re analysis of faunal assemblages from the haua fteah and other late quaternary archaeological sites in cyrenaican libya in preliminary reports based on approximately 5000 identified bones from the haua fteah cyrenaica e s higgs concluded that changes in the abundance of bovines versus barbary sheep reflected climatic change from drier last interglaciation to wetter last glaciation and back to drier present interglaciation higgs also reported the earliest occurrence of domestic caprines in africa in haua fteah neolithic layers dated to about 6800 bp a new analysis based on roughly 9000 identified specimens supports the broad pattern of faunal change that higgs found but suggests that it reflects wetter when higgs proposed drier and vice versa the new analysis failed to confirm the early date for domestic caprines mainly because of uncertainty concerning the stratigraphic provenience of key specimens finally the new analysis produced some additions to the species list most notably eland and provided previously unavailable information on skeletal part representation and on the ages of animals at time of death with respect to skeletal parts smaller ungulates tend to be represented by a wider variety than larger ones a contrast that is almost universal in stone age sites with regard to age profiles the largest and most reliable one for barbary sheep from the neolithic layers implies the animals were captured by driving over cliffs or into other traps restudy of small additional samples from the cyrenaican sites of hagfet et tera hagfet ed dabba and sidi el hajj creiem fully supports taxonomic and paleoenvironmental conclusions drawn earlier by higgs and bate

block models of crustal motion in southern california constrained by gps measurements 1 we estimate slip rates on major active faults in southern california using a block model constrained by global positioning system measurements of interseismic deformation the block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle our estimates of the right lateral strike slip rate on the san andreas fault vary by at least a factor of 5 from a high of 35 9 0 5 mm yr in the carrizo plain to a low of 5 1 1 5 mm yr through the san bernadino segment shortening across the puente hills thrust and left lateral slip on the raymond hill fault are consistent with both thickening and escape tectonics in the los angeles basin discrepancies between geodetic and geologic slip rate estimates along the san andreas and san jacinto faults as well as in the eastern california shear zone may be explained by a temporal change in fault system behavior we find no substantial evidence for long term postseismic relaxation and infer that the viscosity of the lower crust upper mantle may be relatively high 1019 pa s

eastern mediterranean sapropel s1 interruption an expression of the onset of climatic deterioration around 7 ka bp we discuss the palaeoclimatic interpretation of unprecedented high resolution micropalaeontological studies of shortterm 2 to 4 centuries interruptions within early holocene organic rich layer sapropel s1 from the eastern mediterranean results for cores from the adriatic and aegean seas that contain double s1 sapropels indicate that these interruptions which are centred roughly around 7000 years 14 cnc bp are genuine and related to climatic deterioration this interpretation is endorsed by a coeval dry event recorded in terrestrial records and indications of climatic deterioration affecting human migration patterns and early societies in egypt the presence of sapropel interruptions in the two major source areas of deep water for the entire eastern mediterranean likely implies that similar intervals may be found throughout the basin provided that sedimentation rates and sampling resolutions allow the detection of events with a duration of only several centuries moreover our results show that the sapropel mode of circulation comprises a delicate balance between reduced ventilation and enhanced productivity which is easily disturbed through surface water cooling triggering a short time of improved deep water ventilation 1999 elsevier science b v all rights reserved

active surface deformation and sub lithospheric processes in the western mediterranean constrained by numerical models we present the results of dynamic modeling of the western mediterranean that accounts for observed global positioning system gps surface deformation of the alboran sea and surrounding rif and betic mountains as the result of the combined effects of relative motion of the eurasian and nubian plates low strength in the alboran sea region and sub lithospheric processes occurring beneath the external rif domain assuming that the lithosphere behaves elastically over the short time period of the gps observations an elastic plate model is considered in our study including an area of weak lithosphere factor of 10 centered on the alboran sea and in which lateral boundary conditions consist of the nubia eurasia oblique convergence sub crustal processes are modeled by application of a horizontal traction on a small area patch at the base of the elastic plate our modeling studies demonstrate the need for sub crustal or sub lithospheric southwestward directed forcing to account for observed southwestward motion of the rif and betic domains based on the location orientation and small area of the traction patch we hypothesize that forcing is associated with delamination and rollback of the subducted african continental lithospheric mantle beneath the external rif zone due to the pull of the oceanic part of the western mediterranean slab a dynamic process that may be similar to that where the over riding plate is driven toward the subduction zone during slab rollback

carbon dioxide injection and associated hydraulic fracturing of reservoir formations the storage potential of subsurface geological systems makes them viable candidates for long term disposal of significant quantities of co2 the geo mechanical responses of these systems as a result of injection processes as well as the protracted storage of co2 are aspects that require sufficient understanding a hypothetical model has been developed that conceptualises a typical well reservoir system comprising an injection well where the fluid co2 is introduced and a production abandoned well sited at a distant location this was accomplished by adopting a numerical methodology discrete element method specifically designed to investigate the geo mechanical phenomena whereby the various processes are monitored at the inter particle scale fracturing events were simulated in addition the influence of certain operating variables such as injection flow rate and fluid pressure was studied with particular interest in the nature of occurring fractures and trend of propagation the pattern and magnitude of pressure build up at the well vicinity pressure distribution between well regions and pore velocity distribution between well regions modelling results generally show an initiation of fracturing caused by tensile failure of the rock material at the region of fluid injection however fracturing caused by shear failure becomes more dominant at the later stage of injection furthermore isolated fracturing events were observed to occur at the production abandoned wells that were not propagated from the injection point this highlights the potential of co2 introduced through an injection well which could be used to enhance oil gas recovery at a distant production well the rate and magnitude of fracture development are directly influenced by the fluid injection rate likewise the magnitude of pressure build up is greatly affected by the fluid injection rate and the distance from the point of injection the dem modelling technique illustrated provides an effective procedure that allows for more specific investigations of geo mechanical mechanisms occurring at subsurface systems the application of this methodology to the injection and storage of co2 facilitates the understanding of the fracturing phenomenon as well as the various factors governing the process

middle stone age human occupation and dispersals in the messak plateau sw libya central sahara abstract research conducted since the 1990s in sw libya has provided wide ranging data on the pleistocene archaeology of this vast region which principally relies on surface scatters of lithic artefacts a series of soundings and two msa aterian dated sites the middle stone age of the region is thought to date from roughly mis 6 5 to approximately 60 ka the latest dated aterian occurrence its distribution varies from sand seas to mountain ranges with different states of preservation and archaeological visibility this paper presents data from the last surveys 2010 2011 carried out on 46 transects across the messak massif one component of the research strategy was specifically designed to handle the impressive pleistocene record through sampling a series of spots placed at fixed distances along predetermined survey strips field documentation of the techno typological traits allowed the creation of a territorial data set used to infer patterns of raw material exploitation technological variability and the significance of the principal chrono cultural markers quartzarenite the most available and used raw material is a diffusely distributed resource this should have played a role in patterns of land use and mobility and ultimately in the composition of archaeological assemblages mostly characterised by complete reduction sequences variability in the application of the levallois method highlights widespread adoption of recurrent and lineal schemes among the latter point production is extremely rare the retouched blanks inventory is dominated by scrapers and notches whereas more specialised tool classes i e tanged pieces points foliates are less common the dimensions of a small sample of aterian artefacts provisionally signal a higher degree of homogeneity among pointed tanged specimens than other types despite the overwhelming presence of roughly labelled msa contexts these show little evidence of a msa stricto sensu chrono cultural signature among which scanty but precise elements are comparable with the sub saharan and nile valley early middle stone age reinforcing the picture of multiple dispersals across the sahara and north africa around mis 6 5 the evolution of msa occupation and its cultural trajectories is difficult to assess while the last phases represented here by the aterian can be framed in hyperarid mis 4 after the dates from acacus and likely represent the adaptation of residual groups almost confined to mountain environments

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

hydrological factors in the interpretation of stable isotopic proxy data present and past a european perspective in the context of this paper stable isotopic proxies are those preserving directly or via known or calculable fractionation factors a record of 18o 16o and or 2h 1h in the water which contributed to their growth suitable proxies include amongst others tree ring cellulose bone phosphate lake sediment minerals and speleothem fluid inclusions a principal aim of studying isotopic proxies is to gain more information about past climates through a knowledge of how rainfall isotope compositions have changed over time however converting back from proxy to rainfall is not necessarily straightforward because however well the isotopic fractionation due to proxy growth or formation is understood a variety of modifying processes may have intervened between this and the actual rainfall events three main reservoirs of environmental water may contribute to the isotopic compositions of terrestrial proxy indicators surface waters soil moisture and groundwater each of these can in principle be isotopically modified compared to rainfall in the locality this review examines these effects and how they may change under different european climate types at the present day it is concluded that while groundwater isotopic compositions typically represent closely the bulk composition of rainfall under a variety of climatic regimes soil and particularly lake waters require detailed study if their isotope systematics are to be adequately understood the review also finds that to a large extent the present is the key to the past in terms of recharge processes during the late pleistocene though glaciation may have had profound isotopic consequences in certain areas while a more general aridity led to the apparent absence of recharge in most areas for much of the late devensian

viscoelastic cycle model of interseismic deformation in the northwestern united states summary we apply a viscoelastic cycle model to a compilation of gps velocity fields in order to address the kinematics of deformation in the northwestern united states a viscoelastic cycle model accounts for time dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field building on the approach taken in pollitz et al we construct a deformation model for the entire western united states based on combined fault slip and distributed deformation and focus on the implications for the mendocino triple junction mtj cascadia megathrust and western washington we find significant partitioning between strike slip and dip slip motion near the mtj as the tectonic environment shifts from northwest directed shear along the san andreas fault system to east west convergence along the juan de fuca plate by better accounting for the budget of aseismic and seismic slip along the cascadia subduction interface in conjunction with an assumed rheology we revise a previous model of slip for the m 9 1700 cascadia earthquake in western washington we infer slip rates on a number of strike slip and dip slip faults that accommodate northward convergence of the oregon coast block and northwestward convergence of the juan de fuca plate lateral variations in first order mechanical properties e g mantle viscosity vertically averaged rigidity explain to a large extent crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure our analysis also shows that present crustal deformation measurements particularly with the addition of the plate boundary observatory can constrain such lateral variations

quantification and propagation of errors when converting vertebrate biomineral oxygen isotope data to temperature for palaeoclimate reconstruction oxygen isotope analysis of bioapatite in vertebrate remains bones and teeth is commonly used to address questions on palaeoclimate from the eocene to the recent past researchers currently use a range of methods to calibrate their data enabling the isotopic composition of precipitation and the air temperature to be estimated in some situations the regression method used can significantly affect the resulting palaeoclimatic interpretations furthermore to understand the uncertainties in the results it is necessary to quantify the errors involved in calibration in some situations the regression method used can significantly affect the resulting palaeoclimatic interpretations while quantification of the errors involved in calibration is necessary to understand the uncertainties in the results studies in which isotopic data are converted rarely address these points and a better understanding of the calibration process is needed this paper compares regression methods employed in recent publications to calibrate isotopic data for palaeoclimatic interpretation and determines that least squares regression inverted to is the most appropriate method to use for calibrating causal isotopic relationships we also identify the main sources of error introduced at each conversion stage and investigate ways to minimise this error we demonstrate that larger sample sizes substantially reduce the uncertainties inherent within the calibration process typical uncertainty in temperature inferred from a single sample is at least 4oc which multiple samples can reduce to 1 2oc moreover the gain even from one to four samples is greater than the gain from any further increases we also show that when converting 18oprecipitation to temperature use of annually averaged data can give significantly less uncertainty in inferred temperatures than use of monthly rainfall data equations and an online spreadsheet for the quantification of errors are provided for general use and could be extended to contexts beyond the specific application of this paper palaeotemperature estimation from isotopic data can be highly informative for our understanding of past climates and their impact on humans and animals however for such estimates to be useful there must be confidence in their accuracy and this includes an assessment of calibration error we give a series of recommendations for assessing uncertainty when making calibrations of 18obioapatite 18oprecipitation temperature use of these guidelines will provide a more solid foundation for palaeoclimate inferences made from vertebrate isotopic data

inversion of synthetic geodetic data for dip slip faults clues to the effects of lateral heterogeneities and data distribution in geological environments typical of the apennines italy

influences on the stable oxygen and carbon isotopes in gerbillid rodent teeth in semi arid and arid environments implications for past climate and environmental reconstruction abstract the stable isotope composition of small mammal tissues has the potential to provide detailed information about terrestrial palaeoclimate and environments because their remains are abundant in palaeontological and archaeological sites and they have restricted home ranges applications to the quaternary record however have been sparse and limited by an acute lack of understanding of small mammal isotope ecology particularly in arid and semi arid environments here we document the oxygen and carbon isotope composition of gerbillinae gerbil tooth apatite across a rainfall gradient in northwestern africa in order to test the relative influences of the 18o 16o in precipitation or moisture availability on gerbil teeth values the sensitivity of tooth apatite 13c 12c to plant responses to moisture availability and the influence of developmental period on the isotopic composition of gerbil molars and incisors the results show that the isotopic composition of molars and incisors from the same individuals differs consistent with the different temporal periods reflected by the teeth molar teeth are permanently rooted and form around the time of birth whereas incisors grow continuously the results indicate that tooth choice is an important consideration for applications as proxy quaternary records but also highlights a new potential means to distinguish seasonal contexts the oxygen isotope composition of gerbil tooth apatite is strongly correlated with mean annual precipitation map below 600 mm but above 600 mm the teeth reflect the oxygen isotope composition of local meteoric water instead predictably the carbon isotope composition of the gerbil teeth reflected c3 and c4 dietary inputs however arid and mesic sites could not be distinguished because of the high variability displayed in the carbon isotope composition of the teeth due to the microhabitat and short temporal period reflected by the gerbil we show that the oxygen isotope composition of small mammal teeth strongly reflects moisture availability in semi arid and arid environments and would provide an excellent record of palaeo aridity in a terrestrial setting the results illustrate that an understanding of an animal s physiology is essential for interpreting the animal s isotopic responses to external contexts especially in arid zones

direct observation of microcrack development in marble caused by thermal weathering one of the properties that makes marble such an excellent construction and ornamental material is its low porosity it is very difficult for water or decay agents to penetrate the internal structure of materials with no or few pores so enhancing the durability of these materials however environmental temperature fluctuations bring about significant physical changes in marbles that result in an increase in porosity due to the appearance of new microcracks and the expansion of existing ones these cracks offer new paths into the marble which make it easier for solutions containing pollutants to penetrate the material thermal expansion tests were performed on three different types of marble known as white tranco and yellow macael almeria spain after which an increase in porosity from 17 to 73 depending on marble type was observed mainly due to crack formation the structural changes occurring during thermal expansion tests were more significant in the case of white macael samples a fact that is not only related to its mineralogical composition but also to the morphology of the grains grain boundaries and crystal size our research suggests that thermally weathered white macael marble could be more susceptible to decay by other contaminant agents than tranco or yellow macael the use of hot stage environmental scanning electron microscopy is proposed as a valid tool for observing both in situ and at high magnification changes in the fracture system of building stones induced by thermal stress

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

computer simulations of california tectonics confirm very low strength of major faults recent improvements in the technique of modeling fault networks with thin plate finite elements yield full convergence of the solutions without any compromise in the representation of the frictional rheology of the upper crust or the transition to dislocation creep in the lower crust we apply these techniques to model the california region incorporating all faults with estimated slip rate over 1 mm yr as well as variations in elevation heat flow and crustal thickness velocity boundary conditions on the model sides are based on the nuvel 1 plate model and an approximation of deformation in the great basin the frictional and dislocation creep rheologic constants of the crust are calibrated to reproduce the observed variations in the maximum depth of seismicity which occurs at model temperatures of 350 410 c this leaves two free parameters the time averaged coefficient of friction on faults and the apparent activation energy for creep in the lower crust these parameters are systematically varied in three sets of 10 81 and 64 experiments respectively the predictions of each model are tested against three published data sets a set of 79 geologic limits on average slip rate on faults a set of 221 principal stress directions and a set of 841 secular rates of geodetic baselines both trilateration and vlbi very long baseline interferometry the patterns of model scores indicate that the time averaged friction coefficient of major faults is only 0 17 0 25 or only 20 30 of the value 0 85 that is assumed for the friction in the intervening blocks the laser trilateration data taken alone would indicate a preference for a high stress model but this model is one with very little fault slip and seismicity which can be rejected on other grounds in the final three parameter set of 64 models we test whether the anomalous weakness of faults is uniform or proportional to net slip with slip dependent weakening there is a general reduction in prediction errors which supports the hypothesis the geologic data and geodetic data agree in implying that fault weakness that is friction of 0 17 is general with an additional 30 slip dependent weakening of the san andreas to friction of 0 12 or 14 of normal the stress data however are fit best if all weakness is slip dependent effectively only the san andreas is weak thus the hypothesis that all weakening is slip dependent should not be rejected the best models predict all available data with rms root mean square mismatch of as little as 3 mm yr 6 of the relative plate velocity so their predictions may be useful for seismic hazard estimation at least along faults where no data are available this study extends the finding of very low friction from subduction zones where it was previously documented to a dominantly strike slip system in which underthrusting of wet sediment is not widespread return of previously subducted water from the mantle and its chemical or physical binding in fine grained gouge are possible explanations for the very low friction

correlation between the oxygen isotope ratio of north american bison teeth and local waters implication for paleoclimatic reconstructions abstract the oxygen isotope ratios of tooth enamel carbonate from 64 north american bison bison bison from eleven locations were measured the mean enamel oxygen isotope ratios for bison populations ranged from 28 3 to 15 9 smow and correlated well with the annual mean oxygen isotope ratios of local surface waters and precipitation the standard deviation of oxygen isotope values among different individuals within each bison population averaged 1 0 and ranged from 0 7 to 1 4 the variability of enamel oxygen isotope ratios was not significantly different among different populations and did not correlate with changes in temperature precipitation or relative humidity these results demonstrate that the average oxygen isotope values of bison tooth enamel can be used for use as a quantitative proxy for reconstructing the values of surface waters and therefore may provide valuable paleoclimatic information this study provides a baseline comparison for analyses of the oxygen isotope ratios of bison and other large herbivores from across north america

analytical solutions for leakage rates through abandoned wells 1 disposal of waste fluids via injection into deep saline aquifers is practiced in a variety of industries injection takes place in sedimentary basins that often have a history of oil and gas exploration and production which means that wells other than those used for waste disposal may exist in the vicinity of the injection site these existing wells provide possible pathways for leakage of waste fluids toward the shallow subsurface and the land surface for single phase flows of liquids with essentially constant properties the equations governing the system are linear and solutions may be written using the superposition principle because leakage through existing wells produces a time varying flux rate the solution of the governing equations involves convolution integrals previous solutions have addressed the problem of one injection well one existing passive well and a simple geometry of two aquifers separated by an aquitard by use of laplace transforms even for this simple case inversion of the transform is difficult solutions involving more than one passive well have not been developed nor have solutions been developed for more than two aquifers and one aquitard realistic injection cases often involve layered systems with multiple aquifers and aquitards as well as multiple passive wells sometimes numbering in the hundreds solutions for the general case of multiple aquifers and wells may be developed through introduction of approximations to the well function and appropriate simplification of the convolution integral such a solution is computationally simple comparison to solutions using the full laplace transform solution indicates that the new solution procedure produces excellent results application of the new solution to a case of multiple passive wells shows that the cumulative leakage flux in the passive wells is not a simple sum of the single well case owing to leakage induced drawdown around the passive wells in addition application to the case of multiple aquifers and aquitards demonstrates the importance of leakage into intervening aquifers as a mechanism to mitigate leakage into shallow zones a process referred to as the elevator model the new analytical solution provides a tool to analyze practical injection problems and forms a foundation on which more complex solutions such as those involving injection of a nonaqueous fluid into a deep brine formation may be based

oxygen isotopic composition of the mediterranean sea since the last glacial maximum constraints from pore water analyses abstract interstitial waters recovered from ocean drilling program leg 161 site 976 in the western mediterranean sea are used in conjunction with a numerical model to constrain the 18o of seawater in the basin since the last glacial maximum including sapropel event 1 to resolve the oxygen isotopic composition of the deep mediterranean we use a model that couples fluid diffusion with advective transport thus producing a profile of seawater 18o variability that is unaffected by glacial interglacial variations in marine temperature comparing our reconstructed seawater 18o to recent determinations of 1 0 for the mean ocean change in glacial interglacial 18o due to the expansion of global ice volume we calculate an additional 0 2 increase in mediterranean 18o caused by local evaporative enrichment this estimate of 18o change due to salinity variability is smaller than previous studies have proposed and demonstrates that mediterranean records of foraminiferal calcite 18o from the last glacial period include a strong temperature component paleotemperatures determined in combination with a stacked record of foraminiferal calcite depict almost 9 c of regional cooling for the last glacial maximum model results suggest a decrease of 1 1 in seawater 18o relative to the modern value caused by increased freshwater input and reduced salinity accompanying the formation of the most recent sapropel the results additionally indicate the existence of isotopically light water circulating down to bottom water depths at least in the western mediterranean supporting the existence of an anti estuarine thermohaline circulation pattern during sapropel event 1

wet phases in the sahara sahel region and human migration patterns in north africa the carbon isotopic composition of individual plant leaf waxes a proxy for c3 vs c4 vegetation in a marine sediment core collected from beneath the plume of sahara derived dust in northwest africa reveals three periods during the past 192 000 years when the central sahara sahel contained c3 plants likely trees indicating substantially wetter conditions than at present our data suggest that variability in the strength of atlantic meridional overturning circulation amoc is a main control on vegetation distribution in central north africa and we note expansions of c3 vegetation during the african humid period early holocene and within marine isotope stage mis 3 50 45 ka and mis 5 120 110 ka the wet periods within mis 3 and 5 coincide with major human migration events out of sub saharan africa our results thus suggest that changes in amoc influenced north african climate and at times contributed to amenable conditions in the central sahara sahel allowing humans to cross this otherwise inhospitable region

sea land oxygen isotopic relationships from planktonic foraminifera and speleothems in the eastern mediterranean region and their implication for paleorainfall during interglacial intervals the oxygen and carbon stable isotope compositions of cave speleothems provide a powerful method for understanding continental climate change here we examine the question of the regionality of this isotopic record and its linkage with the marine isotopic record in the eastern mediterranean em region the study presents a new accurately dated 250 kyr 18o and 13c record determined from speleothems of the peqiin cave northern israel its comparison with the continuous 185 kyr isotopic record of the soreq cave speleothems from central israel reveals striking similarities thus a strong regional climatic signal brought about by variations in temperature and rainfall amount is reflected in both cave records low 18o minima in the peqiin profile for the last 250 to 185 kyr period interglacial marine isotopic stage 7 match the timing of sapropels 9 to 7 and are indicative of high rainfall in the em region at these times the combined soreq and peqiin 18o record for the last 250 kyr excellently matches the published globigerinoides ruber g ruber marine 18o record for the em sea with the isotopic compositional difference g ruber speleothems remaining relatively constant at 5 6 0 7 thus establishing for the first time a robust exploitable link between the land and the marine isotopic records the correspondence of low 18o speleothem values and high cave water stands with low g ruber 18o values during interglacial sapropel events indicates that these periods were characterized by enhanced rainfall in the em land and sea regions by use of sea surface temperatures derived from alkenone data as a proxy for land temperatures at the soreq cave we calculate the paleorainfall 18o values and its amounts maximum rainfall and lowest temperature conditions occurred at the beginning of the sapropel events and were followed by decrease in rainfall and increase in temperatures leading to arid conditions the record for the last 7000 yr shows a trend toward increasing aridity and agrees well with climatic and archeological data from north africa and the middle east

catastrophic arid episodes in the eastern mediterranean linked with the north atlantic heinrich events the response of continental climate to the well documented climate oscillations during the last glacial period has been a subject of intense interest yet much less is known about the influence on regional continental climates than in the marine or polar realms of earth the detailed lake level history of the closed lake lisan paleo dead sea in the middle east has been reconstructed from shoreline indications and high resolution u th and 1 4 c chronologies thus providing data on the response of the lake s catchment area to the climate changes during the corresponding period we present a correlation between the newly developed lake lisan level curve for the past 55 k y and the north atlantic heinrich events the correlation indicates a closely connected climate response between these north atlantic events and the hydrologic conditions that prevailed in the eastern mediterranean our findings show that although the generally cooler conditions that prevailed during the last glaciation favored high levels of the lake catastrophic events in the north atlantic which are associated with maximum cooling have been responsible for droughts in the eastern mediterranean we infer that cold water input to the mediterranean originating in the collapse of the north atlantic deep water circulation caused the reduction of evaporation and less precipitation in the eastern mediterranean

constraints on the ocean oxygen isotopic enrichment between the last glacial maximum and the holocene paleoceanographic implications abstract we review the various methods which have been applied to estimate the change of seawater 18 o w between the last glacial maximum lgm and the holocene the most accurate constraints on these estimates are provided by the measurement of pore waters 18 o and by high resolution records of benthic foraminifer 18 o in the high latitude oceans of both hemispheres they show that the 18 o of seawater in the deep ocean during the lgm was 1 05 0 20 heavier than today with significant regional variations constraints resulting from ice sheet models are less accurate because both the volume and isotopic composition of each ice sheet are still poorly known the amplitude of the benthic 18 o change between the lgm and the holocene together with the 18 o and 13 c values of the benthic foraminifera genus cibicides during the lgm show that the southern ocean deep waters were extremely cold close to the freezing point during this time deep waters of the south atlantic and the pacific oceans were at least 1 3 c warmer than those of the southern ocean overall the glacial deep ocean below 2500 m was characterized by extremely cold temperatures everywhere lower than 0 c 18 o values of benthic foraminifer from the north atlantic are highly variable this variability suggests that deep atlantic waters were not homogeneous probably because they resulted from the sinking of different surface water masses at various locations during winter the deep waters in the north atlantic were at most 2 c warmer than in southern ocean alternatively they could have been nearer the freezing point with a 18 o value lighter than the mean ocean water brine formation during winter would preserve such light 18 o values of the northern north atlantic surface water

at what stress level is the central indian ocean lithosphere buckling internal contrasts in strength are responsible for lithospheric buckling these are quantified by comparing the indian ocean data to two dimensional visco elasto plastic numerical models where the material properties depend on temperature and pressure the central indian basin is known for its intraplate seismicity and long wavelength undulations of the sea floor and associated gravity signatures to simulate the amplitudes of undulations that reach 1 km within about 11 ma of compression and 60 km of shortening the required mean yield strength of the lithosphere is 400 mpa if either a hydrostatic fluid pressure is considered in the crust or a mechanical decoupling at the depth of the moho small crustal wavelengths are superimposed on the long wavelength deformation in agreement with observations it is then possible to match the alternative indication that buckling commenced only 4 ma ago with a total amount of shortening of 30 km and with a required yield strength of 200 mpa about 10 of homogeneous thickening accompanies buckling taking into account variable thermal conductivity demonstrates that a change in the geotherm is sufficient to increase buckling amplitudes by 10 within 5 ma fl 2000 elsevier science b v all rights reserved

temperature control of continental lithosphere elastic thickness te vs vs article i nfo the elastic thickness of the continental lithosphere is closely related to its total strength and therefore to its susceptibility to tectonic deformation and earthquakes recently it has been questioned whether the lithosphere thickness and strength are dependent on crustal and upper mantle temperatures and compositions as predicted by laboratory data we test this dependence regionally by comparison in northwestern north america of the effective elastic thickness te from topography gravity coherence with upper mantle temperatures mapped by shear wave tomography velocities vs and other temperature indicators the te values are strongly bimodal as found globally less than 20 km for the hot cordillera backarc and over 60 km for the cold stable craton these te correspond to low vs beneath the cordillera and high vs beneath the craton model temperature depth profiles are used to estimate model te for comparison with those observed only limited areas of intermediate thermal regimes i e thermotectonic ages of 300 ma have intermediate te that suggest a weak lower crust over a stronger upper mantle there are large uncertainties in model te associated with composition water content strain rate and decoupling stress threshold however with reasonable parameters model yield stress envelopes correspond to observed te for thermal regimes with 800 900 c at the cordillera moho and 400 500 c for the shield in agreement with temperatures from vs and other estimators our study supports the conclusion that lithosphere elastic thickness and strength are controlled primarily by temperature and that laboratory based rheology generally provides a good estimate of the deformation behaviour of the crust and upper mantle on geological time scales

geodetic constraints on areal changes in the pacific north america plate boundary zone what controls basin and range extension using 1500 geodetic velocities we model the present day spatial patterns of areal changes inside the pacific north america plate boundary zone from this model we show that between the central gulf of california and the queen charlotte islands there is no significant net change in surface area this zero net areal change result allows us to relate regions of areal growth to areas of equivalent contraction elsewhere within the plate boundary zone we find that areal growth of the basin and range province brp and its eastern margin 5 2 0 1 10 3 m 2 yr is balanced by areal reduction near northwestern california between 38 n and 42 n the san andreas fault system south of 38 n and the plate boundary zone north of 42 n including the juan de fuca and gorda ridge systems each have no significant net areal change our results suggest a kinematic relationship between extension in the brp and contraction near the northern california coast ranges and klamath mountains from these observations we propose that although brp extension may be caused by internal forces the southernmost cascadia subduction zone provides a window of escape that acts as a stress guide to brp extension as well as northwestward sierra nevada motion such a dynamic model is consistent with independent findings that 1 the least principal horizontal stress orientations in the brp are toward northern california 2 extension directions in the brp have changed orientation to track the northward migration of the mendocino triple junction and 3 the southernmost cascadia subduction zone is a relatively weak plate boundary

oxygen isotope variations in phosphate of biogenic apatites iv mammal teeth and bones groups of rats grown from birth to death in identical conditions but with different 18o of drinking water w were studied for variations of 18o of their body water bw and bone phosphate p there is a high linear correlation r 0 99 between bw and between p and w the regression lines have similar slope coefficients 0 53 and 0 49 values of p of different teeth and bones are the same within the precision of the method 0 5 the isotopic fractionation coefficient between phosphate and body water is 1 0178 and close to the estimated value of 1 0173 derived from the phosphate paleotemperature equation deviations from constant fractionation between bone phosphate and environmental drinking water depend primarily on rates of drinking and metabolism environment conditions have relatively little effect on oxygen isotope fractionation between water sources and bone phosphate

rayleigh wave phase velocities small scale convection and azimuthal anisotropy beneath southern california 1 we use rayleigh waves to invert for shear velocities in the upper mantle beneath southern california a one dimensional shear velocity model reveals a pronounced low velocity zone lvz from 90 to 210 km the pattern of velocity anomalies indicates that there is active small scale convection in the asthenosphere and that the dominant form of convection is three dimensional 3 d lithospheric drips and asthenospheric upwellings rather than 2 d sheets or slabs several of the features that we observe have been previously detected by body wave tomography these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern sierra nevada and walker lane region sinking lithosphere beneath the southern central valley upwelling beneath the salton trough and downwelling beneath the transverse ranges our new observations provide better constraints on the lateral and vertical extent of these anomalies in addition we detect two previously undetected features a high velocity anomaly beneath the northern peninsular range and a low velocity anomaly beneath the northeastern mojave block we also estimate the azimuthal anisotropy from rayleigh wave data the strength is 1 7 at periods shorter than 100 s and decreases to below 1 at longer periods the fast direction is nearly e w the anisotropic layer is more than 300 km thick the e w fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms pure shear in the lithosphere due to n s tectonic shortening and simple shear in sublithosphere mantle due to mantle flow

resource pressure and environmental change on the north african littoral epipalaeolithic to roman gastropods from cyrenaica libya abstract this paper discusses the marine and terrestrial shell on epipalaeolithic to classical period sites in the cyrenaican coastlands northeast libya with particular reference to the haua fteah with parallel studies at a late roman farmstead and two small caves together they provide evidence for coastal and terrestrial environments and for the continued nutritional importance of gastropods to humans during the holocene land snail evidence is consistent with regional vegetation in coastal cyrenaica becoming increasingly open through the holocene as a result of some combination of climate change and human impact marine species suggest that the coastline near the haua had been rocky throughout the holocene at hagfet al gama changing faunas provide evidence for sand encroachment onto a previously rocky shoreline in hellenistic times a biometric study of osilinus turbinatus shows that in the archaeological sites these shells are systematically smaller than modern specimens providing evidence for long term dietary stress in the human populations around the haua fteah with particularly severe stress in parts of the epipalaeolithic a biometric study of patella spp provided evidence for size selection but also seems to show evidence for resource pressure it is unlikely that variations in resource pressure seen in the mollusc biometrics are the result of climatic stress or natural ecological factors and explanations must be sought in society environment dynamics

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

quick look assessments to identify optimal co2 eor storage sites a newly developed multistage quick look methodology allows for the efficient screening of an unmanageably large number of reservoirs to generate a workable set of sites that closely match the requirements for optimal co2 enhanced oil recovery eor storage the objective of the study is to quickly identify miscible co2 eor candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities of selected top options through dimensionless modeling and reservoir characterization quick look assessments indicate that the co2 eor resource potential along the us gulf coast is 4 7 billion barrels and co2 sequestration capacity is 2 6 billion metric tons in the first stage oil reservoirs are screened and ranked in terms of technical and practical feasibility for miscible co2 eor the second stage provides quick estimates of co2 eor potential and sequestration capacities in the third stage a dimensionless group model is applied to a selected set of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties disregarding reservoir architecture and sweep design the fourth stage validates and refines the results by simulating flow in a model that describes the internal architecture and fluid distribution in the reservoir the stated approach both saves time and allows more resources to be applied to the best candidate sites

asymmetry in elastic properties and the evolution of large continental strike slip faults 1 we use geodetic studies to quantify several cases of significant asymmetry in interseismic and coseismic effects along large continental strike slip faults using simple two dimensional edge dislocation models we first show that asymmetric elastic loading characterizes the present main marmara fault a portion of the north anatolian fault along the northern margin of the sea of marmara the ratio of asymmetry there is about 10 this ratio is even larger about 30 along the northern sumatra fault near lake toba caldera we then examine two profiles near point reyes and point arena across the northern san andreas fault that have been previously proposed as affected by asymmetry both in interseismic and coseismic effects we show that an asymmetry ratio of 1 6 in interseismic loading exists near point arena with the southwest side of the fault being more rigid than the northeast one on the other hand we do not find significant asymmetry for the point reyes profile that was previously described as highly asymmetric we examine coseismic motion during the 1906 earthquake along the same two profiles ratios of 1 2 and 1 7 are found for the point arena and point reyes profiles respectively we discuss the possible causes of asymmetry contrasts in seismic velocity in the brittle portion suggest ratios generally not exceeding 2 5 for the dynamic rigidity in the upper brittle section larger ratios may involve other complex causes such as differences between static and dynamic rigidities contrasts in rheology in the deeper creeping sections and postseismic transients we conclude that asymmetry should be systematically included within the parameters to be inverted when dealing with the mechanics of large scale strike slip faults

gps measurements of near field deformation along the southern dead sea fault system 1 analysis of short term deformation along the southern part of dead sea fault dsf provides a systematic view of kinematics this part of the continental transform the southern dsf consists of two principal segments the wadi araba and jordan valley faults in addition to other regional continuous gps data this study uses new data from 25 survey sites and 4 continuous gps stations in jordan for improved near field observations resulting velocities are reported with 1 uncertainties ranging from 0 4 1 0 mm yr application of elastic dislocation models yields estimates of slip rates for wadi araba and jordan valley faults are 4 9 0 4 mm yr and 4 7 0 4 mm yr respectively modeling also suggests different depths of effective fault locking with 15 5 km and 8 5 km for the wadi araba and jordan valley faults respectively these slip rates are generally consistent with the upper end of the range of slip rates estimated from late quaternary geology spatial variations in effective fault locking generally correspond with a heterogeneous mantle lithosphere a similar observation can be observed along the southern san andreas fault and this may reflect the influence of heterogeneity in the uppermost mantle on crustal faulting processes

plate rigidity inversion in southern california using interseismic gps velocity field summary this paper presents an inversion method using the interseismic velocity field to determine effective rigidity of the lithosphere the method is based on the minimization of a cost function defined as the quadratic measure of the difference between measured and modelled velocity fields on a discrete set of points the continuous mapping of the rigidity is fulfilled with a limited set of parameters and the forward solution is achieved using a plane stress finite element code the computation of the cost function gradient in the parameters space allows one to iteratively find the best parameters set through a suitable optimization algorithm we first design a benchmark including an abrupt rigidity variation that cannot be described by a continuous function for such a case we show that increasing the number of parameters is a way to accurately describe sharp variations of the rigidity map then we use a dense gps velocity field over the southwestern united states to estimate the corresponding rigidity variations for different spatial resolutions of the parameters grid we analyse the conceptual and practical difficulties associated with our methodology finally rigidity maps obtained by our inversion method in southwestern united states and particularly across the san andreas fault system are reviewed and compared to current plate rigidity estimates and geophysical data over this area

lithosphere rigidity by adjoint based inversion of interseismic gps data application to the western united states while vertical motion induced by long term geological loads is often used to estimate the flexural rigidity of the lithosphere we intend to evaluate the shear rigidity of the lithosphere using horizontal motion our approach considers that the rigidity of the lithosphere may be defined as its resistance to horizontal tectonic lateral forces in this case a spatial distribution of an effective shear rigidity can be estimated from the analysis of the interseismic velocity fields we consider the western united states zone where weakly strained areas e g the sierra nevada are connected with areas of large strain rate e g san andreas fault system by inverting interseismic strain distribution measured by geodetic methods we infer the effective shear rigidity of the lithosphere the forward problem is defined using the equations of linear elasticity the inversion relies on the minimization of the sum of a quadratic measure of the differences between measured and modelled velocity fields the functional also includes regularization terms for the parameters of the model the gradient of the functional with respect to the minimization parameters is computed using an adjoint formulation this permits the treatment of large dimensional minimization problems finally a measure of the uncertainty of our inversion is illustrated through the covariance matrix of the parameters at the optimum the optimization chart is validated on two synthetic velocity distributions then the effective shear rigidity variations of the western united states are estimated using the cmm3 interseismic velocities the inversion displays low effective rigidities along the san andreas fault system the mojave desert and in the eastern california shear zone while rigid areas are found in the sierra nevada and in the south basin and range finally we discuss the differences between our strain rate and rigidity maps with previously published results for the western united states

geologic and infrastructure factors for delineating areas for clean coal examples in texas usa texas has a wide variety of areas that can be targeted for new clean coal facilities these areas are delineated by mapping spatial linkages between coal and lignite bearing formations groundwater and surface water resources and co2 sinks in brine formations for long term co2 storage or in mature oil fields with potential for enhanced oil recovery eor however a variety of infrastructure factors make it feasible to also target numerous areas outside coal and lignite basins in texas these infrastructure factors include pipelines for delivery of co2 to subsurface sinks and delivery of coal produced hydrogen to refineries ease of connection to existing transmission lines distribution of nonattainment areas where new clean coal facilities could be constructed and be compliant with strict air quality standards and railroads that can transport coal and other feedstock to new clean coal facilities primary regions in texas where favorably co located co2 source sink factors related to coal and lignite trends include the gulf coast the eastern shelf of the permian basin and the fort worth basin however areas outside coal and lignite basins particularly the permian basin where a new clean coal facility is being planned also have clean coal potential because of existing co2 pipelines and proximity to eor fields that can economically sustain new clean coal facilities

pleistocene and holocene palaeoclimates in the gebel akhdar libya estimated using herbivore tooth enamel oxygen isotope compositions abstract the palaeoclimate of the gebel akhdar massif in cyrenaica northeast libya is investigated using the stable oxygen isotope ratio 18 o of herbivore tooth enamel from the archaeological faunal assemblages of the haua fteah and hagfet ed dabba caves samples accumulated through human activity at the sites thus climatic interpretations are in direct chronological association with periods of human presence in the local landscape wild ammotragus lervia barbary sheep and bos sp auroch and domestic ovis sp and capra sp from the levalloiso mousterian 73 3 43 5 ka to the neolithic 9 3 5 4 ka cultural phases are analysed results indicate that the most arid environment represented by the samples occurred at 32 ka when populations associated with dabban lithic assemblages were present within the region climatic instability increased during oxygen isotope stage 2 consistent with other palaeoenvironmental investigations in the gebel akhdar there is no evidence for hyper arid events during the last glacial and surface water most probably in the form of local springs was available throughout the time periods considered overall results indicate that different cultural groups occupied the gebel akhdar landscape under different climatic conditions but that climate variations appear to have been of lower magnitude than those that occurred at inland north african locations these reconstructions provide further support to the theory that the gebel akhdar may have served as a refugium for human populations in north africa during times of global climatic extremes

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

microscopic modelling of the hydraulic fracturing process a microscopic perspective is introduced in this study which offers a detailed insight at the inter particle level to the geo mechanical responses caused by fluid injection and the resulting pressure build up this was achieved by employing the discrete element method dem to model the pressure development and the subsequent fracturing and or cavity propagation this technique represents the formation material as an assembly of discrete particles linked to each other through contacts numerical experiments were carried out on two sample materials for the first instance tests were carried out on a bulk material representative of a generic intact rock with the breakage of inter particle bonds indicating the formation of cracks the second series of tests was carried out on granular type materials such as sand where particle separation signified cavity initiation and separation it was observed from the dem modelling results that the intact rock material showed a predominance of mode ii fracturing at high fluid velocities however when the fluid velocity is reduced considerably the fracturing behaviour tended towards more of mode i also records of the pressure development were taken from the numerical results and were used to monitor the fracturing events the outcome of this study highlights important aspects of the hydraulic fracturing process especially at the particle particle scale and thus provides a strong basis for more exhaustive studies involving larger scale reservoir modelling and more complex fracturing scenarios

precipitation source inferred from stable isotopic composition of pleistocene groundwater and carbonate deposits in the western desert of egypt an atlantic source of precipitation can be inferred from stable isotopic data h and o for fossil groundwaters and uranium series dated carbonate spring deposits from oases in the western desert of egypt in the context of available stable isotopic data for fossil groundwaters throughout north africa the observed isotopic depletions delta d 72 to 81 per thousand delta sup 18 o 10 6 to 11 5 per thousand of fossil ge 32 000 yr b p groundwaters from the nubian aquifer are best explained by progressive condensation of water vapor from paleowesterly wet oceanic air masses that traveled across north africa and operated at least as far back as 450 000 yr before the present the values of delta sup 18 o 17 1 to 25 9 per thousand for 45 000 to 450 000 yr old tufas and vein filling calcite deposits from the kharga and farafra oases are consistent with deposition from groundwaters having oxygen isotopic compositions similar to those of fossil groundwaters sampled recently at these locations

tooth enamel sampling strategies for stable isotope analysis potential problems in cross method data comparisons abstract the stable isotope composition of a given sample of tooth enamel is a function of the mineralisation process the isotopic composition of the input signal and sampling geometry as the dominant axis of tooth growth is orientated from the occlusal surface to the enamel root junction the isotopic composition of an enamel sample that spans the full length of this axis is often taken to represent a whole tooth or bulk average while serial or intra tooth samples taken along the same axis are considered to track isotopic variation across the period of tooth formation a bulk sample of enamel should therefore approximate the mean of the serial samples and in teeth that form over a complete annual cycle bulk and serial sampling methods are often assumed to possess an annual seasonal relationship however this does not take into account the effect of the mineralisation process and sampling geometry on the derived isotope signals here we investigate the reproducibility of both the bulk and serial sampling methods as independent stand alone techniques and then explore the assumed relationship between the two each method shows good reproducibility in the oxygen 18o and carbon 13c isotope results across paired left and right molars however cross method comparisons reveal a systematic offset between bulk and serial results within a single population with 19 out of 23 18o bulk tooth values being lower and 22 out of 23 13c bulk tooth values being higher than the means of their respective intra tooth sequences in 4 out of 19 cases for 18o and 6 out of 22 cases for 13c the bulk tooth results fall completely out of the range observed in the corresponding intra tooth sequence this finding has implications for cross method data comparisons and questions the assumed temporal relationship between serial and bulk isotope data

record of holocene aridification 6000 7000bp in egypt ne africa authigenic carbonate minerals from laminated sediments in lake qarun abstract the origin and climate implications of authigenic carbonate minerals from lake qarun egypt were examined in relation to the mid late holocene climate changes these minerals occur as very thin 0 5 3 mm very fine well sorted white to pale yellow aragonite or calcite laminae intercalated with olive green clayey silt with sharp and horizontal contacts under the scanning electron microscope sem aragonite appears as dense euhedral and ellipsoidal rice grained crystals that range in length from 0 5 to 1 micron and in width from 0 2 to 0 5 micron the calcite crystals are stubby equant or blocky polyhedra of about 5 microns in length 18 o values range between 2 7 and 3 7 for the calcite and between 2 1 and 6 for the aragonite 13 c values range between 0 4 and 1 for the calcite and between 0 5 and 3 4 for the aragonite a very strong positive correlation is observed between carbon and oxygen isotopes for the aragonite r 2 0 9 and a more moderate positive correlation with calcite r 2 0 6 the complete absence of biological and other no carbonate grains the sharp contacts of laminae basal and the occurrence of calcite and aragonite as individual euhedral crystals rather than clusters of grain aggregation indicate that aragonite and calcite layers represent rapid inorganic precipitation from the lake water endogenic the positive values of 18 o and 13 c and the strong positive correlation between 18 o and 13 c suggest prevalence of a low lake level saline and dry climatic conditions during their formation the change from calcite to aragonite indicates a change in the formational conditions from less arid conditions in the case of calcite to severe arid conditions in the case of aragonite the relative abundance of diatoms in calcite rich laminae and the less strong positive correlation between 18 o and 13 c of calcite support this interpretation the arid conditions in which the carbonate minerals were formed could correspond to the aridification period of the north east africa between ca 6000 8500 bp due to the north south shifts of the intertropical convergence zone itcz that control the evaporation precipitation balance over north east africa and or to dry climate and desert environment conditions in egypt at the same period these results are also consistent with the aridification conditions during the mid late holocene suggesting its global trend

a three dimensional crustal seismic velocity model for southern california from a composite event method we present a new crustal seismic velocity model for southern california derived from p and s arrival times from local earthquakes and explosions to reduce the volume of data and ensure a more uniform source distribution we compute composite event picks for 2597 distributed master events that include pick information for other events within spheres of 2 km radius the approach reduces random picking error and maximizes the number of s wave picks to constrain absolute event locations and shallow velocity structure we also use times from controlled sources including both refraction shots and quarries we implement the simulps tomography algorithm to obtain three dimensional 3 d v p and v p v s structure and hypocenter locations of the composite events our new velocity model in general agrees with previous studies resolving low velocity features at shallow depths in the basins and some high velocity features in the midcrust using our velocity model and 3 d ray tracing we relocate about 450 000 earthquakes from 1981 to 2005 we observe a weak correlation between seismic velocities and earthquake occurrence with shallow earthquakes mostly occurring in high p velocity regions and midcrustal earthquakes occurring in low p velocity regions in addition most seismicity occurs in regions with relatively low v p v s ratios although aftershock sequences following large earthquakes are often an exception to this pattern

flexure and isostatic residual gravity of the sierra nevada the sierra nevada of california displays an isostatic gravity anomaly of 35 mgal over the western foothills and 45 mgal at the crest of the range a flexural isostatic model designed to explain the rapid neogene uplift of the sierra nevada is consistent with these observations and can explain a portion of both gravity anomalies by contributions from moho depths the present day crustal root causing regional compensation in this model differs from the simple local airy compensation assumed for the sierra in calculating the isostatic residual gravity two dimensional gravity modeling indicates that this difference results in a residual gravity high of 9 mgals over the western foothills which are buoyed up by the excess root to the east and a low of 16 mgals over the crest of the sierra the remainder of the isostatic gravity anomaly is attributed to upper crustal density contrasts because high density rocks underlie the foothills and a low density batholith forms the crest any model for the isostatic residual gravity must assume implicitly or explicitly a flexural response of the lithosphere with the stiff sierran lithosphere the isostatic deflection of the moho due to the upper crustal bodies will be small if a similar gravity model were to assign no stiffness to the lithosphere local airy compensation the mass anomalies of the upper crustal bodies would necessitate a change in depth of the moho to achieve compensation this deflection of the moho would significantly reduce the amplitude of the anomaly produced by the upper crustal block for the unbroken pre uplift case of the sierra nevada of 10 ma our model predicts an isostatic gravity low over the range crest of approximately 80 mgals and a flanking high of 55 mgals these values are larger than would be predicted for a more typical eroded magmatic arc that does not have abnormally low heat flow and consequent high flexural rigidity

reservoir induced deformation and continental rheology in vicinity of lake mead nevada lake mead is a large reservoir in nevada formed by the construction of the 221 m high hoover dam in the black canyon of the colorado river the lake encompasses an area of 635 km2 and the total volume of the reservoir is 35 5 km3 filling started in february 1935 on the basis of a first order leveling in 1935 several levelings were carried out to measure the deformation induced by the load of the reservoir subsidence in the central parts of the lake relative to the first leveling was around 120 mm 1941 218 mm 1950 and 200 mm 1963 the subsidence pattern clearly shows relaxation of the underlying basement due to the water load of the lake which ceased after 1950 modeling of the relaxation process by means of layered viscoelastic compressible flat earth models with a detailed representation of the spatial and temporal distribution of the water load shows that the thickness of the elastic crust underneath lake mead is 30 3 km the data are also consistent with a 10 km thick elastic upper crust and a 20 km thick viscoelastic lower crust with 1020 pa s as a lower bound for its viscosity the subcrust has an average viscosity of 1018 0 2 pa s a surprisingly low value the leveling data constrain the viscosity profile down to 200 km depth

the oxygen isotopic composition of seawater during the last glacial maximum high resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep sea sediments from sites in the north and south atlantic the data provide direct measurements of changes in the isotopic composition of bottom waters during the last glacial maximum lgm results from ocean drilling program odp site 981 in the north atlantic currently bathed in north atlantic deep water nadw reproduces previous results from the ceara and bermuda rises constraining the glacial interglacial change in 18 o of the deep atlantic to be 0 7 0 8 results from site 984 which is located north of site 981 and at a shallower water depth yield a similar value 0 8 providing insight into the properties of glacial north atlantic intermediate water gnaiw sites from odp leg 177 in the south atlantic span the modern boundary between northern and southern sources of deep water data from the northern site 1088 yield a similar result to sites in the tropical and north atlantic 0 7 at the southern site 1093 located south of the polar front the change is substantially larger 1 1 representing the change in 18 o of southern source waters since the lgm these results confirm previous estimates that the global average change in 18 o of seawater is 1 0 0 1 hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations giving further support to these results at all sites studied the temperature of the deep ocean during the lgm calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera was within 1 c of the freezing point of seawater

temperature and the seismic aseismic transition observations from the 1992 landers earthquake an important constraint on the size and destructive potential of earthquakes is the depth extent of rupture laboratory studies of the transition from unstable to stable sliding along with observed relationships between surface heat flow and the thickness of the seismogenic crust provide strong evidence for the significance of temperature in determining the maximum nucleation depth of large earthquakes the june 28 1992 mw 7 3 landers earthquake ruptured fault segments within 20 km of 11 pre existing heat flow measurements and shallowing of the base of aftershock seismicity along strike correlates with an increase in heat flow crustal geotherms estimated from these measurements place the base of seismicity along the 250 c isotherm this temperature is consistent with predictions from laboratory studies of the frictional stability of westerly granite but estimated temperatures for the seismic aseismic transition along other faults within the san andreas fault system are in the range of 350 to 400 c variations in country rock and fault gouge composition together with higher slip rates may account for this difference although part of the landers seismogenic crust might remain unruptured

present day strain distribution across a segment of the central bend of the north anatolian fault zone from a persistent scatterers insar analysis of the ers and envisat archives

toward a better understanding of palaeoclimatic regimes that recharged the fossil aquifers in north africa inferences from stable isotope and remote sensing data abstract the isotopic composition of modern precipitation collected monthly from the international atomic energy agency iaea stations over north africa is enriched average d morocco 25 8 algeria 21 3 tunisia 20 6 libya 17 7 egypt 11 7 compared to fossil groundwater across north africa which shows progressive west to east depletion this indicates that precipitation from paleowind regimes was different from those prevailing in the present day late holocene however a few monthly records march 1982 december 1987 december 1991 march 2002 and april 2002 collected from iaea stations sidi barrani cairo rafah and el arish showed isotopic depletions d 56 to 43 7 approaching those of the fossil groundwater in egypt for each of the five events we investigated the direction of cloud propagation in relation to the isotopic composition of precipitation as it travels over the african continent and surroundings cloud propagation directions and air parcel flow paths were extracted from temporal every 30 min meteosat image products 1 infra red eumetsat 2 cloud motion winds cmw and 3 back trajectory models btm the inferred wind regimes for each of these events were then compared to those for the remaining egyptian records 160 that produced precipitation with enriched to intermediate isotopic compositions d 39 7 to 34 6 the extracted cloud propagation directions and the observed spatial variation in the isotopic compositions of the precipitating rain support a model that attributes previous wet climatic periods over north africa to the intensification of palaeowesterlies during glacial periods

changing patterns of eastern mediterranean shellfish exploitation in the late glacial and early holocene oxygen isotope evidence from gastropod in epipaleolithic to neolithic human occupation layers at the haua fteah cave libya abstract the seasonal pattern of shellfish foraging at the archaeological site of haua fteah in the gebel akhdar libya was investigated from the epipaleolithic to the neolithic via oxygen isotope 18 o analyses of the topshell phorcus osilinus turbinatus to validate this species as faithful year round palaeoenvironmental recorder the intra annual variability of 18 o in modern shells and sea water was analysed and compared with measured sea surface temperature sst the shells were found to be good candidates for seasonal shellfish forging studies as they preserve nearly the complete annual sst cycle in their shell 18 o with minimal slowing or stoppage of growth during the terminal pleistocene early epipaleolithic locally known as the oranian with modeled dates of 17 2 12 5 ka at 2 probability douka et al 2014 analysis of archaeological specimens indicates that shellfish were foraged year round this complements other evidence from the archaeological record that shows that the cave was more intensively occupied in this period than before or afterwards this finding is significant as the period of the oranian was the coldest and driest phase of the last glacial cycle in the gebel akhdar adding weight to the theory that the gebel akhdar may have served as a refugium for humans in north africa during times of global climatic extremes mollusc exploitation in the latest pleistocene and early holocene during the late epipaleolithic locally known as the capsian c 12 7 to 9 ka and the neolithic c 8 5 to 5 4 ka occurred predominantly during winter other evidence from these archaeological phases shows that hunting activities occurred during the warmer months therefore the timing of holocene shellfish exploitation in the gebel akhdar may have been influenced by the seasonal availability of other resources at these times and possibly shellfish were used as a dietary supplement when other foods were less abundant

evidence for a large extended paleolake in the eastern sahara as revealed by spaceborne radar lab images recently processed radar images from the two flights of the space shuttle endeavour by the spaceborne imaging radar c x band synthetic aperture radar instrument in 1994 give a clear view of widely distributed sediments of a palaeolake in today s hyperarid eastern sahara nw sudan although a few of the sites of lacustrine sediments were previously examined in the field their extent now visible on the images yields a new perspective on the early to mid holocene wet phase that affected northern africa freshwater wetlands across an area exceeding 15 000 km2 existed between 8800 and 4500 b p owing to a significant increase in rainfall the phenomenon called the west nubian lake constitutes the largest scale hydrographic evidence in the eastern sahara for a northward shift of the tropical rain belt given that the region now receives less than 15 mm of precipitation per year on average the former open water body and its vegetated catchment may have acted as a modifier of the regional climate in connection with the detection of a buried major palaeodrainage system near kufra se libya the west nubian lake confirms the new multifrequency and multipolarization radar imaging as a powerful tool for the reconstruction of arid land palaeohydrology

multiscale estimation of gps velocity fields we present a spherical wavelet based multiscale approach for estimating a spatial velocity field on the sphere from a set of irregularly spaced geodetic displacement observations because the adopted spherical wavelets are analytically differentiable spatial gradient tensor quantities such as dilatation rate strain rate and rotation rate can be directly computed using the same coefficients in a series of synthetic and real examples we illustrate the benefit of themultiscale approach in particular the inherent ability of the method to localize a given deformation field in space and scale as well as to detect outliers in the set of observations this approach has the added benefit of being able to locally match the smallest resolved process to the local spatial density of observations thereby both maximizing the amount of derived information while also allowing the comparison of derived quantities at the same scale but in different regions we also consider the vertical component of the velocity field in our synthetic and real examples showing that in some cases the spatial gradients of the vertical velocity field may constitute a significant part of the deformation this formulation may be easily applied either regionally or globally and is ideally suited as the spatial parametrization used in any automatic time dependent geodetic transient detector

a late pleistocene refugium in mediterranean north africa palaeoenvironmental reconstruction from stable isotope analyses of land snail shells haua fteah libya abstract the late pleistocene to holocene archaeological record of north africa is key to understanding the emergence of anatomically modern humans into west asia and europe and the broadening of subsistence strategies in the shift from hunter gatherer to pastoral agricultural lifeways some contend that these developments were modulated by major shifts in climate and environment evaluation of this hypothesis requires the pairing of local and regional climate records with well dated archaeological sequences the haua fteah archaeological site in the gebel akhdar region of libya provides a key site to test this hypothesis as the cave contains one of the longest and most complete sequences of human occupation in north africa as well as abundant material for palaeoenvironmental reconstruction this study uses stable isotope analyses 18o and 13c of the terrestrial mollusc helix melanostoma to construct a palaeoenvironmental framework for interpreting north african human environment interactions from the upper palaeolithic to the neolithic 30 000 to 5000 years ago the land snail stable isotope records from haua fteah suggests that cool arid conditions in the cave peaked during marine isotope stage mis 2 this stage was however only marginally drier than previous and subsequent stages and coincided with an increase in occupation density in the cave this suggests that the gebel akhdar may have served as an environmental refugium from the more extreme aridity in the surrounding sahara and arid coastal plains for late stone age lsa populations in north africa conditions became progressively wetter towards the holocene however generally wetter conditions were interrupted by two arid episodes at c 8 0 ka and 7 3 ka that appear to coincide with regional changes reflected elsewhere in the mediterranean basin

pleistocene and holocene herbivore diets and palaeoenvironments in the gebel akhdar libya implications for past human populations the gebel akhdar massif in cyrenaica northeast libya has yielded a long record of human occupation going back at least 100 000 years to date there is only a limited understanding of how the landscape of the region varied in response to the climatic fluctuations of the last glacial interglacial cycle and the implications of these changes for local human populations remain largely unexplored this study provides an isotope based interpretation of past environments directly linked to the archaeological record tooth enamel stable carbon isotope ratios 13c from herbivore species hunted by past human populations are used to infer the isotopic characteristics of past diet and vegetation and in turn the likely environmental conditions that prevailed during periods when humans were active within the landscape to provide a baseline from which to interpret the archaeological 13c data modern samples are considered in relation to their diet and environmental origin archaeological samples come from 2 cave sites haua fteah and hagfet ed dabba and span a period from oxygen isotope stage 4 to the mid holocene whilst results indicate a more arid environment in the pleistocene and an increase in humidity at the onset of the holocene the overall picture is one of relative environmental stability the biggest landscape change observed in the data occurs during the mid holocene neolithic when c4 plant species become evident in the herbivore diet for the first time there is little evidence to suggest that this occurred at a time of any large scale climate variation and thus the contribution of anthropogenic influences to vegetation change is considered likely

the effective elastic thickness of the india plate from receiver function imaging gravity anomalies and thermomechanical modelling summary the range and the meaning of the effective elastic thickness eet in continental areas have been subject to controversy over the last two decades here we take advantage of the new data set from the hi climb seismological experiment to re estimate the eet of the india plate along a south north profile extending from the ganges basin to central tibet receiver functions give a high resolution image of the base of the foreland basin at 5 km depth and constrain the crustal thickness which increases northwards from 35 km beneath the indo gangetic plain to 70 km in southern tibet together with available data sets including seismic profiles seismological images from both indepth and himnt experiments deep well measurements and bouguer anomaly profiles we interpret this new image with 2 d thermomechanical modelling solutions using different type of crustal and mantle rheologies we find that 1 the eet of the india plate decreases northwards from 60 80 to 20 30 km as it is flexed down beneath himalaya and tibet due to thermal and flexural weakening 2 the only resistant layer of the india plate beneath southern tibet is the upper mantle which serves as a support for the topographic load and 3 the most abrupt drop in the eet located around 200 km south of the mft is associated with a gradual decoupling between the crust and the mantle we show that our geometrical constraints do not allow to determine if the upper and lower crust are coupled or not our results clearly reveal that a rheology with a weak mantle is unable to explain the geometry of the lithosphere in this region and they are in favour of a rheology in which the mantle is strong

the last 140 ka in the afro asian arid semi arid transitional zone abstract during the last ten years a great number of geological or other proxy records provided radiocarbon u th or tl dated information on the past climatic oscillations in the arid semi arid zones extending between the atlantic and the pacific comparisons and a synthetic view of these results can now be attempted for the last 140 ka and compared with global changes as registered in oceanic or ice cores and with palaeomonsson models for this purpose wide spatial and time scales have to be used on the whole arid humid alternations roughly fit global changes cold phases corresponding to an extension of the arid areas to the south warm phases corresponding to the shrinking of the same to the north the last interglacial is associated with an increase of precipitation throughout the area considered isotopic stage 4 brings no evidence whatsoever of humid conditions two wetter episodes are registrated during stage 3 a major rainfall decrease is everywhere associated with the last glacial maximum 21 15 ka in most regions the arid or semi arid zones extending several hundred kilometers southwards relative to the present day pattern the two abrupt deglaciation steps and the younger dryas are recorded in all of the most sensitive regions at the margins of the present day monsoonal range during the holocene the precipitation increases everywhere by 100 400 mn relative to the present day values the optimum being at 8 5 6 5 ka a climatic deterioration follows with an irregular pattern of dry wet episodes according to the different geographic conditions the humid phase terminates at 3 5 3 ka in the whole transitional zone the major southward shift of the monsoonal precipitation range since its optimum some 8000 years ago fits the astronomical neoglacial trend and may possibly be correlated with past stage 5d although its rapidity and spatial importance may just reflect one of the sharp successive cold warm variations registered by grip during the whole stage 5

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

site formation processes in caves the holocene sediments of the haua fteah cyrenaica libya caves have yielded some of the most globally important archaeological sequences but often their interpretation has suffered from assumptions about cave sedimentary processes caves contain distinctive sedimentary environments this has major implications for the understanding of contained archaeological materials this paper describes and analyses the holocene sediments in the haua fteah a sequence regarded as essentially continuous by the original excavator 50 years after it was first excavated the haua s epipalaeolithic to post classical chronological range and rich finds make it still the key holocene archaeological site in north africa the reassessment shows however that the sequence is strongly discontinuous and this has major implications for the reinterpretation of the site as the highly resolved archaeological record is thus likely to reflect a series of brief occupations rather than continuous human activity as with many caves the sedimentary record in the haua fteah is an extremely sensitive indicator of environments and processes in the wider landscape secure understanding of sedimentary process from analysis of the highly individual records found in caves is essential for full understanding of their contained archaeology

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

slicing up the san francisco bay area block kinematics and fault slip rates from gps derived surface velocities received 26 october 2004 revised 11 february 2005 accepted 10 march 2005 published 16 june 2005 i observations of surface deformation allow us to determine the kinematics of faults in the san francisco bay area we present the bay area velocity unification bavu bay view a compilation of over 200 horizontal surface velocities computed from campaign style and continuous global positioning system gps observations from 1993 to 2003 we interpret this interseismic velocity field using a three dimensional block model to determine the relative contributions of block motion elastic strain accumulation and shallow aseismic creep the total relative motion between the pacific plate and the rigid sierra nevada great valley sngv microplate is 37 9 0 6 mm yr 1 directed toward n30 4 w 0 8 at san francisco 2 fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data notable right lateral slip rates in mm yr 1 san gregorio fault 2 4 1 0 west napa fault 4 0 3 0 zone of faulting along the eastern margin of the coast range 5 4 1 0 and mount diablo thrust 3 9 1 0 of reverse slip and 4 0 0 2 of right lateral strike slip slip on the northern calaveras is partitioned between both the west napa and concord green valley fault systems the total convergence across the bay area is negligible poles of rotation for bay area blocks progress systematically from the north america pacific to north america sngv poles the resulting present day relative motion cannot explain the strike of most bay area faults but fault strike does loosely correlate with inferred plate motions at the time each fault initiated