tomographic images of the upper crust from the los angeles basin to the mojave desert california results from the los angeles region seismic experiment we apply inversion methods to first arriving p waves from explosive source seismic data collected along line 1 of the los angeles region seismic experiment larse extending northeastward from seal beach california to the mojave desert in order to determine a seismic model of the upper crust along the profile we use resolution information to quantify the extent of blurring in the larse images and to smooth a damped least squares dls image by postinversion filtering pif most of the original data fit is preserved while minimizing model artifacts we compare dls pif and smoothing constraint inversion images using both real and synthetic data a preferred pif image includes larger scale features in the smoothing constraint inversion image and finer scale features in the dls inversion image that are consistent with geologic information we interpret principal model features in terms of geology including faulting the maximum depth of low velocity sedimentary and volcanic rocks in the los angeles basin is 8 9 km and in the san gabriel valley is 4 5 5 km a horst like uplift of basement rocks occurs between these basins the northeastern boundary of the san gabriel valley is imaged as a tabular moderately north dipping low velocity zone that projects to the surface at the southernmost trace of the sierra madre fault system in the central and southern san gabriel mountains velocity depth profiles are consistent with intermediate velocity mylonites overlying lower velocity pelona schist along a shallowly southwest dipping vincent thrust fault tomography does not provide a definitive dip for the san andreas fault but combined with other larse results is consistent with a vertical to steep northeast dip

fluvial responses to tectonics and climate change during the late weichselian in the eastern part of the pannonian basin hungary abstract fine grained sandy silty channel belt and floodplain deposits of the berettyo koros rivers a main eastern transverse tributary system of the modern tisza river in the eastern part of the pannonian basin were deposited during the late pleistocene under net subsiding conditions the palaeo drainage network pattern of a 2500 km 2 large part of the alluvial plain was reconstructed based on interpretation of airborne photographs and analysis of 18th century topographic maps which show the natural river patterns that predate the introduction of river regulation schemes the investigation showed that a large meandering river system with two main channel belts surrounding a floodbasin entered the alluvial plain from the northeast and a braided river entered the alluvial plain from the southeast detailed sedimentary logs of seven continuous corings and several sand and clay pit sections were used to characterize different alluvial units optical luminescence dating osl of 25 quartz samples and four 14 c datings showed that the sediments are of late pleniglacial to late glacial age transport directions inferred from heavy mineral analyses combined with the osl ages strongly suggest that the large meandering system represents the palaeo tisza river which supposedly flowed along the northeast southwest striking ermellek depression during the late pleniglacial the braided river can be regarded as a precursor to the fekete and feher koros rivers which entered the alluvial plain from the southeast during the late glacial the interpretation of seismic profiles field measurements of neotectonic activity and variations in thickness of sediments along the studied profile revealed that river development was largely controlled by subsidence along the ermellek depression until 14 to 16 ky and by uplift of the southeastern part of the catchment area the studied fluvial successions also document the response of the palaeo tisza and koros system to the climate changes of the weichselian late pleniglacial late glacial period much of the sand from the meandering zones was deposited during the bolling allerod and sagvar lascaux interstadials whereas some dated sand units from the braided zone represent the older and younger dryas the error ranges of osl dates which often exceed the duration of weichselian substages and subdivisions prevented an unambiguous correlation of the studied sections with the millennial scale climate changes of the last 25 ky meandering and braided river activity coexisted under different climate conditions whereas locations of the main channel belts are related to subsidence anomalies the results of our study thus clearly indicate that tectonics was the primary control on river development

an investigation of seamount phosphorites in the eastern equatorial atlantic abstract phosphorites with p2o5 contents up to 33 have been recovered from the eastern atlantic between 6 n and 9 n formed from the replacement of shallow water reef limestones of middle eocene age the deposits are exposed on the crests of three subsided seamounts lighthill hirondelle and carter at depths of 794 1246 1161 1176 and 552 1158 m respectively phosphates exposed on the sea floor are associated with high levels of acoustic backscatter recorded using a ship s echo sounder and a 10 khz pinger towed 30 m above the bottom seabed scintillometer measurements on carter seamount near 9 n 21 w revealed high ray emission where phosphorites are known to crop out from photography and sampling uranium contents of the deposits lie in the range 9 46 ppm values which are lower than those found in continental margin phosphates but similar to concentrations in pacific seamount phosphorites 87sr 86sr ratios indicate that phosphatisation of the middle eocene reef limestones occurred in the early middle miocene 16 23 ma on carter and hirondelle seamounts and in the late miocene 6 ma on lighthill seamount upwelling near the palaeo equator probably played a vital role in diagenesis by promoting high biological productivity and a large flux of phosphorus to pore waters in the seamount limestones phosphorites are probably widespread on other sediment capped seamounts and fracture zone ridges in the equatorial atlantic

behavior of the southernmost san andreas fault during the past 300 years surficial creep occurs at low rates along the coachella valley segment of the san andreas fault which has not produced a large earthquake during the period of historical record geodetic data indicate however that the crust adjacent to this segment of the san andreas fault is accumulating strain at a high rate furthermore neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries in view of its long term behavior the occurrence of creep along the surficial trace of the fault in the coachella valley is of particular interest along two short reaches of the san andreas fault in the coachella valley measurements of offset geological deposits and man made structures and from alignment arrays and creep meters show that slip rates of 2 4 mm yr near indio and near the salton sea have persisted for the past three centuries this slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault we suggest that the coachella valley segment of the san andreas fault creeps in its upper few kilometers this behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault

long term fluvial archives in hungary response of the danube and tisza rivers to tectonic movements and climatic changes during the quaternary a review and new synthesis abstract the paper discusses the quaternary evolution of the danube and tisza rivers and their main tributaries in the context of evolution of the entire pannonian basin which is europe s largest intramontane basin within the alp carpathian orogen the palaeo drainage reconstruction of the pannonian basin for the pre quaternary period is outlined in connection with the gradual regression of lake pannon since the late miocene deltas of rivers that entered the basin from the northwest and northeast were gradually transformed into extended alluvial plains thus the earliest possible ancestor of the danube coming southeastwards from the alps could be as old as late miocene by the pliocene the whole lake pannon was infilled the former extensional basin formation was replaced by a compresional stress field which resulted in an uplift of the marginal flanks and late stage subsidence anomalies the increasing relief led to the formation of the quaternary drainage pattern the actively subsiding young basins were filled by fluvial sediments transported by the danube and tisza river systems from the uplifting mountains between the subsiding regions of the little and great plains the danube has formed an antecedent valley with terrace staircases between the uplifting sections of the transdanubian range and the north midmountains the formation of the terraces is attributed to periodic climate changes during the pleistocene combined with differences in the uplift rate the paper gives a complex overview of the classical chronology of the six terraces based on various data sources mostly dating of loess paleosol sequences travertines aeolian sand and tephra strata overlying the fluvial sediments complemented by scattered vertebrate faunal data and archaeological evidence directly from the terrace sediments the quaternary drainage pattern evolution of the great plain with a strong tectonic control is discussed in detail rivers originating from the uplifting marginal areas were drawn towards the subsiding depressions which served as local base level changes in subsidence rates in space and time throughout the quaternary resulted in the evolution of a complex drainage pattern a special emphasis is placed on the late pleistocene holocene development of the middle tisza region and the koros basin where the berettyo koros rivers form an eastern tributary system of the tisza river a comparative evaluation of these two areas is especially relevant as they provide insights into large scale late pleistocene avulsion of the tisza river osl dating complemented with inferred transport directions determined from heavy mineral analysis of fluvial sediments in the koros basin has revealed an ancient large meandering river system that can be identified with the palaeo tisza which was flowing along a tectonically controlled depression during the late pleniglacial successions in the middle tisza region have allowed differentiation between the older channels of the palaeo bodrog river and the sajo hernad alluvial fan and the younger meander belts of the new course of the tisza in the tisza system changes in river style braided to various scales of meandering show correspondence to millennial scale climate changes of the last 25 ka while in the koros basin the effects of tectonics are overprinted onto the regional climatic signals

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

three dimensional imaging of active structures using earthquake aftershocks the northridge thrust california abstract aftershocks of the 1994 northridge earthquake m 6 8 allow us to image the structure beneath the san fernando valley in northwestern los angeles in three dimensions we combine aftershocks and geological data to build an image of the three dimensional 3 d geometry of the previously unrecognized north vergent northridge blind thrust to a depth of 21 km the most striking feature of the imaged fault is mega corrugations oriented parallel to the mean aftershock slip vector with most of the 1994 slip confined to west of the largest corrugation we also image the partially overlying south vergent san fernando thrust which broke to the surface in a complex rupture in 1971 m 7 1 both thrusts produce fault related folding because of either fault propagation or fault bends however this deeper folding is masked by overlying complex deformation in the cover which is one reason why the northridge thrust was not identified until it ruptured in 1994 we use trishear fold modeling based on our 3 d fault geometry to evaluate possible folding due to slip on the northridge thrust as well as its interaction with the overlapping san fernando thrust and with shallow structures in the cover this example illustrates the importance of earthquake data to structural geology and the value of its 3 d integration with surface and near surface geological data

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

fracture zones in the equatorial atlantic and the breakup of western pangea the early breakup of western pangea has been investigated by mapping the pattern of fracture zones and distribution of seismic reflectors within the sedimentary cover of the atlantic between the cape verde islands and the equator two distinct sets of transverse oceanic lineaments are present separated by the guinea fracture zone near lat 10 sup 0 n lineaments to the north are associated with the formation of the central atlantic in the late jurassic and early cretaceous those in the south relate to the cretaceous opening of the south atlantic the guinea fracture zone is thus the conjugate of the jurassic transform boundary under peninsular florida which linked the atlantic with the gulf of mexico the distribution of dated seismic reflectors suggests that deposition of deep water sediments was confined to the region north of the guinea transform until aptian time when the sierra leone basin began to open the latter started to widen at least 15 m y after the initiation of the cape basin off southwest africa an age difference that can be explained if a short lived plate boundary developed in either africa or south america during the early cretaceous neither the trends of the equatorial fracture zones nor the seismic stratigraphymore supports the existence of a predrift gap between west africa and brazil less

holocene sediment dynamics in the environs of the fortification enclosure of cornesti iarcuri in the romanian banat abstract the presented study combines data from geomorphological geochemical sedimentological chronometric and archaeological records providing first insights into the holocene landscape development in the environs of the late bronze age fortification enclosure cornesti iarcuri this large scale archaeological site is located in a loess covered undulating landscape at the eastern edge of the great hungarian plain in western romania sediment archives from geomorphologically different locations closely related to the copper age to late bronze age settlements are presented mainly stable geomorphic conditions throughout the holocene occurred on the high plains of the vinga plain as indicated by chemical alteration of the loss deposits and soil formation processes exceeding 2 m in contrast two cores from an alluvial fan of a minor drainage system in direct vicinity of the archaeological site document varying morphodynamics throughout the holocene phases of geomorphic activity and stability are indicated by the formation of fan deposits and paleosols developed in these sediments 14 c dates from charcoal extracted from the fan sediments show maximum deposition ages between c 4400 cal bp and c 2900 cal bp thus the formation of the charcoal coincides with the copper age to late bronze age development of the settlement sites daub pieces incorporated into these reworked soil sediments provide evidence for human activities in the catchment this in turn may indicate that the erosion processes that led to the fan formation are linked to those activities however reworking and redeposition of the charcoal and daub bearing sediments due to retrogressive erosion during the last millennia cannot be excluded

rapid full wave centroid moment tensor cmt inversion in a three dimensional earth structure model for earthquakes in southern california summary a central problem of seismology is the inversion of regional waveform data for models of earthquake sources in regions such as southern california preliminary 3 d earth structure models are already available and efficient numerical methods have been developed for 3 d anelastic wave propagation simulations we describe an automated procedure that utilizes these capabilities to derive centroid moment tensors cmts the procedure relies on the use of receiver side green s tensors rgts which comprise the spatial temporal displacements produced by the three orthogonal unit impulsive point forces acting at the receivers we have constructed a rgt database for 219 broad band stations in southern california using a tomographically improved version of the 3 d scec community velocity model version 4 0 cvm4 and a staggered grid finite difference code finite difference synthetic seismograms for any earthquake in our modelling volume can be simply calculated by extracting a small source centred volume from the rgt database and applying the reciprocity principle the partial derivatives needed for the cmt inversion can be generated in the same way we have developed an automated algorithm that combines a grid search for suitable focal mechanisms and hypocentre locations with a gauss newton optimization that further refines the grid search results using this algorithm we have determined cmt solutions for 165 small to medium sized earthquakes in southern california preliminary comparison with the cmt solutions provided by the southern california seismic network scsn shows that our solutions generally provide better fit to the observed waveforms when applied to a large number of earthquakes our algorithm may provide a more robust cmt catalogue for earthquakes in southern california

seismic reflection constraints on the structure of the crust beneath the san bernardino mountains transverse ranges southern california a 30 km long n s seismic reflection line was shot by california consortium for crust studies calcrust across the southern mojave desert and onto the northern flank of the san bernardino mountains in southern california on the northern end of the seismic section the reflectivity increases markedly in the midcrust at a depth corresponding to a two way travel time of 4 to 5 s 12 15 km suggesting a transition between nonreflecting brittle upper crust and reflecting ductile lower crust the high reflectivity disappears at about 8 s 24 km and may be correlated with a change in seismic velocity in the lower crust from 6 3 km s to 6 8 km s a band of reflectivity between 9 5 and 10 s 27 30 km is believed to represent the moho the midcrustal relectivity transition and moho both deflect downward toward the san bernardino mountains uplift over the entire length of the profile the deflection of the midcrustal transition 12 appears greater than that of the moho 6 resulting in a thinning of the lower crust to the south beneath the uplift in addition the midcrustal transition coincides with the base of the seismogenic zone brittle ductile transition which is also dipping southward beneath the san bernardino mountains while the moho deflection is consistent with elastic flexure resulting from edge loading by the san bernardino mountains which have been thrust over the mojave block it is suggested that the thinning of the lower crust beneath the san bernardino mountains is a result of north directed ductile flow in response to loading by the over thickened upper crust since a portion of the load is transmitted through the lower crust to the moho the time constant for flow equilibrium must be of the order of or greater than that for the time of uplift 2 m y

channel avulsion on alluvial fans in southern arizona historical aerial photographs and field observations on five fluvially dominated alluvial fans in southern arizona demonstrate that channel avulsion invariably occurs where bank heights are low and often at channel bends channel abandonment occurs through stream capture when overland flow from the main channel accelerates and directs headward erosion of smaller channels heading on the fan surface five distinct channel morphologies observed on the fans are related to different stages of the avulsion process and can be used to identify areas on a fan surface that are prone to avulsion a descriptive model of channel avulsion illustrates how the morphology of a single channel reach will evolve through time as it captures the main flow path and is itself eventually abandoned immediately following avulsions small preexisting channels that capture flow from the main channel will typically experience three fold or greater increases in channel width subsequent large floods can be stably conveyed through these high capacity reaches an uninterrupted sequence of sediment charged small flows however will eventually begin to back fill the wide channels as vegetation growth stabilizes the banks the stabilized and back filled channels are now prone to abandonment during large floods because the decrease in the channel s capacity leads to the generation of overland flow beyond the margins of the shallowed channels the action of the small aggrading floods is critical in the avulsion process since the greatest amount of overland flow is generated where bank heights are lowest as a result both small and large floods are effective agents of landscape change on the fans channel avulsions on the five fans are not completely random events in space and time because their occurrence is controlled by the relative positioning of low banks along the main channel and smaller channels draining the fan surface consequently the location and timing of future channel avulsions can potentially be anticipated in an effort to improve flood hazard assessment on fluvial fans in the rapidly urbanizing southwestern united states

systematic stress variations in the southern san joaquin valley and along the white wolf fault implications for the rupture mechanics of the 1952 ms 7 8 kern county earthquake and contemporary seismicity the southern san joaquin valley ssjv stress state is characterized by systematic variations in the regional principal stress directions and relative magnitudes as well as local and possibly temporal variations that appear to be the result of the 1952 ms 7 8 kern county earthquake the regional maximum horizontal principal stress shmax orientation in the san joaquin valley systematically rotates from ne sw compression along the western margins of the valley to n s compression in the ssjv this n s shmax stress direction in the ssjv is consistent with active development of a e w trending structural fabric of fold axes and shallow thrust and the reverse dip slip motion observed during the kern county earthquake on the south southeast dipping white wolf fault contemporary seismicity 30 40 years after the mainshock clusters in two separate areas along the white wolf fault the southwest region where the 1952 earthquake nucleated and the northeast region near where the earthquake rupture terminated earthquakes in the southwest and northeast regions show a diversity of focal mechanisms that include strike slip reverse oblique and to a lesser extent normal slip inversion of earthquake focal mechanisms for in situ stress in the southwest region indicates a strike slip reverse stress regime with s1 oriented approximately perpendicular to the ruptured fault plane implying low frictional strength in the nucleation zone of the 1952 earthquake inversion of focal plane mechanisms in the northeast region indicates a strike slip stress regime with s2 nearly perpendicular to secondary 1952 rupture planes also implying low frictional strength these results indicate near complete stress drops for fault planes associated with the 1952 earthquake and some of the contemporary earthquakes implying fault surfaces which are frictionally weak i e slip planes subparallel to principal stress planes based on the observed stress state in the southern san joaquin valley much of the seismicity may be the result of elevated fluid pressures within these active fault zones

terashake2 spontaneous rupture simulations of mw 7 7 earthquakes on the southern san andreas fault abstract previous numerical simulations terashake1 of large m w 7 7 southern san andreas fault earthquakes predicted localized areas of strong amplification in the los angeles area associated with directivity and wave guide effects from northwestward propagating rupture scenarios the terashake1 source was derived from inversions of the 2002 m w 7 9 denali alaska earthquake that source was relatively smooth in its slip distribution and rupture characteristics owing both to resolution limits of the inversions and simplifications imposed by the kinematic parameterization new simulations terashake2 with a more complex source derived from spontaneous rupture modeling with small scale stress drop heterogeneity predict a similar spatial pattern of peak ground velocity pgv but with the pgv extremes decreased by factors of 2 3 relative to terashake1 the terashake2 source excites a less coherent wave field with reduced along strike directivity accompanied by streaks of elevated ground motion extending away from the fault trace the source complexity entails abrupt changes in the direction and speed of rupture correlated to changes in slip velocity amplitude and waveform features that might prove challenging to capture in a purely kinematic parameterization despite the reduced pgv extremes northwest rupturing terashake2 simulations still predict entrainment by basin structure of a strong directivity pulse with pgvs in los angeles and san gabriel basins that are much higher than predicted by empirical methods significant areas of those basins have predicted pgv above the 2 probability of exceedance poe level relative to current attenuation relationships even when the latter includes a site term to account for local sediment depth and wave guide focusing produces localized areas with pgv at roughly 0 1 0 2 poe about a factor of 4 5 above the median in contrast at rock sites in the 0 100 km distance range the median terashake2 pgvs are in very close agreement with the median empirical prediction and extremes nowhere reach the 2 poe level the rock site agreement lends credibility to some of our source modeling assumptions including overall stress drop level and the manner in which we assigned dynamic parameters to represent the mechanical weakness of near surface material future efforts should focus on validating and refining these findings assessing their probabilities of occurrence relative to alternative rupture scenarios for the southern san andreas fault and incorporating them into seismic hazard estimation for southern california

high resolution seismic reflection profiling of the santa monica fault zone west los angeles california high resolution seismic reflection data obtained across the santa monica fault in west los angeles reveal the near surface geometry of this active oblique reverse left lateral fault although near surface fault dips as great as 55 cannot be ruled out we interpret the fault to dip northward at 30 to 35 in the upper few hundred meters steepening to 65 at 1 to 2 km depth a total of 180 m of near field thrust separation fault slip plus drag folding has occurred on the fault since the development of a prominent erosional surface atop 1 2 ma strata in the upper 20 to 40 m strain is partitioned between the north dipping main thrust strand and several closely spaced near vertical strike slip faults observed in paleoseismologic trenches the main thrust strand can be traced to within 20 m of the ground surface suggesting that it breaks through to the surface in large earthquakes uplift of a 50 000 year old alluvial fan surface indicates a short term dip slip rate of 0 5 mm yr similar to the 0 6 mm yr dip slip rate derived from vertical separation of the oxygen isotope stage 5e marine terrace 3 km west of the study site if the 0 6 mm yr minimum dip slip only rate characterizes the entire history of the fault then the currently active strand of the santa monica fault probably began moving within the past 300 000 years

seismic tomography of the southern california crust based on spectral element and adjoint methods we iteratively improve a 3 d tomographic model of the southern california crust using numerical simulations of seismic wave propagation based on a spectral element method sem in combination with an adjoint method the initial 3 d model is provided by the southern california earthquake center the data set comprises three component seismic waveforms i e both body and surface waves filtered over the period range 2 30 s from 143 local earthquakes recorded by a network of 203 stations time windows for measurements are automatically selected by the flexwin algorithm the misfit function in the tomographic inversion is based on frequency dependent multitaper traveltime differences the gradient of the misfit function and related finite frequency sensitivity kernels for each earthquake are computed using an adjoint technique the kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient based minimization algorithm the inversion involved 16 iterations which required 6800 wavefield simulations the new crustal model m 16 is described in terms of independent shear v s and bulk sound v b wave speed variations it exhibits strong heterogeneity including local changes of 30 per cent with respect to the initial 3 d model the model reveals several features that relate to geological observations such as sedimentary basins exhumed batholiths and contrasting lithologies across faults the quality of the new model is validated by quantifying waveform misfits of full length seismograms from 91 earthquakes that were not used in the tomographic inversion the new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment

holocene aeolian sand mobilization vegetation history and human impact on the stabilized sand dune area of the southern nyirseg hungary abstract almost 20 of the territory of hungary is covered by stabilized dunes formed during the pleistocene with the climate amelioration during the early holocene the aeolian activity ceased however various environmental and anthropogenic factors could have reactivated the aeolian processes today there is an increasing climatic stress on the dune fields of the carpathian basin which is coupled with inadequate land use it is therefore necessary to determine the timing and circumstances of sand mobilization during the holocene the site of the present study is located in a dune interdune system on the southern part of the nyirseg alluvial fan where periods of holocene aeolian activity and environmental change were investigated using palynological and sedimentological methods optically stimulated luminescence and radiocarbon dating the data achieved show climate driven boreal aeolian activity at approximately 8 2 ka and also demonstrate for the first time that during the atlantic phase 6 4 and 5 3 ka in spite of the relatively humid climate and dense vegetation aeolian activity has taken place induced probably by agricultural practices following subboreal morphological stability aeolian activity occurred several times in the subatlantic phase 2 4 2 2 1 2 0 8 and 0 4 0 1 ka as a result of vegetation changes and human activity

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

surface sediment characteristics and present dynamics in alluvial fans of the central spanish pyrenees three alluvial fans in the ribera de biescas upper gallego valley and central spanish pyrenees have been studied in order to explain the most recent changes and to identify the spatial organization of the sediment in the alluvial fans surveyed the proximal area is dominated by debris flows which pass downslope into transitional and fluvial deposits the relative importance of each type of sediment is closely related to the size and gradient of the alluvial fan as well as to the gradient in the final stretch of the stream in general the size of the sediment decreases from the proximal to the distal area while the roundness increases nevertheless there are noticeable irregularities in the trend both in longitudinal and transverse transects due mainly to the sedimentary dynamics of the debris flows as they advance towards the inner part of each alluvial fan during the most intense peak flows a sudden shrinkage of the most active area and incision along the fan channels has been assessed and related to land use changes in the catchments

influence of lithosphere viscosity structure on estimates of fault slip rate in the mojave region of the san andreas fault system 1 it is well known that slip rate estimates from geodetic data are nonunique because they depend on model assumptions and parameters that are often not known a priori estimates of fault slip rate on the mojave segment of the san andreas fault system derived from elastic block models and gps data are significantly lower than estimates from geologic data to determine the extent to which the slip rate discrepancy might be due to the oversimplified models of the rheology of the lithosphere we develop a two dimensional linear maxwell viscoelastic earthquake cycle model and simultaneously estimate fault slip rates and lithosphere viscosity structure in the mojave region the model consists of episodic earthquakes in an elastic crust overlying layers with different viscosities that represent the lower crust uppermost mantle and upper mantle we use gps measurements of postseismic relaxation following the 1992 landers earthquake triangulation measurements spanning 1932 1977 gps measurements of the contemporary velocity field and paleoseismic data along the san andreas fault we infer lower crustal 15 30 km depth viscosity of 1019 10 20 pa s uppermost mantle 30 60 km viscosity of 10 20 22 pa s and underlying upper mantle viscosity of 10 18 10 19 pa s consistent with inferences from laboratory experiments of relatively high viscosity lithospheric mantle and lower viscosity lower crust and underlying asthenospheric mantle we infer a 20 30 mm yr slip rate on the san andreas fault in agreement with the lower end of geologic estimates inversions of geodetic data with models that do not incorporate layered viscosity structure may significantly misestimate slip rates

mantle heterogeneities and the scec reference three dimensional seismic velocity model version 3 we determine upper mantle seismic velocity heterogeneities below southern california from the inversion of teleseismic travel time residuals teleseismic p wave arrival times are obtained from three temporary passive experiments and southern california seismic network scsn stations producing good raypath coverage the inversion is performed using a damped least squares conjugate gradient method lsqr the inversion model element spacing is 20 km before the inversion the effects of crustal velocity heterogeneities represented by the southern california earthquake center scec seismic velocity model version 2 are removed from the teleseismic travel times the p wave inversion produces a variance reduction of 43 s wave velocities are determined from laboratory vp vs ratios the most prominent features imaged in the results are high p wave velocities 3 in the uppermost mantle beneath the northern los angeles basin and the previously reported tabular high velocity anomaly 3 to depths of 200 km beneath the transverse ranges crosscutting the san andreas fault we incorporate the upper mantle seismic velocity heterogeneities into the scec southern california reference seismic velocity model the prior accounting for the crustal velocity heterogeneity demonstrates the utility of the top down method of the scec seismic velocity model development

response of alluvial fan systems to the late pleistocene to holocene climatic transition contrasts between the margins of pluvial lakes lahontan and mojave nevada and california usa abstract dated shorelines of late pleistocene pluvial lakes lahontan great basin desert northwest nevada and mojave mojave desert eastern california provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late pleistocene to early holocene two sets of alluvial fan systems have been mapped the stillwater fans feeding lake lahontan and the zzyzx fans feeding lake mojave their contrasting morphologies suggest different responses of the two fan systems to late pleistocene to early holocene climatic change at the time the stillwater fan systems underwent minimal sedimentation with the catchment hillslopes apparently stable the zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes there was a major phase of hillslope debris flow activity followed by fanhead trenching and distal fan progradation both areas were wetter and colder in the late pleistocene than they are today but during the transition to the holocene the zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the southwest vegetation reconstructions for the late pleistocene to the early holocene suggest that catchment hillslopes in the mojave supported a desert shrub vegetation but those in the stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the pleistocene to holocene climatic transition after the falls in lake levels of lakes lahontan and mojave in the early holocene both areas underwent aridification resulting in reductions in hillslope vegetation cover increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans variations in fan style at that time may relate primarily to base level conditions resulting from different gradients on the exposed lake shores

structure of the european upper mantle revealed by adjoint tomography the structure of the european crust and upper mantle is precisely known only in limited regions a new tomographic model for the entire european upper mantle identifies northeastward subduction of the adria plate beneath the dinarides mountains volcanism related to the upwelling eifel hotspot and mantle delamination beneath scandinavia

fault systems of the 1971 san fernando and 1994 northridge earthquakes southern california relocated aftershocks and seismic images from larse ii we have constructed a composite image of the fault systems of the m 6 7 san fernando 1971 and northridge 1994 california earthquakes using industry reflection and oil test well data in the upper few kilometers of the crust relocated aftershocks in the seismogenic crust and larse ii los angeles region seismic experiment phase ii reflection data in the middle and lower crust in this image the san fernando fault system appears to consist of a decollement that extends 50 km northward at a dip of 25 from near the surface at the northridge hills fault in the northern san fernando valley to the san andreas fault in the middle to lower crust it follows a prominent aseismic reflective zone below and northward of the main shock hypocenter interpreted upward splays off this decollement include the mission hills and san gabriel faults and the two main rupture planes of the san fernando earthquake which appear to divide the hanging wall into shingle or wedge like blocks in contrast the fault system for the northridge earthquake appears simple at least east of the larse ii transect consisting of a fault that extends 20 km southward at a dip of 33 from 7 km depth beneath the santa susana mountains where it abuts the interpreted san fernando decollement to 20 km depth beneath the santa monica mountains it follows a weak aseismic reflective zone below and southward of the main shock hypocenter the middle crustal reflective zone along the interpreted san fernando decollement appears similar to a reflective zone imaged beneath the san gabriel mountains along the larse i transect to the east in that it appears to connect major reverse or thrust faults in the los angeles region to the san andreas fault however it differs in having a moderate versus a gentle dip and in containing no mid crustal bright reflections

late quaternary dynamics of a south african floodplain wetland and the implications for assessing recent human impacts abstract knowledge of the long term geomorphological dynamics of wetlands is limited so currently there is an inadequate scientific basis for assessing anthropogenically induced changes and for developing conservation remediation and or sustainable management guidelines for these fragile ecosystems along the upper klip river eastern south africa geomorphological and sedimentological investigations geochronology and remote sensing have been used to establish the late quaternary dynamics of some internationally important floodplain wetlands thus providing a reference condition against which to assess the extent of recent human impacts optically stimulated luminescence dating reveals that the wetlands have developed over at least the last 30 ky as a result of slow meander migration 1 irregular cutoff events and infrequent avulsions approximately one every 3 6 ky that have occurred autogenically as a natural part of meander belt development following european settlement in the klip valley late nineteenth century however modifications to local flora and fauna as well as the initiation of local wetland drainage schemes have had major impacts in particular proliferation of exotic willows and associated debris jams and the artificial excavation of a 1 2 km long channel section across the wetlands have initiated an ongoing avulsion that is characterised by failure gradual abandonment of the main channel and rapid incision of a headcutting channel compared to the pre settlement condition little change in lateral migration activity has occurred but this avulsion provides a clear example of anthropogenically accelerated change occurring only 1 ky after the last natural avulsion and in a part of the wetlands where avulsions have not occurred previously subsequent human interventions have included installing weirs in an attempt to control the resulting erosion and promote reflooding but ongoing maintenance has been required in areas that were not glaciated during the quaternary many other floodplain wetlands may be of similar antiquity but the klip river illustrates their sensitivity to direct and indirect human impacts

earthquake locations in southern california obtained using source specific station terms we relocate 297 400 events recorded by the southern california seismic network scsn between 1975 and 1998 using spatially varying station terms to improve relative location accuracy our method uses existing scsn p and s picks a smooth one dimensional velocity model and an iterative grid search approach based on the l1 norm we apply empirical corrections for three dimensional structure by computing station timing corrections that continuously vary as a function of source position station terms for each event are obtained by smoothing the residuals from nearby events using a natural neighbor delaunay tessellation of the seismicity and then iterating until a stable set of locations and station terms is achieved our approach achieves relative location accuracy comparable locally to master event methods but can be applied uniformly over large regions median estimated standard errors for our final locations are 328 m in horizontal position and 741 m in depth our locations exhibit much less scatter particularly in depth than those of the scsn catalog and a greater tendency to align into linear and planar features suggestive of fault structures our results appear comparable to and in some cases better than previous scsn relocation studies using joint hypocenter velocity inversion techniques plots of daytime versus nighttime events permit discrimination between clusters of natural and artificial seismicity we observe no simple relationship between the maximum depth of seismicity and surface geology

the dynamics of strike slip step overs with linking dip slip faults fault step overs with linking dip slip faults are common features on long strike slip fault systems worldwide it has been noted by various researchers that under some circumstances earthquakes can jump across fault step overs to cascade into large events while under other circumstances rupture is arrested at step overs there is also evidence that fault step overs may be preferential locations for earthquake nucleation the present work uses the 3d finite element method to model the dynamics of strike slip fault systems with step overs and linking dip slip faults i find that the presence of a linking normal or thrust fault greatly increases the ability of earthquake rupture to propagate across the step over leading to a larger event additionally dilational step overs with linking normal faults are more prone to through going rupture than compressional step overs with linking thrust faults this difference is due to the sign of the normal stress increment on the dip slip fault caused by slip on the strike slip segments slip on the strike slip segments causes a negative unclamping normal stress increment on the linking normal fault in a dilational step over whereas the opposite effect occurs on the linking thrust fault in a compressional step over even in cases for which both dilational and compressional step overs can experience through going rupture dilational step overs typically experience higher slip particularly on the linking normal fault in the compressional case rupture nucleation on the linking thrust fault may increase the likelihood of through going rupture compared to nucleation on one of the strike slip segments near the intersections between the fault segments the stress interaction between the fault segments also causes a significant rotation of rake away from that which would be inferred from the regional stress field the results help to emphasize the importance of two way interactions between nearby fault segments during the earthquake rupture process the results also may have implications for the probability of large earthquakes along geometrically complex strike slip fault systems and may help explain why step overs sometimes act as barriers and other times as nucleation locations for large earthquakes

late quaternary paleodrainage reconstruction of the maros river alluvial fan abstract the surface of the extensive maros alluvial fan is densely 0 78 km km 2 covered by paleochannels the aim of the present study is to reconstruct the final late quaternary stage of the alluvial fan development by identifying paleodrainage directions and determining morphology and pattern of the paleochannels and the age of their activity on the surface of the alluvial fan 18 meandering braided anastomosing or misfit paleochannel zones were identified the existence of these channels indicates that the main process of the fan development was avulsion rather than lateral channel shift and the overbank floodplain accumulation played a minor role as the paleochannels were not buried the oldest paleodrainages a c shifted towards north from the east west axis of the alluvial fan draining water to the koros basin the similar age 18 7 2 3 ka 14 2 1 4 ka of the paleochannel zones indicates rapid avulsions or the coexistence of paleodrainages in the northern half of the alluvial fan the last large d paleodrainage change occurred 12 4 2 1 ka when the channel turned westward a large meandering channel functioned for a period 12 4 2 1 ka 9 6 1 3 ka and with the coexisting misfit channels these channels drained a considerable amount of water q b 2500 m 3 s in the next development phase e paleodrainages the maros flowed north but after a sharp bend it turned toward the south and it started to form the southern lobe of the alluvial fan these channels existed between 8 5 0 9 ka and 3 5 0 4 ka and had a bankfull discharge of 1000 2000 m 3 s the last f paleodrainage of the maros river existed for a short time 1 9 0 3 ka 1 6 0 3 ka and indicated decreasing discharge q b 1400 m 3 s in the final phase of the alluvial fan evolution the present day course of the river was developed and its discharge decreased further 680 m 3 s

adjoint analysis of the source and path sensitivities of basin guided waves summary simulations of earthquake rupture on the southern san andreas fault saf reveal large amplifications in the san gabriel and los angeles basins sgb and lab apparently associated with long range path effects geometrically similar excitation patterns can be recognized repeatedly in different saf simulations e g love wave like energy with predominant period around 4 s channelled southwestwardly from the sgb into lab yet the amplitudes with which these distinctive wavefield patterns are excited change depending upon source details slip distribution direction and velocity of rupture we describe a method for rapid calculation of the sensitivity of such predicted wavefield features to perturbations of the source kinematics using a time reversed adjoint wavefield simulation the calculations are analogous to those done in adjoint tomography and the same time reversed calculation also yields path sensitivity kernels that give further insight into the excitation mechanism for rupture on the southernmost 300 km of saf lab excitation is greatest for slip concentrated between the northern coachella valley and the transverse ranges propagating to the ne and with rupture velocities between 3250 and 3500 m s 1 along that fault segment that is within or slightly above the velocity range between rayleigh and s velocities that is energetically precluded in the limit of a sharp rupture front highlighting the potential value of imposing physical constraints such as from spontaneous rupture models on source parametrizations lab excitation is weak for rupture to the sw and for ruptures in either direction located north of the transverse transverse ranges whereas ventura basin vtb is preferentially excited by ne ruptures situated north of the transverse ranges path kernels show that lab excitation is mediated by surface waves deflected by the velocity contrast along the southern margin of the transverse ranges having most of their energy in basement rock until they impinge on the eastern edge of sgb through which they are then funnelled into lab vtb amplification is enhanced by a similar waveguide effect

accelerated overbank accumulation after nineteenth century river regulation works a case study on the maros river hungary abstract in the nineteenth century the meandering rivers of the carpathian basin were extensively regulated and their large up to 100 km wide floodplains were confined by artificial levees on the narrow 0 5 4 km artificial floodplains confined by these levees overbank sedimentation has become the dominant geomorphological process resulting in rising floodplain levels during the last century the maros river is an extreme example of this process as it carries a significant amount of suspended sediment 4 6 10 6 m 3 y and because its lowland reach was drastically shortened by cutoffs resulting in bed scour and an increased sediment load simultaneously a flood embankment system was constructed reducing the floodplain width by 70 80 the resulting accelerated overbank sediment accumulation increases the flood hazard along the river the aim of this study is to determine the spatial and temporal pattern of overbank sediment accumulation on the artificial floodplain of the lower maros river over the last 150 years and to identify its influencing factors the lateral slope of the protected natural floodplain was projected towards the present day channel allowing the volume m 3 and rate cm y of overbank sedimentation to be calculated using digital terrain modelling dtm changes in the rate of sedimentation were determined by pollen analysis the studied reach was divided into five sections based on the rate of aggradation i the distal surface of the alluvial fan where no sedimentation was measured only incision ii the original front of the alluvial fan 1 0 0 4 cm y iii the recently formed secondary alluvial fan 1 4 0 3 cm y iv the low lying floodplain 0 4 0 2 cm y and v the outlet unit 2 0 0 5 cm y the aggradation rate was slower on elevated forms such as the pre regulation natural levee 0 2 cm y and greater on the low lying floodplain 0 6 cm y the greatest accumulation rate 1 3 2 4 cm y was measured in cutoffs the sedimentation rate was high during the regulation period 1 9 2 4 cm y but later decreased to 0 5 0 9 cm y the rate of aggradation was determined by the width height and slope conditions of the floodplain the impoundment of the main river and the land use in the area

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

crustal structure and tectonics from the los angeles basin to the mojave desert southern california a seismic refraction and low fold reflection survey known as the los angeles region seismic experiment larse was conducted along a transect line 1 extending from seal beach california to the mojave desert crossing the los angeles and san gabriel valley basins and san gabriel mountains the chief result of this survey is an interpreted cross section that addresses a number of questions regarding the crustal structure and tectonics of southern california that have been debated for decades and have important implications for earthquake hazard assessment the results or constraints are as follows 1 the maximum depth of the los angeles basin along line 1 is 8 9 km 2 the deep structure of the sierra madre fault zone in the northern san gabriel valley is as follows the duarte branch of the sierra madre fault zone forms a buried 2 5 km high moderately north dipping buttress between the sedimentary and volcanic rocks of the san gabriel valley and the igneous and metamorphic rocks of the san gabriel mountains for deeper structure see following 3 there are active crustal decollements in southern california at middle crustal depths the sierra madre fault zone appears to sole into a master decollement that terminates northward at the san andreas fault and projects southward beneath the san gabriel valley to the puente hills blind thrust fault 4 the dip and depth extent of the san andreas fault along line 1 dips steeply 83 northward and extends to at least the moho 5 the subsurface lateral extent of the pelona schist in southern california is as follows along line 1 the pelona schist underlies much if not all of the san gabriel mountains south of the san andreas fault to middle crustal depths north of the san andreas fault it is apparently not present along the transect

full 3d tomography for the crustal structure of the los angeles region we apply full 3d tomography f3dt to a regional dataset in the los angeles area in f3dt the starting model as well as the model perturbation is three dimensional and the sensitivity frechet kernels are computed using numerical schemes that account for the full physics of 3d wave propagation f3dt can account for the nonlinearity of structural inverse problem through iteration thus providing the most efficient means for assimilating seismic observations into dynamic ground motion models we have successfully applied a scattering integral si formulation of f3dt to improve a 3d elastic structure model the southern california earthquake center scec community velocity model version 3 0 cvm3 0 with lowest shear velocity clamped at 1 km sec in the los angeles region our data are time and frequency localized measurements of phase delay anomalies relative to synthetics computed from the 3d elastic starting model the frechet kernels for our measurements were computed by convolving the earthquake wave fields generated by point earthquake sources with the receiver green tensors rgts which are the spatial temporal fields produced by three orthogonal unit impulsive point forces acting at the receiver locations we inverted 7364 phase delay measurements of p and s body waves by using the lsqr method the revised 3d model laf3d provides substantially better fit to the observed waveform data than the 3d starting model to our knowledge this study is the first successful application of f3dt using real data in structural seismology

regional tectonics of the coso geothermal area along the intracontinental plate boundary in central eastern california three dimensional vp and vp vs models spatial temporal seismicity patterns and seismogenic deformation we synthesize the tectonics of the southern walker lane belt and coso range in central eastern california using regional earthquake data first we invert for three dimensional models of the v p and v p v s structure of the upper and middle crust using these models we also determine three dimensional vs and poisson s ratio models the changes in seismic velocities across the region are small except for low velocities in sedimentary basins and a 2 km positive elevation of the basement velocities v p 6 km s beneath the southern sierra nevada localized low v p and low v s zones beneath the central coso range image a geothermal reservoir at 0 to 3 km depth as well as distinct low velocity anomalies in the depth range of 8 to 12 km because the v p v s has average crustal values within this broader zone we interpret the anomaly to indicate a zone of few percent geothermal brines extending from 8 to 12 km depth in addition an embedded highly localized poorly resolved zone possibly as small as 1 km 3 of slightly above average v p v s and higher poisson s ratio is a tentative suggestion of a small volume percent of magma present at depth of 10 km second we relocated the seismicity in the region using absolute traveltimes and differential traveltimes determined from waveform cross correlation the relocated seismicity forms several spatially clustered lineaments along the southeast side of the sierra nevada and in the indian wells valley and vicinity of the coso geothermal field which coincide with mapped late quaternary faults in the region the base of seismicity shallows from a regional depth of about 11 to 5 km beneath the central coso range which we interpret as evidence for shallowing of the brittle ductile transition zone beneath the geothermal field in addition to abundant background seismicity two large earthquake swarms located 5 to 8 km to the west of coso occurred in april to may 1992 and may to june 2001 two dual main shock aftershock sequences also occurred as follows the 1994 sequence near ridgecrest and the later coso earthquake sequence from late 1996 to early 1998 with the pairs of main shocks spaced 47 days and 16 months apart respectively kinematic analysis of the focal mechanisms indicates that the crustal stress loading process varies across the region the low vp anomaly abundant seismicity and crustal thinning provide quantitative evidence for the coso region being an extensional releasing step over between two northwest striking dextral faults the little lake and airport lake fault zones to the south and the owens valley fault to the north

the san gabriel mountains bright reflective zone possible evidence of young mid crustal thrust faulting in southern california abstract during the los angeles region seismic experiment larse a reflection refraction survey was conducted along a line extending northeastward from seal beach california to the mojave desert crossing the los angeles basin and san gabriel mountains shots and receivers were spaced most densely through the san gabriel mountains for the purpose of obtaining a combined reflection and refraction image of the crust in that area a stack of common midpoint cmp data reveals a bright reflective zone 1 s thick that dominates the stack and extends throughout most of the mid crust of the san gabriel mountains the top of this zone ranges in depth from 6 s 18 km depth in the southern san gabriel mountains to 7 5 s 23 km depth in the northern san gabriel mountains the zone bends downward beneath the surface traces of the san gabriel and san andreas faults it is brightest between these two faults where it is given the name san gabriel mountains bright spot sgmbs and becomes more poorly defined south of the san gabriel fault and north of the san andreas fault the polarity of the seismic signal at the top of this zone is clearly negative and our analysis suggests it represents a negative velocity step the magnitude of the velocity step is approximately 1 7 km s in at least one location an event with positive polarity can be observed 0 2 s beneath the top of this zone indicating a thickness of the order of 500 m for the low velocity zone at this location several factors combine to make the preferred interpretation of this bright reflective zone a young fault zone possibly a master decollement 1 it represents a significant velocity reduction if the rocks in this zone contain fluids such a reduction could be caused by a differential change in fluid pressure between the caprock and the rocks in the sgmbs near lithostatic fluid pressure is required in the sgmbs such differential changes are believed to occur in the neighborhood of active fault zones where fault value action has been postulated less likely alternative explanations for this velocity reduction include the presence of magma and a change in composition to serpentinite or metagraywacke 2 it occurs at or near the brittle ductile transition at least in the southern san gabriel mountains a possible zone of concentrated shear 3 a thin reflection rising from its top in the southern san gabriel mountains projects to the hypocenter of the 1987 m 5 9 whittier narrows earthquake a blind thrust fault earthquake with one focal plane subparallel to the reflection alternatively one could argue that the bends or disruptions in the reflective zone seen at the san gabriel and san andreas faults are actually offsets and that the reflective zone is therefore an older feature possibly an older fault zone

provenance of oligocene miocene alluvial and fluvial fans of the northern ebro basin ne spain an xrd petrographic and sem study abstract this paper combines stratigraphic and sedimentological data with xrd petrographic and sem techniques in order to investigate the fluvial and alluvial fans that were developed during the oligocene and the lower miocene in the central area of the northern ebro basin spain and their respective source areas the proximal sectors of the coeval depositional systems can be separated on the basis of lithofacies criteria conglomerate features reveal that the source areas for the alluvial fans were limited to the south pyrenean sierras whereas those of the fluvial fans included more northern pyrenean areas such as the axial zone or the clastic tremp graus basin far from the basin margin the distal alluvial facies interdigitate with the middle distal fluvial deposits in these areas only detailed mineralogical and petrographic analysis of the rocks can determine their origin thus the methods used have allowed us to differentiate between authigenic and detrital phases on the basis of these observations three different types of coarse sandstone petrofacies have been distinguished 1 carbonate rich sandstone 2 high quartz sandstone and 3 high lithic fragment sandstone rich in shale and feldspars grains the first corresponds to the alluvial samples and corroborates the south pyrenean sierras as alluvial fans source area the high quartz and the high lithic fragment sandstone correspond to the fluvial samples and evidence that the drainage basin of the fluvial fans included the clastic tremp graus basin and the axial zone the high lithic fragment petrofacies is representative of the most ancient fluvial rocks whereas the high quartz sandstone corresponds to the recent and nonconforming fluvial rocks this change in the fluvial petrofacies allows us to recognise the changing importance of each region as a source area of the fluvial fans over time which can be correlated with pyrenean tectonic activity during the oligocene

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

san andreas fault dip peninsular ranges mafic lower crust and partial melt in the salton trough southern california from ambient noise tomography we use ambient noise tomography to improve cvm h11 9 a community velocity model of southern california our new 3d shear velocity model with 0 05 x0 05 lateral and 1 km vertical blocks reveals new structure beneath the san andreas fault saf peninsular ranges batholith prb southern sierra nevada batholith snb and the salton trough st we use four years of data recorded on 849 broadband stations vastly more than previous studies and including our own broadband salton seismic imaging project a 40 station transect across the st as well as other campaign stations in both mexico and the u s a mean lower crust and upper mantle wavespeeds 3 6 km s 20km 4 2 km s 40km are low by global standards across the saf southeast of san gorgonio pass we observe vertical to steeply dipping lateral velocity contrasts that extend beneath the moho beneath the western prb and westernmost southern snb we observe relatively high shear velocities 3 8 km s in the lower crust that we interpret as the mafic roots of the overlying arc relatively high velocity upper mantle up to 4 5 km s may be part of the intact arc or possibly a remnant of the farallon plate beneath the st we observe zones of low shear velocity in the lower crust and upper mantle which permit up to 4 5 melt in the lower crust and up to 6 melt in the upper mantle depending on the assumed composition and pore geometry our results preclude the existence of older continental crust beneath the st and support the creation of new crust beneath the st this article is protected by copyright all rights reserved

tectonic and geomorphic controls on the fluvial styles of the eslida formation middle triassic eastern spain abstract the eslida fm is an alluvial unit of the buntsandstein facies of the iberian ranges deposited in a half graben basin over a period of 2 2 5 ma during the lower anisian middle triassic it can be subdivided into six cycles that can be correlated along the basin the overall architecture and cyclicity were controlled by the episodic activity of the basin boundary fault two proximal source areas of minor importance and a distal one of major importance are identified the petrological composition of the sandstones is arkosic to subgrauwackic indicating source areas containing both low metamorphic rocks and gneiss and granitic rocks alluvial fans very common in rift basins were not developed because of slow fault scarp retreat and the lack of large antecedent rivers cutting across the rift shoulders paleocurrents point to the se except for a zone in the middle part of the basin where interference with a ne sw fault system deflected the channels to the s the infilling of the basin is asymmetric in a transverse section with channel facies near the basin boundary fault to the ne and overbank facies in the distal sw part

three dimensional seismic velocity structure and precise earthquake relocations in the salton trough southern california abstract i present a new 3d seismic velocity model and high precision earthquake relocations between 1981 and 2010 near the salton trough and the san jacinto fault zone the simul2000 tomography algorithm is applied to derive the 3d v p and v p v s models using first arrivals of a composite event data set the final v p model correlates with geological features at shallow depths and is more consistent with the refraction studies than the starting 3d regional scale model the v p v s model shows strong variations in the upper crust and is dominated by relatively low values below 1 7 in the middle crust except for the salton trough and the imperial valley the newly resolved model is used to relocate all the seismicity in the study area i then apply the similar event cluster analysis and differential time relocation approach based on waveform cross correlation data to the 3d relocated events a dramatic sharpening of seismicity patterns is obtained after using these methods the new locations are more tightly clustered than the previous catalogs mainly due to the different absolute locations the depth distribution along a basal surface may suggest the existence of a detachment fault from the north end of the salton trough to united states mexico border the fine scale velocity structure and precise earthquake relocations will be helpful for investigating the fault geometry seismicity stress interaction and other seismological studies for southern california online material figures of model resolution tests cross sectional comparisons of different p velocity models and earthquake depth distributions

radioactivity of the ocean floor and marine phosphorite deposits observations with a new deep towed scintillometer a new bottom towed scintillometer has been deployed in the tropical atlantic to investigate whether lithological changes on the deep sea bed can be determined from variations in its natural radioactivity although count rates over the blanket of recent pelagic carbonates fall within the seawater background high rates of gamma ray emission were detected on the crest of a seamount near 9 n 21 w seismic profiles bottom sampling and photography demonstrate that the radiometric anomalies coincide with areas in which the veneer of pelagic ooze is locally absent and phosphatized limestones of cenozoic age p2o5 14 are exposed the contrast in the u contents of the phosphorites 30 ppm and pelagic carbonates 100 ppm profiling the levels of seabed radioactivity would be a relatively rapid means of defining the distribution of phosphorite in many parts of the oceans

investigating the use of alluvial fan volume to represent fan size in morphometric studies studies of the morphometric properties of alluvial fans have predominantly used a two dimensional planimetric area to represent fan size even though fans are three dimensional sediment deposits but the validity of this substitution has been questioned volumes of fans in nonsubsiding settings were estimated with the objective of investigating the relationship between fan volume and fan area a simple geometric approach was developed so that volumes of noncoalescent fans could be estimated with measurements from topographic maps data were collected from two study areas with humid temperate climates the bow valley in alberta canada and the absaroka range in wyoming usa because these landscapes were glaciated the fans are of paraglacial origin and are not related to contemporaneous tectonic subsidence using functional relation analysis results indicate that the proportional power law relationship between fan volume and fan area is not significantly different from 1 1 in both study areas morphometric relationships between fans and drainage basins are also examined with fan volume and cumulative sediment yield employed as variables

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

luminescence dating of fault related alluvial fan sediments in the southern arava valley israel abstract infrared stimulated luminescence irsl from coarse grained alkali feldspars was used to date alluvial and colluvial deposits from nahal shehoret situated in the hyperarid southern arava valley israel late pleistocene gravelly and sandy wadi deposits associated with fault related colluvial sediments were exposed in trench 17 t 17 which was excavated across a distinct fault scarp deposition of the lower alluvial beds in t 17 took place between 90 and 100 ka this was followed by the first period of tectonic activity and by erosion the age of the upper alluvial bed ranges from 75 to 60 ka a period of stability and reg soil formation was then followed by two scarp forming faulting events resulting in colluviation the colluvium deposited after the second event was dated to 36 ka modern colluvial sediments from nahal shehoret have residual irsl ages of a few hundred years whereas modem alluvial sediments have ages of a few thousand years colluvial sediments may therefore be more suitable for luminescence dating in arid regions

differential effects of base level tectonic setting and climatic change on quaternary alluvial fans in the northern great basin nevada usa

a new perspective on the geometry of the san andreas fault in southern california and its relationship to lithospheric structure the widely held perception that the san andreas fault saf is vertical or steeply dipping in most places in southern california may not be correct from studies of potential field data active source imaging and seismicity the dip of the saf is significantly nonvertical in many locations the direction of dip appears to change in a systematic way through the transverse ranges moderately southwest 55 75 in the western bend of the saf in the transverse ranges big bend vertical to steep in the mojave desert and moderately northeast 37 65 in a region extending from san bernardino to the salton sea spanning the eastern bend of the saf in the transverse ranges the shape of the modeled saf is crudely that of a propeller if confirmed by further studies the geometry of the modeled saf would have important implications for tectonics and strong ground motions from saf earthquakes the saf can be traced or projected through the crust to the north side of a well documented high velocity body hvb in the upper mantle beneath the transverse ranges the north side of this hvb may be an extension of the plate boundary into the mantle and the hvb would appear to be part of the pacific plate

full 3 d tomography for crustal structure in southern california based on the scattering integral and the adjoint wavefield methods we have successfully applied full 3 d tomography f3dt based on a combination of the scattering integral method si f3dt and the adjoint wavefield method aw f3dt to iteratively improve a 3 d starting model the southern california earthquake center scec community velocity model version 4 0 cvm s4 in f3dt the sensitivity frechet kernels are computed using numerical solutions of the 3 d elastodynamic equation and the nonlinearity of the structural inversion problem is accounted for through an iterative tomographic navigation process more than half a million misfit measurements made on about 38 000 earthquake seismograms and 12 000 ambient noise correlagrams have been assimilated into our inversion after 26 f3dt iterations synthetic seismograms computed using our latest model cvm s4 26 show substantially better fit to observed seismograms at frequencies below 0 2 hz than those computed using our 3 d starting model cvm s4 and the other scec cvm cvm h11 9 which was improved through 16 iterations of aw f3dt cvm s4 26 has revealed strong crustal heterogeneities throughout southern california some of which are completely missing in cvm s4 and cvm h11 9 but exist in models obtained from previous crustal scale 2 d active source refraction tomography models at shallow depths our model shows strong correlation with sedimentary basins and reveals velocity contrasts across major mapped strike slip and dip slip faults at middle to lower crustal depths structural features in our model may provide new insights into regional tectonics when combined with physics based seismic hazard analysis tools we expect our model to provide more accurate estimates of seismic hazards in southern california

differential features of alluvial fans controlled by tectonic or eustatic accommodation space examples from the betic cordillera spain abstract the creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area along basin margin faults or to a rise in base level depending amongst others on the relative importance of these two factors the margins of terrestrial sedimentary basins where alluvial fans develop produce aggradational progradational or retrogradational stratigraphic architecture we studied a total of 43 quaternary alluvial fans in the granada and bajo segura basins betic cordillera spain the analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns which is the result of differences in eustasy and tectonics the qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related in each case to the main mechanism operative in the creation of accommodation space these patterns are described as follows 1 alluvial aggradation is the main result of high tectonic subsidence with the development of quite open but small fans with a constant steep slope lacking incised channels and headward eroding gullies 2 in contrast when the principal mechanism in creating accommodation space is low tectonic subsidence progradation occurs and the fans are narrower and larger moreover the slopes of such fans are less steep in relation to the drainage area than in the above case being constant or even concave in longitudinal profile they also have short deep incised channels culminating downfan in a depositional lobe in inactive zones long deep headward eroding gullies develop 3 areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin although with a pronounced mountain embayment which gives them a characteristic mushroom shape in plan view in the latter case retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas usually showing a segmented longitudinal profile with a low gradient the feeder channels do not surpass stream order 3 and various extremely long and shallow incised channels can appear 4 contrary to the case of fans developing under a regime of subsidence when the accommodation is due to base level rise the fan slopes bear no relation to the extent of the catchment basins in such a case the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet flows over the alluvial surface

crustal structure determined from ambient noise tomography near the magmatic centers of the coso region southeastern california we apply seismic ambient noise tomography to image and investigate the shallow shear velocity structure beneath the coso geothermal field and surrounding areas data from a passcal experiment operated within the coso geothermal field between 1998 and 2000 and surrounding broadband stations from the southern california seismic network are acquired and processed daily cross correlations of ambient noise between all pairs of stations that overlapped in time of deployment were calculated and then stacked over the duration of deployment phase velocities of rayleigh waves between 3 and 10 s periods are measured from the resulting cross correlations depending on the period between about 300 and 600 reliable phase velocity measurements are inverted for phase velocity maps from 3 to 10 s periods which in turn are inverted for a 3 d shear velocity model beneath the region the resulting 3 d model reveals features throughout the region that correlate with surface geology beneath the coso geothermal area shear velocities are generally depressed a prominent low velocity anomaly is resolved clearly within the top 2 km no significant anomaly is seen below about 14 km depth and a weakly resolved anomaly is observed between 6 and 12 km depth the anomaly in the top 2 km probably results from geothermal alteration in the shallow subsurface no magmatic body is imaged beneath 14 km depth but the shear velocity anomaly between 6 and 12 km may be attributable to partial melt the thickness and amplitude of the magma body trade off in the inversion and are ill determined low velocities in the regions surrounding coso at depths near 7 km underlie areas with miocene to recent volcanism suggesting that some magmatic processing of the crust could be focused near this depth

subsurface fault geometries in southern california illuminated through full 3d seismic waveform tomography f3dt abstract more precise spatial descriptions of fault systems play an essential role in tectonic interpretations deformation modeling and seismic hazard assessments the recent developed full 3d waveform tomography techniques provide high resolution images and are able to image the material property differences across faults to assist the understanding of fault systems in the updated seismic velocity model for southern california cvm s4 26 many velocity gradients show consistency with surface geology and major faults defined in the community fault model cfm plesch et al 2007 which was constructed by using various geological and geophysical observations in addition to faults in cfm cvm s4 26 reveals a velocity reversal mainly beneath the san gabriel mountain and western mojave desert regions which is correlated with the detachment structure that has also been found in other independent studies the high resolution tomographic images of cvm s4 26 could assist the understanding of fault systems in southern california and therefore benefit the development of fault models as well as other applications such as seismic hazard analysis tectonic reconstructions and crustal deformation modeling

slip rates and off fault deformation in southern california inferred from gps data and models 1 in southern california fault slip rate estimates along the san andreas fault saf and garlock fault from geodetically constrained kinematic models are systematically at the low end or lower than geologic slip rate estimates the sum of geodetic model slip rates across the eastern california shear zone is higher than the geologic sum however the ranges of reported model and geologic slip rate estimates in the literature are sufficiently large that it remains unclear whether these apparent discrepancies are real or attributable to epistemic uncertainties in the two types of estimates we further examine uncertainties in geodetically derived slip rate estimates on major faults in southern california by conducting a suite of inversions with four kinematic models long term rigid elastic block models constrained by the geologic slip rates cannot fit the present day gps derived velocity field deforming permanent off fault strain elastic block models and viscoelastic earthquake cycle block models constrained by geologic slip rates can fit the present day gps derived velocity field with 28 33 of the total geodetic moment rate occurring as distributed deformation off of the major faults models incorporating viscoelastic mantle flow predict systematically higher slip rates than purely elastic models on many of the major southern california faults with ranges of elastic viscoelastic 29 34 30 37 mm yr for the carrizo saf segment 20 24 20 32 mm yr for the mojave saf segment 14 17 18 22 mm yr for the coachella saf segment 13 19 14 22 mm yr for the san jacinto fault and 5 11 5 11 mm yr for the western garlock fault

a topographic fingerprint to distinguish alluvial fan formative processes we demonstrate here a topographic fingerprint derived from a 1 m high resolution elevation model dem developed from airborne laser swath mapping alsm that distinguishes between formative processes from surface form in alluvial fans generated through relatively dry debris flows df and those surfaces formed primarily by fluvial sediment transport mf we selected alluvial fans with primarily holocene age surficial deposits along the eastern side of death valley california fans were initially classified in the field into df and mf types largely on the basis of sedimentological characteristics and surface morphometry trend surface analyses were performed on dems of the individual fans in order to remove the long wavelength trends both profile and planimetric from the residual data we found that high resolution surface data distinguishes process information in two ways 1 local relief increases as a function of length scale especially at length scales less than 40 60 m and 2 local relief is significantly higher for debris flow dominated fans than for fluvially dominated fans this fingerprint which is directly related to the dominant surface processes is unavailable from standard 30 m resolution data providing significant support for the acquisition of high quality high resolution data this fingerprint can be used to help calibrate numerical simulations of alluvial fan development and has the potential for similar applications to distinguish between processes of similar landforms on other planetary bodies within our solar system