neogene tectonic rotation of the santa ynez range western transverse ranges california suggested by paleomagnetic investigation of the monterey formation a paleomagnetic investigation was conducted on dolomite beds in the middle and upper miocene monterey formation in order to determine the timing and amount of post early miocene tectonic rotation experienced by the santa ynez range part of the western transverse ranges province of california five stratigraphic sections of the monterey formation exposed along the coastline west of santa barbara were extensively sampled the sections were correlated using tuff beds and ages were assigned to each dolomite bed on the basis of magnetostratigraphy and diatom biostratigraphy the dolomite beds possess stable primary remanent magnetic directions which pass fold tests and reversal tests and show a consistent decrease in magnetic declination with decreasing age rocks 14 8 to 15 8 m y old have a mean magnetic declination of 92 7 whereas rocks 8 to 11 m y old have a mean magnetic declination of 36 7 the consistent upsection decrease in magnetic declination within these stratigraphic sections is attributed to a rapid 56 10 clockwise rotation of the entire santa ynez range between 15 2 0 1 and 10 1 m y b p the mean magnetic declination of 36 7 in rocks 8 to 11 m y old is probably due to continued clockwise rotation of the santa ynez range during the plio pleistocene an early miocene palinspastic reconstruction is proposed in which the area of the presently east west trending santa ynez range is restored to an initially north south orientation

the notion of climate driven strath terrace production assessed via dissimilar stream process response to late quaternary climate abstract previous research results from the gabilan mesa are combined with new optically stimulated luminescence osl age estimates and sedimentological analyses with the aim of identifying factors that inhibit climate driven strath terrace production and factors that make possible strath terrace production independent of climate forcing the factors are revealed by comparing the morphostratigraphy and osl age estimates of terraces in the adjacent san lorenzo creek and pancho rico creek drainage basins of the central california coast ranges osl age estimates on san lorenzo creek fill terrace alluvium overlying bedrock at two paleofluvial levels range between 50 5 and 41 3 ka and between 33 4 and 18 2 ka these osl age estimates indicate that although the channel of pancho rico creek was degrading at these times san lorenzo creek aggradation was synchronous with previously documented regional climatically driven aggradation that elsewhere in southern california led to strath production and alluvial deposition the regional scale climate forcing events had different effects on san lorenzo and pancho rico creeks because of the influences of drainage basin lithology on bedload size and tectonic tilting direction on base level fall the holocene history of channel denudation and strath production of pancho rico creek is also different from that of san lorenzo creek and different from that of many other streams in southern california after pancho rico creek captured the upper part of the drainage basin of san lorenzo creek sometime after 15 5 to 11 7 ka pancho rico creek has been producing unpaired erosional strath terraces the weak clay rich fine grained sedimentary rock underlying pancho rico valley is an ideal substrate in which to form straths the meandering channel of pancho rico creek produces straths and weathering resistant relatively hard bedload introduced by stream capture ensures their preservation as strath terraces

the land sea breeze of the red sea observations simulations and relationships to regional moisture transport unique in situ observations of atmospheric conditions over the red sea and the coastal arabian peninsula are examined to study the dynamics and regional impacts of the local land sea breeze cycle lsbc during a 26 month data record spanning 2008 2011 observed lsbc events occurred year round frequently exhibiting cross shore wind velocities in excess of 8 m s observed onshore and offshore features of both the land and sea breeze phases of the cycle are presented and their seasonal modulation is considered weather research and forecasting climate downscaling simulations and satellite measurements are used to extend the analysis in the model the amplitude of the lsbc is significantly larger in the vicinity of the steeper terrain elements encircling the basin suggesting an enhancement by the associated slope winds observed and simulated conditions also reflected distinct gravity current characteristics of the intrinsic moist marine air mass during both phases of the lsbc specifically the advance and retreat of marine air mass was directly tied to the development of internal boundary layers onshore and offshore throughout the period of study convergence in the lateral moisture flux resulting from this air mass ascending the coastal topography sea breeze phase as well as colliding with air masses from the opposing coastline land breeze phase further resulted in cumulous cloud formation and precipitation

vector constraints on western u s deformation from space geodesy neotectonics and plate motions the rate of slip vector on the san andreas fault in central california estimated from geodetic and holocene geological data 34 3 mm yr n41 w 2 is inconsistent with the prediction of rigid plate models such as rm2 56 3 mm yr n35 w 2 this well known san andreas discrepancy is diagnostic of plate deformation distributed both east of the fault in the basin and range and west of the fault along the california continental margin we construct constraints on the integrated deformation rates across these two regions consistent with 1 the kinematical boundary conditions imposed by the rigid plate model 2 neotectonic and paleoseismic estimates of deformation rates 3 ground based geodetic measurements and 4 rates of change observed by very long baseline interferometry along seven baselines to western u s sites the space geodetic data on basin and range extension taken over a 4 year interval are compatible with geological observations averaged over the holocene the best estimate of its integrated deformation rate provided by the joint inversion of both data types is 9 7 2 1 mm yr n56 w 10 too small and in the wrong direction to account entirely for the san andreas discrepancy we therefore attribute much of it to deformation west of the sierra nevada great valley block accommodated for example on faults such as the san gregorio hosgri system of coastal california the integral of this deformation estimated by subtracting the basin and range contribution from the discrepancy vector requires significant right lateral shear parallel to the san andreas 13 5 mm yr and some compression perpendicular to it 9 3 mm yr

devils hole nevada δ18o record extended to the mid holocene abstract the mid to late pleistocene devils hole 18 o record has been extended from 60 000 to 4500 yr ago the new 18 o time series in conjunction with the one previously published is shown to be a proxy of pacific ocean sea surface temperature sst off the coast of california during marine oxygen isotope stages mis 2 and 6 the devil hole and sst time series exhibit a steady warming that began 5000 to 10 000 yr prior to the last and penultimate deglaciations several possible proximate causes for this early warming are evaluated the magnitude of the peak 18 o or sst during the last interglacial lig is significantly greater 1 per mill and 2 to 3 c respectively than the peak value of these parameters for the holocene in contrast benthic 18 o records of ice volume show only a few tenths per mill difference in the peak value for these interglacials statistical analysis provides an estimate of the large shared information variation between the devils hole and eastern pacific sst time series from 41 to 2 n and enforces the concept of a common forcing among all of these records the extended devils hole record adds to evidence of the importance of uplands bordering the eastern pacific as a source of archives for reconstructing pacific climate variability

shelf construction in a foreland basin storm beds shelf sandbodies and shelf slope depositional sequences in the upper cretaceous mesaverde group book cliffs utah the upper cretaceous campanian kenilworth member of the blackhawk formation mesaverde group is part of a series of strand plain sandstones that intertongue with and overstep the shelfal shales of the western interior basin of north america analysis of this section at a combination of small sedimentological and large stratigraphical scales reveals the dynamics of progradation of a shelf slope sequence into a subsiding foreland basin four major lithofacies are present in the upper mancos and kenilworth beds of the book cliffs a lag sandstone and channel fill shale lithofacies constitutes the thin basal transgressive sequence which rests on a marine erosion surface it was deposited in an outer shelf environment shale interbedded sandstone and shale and amalgamated sandstone lithofacies were deposited over the transgressive lag sandstone lithofacies as a wave dominated delta and its flanking strand plains prograded seaward analysis of grain size and primary structures in kenilworth beds indicates that there are four basic strata types which combine to build the observed lithofacies the fine to very fine grained graded strata of the interbedded facies are tempestites deposited out of suspension by alongshelf storm flows geostrophic flows there is no need to call on cross shelf turbidity currents density underflows to explain their presence very fine to fine grained hummocky strata are likewise suspension deposits created by waning storm flows but were deposited under conditions of more intense wave agitation on the middle shoreface cross strata sets in this region are bed load deposits that accumulated on the upper shore face in the surf zone lag strata are multi event bed load deposits that are the product of prolonged storm winnowing they occur on transgressive surfaces while the graded beds are tempestites in the strict sense all four classes of strata are storm deposits the distribution of strata types and their palaeocurrent orientations suggests a model of the kenilworth transport system driven by downwelling coastal storm flows and probably by a northeasterly alongshore pressure gradient the stratification patterns shift systematically from upper shoreface to lower shoreface and inner shelf lithofacies partly because of a reduction in fluid power expenditure with increasing water depth but also because of progressive sorting which resulted in a decrease in grain size in the sediment load delivered to successive downstream environments the kenilworth member and an isolated outlier the hatch mesa lentil constitute a delta prodelta shelf depositional system their rhythmically bedded lenticular sandstone and shale successions are a prodelta shelf facies and may be prodelta plume deposits major upper cretaceous sandstone tongues in the book cliffs are underlain by erosional surfaces like that beneath the blackhawk formation which extend for many tens of kilometres into the mancos shale these surfaces are the boundaries of upper cretaceous depositional sequences the sequences are large scale genetic stratigraphic units they result from the arranging of facies into depositional systems the depositional systems are in turn stacked in repeating arrays which constitute the depositional sequences the anatomy of these foreland basin sequences differs

formation evolution and inversion of the middle tertiary diligencia basin orocopia mountains southern california the diligencia basin located in the eastern orocopia mountains of southern california contains 1500 2000 m of oligocene miocene continental siliciclastic sedimentary rocks and subordinate limestone and evaporite deposits intercalated with basaltic lavas these rocks are locally intensely folded and faulted defining in present day coordinates an elongate east west trending basin and are unconformably overlain by flat lying late pliocene and pleistocene alluvial deposits the sedimentological stratigraphic and structural history of the basin is compatible with late oligocene early miocene formation as a half graben basin produced by orthogonal basin and range type extension and latest miocene to pliocene basin inversion in either a localized transpressional transverse range regime or a more diffuse compressional regime associated with north south shortening of the entire mojave block facies associations in the lower part of the diligencia basin display a distinctly asymmetric distribution across the basin indicating deposition in a half graben with a steep possibly fault controlled south facing northern escarpment and a more gentle north facing southern slope paleocurrent data particularly from high energy deposits on the northern basin margin indicate stream flow toward the southeast to south southeast oblique to the deformed basin margins and suggest an approximate northeast to east northeast strike for the basin before deformation previously published paleomagnetic data however indicate that the elongate currently east west trending fault block containing the diligencia basin has rotated clockwise by as much as 110 about a vertical axis angle depends on data and model used since deposition ceased if correct this would suggest that the basin may have originally opened to between the northeast and east northeast subparallel to well documented extension directions in miocene age basins in the mojave desert to the east clockwise rotation on east west fault blocks exposed in this region has previously been bracketed as between ca 10 and 4 5 ma structural and paleomagnetic data indicate that inversion of the diligencia basin occurred after block rotation implying a latest miocene to pliocene age for inversion we speculate that basin inversion within a north south and still active compressive stress field resulted from the locking and subsequent internal deformation of this previously passively rotating elongate crustal block

taking apart the big pine fault redefining a major structural feature in southern california 1 new mapping along the big pine fault trend in southern california indicates that this structural alignment is actually three separate faults which exhibit different geometries slip histories and senses of offset since miocene time the easternmost fault along the north side of lockwood valley exhibits left lateral reverse quaternary displacement but was a north dipping normal fault in late oligocene to early miocene time the eastern big pine fault that bounds the southern edge of the cuyama badlands is a south dipping reverse fault that is continuous with the san guillermo fault the western segment of the big pine fault trend is a north dipping thrust fault continuous with the pine mountain fault and delineates the northern boundary of the rotated western transverse ranges terrane this redefinition of the big pine fault differs greatly from the previous interpretation and significantly alters regional tectonic models and seismic risk estimates the outcome of this study also demonstrates that basic geologic mapping is still needed to support the development of geologic models

numerical modelling of the offshore extent of sea breezes two and three dimensional versions of a nonlinear atmospheric model were used to investigate environmental controls on the offshore influence of sea breeze circulations the temperature of the water surface relative to the atmospheric temperature had a small effect when the water was colder than the overlying air and a greater effect when the water temperature was high enough to create convective mixing in the planetary boundary layer over the water ambient thermal stratification including elevated inversions with thermal stratification similar to trade wind inversions had a small influence the predicted offshore extent of the sea breeze was substantially affected by latitude the effects of both ambient stratification and latitude were generally consistent with predictions of linear theory prevailing synoptic winds were also found to have a significant effect on the sea breeze offshore with offshore influence greatly suppressed by onshore large scale flow curvature of the coastline produces slightly stronger winds offshore for a concave coast than for a convex coast the subsidence offshore also extends further over the water for a concave coast than for a convex coast the model predictions were compared with previous investigations which used linear theory it was found that the present results agreed with the linear theory of r rotunno with regard to the effects of latitude and ambient thermal stability linear theory is less suitable for explaining the effects of water temperature owing to the simplified treatment of turbulent exchange necessary for a tractable linear model

two dimensional magnetotelluric inversion of blocky geoelectrical structures 1 this paper demonstrates that there are alternative approaches to the magnetotelluric mt inverse problem solution based on different types of geoelectrical models the traditional approach uses smooth models to describe the conductivity distribution in underground formations in this paper we present a new approach based on approximating the geology by models with blocky conductivity structures we can select one or another class of inverse models by choosing between different stabilizing functionals in the regularization method the final decision whose approach may be used for the specific mt data set is made on the basis of available geological information this paper describes a new way of stabilizing two dimensional mt inversion using a minimum support functional and shows the improvement that it provides over traditional methods for geoelectrical models with blocky structures the new method is applied to mt data collected for crustal imaging in the carrizo plain in california and to mt data collected for mining exploration by inco exploration

interaction between the controls on fluvial system development tectonics climate base level and river capture rio alias southeast spain fluvial systems in uplifting terrain respond to tectonic climatic eustatic and local base level controls modified by specific local factors such as river capture the rio alias in southeast spain is an ephemeral transverse to structure fluvial system the river drains two interconnected neogene sedimentary basins the sorbas and almeria basins and crosses two major geological structures the sierras de alhamilla cabrera and the carboneras fault zone regional epeirogenic uplift resulted in sustained fluvial incision during the quaternary punctuated by major climatically driven periods of aggradation and dissection which created a suite of five river terraces the river terrace sequence was radically modified in the late pleistocene by a major river capture itself a response to regional tectonics localized tectonic activity and eustatic base level change the rio alias is defined by four reaches within each the climatically generated region wide fluvial response was modified by tectonics base level change or river capture to varying degrees in the upper part of the basin lucainena reach climate was the dominant control on river development with limited modification of the sequence by uplift of the sierra alhamilla and local drainage reorganization by a local river capture downstream of the sierra alhamilla in the polopus reach the climatic signal is dominant but its expression is radically modified by the response to a major river capture whereby the alias system lost up to 70 of its pre capture drainage area in the reach adjacent to the carboneras fault zone argamason reach modification of the terrace sequence by local tectonic activity and a resultant local base level fall led to a major local incisional event propagating c 3 4 km upstream from the area of tectonic disturbance at the seaward end of the system el saltador reach quaternary sea level changes modified the patterns of erosion and incision and have resulted in steep incisional terrace profiles the signals generated by regional tectonics and the quaternary climate change can be identified throughout the basin but those generated by ongoing local tectonics river capture and sea level change are spatially restricted and define the four reaches the connectivity of the system from the headwaters to the coast decreased through time as incision progressed resulting in changes in local coupling characteristics copyright 2012 john wiley sons ltd

russell fault early strike slip fault of california coast ranges the subsurface russell fault is a controlling structure for oil fields in the cuyama basin in the southern salinian block of coastal california movement on the russell fault began at about 23 ma following deposition of the oligocene simmler formation in extensional basins bounded on the south by normal fault ancestors of the la panza and ozena reverse faults right lateral strike slip on the russell fault began with deposition of the soda lake shale member of the vaqueros formation the soda lake shale member and painted rock sandstone member of the vaqueros formation were deposited in west trending right stepping troughs while most of the right slip on the russell fault accumulated 23 19 ma pre vaqueros strata are offset 26 29 km but vaqueros isopachs are offset onl 3 7 km the whiterock bluff shale member of the monterey formation is dated as 16 5 14 ma the facies boundary between the whiterock bluff shale member and the branch canyon sandstone is offset 3 3 4 km coeval subsidiary faults near the russell fault in miocene strata at least as young as 11 ma also support distributed right lateral shear the russell fault is overlain unconformably by the morales formation which includes strata as old as 4 ma 1 m y north of russell ranch oil field the russell fault bifurcates into a western strand that joins the chimeneas fault and an eastern strand that is overridden by the big spring reverse fault the russell fault may continue to the southeast as the ozena fault and be offset across the big pine fault right slip began 6 7 m y after the predicted time of first contact of the pacific and north american plates slip rates were 6 5 7 mm yr during 23 19 ma 0 1 0 3 mm yr during 19 14 ma and 0 3 1 1 mm yr during 14 4 ma the sudden decrease in slip rate occurred as the basin deepened at the time of monterey formation deposition which began about 19 ma the relation of development of vaqueros basins containing soda lake shale member to strike slip on the russell fault suggests that a reconstruction of the early miocene strike slip tectonics of the southeastern coast ranges may permit exploration for other hidden vaqueros basins elsewhere in the salinian block

reconciling patterns of interseismic strain accumulation with thermal observations across the carrizo segment of the san andreas fault article i nfo the carrizo segment of the san andreas fault separates rocks of the salinian block southwest of the fault characterized by high heat flow 75 95 mw m 2 and shallow seismicity b 10 km depth from rocks of the franciscancomplexandgreatvalleygroupnortheastofthefaultassociatedwithlowheat flow 50 60 mw m 2 and deeper seismicity b 20 km depth gps data from this region suggest that the northeast side of the fault accommodates more interseismic strain than the southwest side we show that by incorporating variations in depthtothebrittleductiletransitioninferredbasedonheat flowandseismicitydata we fitthegeodeticdatawell and achieve agreement with geologically accepted long term average slip rates with a 20 km wide zone with lowyoung smodulusneofthefault thiswidecompliantzoneisconsistentwithobservationssuggestingthatthe presence of large overpressures may be decreasing the elastic moduli in this region

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

depositional environments in the monterey formation cuyama basin california the monterey formation of the cuyama basin accumulated in an inboard basin within a miocene borderland analogous to the recent continental borderland off southern california analysis of benthic foraminiferal biofacies lithology and sedimentary structures permits recognition of several depositional environments within the monterey formation in this basin the lower member of the monterey formation the saltos shale early miocene contains basin plain slope and various submarine fan subenvironments these predominantly terrigenous rocks are interbedded with impure carbonates composed primarily of foraminifera and calcareous nannofossils the upper member the whiterock bluff shale middle miocene contains highly biogenous deposits representing slope and basin plain environments both siliceous and calcareous biogenous rocks are prominent in this unit the complex array of lithofacies within the monterey formation is the product of the interplay between terrigenous and biogenous sedimentation various factors control this interplay including global sea level climate paleo oceanographic changes local tectonics and paleogeography the monterey formation in the cuyama basin is more terrigenous than coeval sections in more outboard basins of the miocene borderland as represented by the santa barbara basin these latter areas contain many lithofacies indicative of low terrigenous sedimentation rates highly siliceous and calcareous rocks phosphatic rocks and highly organic rocks the inboard cuyama basin acted as a sediment trap during much of the miocene and is partly responsible for these lithofacies patterns both inboard and outboard basins contain variations in bulk accumulation rates that correlate to variations in relative sea level this study demonstrates the importance of depositional patterns paleogeography and multidisciplinary analysis for understanding the complex stratigraphic units found along active continental margins

internal structure of the precordilleran fault system chile insights from structural and geophysical observations abstract geological field work and audiomagnetotelluric data from two profiles crossing the west fissure zone in northern chile were used to describe the geometry and structure of the fracture damaged zone surrounding this strike slip fault system the w e profiles show that the width of the west fissure zone based on the fracture density distribution derived from aerial photographs is 4000 m on profile a and 7000 m on profile b the estimated widths correspond roughly to the region where the fault is kinematically uniform the ratio of the fault width to the fault length ranges from 0 024 to 0 041 this ratio compares favourably with the measured ratio of small metre scale natural faults audio frequency magnetotelluric imaging shows low electrical resistivity zones resistivity of 5 30 m coincident with the mapped surface traces of the fault however these zones are very narrow width about 100 m and only 50 m profile a and 200 m profile b deep respectively on profile b the shallow high conductive zone is underlain by a resistive zone 1000 m the conductivity enhancement in these shallow and narrow zones contrasts with the broad process zone revealed by structural analysis we assume that the conductivity enhancement is due to meteoric water entering a zone of ruptured rocks along the fault trace fault core at present we have no indication for seismic slip along the investigated segments of the west fissure zone fault models have shown that during aseismic periods of fault evolution fault healing i e strength recovery due to compaction and cementation is active fluids and fluid transport which are probably responsible for enhanced conductivity are confined to the remaining fractures of the fault core at shallow depth

robust smooth magnetotelluric transfer functions jimmy c larsen randall l mackie 2 adele man e l l a adolfo fiordelisi4 and shirley rieven2 pacific marine environmental laboratory national oceanic and atmospheric administration 7600 sand point way ne seattle wa 981 15 0070 usa wassachusetts institute of technology 42 carleton street cambridge m a 02142 usa cnr international institute for geothermal research piazza soljerino 2 pisa 56126 italy enel esplorazione mineraria via andrea pisano 120 pisa 56122 italy

an oceanic general circulation model ogcm investigation of the red sea circulation 2 three dimensional circulation in the red sea 1 the three dimensional circulation of the red sea is studied using a set of miami isopycnic coordinate ocean model micom simulations the model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation the main findings of this analysis include an intensification of the along axis flow toward the coasts with a transition from western intensified boundary flow in the south to eastern intensified flow in the north and a series of strong seasonal or permanent eddy like features model experiments conducted with different forcing fields wind stress forcing only surface buoyancy forcing only or both forcings combined showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind driven part of the circulation the main circulation pattern is related to the seasonal buoyancy flux mostly due to the evaporation which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface the response of the eastern boundary to the associated mean crossbasin geostrophic current depends on the stratification and b effect in the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of kelvin waves while in the south the traditional westward intensification due to rossby waves takes place the most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of red sea outflow water rsow beneath the surface boundary currents are similarly intensified southward undercurrents that carry the rsow to the sill to flow out of the basin into the indian ocean index terms 4243 oceanography general marginal and semienclosed seas 4255 oceanography general numerical modeling 4532 oceanography physical general circulation keywords red sea marginal sea oceanic general circulation model water mass formation

significant resistivity changes in the fault zone associated with the 1999 chi chi earthquake west central taiwan abstract the purpose of this paper is to demonstrate the possible influence of an earthquake on the resistivity distribution in a fault zone we collected resistivity image profiles across a proposed fault trace prior to the 7 3 magnitude 1999 shallow earthquake in the chi chi area of taiwan significant positive resistivity anomalies were observed in the hanging wall after the earthquake however there were negligible resistivity changes in the footwall from an examination of geoelectric phenomena and surface rupture in the fault zone it is believed that geoelectric anomalies are associated with abrupt displacement along the active chelungpu fault this result indicates a potential for resistivity methods to provide a basis for the monitoring of an active fault

carbon enhanced electrical conductivity during fracture of rocks changes in electrical resistance during rock fracture in the presence of a carbonaceous atmosphere have been investigated using nugget sandstone and westerly granite the experiments were performed in an internally heated gas pressure vessel with a load train that produced strain rates between 10 6 and 10 5 s 1 samples were deformed at temperatures of 354 to 502 c and pressures of 100 to 170 mpa in atmospheres of ar or mixtures of 95 co2 with 5 co or 5 ch4 compositions that are well within the field of graphite stability at the run conditions in experiments using nugget sandstone resistance reached a minimum value when the maximum temperature was achieved and good electrode contact was made the resistance then increased as the experiment continued probably due to dry out of the sample a change in the oxidation state of the fe oxide associated with the cement or destruction of current bearing pathways at approximately 200 mpa end load the rock sample failed plots of load and resistance versus time show several interesting features in one experiment for example as the end load reached about 175 mpa resistance stopped increasing and remained fairly constant for a period of approximately 0 5 hour during loading the end load displayed small decreases that were simultaneous with small decreases in resistance when the end load and the displacement indicated rock failure resistance decreased dramatically from 150 m to 100 m in a single experiment the westerly granite also showed a decrease in resistance during dilatancy the nature and distribution of carbon in the run products were studied by electron microprobe and time of flight secondary ion mass spectroscopy top sims carbon observed by mapping with the former is clearly observed on micro cracks that based on the microtexture are interpreted to have formed during the deformation the tof sims data confirm the electron probe observations that carbon is present on fracture surfaces these observations and experimental results lead to the hypothesis that as microfractures open in the time leading up to failure along a fracture carbon is deposited as a continuous film on the new reactive mineral surfaces and this produces a decrease in resistance subsequent changes in resistance occur as connectivity of the initial fracture network is altered by continued deformation such a process may explain some electromagnetic effects associated with earthquakes

structural transect of the western transverse ranges california implications for lithospheric kinematics and seismic risk evaluation a retrodeformable cross section that integrates surface and subsurface data across the western transverse ranges california illustrates an actively developing fold and thrust belt that began forming at 2 3 ma high level thrusts are interpreted to root in a mid crustal detachment at 12 15 km depth which coincides with the maximum depth of earthquakes the cross section documents 53 km of convergence above the mid crustal detachment dividing this by the time since onset of deformation yields convergence rates of 17 6 26 5 mm yr the high density lithospheric anomaly beneath the transverse ranges is related to subduction of lower crust and lithosphere below the mid crustal detachment to balance the shallow crustal shortening thrust ramps coincide with zones of high seismicity in the transverse ranges this suggests that ramp regions have the highest potential for compressive earthquake events e g the recent whittier narrows earthquake of october 1 1987 m sub l 5 9 occurred along the eastern part of a ramp zone

the determination of displacement fields from geodetic data along a strike slip fault observations of angles or distances between stations of a geodetic network are commonly used to infer information about the movement of the surface of the earth the absence of any observations external to the network leads to an ambiguous displacement field existing techniques for eliminating this ambiguity are all unsatisfactory in some respect the best technique an inner coordinate solution is not appropriate for networks located in a strike slip fault environment the inner coordinate solution zeros the rotation of all stations about their center of mass along a strike slip fault like the san andreas however motion normal to the fault is less likely than motion parallel to the fault the solution presented here an outer coordinate solution finds the rotation of the network that minimizes the components of displacement normal to the fault since motion along a strike slip fault is generally expected to be parallel to the fault the displacements obtained with the outer coordinate solution are more reasonable than those obtained with other techniques examination of a trilateration network near san francisco bay demonstrates the large effect that the choice of adjustment technique can have on the inferred relative motion of the two sides of the fault the inner coordinate solution gave a rate of about 1 mm yr whereas the preferred outer coordinate solution rate was 36 mm yr

the morphology and surface processes of comet 19 p borrelly the flyby of the nucleus of the comet 19p borrelly by the deep space 1 spacecraft produced the best views to date of the surface of these interesting objects it transformed borrelly from an astronomical object shrouded in coma of gas and dust into a geological object with complex surface processes and a rich history of erosion and landform evolution based on analysis of the highest resolution images stereo images photometry and albedo we have mapped four major morphological units and four terrain features the morphological units are named dark spots mottled terrain mesas and smooth terrain the features are named ridges troughs pits and hills in strong contrast to asteroids unambiguous impact craters were not observed on borrelly s surface because of the relatively short period of this comet surface erosion by volatile sublimation is in geologic terms a very active process the formation and the morphologies of units and features appear to be driven by differential rates of sublimation erosion erosional rates across the comet are probably controlled by solar energy input and the location of the subsolar point during perihelion differences in energy input may produce different varieties of sublimation erosional landforms the terrains on borrelly suggest that solar energy input could map directly into erosional processes and landforms

the geometry of listric growth faults in the devonian basins of sunnfjord w norway thick devonian clastic sequences accumulated in fault bounded basins in w norway at the close of the caledonian orogeny and mark the beginning of a phase of crustal extension traditionally the eastern boundary fault to the devonian basins has been regarded as a thrust but cross sections based on the use of a branch line reveal it to be an extension fault there is clear omission of structural section across the boundary and by matching up metamorphic rocks in the hanging and foot walls of the boundary fault over 40 km of extensional dip slip can be measured at the n end of the fault the boundary fault is a flat lying listric fault with rollover anticlines in the hanging wall the fault also cuts up and down section along strike to form lateral ramps parallel to the movement direction these ramps appear as wrench faults in outcrop the ramp flat geometry of the fault may have been inherited from a precursor caledonian thrust fault which reversed its sense of slip in early middle devonian times to form the basins over 25 km of onlapping sediment accumulated in the largest basin during faulting in 14 ma with an average slip rate on the fault of 3 mm yr 1

electrical resistivity changes not observed with the 28 september 2004 m6 0 parkfield earthquake on the san andreas fault california 1 an 18 a long experiment to capture changes in electrical resistivity prior to during and after a m6 earthquake on the san andreas fault at parkfield california culminated with an event of that magnitude on 28 september 2004 resistivity was monitored with a telluric array giving precisions in measured parameters of 0 2 or less no coseismic resistivity changes greater than 5 could have occurred or they would have been detected by the array and any precursory changes would have been much smaller because maximum possible precursory strains were 4000 times smaller than the coseismic strain given that the earthquake ruptured directly beneath the telluric array this experiment places a bound on the amount resistivity might change at the hypocentral location changes measured with instruments farther from earthquakes can only be smaller it is still possible that a measurable change with a larger earthquake or other fault geometries are capable of generating larger signals but our results show clearly that future experiments should be designed with precisions of much better than 0 1 if they are to be successful

resistivity structure of a seismic gap along the atotsugawa fault japan abstract seismicity along the atotsugawa fault located in central japan shows a clear heterogeneity the central segment of the fault with low seismicity is recognized as a seismic gap although a lot of micro earthquakes occur along this fault in order to elucidate the cause of the heterogeneity in seismicity the electrical resistivity structure was investigated around the atotsugawa fault by using the magnetotelluric mt method the regional geoelectrical strikes are approximately parallel to the fault in a low frequency range we constructed two dimensional resistivity models across the fault using tm mode mt responses to minimize three dimensional effects on the modeling process a smooth inversion algorithm was used and the static shifts on the apparent resistivity were corrected in the inversion process a shallow low resistivity zone along the fault is found from the surface to a depth of 1 2 km in the best fit model across the high seismicity segment of the fault on the other hand the corresponding low resistivity zone along the low seismicity segment is limited to a shallower depth less than 1 km the low resistivity zone along the atotsugawa fault is possibly due to fluid in the fracture zone the segment with higher levels of seismicity may have higher fluid content in the fault zone compared with the lower seismicity segment on a view of the crustal structure a lateral resistivity variation in a depth range of 3 12 km is found below the fault trace in the high seismicity segment while a resistive layer of wide extent is found at a depth of about 5 km below the fault trace in the low seismicity segment the resistive layer is explained by less fluid condition and possibly characterized as high rigidity differences in the resistivity structures between low and high seismicity segments of the fault suggest that the seismic gap in the central part of the atotsugawa fault may be interpreted as a locked segment thus mt is an effective method in evaluating a cause and future activity of seismic gaps along active faults the lower crust appears as a conductive zone beneath the low seismicity segment less conductive beneath the high seismicity segment fluid is inferred as a preferable cause of the conductive zone in this study it is suggested that the conductive lower crust beneath the low seismicity segment is recognized where fluid is trapped by an impermeable layer in the upper crust on the other hand fluid in the lower crust may upwell to the surface along the high seismicity segment of the fault

oligocene tectonics and sedimentation california abstract during the oligocene epoch california was marked by extensive nonmarine sedimentation in contrast to its pre oligocene and post oligocene depositional history the oligocene continental deposits are especially widespread in southern california and fill a number of small and generally partly restricted basins fluvial facies in many basins prograded over previously deposited lower tertiary turbidites volcanism from widespread centers was associated with the nonmarine sedimentation however some basins remained marine and a few contain oligocene turbidites and pelagic sediments deposited at bathyal depths the oligocene redbeds of california do not form a post orogenic molasse sequence comparable to the old red sandstone or alpine molasse they are synorogenic and record local uplift of basins and surrounding source areas late cretaceous to contemporary orogenesis in california has been generally characterized by the formation of small restricted basins of variable depth adjacent to small upland areas in response to strike slip faulting deposition of oligocene redbeds was associated with climatic change from warm and humid to cold and semiarid and a global lowering of sea level oligocene tectonism occurred during the transition from subduction of the farallon plate to initiation of the modern san andreas transform system however the major influence that caused uplift formation of fault bounded basins and extensive redbed deposition especially in southern california was the approach of the pacific farallon spreading ridge to the western margin of california

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

paleogeography of monterey formation cuyama basin california the cuyama basin is one of several discrete middle cenozoic basins that formed a continental borderland in the coastal california province during the miocene the monterey formation is lithologically and stratigraphically complex it varies widely in thickness up to 4 500 ft 1 400 m reflecting variable subsidence within the basin thinning over anticlines and the cox fault zone suggests structural movement occurred contemporaneously with sedimentation beginning in the late saucesian early miocene the age of the monterey formation also varies becoming younger to the northwest areas of maximum subsidence migrated from southeast cuyama valley to northwest northern la panza range schematic paleogeographic maps constructed on 4 time slices illustrate that the depositional history of the basin reflects these subsidence patterns and various depositional controls late saucesian relizian early miocene time is characterized by relatively low sea level maximum subsidence in the southeast and basinal sedimentation varying from calcareous biogenous sediments to sandy submarine fan deposits luisian early mohnian middle miocene patterns reflect high sea level maximum subsidence in the northwest and basinal sediments of a calcareous or siliceous biogenous nature finally the entire southern salinian block shoaled to shallow marine or nonmarine conditions by the end of mohnian late miocene time modified journal abstract

structure of the cuyama valley caliente range and carrizo plain and its significance to the structural style of the southern coast ranges and western transverse ranges a concerted exploration program in the cuyama area by arco during the last 10 years employing surface mapping deep drilling high quality seismic profiles biostratigraphic analysis and balanced cross sections has revealed several significant structural characteristics 1 thrust faults such as the morales and white rock flatten under the caliente range and merge into a single system with up to 14 km of slip this system intersects the san andreas fault at a high angle and may detach the san andreas fault at depth from 7 to 8 km 2 integration of surface and subsurface mapping shows that these thrust faults have little or no component of strike slip and are younger than 3 ma 3 major surface folds such as the caliente mountain anticline are due to thrust faults ramping upsection and producing fault bend and fault propagation folds 4 the young thrust system has cut across a late oligocene to early miocene extensional fault controlled basin and both tectonically transported and overthrust portions of this older basin these structural characteristics strongly suggest that the structural style of the cuyama area and possibly adjacent areas in the southern coast ranges and western transverse ranges is that of a fold and thrust belt and is not relatedmore to wrench tectonics less

magnetotelluric evidence for crustal suture zones bounding the southern great valley california a geoelectric section inferred from a regional magnetotelluric study across the coast ranges the great valley and the sierra nevada reveals significant variations in electrical resistivity zones of lower resistivity interpreted at depths from 10 km to at least 30 km lie near mapped geologic boundaries between the coast ranges and the great valley and beneath the eastern side of the great valley the former boundary is inferred by others to separate the subduction complex of the coast ranges from the mafic basement of the great valley the lower resistivities are most likely associated with metasediments trapped between the coast ranges ophiolite and the former oceanic crust beneath the great valley the latter boundary is problematic but may be evidence for a deep metasedimentary section trapped between the ophiolites beneath the great valley and the granitic rocks of the sierra nevada the lack of change in the magnetotelluric phase across the great valley indicates that a suture zone marked by lower resistivities is unlikely to be present beneath the valley however this does not preclude the existence of a resistive suture zone

the influence of upper crust lithology on topographic development in the central coast ranges of california abstract a fundamental geological tenet is that as landscapes evolve over graded to geologic time geologic structures control patterns of topographic distribution in mountainous areas such that terrain underlain by competent rock will be higher than terrain underlain by incompetent rock this paper shows that in active orogens where markedly weak and markedly strong rocks are juxtaposed along contacts that parallel regional structures relatively high topography can form where strain is localized in the weak rock such a relationship is illustrated by the topography of the central coast ranges between the pacific coastline and the san andreas fault zone safz and along the length of the gabilan mesa the gabilan mesa segment of the central coast ranges within the gabilan mesa segment the granitic upper crust of the salinian terrane is in contact with the accretionary prism melange upper crust of the nacimiento terrane along the inactive nacimiento fault zone a prominent topographic lineament is present along most of this lithologic boundary approximately 50 to 65 km southwest of the safz with the higher topography formed in the melange on the southwest side of the nacimiento fault this paper investigates factors influencing the pattern of topographic development in the gabilan mesa segment of the central coast ranges by correlating shortening magnitude with the upper crust compositions of the salinian and nacimiento terranes the fluvial geomorphology of two valleys in the gabilan mesa which is within the salinian terrane and alluvial geochronology based on optically stimulated luminescence osl age estimates reveal that the magnitude of shortening accommodated by down to the southwest tilting of the mesa since 400 ka is less than 1 to 2 m our results combined with those of previous studies indicate that at least 63 to 78 of late cenozoic northeast southwest directed upper crustal shortening across the gabilan mesa segment has been accommodated within the nacimiento terrane this is significant because perpendicular to orogenic strike the nacimiento terrane constitutes less than of the distance between the coast and the safz and the other or greater of the distance between the coast and the safz is underlain by the granitic upper crust of the salinian terrane we propose that strain and mountain building are localized within the nacimiento terrane because it consists predominantly of the relatively weak franciscan complex melange and because the upper crust of the salinian terrane is composed of relatively strong granitic rocks our hypothesis is supported by the distribution of post seismic surface uplift associated with the 2003 6 5 m w san simeon earthquake which mimics the topography of the southwestern part of the gabilan mesa segment of the central coast ranges

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

structure and formation of the highly stable marine boundary layer over the gulf of maine 1 a shallow stable boundary layer is ubiquitous over the cool waters of the gulf of maine in summer this layer affects pollutant transport throughout the region by isolating overlying flow from the surface in this paper we explore how the stable boundary layer is formed and describe its characteristics the temperature profile of the lowest 1 2 km of the atmosphere over the gulf of maine is remarkably similar regardless of transport time over water or the time of day when the flow left the land provided only that the flow is offshore this similarity is forced by the roughly constant water temperature and the roughly constant temperature of the free troposphere over the continent however the processes leading to the similar profiles are quite different depending on the time of day when the flow crosses the coast air leaving the coast at night already has a stable profile whereas air leaving the coast at midday or afternoon has a deep mixed layer in the latter case the stable layer formation over the water is of interest using observations of surface fluxes profiles and winds on the noaa research vessel ronald h brown from the 2004 international consortium for atmospheric research in transport and transformation icartt new england air quality study we show that the formation of the stable layer which involves cooling a roughly 50 to 100 m deep layer by 5 15 k occurs within 10 km and a half hour after leaving the coast the internal boundary layer near shore is deeper than predicted by standard relationships historical data are explored and also show deeper internal boundary layers than predicted we also describe one exceptional case where a 200 m deep neutral layer was observed and discuss the degree of isolation of the stable boundary layer and its duration

the stable internal boundary layer over a coastal sea part ii gravity waves and the momentum balance abstract observations of the mean and turbulent structure of the marine atmospheric boundary layer mabl obtained using the u k meteorological research flight c 130 hercules aircraft are used to investigate the momentum balance over the irish sea when warm air is advected offshore the marine boundary layer is made up of two layers a strongly stable internal boundary layer ibl and a stable residual layer located between the top of the ibl and the base of the planetary boundary layer inversion measurements obtained near the upwind coast indicate that the flow is highly ageostrophic downwind of the irish coast there is a transition toward equilibrium between the geostrophic coriolis and friction components of the flow along part of the flight track however another segment of the flight track indicates an imbalance between the pressure gradient and the other measured terms which may be attributable to gravity waves affecting the adjustment process this is more apparent in the leg perpendicula

marine magnetotellurics for base of salt mapping gulf of mexico field test at the gemini structure a sea floor magnetotelluric mt survey was conducted over the gemini subsalt petroleum prospect in the gulf of mexico gom to demonstrate that the base of salt can be mapped using marine magnetotelluric mmt methods the high contrast in electrical resistivity between the salt and the surrounding sediments provides an excellent target for mmt the gemini salt body located at 28 46 n 88 36 w is a relatively complex shape buried 2 5 km below the sea floor in 1 km deep water its geometry has been previously determined using 3 d seismic prestack depth migration with well log control in order not to confuse limitations in interpretation technique with limitations in data acquisition numerical forward and inverse modeling guided the survey design to locate a profile that would be amenable to 2 d inversion even though the body was clearly 3 d the seismic imaging of the base of salt along the chosen profile is considered good thus providing a good control for testing the mt method in many other ar

global observations of the land breeze 1 four times daily satellite wind observations from the quikscat and adeos ii tandem scatterometer mission are used to study the land sea breeze circulation these observations provide a global view of diurnal wind variations over the ocean results agree with frictional linear theory winds follow an elliptical hodograph through the course of the day but indicate that diurnal wind variations propagate offshore progressively like nonlinear gravity waves and are detectable several hundred kilometers from the coast

sharp boundary inversion of 2d magnetotelluric data we consider 2d earth models consisting of laterally variable layers boundaries between layers are described by their depths at a set of nodes and interpolated laterally between nodes conductivity within each layer is described by values at a set of nodes fixed within each layer and is interpolated laterally within each layer within the set of possible models of this sort we iteratively invert magnetotelluric data for models minimizing the lateral roughness of the layer boundaries and the lateral roughness of conductivities within layers for a given level of data misfit this stabilizes the inverse problem and avoids superfluous detail this approach allows the determination of boundary positions between geological units with sharp discontinuities in properties across boundaries while sharing the stability features of recent smooth conductivity distribution inversions we compare sharp boundary inversion results with smooth conductivity distribution inversion results on a numerical example and on inversion of field data from the columbia river flood basalts of washington state in the synthetic example where true positions and resistivities are known sharp boundary inversion results determine both layer boundary locations and layer resistivities accurately in inversion of columbia flood basalt data sharp boundary inversion recovers a model with substantially less internal variation within units and less ambiguity in both the depth to base of the basalts and depth to resistive basement

a magnetotelluric investigation of the san andreas fault at carrizo plain california high quality wide band magnetotelluric data were collected along two profiles crossing the san andreas fault at carrizo plain california for crustal imaging as part of the san andreas deep drilling project two dimensional inversions of the data indicate that the upper crustal part of the san andreas fault does not appear here as an anomalously conductive zone additionally a broad resistive zone under the temblor mountains east of the fault suggests resistive crystalline or metamorphic rocks may be present here as opposed to the more conducting franciscan assemblage contradicting the generally accepted geologic model

electrical structures of the source area of the 1999 chi chi taiwan earthquake spatial correlation between crustal conductors and aftershocks abstract wide band magnetotelluric mt data were collected on an east west profile approximately perpendicular to the local strike of the chelungpu thrust through the hypocentral area of the chi chi earthquake for imaging the seismogenic structure mt data were then inverted for two dimensional resistivity models plus best fitting static shift parameters using a nonlinear conjugate gradient algorithm that minimizes the sum of the normalized data misfits and the smoothness of the model as shown in the inverted 2d resistivity models presented in this paper an electrical conductor beside the hypocenter of the chi chi earthquake indicates that deep crustal fluids may participate in the rupture process of the chi chi earthquake a striking spatial correlation between the crustal conductor and occurrence of aftershocks beneath the chelungpu fault suggests a postseismic pore pressure adjustment ongoing after the mainshock additionally the hypocenter exhibits an electrical resistive zone consistent very well with a predicted compact zone from a crustal deformation and transient fluid flow modeling

late quaternary alluviation and offset along the eastern big pine fault southern california abstract determining late quaternary offset rates on specific faults within active mountain belts is not only a key component of seismic hazard analysis but sheds light on regional tectonic development over geologic timescales here we report an estimate of dip slip rate on the eastern big pine oblique reverse fault in the upper cuyama valley within the western transverse ranges of southern california and its relation to local landscape development optically stimulated luminescence osl dating of sandy beds within coarse grained alluvial deposits indicates that deposition of alluvium shed from the pine mountain massif occurred near the southern margin of the cuyama structural basin at the elevation of the cuyama river between 25 and 14 ka this alluvial deposit has been offset 10 m vertically by the eastern big pine fault providing a latest quaternary dip slip rate estimate of 0 9 m ky based on a 50 fault dip incision of the adjacent cuyama river has exposed a section of older cuyama river sediments beneath the pine mountain alluvium that accumulated between 45 and 30 ka on the down thrown footwall block of the eastern big pine fault corroborative evidence for holocene reverse slip on the eastern big pine fault is 1 m of incised bedrock that is characteristically exposed beneath 2 3 5 ka fill terraces in tributaries south of the fault the eastern big pine fault in the cuyama valley area has no confirmed record of historic rupture however based on our results we suggest the likelihood of multiple reverse slip rupture events since 14 ka

global positioning system network analysis with phase ambiguity resolution applied to crustal deformation studies in california a 5 year campaign is in progress in central and southern california to monitor tectonic motions using observations of the global positioning system gps satellites evidence from geological and space geodetic data indicates that significant horizontal deformations of order 10 mm yr are occurring west of the san andreas fault along the california margin we demonstrate using data from initial epoch measurements in january 1987 that the goal of measuring horizontal deformations with an accuracy of 5 mm yr over the duration of the campaign should be readily achievable the gps network was designed to span a wide range of baseline lengths within california and across north america to aid in phase ambiguity resolution an important factor in achieving highest accuracy baseline determinations we present an efficient algorithm for multisession network analysis of gps data with simultaneous orbit determination and ambiguity resolution using this algorithm with the california data we demonstrate the improvement obtained in station position and satellite orbit estimation when the phase ambiguities are resolved we demonstrate several millimeters 1 part in 108 short term repeatability over five single session daily analyses for horizontal baseline components and length and several tens of millimeters for the vertical comparison with the independently determined very long baseline interferometry baseline between mojave and owens valley suggests that the accuracy is at the same level as the repeatability we show that simultaneous multisession analyses with ambiguity resolution improve the baseline and satellite orbit estimates compared to the single session analyses with the single session analyses we were able to resolve all phase ambiguities on baselines within california with the multisession analyses we were able to resolve the phase ambiguities for most of the network over regional and continental scales

high resolution electromagnetic imaging of the san andreas fault in central california although there is increasing evidence that fluids may play a significant role in the earthquake rupture process direct observation of fluids in active fault zones remains difficult since the presence of an electrically conducting fluid such as saline pore water strongly influences the overall conductivity of crustal rocks electrical and electromagnetic methods offer great potential for overcoming this difficulty here we present and compare results from high resolution magnetotelluric mt profiles across two segments of the san andreas fault saf which exhibit very different patterns of seismicity parkfield which has regular small earthquakes and creep events and in the carrizo plain where the fault is seismically quiescent and apparently locked in both surveys electric fields were sampled continuously with 100 m long dipoles laid end to end across the fault from 100 to 0 1 hz the data from both profiles are consistent with a two dimensional 2 d fault parallel resistivity model when both transverse electric and magnetic te and tm mode data are included in the interpretation narrow approximately 300 endash 600 m wide zones of low resistivity extending to depths of 2 endash 4 km in the core of the fault are required at both locations however at parkfield the conductance conductivity thickness product of the anomalous region ismore an order of magnitude larger than at carrizo plain suggesting much higher concentrations of fluids for the more seismically active parkfield segment we also image structural differences between the two segments at carrizo plain resistive presumably crystalline rocks are present on both sides of the fault at depths below 3 endash 4 km in particular we clearly image resistive basement extending approximately 10 km or more east of the saf beneath the elkhorn hills and temblor range at parkfield the situation is quite different with a resistive block of salinian granite west of the fault and an electrically conductive presumably fluid rich franciscan complex to the east it is possible that these structural differences control the difference in mechanical behavior of the fault either directly by affecting fault strength or indirectly by controlling fluid supply copyright 1999 american geophysical union less

regional aquifer mapping using combined ves tem amt emap methods in the semiarid eastern margin of parnaiba basin brazil as part of a program to evaluate the utility of integrated geoelectrical methods for subsurface structural mapping and groundwater resource investigation in the semiarid eastern margin of the parnaiba basin in brazil several vertical electrical soundings ves and transient electromagnetic tem and tensorial audio magnetotelluric amt measurements were carried out along a 250 km long east west transect passing through major towns and cities and a 127 km long north south profile passing through small farm settlements the various data sets have been jointly processed using a novel integration scheme and a constrained 1 d inversion technique to yield the resistivity structure underneath each observation station regularized 2 d inversion of static shift corrected dual mode amt data provided additional deep structural information and together with the joint 1 d results enabled an assessment of the distribution of aquifers and major structural controls in the region the east west regional geoelectrical model evokes a picture of a gently dipping succession of conductive and resistive units in good agreement with the alternating shaly and sandy formations evinced from preexisting borehole data and previous geological studies the geoelectric models also show the presence of the large scale transbrazilian lineament and other graben like structures previously inferred from aeromagnetic data which may have some control on groundwater distribution the agreement with geology and aeromagnetic interpretation emphasizes the importance of integrated geoelectrical surveying as a complementary or independent means of obtaining useful stratigraphic and structural information for hydrogeological studies in this region

electrical structure of the tectonically active kalabsha fault aswan egypt in this work we use the magnetotelluric mt method to detect geoelectrical conductivity anomalies in the earth s crust and link them to local seismic activity this application affords the unusual opportunity to study the percolation of water from a lake into a fault system and its effect on the induced seismicity mt measurements were carried out in the period range 0 0046 420 s at nine sites along a 15 km long north south profile crossing the kalabsha fault on the western bank of lake aswan data were analysed by 2d simultaneous inversion of both polarisations the resulting model is compared with the local seismicity map and reveals the conductive signature of the fault as well as geological and tectonic stresses prevailing in the aswan area our mt investigations show the following features the measured mt strike aligns with the seismic epicentre axis corresponding to the kalabsha fault while crossing the fault enhanced conductivity is found down to depths of 5 km on a 1 2 km profile segment at mid crustal depths 20 km a very high conductive body is found to coincide with the main seismic cluster in the aswan area these observations indicate that seismic activity and high electrical conductivity are related the link between them is the presence of crustal fluids which are presumably the cause of the high conductivity observed their presence is also required to trigger the observed seismicity in addition we explain the lower conductivity of the local upper crust in terms of stress modulated rock porosity we believe that these results are of general significance as they could explain the mid crustal seismicity of tectonically active zones d 2005 elsevier b v all rights reserved

miocene phosphate accumulation in the cuyama basin southern california abstract middle and upper miocene phosphatic strata in the cuyama basin of southern california contain approximately 6 4 10 9 metric tons 2 1 10 14 mol of phosphorus p that accumulated in slope and shelf strata at rates between 0 9 and 3 8 mol p cm 2 year 1 from 15 5 to 10 8 ma an estimated 63 of all phosphorus lies in a single third order sequence deposited between 14 8 and 13 ma the main impetus for this brief phosphogenic event was a 200 m relative sea level rise that resulted from strike slip faulting immediately east of the basin minor element and petrologic analyses suggest the overall increase in phosphorus accumulation correlates with less reducing conditions in the shallowly buried marine sediments on the slope and the expansion of phosphogenesis to the outer shelf both events were probably related to landward shifts of the pacific oxygen minimum zone and coastal upwelling centers during the relative sea level rise whereas these tectonic events were apparently local the phosphatic deposits of the cuyama basin clearly demonstrate that tectonism can strongly influence phosphate accumulation rates in marginal marine environments

zonal surface wind jets across the red sea due to mountain gap forcing along both sides of the red sea 1 mesoscale atmospheric modeling over the red sea validated by in situ meteorological buoy data identifies two types of coastal mountain gap wind jets that frequently blow across the longitudinal axis of the red sea 1 an eastward blowing summer daily wind jet originating from the tokar gap on the sudanese red sea coast and 2 wintertime westward blowing wind jet bands along the northwestern saudi arabian coast which occur every 10 20 days and can last for several days when occurring both wind jets can attain wind speeds over 15 m s 1 and contribute significantly to monthly mean surface wind stress especially in the cross axis components which could be of importance to ocean eddy formation in the red sea the wintertime wind jets can cause significant evaporation and ocean heat loss along the northeastern red sea coast and may potentially drive deep convection in that region an initial characterization of these wind jets is presented

a model simulation of the summer circulation from the eastern mediterranean past lake kinneret in the jordan valley abstract a model is described for the representation and study of air flow from the eastern mediterranean on the west side of the model s domain past lake kinneret in the jordan valley about 210 m below msl and beyond to the east on the east side of the model in the summer months the primary purpose of the model is to improve our understanding of two striking features of the meteorology of the lake area in summer 1 the almost daily development of strong winds and an associated storm on the lake in the afternoon and 2 a nearly 50 drop in wind speed across the lake from the western to the eastern shore over a distance of only 10 km again in the afternoon the model is two dimensional it uses the sigma coordinate system and is thus hydrostatic the horizontal grid distance is 4 km it has 10 levels in the vertical between the surface and the top at 750 mb the first level in the vertical is 10 m above the surface and each of the higher levels is at an attitude that is approximately twice the

late cenozoic fold and thrust belt of the southern coast ranges and santa maria basin california 1 balanced cross sections across the santa maria basin and southern coast ranges of california show the pliocene to quaternary convergence to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by compressive earthquakes geodetic measurements of present shortening and folded quaternary deposits the pliocene and quaternary structure of the southern coast ranges is dominated by a series of large anticlinal structures that include the lompoc purisima trend the casmalia orcutt trend the point san luis anticline the santa lucia range anticlinorium and the la panza range anticlinorium the anticlinal trends are interpreted to be fault bend and fault propagation folds resulting from thrust ramps off thrust flat and a regional detachment at 11 14 km depth most of the thrust faults do not reach the surface blind thrust the southwestern range front of the san rafael mountains is interpreted to be the result of uplift above a ramp in the point san luis thrust the cross section across the southern coast ranges shows 26 8 km of shortening from the edge of the continental margin to the san andreas fault region wide shortening is interpreted to have begun between 2 0 and 4 0 ma which yields an average regional convergence rate of 6 7 13 4 mm yr the late pliocene and quaternary convergence across the onshore santa maria basin is interpreted to be 9 2 km and the average convergence rate is 2 3 4 6 mm yr compressive focal mechanisms and our structural analysis suggest that the ramp parts of the thrust system are the most likely sources for earthquakes the historic seismic record and length of the anticlinal trends suggest that the thrust ramps probably are capable of generating moderate to large earthquakes 5 0 m w 7 5 major thrust ramps underlie the city of san luis obispo and adjacent coastal towns cross section restoration reveals early formed hydrocarbon traps and accounts for the abundant hydrocarbon accumulations along the casmalia orcutt anticlinal trend and under the santa maria valley the cross sections and restorations also illustrate the importance of miocene and early pliocene normal faults to oil maturation and trapping concealed normal faults along the flanks of the major anticlinal trends and the subthrust area along the north side of the casmalia orcutt anticlinal trend form two relatively untested trap styles

coarse grained deltaic sedimentation in the miocene cuyama strike slip basin california coast ranges abstract the cuyama basin located in the southern coast ranges of california southwest of the san andreas fault developed early in the history of the san andreas transform system the miocene marine basin formed in a transtensional setting along a dextral strike slip fault of the transform system following oligocene non marine basin formation in an extensional setting the lower and middle miocene vaqueros formation in the northwestern part of the basin which represents the first of two transgressive regressive cycles is described here in terms of nine facies in two broad facies groups the 400 m thick soda lake shale member of the vaqueros comprises deep basin and starved basin facies a thin transgressive facies occurs locally at the base of the formation the overlying painted rock sandstone member of the vaqueros which is more than 2200 m thick and consists mostly of coarse grained sandstone and pebbly sandstone constitutes a delta complex of prodelta slope channel delta front tide influenced distributary channel interdistributary bay and fluvial channel facies the basinal depositional system consisted of turbidite mud and sand and hemipelagic and pelagic sediments of the basinal facies deposited in a rapidly subsiding basin the delta depositional system consisted of the delta complex facies that prograded into the deep basin and had a steep prodelta slope that extended to bathyal depths the delta is inferred to be a mixed fluvial wave dominated fan delta analogous in its delta front morphology and processes to a fjord delta in which coarse sediment delivered to the delta front by braided streams was transported down the prodelta slope into deep water by sediment gravity flows transgression and rapid deepening of the basin in the early miocene coincided with rapid tectonic subsidence deepening culminated with deposition of a starved basin facies or condensed section at the time of maximum transgression which was followed by the beginning of a regression and basin shallowing the overall basin history and geometry of the northwestern cuyama basin are typical of strike slip basins the initial rapid subsidence to bathyal depths at rates of more than 500 m m y in the early miocene is interpreted to be a result of extension at the releasing bend of a dextral strike slip fault

pliocene transpressional modification of depositional basins by convergent thrusting adjacent to the big bend of the san andreas fault an example from lockwood valley southern california 1 the big bend of the san andreas fault in the western transverse ranges of southern california is a left stepping flexure in the dextral fault system and has long been recognized as a zone of relatively high transpression compared to adjacent regions the lockwood valley region just south of the big bend underwent a profound change in early pliocene time 5 ma from basin deposition to contraction accompanied by widespread folding and thrusting this change followed the recently determined initiation of opening of the northern gulf of california and movement along the southern san andreas fault at about 6 1 ma with the concomitant formation of the big bend lockwood valley occupies a 6 km wide fault bounded structural basin in which converging blocks of paleoproterozoic and cretaceous crystalline basement and upper oligocene and lower miocene sedimentary rocks plush ranch formation were thrust over miocene and pliocene basin fill sedimentary rocks in ascending order caliente formation lockwood clay and quatal formation all the pre quatal sedimentary rocks and most of the pliocene quatal formation were deposited during a mid tertiary period of regional transtension in a crustal block that underwent little clockwise vertical axis rotation as compared to crustal blocks to the south ensuing pliocene and quaternary transpression in the big bend region began during deposition of the poorly dated quatal formation and was marked by four converging thrust systems which decreased the areal extent of the sedimentary basin and formed the present lockwood valley structural basin none of the thrusts appears presently active estimated shortening across the center of the basin was about 30 percent the formerly defined eastern big pine fault now interpreted to be two separate oppositely directed contractional reverse or thrust faults marks the northwestern structural boundary of lockwood valley the complex geometry of the lockwood valley basin is similar to other tertiary structural basins in southern california such those that underlie cuyama valley the ridge basin and the east ventura basin

carrier phase ambiguity resolution for the global positioning system applied to geodetic baselines up to 2000 km the global positioning system gps carrier phase data are biased by an integer number of cycles a successful strategy has been developed and demonstrated for resolving these integer ambiguities for geodetic baselines of up to 2000 km in length resulting in a factor of 3 improvement in baseline accuracy and giving centimeter level agreement with coordinates inferred by very long baseline interferometry in the western united states for this experiment a method using pseudorange data is shown to be more reliable than one using ionospheric constraints for baselines longer than 200 km an automated algorithm exploits the correlations between the many phase biases of a gps receiver network to enable the resolution of ambiguities for very long baselines a method called bias optimizing has been developed which unlike traditional bias fixing does not require an arbitrary confidence test bias optimizing is expected to be preferable to bias fixing for poorly configured networks in order to enable ambiguity resolution for long baselines it is recommended that future gps networks have a wide spectrum of baseline lengths ranging from 1000 km and that gps receivers be used which can acquire dual frequency p code data

geophysical images of the dead sea transform in jordan reveal an impermeable barrier for fluid flow 1 high resolutionseismictomography and magneto telluric mt soundings of the shallow crust show strong changes in material properties across the dead sea transform fault dst in the arava valley in jordan 2d inversion results of the mt data indicate that the dst is associated with a strong lateral conductivity contrast of a highly conductive layer at a depth of approximately 1 5 km cut off at a position coinciding with the surface trace of the dst at the same location we observe a sharp increase of p wave velocities from 5 km s to the east the high velocities in the east probably reflect precambrian rocks while the high electrical conductivity west of the dst is attributed to saline fluids within the sedimentary filling in this sense the dst appears to act as an impermeable barrier between two different rock formations such a localized fluid barrier is consistent with models of fault zone evolution but has so far not been imaged by geophysical methods the situation at the dst is remarkably different from active segments of the san andreas fault which typically show a conductive fault core acting as a fluid conduit

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

the cuyama strike slip basin california u s a an exemplar of contrasting syntectonic and post tectonic strata abstract miocene strata in the cuyama basin of southern california exemplify syntectonic and post tectonic stratigraphic development in a strike slip basin integrated seismic well log and outcrop data provide a detailed portrayal of the seismic stratigraphy and sedimentary facies in the previously unstudied middle and upper miocene sequences results show sharp contrast among syntectonic and post tectonic strata from composition and texture of sediments to lateral distribution and thickness of facies seven post tectonic sequences were mapped across the basin sequences contain eolian to fluvial terrestrial facies wave and tide dominated nearshore facies biosiliceous dolomitic and phosphatic outer shelf and slope mudstones and shale rich submarine fans in basinal environments authigenic dolomites and phosphates are pervasive in outer shelf and slope facies and indicate the possibility of restricted sediment supply post tectonic sequences are thin but laterally continuous and they exhibit little depositional asymmetry minor erosion is distributed equally among regressive and transgressive relative sea level changes asynchronous changes in tectonism sediment supply and eustatic sea level change created dramatic differences among syntectonic and post tectonic sequences interbasinal tectonic quiescence led to the abrupt end of stratigraphic mismatches and the accumulation of sediment during brief episodic periods multiple points of progradation persisted through several million years of post tectonic basin development and highlight the importance of extrabasinal sediment supply to the development of all sequences the eventual loss of most accommodation space promoted the importance of eustatic sea level change and reduced the prominence of asymmetric facies and abrupt lateral facies changes

uncertainties and implications of the late cretaceous and tertiary position of north america relative to the farallon kula and pacific plates we present updated global plate reconstructions and calculated uncertainties of the pacific kula and farallon vancouver plates relative to north america for selected times since 68 ma improved magnetic data from the indian ocean decrease the uncertainties in the global plate circuit approach these uncertainties are now considerably smaller than those inherent in equivalent reconstructions based on the assumption of fixed hotspots major differences between these results and those of others are due to our use of more detailed africa north america reconstructions separate vancouver and farallon plate reconstructions and the assumption of a rigid antarctica plate during cenozoic time the uncertainties in the relative positions of the pacific and north america plates since the time of anomaly 7 26 ma range up to 100 km in position or from 1 to 3 m y in time if the mendocino triple junction initiated at about 28 5 ma its position would have been at 31 3 n 130 km relative to fixed north america unacceptable overlap of oceanic crust of the pacific plate with continental crust of western north america in the anomaly 10 30 ma reconstruction is a minimum of 340 200 km along an azimuth of n60 e and may be accounted for by basin and range extension pacific north america displacement in the past 20 ma is found to be considerably less than that calculated by fixed hotspot reconstructions farallon vancouver north america convergence velocity decreased greatly between the times of anomalies 24 and 21 56 to 50 ma prior to the 43 ma age of the hawaiian emperor bend and the often quoted 40 ma end of the laramide orogeny a change in direction of farallon north america convergence occurred sometime between 50 and 42 ma and also may not correlate with the time of the hawaiian emperor bend the lack of data from subducted parts of the farallon and kula plates permits many possibilities regarding the position of the kula farallon ridge the age of subducted crust or the position of oceanic plateaus during the laramide orogeny leaving open the question of the relationship between plate tectonic scenarios and tectonic style during laramide time displacements of points on the various oceanic plates along the west coast of an arbitrarily fixed north america during the interval between anomalies 30 31 and 18 68 to 42 ma are found to be pacific plate 1700 200 km northward farallon plate 3200 400 km northeastward vancouver plate 3000 400 km northeastward kula plate if attached to the pacific plate after a24 time 2500 400 km northward

are the circular dark features on comet borrelly s surface albedo variations or pits abstract the highest resolution images of comet 19p borrelly show many dark features which upon casual inspection appear to be low albedo markings but which may also be shadows or other photometric variations caused by a depression in the local topography in order to distinguish between these two possible interpretations we conducted a photometric analysis of three of the most prominent of these features using six of the highest quality images from the september 22 2001 deep space 1 ds1 flyby we find that 1 the radiance in the darkest parts of each feature increases as phase angle decreases similarly to the radiance behavior of the higher albedo surrounding terrain the dark features could be either fully illuminated low albedo spots or alternatively they could be depressions no part of any of the three regions was in full shadow 2 one of the regions has a radiance profile consistent with a rimmed depression the second with a simple depression with no rim and the third with a low albedo spot 3 the regolith particles are backscattering and carbon black is one of the few candidate regolith materials that might explain this low albedo we conclude that borrelly s surface is geologically complex to the limit of resolution of the images with a combination complex topography pits troughs peaks and ridges and some very dark albedo markings perhaps a factor of two to three darker than the average 3 4 albedo of the surrounding terrains our technique utilizing measured radiance profiles through the dark regions is able to discriminate between rimmed depressions rimless depressions and simple albedo changes not associated with topography

initiation of a mesoscale convective complex over the ethiopian highlands preceding the genesis of hurricane alberto 2000 1 a tropical disturbance which would later become hurricane alberto 2000 was traced back in time as a mesoscale convective complex mcc to the ethiopian highlands eh where the mcc first developed meteosat 7 imagery indicates that the mcc develops during the late afternoon and evening of 28 july 2000 and that a mesovortex mv was evident on the morning of 29 july 2000 a preliminary mesoscale model simulation features the development of two areas of maximum relative vorticity in the middle troposphere with the maturation of one of the vorticity maxima into a significant mv the higher level vorticity center of the simulated mv tracks westward and is nearly collocated with the vortex signature in satellite imagery while the lower level center remains near the lee side of the eh the vortex signature in satellite imagery was traceable to the cyclogenesis stage over the eastern atlantic ocean

crustal structure of the north anatolian and east anatolian fault systems from magnetotelluric data abstract magnetotelluric mt studies can map subsurface resistivity structure and have located zones of low resistivity high conductivity within major strike slip fault zones worldwide which have been interpreted as regions of elevated fluid content this study describes mt data from the eastern part of the north anatolian and the east anatolian fault systems nafs and eafs and presents the results of the first mt studies of these faults the inversion of the mt data produced 2 d resistivity models which showed that both fault systems are underlain by a broad low resistivity zone that extended into the lower crust however the resistivity beneath the east anatolian fault system was much lower than beneath the eastern part of the north anatolian fault system these conductors begin at a depth of 10 km not at the surface as on the central san andreas fault safs this difference is interpreted as being due to the fact that the eafs and nafs are young fault systems characterized in the upper crust by multiple fault traces as opposed to the safs that has evolved into a single through going fault different stages of the seismic cycle may also influence the resistivity structure although this is difficult to constrain without knowledge of time variations in resistivity structure at each location

a magnetotelluric mt study across the koyna seismic zone western india evidence for block structure abstract wide band magnetotelluric measurements were carried out at 16 sites along guhaghar sangole traverse across the koyna seismicity zone the results of the study besides providing details of deccan trap thickness variation along the traverse brought out several structural characteristics of the subsurface extending to deep crustal levels the koyna fault zone is characterized by a weak expression of a moderately conductive feature extending only up to a depth of 4 5 km two dimensional modeling results bring out distinct block structure in the koyna region and are compared with velocity and density structure of the region the deep electrical structure is interpreted in terms of lateral lithological heterogeneities

structures that accommodated differential vertical axis rotation of the western transverse ranges california 1 new paleomagnetic and structural data from the northwestern transverse ranges of california define the location geometry and kinematics of structures that facilitated differential vertical axis rotation paleomagnetic declinations in the southern coast ranges indicate negligible amounts of vertical axis rotation which contrasts sharply with data from rocks of the same age in the western transverse ranges that record approximately 90 of clockwise rotation since early miocene time this change in paleomagnetic declinations occurs across an east west trending zone of reverse faults and folds that includes the western big pine pine mountain fault the santa ynez fault and the structures in between the structures in this zone exhibit increased amounts of shortening to the west such that the zone closed in a fan like fashion resulting in rotation of the southern edge with respect to the northern edge the new data and interpretations refine previous models of vertical axis rotation in southern california by describing the deformation present at rotation boundaries that allowed distinct areas to rotate relative to the surrounding crust

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

conductivity structure of the san andreas fault parkfield revisited 1 a previous interpretation of a high resolution magnetotelluric profile across the san andreas fault at parkfield attributed an anomalously conductive region just west of the fault and extending to depths of 3 km to fractured rock saturated with brines laboratory measured electrical resistivities of samples of sedimentary rocks known to border the fault to the east are comparable to resistivities of the anomalous zone we suggest that the anomalous region results from conductive sedimentary rocks in a plunging syncline that is adjacent to the fault rather than caused by fractured rock if correct the current surface trace of the san andreas fault at middle mountain does not form the boundary between the salinian block and the north american plate instead that boundary is 1 km west and collocated with current seismicity

when land breezes collide converging diurnal winds over small bodies of water over enclosed and semi enclosed bodies of water the land breeze sea breeze circulation is expected to be modified by the presence of opposing coastlines these effects are studied using satellite scatterometer surface wind observations from the quikscat and adeos 2 tandem mission from april october 2003 winds are studied for six bodies of water the red sea the gulf of california the mediterranean the adriatic sea the black sea and the caspian sea these bodies of water are large enough for the geographic orientation of the diurnal winds relative to the coastline to match the expected orientation for a straight coastline land breezes from opposite coastlines converge in the middle of these bodies of water and in some cases the convergence line is shifted substantially away from the midpoint between opposite coastlines displacements in the convergence line appear likely to be explained by differences in the strength of the diurnal winds emanating from opposite coastlines associated with differential heating or island peninsula effects and by geographic displacements associated with large scale mean wind patterns

correlation of electrical conductivity and structural damage at a major strike slip fault in northern chile 1 large scale strike slip fault zones are often imaged as electrically conductive structures in the brittle crust however the relationship of conductivity and internal architecture of the fault zone remains largely unclear this paper presents results of a study designed to compare the record of structural deformation across a fault zone with its electrical conductivity image two high resolution magnetotelluric profiles trend perpendicularly across the west fault a branch of the precordilleran fault system in northern chile the magnetotelluric and geomagnetic response functions in the frequency range from 1000 hz to 0 1 hz clearly image a fault zone conductor fzc about 350 m wide and 1500 m deep trending along the surface trace of the fault the position of the fzc and its geometric properties width dip correlate with a region of intense fluid alteration and the orientation of fault related damage elements minor faults fractures according to estimates of fluid salinity and rock porosity the conductivity anomaly results from meteoric water penetrating into a permeable zone this suggests that the increase in electrical conductivity is causally related to a mesh of minor faults and fractures acting as a pathway for fluids the fzc reflects the central and most fractured part of the damage zone in view of similar published magnetotelluric studies we infer a dependency of a fault s state of activity and the characteristics of the fzc such as its conductance width and depth extent ongoing deformation is the controlling factor for maintaining a permeable and electrically conductive fracture network

active tectonics at wheeler ridge southern san joaquin valley california wheeler ridge is an east west trending anticline that is actively deforming on the upper plate of the pleito wheeler ridge thrust fault system holocene and late pleistocene deformation is demonstrated at the eastern end of the anticline where salt creek crosses the anticlinal axis uplift tilting and faulting associated with the eastward growth of the anticline are documented by geomorphic surfaces that are higher and older to the west faulting and associated folding is propagating eastward as indicated by increases in both the degree of surface dissection and the degree of soil development from east to west distinct topographic areas having distinct degrees of surface dissection bounded by tear faults suggest that faulting and folding have propagated eastward in discrete segments numerical dates indicate 1 the anticline is propagating eastward at a rate of about 30 mm yr about 10 times the rate of uplift 2 folding was initiated about 400 ka 3 a prominent wind gap was formed during q3 time about 60 ka when an antecedent stream was defeated forcing the stream east around the nose of the fold today drainage through the ridge is by way of two antecedent streams water gaps east of the wind gap and 4 the rate of uplift at the easternmost and youngest past 1 k y part of the fold is at least 3 mm yr investigations of the tectonic geomorphology of wheeler ridge support the hypothesis that climatic perturbations are primarily responsible for producing geomorphic surfaces such as alluvial fan segments and river terraces tectonic perturbations deform the surfaces

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

electromagnetic images of a strike slip fault the tintina fault northern canadian 1 wideband magnetotelluric mt data were acquired along three profiles crossing the strike slip tintina fault in northwestern canada the mt responses obtained exhibit remarkable similarity from all three profiles implying similar two dimensional 2 d electromagnetic behavior of the fault zone over a strike length of at least 350 km analyses of the mt responses for dimensionality corroborate the validity of assuming regional 2 d structures in interpretation several high conductivity anomalies at different depth scales are present in the models obtained and we suggest that both the shallow structures and the deep crustal scale anomalies are caused by electronic conduction mechanisms in interconnected mineralized zones intriguingly the middle and lower crust beneath the surface expression of the tintina fault is highly resistive in contrast to some other large scale strike slip faults this implies that fault zone processes that result in interconnected conducting phases are not generic in nature but are controlled by local conditions

the tejon pass earthquake of 22 october 1916 an m 5 6 event on the lockwood valley and san andreas faults southern california on 22 october 1916 a moderate earthquake occurred in the vicinity of tejon pass and was felt over much of southern california an intriguing aspect of this event involves reports of ground cracks that formed during the earthquake we evaluate the reports of ground cracking and attempt to precisely locate the cracks with respect to active faults we infer that the earthquake produced minor fault rupture along a newly discovered trace of the easternmost lockwood valley fault formerly mapped as the easternmost big pine fault and or along the san andreas fault we also re evaluate and present new intensity data and we use a grid search algorithm derived from empirical analysis of modern earthquakes to find the magnitude most consistent with the reported intensities although previous authors have attempted to use intensity data to constrain the magnitude of this event the algorithm we use provides an alternative and statistically more robust determination of the magnitude our results suggest m 5 6 0 3 0 2 at 95 confidence for the 1916 event which is consistent with earlier work the 1916 earthquake appears to have been a rare and remarkable event in terms of its size and location and the production of minor surface rupture

electrical resistivity structure at the northern margin of the tibetan plateau and tectonic implications 1 the ene wsw striking altyn tagh fault atf and the wnw ese trending western qilian mountains define the northern margin of the tibetan plateau new magnetotelluric data were collected along three profiles crossing the eastern section of the atf and the southern qilian mountains the basic sounding bandwidth ranged from 0 003 to 7000 s the transverse electric and transverse magnetic mode data sets were inverted into resistivity sections using a conventional two dimensional 2d inversion code and data at periods of 0 3333 5464 s were inverted using a commonly employed three dimensional 3d code the 3d results constrain the interpretation of the 2d models and the final interpretative resistivity models show that lithospheric structures are spatially variable along the atf and across southern qilian in profiles across the atf the main fault is imaged as a vertical resistivity boundary and the high resistivity body in the western profile extends about 15 km deeper than the corresponding body in the eastern profile positive flower structures are apparent in the western profile but are only weakly visible in the eastern profile these observations suggest that the depth of the atf is spatially variable mantle resistivity images indicate a relatively cold and rigid tarim lithosphere which is consistent with a geodynamic model of oblique subduction of the tarim basin below the atf a high resistivity body in the crust of southernmost qilian indicates a huge thick skinned structure low resistivity bodies at the crust mantle boundary south of the main atf are presumed to form a weak layer beneath northern tibet

magnetotelluric response and geoelectric structure of the great slave lake shear zone the great slave lake shear zone gslsz is a northeast trending 25 km wide dextral continental transform fault from the foothills of the rocky mountains in northeast british columbia to the southeast side of great slave lake based on its magnetic expression the gslsz can be correlated for at least 1300 km mostly in the subsurface magnetotelluric mt soundings were made at 60 sites in the southwest part of the northwest territories canada along the lithoprobe slave northern cordillera lithospheric evolution snorcle transect corridors 1 and 1a in the summer and autumn of 1996 of these 15 sites were along corridor 1a which crossed the gslsz the great bear magmatic arc and hay river terrane to the northwest of the shear zone and the buffalo head terrane to the southeast the primary objective of the corridor 1a deployments was to image the structure of the gslsz analysis of mt data indicates that along the corridor 1a the resistivity structure is approximately 1d at shallow depth 6 1 km corresponding to phanerozoic sedimentary rocks 2d in the upper to mid crust with a strike vn30 e and approximately 2d in the lower crust to lithospheric mantle with a strike of vn60 e the direction in the upper crust is interpreted to represent the local scale 6 50 km horizontal strike of the gslsz whereas the direction in the mantle is parallel to the larger scale strike of the gslsz 2d inversions of the mt data reveal that the gslsz forms a crustal scale resistive zone s 5000 6m that is spatially correlated with a magnetic low the gslsz comprises greenschist to granulite facies mylonites its high resistivity is interpreted to be due to the resistive nature of the granitic protolith of the mylonites and that mylonites are dominated by rocks deformed in the ductile regime to the northwest of gslsz the mt profile reveals crustal conductors beneath the great bear magmatic arc and hay river terrane the enhanced conductivity occurring beneath the great bear magmatic arc is interpreted to be caused by electronic conduction within deformed and metamorphosed rocks of the hottah terrane or the coronation supergroup the mt results also reveal a mantle conductor beneath the margin of the hottah terrane and great bear magmatic arc that is interpreted to be associated with the subduction of oceanic lithosphere a second mantle conductor to the southeast is truncated at the gslsz suggesting an older source for the enhanced conductivity and that the gslsz includes significant strike slip motion of sub crustal lithosphere fl 2002 elsevier science b v all rights reserved

the sea breeze with mean flow a quasi geostrophic mean flow can form the basic state upon which a sea breeze is superimposed a model is described with a mean flow perpendicular to the coast the speed of the sea breeze front is shown to be a linear function of the onshore component of the mean flow when a constant mean flow is introduced the general structure of the sea breeze is unchanged in particular for a constant energy input the intensity is also unaltered in contrast a shear changes the general qualitative structure but leaves the speed of the front and the intensity of the sea breeze unchanged these features are consistent with the available potential energy of the system and a constant transfer per unit area of this into kinetic energy model results and other studies are discussed

neogene non marine sedimentation and tectonics in small pull apart basins of the san andreas fault system sonoma county california the san andreas fault system in northern california forms an 80 90 km wide zone of right lateral shear extensional tectonism within this broad shear zone is indicated by both neogene silicic volcanic rocks that gradually young in the direction of shear propagation to the north west and by numerous neogene faultbounded structural basins filled with thick non marine sequences the little sulphur creek basins three well exposed 1 5 2 km wide pull apart basins within this shear system have sedimentation patterns analogous to those of much larger pull apart basins they were formed and subsequently deformed by east west extension and by north west to south east orientated right slip concurrently with basin filling palaeocurrent and maximum clast size data indicate both lateral sediment transport from fault bounded basin margins and longitudinal transport down the basin axes the basins are filled primarily with coarse alluvial fan and streamflow deposits derived from a surrounding igneous sedimentary and metamorphic provenance two of the basins contain basin plain type lacustrine turbidites that grade laterally into distal alluvial fan fan delta and sublacustrine delta deposits talus deposits along the south west margin of the basins contain megabreccia indicative of active uplift structures indicative of dewatering liquefaction and slumping suggest penecontemporaneous tectonism

bedrock landscape development modeling calibration using field study geochronology and digital elevation model analysis stream power based models of bedrock landscape development are effective at producing synthetic topography with realistic fl uvial network topology and three dimensional topography but they are diffi cult to calibrate this paper examines ways in which fi eld observations geochronology and digital elevation model dem data can be used to calibrate a bedrock landscape development model for a specifi c study site we fi show how uplift rate bedrock erodibility and landslide threshold slope are related to steady state relief hypsometry and drainage density for a wide range of synthetic topographies produced by a stream power based planform landscape development model our results indicate that low uplift rates and high erodibility result in low relief high drainage density fl uvially dominated topography and high uplift rates and low erodibility leads to high relief low drainage density mass wasting dominated topography topography made up of a combination of flchannels and threshold slopes occurs for only a relatively narrow range of model parameters using measured values for hypsometric integral drainage density and relief quantitative values of bedrock erodibility can be further constrained particularly if uplift rates are independently known we applied these techniques to three sedimentary rock units in the western transverse ranges in california that have experienced similar climate uplift and incision histories the 10 be surface exposure datincision of initially low relief topography there occurred during the last 60 k y we estimated the relative dependence of drainage area and channel slope on erosion rate in the stream power law from slope area data and inferred values for bedrock erodibility ranging from 0 09 to 0 3 m 0 2 0 4 k y 1 for the rock types in this study area

comparison of usgs and dlr topographic models of comet borrelly and photometric applications stereo analysis of images obtained during the 2001 flyby of comet borrelly by nasa s deep space 1 ds1 probe allows us to quantify the shape and photometric behavior of the nucleus the shape is complex with planar facets corresponding to the dark mottled regions of the surface whereas the bright smooth regions are convexly curved the photometric as well as textural differences between these regions can be explained in terms of topography roughness at and below the image resolution without invoking significant variations in single particle properties the material on borrelly s surface could be quite uniform a statistical comparison of the digital elevation models dems produced from the three highest resolution images independently at the usgs and dlr shows that their difference standard deviation is 120 m consistent with a matching error of 0 20 pixel similar to reported matching accuracies for many other stereo datasets the dems also show some systematic differences attributable to manual versus automatic matching disk resolved photometric modeling of the nucleus using the dem shows that bright smooth terrains on borrelly are similar in roughness hapke roughness 20 to c type asteroid mathilde but slightly brighter and more backscattering single scattering albedo w 0 056 henyey greenstein phase parameter g 0 32 the dark mottled terrain is photometrically consistent with the same particles but with roughnesses as large as 60 intrinsically darker material is inconsistent with the phase behavior of these regions many local radiance variations are clearly related to topography and others are consistent with a topographic explanation one need not invoke albedo variations greater than a few tens of percent to explain the appearance of borrelly

geodetic measurement of tectonic deformation in the santa maria fold and thrust belt california we have analyzed geodetic observations to resolve tectonic deformation across the santa maria fold and thrust belt northwest of santa barbara california the geodetic network forms a braced quadrilateral with 40 km sides whose southwest corner is the vandenberg very long baseline interferometry station the data include 1 historical triangulation from the 1880s 1920s and 1950s 2 electronic distance measurement trilateration from 1971 and 1985 and 3 global positioning system observations from 1986 and 1987 we combine the three different types of data to estimate two dimensional station positions and strain rate parameters simultaneously using a model which constrains the relative velocity field to be linear in space and constant in time we find significant strain rates the maximum compressive strain is oriented n17 e 5 e and the compressive strain rate in this direction is 0 13 0 03 strain yr under the assumption that the unresolved rotational component of the velocity field is zero we estimate that the integrated rate of deformation across the basin is 7 1 mm yr oriented at n03 e 13 this vector can be decomposed into 6 2 mm yr of crustal shortening on the general structural trend of n30 e and 3 1 mm yr of right lateral shear across this axis on the basis of these values and earthquake focal mechanisms in the area we infer that the deformation occurs on northwest trending folds and thrusts within the belt these results are consistent with the rate and direction of deformation across the central california coast ranges inferred by balancing pacific north america plate motion against san andreas slip and basin and range extension they imply that the santa maria fold and thrust belt is the primary active element in transforming motion from the coast ranges to the western transverse ranges and the santa barbara channel