fault related folding near the wind river thrust wyoming usa reflection profiles across the wind river uplift in wyoming usa show that folding of basement rocks occurs in the footwall of the main fault at depths between 6 and 10km it is shown using elastic modelling that these features are a consequence of uneven fault slippage slip on the fault must be greater at depths between 3 and 18 km but reduced outside this range this is the depth range of catastrophic rupture associated with earthquakes in the continental crust

seismic investigation of an active fault off kobe another disaster in the making on 17 january 1995 a magnitude 7 2 earthquake struck the kinki district of southwestern japan this earthquake called the hyogo ken nanbu earthquake but most familiarly known as the kobe earthquake killed more than 6000 people injured about 40 000 people and destroyed about 100 000 houses the hypocenter was about 16 km beneath the akashi strait between akashi city and the northern awaji island figure 1 its focal mechanism is right lateral slip trending northeast southwest which is produced by a regional compressive stress field that trends east west the aftershocks were aligned northeast southwest from north of kobe to the northern awaji island surface ruptures appeared along the nojima fault on the northwest coast of awaji island but no surface ruptures were observed in the kobe area

geographical distribution of surface wave velocities and 3 d upper mantle structure in africa summary long period records of surface waves from wwssn gdsn ida and geoscope stations are analysed to retrieve purely continental dispersion of the african continent in the period range of 20 200 s for rayleigh waves and 20 125 s for love waves the phase and group velocities are obtained by two station and single station methods with earthquakes within or near the continent a regionalization without any a priori constraints is performed over the whole african continent to retrieve local phase and group velocities phase and group velocity geographical distributions show in the northeast of africa near the red sea a region with lower velocities extending to the west and high velocities in the northwestern and southern parts of africa at long periods there is a general agreement with global models but the resolution is improved in this regional study in the resulting 3 d structure cratonic areas show a fast lithosphere from the nw to the se whereas the high sv velocities of the nw area extend deeper than 200 km lower velocities appear below this depth in the centre in the red sea region low velocities are locally deep rooted with a slow lithospheric layer 150 km thick extending to the west in this region polarization anisotropy is evidenced by love rayleigh incompatibility short period lateral variations are used to model the crustal thickness

climatology of 500 mb cyclones and anticyclones 1950 85 abstract the geographical and monthly frequencies of 500 mb cyclones and anticyclones in the national meteorological center analyses over the western half of the northern hemisphere are investigated for the period 1950 85 these cyclones and anticyclones defined by the appearance of at least one closed approximately 6 dekameter contour around relatively low or high heights in the 500 mb height field are generally observed less than ten percent of the time in any 10 by 10 latitude longitude quadrangle with cyclones being more numerous than anticyclones the 500 mb cyclones are found primarily at middle and high latitudes while anticyclones are observed most frequently over the subtropics cyclone frequency increases over the northern oceanic regions during summer while anticyclone frequency increases throughout the subtropics during summer especially over southwestern north america exceptions to these rules are observed relatively high springtime 500 mb anticyclone frequency is found over the n

magnetostratigraphy of plio pleistocene sediments in a 1700 m core from osaka bay southwestern japan and short geomagnetic events in the middle matuyama and early brunhes chrons abstract a magnetic polarity stratigraphy spanning more than the past 3 2 myr was determined for a long 1545 m continuous sedimentary sequence of marine fluvial and lacustrine deposits from the osaka basin southwestern japan additionally two short geomagnetic reversal events were identified a short event at about 0 69 ma lasting for about 7 kyr in the early brunhes chron around the lower boundary of a marine clay deposited during a period of eustatic high sea level during the marine oxygen isotope stage 17 and another short matuyama event 1 60 1 58 ma correlated with stage 54 event and the early stage of the sangiran excursion accumulation rate was 0 3 0 4 mm yr from 3 to 2 ma and then increased by about 50 with a rate of 0 51 mm yr during the olduvai subchron high values of 0 59 mm yr were maintained from the upper olduvai boundary to the brunhes matuyama boundary from 1 77 to 0 78 ma with a peak at 0 74 mm yr during the jaramillo subchron these changes in accumulation rate probably reflect the history of tectonic subsidence of the drilling site the magnetic polarity stratigraphy provides a chronological framework for sedimentological paleoenvironmental tephrochronological and tectonic studies of the osaka basin

propagation history of the osaka wan blind thrust japan from trishear modeling abstract mapping the nucleation and 3d fault tip growth of the active osaka wan blind thrust provides an opportunity to asses how reactivated thrusts build slip from preexisting faults and the threat they pose as sources of large earthquakes analysis of folded growth strata based on 2d trishear inverse modeling allows a range of best fit models of the evolution of slip and propagation of the fault to be defined the depth of the fault tip at 1200 ka varies between 1 5 4 5 km suggesting the fault grew upward from high in the crust and that it is reactivated from its onset at 1500 ka the fault grew rapidly along strike in 300 ky and upwards with a p s ratio of 2 5 3 0 but variable fault slip in space and time shallower depths of the fault tip at initiation and thinner basin fill correlates with slower propagation with time contradicting models that argue for sediments as inhibitors of fault growth results also suggest the displacement profile of the currently active thrust is offset from its predecessor assuming shallower depths to the original fault correlate with greater displacement in its prior history these results suggest reactivated faults may accrue slip differently than newly developed ones based on the history of upward fault propagation

basin formation at a contractional bend of a large transcurrent fault plio pleistocene subsidence of the kobe and northern osaka basins japan abstract the basin formation process at a contractional bend of a large transcurrent fault is studied here from the viewpoint of extensive subsidence history the kobe and northern osaka basins in southwest japan are located at the easternmost left stepping bend of the dextral median tectonic line mtl a fault system activated throughout the quaternary many subordinate faults in these basins accommodate compressive stress whereas differential vertical motion of fault bounded blocks results in complex sedimentation patterns within the basins we compiled stratigraphic information of the late pliocene to pleistocene osaka group using core samples of 19 drill holes distributed in the study area on the basis of magnetostratigraphy tephrochronology and paleoenvironmental analysis 15 datum horizons of transgression which are recognized as bases of marine clays ma 1 to 13 in cores are assigned to the oxygen isotope events an interval accumulation rate between two successive horizons represents a cycle of eustatic sea level changes and thus provides us with an indicator of tectonic subsidence rate subsidence curves and temporal changes in subsidence rates at the drill holes visualize differential subsidence in detail the northern osaka basin is divided into western and eastern depocenters and the central n s uemachi basement high which grew rapidly during the ma 7 8 interval ca 550 kyr whereas the subsidence pattern in the kobe basin is controlled by constant vertical displacements on the ne sw wada misaki fault an interbasinal tectonic episode of sharp decline in subsidence is also detected in the ma 5 6 interval ca 670 kyr coinciding with the mantidani unconformity in the osaka group

numerical modeling of trishear fault propagation folding in contrast to kink band migration modeling methods trishear numerical models produce fault propagation folds with smooth profiles and rounded hinges modeled fold hinges tighten and converge downward within a triangular zone of distributed deformation which is focused on the fault tip such features have been reported from field studies and are also seen in analogue models of compressional deformation however apart from its initial application to laramide folds little quantitative work has been undertaken on trishear fault propagation folding in other settings in addition no study has been undertaken into the growth strata which might be associated with such structures this paper uses an equivalent velocity description of the geometric model of trishear together with models of erosion and sedimentation to investigate trishear fault propagation folding of both pregrowth and growth strata the trishear model is generalized to include a variety of fault propagation to slip ratios and fault propagation from a flat decollement the models show continuous rotation of the forelimb with the characteristic development of cumulative wedges within growth strata when total slip on a structure is high the model predicts overturned pregrowth and growth strata during the initial stages of deformation beds in the forelimb thicken but later thin when they become steep or overturned the effect of variations in fault propagation to slip ratios on two dimensional finite strain in the models is assessed by the use of initially circular strain markers high fault propagation to slip p s ratios lead to narrow zones of high finite strain while lower p s ratios lead to more ductile deformation and broader zones of high strain in all cases hanging wall anticlines and footwall synclines originate as early ductile folds which are later cut by the propagating fault modeled structures are compared with natural examples

climatological features of cutoff low systems in the northern hemisphere this study presents the first multidecadal climatology of cutoff low systems in the northern hemisphere the climatology was constructed by using 41 yr 1958 98 of ncep ncar reanalysis data and identifying cutoff lows by means of an objective method based on imposing the three main physical characteristics of the conceptual model of cutoff low the 200 hpa geopotential minimum cutoff circulation and the specific structure of both equivalent thickness and thermal front parameter fields several results were confirmed and climatologically validated 1 the existence of three preferred areas of cutoff low occurrence the first one extends through southern europe and the eastern atlantic coast the second one is the eastern north pacific and the third one is the northern china siberian region extending to the northwestern pacific coast the european area is the most favored region 2 the known seasonal cycle with cutoff lows forming much more frequently in summer than in winter 3 the short lifetime of cutoff lows most cutoff lows lasted 2 3 days and very few lasted more than 5 days and 4 the mobility of the system with few cutoff lows being stationary furthermore the long study period has made it possible i to find a bimodal distribution in the geographical density of cutoff lows for the european sector in all the seasons with the exception of winter a summer displacement to the ocean in the american region and a summer extension to the continent in the asian region and ii to detect northward and westward motion especially in the transitions from the second to third day of occurrence and from the third to fourth day of occurrence the long term cutoff low database built in this study is appropriate to study the interannual variability of cutoff low occurrence and the links between cutoff lows and jet stream systems blocking or major modes of climate variability as well as the global importance of cutoff low in the stratosphere troposphere exchange mechanism which will be the focus of a subsequent paper

extensional fault propagation folding and base level change as controls on growth strata geometries abstract outcrop and analogue modelling studies indicate that upward widening zones of distributed deformation often monoclinal folds form above blind normal faults and are particularly common features at the depositional surface during the early stages of rifting with increasing displacement strain such folds are cut by faults as they propagate upwards into the cover we use a kinematic model of fault propagation folding above a blind extensional fault together with a sedimentary model of coarse grained clastic deposition to investigate growth strata geometries associated with fault tip monoclines in particular we consider coarse grained deltaic deposition where sedimentary geometries are markedly different from the simple sub horizontal fill to the top sedimentation used in most growth strata models for a given fault dip and slip rate growth strata geometries are strongly influenced by the fault propagation to slip ratio p s and the width of the zone of distributed deformation however base level changes also act as fundamental controls on sequence development the results of a number of experiments compare favourably to well documented examples of growth strata this study highlights the importance of integrating structural and stratigraphic studies in interpreting both fault fold kinematics and the controls on stratigraphy kinematic studies need to address the depositional geometry of stratal surfaces whereas sequence stratigraphic interpretation of stratal patterns must deconvolve tectonic rotation and translation from depositional architecture

fault displacement rates on a range of timescales abstract displacements on tectonic faults primarily accrue during earthquakes at rates that vary through time to examine the processes that underlie the temporal changes in fault displacement rates we analyse displacements and displacement rates for time periods from the present to 5 10 20 300 500 1000 and 5000 kyr for 261 active reverse or normal faults from a worldwide dataset displacement rates depart from million year average rates by up to three orders of magnitude with the size of these departures inversely related to the duration of the sample period and to fault length short term 20 kyr displacement rates generally span a greater range on small faults than large a feature which suggests more variable growth on smaller faults simple earthquake slip modeling shows that variations in displacement rates require changes in both recurrence interval and slip per event and do not support the characteristic slip earthquake model as long as fault system strain rates are uniform displacement rates generally become constant over time periods between 20 and 300 kyr with the length of time required to reach stability being inversely related to the regional basin wide strain rates stable long term displacement rates and fluctuations in earthquake recurrence intervals and slip arise in part due to fault interactions

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

coseismic elastic models of folds above blind thrusts in the betic cordilleras spain and evaluation of seismic hazard abstract although it is generally considered that near surface earthquakes result from movements along faults that cut through the surface several recent large earthquakes have been partly attributed to blind thrusts movements along blind thrusts lead to the formation of surface folds which are highly dependent upon fault geometry at depth and often not considered in seismic hazard evaluation several authors have studied the relationship between surface folding and thrusting for geological situations in which fault geometries are quite simple however active fault geometries can be quite complex e g segmented thrust faults associated with strike slip faults the aim of this contribution is to reconstruct the fault kinematics at depth for a relatively complex geological structure located in the eastern betic cordilleras orihuela guardamar torrevieja region using the patterns of kilometre scale folds observed in the field in order to model surface deformation the assumption is made that surface km scale folds have been created by coseismic deformation associated with movement along blind thrusts by means of a coseismic deformation model movements at depth have been calculated for three possible hypotheses hypothesis 1 assumes that each superficial fold is created by an independent fault hypotheses 2 and 3 assume that a sequence of two superficial folds can be created by movement along a single fault displaying a flat and ramp geometry in hypothesis 2 the flat is a superficial decollement level between the sedimentary cover and the betic basement in hypothesis 3 it is a deeper decollement level within the betic basement knowing the approximate age of surface deformation rough estimates of fault slip rates and recurrence periods for two possible earthquake magnitudes 7 ms and 6 7 ms have been made from calculated dislocations at depth slip rates and recurrence periods for flat and ramp fault geometries are in the range of 0 75 1 mm yr and 1000 2000 yr respectively these values are close to those calculated by direct methods in similar seismotectonic contexts

climatological features of cutoff low systems in the southern hemisphere abstract this study presents the first multidecadal climatology of cutoff low systems in the northern hemisphere the climatology was constructed by using 41 yr 1958 98 of ncep ncar reanalysis data and identifying cutoff lows by means of an objective method based on imposing the three main physical characteristics of the conceptual model of cutoff low the 200 hpa geopotential minimum cutoff circulation and the specific structure of both equivalent thickness and thermal front parameter fields several results were confirmed and climatologically validated 1 the existence of three preferred areas of cutoff low occurrence the first one extends through southern europe and the eastern atlantic coast the second one is the eastern north pacific and the third one is the northern china siberian region extending to the northwestern pacific coast the european area is the most favored region 2 the known seasonal cycle with cutoff lows forming much more frequently in summer than in winter 3 the short

integrated study of high resolution geophysical and geological information of osaka bay southwest japan abstract the stratigraphic framework of quaternary sediments in the osaka basin southwest japan was revealed by high resolution geophysical and geological surveys acquired after the 1995 kobe earthquake osaka bay is located in the central part of the osaka basin and is underlaid with pre neogene basement rocks covered by an unconsolidated sequence of plio pleistocene marine fluvial and lacustrine sediments fifteen laterally continuous marine clays from ma 1 to ma13 in ascending order have been identified throughout the osaka basin that have been correlated with the marine eustatic record deep borehole and high resolution seismic data were acquired in kobe northern part of the basin and kansai international airport southern part of the basin sequence stratigraphy defined by seismic reflectors was used to reveal the stratigraphic differences between the two areas by identifying reflectors as marine clay layers throughout the basin we were able to divide the study area into three parts northern middle and southern parts and to estimate the sedimentation rate in each location the sedimentation rate increases from the northern and southern margins of the basin towards central osaka bay in the middle of the basin in the southern parts the sharp decline of sedimentation rate between ma2 and ma4 and thinning or complete lack of the reflectors corresponding to ma5 and ma6 layers result from tilting in this region

geometry numerical models and revised slip rate for the reelfoot fault and trishear fault propagation fold new madrid seismic zone abstract the geometry and structural relief of late holocene sediments folded across the reelfoot scarp are characterized with trench excavations shallow borings a digital elevation model dem of topography and reelfoot lake rl bathymetry results suggest the scarp forms by heterogeneous shear in the forelimb of a fault propagation fold seismic data and the accompanying structural analysis support the argument that the reelfoot fault does not offset the surface and that the reelfoot scarp is a fold limb structural relief measured across the reelfoot scarp is slightly higher than previous determinations and varies from 7 to 11 m along the western shoreline of rl numerical models based on trishear kinematics constrain growth of the reelfoot monocline and indicate that the underlying reelfoot thrust fault is steeply dipping the shallowest portion of the central reelfoot thrust segment dips 75 where the fault tip has propagated upward from 911 m to its current location 465 m beneath the surface the models indicate that the shallowest section of the southern thrust segment in the reelfoot thrust system dips even more steeply at 80 but has propagated upward only a few tens of meters to its present location 1016 m beneath the surface the thrust is flatter at deeper levels based on the location of earthquake hypocenters strain across the reelfoot scarp is partitioned into two or three separate fold scarps that collectively record a late holocene fault slip rate of 3 9 0 1 mm yr the slip rate is based on 9 m of structural relief the 2290 60 ybp age of folded sediment and a 75 dip for the fault this implies a rate of horizontal contraction in the seismic zone of 1 0 mm yr this rate is strongly dependent on the dip of the thrust calculated by the structural analysis the numerical models argue for reactivation of faults that previously offset paleozoic strata

a geomagnetic excursion during the late matuyama chron the osaka group southwest japan abstract duplicate records of a geomagnetic excursion during the late matuyama chron were obtained from sediments gathered at the takatsuki and izumi sites in southwest japan the excursion is dominated by westerly declinations with shallow inclinations and was found just above the volcanic ash known as the azuki tuff in a marine clay layer of the osaka group the excursion occurred at about 0 85 ma a recently revised age for the azuki tuff by extrapolating constant sedimentation rates for the holocene marine clay dated by the radiocarbon method the duration of the excursion is estimated at about 240 yr with a range of 200 500 yr if we consider possible fluctuations in sedimentation rates the kamikatsura excursion previously reported around this time from the osaka group data is estimated to be a few tens of thousands of years older than the excursion reported in this study based on correlations of changes in sea level recorded in the sediments of the osaka group and the oxygen isotope record of deep sea cores these two excursions in japan together with short normal events reported in the southern ocean north america and china suggest that during the period from 0 87 0 84 ma the geomagnetic field may have been unstable and excursions or short reversals may have occurred regionally and sporadically over the earth

a simple identification scheme for upper level troughs and its application to winter precipitation variability in northwest africa abstract a simple algorithm for the identification of upper level trough axes is introduced in contrast to the assumption of a basically circular geometry in many comparable routines found in the literature the presented identification scheme is based on the east west gradient in the 500 hpa geopotential height field accounting for the meridionally elongated troughs often found in the subtropics on the basis of the ncep ncar reanalysis data from 1958 to 1998 climatological aspects are discussed for the area 22 5 47 5 n 38 5 w 18 5 e for the period from 1977 to 1998 12 hourly precipitation reports from 37 stations in northwestern africa are used to investigate the influence of the identified troughs on winter precipitation it is demonstrated that more than 90 of the precipitation in this region can be assigned to nearby trough axes a comparison of rainy periods with the climatology reveals a significant enhancement of the occurrence of trough axes in a range of 10 15 longitude close to the re

estimation of fault propagation distance from fold shape implications for earthquake hazard assessment a numerical grid search using the trishear kinematic model can be used to extract both slip and the distance that a fault tip line has propagated during growth of a fault propagation fold the propagation distance defines the initial position of the tip line at the onset of slip in the santa fe springs anticline of the los angeles basin we show that the tip line of the underlying puente hills thrust fault initiated at the same position as the 1987 magnitude 6 0 whittier narrows earthquake

wind regimes and aeolian transport in the great basin u s a abstract the modern great basin of the interior western united states is characterized by surface winds with considerable spatial and temporal variabilities wind records from the second half of the 20th century for 12 great basin localities analyzed with standard aeolian sediment transport methods developed elsewhere in the world reflect this complexity the drift potential dp for aeolian deposits is generally moderate dp 200 400 in the western great basin and weak dp 300 at the eastern edge of the great basin where the dominant prevailing wind direction is south southwesterly both dp and resultant drift direction rdd are consistent with synoptic meteorological observations of the evolution of cold fronts in the great basin meteorological observations show that effective winds to produce dunes are most commonly the result of late winter early spring cyclogenesis there has been considerable temporal variability of dp in the latter half of the 20th century most of the great basin has experienced decreasing wind strength since 1973 consistent with recent studies of wind strength in north america and elsewhere dune morphology matches both localized rdd and temporal variations in dp reasonably well in the great basin the results demonstrate that local topography can have an important influence on wind directionality thus providing a cautionary note on the interpretation of dune morphology in the paleoclimatic and stratigraphic record

a midlatitude climatology and interannual variability of 200 and 500 hpa cut off lows abstracta climatology of midlatitude 200 and 500 hpa cut off low systems in the northern and southern hemispheres is constructed from the ncep ncar reanalysis by detecting and tracking under one

a climatology of the northern hemisphere winter anticyclones 1 a climatology of the northern hemisphere winter anticyclonic activity is presented based on the european centre for medium range weather forecasts reanalysis data set for the 1957 2002 period era 40 and a system centered method of tracking diagnostics the method tracks the anticyclonic systems and monitors their evolution along their paths thus allowing documentation of aspects that have been previously overlooked due to the common perception of anticyclones as semi stationary relatively uniform slowly evolving structures the anticyclonic signal is examined in a wide range of meteorological fields and at multiple levels over the continental masses over the subtropical ocean basins and over the sectors where blocking highs tend to develop structural features thermal and vorticity properties and mobility characteristics of the corresponding anticyclones are highlighted over continental regions an association with low level pools of cold air is found to be prevalent for the eurasian anticyclones but less so for the north american anticyclones in the subtropical zone the anticyclonic signal in the regions affected by the winter monsoon including southeastern asia and the western pacific features prominently in the upper levels in the eastern sectors of the subtropical ocean basins the anticyclonic signal is less deep intense anticyclonic development at low levels is also identified over the western sectors of the subtropical continents where it appears associated to the effect of orography and of low level cooling the dominant type of anticyclone observed in the regions of blocking is characterized by 5 6 days timescales and considerable eastward mobility