault tip depth of 360 m

low frequency circulation on the texas louisiana continental shelf for the texas louisiana coast west of 92 5 w long series of data from near freeport texas together with shorter series from other locations show strong response of coastal current to wind stress in agreement with coastal jet concepts we infer from coastal winds scattered current measurements and distributions of sea surface salinity and geopotential that a cyclonic gyre elongated along the shelf is the dominant feature of the prevailing shelf circulation the inshore limb of the gyre is the coastal jet driven by wind with a west or southward downcoast component which prevails along much of the coast except in july august because the coast is concave the shoreward prevailing wind results in a convergence of coastal currents which marks the downcoast extent of the gyre corresponding to the convergence is a seaward flow which forms the southwest limb of the gyre a prevailing countercurrent north or eastward flow along the shelf break includes the outer limb of the gyre the eastern shoreward flowing limb of the gyre corresponds to divergence along the coast centered near 92 5 w the convergence at the western or southern end of the gyre migrates seasonally with the direction of the prevailing wind reaching south of the rio grande mouth in fall and the cameron offing in july the gyre is normally absent in july but reappears in august september when a downcoast wind component develops

sedimentological response of an alluvial system to neogene thrust tectonics atacama desert northern chile the llano de la paciencia is a thrust sheet top basin in which the sedimentological and topographic evolution can be linked to thrust tip propagation it is an elongate gravel plain which borders the salar de atacama a major intermontane basin in the andean forearc of northern chile the llano is bounded to the west by the cerros de purilactis a cretaceous paleocene sequence uplifted by the frontal domeyko thrust the eastern margin of the llano is formed by the cordillera de la sal which was uplifted by a linked back thrust frontal thrust system the salar de atacama is thus divided into a number of discrete sub basins the llano de la paciencia the pampa visachita and the western sub llano which from east west are bounded by the cordillera de la sal the northern imbricates and the ignimbrite back thrust two phases of sedimentological evolution can be distinguished within the llano on the basis of quaternary to recent sediment dispersal patterns initially phase 1 alluvial fan lobes prograded eastwards into the main salar de atacama basin subsequently uplift of the cordillera de la sal deflected drainage systems southwards parallel to the structural strike these phase 2 alluvial deposits drain into the salar de atacama at the lateral termination of the cordillera de la sal frontal thrust in places where thrust tip ramps are emergent within the llano gullies have been incised into the drainage pathways this has resulted in the reworking of the early phase 1 gravels and progradation of the phase 2 fan lobes the evolution of the llano de la paciencia illustrates the close link between topography and syntectonic alluvial drainage patterns in an arid intermontane basin

eddy and wind forced shelf circulation cochrane and kelly 1986 proposed a cyclonic gyre as the large scale mean circulation on the louisiana texas latex shelf produced by a convergence of coastal currents in the west and a divergence in the east while currents near the coast are presumably wind and buoyancy driven the origin of the eastward flow on the outer shelf and shelf break which forms the seaward limb of the gyre as well as the near shore convergence and divergence are not well understood a numerical model is used to show that the western convergence and shelf break current are driven by collision and stalling of westward propagating loop current eddies in the northwest gulf of mexico and the divergence in the east is caused by shoreward intrusion in the mississippi canyon the western convergence and shelf break current are modulated by the wind curl strongest in summer and weakest in winter on the shelf westward transport is comparable to that observed 0 15 sv 1 sv 106 m3 s 1 only when the westward wind stress is significant 0 3 dyn cm 1 a peak transport of 0 21 to 0 25 sv occurs in autumn of which 0 1 sv is due to wind 0 07 sv is due to river buoyancy and 0 04 to 0 08 sv is due to eddies without the mean westward wind buoyant waters from the mississippi do not spread onto the latex shelf

geomorphology and surface tilting in an active extensional basin sw montana usa the valley and alluvial cone of the antecedent madison river in the missouri flats area of sw montana lie in a half graben bounded by a prominent prehistoric fault scarp footwall sourced alluvial fans and fans derived from a major transfer zone have prograded onto the oldest of a prominent suite of three paired terraces of holocene age which bound the modern braided floodplain of the river the terraces have been cut into the pleistocene alluvial cone and are cut by the prehistoric fault scarp levelling studies on the terrace surfaces in the hangingwall reveal that movement on the fault has caused surface tilting erosion and deposition a suite of terraces present in the footwall of the fault shows backtihing consistent with footwall uplift having occurred

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

evolution of coseismic fault related folds induced by the chi chi earthquake a case study of the wufeng site central taiwan by using 2d distinct element modeling abstract coseismic fault propagation folds are generally associated with blind faults which are of considerable academic interest and have recently been recognized as critical for assessing seismic hazards the wufeng excavation site was characterized by a major east dipping basal thrust exhibiting a dip angle of 34 and 2 opposing vergent thrusts generated a pop up anticlinal fold in soil cover induced by the 1999 chi chi earthquake mw 7 6 in order to represent the soft soil behavior we set up a direct shear simulation test to obtain valid parameters for soil a series of 2d distinct element models possessing different bonding types and strengths was conducted to determine the deformation pattern near the surface and the evolution of the fault tip propagation the coseismic deformation features of soft and plastic soil cover like the mutative limb thickness complex ruptures and the overturned forelimbs in small scale caused by the propagation of the blind fault tip were accurately predicted by contact bond model in which grains were allowed to rotate and slip without cements breaking our results show that the alternative thrusts and pop up structure developed before the main basal thrust fault ruptured through the ground surface at the wufeng excavation site we evaluated the slipping distance of the main fault at approximately 6 m in wufeng during the 1999 chi chi earthquake

can general circulation models be assessed and their output enhanced with drifter data drifter data from the gulf of mexico are used to assess and enhance the output of a primitive equation general circulation model the analysis is made in a 450 km 450 km open subdomain encompassing a loop current ring the model velocity field is compared with position data from four drifters at the drogue depth of 50 m using geometrical orthogonal functions gof an eulerian velocity field is reconstructed from the model velocity field and drifter velocities this reconstructed velocity improves 8 day numerical trajectories relative to the model field by at least an order of magnitude as quantified by two lagrangian error metrics referenced to the real drifter paths an eulerian metric that compares the two fields however does not exceed 7 for the 20 day assessment period thus the drifter data may be reproduced with modest impact on the model velocity enhancement of the model velocity field is determined by two tests the ability of the gof velocity field to 1 improve the forecast of drifter positions using only a posteriori data and 2 improve the forecast of withheld drifter data using a posteriori data the 20 day temporal mean of the position error is improved for all drifters by 87 89 for 6 hour and 26 38 for 30 hour forecasts for 6 days a withheld drifter is 35 40 km from a drifter whose velocity is used in the reconstructed velocity field the temporal mean of the position error during this period is improved by 20 for 6 hour and 26 for 30 hour forecasts

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

near surface currents in desoto canyon 1997 99 comparison of current meters satellite observation and model simulation this study evaluates a data assimilated model simulation of near surface circulation in desoto canyon dsc gulf of mexico with emphasis on analyzing moored current meter observations and comparing them with satellite data and model results the study period is for two years from april 1997 to april 1999 the model results are from a high resolution gulf of mexico model forced by analyzed wind and surface heat flux two types of data are used to deduce near surface circulation moored current meters at 13 locations in the dsc and satellite sea level anomaly the moored currents are mapped through multivariate objective analysis to produce surface currents and surface geopotentials against which satellite and model derived sea surface heights and geostrophic currents are compared coupled patterns between the observations model results and satellite data are obtained using the singular value decomposition svd analysis there are two dominant modes a single eddy mode in which currents are concentrated at the foot of the canyon and an eddy pair mode in which one eddy is at the foot of the canyon and the other a counterrotating eddy is over the head of canyon mode 1 appears to be associated with the mesoscale eddy traveling around the loop current crest and trough and mode 2 is associated with the intrusion of loop current crest and trough over the west florida shelf the observed and model currents are in good agreement about the means and variances the model currents also appear to be well constrained by the steep topography however the model velocity field contains only the first mode the satellite derived velocity field on the other hand contains both the first and second modes though the satellite field does not adequately resolve the velocity structures over the slope

late pleistocene shortening rate on the northern margin of the yanqi basin southeastern tian shan nw china abstract how strain is distributed and partitioned on individual faults and folds on the margins of intermontane basins remains poorly understood the haermodun ha anticline located along the northern margin of the intermontane yanqi basin on the southeastern flank of the tian shan preserves flights of passively deformed alluvial terraces these terraces cross the active anticline and can be used to constrain local crustal shortening and uplift rates geologic and geomorphic mapping in conjunction with high resolution dgps topographic surveys reveal that the terrace surfaces are perpendicular to the fold s strike and display increased rotation with age implying that the anticline has grown by progressive limb rotation combined with the open sinusoidal curve model and excess area method we calculated uplift and shortening values for each terrace since abandonment using the published exposure ages of each terrace we found the vertical uplift rate gradually decreased from 0 43 to 0 11 mm a whereas the shortening rate remained constant at 0 3 mm a since the anticline began to grow a fresh fault scarp 0 4 0 1 m high is visible along the southern portion of the ha anticline and is interpreted to be the most recent evidence of seismic activity using an estimated rupture area and the length of the fresh offset created by this earthquake we estimate that the main thrust underlying the ha anticline has generated moderate m

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

fall winter current reversals on the texas louisiana continental shelf abstract fall winter recurrence of current reversal from westward to eastward is identified on the texas louisiana continental shelf using the current meter texas louisiana shelf physical oceanography program latex a and near surface drifting buoy surface current and lagrangian drift program sculp 1 observations in 1993 and 1994 reversal events roughly satisfy the poisson distribution with one current reversal nearly every 12 days synoptic winds seem responsible for the current reversal events other processes such as offshore eddies shed from the loop current and river runoff are less important to change alongshore flow direction at synoptic scales a statistical model is established to predict the synoptic current reversal using the surface wind observations

low frequency waves in the santa barbara channel observed by high frequency radar are antisymmetric with a mean propagation speed of 5k m d 1 and relative vorticity of order 0 1 f complex empirical orthogonal function decomposition in the 10 20 day passband partitions variance into two dominant modes the first mode represents the vortices with an average period of 14 4 days the second mode represents alongshore fluctuations with an average period of 13 3 days amplitude functions of the two modes correlate with in situ current time series at 5 and 45 m depths obtained from moorings at the east and west channel entrances suggesting coupling with the larger scale circulation of the northern southern california bight the observations support interpretation of mode 2 as a coastal trapped wave since the period and alongshore flow are consistent with previous observations and predictions we hypothesize that mode 1 is a resonant response of the santa barbara basin in the form of a trapped topographic rossby mode the spatial mode resembles the predicted pattern based on a simplified analytical model of the fundamental mode the amplitude of mode 1 is consistently large when the frequencies of modes 1 and 2 converge suggesting that the vortices are a basin scale resonant response to coastal trapped waves index terms 4520 oceanography physical eddies and mesoscale processes 4512 oceanography physical currents 4508 oceanography physical coriolis effects 4516 oceanography physical eastern boundary currents 4544 oceanography physical internal and inertial waves keywords propagating eddies santa barbara channel coastal trapped waves citation beckenbach e and l washburn 2004 low frequency waves in the santa barbara channel observed by high frequency radar j geophys res 109 c02010 doi 10 1029 2003jc001999

near resonant ocean response to sea breeze on a stratified continental shelf abstract the spatial structure and temporal characteristics of sea breeze and the associated coastal ocean response in the northwest gulf of mexico are investigated using moored instruments hydrographic stations and wind measurements near the study area of 30 n motions in the diurnal inertial band dib may be significantly enhanced by a near resonant condition between local inertial and diurnal forcing frequencies wavelet analysis is used to quantify the results results indicate that diurnal sea breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation the maximum dib oceanic response occurs in june when there is a shallow mixed layer strong stratification and an approximately 10 day period of continuous sea breeze forcing dib current variance decreases in july and august as the consequence of the deepening of the mixed layer and a more variable phase relationship between the wind and current river discharge varies interannually and can s

climatically controlled formation of river terraces in a tectonically active region along the southern piedmont of the tian shan nw china abstract combined tectonic uplift and quaternary climate variability control the deposition and abandonment of terraces along the southern tian shan in northwest china several preserved terraces have been deformed by an actively growing anticline within the uplifted frontal thrust system of the southern tian shan we combine geomorphic mapping topographic surveys of the deformed terrace surfaces 10be terrestrial cosmogenic nuclide tcn depth profile dating and optically stimulated luminescence osl dating to develop a new chronology for the terraces along the huangshui he since 550 ka our in situ 10be dating of fluvial gravels capping strath terraces suggests a relationship between the formation and abandonment of the terraces and glacial climate cycles since the middle late pleistocene these data indicate that the formation of the four terraces occurred at 550 430 350 and 60 ka we suggest that episodes of aggradation were facilitated by high sediment supply during glacial periods followed by subsequent incision that led to abandonment of these terraces during deglaciation we also estimate that tectonically induced river incision may account for about 60 70 of the total incision however during the intervening time between 350 ka and present only one terrace was formed and preserved we suggest that this record might be caused by a gradually decreasing uplift rate of the anticline through time and thus has influenced the preservation of terraces therefore our results demonstrate the utility of chronologic records from southern tian shan for deconvolving the effects of tectonics and climate on fluvial incision

anomalous streamflow and groundwater level changes before the 1999 m7 6 chi chi earthquake in taiwan possible mechanisms streamflow recorded by a stream gauge located 4 km from the epicenter of the 1999 m7 6 chi chi earthquake in central taiwan showed a large and rapid anomalous increase of 124 m3 s starting 4 days before the earthquake this increase was followed by a comparable co seismic drop to below the background level for 8 months in addition groundwater levels recorded at a well 1 5 km east of the seismogenic fault showed an anomalous rise 2 days before the earthquake and then a unique 4 cm drop beginning 3 h before the earthquake the anomalous streamflow increase is attributed to gravity driven groundwater discharge into the creek through the openings of existing fractures in the steep creek banks crossed by the upstream shueilikun fault zone as a result of pre earthquake crustal buckling the continued tectonic movement and buckling together with the downward flow of water in the crust may have triggered the occurrence of some shallow slow slip events in the shueilikun and other nearby fault zones when these events propagate down dip to decollement where the faults merges with the seismogenic chelungpu fault they may have triggered other slow slip events propagating toward the asperity at the hypocenter and the chelungpu fault these events may then have caused the observed groundwater level anomaly and helped to trigger the earthquake

the fate of terrigenous dissolved organic carbon in a river influenced ocean margin the mineralization of terrigenous dissolved organic carbon tdoc discharged by rivers can impact nutrient and trace metal cycling biological productivity net ecosystem metabolism and air sea co2 exchange in ocean margins however the extreme heterogeneity of river influenced ocean margins represents a major challenge for quantitative assessments of tdoc transformations and thereby obscures the role of tdoc in biogeochemical cycles here a lignin based optical proxy for tdoc and a shelf wide mass balance approach were used to quantitatively assess the fate of tdoc discharged from the mississippi atchafalaya river system m ars to the louisiana shelf the mass balance revealed that 40 of the tdoc discharged by the m ars during march 2009 2010 was mineralized to co2 on the louisiana shelf with two thirds of the mineralization taking place in the mixed layer a strong seasonality in tdoc mineralization was observed with mineralization rates severalfold higher during summer than during winter independent assessments of specific mineralization processes indicated biomineralization accounted for 94 of the tdoc mineralization on an annual basis and suggest that photochemical transformations of tdoc enhanced biomineralization by 50 in the mixed layer direct photomineralization accounted for a relatively small fraction 6 of the tdoc mineralization on an annual basis this quantitative assessment directly confirms that ocean margins are major sinks of the tdoc discharged by rivers and indicates that tdoc mineralization rates in the shelf mixed layer are sufficiently large to influence whether the louisiana shelf is a net sink or source of atmospheric co2

evolution of the surface deformation profile and subsurface distortion zone during reverse faulting through overburden sand abstract the 2d distinct element method was used to investigate the propagation of fault rupture traces through overlying sand during reverse faulting along a range of dip angles and at different vertical throws calibrated micromechanical material parameters were used in the numerical simulations which were validated through a comparison of the simulation results with those obtained from a centrifuge experiment involving acceleration at 80 g the gompertz sigmoid function with three parameters provided the best fit to the normalized surface deformation profiles obtained both from the numerical simulation and from centrifuge experiments the three parameters that characterized the gompertz sigmoid function were the normalized scarp height the maximum slope on the scarp and the location of the reverse fault outcropping a surface deformation profile slope of 1 150 was used as the setback criterion the normalized affected width and fault outcrop relative to the fault tip were determined for reverse faults having a variety of dips and throws the dip angle significantly affected the kinematic mechanism underlying reverse faulting at a given vertical throw the scarp height increased as the dip angle decreased in the cases of 45 as the dip angle decreased the location of the fault outcropping shifted toward the footwall and the maximum slope on the scarp increased the horizontal displacement played a significant role at low dip thrusts 22 5 30 37 5 a back thrust fault developed and an inverted triangle wedge formed in the subsurface

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

the annual cycle of riverine influence in the eastern gulf of mexico basin 1 the annual cycle of the surface salinity field in the eastern gulf of mexico gom basin is investigated with a numerical model and observational data a tongue of low salinity water is evident in the model climatology spreading southward from the mississippi alabama florida mafla shelf and de soto canyon in the summer the model salinity climatology along this path compares well to historical observations this climatological feature is a consequence of the seasonal availability of low salinity water over the mafla shelf and de soto canyon for entrainment into jets associated with the mesoscale eddy field in the northern gom additionally the chlorophyll a monthly climatology from satellite data shows elevated concentrations in a tongue like pattern similar to the low salinity feature found in the model suggestive of a biological connection between the eastern gom basin and river discharge in the northern gom

quaternary folding of the eastern tian shan northwest china abstract the tian shan east west trending more than 2000 km is one of most active intracontinental mountain building belts that resulted from india eurasia collision during cenozoic in this study quaternary folding related to intracontinental mountain building of the tian shan orogenic belt is documented based on geologic interpretation and analyses of the satellite remote sensing images landsat thematic mapper tm enhanced thematic mapper etm and india remote sensing irs pan combined with field geologic and geomorphic observations and seismic reflection profiles analyses of spatial temporal features of quaternary folded structure indicate that the early quaternary folds are widely distributed in both piedmont and intermontane basins whereas the late quaternary active folds are mainly concentrated on the northern range fronts field observations indicate that quaternary folds are mainly characterized by fault related folding the formation and migration of quaternary folding are likely related to decollement surfaces beneath the fold and fault zone as revealed by seismic reflection profiles moreover analysis of growth strata indicates that the quaternary folding began in late stage of early pleistocene 2 1 1 2 ma finally tectonic evolution model of the quaternary deformation in the tian shan is presented this model shows that the quaternary folding and faulting gradually migrate toward the range fronts due to the continuous compression related to india eurasia collision during quaternary time as a result the high topographic relief of the tian shan was formed