gradual fault weakening with seismic slip inferences from the seismic sequences of l aquila 2009 and northridge 1994 we estimate seismological fracture energies from two subsets of events selected from the seismic sequences of l aquila 2009 and northridge 1994 57 and 16 selected events respectively including the main shocks following abercrombie and rice geophys j int 162 406 424 2005 we postulate that fracture energy g represents the post failure integral of the dynamic weakening curve which is described by the evolution of shear traction as a function of slip following a direct wave approach we compute mainshock aftershock source spectral ratios and analyze them using the approach proposed by malagnini et al pure appl geophys this issue 2014 to infer corner frequencies and seismic moment our estimates of source parameters including fracture energies are based on best fit grid searches performed over empirical source spectral ratios we quantify the source scaling of spectra from small and large earthquakes by using the mdac formulation of walter and taylor a revised magnitude and distance amplitude correction mdac2 procedure for regional seismic discriminants 2001 the source parameters presented in this paper must be considered as point source estimates representing averages calculated over specific ruptured portions of the fault area in order to constrain the scaling of fracture energy with coseismic slip we investigate two different slip weakening functions to model the shear traction as a function of slip i a power law as suggested by abercrombie and rice geophys j int 162 406 424 2005 and ii an exponential decay our results show that the exponential decay of stress on the fault allows a good fit between measured and predicted fracture energies both for the main events and for their aftershocks regardless of the significant differences in the energy budgets between the large main and small earthquakes aftershocks using the power law slip weakening function would lead us to a very different situation in our two investigated sequences if the aftershock scaling is extrapolated to events with large slips a power law a la abercrombie and rice would predict unrealistically large stress drops for large main earthquakes we conclude that the exponential stress evolution law has the advantage of avoiding unrealistic stress drops and unbounded fracture energies at large slip values while still describing the abrupt shear stress degradation observed in high velocity laboratory experiments e g di toro et al fault lubrication during earthquakes nature 2011

uplift and a possible moho offset across the dead sea transform abstract the east africa rifts and the red sea spreading center are characterized by uplifted shoulders and sunken median valleys the dead sea transform on the northern extension of the arabian african plate boundary has a similar morphological character despite its well documented strike slip motion to understand the rift morphology and the crustal structure beneath the transform we compiled a 320 km long gravity and topography profile perpendicular to the dead sea transform the gravity field and the topography in the region surrounding the profile are generally parallel to the trend of the dead sea transform justifying the two dimensional approximation of the analysis the gravity profile was modeled using constraints from seismic refraction borehole and surface geology data the observed gravity anomaly can be explained by the juxtaposition of two different sedimentary and crustal sections which have been offset by a 105 km left lateral displacement across the transform boundary suggesting a step in the depth to moho the existence of a significant density anomaly under the median valley is not required by the model the current elevation of the transform shoulders appears not to be compensated locally assuming a state of local isostasy prior to the development of the transform the magnitude of the uplift in the vicinity of the profile is estimated at 700 900 m with a half width of 100 125 km this topography uplift can be fitted equally well by models which assume either dynamic support or regional compensation it is suggested that if the source of the uplift is thermal it is located within the upper mantle since there is no requirement for a shallow density anomaly under the rift itself or in the crust nearby

earthquake modeling in the dead sea basin 1 we simulate 75 seconds of 1 5 hz wave propagation of the 1927 jericho earthquake ml 6 2 using a staggered grid finite difference fd method from the time histories we compute peak ground velocities and pseudo acceleration responses at 1 hz in a 3d model including the dead sea basin substructure we compare the accelerations to values computed a for a homogeneous model and b using an attenuation relation similar to the one integrated in the building code 413 of israel with accelerations at 1 hz we show that the dead sea basin substructure is responsible for a significant radiation anisotropy in ground motion attenuation when the source is located within the basin rupture dynamics effects of strike slip events along faults bounding the basin enhance this behaviour we show that both the homogeneous model and the attenuation relation underestimate the spectral responses on average by factors between 1 5 and 5

prolonged magmatism on 4 vesta inferred from hf w analyses of eucrite zircon the asteroid 4 vesta is the second most massive planetesimal in the solar system and a rare example of a planetary object that possibly can be linked to a specific group of differentiated meteorites the howardite eucrite diogenite suite the 182hf 182w chronometry of individual zircon grains from six basaltic eucrites revealed distinct growth episodes ranging from 4532 11 6 ma to 4565 0 0 9 ma and constrains the early thermal history of 4 vesta indicating that its mantle generated basaltic melts for at least 35 million years myr initially the energy needed for melting was provided by decay of short lived isotopes mostly 26al the long duration of magmatism despite the short lifetime of 26al implies that the asteroid must have accreted within the first 4 myr of solar system formation similar to the formation of iron meteorite parent bodies and that its interior must have been thermally well insulated by an early formed crust that prevented heat loss

origin of zoned metal grains in the que94411 chondrite laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure distributions of the siderophile elements p v cr fe co ni mo ru rh pd w re os ir and pt in metal grains in the metal rich chondrite que94411 with a spatial resolution of similar to 30 mum the platinum group elements pges except pd exhibit radial zoning in these grains that mimics that previously observed in ni and co the concentrations of these elements decreases from the cores to the rims of the grains the pge distributions support a condensation origin for the enhanced refractory element abundances in the zoned grains the lack of zoning in pd refutes an origin by a redox controlled process and none of the pge ni relationships support an origin by fractional crystallization from a metallic melt several models of grain formation were explored including equilibrium fractional condensation which failed to yield the correct radial zoning the zoning may be the product of a nonequilibrium fractional condensation process in which the refractory siderophiles remained supersaturated in the cooling solar nebula or of diffusion between refractory enhanced fe ni cores and other fe ni metal that may have been deposited later from the solar nebula copyright c 2001 elsevier science ltd

three dimensional simulations of ground motions in the san bernardino valley california for hypothetical earthquakes on the san andreas fault three dimensional finite difference simulations of elastic waves in the san bernardino valley were performed for two hypothetical earthquakes on the san andreas fault a point source with moment magnitude m5 and an extended rupture with m6 5 a method is presented for incorporating a source with arbitrary focal mechanism in the grid synthetics from the 3 d simulations are compared with those derived from 2 d vertical cross section and 1 d flat layered models the synthetic seismograms from the 3 d and 2 d simulations exhibit large surface waves produced by conversion of incident s waves at the edge of the basin seismograms from the flat layered model do not contain these converted surface waves and underestimate the duration of shaking the seismograms from the 3 d simulations have larger amplitude coda than do the seismograms from the 2 d case because of the presence of off azimuth surface wave arrivals in the 3 d simulations that are not included in the 2 d simulations snapshots of the wavefield of the 3 d simulation show that these off azimuth arrivals represent surface waves reflected from the edges of the basin the anelastic attenuation of the sediments is a key parameter controlling the overall duration of motion some of the coda energy at rock sites near the basin edges represents leakage of surface wave energy out of the basin for the m6 5 earthquake simulation the largest ground velocities occur where surface waves reflected from the edge of the basin interfere constructively with the trapped waves that follow the direct s wave maps of maximum ground velocity are produced for two directions of rupture propagation the largest velocities occur in localized portions of the basin the location of the largest velocities changes with the rupture propagation direction contours of maximum shaking are also dependent on asperity positions and radiation pattern

high frequency ground motion in the erzincan region turkey inferences from small earthquakes this study has been supported by istituto nazionale di geofisica e vulcanologia ingv internal project attenuazione e leggi di scala nei paesi dell area mediterranea internally funded r b herrmann s participation was supported by ingv and by the earthquake engineering research centers program of the national science foundation under award number eec 9701785

thermal anomalies associated with forced and free ground water convection in the dead sea rift valley the dead sea rift valley is a left lateral transform along which several rhombshaped grabens were formed at the sea of galilee which is one of these rhomb shaped grabens ambiguous heat fluxes were measured 70 80 mw m 2 at the central part of the lake 36 mw m 2 at the lake s southern coast 10 km apart and most surprising about 135 mw m 2 at the southern golan heights 6 8 km east of the graben margin a detailed geologic cross section traversing the entire sedimentary basin was constructed the hydrodynamics in this cross section were analyzed quantitatively using a two dimensional finite element code that solves the coupled variable density ground water flow and conductive convective heat transfer equations on the basis of numerical simulations different mechanisms of basin scale groundwater convection are suggested for the two sides of the rift that could influence the transport of heat 1 forced convection gravitydriven flow of hot brines from deeper aquifers to the land surface at the western side and 2 large scale free convection buoyancy driven flow of deep ground water at the eastern side the different heat fluxes within the rift valley are attributed to the different lithologies and to the locations of specific conduits through which the hot ground waters ascend from deeper horizons these simulations also explain the different salinities of the hot springs on the two sides of the rift

the accumulation of silver in marine sediments a link to biogenic ba and marine productivity 1 the concentrations of ag and a suite of redox sensitive trace metals re cd and mo were measured in surface sediments from the western canadian mexican peruvian and chilean continental margins in all regions ag content increases from 80 ng g 1 i e lithogenic values on the shelf up to as high as 1483 ng g 1 on the lower slope however the trend of increasing ag with increasing water depth breaks down at deepwater sites 2500 m where only lithogenic concentrations are documented silver content does not correlate with the distributions of redox sensitive trace metals suggesting that sedimentary redox conditions are not the primary control on ag accumulation instead a positive correlation between ag and ba in surface and near surface sediments suggests that ag is scavenged by and delivered to the sediment with the organic particle flux scavenging probably results from the precipitation of ag2s within the organic particles due to the development of anoxia and sulfate reduction if this hypothesis is correct then ag has the potential to be a paleoproductivity proxy

weak motion based attenuation relationships for israel summary we performed a regional study of earthquake ground motion scaling relations to provide the seismic hazard community of israel with a new attenuation relationship that could be used for the prediction of earthquake induced ground motion strong earthquakes are rather scarce in israel and the existing collection of records from strong earthquakes is not sufficient to allow the use of traditional regression methods to develop a regional attenuation relationship we used velocity seismograms from the israel seismic network to estimate the distance and frequency dependence of ground motion in the israel region from frequent smaller regional earthquakes our analyses included 4814 waveforms recorded by 30 stations of the israel seismic network from 2000 to 2005 we restricted our analysis to 330 events recorded at five or more stations with duration magnitudes ranging between 1 0 and 5 2 we derived empirical excitation site and regional attenuation terms by regressing the peak amplitudes of narrowband filtered seismograms around the shear wave arrivals and the rms fourier spectral amplitudes taken around the specific sampling frequency in order to optimize the attenuation parameters in our scaling model we used a simple grid search an optimal solution for minimal error between empirical and theoretical attenuation function was found for the quality parameter q f 298f0 67 and the geometrical spreading g r parametrized as a bilinear piecewise function r 0 74 for r 60 km and r 0 47 for r 60 km the spectral parameters of 0 015 s and stress drop increasing from 0 3 to 4 mpa were used to model the excitation spectra a theoretical modelling effort based on brune s source spectrum and random vibration theory rvt was performed on the attenuation and source parameters estimated in this study comparison of the attenuation relationship derived with locally measured ground motions shows excellent agreement with the data in the magnitude range for which we have observations and seems to be adequate for predictions of earthquake ground motion for the israel region comparison of peak ground acceleration pga predictions based on our scaling relationship with those that have been recently used for seismic hazard analysis in israel shows that our attenuation relationship predicts significantly lower ground motions than other relations

high frequency attenuation in the lake van region eastern turkey we provide a complete description of the characteristics of excitation and attenuation of the ground motion in the lake van region eastern turkey using a data set that includes three component seismograms from the 23 october 2011 m w 7 1 van earthquake as well as its aftershocks regional attenuation and source scaling are parameterized to describe the observed ground motions as a function of distance frequency and magnitude peak ground velocities are measured in selected narrow frequency bands from 0 25 to 12 5 hz observed peaks are regressed to define a piecewise linear regional attenuation function a set of excitation terms and a set of site response terms results are modeled through random vibration theory see cartwright and longuet higgins 1956 in the log log space the regional crustal attenuation is modeled with a bilinear geometrical spreading graphic 1 characterized by a crossover distance at 40 km graphic 2 fits our results at short distances r is better at larger distances 40 r 200 km a frequency dependent quality factor q f 100 f f ref 0 43 in which f ref 1 0 hz is coupled to the geometrical spreading because of the inherent trade off of the excitation attenuation parameters and their specific values strongly depend on the choice made for the stress drop of the smaller earthquakes after choosing a brune stress drop brune 4 mpa at m w 3 5 we were able to define 1 an effective high frequency distance and magnitude independent roll off spectral parameter eff 0 03 s and 2 a size dependent stress drop parameter which increases with moment magnitude from brune 4 mpa at m w 3 5 to brune 20 mpa at m w 7 1 the set of parameters mentioned here may be used in order to predict the earthquake induced ground motions expected from future earthquakes in the region surrounding lake van 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

old radiocarbon ages in the southwest pacific ocean during the last glacial period and deglaciation marine radiocarbon 14c dates are widely used for dating oceanic events and as tracers of ocean circulation essential components for understanding ocean climate interactions past ocean ventilation rates have been determined by the difference between radiocarbon ages of deep water and surface water reservoirs but the apparent age of surface waters currently approximately 400 years in the tropics and approximately 1 200 years in antarctic waters might not be constant through time as has been assumed in radiocarbon chronologies and palaeoclimate studies here we present independent estimates of surface water and deep water reservoir ages in the new zealand region since the last glacial period using volcanic ejecta tephras deposited in both marine and terrestrial sediments as stratigraphic markers compared to present day values surface reservoir ages from 11 900 14c years ago were twice as large 800 years and during glacial times were five times as large 2 000 years contradicting the assumption of constant surface age furthermore the ages of glacial deep water reservoirs were much older 3 000 5 000 years the increase in surface to deep water age differences in the glacial southern ocean suggests that there was decreased ocean ventilation during this period

lower crustal strength under the dead sea basin from local earthquake data and rheological modeling we studied the local seismicity of the dead sea basin for the period 1984 1997 sixty percent of well constrained microearthquakes ml 3 2 nucleated at depths of 20 32 km and more than 40 occurred below the depth of peak seismicity situated at 20 km with the moho at 32 km the upper mantle appeared to be aseismic during the 14 year data period a relocation procedure involving the simultaneous use of three regional velocity models reveals that the distribution of focal depths in the dead sea basin is stable lower crustal seismicity is not an artifact created by strong lateral velocity variations or data related problems an upper bound depth uncertainty of 5 km is estimated below 20 km but for most earthquakes depth mislocations should not exceed 2 km a lithospheric strength profile has been calculated based on a surface heat flow of 40 mw m 2 and a quartz depleted lower crust a narrow brittle to ductile transition might occur in the crust around 380 c at a depth of 31 km for the upper mantle the brittle to ductile transition occurs in the model at 490 c and at 44 km depth the absence of micro seismicity in the upper mantle remains difficult to explain

the oldest zircons in the solar system abstract here we report the occurrence chemistry and u th pb isotopic systematics of three meteoritic zircon assemblages two from the vaca muerta mesosiderite and one from the simmern h5 chondrite one of the vaca muerta zircons occurs in the mesosiderite proper the other in a eucritic clast associated with chromite ilmenite and tridymite whereas the simmern zircon occurs in a chondrule composed predominantly of chromite and feldspar like terrestrial zircons the meteoritic zircons are enriched in the heavy rare earth elements but unlike terrestrial zircons they do not show a positive ce anomaly this feature is also absent in one lunar zircon analyzed and probably reflects the oxidation state of the formation environment under oxidising conditions ce4 which can substitute for zr4 in the zircon structure is stabilized whereas under relatively reducing conditions ce3 is stable the zircon from simmern has depletions in the relative abundances of tm and yb a characteristic of volatility fractionation of the ree the u concentrations of the two vaca muerta zircons are quite different at 1 and 50 ppm respectively both zircons have extremely low initial lead and give radiogenic ages that are the same albeit with relatively large errors on vm 1 zircon because of its much lower u concentration and hence radiogenic pb concentration the mean of the two analyses made on vm 2 zircon is concordant with a207pb 206pb age of 4563 15 ma 2 the simmern zircon has an exceptionally low u concentration of around 180 ppb and only a poorly constrained 207pb 206pb age of 4100 700 ma could be obtained

high frequency earthquake ground motion scaling in utah and yellowstone velocity seismograms from the university of utah seismograph stations are used to quantify high frequency ground motion scaling for the yellowstone region and the wasatch front in utah this study uses a data set consisting of over 3000 waveforms from 93 stations and 506 regional earthquakes and mining associated seismic events that occurred in the years 1995 2001 all events lie within the upper crust with magnitudes less than 5 5 the signals were processed to examine the peak ground velocity and fourier velocity spectra in the frequency range of 1 0 16 0 hz regression results for utah are characterized by rapid decreases of amplitude at short distances which requires low q and a rapid geometrical spreading g r for the forward modeling q f 160 f 0 75 eff 0 05 sec and 300 bars are selected to predict the excitation terms when combined with the derived geometrical spreading the frequency dependent excitation of mining associated events differs significantly from that of earthquakes because of either an additional attenuation due to shallow source depth or apparent low stress drops associated with the slow collapse of long tunnels a q f 140 f 0 70 and geometrical spreading less rapid than r 1 0 at short distance ranges are used to describe the wave propagation distance dependence in the yellowstone region the yellowstone attenuation functional d r f is very different from that of utah perhaps because a shallow wave guide in the caldera traps more energy the yellowstone excitation spectra were modeled using 30 bars and eff 0 04 sec manuscript received 24 october 2003

micro and macroseismicity of the dead sea rift and off coast eastern mediterranean abstract the seismicity of israel has been evaluated from documented earthquake records of the present century and two years of routine monitoring of microearthquake activity by means of eleven stations spreading from the gulf of elat to northern galilee the dead sea rift asserts itself as the tectonic feature that accounts for the seismicity of our region the activity peaks at zones where the fault branches sideways or at a junction with other fault systems in particular the crescent fault of wadi faria seems to be a zone of high strain accumulation this is probably the site of many historical earthquakes which caused inland and coastal damage it is thus found that the most active fault today which constitutes the greatest seismic risk to israeli metropolitan areas extends along the dead sea rift from 31 2 n to 33 4 n the seismicity around the dead sea conforms with the proposed movement along en echelon faults while the southwest segment is presently inactive most of the seismic activity there is limited to the neighbourhood of its eastern shore with extreme seismicity at its southern tip near the prehistorical site of bab a dara a the seismicity of the arava is much lower than the jordan dead sea section the seismicity of the israeli coast was found to be somewhat higher than that of the arava

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

parameterization of a composite attenuation relation for the dead sea area based on 3 d modeling of elastic wave propagation 3 d simulations of elastic wave propagation generated by earthquakes with magnitudes between 5 5 and 7 0 are used to parameterize strong ground motion attenuation relations for the dead sea rift dsr graben structure the results show that standard attenuation relations with an isotropic distance parameter are inadequate for a graben structure with a deep sedimentary trough a new strategy is devised for the parameterization of attenuation relations in graben structures by looking at the statistical properties of 53 simulated earthquakes of variable magnitudes located at various sites along the western boundary fault of the dsr graben an exemplary attenuation relation is designed from the synthetics for the 1 hz spectral acceleration modifying the joyner boore type parametrization by adding coefficients suited for three different source to sensor configurations within the graben beyond the graben and path unaffected by the graben structure

initial 182hf 180hf in meteoritic zircons zircons from the simmern h5 chondrite and pomozdino eucrite have been analyzed for their hf w isotope systematics zircons have high intrinsic hf contents and coupled with low w make them ideal hf w chronometers however measurements of 182hf 180hf 0 are far from straightforward with low signals of radiogenic 182w and difficulties in calibrating hf w ratios zircons were analyzed from the simmern chondrite and the pomozdino eucrite the simmern zircon has an ultrarefractory enriched trace element pattern a feature commonly associated with refractory inclusions analyses of simmern zircon show variable hf w that is likely due to surface contamination simmern chondrite zircon yields a 182hf 180hf 0 of 7 2 4 5 10 5 pomozdino eucrite zircon analyses show very high hf w values indicating 182hf 180hf 0 of 1 7 1 1 10 5 the simmern value is in good agreement with the initial value of the solar system indicated from hf w systematics of chondrites the pomozdino value is lower than expected if eucrites formed within several million years of refractory inclusions as suggested from al mg systematics of eucrites

u pb and hf w dating of young zircon in mesosiderite asuka 882023 mesosiderites are unique stony iron meteorites composed of eucrite like silicates and fe ni metals their formation including silicate metal mixing and metamorphisms provide important insights into early planetary processes in the inner solar system this report describes the first in situ u pb and hf w dating of zircon in a mesosiderite asuka 882023 the u pb 4502 75 ma and hf w 4532 8 5 7 10 5 ma ages may represent timing of the zircon formation which is considerably younger than crustal differentiation of the parent body this evidence combined with earlier studies of chronology implies that mesosiderites were reheated at 4530 4520 ma clearly after the silicate metal mixing

assessing the depth resolution of tomographic models of upper mantle structure beneath iceland 1 earlier inversions of body wave delay time data recorded during the icemelt portable broadband experiment imaged a cylindrical plume like low velocity anomaly extending to at least 400 km depth beneath iceland but the depth extent of the anomaly resolvable by tomography has recently been called into question we have performed several additional resolution tests to evaluate the depth resolution of tomographic models of the icelandic upper mantle the distribution of paths of body waves recorded by icemelt can distinguish among three different types of models a a wide and shallow anomaly b a narrow and deep anomaly and c a narrow and shallow anomaly while tomographic models contain an element of nonuniqueness these tests illustrate that the depth resolution of passive seismic experiments spanning subaerial iceland is adequate for distinguishing among alternative geodynamic models

seismicity of the eastern mediterranean region perspective from the sinai subplate we conducted a comprehensive study of the seismicity of the eastern mediterranean and examined its relation to the regional plate tectonics based on various published catalogs we have constructed a new list of ml 4 earthquakes which were recorded during the years 1900 1991 and represents most of the seismic moment released in the area over this period b values are 1 02 1 0 and 1 07 for the whole sinai subplate the dead sea transform and the cypriot arc respectively seismic efficiency of the dead sea transform is very low about 7 stressing the role of aseismic deformation in that plate border most of the major and moderate events ml 5 occur in belts associated with the geologically documented borders of the sinai subplate the cypriot convergent arc in the north the dead sea transform in the east and the rift of suez in the southwest the latter like the gulf of eilat aqaba was considered aseismic during the first half of the century the northwestern border however could not be delineated low level activity appears within the subplate especially north of latitude 32 n reflecting the breakdown of this part of sinai as it approaches the cypriot convergence zone though most of the seismic moments tend to concentrate along the subplate borders some moderate activity spreads out in wide belts which reflect the complexity of deformation accompanying motion along the subplate borders

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

influence of biological productivity on silver and redox sensitive trace metal accumulation in southern ocean surface sediments pacific sector abstract accurate interpretation of paleoproductivity proxies in the southern ocean requires ground truthing these proxies here the concentrations of total ba organic carbon c org and biogenic silica si bio along with other redox sensitive trace metals cd re and mo are compared with the distribution of silver ag in core top sediments from the pacific sector of the southern ocean conventional thinking holds that enrichment of trace metals should be muted or absent in southern ocean sediments despite high export of c org from surface waters because deposition under well oxygenated bottom waters inhibits accumulation of reduced metal phases while our data support this prediction detectable preserved vertical fluxes of ag cd and re exist beneath the opal belt and faithfully record surface productivity patterns therefore we suggest ag fluxes into southern ocean sediments occur via biodetritus associated with high export production rather than accumulation by redox driven diagenetic processes sedimentary ag concentrations are likely altered at the seafloor by biogenic particle remineralization due to high bottom water o 2 nevertheless zonal ag fluxes are similar to surface productivity patterns highlighting the potential of ag to serve as a proxy for diatom export production

early diagenesis of germanium in sediments of the antarctic south atlantic in search of the missing ge sink pore water and solid phase geochemistry profiles were obtained from several cores between 41 degree s and 53 degree s in the atlantic sector of the southern ocean pore water nitrate manganese and iron profiles delineate standard redox zones in these sediments and help characterize those with classic vs burn down behaviors pore water si and ge profiles demonstrate that ge released during opal dissolution is removed pervasively throughout the uppermost interval of silicate release and also downwards into the suboxic zone by as yet unidentified precipitation mechanisms these results indicate that early diagenesis of ge is uncoupled from that of opal solid phase extractions fe mn u mo ge cu ni co v and cd in a few cores suggest that anthigenic ge removal in the suboxic zone is not associated with peaks in authigenic mn cycling mno sub 2 and related metals but rather with processes deeper in the sediments perhaps fe or u diagenesis below the interval of ge removal pre water ge increases linearly with depth by over two orders of magnitude indicating a deep below recovery source of large magnitude the fraction of opal derived ge precipitated authigenically in these sediments ranges from approximately 1 to 96 and correlates strongly with the detrital fraction asmore well as the detrital to opal ratio both of which generally decrease from north to south the ge sink observed in these sediments would need to be globally representative to account for the entire missing ge sink in today s oceanic ge balance which seems unlikely benthic fluxes of ge and si estimated from these pore water profiles and from measurements in three benthic flux chamber experiments at high carbon rain continental margin sites demonstrate that the ge si rate released from the seafloor in locations with high benthic silicate and carbon fluxes is congruent with holocene opal dissolution ge si approximately 0 7 x 10 sup minus 6 in contrast ge si flux ratios in areas with low silicate fluxes are ge depleted ge si 0 5 x 10 sup minus 6 the authors speculate that glacial interglacial changes in oceanic ge si as recorded in diatoms may be due in part to variations in this authigenic ge sink perhaps related to shifts in siliceous productivity from open ocean antarctic siliceous oozes during interglacials to areas of higher detrital input sub antarctic continental margins and possibly also to generally more reducing conditions in sediments during glacials less

attenuation of coda waves in the dead sea region abstract coda waves of local small earthquakes in the dead sea region part of the jordan rift structure show frequency invariant codas that is q c q 0 f f 0 n with q 0 65 5 f 0 1 hz and n 1 05 0 04 for hypocentral distances between 10 and 55 km and lapse times less than 60 sec this justifies for example the use of part of the coda for relative site response studies lacking direct q measurements q c might be considered as a first approximation of q for the region for short hypocentral distances r q c with lapse time t has been observed

the geologic history of vesta inferred from combined 207pb 206pb and 40ar 39ar chronology of basaltic eucrites abstract eucrites represent samples of mafic crust of the parent body likely vesta and record a complex geologic history involving magmatism metamorphism impact processing and metasomatism for better understanding of the geologic history we present combined 207pb 206pb and 40ar 39ar chronology of four basaltic eucrites showing distinct petrologic features agoult an equilibrated eucrite with granulitic textures camel donga a brecciated equilibrated eucrite enriched in metallic iron dag 380 a partially equilibrated monomict eucrite and nwa 049 a metasomatized polymict eucrite comprising mostly unequilibrated clasts the 207pb 206pb dating in combination with the acid washing technique was applied to pyroxene rich and plagioclase rich fractions while the 40ar 39ar dating was performed mainly on plagioclase grains using the laser incremental heating method the pb isotopic data for acid leaching residues are more radiogenic than those for acid washes reflecting efficient removal of non radiogenic pb components by the acid washing among the residues however only those of the agoult and camel donga plagioclase rich fractions yielded isochrons rather than errorchrons with 207pb 206pb ages of 4532 39 0 87 ma and 4515 43 0 42 ma respectively the trace element systematics further suggest that these residues essentially represent contaminant oxide minerals such as ilmenite and chromite rather than plagioclase on the other hand the ar isotopic data for agoult and camel donga yielded plateau ages with weighted means of 4494 9 ma and 3749 25 ma in contrast to those for dag 380 and nwa 049 that did not return any plateau the 207pb 206pb and 40ar 39ar ages of agoult are interpreted to reflect the time of the u pb and k ar system closure during a prolonged thermal metamorphism by combining the ages reported here and in the literature with the calculated closure temperatures the cooling rate of agoult is determined to be 11 2 c ma this cooling rate corresponds to a burial depth of 10 20 km indicating that granulitic eucrites were originally crystallized near the surface and were subsequently buried and metamorphosed the 20 ma younger 207pb 206pb ages of camel donga than agoult are considered to reflect delayed burial metamorphism in the source region whereas the plateau 40ar 39ar age would record the time of an impact causing brecciation and efficient ar degassing of the buried crust furthermore the model 207pb 206pb dates calculated for acid washed pyroxenes imply that the burial metamorphism of agoult and dag 380 were broadly contemporaneous and also that nwa 049 was metasomatized by fluids within the uppermost crust later than 4 4 ga

seismic behaviour of the dead sea fault along araba valley jordan the dead sea fault zone is a major left lateral strike slip fault south of the dead sea basin the wadi araba fault extends over 160 km to the gulf of aqaba the dead sea fault zone is known to have produced several relatively large historical earthquakes however the historical events are unequally distributed along the fault and only four events have been reported in the araba valley over the last few thousands of years magnitudes estimated from the historical record are probably slightly smaller than that of the m w 7 3 earthquake that struck the gulf of aqaba in 1995 the fault cuts straight across pleistocene to holocene alluvium and shows morphologic evidence for essentially pure strike slip motion regional seismic monitoring reveals little microseismicity along the fault except around the dead sea and gulf of aqaba where the fault splays into complex pull apart basin fault systems we have investigated the fault zone at several sites selected from spot images and the study of aerial photography at the site of the now destroyed tilah castle a well preserved wall dated to be about 1200 yr bp 14 c age on charcoal is cut by the fault and offset by 2 2 m comparison with offset gullies at a nearby site 3 km to the north and at three other sites respectively 25 50 and 65 km to the south reveals that this specific fault displacement is probably related to the last seismic event that ruptured that fault segment possibly in ad 1458 moreover the offset gullies suggest a characteristic slip behaviour with recurring slip of about 1 5 m on average given the 4 2 mm yr 1 slip rate derived for this fault segment we infer that the fault should produce m w 7 earthquakes along some segment in the araba valley about every 200 years the historical period with only four well documented large earthquakes in ad 1068 ad 1212 ad 1293 and ad 1458 thus appears to have been relatively quiescent with a 20 per cent deficit of m w 7 earthquakes however our data do not exclude the possibility of larger m w 7 6 earthquakes or time clustering of earthquakes over longer timespans an alternative seismic behaviour involves m w 7 6 earthquakes about every 6000 years and m w 7 earthquakes about every 250 years the historical catalogue would then appear to be complete for m w 7 earthquakes

evidence from authigenic uranium for increased productivity of the glacial subantarctic ocean authigenic uranium is precipitated in reducing sediments and therefore responds both to changes in particulate organic carbon flux to the sediment and to changes in the oxygen concentration of bottom waters by examining a large number of cores over a wide latitudinal and depth range in the atlantic sector of the southern ocean we hope to distinguish between a predominantly productivity driven authigenic u signal and a circulation or sediment focusing signal we find little to no authigenic u in holocene sediments throughout the south atlantic ocean glacial sediments north of 40 s lack authigenic u whereas sediments from the subantarctic zone show substantial enrichments in authigenic u relative to the holocene up to 5 3 ppm the widespread distribution of glacial u enrichment even in cores with no glacial interglacial change in mass accumulation rate implies that u deposition was not caused by an increased supply of organic carbon via sediment focusing authigenic u and organic carbon in a shallow core 1000 m from the subantarctic region show the same glacial increase found in the deep cores because this site was well ventilated during the last glacial maximum its record provides further evidence that increased glacial productivity of the subantarctic region contributed to the high concentrations of authigenic u found in the glacial sections of deep cores

contrasting molybdenum cycling and isotopic properties in euxinic versus non euxinic sediments and sedimentary rocks refining the paleoproxies abstract the redox sensitive transition element molybdenum is present in the earth s crust at trace concentrations but is abundant in seawater marine sediments and ancient sedimentary rocks these occurrences have led to the development of a suite of paleoredox proxies based on the bulk concentration of mo its isotopic composition and the covariation of mo with total organic carbon toc in ancient black shales however these proxies have almost exclusively targeted the identification and interpretation of euxinic environments where bottom waters are both anoxic and sulfidic here we present a discussion of the mo geochemistry of non euxinic sediments where hydrogen sulfide is sometimes present yet always restricted to pore waters we propose a new paleoredox application that uses mo concentrations to help distinguish between environments where sulfide was present in the bottom waters and environments where sulfide was restricted to pore waters under ideal conditions it is also possible to infer the presence of mn oxides recycling in non euxinic paleoenvironments based on the mo isotope composition of ancient black shales providing a critical constraint on bottom water oxygenation

radiocarbon and stable isotope constraints on last glacial maximum and younger dryas ventilation in the western north atlantic 1 foraminiferal abundance 14c ventilation ages and stable isotope ratios in cores from high deposition rate locations in the western subtropical north atlantic are used to infer changes in ocean and climate during the younger dryas yd and last glacial maximum lgm the 18o of the surface dwelling planktonic foram globigerinoides ruber records the present day decrease in surface temperature sst of 4 c from gulf stream waters to the northeastern bermuda rise if during the lgm the modern 18o salinity relationship was maintained this sst contrast was reduced to 2 c with lgm to interglacial 18o changes of at least 2 2 ssts in the western subtropical gyre may have been as much as 5 c colder above 2 3 km glacial 13c was higher than today consistent with nutrient depleted younger bottom waters as identified previously below that 13c decreased continually to 0 5 about equal to the lowest lgm 13c in the north pacific ocean seven pairs of benthic and planktonic foraminiferal 14c dates from cores 2 5 km deep differ by 1100 340 years with a maximum apparent ventilation age of 1500 years at 4250 m and at 4700 m apparent ventilation ages are presently unavailable for the lgm 2 5 km because of problems with reworking on the continental slope when sea level was low because lgm 13c is about the same in the deep north atlantic and the deep north pacific and because the oldest apparent ventilation ages in the lgm north atlantic are the same as the north pacific today it is possible that the same water mass probably of southern origin flowed deep within each basin during the lgm very early in the yd dated here at 11 25 0 25 n 10 conventional 14c kyr bp equal to 12 9 calendar kyr bp apparent ventilation ages 2 3 km water depth were about the same as north atlantic deep water today below 2 3 km four yd pairs average 1030 400 years the oldest apparent ventilation age for the yd is 1600 years at 4250 m this strong contrast in ventilation which indicates a front between water masses of very different origin is similar to glacial profiles of nutrient like proxies this suggests that the lgm and yd modes of ocean circulation were the same

micrometer scale u pb age domains in eucrite zircons impact re setting and the thermal history of the hed parent body meteoritic zircons are rare but some are documented to occur in asteroidal meteorites including those of the howardite eucrite diogenite hed achondrite clan rubin a 1997 meteorit planet sci 32 231 247 the heds are widely considered to originate from the asteroid 4 vesta vesta and the other large main belt asteroids record an early bombardment history to explore this record we describe sub micrometer distributions of trace elements u th and 235 238 u 207 206 pb ages from four zircons 7 40lm separated from bulk samples of the brecciated eucrite millbillillie ultra high resolution 100 nm ion microprobe depth profiles reveal different zircon age domains correlative to mineral chemistry and to possible impact scenarios our new u pb zircon geochronology shows that vesta s crust solidified within a few million years of solar system formation 4561 13 ma in good agreement with previous work e g carlson r w lugmair g w 2000 timescales of planetesimal formation and differ entiation based on extinct and extant radioisotopes in canup r righter k eds origin of the earth and moon university of arizona press tucson pp 25 44 younger zircon age domains ca 4530 ma also record crustal processes but these are interpreted to be exogenous because they are well after the effective extinction of 26

ocean ventilation and sedimentation since the glacial maximum at 3 km in the western north atlantic 1 stable isotope sedimentological and radiocarbon data from cores at 3 km water depth on the blake ridge western subtropical north atlantic reveal the history of deep water ventilation since the last glacial maximum lgm bulk sediment accumulation rates varied locally by a factor of 2 under the influence of bottom currents in this sediment drift environment but the sand flux mostly foraminifera was nearly identical at a given time this suggests that the rain rate of foraminifera mostly planktonic was constant that transport of foraminifera was negligible and that current controlled differences in clay and silt transport drive bulk accumulation in two of the cores flux peaks in the benthic foraminifera cibicidoides and uvigerina peregrina occurred during the younger dryas yd cold event and at 18 2 19 6 21 1 25 0 and 28 1 ka radiocarbon measurements on those benthic foraminifera show the ventilation age of bottom waters was 1000 years during the yd and for older events it was as great as 2000 years these results contrast with holocene ventilation which was 500 years and 700 years at 1500 years and 7100 years before present respectively

39ar 40ar dating of mesosiderites evidence for major parent body disruption 4 ga ago 39ar 40ar ages were measured on 17 samples of 14 different mesosiderites and indicate major degassing of ar by one or more thermal events less than 4 0 ga ago three samples gave release patterns of constant age whereas the other samples typically showed 200 400 ma increases in 39ar 40ar age with increasing gas extraction temperature these stepwise releases indicate ages of 3 4 3 8 ga 1 ga 109 a averaged ages for individual meteorites are 3 45 3 82 ga no substantial evidence exists in the temperature releases for 39ar 40ar ages older than 4 0 ga and the ar ages appear to be in contradiction to 244pu fission track ages previously reported for a few mesosiderites the ar ages probably date the event that caused disturbance in previously reported rb sr sm nd and pb pb ages of estherville and other mesosiderites data on release of ar as a function of extraction temperature were used in arrhenius plots to estimate activation energies for ar diffusion of 18 52 kcal mol these values were then used to calculate closure temperatures against ar loss of 2 340 c and 180 600 c for assumed cooling rates of 1 c ma and 1 c a respectively the ar data suggest that for certain assumed models of mesosiderite formation the 39ar 40ar ages may date the time of formation of those metal textures in mesosiderites which have led others to calculate cooling rates of 1 c ma models which call for metal silicate mixing 4 5 ga ago followed by cooling at 1 c ma from temperatures 1150 c seem unlikely single event models which produce the silicate metal mixture at high temperatures rapidly cool the objects to temperatures of 500 c followed by cooling of 1 c ma and are not consistent with the ar data unless the thermal event occurred 500 c and left them deeply buried to undergo slow cooling

four thousand years of seismicity along the dead sea rift a study of major earthquake occurrence along the dead sea transform 35 5 36 5 e 27 2 37 5 n during the past four millenia has been attempted geological archaeological biblical historical and seismological evidence were integrated in an effort to quantify the space time distribution of seismicity in the said province the overall earthquake activity in the conterminous near east indicates a stable pattern and appeared to have been stationary over the examined time window about 110 earthquakes in the magnitude range 6 7 ml 8 3 affected the area during the past 2500 years of these 42 originated along the dead sea fault system itself while 68 were imported from the helenic cyprian arcs and the anatolian elburz zagros fault systems these events were responsible for the repeated destruction of many cultural centers in the dead sea region proper the major seismic activity since 2100 b c e before christian era has been confined to the vicinity of its eastern shore with extremal seismicity at its southern tip near the prehistorical site of bab a dara a 31 15 n 35 32 e this may constitute the first solid evidence that the biblical cities of the plain sodom gommorah etc were located there recent studies of earthquake deformations in the lisan deposits near bab a dara a agree with our findings at the present time a magnitude 6 earthquake is pending at the northern edge of the levant rift with its average recurrence interval 83 years exceeded by one standard deviation 32 years

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

terrigenous input and paleoproductivity in the southern ocean the geochemistry of several sites along the polar front zone of the southern ocean revealed significant changes in terrigenous input and productivity on glacial timescales our records indicate concentrations and fluxes of terrigenous elements i e fe al and ti are low during interglacials and increase tenfold to twentyfold during glacials phosphorus accumulation reactive p concentrations and p ti ratios exhibit similar trends as the terrigenous components suggesting increased export production during glacials in all cores elemental ratios remain relatively constant indicating terrigenous sources at each site have not likely varied over the past 250 kyr iron accumulation rates for these sites are 10 times higher during glacials than interglacials and exceed the estimated regional eolian fluxes by 50 times the source of this terrigenous material is thus likely to be hemipelagic rather than direct eolian input or ice rafting and we speculate fe upwelled from this source may have stimulated glacial productivity in the southern ocean

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

attenuation of ground motion spectral amplitudes and its variations across the central alborz mountains we selected 136 earthquakes recorded at stations of the institute of geo physics of the university of tehran igut during 1996 2007 in order to estimate the average attenuation parameters and variations of station corrections across the central alborz mountains the northern extension of the alpine himalayan orogeny in wes tern asia the selected events provide 1260 high signal to noise ratio snr records with relatively good spatial coverage we graphically find the distances at which the nature of geometrical spreading attenuation r b changes significantly using a locally weighted scatterplot smoothing lowess local regression smoothing method called robust lowess a trilinear function with hinges at distances of about 80 and 160 km describes the geometric spreading attenuation with distance by regressing to the hinged trilinear function we found that b1 1 15 0 21 b2 0 09 0 31 and a fixed b3 0 5 minimize the average absolute value of the fourier spectrum amplitude residuals using an anelastic attenuation coefficient at different frequencies the direct quality factor q in the central alborz region is obtained as q 109 2f 0 64 0 04 the geographical distribution of station corrections at 1 hz can be clearly separated along a dividing line connecting the north tehran mosha and attari faults into two regions the northern low attenuating and the southern high attenuating regions the stations with strong positive station corrections clearly align along the dividing line this suggests the existence of a higher attenuation zone south of the dividing line the presence of thick tertiary quaternary sedimentary rocks with thick layers of salt in the southern region may explain the observed greater attenuation of seismic waves

source parameters and scaling relationships of earthquakes in israel abstract determination of earthquake dynamic source parameters such as the seismic moment stress drop and rupture area are often based purely on theoretical considerations in reality however some of the corrected coefficients utilized in the computations should preferably be defined empirically in the present study 39 earthquakes of ml between 3 0 and 6 7 are used to define the correction coefficients associated with distance geometric and unelastic attenuation and ratios between zero frequency spectral amplitides of s waves recorded by vertical and horizontal seismographs these are used in turn to determine the seismic moment m0 and the empirical correlation between log m0 and ml magnitudes for that region the validity of using constant stress drop assumption and correlation between moment and corner frequency is also discussed

microseismicity of three locations along the jordan rift abstract from september 1981 until june 1984 a portable seismograph station array was in operation at three different locations along the jordan rift system covering a the dead sea area b the hula valley area and c the southern part of the arava valley based on the seismological data obtained by these arrays a comparison of the microseismic activity in these areas is made these observations are also compared with the data from the countrywide network issn some preliminary conclusions regarding the seismicity of the investigated areas and the performance of the arrays are suggested

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

relationship between antarctic sea ice and southwest african climate during the late quaternary here we compare late quaternary southwest african climate records from the west coast of southern africa published winter rainfall and trade wind intensity records from a core off the coast of namibia to records of antarctic sea ice extent this comparison reveals coherent changes between antarctic sea ice extent and the southwest african winter rain region since 45 k y b p with enhanced winter rainfall and trade wind vigor during periods of increased sea ice presence we propose an oceanic and atmospheric coupling between antarctic sea ice and the winter rainfall zone of southwest africa that may lead to increased desertification in the region if global warming persists

u pb and 207pb 206pb ages of zircons from basaltic eucrites implications for early basaltic volcanism on the eucrite parent body we have undertaken petrologic and shrimp u th pb isotopic studies on zircons from basaltic eucrites yamato y 75011 y 792510 asuka a 881388 a 881467 and padvarninkai with different thermal and shock histories eucritic zircons are associated with ilmenite in most cases and have subhedral shapes in unmetamorphosed and metamorphosed eucrites some zircons in highly metamorphosed eucrites with granulitic texture occur alone in pyroxene and typically have rounded to subrounded shapes due to recrystallization superchondritic zr hf ratios of eucritic zircons indicate that they crystallized from incompatible element rich melts after crystallization of ilmenite concentrations of uranium and thorium in zircons in the unmetamorphosed eucrite y 75011 are higher than those in metamorphosed eucrites the u pb systems of eucritic zircons are almost concordant but some zircon grains show reverse discordance radiogenic lead loss up to 48 from zircons is observed in the shock melted eucrite padvarninkai the 207pb 206pb ages of zircon in y 75011 4550 9 ma n 5 are nearly identical within analytical uncertainty to the ages of zircons from the metamorphosed eucrite y 792510 4545 15 ma n 13 the highly metamorphosed eucrites a 881388 4555 54 ma n 5 and a 881467 4558 13 ma n 8 and the shock melted eucrite padvarninkai 4555 13 ma n 18 the averaged 207pb 206pb age of zircon from five eucrites analyzed in this study is 4554 7 ma 95 confidence limits n 49 indistinguishable from the averaged u pb age 4552 9 ma of the same samples because of the high closure temperature of lead in zircon tclosure 1050 c with a cooling rate of 0 2 c yr the 207pb 206pb ages of eucritic zircon do not represent metamorphic ages but crystallization ages of extrusive lavas this fact strongly suggests that volcanism of the eucrite parent body occurred at a very early stage of the solar system history 7 20 ma after cai formation 4567 2 0 6 ma thus basaltic eucrites crystallized from parental magmas within a short interval following the differentiation of their parent body the u pb ages of eucritic zircons are older than the u pb sm nd and rb sr ages of some basaltic eucrites which is consistent with differences in closure temperatures of each isotopic system and suggests that thermal and shock metamorphism affected the isotopic systems of pyroxene plagioclase and phosphates

heat flow and continental breakup the gulf of elat aqaba heat flow measurements were made at five sites in the major basins of the gulf of elat aqaba northern red sea the gulf is located at the southern portion of the dead sea rift which is a transform plate boundary vertical temperature gradients were measured with a probe which allows multiple penetration of the bottom during a single deployment and thermal conductivities were determined by needle probe measurements on sediment cores a mean heat flux of about 80 mwm 2 was found and the values tend to increase from north to south this latitudinal gradient corresponds to the general trend of gradual thinning of the continental crust of the gulf toward the red sea where oceanic crust exists the heat flow data together with other geophysical data are consistent with a propagation of rifting from the red sea northward along the dead sea rift where the fractures are primarily shear the gulf forms a transition between these two tectonic regimes extensional red sea to the south and transform dead sea to the north

hf w internal isochrons for ordinary chondrites and the initial 182hf 180hf of the solar system abstract three ordinary chondrites forest vale h4 ste marguerite h4 and richardton h5 have been studied with 182 hf 182 w system t1 2 9 million years m y in order to provide constraints on the initial 182 hf 180 hf for the chondritic parent body and the solar system all three samples display positive correlations between 182 w 184 w and 180 hf 184 w providing confirmation that live 182 hf was present in these samples the best fit lines define comparable slopes passing through or close to the data for the bulk carbonaceous chondrites allende and murchison at the current level of resolution this indicates a common and well mixed chondritic reservoir in terms of the hf w isotope system forest vale yields the most precise results with an apparent initial 182 hf 180 hf of 1 87 0 16 10 4 and an initial 182 w 184 w of 0 864710 15 if the pb pb phosphate age of forest vale 5 m y younger than the pb pb age of allende cai is a formation age the bulk solar system initial 182 hf 180 hf is estimated to be 2 75 0 24 10 4 comparable to previous estimates based on the differences in w isotopic compositions between iron meteorites and the mean of carbonaceous chondrites the solar system 182 w 184 w initial of 0 86457 4 ew 4 99 0 46 is similar to the least radiogenic w reported for iron meteorites suggesting an extremely early origin of their parent bodies and the segregation of metallic cores from planetesimals the solar system 182 hf 180 hf initial obtained in this study is high relative to the initial abundances of other short lived nuclides including those with longer half lives such as 129 i t1 2 16 m y however this result is explicable with the model of wasserburg et al wasserburg g j busso m gallino r 1996 abundances of actinides and short lived nonactinides in the interstellar medium diverse supernova sources for the r processes astrophys j 466 l109 113 who have proposed that 182 hf is synthesized in the same r process supernovae events that produced the actinides over most of galactic history

modern u pb chronometry of meteorites advancing to higher time resolution reveals new problems in this paper we evaluate the factors that influence the accuracy of lead pb isotopic ages of meteorites and may possibly be responsible for inconsistencies between pb isotopic and extinct nuclide timescales of the early solar system instrumental mass fractionation and other possible analytical sources of error presence of more than one component of non radiogenic pb migration of ancient radiogenic pb by diffusion and other mechanisms possible heterogeneity of the isotopic composition of uranium u uncertainties in the decay constants of uranium isotopes possible presence of freshly synthesized actinides with short half life e g 234u in the early solar system possible initial disequilibrium in the uranium decay chains and potential fractionation of radiogenic pb isotopes and u isotopes caused by alpha recoil and subsequent laboratory treatment we review the use of 232th 238u values to assist in making accurate interpretations of the u pb ages of meteorite components we discuss recently published u pb dates of calcium aluminum rich inclusions cais and their apparent disagreement with the extinct nuclide dates in the context of capability and common pitfalls in modern meteorite chronology finally we discuss the requirements of meteorites that are intended to be used as the reference points in building a consistent time scale of the early solar system based on the combined use of the u pb system and extinct nuclide chronometers

northridge earthquake damage caused by geologic focusing of seismic waves despite being located 21 kilometers from the epicenter of the 1994 northridge earthquake magnitude 6 7 the city of santa monica experienced anomalously concentrated damage with mercalli intensity ix an intensity as large as that experienced in the vicinity of the epicenter seismic records from aftershocks suggest that the damage resulted from the focusing of seismic waves by several underground acoustic lenses at depths of about 3 kilometers formed by the faults that bound the northwestern edge of the los angeles basin the amplification was greatest for high frequency waves and was less powerful at lower frequencies which is consistent with focusing theory and finite difference simulations

high resolution holocene n2o ice core record and its relationship with ch4 and co2 1 nitrous oxide n 2 o concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today s interglacial and for one of the fast climate variations during the last ice age little is known however about possible n 2 o variations during the more stable climate of the present interglacial holocene spanning the last 11 thousand years here we fill this gap with a high resolution n 2 o record measured along the european project for ice coring in antarctica epica dome c antarctic ice core on the same ice we obtained high resolution methane and carbon dioxide records this provides the unique opportunity to compare variations of the three most important greenhouse gases after water vapor without any uncertainty in their relative timing the co 2 and ch 4 records are in good agreement with previous measurements on other ice cores the n 2 o concentration started to decrease in the early holocene and reached minimum values around 8 ka 260 ppbv before a slow increase to its preindustrial concentration of 265 ppbv

a revised age for the kawakawa oruanui tephra a key marker for the last glacial maximum in new zealand abstract the kawakawa oruanui tephra kot is a key chronostratigraphic marker in terrestrial and marine deposits of the new zealand nz sector of the southwest pacific erupted early during the last glacial maximum lgm the wide distribution of the kot enables inter regional alignment of proxy records and facilitates comparison between nz climatic variations and those from well dated records elsewhere we present 22 new radiocarbon ages for the kot from sites and materials considered optimal for dating and apply bayesian statistical methods via oxcal4 1 7 that incorporate stratigraphic information to develop a new age probability model for kot the revised calibrated age 2 standard deviations for the eruption of the kot is 25 360 160 cal yr bp the age revision provides a basis for refining marine reservoir ages for the lgm in the southwest pacific

sequence of events during the last deglaciation in southern ocean sediments and antarctic ice cores variation depends on the age model as 14 c determinations cannot be obtained for the time interval of 29 5 14 5 ka assuming a constant sedimentation rate for this interval our data suggest that sea ice and nutrient changes at about 19 ka b p lead the increase in atmospheric pco2 by approximately 2000 years our diatom based sea ice record is in phase with the sodium record of the vostok ice core which is related to sea ice cover and similarly leads the increase in atmospheric co2 if gas exchange played a major role in determining glacial to interglacial co2 variations then a delay mechanism of a few thousand years is needed to explain the observed sequence of events otherwise the main cause of atmospheric pco2 change must be sought elsewhere rather than in the southern ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes 9325 information related to geographic region atlantic ocean keywords biogenic opal stable isotopes diatoms ird last glacial southern ocean

crustal structure of the levant basin eastern mediterranean abstract a seismic refraction wide angle reflection experiment was undertaken in the levant basin eastern mediterranean two roughly east west profiles extend from the continental shelf of israel toward the levant basin the northern profile crosses the eratosthenes seamount and the southern profile crosses several distinct magnetic anomalies the marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources the results of this study strongly suggest the existence of oceanic crust under portions of the levant basin and continental crust under the eratosthenes seamount the seismic refraction data also indicate a large sedimentary sequence 10 14 km thick in the levant basin and below the levant continental margin assuming the crust is of cretaceous age this gives a fairly high sedimentation rate the sequence can be divided into several units a prominent unit is the 4 2 km s layer which is probably composed of the messinian evaporites overlying the evaporitic layer are layers composed of plio pleistocene sediments whose velocity is 2 0 km s the refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single layer oceanic crust takes place along the levant margin the transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual the northern profile north of the carmel structure presents a different structure the continental crust is much thinner there and the transition in the crustal structure is more rapid the crustal thinning begins under western galilee and terminates at the continental slope the results of the present study indicate that the levant basin is composed of distinct crustal units and that the levant continental margin is divided into at least two provinces of different crustal structure

extensive phytoplankton blooms in the atlantic sector of the glacial southern ocean 1 the sources and sinks of atmospheric carbon dioxide over glacial interglacial cycles are under debate variation in productivity of the antarctic circumpolar current acc could potentially play a significant role but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today we present areal and down core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire atlantic sector of the acc particularly in the seasonal ice zone siz linked to higher iron input during the last glacial sea ice acts as an effective transporter of iron and enhances its bioavailability the dominance of the deep living radiolarian cyladophora davisiana in glacial siz sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today

fault geometry and spatial clustering of microearthquakes along the dead sea jordan rift fault zone abstract earthquakes 1 0 m l 5 3 in the region around the dead sea jordan rift fault zone recorded by the israel scismograph station network issn from 1982 until the beginning of 1989 have been analyzed and interpreted the scismicity pattern clearly reveals activity along three fault zones the dead sea jordan rift fault zone the carmel faraa fault zone and the central sinai negev shear zone microearthquake occurrence tends to cluster in or near tensional features rhomb shaped grabens such as the hula sea of gallilee and dead sea depressions further eight representative focal mechanisms of individual earthquakes or earthquake clusters have been derived the seismicity and focal mechanism solutions near the branching of the carmel faraa and the dead sea jordan rift fault zones suggest a complicated tectonic breakup in this region microearthquakes in the arava may indicate a more complex pattern of active faults than was previously assumed

crustal and upper mantle structure across the dead sea rift and israel from teleseismic p wave tomography and gravity data abstract new findings of the structure of the crust and the upper mantle across the dead sea rift and israel were obtained by applying p and pkp wave relative travel time residuals inversion of 612 teleseisms recorded by the seismic networks in israel and jordan independently of the relative teleseismic travel time residuals the bouguer gravity anomalies were used as an additional aid to examine the structure of the crust and upper mantle an examination of the teleseismic travel time residuals in israel suggests the existence of two prominent provinces of distinct crustal structure the northward increase of the teleseismic travel time residuals is in good agreement with a gradual thickening of the sedimentary sequence and a simultaneous thinning of the crust examination of the inverted velocity anomalies indicates that the upper and lower crusts are sub divided into a number of structures we identify several velocity anomalies that are associated with prominent geological structures the southern dead sea basin is characterized with the largest decrease of velocity in both upper and lower crustal layers due to the infilling of light material relative to the surrounding material the velocity anomaly in the carmel structure is probably associated with variations in the upper part of the upper mantle examination of a cross section that traverses the dead sea transform supports the existence of lighter mass density material on the eastern side relative to that on the western side

crustal structure of israel constraints from teleseismic and gravity data summary the structure of the crust in israel was studied using p wave traveltime residuals of 169 teleseisms recorded by a seismic network throughout the country independently of the teleseismic residuals the bouguer gravity anomalies were used as an additional aid to examine the structure of the crust the average time difference between the traveltime residuals in the north and in the south of israel is up to 0 2s three distinct provinces are observed in the teleseismic residuals with distinct boundareis at 31 5 n and 30 25 n similar differences of traveltime residuals were derived for each of the four principal azimuth quadrants most of the difference in traveltime residuals between northern and southern israel can be explained by changes in the sedimentary thickness we suggest that the structure of the northern province is significantly different from the central or the southern provinces if the moho shallows by about 13 15 km along the profile as was previously suggested by seismic refraction data a thickening of the sedimentary sequence to about 15 km in the northern province is needed to satisfy the traveltime residuals similar results are obtained if the bouguer gravity anomalies due to the thickening sediments and the rise of the moho depth are modelled in the eilat region the sedimentary sequence thins in the sse direction from the negev to the gulf of eilat implying a decrease of the moho in the southward direction by about 10 km in agreement with the crustal refraction studies

differentiation and magmatic activity in vesta evidenced by 26al 26mg dating in eucrites and diogenites abstract the 26 al 26 mg short lived chronometer has been widely used for dating ancient objects in studying the early solar system here we use this chronometer to investigate and refine the geological history of the asteroid 4 vesta ten meteorites widely believed to come from vesta 4 basaltic eucrites 3 cumulate eucrites and 3 diogenites and the unique achondrite asuka 881394 were selected for this study all samples were analyzed for their 26 mg and 27 al 24 mg ratios in order to construct both whole rock and model whole rock isochrons mineral separation was performed on 8 of the hed s in order to obtain internal isochrons while whole rock al mg analyses of hed s plot on a regression that could be interpreted as a vestan planetary isochron internal mineral isochrons indicate a more complex history crystallization ages obtained from internal 26 al 26 mg systematic in basaltic eucrites show that vesta s upper crust was formed during a short period of magmatic activity at 2 66 0 58 1 39 million years ma after calcium aluminum inclusions after cai we also suggest that impact metamorphism and subsequent age resetting could have taken place at the surface of vesta while 26 al was still extant cumulate eucrites crystallized progressively from 5 48 0 60 1 56 to 7 25 ma after cai model ages obtained for both basaltic and cumulate eucrites are similar and suggest that the timing of differentiation of a common eucrite source from a chondritic body can be modeled at 2 88 0 12 0 14 ma after cai i e contemporaneously from the onset of the basaltic eucritic crust based on their cumulate texture we suggest cumulate eucrites were likely formed deeper in the crust of vesta diogenites have a more complicated history and their 26 al 26 mg systematics show that they likely formed after the complete decay of 26 al and thus are younger than eucrites this refined chronology for eucrites and diogenites is consistent with a short magma ocean stage on 4 vesta from which the basaltic eucrites rapidly crystallized in order to explain the younger age and the complex history of diogenites we postulate that a second episode of magmatism was possibly triggered by a mantle overturn we bring a refined chronology of the geological history of vesta that shows that the asteroid has known a more complex differentiation than previously thought

characterization of earthquake induced ground motion from the l aquila seismic sequence of 2009 italy summary based only on weak motion data we carried out a combined study on region specific source scaling and crustal attenuation in the central apennines italy our goal was to obtain a reappraisal of the existing predictive relationships for the ground motion and to test them against the strong motion data peak ground acceleration pga peak ground velocity pgv and spectral acceleration sa gathered during the mw 6 15 l aquila earthquake 2009 april 6 01 32 utc the l aquila main shock was not part of the predictive study and the validation test was an extrapolation to one magnitude unit above the largest earthquake of the calibration data set the regional attenuation was determined through a set of regressions on a data set of 12 777 high quality high gain waveforms with excellent s n ratios 4259 vertical and 8518 horizontal time histories seismograms were selected from the recordings of 170 foreshocks and aftershocks of the sequence the complete set of all earthquakes with ml 3 0 from 2008 october 1 to 2010 may 10 all waveforms were downloaded from the iside web page http iside rm ingv it iside standard index jsp a web site maintained by the istituto nazionale di geofisica e vulcanologia ingv weak motion data were used to obtain a moment tensor solution as well as a coda based moment rate source spectrum for each one of the 170 events of the l aquila sequence 2 8 mw 6 15 source spectra were used to verify the good agreement with the source scaling of the colfiorito seismic sequence of 1997 1998 recently described by malagnini et al 2008 finally results on source excitation and crustal attenuation were used to produce the absolute site terms for the 23 stations located within 80 km of the epicentral area the complete set of spectral corrections crustal attenuation and absolute site effects was used to implement a fast and accurate tool for the automatic computation of moment magnitudes in the central apennines

trace metal evidence for a poorly ventilated glacial southern ocean abstract glacial benthic 13c and 14c measurements from the atlantic ocean have been interpreted to indicate the existence of a poorly ventilated southern ocean with greater co2 and nutrient contents compared to present enhanced storage of co2 in the deep ocean predicts that oxygen concentrations should have declined at the same time a prediction increasingly supported by evidence for oxygen depletion in the glacial southern ocean here we take a novel approach by using a suite of redox sensitive trace metals ag cd re and mo to show that southern ocean sediments from two cores in the atlantic sector were suboxic during and prior to deglaciation implying changes to ocean circulation and or elevated export production that significantly altered deep water chemistry in the cape basin enrichments of the authigenically deposited trace metal re are comparable to those found in oxygen minimum zones pointing to substantial decreases in oxygenation furthermore trace metal results suggest potential spatial heterogeneity in the glacial southern ocean and a more complicated oceanographic and oxygenation history than has previously been assumed

new w isotope evidence for rapid terrestrial accretion and very early core formation the short lived hf 182 w 182 isotope system is an ideal clock to trace core formation and accretion processes of planets planetary accretion and metal silicate fractionation chronologies are calculated relative to the chondritic hf 182 w 182 isotope evolution here we report new high precision w isotope data for the carbonaceous chondrite allende that are much less radiogenic than previously reported and are in good agreement with published internal hf w chronometry of enstatite chondrites if the w isotope composition of terrestrial rocks representing the bulk silicate earth is homogeneous and 2 24 epsilon 182w units more radiogenic than that of the bulk earth metal silicate differentiation of the earth occurred very early the new w isotope data constrain the mean time of terrestrial core formation to 34 million years after the start of solar system accretion early terrestrial core formation implies rapid terrestrial accretion thus permitting formation of the moon by giant impact while hf 182 was still alive this could explain why lunar w isotopes are more radiogenic than the terrestrial value copyright c 2002 elsevier science ltd

is pore water oxygen content decoupled from productivity on the california margin trace element results from ocean drilling program hole 1017e san lucia slope california 1 trace element evidence from the california margin ocean drilling program hole 1017e shows significant changes in sediment redox chemistry at intermediate water depths over the last 60 kyr the influence of export production on intermediate water oxygen content can be distinguished from lateral ventilation through comparisons among proxies representing export production flux percent corg and sediment surface i br and pore water mo ag cd re and u oxygenation proxies sulfate reduction within the uppermost sediment column occurred during late quaternary interstadials and the holocene indicating reduced intermediate water ventilation however sulfate reduction was most intense during major interstadials when productivity was enhanced decoupling between export production and pore water oxygen content is demonstrated during deglaciation when the sediment pore water oxygen content increases without a corresponding reduction in export productivity thus both export production and intermediate water ventilation play a role in oxygen minimum zone processes on the california margin

th pb ion microprobe dating of allanite allanite which is a common accessory mineral in a wide variety of rock types typically contains high concentrations of th and u thus an in situ method of u th pb dating of this phase would have broad application we describe a method to permit th pb ages of allanite to be determined with approximately 10 accuracy using a high resolution ion microprobe knowledge of the composition and substitution mechanisms of this complex mineral is key to understanding the relative ion ization efficiencies of th and pb the chemical compositions of three allanite samples used as age standards cima d asta pluton 275 5 1 5 ma atesina volcanic complex 276 3 2 2 ma la posta pluton 94 2 ma were determined using an electron microprobe permitting an assessment of matrix effects on ionization an ion microprobe calibration curve involving elemental and oxide species of th and pb i e 208 pb th vs tho 2 th yields highly scattered apparent ages when allanite age standards with different fe contents are used however a three dimensional plot of 208 pb th vs tho 2 th vs feo sio improves the accuracy of the calibration to about 10 even though this level of uncertainty is substantially greater than that expected for u th pb ion microprobe analyses of zircon or monazite th pb ages of allanite can still be used to address important geologic questions we used this method to date two metamorphic allanite grains from the footwall of the main central thrust nepal himalaya and an allanite grain from the pacoima canyon pegmatite california allanite inclusions in garnet from nepal yield significantly older ages than the coexisting monazite indicating that allanite formation in these rocks records a previous metamorphic cycle that predates slip along the fault the pacoima canyon allanite grain yields a younger age than that reported for zircon implying pb loss during cooling of the pegmatite

observations of basin ground motions from a dense seismic array in san jose california we installed a dense array of 41 digital seismographs in san jose california to evaluate in detail the effects of a deep sedimentary basin and shallow sedimentary deposits on earthquake ground motions this urban array is located near the eastern edge of the santa clara valley and spans the evergreen sedimentary basin identified by gravity data average station spacing is 1 km with three stations initially spaced 110 m apart despite the high noise urban environment the stations of the array successfully triggered on and recorded small local earthquakes m 2 5 2 8 at 10 25 km distance and larger regional events such as the m 5 0 bolinas earthquake 90 km distance m 4 6 5 6 earthquakes near mammoth lakes 270 km distance m 4 9 5 6 events in western nevada 420 km distance and the m 7 1 hector mine earthquake 590 km distance maps of spectral ratios across the array show that the highest amplitudes in all frequency bands studied 0 125 8 hz are generally observed at stations farther from the eastern edge of the santa clara valley larger spectral amplitudes are often observed above the western edge of the evergreen basin snapshots of the recorded wavefield crossing the array for regional events to the east reveal that large low frequency 0 125 0 5 hz arrivals after the s wave travel from south to north across the array a moving window cross correlation analysis finds that these later arrivals are surface waves traveling from the south the timing and propagation direction of these arrivals indicates that they were likely produced by scattering of incident s waves at the border of the santa clara valley to the south of the array it is remarkable that the largest low frequency phases at many of the valley sites for regional events to the east are basin surface waves coming from a direction about 70 degrees different from that of the epicenters basin surface waves emanating from the eastern edge of the valley are also identified by the cross correlation analysis

mobility of authigenic rhenium silver and selenium during postdepositional oxidation in marine sediments sedimentary records of redox sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions records of re can reveal the intensity of past reducing conditions in sediments at the time of deposition whereas records of ag may record the magnitude of past diatom fluxes to the seafloor confidence in paleoenvironmental reconstruction from records of either metal however requires it to have experienced negligible redistribution since deposition this study examines diagenetic rearrangements of re and ag that occur in response to exposure to bottom water o2 in environments of low sedimentation rate including madeira abyssal plain turbidites and eastern mediterranean basin sapropels authigenic re was remobilized quantitatively by oxidation but poorly retained by the underlying sediments all records are consistent with previous work demonstrating that only a limited reimmobilization of re occurs preferentially in corg rich reducing sediments silver was also mobilized quantitatively by oxidation but it was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts and these peaks remain immobile in anoxic conditions during long term burial comparison of ag s and se records from various cores suggests that ag is likely to have been immobilized as a selenide a mechanism previously proposed for hg in similar situations mercone et al 1999 coexisting narrow peaks of ag and hg with se offer a means of assessing whether oxidative burndown has ever occurred at the top of corg and sulfide rich sedimentary units although these results suggest that caution must be used when inferring paleoenvironmental information from records of ag and re in cores with low sediment accumulation rates 5 cm ka 1 they should not affect the promise that authigenic ag and re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously

sims pb pb and u pb age determination of eucrite zircons at 5 μm scale and the first 50 ma of the thermal history of vesta eucrites a subgroup of basaltic achondrites represent the remnants of the earliest magmatic stage of the solar system formation possibly on the asteroid 4 vesta the precise determination of their crystallization age is therefore important for constraining the evolutionary history of the asteroid including melting and differentiation processes of the parent body zircons would be the best mineral for such purpose however extra terrestrial zircons are rare and those found in eucrites are typically small 5 m using a cameca ims 1280 high resolution ion microprobe precise uranium lead u pb and pb pb ages of the non cumulate basaltic eucrite zircons in bereba cachari caldera camel donga and juvinas were determined successfully at scale of 5 m we obtained a weighted average 207pb 206pb age of 4541 11 ma and u pb concordia age of 4525 24 ma for the five eucrite samples studied a synthesis of available age data of howardites eucrites and diogenites indicate a protracted magmatic history on vesta with a most pronounced core mantle differentiation event marked at 4564 2 ma followed by a peak of basaltic magmatism at 4552 7 ma which gradually diminished over the next 50 ma thermal modeling of vesta suggests that partial melt fraction of greater than 10 with temperature well exceeding 1500 k could be maintained over this period throughout its interior this is consistent with the chronological records of eucrites suggesting persistent magmatism on vesta during the first 50 ma in the early solar system

a model for uranium rhenium and molybdenum diagenesis in marine sediments based on results from coastal locations abstract the purpose of this research is to characterize the mobilization and immobilization processes that control the authigenic accumulation of uranium u rhenium re and molybdenum mo in marine sediments we analyzed these redox sensitive metals rsm in benthic chamber pore water and solid phase samples at a site in buzzards bay massachusetts usa that has high bottom water oxygen concentrations 230 300 mol l and high organic matter oxidation rates 390 mol c cm2 y the oxygen penetration depth varies from 2 to 9 mm below the sediment water interface but pore water sulfide is below detection release of rsm to pore waters during the remineralization of solid phases occurs near the sediment water interface at depths above the zone of authigenic rsm formation this release occurs consistently for mo at both sites but only in the winter for re in buzzards bay and intermittently for u at the buzzards bay site re removal to the solid phase extends to the bottom of the profile while the zone of removal is restricted to 2 9 cm for u and mo authigenic re formation is independent of the anoxic remineralization rate which is consistent with an abiotic removal mechanism the rate of authigenic u formation and its modeled removal rate constant increase with increasing anoxic remineralization rates and is consistent with u reduction being microbially mediated authigenic mo formation is related to the formation of sulfidic microenvironments the depth and extent of mo removal from pore water is closely associated with the balance between iron and sulfate reduction and the consumption of pore water sulfide via iron sulfide formation pore water rsm reach constant asymptotic concentrations in sulfidic sediments but only pore water re is constant at depth in buzzards bay the increases in pore water u at the buzzards bay site are consistent with addition via irrigation and subsequent upward diffusion to the removal zone deep pore water mo concentrations exceed its bottom water concentration due to irrigation induced oxidation and remobilization from the solid phase in sulfidic sediments there is no evidence for higher pore water u or mo concentrations at depth due to the absence of irrigation and or the presence of more stable authigenic rsm phases there are good correlations between benthic fluxes and authigenic accumulation rates for u and mo in sulfidic sediments however results from buzzards bay suggest irrigation ultimately results in the partial loss of u and mo from the solid phase with accumulation rates that are 20 30 of the modeled flux irrigation can augment re possibly u or compromise u mo authigenic accumulation in sediments and is important when determining burial rates in continental margin sediments

abyssal atlantic circulation during the last glacial maximum constraining the ratio between transport and vertical mixing transport to vertical diffusivity in the deep atlantic our calculations suggest that the ratio was at least twice as large at the lgm we speculate that the primary cause was reduced mixing between northern and southern component waters associated with movement of this water mass boundary away from the zone of intense mixing near the seafloor the shallower water mass boundary yields an order of magnitude increase in the volume of southern component water suggesting its residence time may have increased substantially our analysis supports the idea that an expanded volume of antarctic bottom water and limited vertical mixing enhanced the abyssal ocean s ability to trap carbon during glacial times

displaced terranes and crustal evolution of the levant and the eastern mediterranean geophysical data from the levant and the eastern mediterranean suggest that this area can be divided into distinct crustal units of different origins for example a marked difference in crustal structure and structural style exists in the levant between samaria and judea south of the carmel structure and the galilee and lebanon north of it on the other hand several microcontinental fragments such as cyprus and the eratosthenes and anaximander seamounts are embedded within the oceanic crust of the eastern mediterranean the present location of these units has resulted from complex tectonic processes which were active during the mid paleozoic mesozoic evolution of this area during this period several crustal units were accreted to the northern margin of africa while others were detached away from it the crustal evolution of the eastern mediterranean and the levant is intimately linked with the closure of the paleo tethys the formation of the neo tethys and its subsequent closure

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation antarctic ice core data reveal that the atmosphere experienced abrupt centennial increases in co2 concentration during the last deglaciation 18 thousand to 11 thousand years ago establishing the role of ocean circulation in these changes requires high resolution accurately dated marine records here we report radiocarbon data from uranium thorium dated deep sea corals in the equatorial atlantic and drake passage over the past 25 000 years two major deglacial radiocarbon shifts occurred in phase with centennial atmospheric co2 rises at 14 8 thousand and 11 7 thousand years ago we interpret these radiocarbon enriched signals to represent two short lived less than 500 years overshoot events with atlantic meridional overturning stronger than that of the modern era these results provide compelling evidence for a close coupling of ocean circulation and centennial climate events during the last deglaciation