nannoplankton successions in the northern red sea during the last glaciation 60 to 14 5 ka bp reactions to climate change abstract due to its restricted connection with the indian ocean the desert enclosed red sea is extremely sensitive to global sea level changes and thus ideally suited for paleoceanographic studies of what occurred during the last glaciation the understanding of its glacial history is however still limited a serious obstacle to obtain satisfactory paleoecological information has been the rarity of microfossil proxy species caused by high salinities here we present a continuous and well dated calcareous nannoplankton record from the northern red sea covering the interval from 60 14 5 ka bp our investigation shows that the composition of the calcareous nannoplankton community varied between 32 ka bp and 14 5 ka bp in response to rapid environmental changes which are closely correlated to climatic fluctuations described from the north atlantic region heinrich events h3 h2 and h1 are dominated by emiliania huxleyi gephyrocapsa oceanica and especially gephyrocapsa ericsonii are abundant between h3 h2 and h2 h1 a less pronounced response of the calcareous nannoplankton to the high latitudinal climatic oscillations is documented prior to 32 ka bp suggesting that a strong atmospheric coupling between the northern red sea and the north atlantic realm was established in the late marine isotope stage 3 in contrast to the previously held view of a sea level related salinity increase as the major cause for changes of the plankton communities within the glacial red sea we interpret the documented variations as being caused by local hydrographic changes under the atmospheric control from the extratropics temperature changes and especially variations of the water stratification appear to be critical selective factors for the calcareous nannoplankton composition

recovery of source time function approximations by homomorphic deconvolution of broad band recorded teleseismic body waves abstract an improved method of interactive cepstral analysis and homomorphic deconvolution is employed to recover basic wavelets representing an approximation of source time functions from broad band records of teleseismic body waves radiated from nine events in the subducting lithosphere of the kurile arc the depths of the events ranged from 5 to 131 km five of them occurred above the slab of the subduction and four inside the slab the recovered wavelets of the deepest event correspond to an explosive implosive like source and those of three shallow events are similar to the theoretical shapes for simple kinematic dislocation models the recovered wavelets of two events inside the slab and some of the obtained impulse traces exhibit anomalies the explanation of which is at present beyond the abilities of the authors the direction of the continuation of the study is outlined

troposphere planetary boundary layer interactions and the evolution of ocean surface density lessons from red sea corals a time series of oxygen isotope d18o measurements of a coral from the northern red sea rs is presented and used as a direct proxy for water surface density rs with a relatively constant subsurface density the generated surface density time series closely tracks water mass formation variability two positive and two negative high amplitude rs anomalies are studied and associated atmospheric and oceanic data are analyzed to understand large scale ocean atmosphere processes the dominant process is lower tropospheric subsidence it dries the boundary layer bl increases surface evaporation and rs and ultimately drives water mass formation the main cause of the subsidence is a temperature increase along the principal axis of the rs from the eastern mediterranean to the convergence zone cz 188 228n the increase entails isentropes sloping down to the southeast crossing pressure surfaces due to their tilt with nearly adiabatic flow along the principal axis air parcels move roughly along the sloped isentropes toward ever increasing pressure that is they subside the subsidence supplies the northern rs bl with upstream air from higher altitudes where humidity is low thus drying the bl the resultant high evaporation north of 258n with low evaporation minus precipitation south of 228n depresses sea levels in the northern rs and thus drives the rs thermohaline circulation and controls water mass formation excluded from the presented picture but probably very important is mixing with the hot dry air of the surrounding deserts

range front fault scarps of the sierra el mayor baja california formed above an active low angle normal fault the canada david detachment a west dipping low angle normal fault juxtaposes pliocene and pleistocene sedimentary units over sheared bedrock in the sierra el mayor baja california along the west central range front the detachment is overlapped by quaternary alluvial fans that are in turn cut by fault scarps up to 7 m high map relationships suggest that scarp forming faults may sole into the detachment at very shallow depth 200 300 m palinspastic restoration of a topographic profile across 15 north striking scarps suggests that the ratio of net heave to net throw along scarp forming faults is 2 consistent with them soling into a low angle 30 fault these 15 scarps may have all formed in one earthquake with rupture propagation from depth to the near surface aided by clay gouge along the detachment the detachment is abandoned in the footwall east of the scarps

listric normal faulting stress refraction and the state of stress in the gulf coast basin the close association of overpressured shales and the coincident flattening of listric normal faults has been noted and is usually explained in terms of gravity sliding models however incorporation of overpressure into mohr coulomb frictional faulting theory does not predict normal faults dipping at angles less than 45 even for very low coefficients of friction we suggest that low angle normal faults may form because of a rotation of the maximum principal stress away from vertical with depth such a rotation occurs if a significant contrast in viscosity exists between two adjacent strata such as a normally pressured sandstone and an underlying overpressured shale or evaporite the stress refraction model renders the presence of a preexisting fault plane or an extremely low coefficient of friction unnecessary to explain listric fault geometry and offers a failure mechanism in agreement with frictional faulting theory based on rheological arguments

northwest basin and range tectonic deformation observed with the global positioning system 1999 2003 1 we use geodetic velocities obtained with the global positioning system gps to quantify tectonic deformation of the northwest basin and range province of the western united states the results are based on gps data collected in 1999 and 2003 across five new quasi linear networks in northern nevada northeast california and southeast oregon the velocities show 3 mm yr westward movement of northern nevada with respect to stable north america west of longitude 119 w the velocities increase and turn northwest parallel to sierra nevada great valley microplate motion and similar to velocities previously obtained to the south the observations are explained by a kinematic model with three domains that rotate around euler poles in eastern oregon and western idaho northeast california experiences internal dextral shear deformation 11 2 3 6 nstrain yr subparallel to pacific north america motion relative motions of the domains imply 2 5 mm yr approximately east west extension in northwest nevada and 1 4 mm yr approximately north south contraction near the california oregon border the northward decreasing approximately east west extension in northwest nevada is consistent with the northern termination of basin and range deformation faulting and characteristic topography no significant extension is detected in the oregon basin and range the oregon cascade arc moves north at 3 5 mm yr and is possibly influenced by the approximately eastward motion of the juan de fuca plate these results disagree with secular northwest trenchward motion of the oregon forearc inferred from paleomagnetic rotations south of latitude 43 however trenchward motion exists and is consistent with block rotations approximately east west basin and range extension and northwest sierra nevada translation

renewal of deep water in the red sea during 1982 1987 between october 1982 and may 1983 the deep water in the northern red sea was ventilated through slope convection the deep water became cooler fresher and more oxygenated dense bottom water formed in the gulf of suez during winter cooling sank down the continental slope thereby entraining near surface and intermediate depth waters from the application of a one dimensional plume model a vertical transport of 0 58 106 m3 s 1 over a period of 7 months was estimated long term time series of atmospheric heat fluxes show that such a major convection event can occur every 4 7 years the corresponding renewal time of the red sea deep water is thus of the order of 40 90 years in agreement with previous estimates

identification of blind geothermal resources in surprise valley ca using publicly available groundwater well water quality data abstract geothermal resource exploration is generally limited to areas with surface expressions of thermal activity fumaroles and hot springs or relies on expensive geophysical exploration techniques in this study the hidden subsurface distribution of geothermal fluids has been identified using a free and publicly available water quality dataset from agricultural and domestic water wells in surprise valley northeastern california thermally evolved waters in surprise valley have element ratios that vary in response to ca carbonate and mg silicate mineral precipitation and have elevated total dissolved solids tds the arid climate in surprise valley leads to surface water evaporation in a closed basin producing high tds na cl co3 so4 brines in three ephemeral alkali lakes and in shallow groundwater under elevated soil co2 conditions evaporated fluids in surprise valley follow a chemical divide that leads to ca carbonate and mg silicate mineral precipitation plots of dissolved element ratios can be used to distinguish groundwater affected by evaporation from water affected by thermal water rock interaction however it is challenging to select components for plotting that best illustrate different fluid evolution mechanisms here we use a principal component analysis of centered log ratio transformed data coupled with geochemical models of fluid evaporation and thermal mixing pathways to identify components to plot that distinguish between groundwater samples influenced by evaporation from those influenced by thermal processes we find that groundwater samples with a thermal signature come from wells that define a coherent linear geographical distribution that closely matches the location of known and inferred faults modification of the general approach employed here provides promise for identifying blind geothermal resources in other locations by applying low cost geochemical modeling and statistical techniques to areas where large groundwater quality geochemical datasets are available

multidecadal variations in the early holocene outflow of red sea water into the arabian sea we present holocene stable oxygen isotope data from the deep arabian sea off somalia at a decadal time resolution as a proxy for the history of intermediate upper deep water these data show an overall 18o reduction by 0 5 between 10 and 6 5 kyr b p superimposed upon short term 18o variations at a decadal centennial timescale the amplitude of the decadal variations is 0 3 prior and up to 0 6 subsequent to 8 1 kyr b p we conclude from modeling experiments that the short term 18o variations between 10 and 6 5 kyr b p most likely document changes in the evaporation precipitation balance in the central red sea changes in water temperature and salinity cause the outflowing red sea water to settle roughly 800 m deeper than today

benthic foraminiferal faunal and isotopic changes as recorded in holocene sediments of the northwest indian ocean 1 historically the holocene has been considered an interval of relatively stable climate however recent studies from the northern arabian sea netherlands indian ocean program 905 suggested high amplitude climate shifts in the early and middle holocene based on faunal and benthic isotopic proxy records we examined benthic foraminiferal faunal and stable isotopic data from ocean drilling program odp site 723 and total organic carbon data from odp site 724 oman margin 808 and 593 m water depths respectively at site 723 the mid holocene shift in 18o values of infaunal benthic species uvigerina peregrina 1 4 is 3 times larger than that of epifaunal benthic species cibicides kullenbergi recorded at site niop 905 off somalia however none of the five other benthic species we measured at hole 723a exhibits such a shift in 18o we speculate that the late holocene 18o decrease in u peregrina represents species specific changes in ecological habitat or food preference in response to changes in surface and deep ocean circulation while the stable isotopic data do not appear to indicate a middle holocene climatic shift our total organic carbon and benthic faunal assemblage data do indicate that the early holocene deep arabian sea was influenced by increased ventilation perhaps by north atlantic deep water and or circumpolar deep water incursions into the indian ocean leading to remineralization of organic matter and a relatively weak early holocene oxygen minimum zone in the northwest arabian sea in spite of strong summer monsoon circulation

geometry of cenozoic extensional faulting dixie valley nevada precise definition of geometric relationships between individual basins and ranges may help to reveal the mechanical processes of basin and range cenozoic extensional faulting at depth previous studies have attempted to identify simple horsts and grabens tilted crustal blocks with planar faulting or tilted crustal blocks with listric faulting in the shallow crust normal faults defining these crustal blocks may root 1 individually in the ductile lower crust 2 in regional or local low angle detachment faults or 3 in igneous intrusions or decoupling surfaces produced by the intrusions the present study in dixie valley west central nevada makes use of a seismic reflection survey gravity models seismograms from earthquakes occurring on december 16 1954 and geometrical block models these data show a structurally asymmetric basin bounded by a single zone of faulting on the northwest and by a downbowed and step faulted floor to the southeast the northwest bounding fault is moderately dipping 50 and planar to a depth of 3 km the southeast boundary is step faulted and altogether the faults indicate an extension of 20 across the valley at the rate of 0 38 mm y for the last 8 my synthetic earthquake seismograms confirm a focal depth of 15 km and fault dip of 62 for the fairview peak earthquake and suggest that the focal depth of the dixie valley earthquake was also 15 km instead of the previously reported 40 km local microearthquakes cluster around 10 15 km the geometrical block models indicate that crustal horst graben faulting and planar high angle normal faults rooted in a low angle detachment surface do not readily account for development of the subsidiary step faults found in dixie valley extension of the crust by intrusion may develop high angle faults and with further intrusion may develop the subsidiary faults and produce a complex sagged asymmetric graben like dixie valley

modes of subsurface intermediate and deep water renewal in the red sea a linear box model of the red sea is presented the model which inverts hydrographic and 3he data for the main features of the width integrated circulation is able to describe a large part of the seasonal and annual mean circulation by combining and reconciling major elements of current theories of the red sea circulation available flow measurements and tracer data the model provides a unified conceptual framework for the understanding of the circulation of the red sea the model forms deep water in the extreme north in two modes as first suggested by cember 1988 the convective mode renews the bottom water at an annual mean rate of 0 04 sv in the winter the isopycnal mode water renews the uppermost part of the deep water mass it flows to the south along the bottom of the pycnocline at an annual mean rate of 0 02 0 04 sv a new feature in the model s near surface circulation scheme is the ventilation of the thermocline in the winter at a mean rate of 0 04 sv also from the extreme north there is also a middepth return flow to the north at an annual mean rate of 0 07 sv this flow has been suggested but never rigorously quantified before

a coral oxygen isotope record from the northern red sea documenting nao enso and north pacific teleconnections on middle east climate variability since the year 1750 a 245 year coral oxygen isotope record from the northern red sea ras umm sidd egypt 28 n in bimonthly resolution is presented the mean annual coral 18o signal apparently reflects varying proportions of both sea surface temperature and 18oseawater variability in conjunction with instrumental observations of climate the coral record suggests for interannual and longer timescales that colder periods are accompanied by more arid conditions in the northern red sea but increased rainfall in the southeastern mediterranean whereas warmer periods are accompanied by decreased rainfall in the latter and less arid conditions in the northern red sea a 70 year oscillation of probably north atlantic origin dominates the coral time series interannual to interdecadal variability is correlated with instrumental indices of the north atlantic oscillation nao the el nino southern oscillation enso and north pacific climate variability the results suggest that these modes contributed consistently to middle east climate variability since at least 1750 preferentially at a period of 5 7 years

cenozoic tectonic evolution of the south ningxia region northeastern tibetan plateau inferred from new structural investigations and fault kinematic analyses abstract the northeastward growth process of the tibetan plateau has been a key issue to be long termly debated which is well documented by the south ningxia region at the northeasternmost periphery of the tibetan plateau due to its cenozoic convex to the northeast arcuate range and basin structures here new structural measurements and fault kinematic analysis together with new geochronological results delineate a two stage cenozoic tectonic evolution in the region providing the new structural evidences to decipher the northeastward growth process of the tibetan plateau the first stage is marked by widespread sedimentary basin formation during the oligocene to late miocene ca 30 10 5 ma under nw se extensional regime and subsequent basin inversion triggered by nw se compression in the late miocene ca 10 5 9 5 ma these events were probably associated mainly with the far field effect of the northwestward subduction of the pacific plate a little related to the plateau growth the second stage largely presents an intensive mountain building process and following re deformation since the late miocene ca 9 5 ma which was predominantly a result of the far field responses to the northeastward growth of the tibetan plateau and partially to the pacific subduction the second stage further comprises three alternating episodes of shortening and extension events the earliest episode of ne sw compression caused intensive crustal shortening in a long period from the late miocene to early pleistocene ca 9 5 1 8 ma leading to a significant mountain building process in this region a gentle ne sw extension subsequently dominated here in the late pleistocene ca 18 ka as manifested by the widespread appearance of paleo lakes along the nw striking boundary faults since the end of the late pleistocene ca 18 ka a youngest tectonic regime affected this region characteristic of a tectonic transpression causing evidently strike slip activities on the primary faults and the development of small scale pull apart basins along the haiyuan fault

on the sources formation and circulation of red sea deep water red sea deep water is renewed from sources in the far north of the red sea upwelling of deep water throughout the basin maintains the sharp pycnocline with its base near the depth of the sill at bab el mandeb before now deep water renewal was thought to occur mainly by means of convective deep water formation in the north which renews the bottom water and gives rise to a southward flowing bottom current carbon 14 and 3he data from the geosecs indian ocean expedition lead to the identification of an additional volumetrically larger mode of northern deep water formation in which new deep water is injected immediately beneath the pycnocline this mode of deep water formation to be called the isopycnal mode also gives rise to a southward flowing current in this case at the top of the deep water mass geosecs data also demonstrate the existence at intermediate depths in the deep water of a return flow to the north the surface history in the nuclear era of the 14c in the deep water source region was reconstructed by direct radiocarbon measurements on annual growth bands of corals calculation then shows that new deep water forms in the convective mode at a rate of 0 05 0 01 sverdrup sv expressed as if the flow were continuous and is due principally to processes occurring in the mouth of the gulf of suez the injection beneath the pycnocline of new deep water formed in the isopycnal mode is 0 11 0 02 sv this new deep water appears to originate mainly in the extreme open northern red sea the gulf of aqaba makes a modest but significant contribution to both modes the total deep water renewal rate is about 0 16 sv yielding a bulk deep water residence time of about 36 years oxygen consumption in the deep water shows approximately exponential decrease of consumption rate with depth as expected on geological and geophysical grounds hydrographically significant fluxes of heat and salt from the sea floor into the red sea deep water are discernible in the hydrography helium 3 flux from the sea floor into the deep water is about 69 1 stp year

migration of activity within normal fault systems examples from the quaternary of mainland greece abstract we examine five areas of mainland greece where active extension occurs on sub parallel systems of normal faults and where geomorphological and stratigraphic evidence indicates that the faulting has migrated basinwards into the original hanging walls in several cases within the late quaternary by comparing fault slip rates estimated from geomorphological data with current extension rates known from geodetic measurements it appears that the newest faults can account for effectively all the present day motions fault migration of this sort is easy to recognize in young systems close to sea level because vertical movements of footwalls and hanging walls are obvious and reveal which faults are currently most active but is less easy to confirm away from reliable reference levels or in older terrains with poorer time resolution it is probably more common than is appreciated and has a profound effect on syn rift sedimentation and erosion patterns fault migration is probably an inevitable consequence of the interplay between stresses generated by the fault related topography and the ultimate strength of major faults it is likely to be further encouraged in places where lower crustal flow or rotations about a vertical axis are important however it is not clear why migration should preferentially occur into the hanging walls as observed in central greece

impact of late quaternary environmental changes on deep sea benthic foraminiferal faunas of the red sea abstract fluctuations in abundance diversity and species composition of benthic foraminifera from two sites of the northern and southern red sea indicate strong variability of deep sea ecosystems during the last four glacial to interglacial cycles in total five and four different benthic foraminiferal assemblages have been identified in the northern core and southern core respectively comparison with recent faunas from the red sea and adjacent oceans allowed the reconstruction of temporal changes in deep water ventilation salinity and food availability at the seafloor generally the abundance of infaunal and miliolid taxa increase during glacial intervals indicating increased organic matter fluxes oxygen decrease and salinity increase in deep waters during these times these fluctuations are attributed to enhanced oxygen consumption rates and temporarily reduced deep water formation in the northern red sea during glacial intervals the recorded environmental changes are a reflection of both high and low latitude climate changes the northern red sea is mainly influenced by glacio eustatic sea level fluctuations that control deep water formation rates and by mid latitude climate changes of the mediterranean region that control surface productivity in contrast deep sea ecosystem variability of the southern red sea is additionally influenced by low latitude climate changes attributed to the ne monsoon intensity that drives the inflow of nutrient rich surface waters from the gulf of aden these results demonstrate the high sensitivity of deep sea ecosystems of the red sea to both global and regional climate changes

volcanic forcing of climate over the past 1500 years an improved ice core based index for climate models 1 understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate we have investigated one of the most important natural causes of climate change volcanic eruptions by using 54 ice core records from both the arctic and antarctica our recently collected suite of ice core data more than double the number of cores ever used before reduces errors inherent in reconstructions based on a single or small number of cores which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects we extracted volcanic deposition signals from each ice core record by applying a high pass loess filter to the time series and examining peaks that exceed twice the 31 year running median absolute deviation we then studied the spatial pattern of volcanic sulfate deposition on greenland and antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month latitude and altitude for the past 1500 years we estimated the uncertainties associated with the choice of volcanic signal extraction criteria ice core sulfate deposition to stratospheric loading calibration factor and the season for the eruptions without a recorded month we forced an energy balance climate model with this new volcanic forcing data set together with solar and anthropogenic forcing to simulate the large scale temperature response the results agree well with instrumental observations for the past 150 years and with proxy records for the entire period through better characterization of the natural causes of climate change this new data set will lead to improved prediction of anthropogenic impacts on climate the new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years as a function of latitude altitude and month is available for download in a format suitable for forcing general circulation models of the climate system

late quaternary paleoseismology of the southern steens fault zone northern nevada the 192 km long steens fault zone is the most prominent normal fault system in the northern basin and range province of western north america we use trench mapping and radiometric dating to estimate displacements and timing of the last three surface rupturing earthquakes e1 e3 on the southern part of the fault south of denio nevada coseismic displacements range from 1 1 to 2 2 0 5 m and radiometric ages indicate earthquake times of 11 5 2 0 ka e3 6 1 0 5 ka e2 and 4 6 1 0 ka e1 these data yield recurrence intervals of 5 4 2 1 k y between e3 and e2 1 5 1 1 k y between e2 and e1 and an elapsed time of 4 6 1 0 k y since e1 the recurrence data yield variable interval slip rates between 0 2 0 22 and 1 5 2 3 mm yr but slip rates averaged over the past 18 k y 0 24 0 06 mm year are similar to long term 8 5 12 5 ma slip rates 0 2 0 1 mm yr measured a few kilometers to the north we infer from the lack of significant topographic relief across the fault in bog hot valley that the fault zone is propagating southward and may now be connected with a fault at the northwestern end of the pine forest range displacements documented in the trench and a rupture length of 37 km indicate a history of three latest quaternary earthquakes with magnitudes of m 6 6 7 1 on the southern part of the steens fault zone

surface faulting of the 1954 fairview peak ms 7 2 and dixie valley ms 6 8 earthquakes central nevada abstract the 1954 fairview peak earthquake was followed 4 min and 20 sec later by the dixie valley earthquake surface ruptures were distributed among six different faults that define a complex north trending zone 100 km long and over 15 km wide the rupture sequence progressed from south to north the initial event produced a 32 km rupture of right oblique slip along the east dipping fairview fault where the components of right lateral offset and vertical separation reached 2 9 and 3 8 m respectively the northernmost ruptures occurred during the subsequent event along a 46 km portion of the east dipping dixie valley fault where the sense of slip was normal and reached a maximum vertical separation of 2 8 m average surface offset for both events is about 1 2 m the west dipping west gate louderback mountains and gold king faults also ruptured during the earthquake sequence these faults form a complex structural linkage within a 15 km left step that separates the surface traces of the fairview and dixie valley faults the west dipping faults likely played an important role in the redistribution of static stress from the fairview peak earthquake and subsequent triggering of the dixie valley earthquake right lateral offsets of more than a meter occurred along both the west gate and louder back mountains faults slip was limited to normal motion of 1 m or less along the gold king fault the change from right oblique motion along the fairview fault to pure normal motion on the dixie valley fault may reflect the transition from principally northwest extension in the south to more westerly extension in the north alternatively slip at the latitude of the dixie valley fault may be partitioned between pure normal slip along the dixie valley fault and strike slip motion on faults immediately to the west observations of fault dip provide insight to the complex three dimensional geometry of the rupture sequence of particular note a significant section of the dixie valley fault appears to be characterized by dip angles as low as 25 at the surface slip variation or earthquake endpoints do not generally appear to have been influenced by changes in bedrock type we do not observe systematic relations between slip variation and aspects of fault trace geometry such as salients and reentrants yet the relative competence of footwall bedrock appears to have influenced the long term development of large salients and reentrants along both the dixie valley and the fairview faults as well as the style of rupture along the southern portion of the dixie valley fault

structural controls on geothermal circulation in surprise valley california a re evaluation of the lake city fault zone faults and fractures play an important role in the circulation of geothermal fluids in the crust and the nature of that role varies according to structural setting and state of stress as a result detailed geologic and geophysical mapping that relates thermal springs to known structural features is essential to modeling geothermal systems published maps of surprise valley in northeastern california suggest that the lake city fault or lake city fault zone is a significant structural feature cutting obliquely across the basin and connecting thermal springs across the valley newly acquired geophysical data audio magnetotelluric gravity and magnetic combined with existing geochemical and geological data suggest otherwise we examine potential field profiles and resistivity models that cross the mapped lake city fault zone while there are numerous geophysical anomalies that suggest subsurface structures they mostly do not coincide with the mapped traces of the lake city fault zone nor do they show a consistent signature in gravity magnetics or resistivities that would suggest a through going fault that would promote connectivity through lateral fluid flow instead of a single continuous fault we propose the presence of a deformation zone associated with the growth of the range front surprise valley fault the implication for geothermal circulation is that this is a zone of enhanced porosity but lacks length wise connectivity that could conduct fluids across the valley thermal fluid circulation is most likely controlled primarily by interactions between n s trending normal faults

the northwestern margin of the basin and range province part 1 reflection profiling of the moderate angle 30 surprise valley fault abstract seismic reflection profiling demonstrates that the active significant offset surprise valley fault that marks the western boundary of the basin and range province in northernmost california dips at a moderate angle only 30 to 2 km depth a nearby seismic refraction wide angle reflection profile albeit of lower resolution shows the fault plane remains approximately planar to at least 7 km depth variably tilted volcanic strata of known ages within the surprise valley basin demonstrate that 7 km of normal slip occurred along the surprise valley fault within the past 8 4 myr at a time averaged slip rate of 1 2 mm yr and that the fault rotated from an initial dip of as much as 60 to its present dip of 30 the rotation of this isolated fault was not accomplished by domino style rotation as seen elsewhere in the basin and range province but rather by flexural rift shoulder uplift aided by mid crustal flow

implications of seismic reflection and potential field geophysical data on the structural framework of the yucca mountain crater flat region nevada seismic reflection and gravity profiles collected across yucca mountain nevada together with geologic data provide evidence against proposed active detachment faults at shallow depth along the pre tertiary tertiary contact beneath this potential repository for high level nuclear waste the new geophysical data show that the inferred pre tertiary tertiary contact is offset by moderate to high angle faults beneath crater flat and yucca mountain and thus this shallow surface cannot represent an active detachment surface the reflection lines reveal that the amargosa desert rift zone is an asymmetric half graben having a maximum depth of about 4 km and a width of about 25 km the east dipping bare mountain fault that bounds this graben to the west can be traced by seismic reflection data to a depth of at least 3 5 km and possibly as deep as 6 km with a constant dip of 64 degree 5 degree along the profile the transition from east to west dipping faults occurs at or just west of the solitario canyon fault which bounds the western side of yucca mountain the interaction at depth of these east and west dipping faults having up to hundreds of meters offset is not imaged by the seismic reflection profile understanding potential seismic hazards at yucca mountain requiresmore knowledge of the subsurface geometry of the faults near yucca mountain since earthquakes generally nucleate and release the greatest amount of their seismic energy at depth the geophysical data indicate that many fault planes near the potential nuclear waste facility dip toward yucca mountain including the bare mountain range front fault and several west dipping faults east of yucca mountain thus earthquake ruptures along these faults would lie closer to yucca mountain than is often estimated from their surface locations and could therefore be more damaging less

vertical water mass mixing and plankton blooms recorded in skeletal stable carbon isotopes of a red sea coral the environmental interpretation of the 13c 12c variations in the skeletons of massive corals is still a matter of debate a 19 year seasonal skeletal 13c 12c record of a shallow water porites coral from the northern red sea gulf of aqaba documents interannual events of extraordinarily large plankton blooms indicated by anomalous 3c depletions in the coral skeleton these blooms are caused by deep vertical water mass mixing convectively driven in colder winters which results in increased supplies of nutrients to the surface waters the deep vertical mixings can sometimes be driven by the cooling occurring throughout the middle east after large tropical volcanic eruptions we therefore have evidence in our coral skeletal 13c 12c record for an indirect volcanic signal of the eruptions of e1 chich6n 1982 and mount pinatubo 1991 deep mixing induced 13c 12c variations of the dissolved inorganic carbon in the surface waters can be neglected at this location we therefore suggest that the 3c skeletal depletions can be best explained by changes in the coral s autotrophy heterotrophy diet through increased heterotrophic feeding on zooplankton during the blooms increased feeding on 3c depleted zooplankton or increased heterotrophy at the expense of autotrophy can both 3 result in a c depleted coral skeleton however this suggestion requires more testing if our conclusions are substantiated seasonal skeletal 3c r2c records of corals which change from autotrophy under normal conditions to increased heterotrophy during bloom events may be used as indicators of ocean paleoproductivity at interannual resolution available from no other source

two phase neogene extension in the northwestern basin and range recorded in a single thermochronology sample we use a combination of apatite 4 he 3 he u th he and fission track thermochronology to date slip on the surprise valley fault in northeastern california by analyzing a single sample from the warner range in the footwall of the fault this sample a granitic clast from a conglomerate yielded a fission track age of 11 6 2 8 ma and a u th he age of 3 02 0 52 ma geologic relationships indicate that this sample was buried to a depth of 3 3 km prior to exhumation during slip on the surprise valley fault fission track age and length data indicate that the sample was fully reset 120 c prior to exhumation which began sometime after 14 ma a single aliquot of nine apatite grains was step heated for 4 he 3 he analysis modeling of the resulting 4 he distribution indicates that cooling from 80 c to 20 c occurred between 3 and 1 ma interconsistent time temperature t t solutions to the combined 4 he 3 he u th he and fission track data require two distinct periods of cooling consistent with non continuous slip on the surprise valley fault early cooling and fault slip took place between 14 and 8 ma followed by more recent fault slip ca 3 ma this timing is consistent with both local geologic relationships and with the regional timing of faulting along the western margin of the basin and range province these data demonstrate the resolving power of combined fission track u th he and 4 he 3 he thermochronometric data to extract low temperature t t information from a single sample close to earth9s surface

oblique slip slip partitioning spatial and temporal changes in the regional stress field and the relative strength of active faults in the basin and range western united states when viewed with stress transformation laws and an idealized physical model observations of oblique slip and slip partitioning in the basin and range western united states are interpreted to show that 1 separate regions with the same net extension direction are not necessarily characterized by the same regional stress field 2 fault systems exhibiting partitioning where one of the faults is near vertical generally do not require temporal changes in the stress field to explain the disparate slip vectors on the adjacent faults and 3 the relative strengths of active fault zones may vary by more than an order of magnitude

the northwestern margin of the basin and range province part 2 structural setting of a developing basin from seismic and potential field data abstract surprise valley in northeastern california offers an ideal opportunity to examine the structural setting of a developing extensional basin due to its late miocene to recent activity in isolation from other major normal fault bound basins seismic velocity and potential field modeling help determine the nature of basin fill and identify intra basin faults based on a detailed gravity and magnetic profile we identify shallow subsurface basalt flows and several faults within the valley that may accommodate hundreds of meters of vertical offset possibly cutting and offsetting the 30 east dipping surprise valley fault that rotated during footwall tilting of the adjacent warner mountains some of these intra basin faults correspond with mapped quaternary fault scarps but others have no surface expression these faults may represent the currently active fault system within the basin if so they would indicate that basin development is transitioning away from the main range front normal fault to a new set of steep intra basin faults that are more favorable for accommodating regional transtensional strain

unusually low rates of slip on the santa rosa range fault zone northern nevada the santa rosa range fault zone srrfz is one of the most topographically prominent normal fault systems in the northern basin and range province of the western united states it has been assigned high rates of vertical slip by others and has been identified as a possible site of the future extension of the central nevada seismic belt cnsb we use detailed trench mapping and luminescence dating to estimate displacements and timing of the last several large magnitude paleoearthquakes on the southern part of the srrfz at a trench site near orovada nevada coseismic vertical displacements ranged from 1 to 2 8 m for each of the last four events luminescence ages provide time limits for the last three events of 125 155 ka 90 108 ka and 11 16 ka these data yield recurrence intervals of 17 65 k y and 74 97 k y and an elapsed time of 11 16 k y since the youngest event slip rate determinations at the orovada site are complicated by multiple fault strands but rates calculated from a variety of data are surprisingly low 0 01 0 16 mm yr given the topographic prominence of the santa rosa range a lack of compelling patterns in a comparison of paleoseismic parameters indicate that the srrfz is no more likely a location for a large magnitude earthquake than previously identified seismic gaps or along faults that lie directly north of the cnsb

crustal scale recycling in caldera complexes and rift zones along the yellowstone hotspot track o and hf isotopic evidence in diverse zircons from voluminous rhyolites of the picabo volcanic field idaho abstract rhyolites of the picabo volcanic field 10 4 6 6 ma in eastern idaho are preserved as thick ignimbrites and lavas along the margins of the snake river plain srp and within a deep 3 km borehole near the central axis of the yellowstone hotspot track in this study we present new o and hf isotope data and u pb geochronology for individual zircons o isotope data for major phenocrysts quartz plagioclase and pyroxene whole rock sr and nd isotope ratios and whole rock geochemistry for a suite of picabo rhyolites we synthesize our new datasets with published ar ar geochronology to establish the eruptive framework of the picabo volcanic field and interpret its petrogenetic history in the context of other well studied caldera complexes in the srp caldera complex evolution at picabo began with eruption of the 10 44 0 27 ma u pb tuff of arbon valley tav a chemically zoned and normal 18o 18o magma 7 9 unit with high zoned 87sr 86sri 0 71488 0 72520 and low e nd 0 18 and e hf 0 28 the tav and an associated post caldera lava flow possess the lowest end 0 23 indicating 40 60 derivation from the archean upper crust normal 18o rhyolites were followed by a series of lower 18o eruptions with more typical lower crustal sr nd hf isotope ratios and whole rock chemistry the voluminous 8 25 0 26 ma west pocatello rhyolite has the lowest 18o value 18omelt 3 3 and we correlate it to a 1 000 m thick intracaldera tuff present in the inel 1 borehole with published zircon ages 8 04 8 35 ma and similarly low 18o zircon values the significant 4 5 decrease in magmatic 18o values in picabo rhyolites is accompanied by an increase in zircon 18o heterogeneity from 1 variation in the tav to 5 variation in the late stage low 18o rhyolites a trend similar to what is characteristic of heise and yellowstone and which indicates remelting of variably hydrothermally altered tuffs followed by rapid batch assembly prior to eruption however due to the greater abundance of low 18o rhyolites at picabo the eruptive framework may reflect an intertwined history of caldera collapse and coeval basin and range rifting and hydrothermal alteration we speculate that the source rocks with pre existing low 18o alteration may be related to 1 deeply buried and unexposed older deposits of picabo age or twin falls age low 18o volcanics and or 2 regionally abundant late eocene challis volcanics which were hydrothermally altered near the surface prior to or during peak picabo magmatism basin and range extension specifically the formation of metamorphic core complexes exposed in the region could have facilitated the generation of low 18o magmas by exhuming heated rocks and creating the large water rock ratios necessary for shallow hydrothermal alteration of tectonically rift zones and volcanically calderas buried volcanic rocks these interpretations highlight the major processes by which supereruptive volumes of magma are generated in the srp mechanisms applicable to producing rhyolites worldwide that are facilitated by plume driven volcanism and extensional tectonics

crustal deformation across the sierra nevada northern walker lane basin and range transition western united states measured with gps 2000 2004 1 global positioning system gps data collected in campaigns in 2000 and 2004 were processed and interpreted with other gps data in the western basin and range province to provide new constraints on the rate style and pattern of deformation of the central and northern walker lane wl which lies near the western boundary of the basin and range across the central wl near 38n latitude the velocities with respect to north america increase westward by 10 mm yr inducing dextral shear farther north between 40 and 41n latitude a western zone of 7 mm yr relative motion undergoes dextral shear and an eastern zone of 3 mm yr relative motion undergoes extension and shear these data show that the northern wl is essentially a dextral shear zone experiencing minor net dilatation ed 2 6 0 8 nstrain yr near most holocene normal faults dilatation inferred from the velocity field is not greater than the uncertainties however near the central nevada seismic belt we detect significant dilatation expressed as extension in a direction approximately normal to the range fronts ed 23 0 3 9 nstrain yr some of which is attributable to transient postseismic deformation following large historic earthquakes a block model constrained by velocities corrected for transient effects shows that the sum of dextral slip rates across the honey lake warm springs east pyramid fault system and mohawk valley faults is 7 mm yr the wl is a zone whose width and dilatation rate increase northwestward consistent with counterclockwise rotation of the sierra nevada microplate and transfer of deformation into the pacific northwest

climatological coastal jet collision intermediate water formation and the general circulation of the red sea the authors present climatologies of a numerical model of the red sea focusing on the dynamics of winter intermediate water formation northward flowing boundary currents are identified as the major dynamical elements at the northern boundary the eastern current follows the geometry eventually turning back to the south at 268n and the western wall the two boundary currents collide at the collision site the denser eastern current subducts under the western boundary current the subduction forces the western boundary current eastward into the interior convection communicates the surface fluxes to the downwelled plume and intermediate water forms the estimated rate 0 11 sv sv 106 m3 s21 agrees with previous estimates the authors identify basin scale sea surface tilt to the north due to variable thermohaline forcings as the key dynamical variable the resultant geostrophic eastward cross channel flow interacts with the boundaries and creates upwelling and surface topography spatial patterns that drive the coastal jets upwelling induced vortex stretching dominates the vorticity balance and governs the separation of the western boundary current from the western wall the process ceases in the summer

a conceptual geochemical model of the geothermal system at surprise valley ca abstract characterizing the geothermal system at surprise valley sv northeastern california is important for determining the sustainability of the energy resource and mitigating hazards associated with hydrothermal eruptions that last occurred in 1951 previous geochemical studies of the area attempted to reconcile different hot spring compositions on the western and eastern sides of the valley using scenarios of dilution equilibration at low temperatures surface evaporation and differences in rock type along flow paths these models were primarily supported using classical geothermometry methods and generally assumed that fluids in the lake city mud volcano area on the western side of the valley best reflect the composition of a deep geothermal fluid in this contribution we address controls on hot spring compositions using a different suite of geochemical tools including optimized multicomponent geochemistry geot models hot spring fluid major and trace element measurements mineralogical observations and stable isotope measurements of hot spring fluids and precipitated carbonates we synthesize the results into a conceptual geochemical model of the surprise valley geothermal system and show that high temperature quartz na k na k ca classical geothermometers fail to predict maximum subsurface temperatures because fluids re equilibrated at progressively lower temperatures during outflow including in the lake city area we propose a model where hot spring fluids originate as a mixture between a deep thermal brine and modern meteoric fluids with a seasonally variable mixing ratio the deep brine has deuterium values at least 3 to 4 lighter than any known groundwater or high elevation snow previously measured in and adjacent to sv suggesting it was recharged during the pleistocene when meteoric fluids had lower deuterium values the deuterium values and compositional characteristics of the deep brine have only been identified in thermal springs and groundwater samples collected in proximity to structures that transmit thermal fluids suggesting the brine may be thermal in nature on the western side of the valley at the lake city mud volcano the deep brine meteoric water mixture subsequently boils in the shallow subsurface precipitates calcite and re equilibrates at about 130 c on the eastern side of the valley meteoric fluid mixes to a greater extent with the deep brine cools conductively without boiling and the composition is modified as dissolved elements are sequestered by secondary minerals that form along the cooling and outflow path at temperatures

moderate rates of late quaternary slip along the northwestern margin of the basin and range province surprise valley fault northeastern california 1 the 86 km long surprise valley normal fault forms part of the active northwestern margin of the basin and range province in northeastern california we use trench mapping and radiocarbon luminescence and tephra dating to estimate displacements and timing of the past five surface rupturing earthquakes on the central part of the fault near cedarville a bayesian oxcal analysis of timing constraints indicates earthquake times of 18 2 2 6 10 9 3 2 8 5 0 5 5 8 1 5 and 1 2 0 1 ka these data yield recurrence intervals of 7 3 4 1 2 5 3 2 2 7 1 6 and 4 5 1 5 ka and an elapsed time of 1 2 0 1 ka since the latest surface rupturing earthquake our best estimate of latest quaternary vertical slip rate is 0 6 0 1 mm a this late quaternary rate is remarkably similar to long term 8 14 ma minimum vertical slip rates 0 4 0 5 0 3 mm a calculated from recently acquired seismic reflection and chronologic and structural data in surprise valley and the adjacent warner mountains however our slip rate yields estimates of extension that are lower than recent campaign gps determinations by factors of 1 5 4 unless the fault has an unusually shallow 30 35 dip as suggested by recently acquired seismic reflection data coseismic displacements of 2 4 5 1 m documented in the trench and probable rupture lengths of 53 65 km indicate a history of latest quaternary earthquakes of m 6 8 7 3 on the central part of the surprise valley fault

geochronology structure and basin range tectonism of the warner range northeastern california the warner range of northeastern california is a north trending horst at the northwest margin of the great basin the 3 000 m thick bedrock section exposed in the southern part of the range is tertiary in age and it dips homoclinally 20 to 25 west southwest much of the section consists of volcanic rocks whose k ar ages range from about 32 m y near the base of the section to about 14 m y at the top rocks older than about 26 m y are principally andesitic lahars those between 26 and 17 m y are andesitic lava flows and rhyolitic welded ash flow tuffs and those younger than about 17 m y are principally basaltic and andesitic lava flows the homoclinal character of the warner section indicates that block faulting responsible for uplift and tilting of the range began after emplacement of the youngest exposed rocks drilling in the deeply alluviated graben adjacent to the eastern face of the range indicates that aggregate vertical offset across the range front fault is at least 3 600 m the difference in elevation between alluvium in the bottom of the deepest bore hole and the crest of the nearby part of the range thus vertical displacement has occurred at a minimum average rate of 26 cm 1 000 yr during the past 14 m y offset of alluvium along the eastern base of the range records the continuation of block faulting into holocene time the onset of block faulting somewhat less than 14 m y ago and the change in character of volcanic rocks from principally andesitic to principally basaltic in mid miocene time are similar to volcano tectonic events of a much broader region proposed by previous workers the warner range is remarkable for the nearly complete record of regional late cenozoic volcanic and tectonic events found within a single horst

elevated shear zone loading rate during an earthquake cluster in eastern california we compare geodetic velocity to geologic fault slip rates to show that tectonic loading was doubled across the eastern california shear zone ecsz during a cluster of major earthquake activity new slip rates are presented for six dextral faults that compose the ecsz in the central mojave desert these rates were determined from displaced alluvial fans dated with cosmogenic 10 be and from a displaced lava flow dated with 40 ar 39 ar we find that the sum geologic mojave ecsz slip rate 6 2 1 9 mm yr is only half the present day geodetically measured velocity of 12 2 mm yr these rates account for cumulative fault slip and geodetic observations that span the 60 km wide shear zone therefore this difference cannot be attributed to postseismic relaxation redistribution of tectonic loading over the earthquake cycle at a regional scale suggests that earthquake clustering may be enhanced via feedback with weakening of ductile shear zones

quaternary faulting history along the deep springs fault california new geologic mapping structural studies geochronology and diffusion erosion modeling along the deep springs fault california shed light on its quaternary faulting history the deep springs fault a 26km long predominantly north northeaststriking west northwestdipping normal fault bounding the eastern side of deep springs valley cuts jurassic batholithic rocks nonconformably overlain by middle miocene to pleistocene stream gravels coarse grained sand tuffaceous sand unwelded to partially welded tuff and bishop ash as well as quaternary coarse to finegrained alluvial fan deposits the 40 ar 39 ar geochronology yields ages of 3 09 0 08 ma for the unwelded tuff and 753 4k a for the bishop ash holocene debris flows a landslide and recent alluvium bury the youngest fault scarp the deep springs fault is characterized by multiple fault planes and fault scarps that become progressively younger toward the basin the dip of the fault plane varies from 20 to 87 and fault plane and striation measurements indicate an average orientation of n23e 47nw and n77e 49sw respectively the offset of bishop ash and underlying tuff across the deep springs fault indicates horizontal extension and vertical slip rates of 0 7 and 0 9 mm yr respectively since the eruption of the bishop tuff and 0 2 and 0 2 mm yr respectively since the eruption of the unwelded tuff if the vertical slip rate since the eruption of the bishop tuff has remained constant through time then slip along the deep springs fault began ca 1 7 ma younger fault scarps to the west of the bedrock fault cut quaternary deposits scarp offset ranges from 0 8 to 17 5 m and scarp slope angle ranges from 8 to 37 topographic profiling of the smallest least eroded fault scarps with an average surface offset of 2 7 m indicates that these scarps developed as the result of a single earthquake and ruptured an 20km long segment of the fault radiocarbon analyses on detrital charcoal located in the footwall block of one of these scarps yield an age of 1 960 0 055 ka diffusion erosion modeling of these fault scarps yields an elapsed time of 1 7 0 5 k y since these fault scarps formed making reasonable assumptions about the depth of this earthquake and shear modulus we estimate a moment magnitude mw 7 0 for this earthquake the deep springs fault is one of several displacement transfer normal faults that define a zone of distributed deformation between subparallel right lateral strike slip faults east of the sierra nevada that make up the northern part of the eastern california shear zone the young age and recent earthquake activity along the deep springs fault are consistent with a model proposed for the kinematic evolution of this part of the eastern california shear zone

rupture terminations and size of segment boundaries from historical earthquake ruptures in the basin and range province abstract the fault segmentation method is commonly used to estimate the potential earthquake size segment boundaries play an important role in arresting earthquake ruptures from event to event in the basin and range province earthquake rupture terminations are commonly associated with structural discontinuities but not all structural discontinuities have the capability to terminate an earthquake rupture the size of structural discontinuities with respect to the rupture length and displacement may play an important role in controlling rupture termination studies of the geometric pattern of seven well documented historical earthquake ruptures in the basin and range province reveal three important relationships between rupture termination and the size of structural discontinuities firstly terminations of normal faulting earthquakes are often associated with structural discontinuities at least for the five historical ruptures studied in this paper secondly the sizes of structural discontinuities at the end of earthquake rupture zones are generally the largest among the structural discontinuities within the rupture zone thirdly there appears to be a trend that larger earthquake ruptures are stopped by larger structural discontinuities the size of structural discontinuities that stopped the earthquake seems to scale with the length and displacement of earthquake surface rupture

mild and arid climate in the eastern sahara arabian desert during the late little ice age the climate of the sahara and arabian deserts during the little ice age is not well known due to a lack of annually resolved natural and documentary archives we present an annual reconstruction of temperature and aridity derived from sr ca and oxygen isotopes in a coral of the desert surrounded northern red sea our data indicate that the eastern sahara and arabian deserts did not experience pronounced cooling during the late little ice age 1750 1850 but suggest an even more arid mean climate than in the following 150 years the mild temperatures are broadly in line with predominantly negative phases of the north atlantic oscillation during the little ice age the more arid climate is best explained by meridional advection of dry continental air from eurasia we find evidence for an abrupt termination of the more arid climate after 1850 coincident with a reorganization of the atmospheric circulation over europe

arctic oscillation signature in a red sea coral we show that the winter time series of the ras umm sidd coral oxygen isotope record from the northern red sea approximately 28 n is linked to the arctic oscillation phenomenon the northern hemisphere s dominant mode of atmospheric variability until now the detection of this mode which is most prominent in winter in proxy climate records was difficult due to the lack of a clear seasonality in most paleoclimatic archives the results suggest that northern red sea corals can provide information about the low frequency variability of the northern hemisphere winter circulation during the pre instrumental period

two phase westward encroachment of basin and range extension into the northern sierra nevada 1 structural geophysical and thermochronological data from the transition zone between the sierra nevada and the basin and range province at latitude 39 n suggest 100 km westward encroachment of basin and range extensional deformation since the middle miocene extension accommodated primarily by east dipping normal faults that bound west tilted range forming fault blocks varies in magnitude from 150 in the wassuk and singatse ranges to the east geological and apatite fission track data from exhumed upper crustal sections in the wassuk and singatse ranges point to rapid footwall cooling related to large magnitude extension starting at 14 15 ma farther to the west geological and thermochronological data indicate a younger period of extension in the previously unextended pine nut mountains the carson range and the tahoe truckee depression initiated between 10 ma and 3 ma and incipient post 0 5 ma faulting to the west of the tahoe truckee area these data imply the presence of an extensional breakaway zone between the singatse range and the pine nut mountains at 14 15 ma forming the boundary between the sierra nevada and basin and range at that time in addition fission track data imply a miocene preextensional geothermal gradient of 27 5 c km 1 in the central wassuk range and 20 5 c km 1 in the singatse range much higher than the estimated early tertiary gradient of 10 5 c km 1 for the sierra nevada batholith this might point to a significant increase in geothermal gradients coupled with a likely decrease in crustal strength enabling the initiation of extensional faulting apatite fission track geophysical and geological constraints across the sierra nevada basin and range transition zone indicate a two stage coupled structural and thermal westward encroachment of the basin and range province into the sierra nevada since the middle miocene

importance of the gulf of aqaba for the formation of bottom water in the red sea received 30 march 2000 revised 8 may 2001 accepted 13 september 2001 published 16 august 2002 1 conductivity temperature depth tracer and direct current measurements collected in the northern red sea in february and march 1999 are used to study the formation of deep and bottom water in that region historical data showed that open ocean convection in the red sea can contribute to the renewal of intermediate or deep water but cannot ventilate the bottom water the observations in 1999 showed no evidence for open ocean convection in the red sea during the winter 1998 1999 the overflow water from the gulf of aqaba was found to be the densest water mass in the northern red sea an anomaly of the chlorofluorocarbon component cfc 12 observed in the gulf of aqaba and at the bottom of the red sea suggests a strong contribution of this water mass to the renewal of bottom water in the red sea the cfc data obtained during this cruise are the first available for this region because of the new signal it is possible for the first time to subdivide the deep water column into deep and bottom water in the northern red sea the available data set also shows that the outflow water from the gulf of suez is not dense enough to reach down to the bottom of the red sea but was found about 250 m above the bottom index terms 4875 oceanography biological and chemical trace elements 4283 oceanography general water masses 4243 oceanography general marginal and semienclosed seas 4271 oceanography general physical and chemical properties of seawater keywords gulf of aqaba red sea formation of bottom water tracer oceanography cfc overflow

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

geologic context of geodetic data across a basin and range normal fault crescent valley nevada geodetic strain and late quaternary faulting in the basin and range province is distributed over a region much wider than historic seismicity which is localized near the margins of the province in the relatively aseismic interior both the magnitude and direction of geodetic strain may be inconsistent with the holocene faulting record we document the best example of such a disagreement across the ne striking 55 nw dipping crescent normal fault where a nw oriented 70 km geodetic baseline records contemporary shortening of 2 mm yr orthogonal to the fault trace in contrast our geomorphic paleoseismic and geochronologic analyses of the crescent fault suggest that a large extensional rupture occurred during the late holocene epoch an excavation across the fault at fourmile canyon reveals that the most recent event occurred at 2 8 0 1 ka with net vertical tectonic displacement of 4 6 0 4 m at this location corresponding to the release of 3 m of accumulated nw se extension measured alluvial scarp profiles suggest a minimum rupture length of 30 km along the range front for the event implying a moment magnitude m w of at least 6 6 no prior event occurred between 2 8 ka and 6 4 0 1 ka the 14 c calender age of strata near the base of the exposed section assuming typical slip rates for basin and range faults 0 3 mm yr these results imply that up to one third or 1 m of the extensional strain released in the previous earthquake could have reaccumulated across the fault since 2 8 ka however the contemporary shortening implies that the fault is unloading due to a transient process whose duration is limited to between 6 years geodetic recording time and 2 8 ka the age of the most recent event these results emphasize the importance of providing accurate geologic data on the timescale of the earthquake cycle in order to evaluate geodetic measurements

oblique slip and the geometry of normal fault linkage mechanics and a case study from the basin and range in oregon abstract map patterns of normal fault linkages near summer lake oregon show a systematic relationship between echelon step sense oblique slip sense and the position of linking faults where the step sense is the same as the sense of oblique slip e g left step and left oblique slip the faults are linked in the lower part of their relay ramp where the step sense and slip sense are opposite e g left step and right oblique slip the faults are linked in the upper part of the ramp a boundary element code is used to calculate the stress field around echelon normal faults during oblique slip and the model results reveal a relationship similar to the field observations if step sense and oblique slip sense are the same there is a greater potential for deformation ahead of the tip of the front fault and in the lower part of the ramp if step sense and oblique slip sense are opposite there is a greater potential for deformation ahead of the tip of the rear fault and in the upper part of the ramp the field model comparison confirms that oblique slip modifies the mechanical interaction among fault segments and thus influences fault growth and the geometry of fault linkage

overlapping faults intrabasin highs and the growth of normal faults normal fault systems bounding extensional basins are typically adjoined by a series of subbasins separated by intrabasin highs the strata within these basins form syndepositional anticlines and synclines whose axes are transverse to the strike of the main bounding fault one possible explanation for these intrabasin highs is that they result from persistent along strike deficits in fault displacement such deficits are incompatible with scaling relationships observed between fault displacement and length based on large populations of faults we present data from active normal faults within the basin and range province and from inactive normal faults of the newark basin of eastern north america demonstrating a clear correlation between the along strike position of overlapping splay faults and the location of intrabasin highs as well as syndepositional transverse folds summed displacements for all faults within an intrabasin high are comparable to the displacements on faults bounding flanking subbasins o

large magnitude late holocene earthquakes on the genoa fault west central nevada and eastern california the genoa fault a principal normal fault of the transition zone between the basin and range province and the northern sierra nevada displays a large and conspicuous prehistoric scarp three trenches excavated across this scarp exposed two large displacement late holocene events two of the trenches contained multiple layers of stratified charcoal yielding radiocarbon ages suggesting the most recent and penultimate events on the main part of the fault occurred 500 600 cal b p and 2000 2200 cal b p respectively normal slip offsets of 3 5 5 m per event along much of the rupture length are comparable to the largest historical basin and range province earthquakes suggesting these paleoearthquakes were on the order of magnitude 7 2 7 5 the apparent late holocene slip rate 2 3 mm yr is one of the highest in the basin and range province based on structural and behavioral differences the genoa fault is here divided into four principal sections the sierra diamond valley carson valley and jacks valley sections and is distinguished from three northeast striking faults in the carson city area the kings canyon carson city and indian hill faults the conspicuous scarp extends for nearly 25 km the combined length of the carson valley and jacks valley sections the diamond valley section lacks the conspicuous scarp and older alluvial fans and bedrock outcrops on the downthrown side of the fault indicate a lower activity rate activity further decreases to the south along the sierra section which consists of numerous distributed faults all three northeast striking faults in the carson city area ruptured within the past few thousand years and one or more may have ruptured during recent events on the genoa fault

compressional and shear wave velocity versus depth relations for common rock types in northern california abstract this article presents new empirical compressional and shear wave velocity vp and vs versus depth relationships for the most common rock types in northern california vp versus depth relations were developed from borehole laboratory seismic refraction and tomography and density measurements and were converted to vs versus depth relations using new empirical relations between vp and vs the relations proposed here account for increasing overburden pressure but not for variations in other factors that can influence velocity over short distance scales such as lithology consolidation induration porosity and stratigraphic age standard deviations of the misfits predicted by these relations thus provide a measure of the importance of the variability in vp and vs caused by these other factors because gabbros greenstones basalts and other mafic rocks have a different vp and vs relationship than sedimentary and granitic rocks the differences in vs between these rock types at depths below 6 or 7 km are generally small the new relations were used to derive the 2005 u s geological survey seismic velocity model for northern california employed in the broadband strong motion simulations of the 1989 loma prieta and 1906 san francisco earthquakes initial tests of the model indicate that the vp model generally compares favorably to regional seismic tomography models but that the vp and vs values proposed for the franciscan complex may be about 5 too high

imprints of high salinity water plumes originating from the red sea during termination ii abstract the investigation of a core collected in the socotran area western indian ocean provides new insights into water mass exchanges between the red sea and the gulf of aden through the strait of bab el mandeb during the penultimate deglaciation the benthic oxygen isotope record documents the occurrence of stillstands and possibly reversals within the general trend of sea level rise plumes of warm and salty waters are recorded at the surface of the arabian sea and as far as the socotran coast for each increase in sea level these plumes disappeared whenever global sea level stopped rising or showed a brief lowering according to their high salinities these plumes can only originate in the red sea the sill of bab el mandeb becoming deeper and wider during the deglaciation allowed greater exchange between both seas and stronger flow out of the red sea at each episode of sea level rise isotopic and faunal evidence suggest a strengthening of coastal upwelling in the arabian sea during these periods this increase in upwelling activity may explain how plumes of highly saline waters were maintained at the surface moreover the high salinity surface plumes may have facilitated upwelling activity through the destabilisation of density stratification in the upper water column the occurrence of at least high salinity salty water outflows during termination ii confirms the step wise non linear structure of the penultimate deglaciation providing a perfect example of the threshold concept in rapid climate changes

can one determine seismic focal parameters from the far field radiation summary a number of postulates concerning the nature of faulting have been used in the construction of kinematical models which give the source parameters of seismic moment fault length and stress drop from the spectral properties of d c level and knee frequency several one dimensional models of faulting calculated as well posed boundary value problems are obtained which give both the source parameters and the far field radiation providing a test for these empirical relations the results for these models show that the high frequency content of the seismogram is usually associated not with the onset of fracture but with the onset of healing that is when the cessation of relative motion on the fault begins in some cases the high frequency part of the seismogram is also associated with the termination of rupture for different distributions of tectonic stress dynamical friction and cohesion healing can take place sonically supersonically or instantaneously over the entire fault the final state of stress may be less than or greater than the dynamical friction for four selected models of one dimensional faulting the calculation of fault parameters from the theoretical seismograms give internally consistent estimates of seismic moment unfortunately the theory shows that the estimates of fault length and stress drop made from the empirical formulas may be completely without value without additional information not usually derived from the radiation spectrum

a rupture model for the 1999 chi chi earthquake from inversion of teleseismic data using the hybrid homomorphic deconvolution method this study investigates the kinematics of the rupture process of the ml 7 3 chi chi taiwan earthquake on september 21 1999 by applying the proposed hybrid homomorphic deconvolution method to deconvolve teleseismic broadband p wave displacement recordings of the earthquake this study derives the apparent source time functions astfs at ten stations located around the epicenter to further characterize the fault the kinematic history of the rupture was inverted from astfs using a genetic algorithm coupled with nonlinear iterative technique the calculated asfts reveal that the total rupture event lasted for approximately 27 s static slip distribution images indicate that most slip occurred at shallower portions of the fault plane especially 20 55 km north of the epicenter the maximum slip reached 20 m at 45 km north of the epicenter and the average slip throughout the observed rupture area was approximately 2 m large asperities on the fault appeared at 25 35 km and 40 50 km north of the hypocenter and coincided with relatively high rupture velocity this suggests that the earthquake s energy may have been released quickly the rupture velocity decreased upon encountering an asperity and increased again after passing the asperity this implies that the rupture required more time to overcome the resistances of the asperities the maximum rupture velocity was 3 8 km s while the average rupture velocity was approximately 2 2 km s the rise time distribution suggests that larger slip amplitudes generally correspond to shorter rise times on the subfaults