ground motion modeling of the 1906 san francisco earthquake part ii ground motion estimates for the 1906 earthquake and scenario events abstract we estimate the ground motions produced by the 1906 san francisco earthquake making use of the recently developed song et al 2008 source model that combines the available geodetic and seismic observations and recently constructed 3d geologic and seismic velocity models our estimates of the ground motions for the 1906 earthquake are consistent across five ground motion modeling groups employing different wave propagation codes and simulation domains the simulations successfully reproduce the main features of the boatwright and bundock 2005 shakemap but tend to over predict the intensity of shaking by 0 1 0 5 modified mercalli intensity mmi units velocity waveforms at sites throughout the san francisco bay area exhibit characteristics consistent with rupture directivity local geologic conditions e g sedimentary basins and the large size of the event e g durations of strong shaking lasting tens of seconds we also compute ground motions for seven hypothetical scenarios rupturing the same extent of the northern san andreas fault considering three additional hypocenters and an additional random distribution of slip rupture directivity exerts the strongest influence on the variations in shaking although sedimentary basins do consistently contribute to the response in some locations such as santa rosa livermore and san jose these scenarios suggest that future large earthquakes on the northern san andreas fault may subject the current san francisco bay urban area to stronger shaking than a repeat of the 1906 earthquake ruptures propagating southward towards san francisco appear to expose more of the urban area to a given intensity level than do ruptures propagating northward

a sulfate control on marine mid depth euxinia on the early cambrian ca 529 521 ma yangtze platform south china abstract given the high oxygen demands of complex metazoans a sound understanding of marine redox conditions is essential to reconstruct the factors that lead to the dramatic increases in ecosystem complexity and biological diversity in the early cambrian in this study we report new fe mo c s geochemical data from black shale rich strata of the early cambrian continental margin yangjiaping section in the yangtze platform south china integrated fe speciation and mo abundance data from the yangjiaping section in combination with previously reported data from shatan inner shelf songtao slope and longbizui basinal sections suggest mid depth euxinic waters coexisting with ferruginous deep waters and oxic surface waters this redox structure is similar to conditions previously suggested for the ediacaran yangtze platform and other proterozoic marine basins indicating that proterozoic layered ocean redox structure in some basins persisted into the early cambrian furthermore the fe mo data demonstrate that the mid depth euxinia was widespread during a marine transgression but shrank gradually along with widespread shelf oxygenation when the basin evolved into subsequent regression excess highly reactive iron fe hr in deep water with a hydrothermal origin may have had a control on the mid depth euxinia given geochemical and geological evidence for basinal hydrothermal activities on the other hand a sulfate limitation on bacterial sulfate reduction bsr and sulfide generation was suggested by a weak correlation r 2 0 22 between pyrite iron versus fe hr and total organic carbon toc form anoxic deep water sections and high toc averagely 6 in the deepest ferruginous water longbizui section furthermore a spatial gradient was observed in sulfur isotopic composition of pyrite averagely from 0 2 to 21 0 consistent with a lateral gradient of sulfate in concentration or and in isotope from shore to distal waters on the transgressive yangtze platform we accordingly proposed that two distinct sources riverine input and ocean reservoir provided sulfate for bsr dominantly in near shore and distal areas respectively and the euxinic retreat observed for the regression can be explained as a response to the progressive sulfate consumption of the ocean reservoir by intensive bsr and pyrite formation during preceding transgression therefore our results support a sulfate control on the spatiotemporal distribution of mid depth marine euxinia on the yangtze platform in early cambrian when complex metazoans rapidly evolved

finite fault inversion of dinsar coseismic displacement of the 2009 l aquila earthquake central italy 1 we define the geometric and kinematic characteristics of the fault activated during the mw 6 3 6 april 2009 l aquila earthquake from the modeling of envisat and cosmo skymed the first ever x band interferogram inverted for a coseismic dislocation study dinsar interferograms our best fit solution for the main shock is represented by a normal fault 16 km long and 12 km wide with a small right lateral component dipping 47 sw with a maximum slip of 90 cm although the seismic dislocation probably ended at 1 km depth the updip projection of the fault plane corresponds to the northern segment of the mapped paganica s demetrio fault where alignment of surface breaks was observed in the field the absence of this fault in existing seismic source catalogues suggests that an improved approach involving detailed surface and subsurface geological and geophysical investigations is needed for a better assessment of the seismic hazard at the local scale

paleoenvironmental conditions of organic rich upper permian dalong formation shale in the sichuan basin southwestern china abstract organic geochemical and trace element analysis of a suite of 33 samples collected from the shangsi section of the upper permian dalong formation located near guangyuan in the northwestern sichuan basin have been used to better understand the marine depositional environment of its shale lithofacies a 15 m thick black shale interval near the middle of the formation is enriched in total organic carbon toc 1 1 14 4 mean 6 4 the n alkane terpane and sterane biomarker distributions of the shale suggest that its organic matter is of predominantly marine algal origin pr ph pr n c17 ph n c18 and gammacerane c30 hopane ratios demonstrate that reducing conditions prevailed during its deposition this interpretation is supported by the redox sensitive abundance of mo and the trace element redox ratios ni co v cr u th and v v ni all of which indicate deposition in a euxinic anoxic setting the mo toc relationship in the dalong shales plots mid way between those of sediments in the present day saanich inlet and cariaco basin suggesting a moderately restricted depocentre however the 13corg values of these shales reveal that their organic matter is isotopically much lighter than that found in modern euxinic sediments implying extremely anoxic bottom waters and a slow down of oceanic circulation during the late permian

regression of martian north polar cap 1990 1997 hubble space telescope observations abstract hubble space telescope imaging of mars from december 13 1990 through april 17 1997 has resulted in the synoptic monitoring of parts of four consecutive martian north polar cap regressional cycles spanningls 335 65 tols 144 56 the 1990 1993 observations were obtained with the wide field planetary camera 1 wfpc1 instrument while subsequent observations from 1994 to 1997 were obtained with the improved optics of the wide field planetary camera 2 wfpc2 mars observations were obtained from the ultraviolet 218 nm to the near infrared 1042 nm which has allowed us to constrain the effects of clouds and dust particulates on cap edge measurements hst observations of the polar cap regressions afterls 0 are fairly consistent from year to year with some variations possible beforels 0 the 1991 observations atls 35 25 andls 59 88 in the longitude range 270 280 possibly support a standstill in cap retreat at a latitude 70 n the standstill in cap retreat reported in previous years at a latitude 67 n was not observed in 1992 1997 comparison with previous ground based and spacecraft observations suggests that interannual variations may be significant they may be due to interannual atmospheric changes such as global dust storm activity lambert albedos of the north polar cap in red and violet bandpasses are similar to those reported before

new c isotope stratigraphy from southwest china implications for the placement of the precambrian cambrian boundary on the yangtze platform and global correlations a high resolution c isotope profile from a fossiliferous section spanning the precambrian cambrian pc c boundary on the yangtze platform southwest china is used to constrain c isotope chemostratigraphy and its global correlation the discovery of a strong negative c isotopic anomaly just below the china marker a indicates that this negative anomaly can be correlated globally and demonstrates that the pc c boundary of the chinese successions should be close to marker a on the basis of c isotope chemostratigraphic constraints and biostratigraphic data we find that c isotopic peak s2 also first reported here from the chinese successions can be correlated with c isotopic peak i in northern siberia and c isotope feature d in southwest mongolia by integrating the data from archaeocyaeothan fauna the c isotopic peak s3 in the middle dahai carbonates may be correlative with feature g in the mongolian section

oceanic anoxia at the precambrian cambrian boundary the precambrian cambrian pc c boundary separates fossils representing two discrete evolutionary phases the neoproterozoic soft bodied ediacarian biotas and cambrian small shelly faunas the biological discontinuity is suspected to have been a result of mass extinction however recent discoveries of the ediacarian biotas in cambrian sediments have led to an understanding that the faunal change was gradual through the pc c transition th u ratios which are high in oxidizing conditions and low in reducing conditions show a considerable positive correlation with 13c values at all studied sites of the pc c boundary this correlation indicates that reported 13c variation across the pc c boundary from numerous localities corresponds to redox variation in the depositional environment the negative 13c anomaly that occurs worldwide at the pc c boundary therefore corresponds to the widespread development of an oxygen deficient shallow marine environment this finding suggests that widespread oceanic oxygen deficiency which has been interpreted to reflect phanerozoic mass extinction events also occurred immediately before the cambrian explosion

relationship between frontal dust storms and transient eddy activity in the northern hemisphere of mars as observed by mars global surveyor we have compiled a catalog of frontal dust storms in the northern hemisphere using mars orbiter camera daily global maps spanning 2 3 martian years of mars global surveyor mgs observations from 1999 to 2003 the most vigorous frontal storms that flush dust to the low latitudes occur in early mid fall and mid late winter away from the northern winter solstice while many streaks are observed in the polar hood during the winter solstice period no frontal dust storms are observed in the vicinity of the north polar region we have also analyzed simultaneous mgs thermal emission spectrometer tes temperature data and found statistically significant negative temperature anomalies associated with frontal storms in the lowest scale height of the atmosphere the geographical and seasonal distributions of temperature standard deviations associated with transient variations agree well with the distributions of frontal storms the correlation deteriorates with increasing altitude suggesting that lower level temperature waves are associated with the frontal dust storms specifically eastward traveling m 3 waves with periods of 2 3 sols appear to be closely related to the development of flushing frontal storms

deterministic ground motion scenarios for engineering applications the case of thessaloniki greece abstract in this article we present a deterministic study to estimate seismic ground motions expected in urban areas located near active faults the purpose was to generate bedrock synthetic time series to be used as seismic input into site effects evaluation analysis and loss estimates for the urban area and infrastructures of thessaloniki northern greece two simulation techniques a full wave method to generate low frequency seismograms 1 hz were used to compute time series associated with four different reference earthquakes having magnitudes from 5 9 to 6 5 and located within 30 km of thessaloniki the propagation medium and different source parameters were tested through the modeling of the 1978 thessaloniki earthquake m 6 5 moreover two different nucleation points were considered for each fault in order to introduce additional variability in the ground motion estimates between the two cases the quasi unilateral rupture propagation toward the city produces both higher median peak ground acceleration pga and peak ground velocity pgv values and higher variability than bilateral ones conversely the low frequency ground motion that is peak ground displacement pgd is slightly influenced by the position of the nucleation point and its variability is related to the final slip distribution on the faults of the reference earthquakes and to the location of the sites with respect to the nodal planes of the radiation pattern to validate our deterministic shaking scenarios we verified that the synthetic peak ground motions pga and pgv and spectral ordinates are within one standard deviation of several ground motion prediction equations valid for the region at specific sites we combined the low and high frequency synthetics to obtain broadband time series that cover the entire frequency band of engineering interest 0 25 hz the use of synthetic seismograms instead of empirical equations in the hazard estimates provides a complete evaluation of the expected ground motions both in frequency and time domains including predictions at short distances from the fault 0 10 km and at periods larger than 2 3 sec

dust storms originating in the northern hemisphere during the third mapping year of mars global surveyor abstract data from the third mars global surveyor mgs mapping year my 26 2003 2005 are used to investigate dust storms originating in the northern hemisphere flushing dust storms which originate as frontal dust storms at the northern polar vortex edge and propagate southward through topographic channels are observed immediately before and after a quiescent period that occurs around the northern winter solstice 240 l s 300 both the pre and post solstice active periods can be further divided into two sub periods the most vigorous of these flushing storms occurred during l s 210 220 and l s 310 320 the lifted dust crossed the equator and accumulated in the southern hemisphere these major dust storms enhanced the hadley circulation and suppressed the lower level baroclinic eddies in the northern mid and high latitudes the 2 3 sol wave number m 3 traveling waves show the best correlation with flushing dust storms and can combine with other wave modes to produce storm tracks and fronts within individual sub periods

coseismic deformation of the destructive april 6 2009 l aquila earthquake central italy from gps data 1 on april 6 2009 01 32 39 gmt the city of l aquila was struck by a mw 6 3 earthquake that killed 307 people causing severe destruction and ground cracks in a wide area around the epicenter four days before the main shock we augmented the existing permanent gps network with five gps stations of the central apennine geodetic network cageonet bordering the l aquila basin the maximum horizontal and vertical coseismic surface displacements detected at these stations was 10 39 0 45 cm and 15 64 1 55 cm respectively fixing the strike direction according to focal mechanism estimates we estimated the source geometry with a non linear inversion of the geodetic data our best fitting fault model is a 13 15 7 km2 rectangular fault sw dipping at 55 3 1 8 consistent with the position of observed surface ruptures the estimated slip 495 29 mm corresponds to a 6 3 moment magnitude in excellent agreement with seismological data

complexity of the mw 6 3 2009 l aquila central italy earthquake 2 broadband strong motion modeling 1 near fault strong ground motions 0 1 10 hz recorded during the mw 6 3 2009 l aquila earthquake exhibit great spatial variability modeling the observed seismograms allows linking distinct features of the observed wavefield to particular source and propagation effects and provides insights on strong motion complexity from this moderate magnitude event we utilize a hybrid integral composite approach based on a k square kinematic rupture model combining low frequency coherent and high frequency incoherent source radiation and providing omega squared source spectral decay several source model features proven to be stable by means of an uncertainty analysis in the preceding low frequency 2 hz

imaging the rupture of the mw 6 3 april 6 2009 l aquila italy earthquake using back projection of teleseismic p waves 1 we present rupture details of the mw 6 3 april 6 2009 l aquila earthquake derived by back projecting teleseismic p waves this technique has previously been applied to large magnitude earthquakes but this is the first application to a moderate size event we processed vertical component seismograms for 60 broadband stations obtained from the incorporated research institutions for seismology iris data center the traces were aligned and normalized using a multi channel cross correlation algorithm and 4th root stacking was used to image the rupture we found that the l aquila earthquake ruptured towards the south and that a second discrete pulse of energy occurred 20 25 km east of the epicenter about 17 18 s after the nominal origin time the spatial extent of the rupture image correlates well with a post seismic survey of damage in the region because the technique is potentially very fast images can be produced within 20 30 minutes of the origin time it may be useful to governmental agencies tasked with emergency response and rescue

earthquake early warning system in southern italy methodologies and performance evaluation we investigate the effect of extended faulting processes and heterogeneous wave propagation on the early warning system capability to predict the peak ground velocity pgv from moderate to large earthquakes occurring in the southern apennines italy simulated time histories at the early warning network have been used to retrieve early estimates of source parameters and to predict the pgv following an evolutionary probabilistic approach the system performance is measured through the effective lead time elt i e the time interval between the arrival of the first s wave and the time at which the probability to observe the true pgv value within one standard deviation becomes stationary and the probability of prediction error ppe which provides a measure of pgv prediction error the regional maps of elt and ppe show a significant variability around the fault up to large distances thus indicating that the system s capability to accurately predict the observed peak ground motion strongly depends on distance and azimuth from the fault

the martian zonal mean circulation angular momentum and potential vorticity structure in gcm simulations abstract analysis of simulations performed with the nasa ames mars gcm shows that under dusty conditions the northern hemisphere winter solstice circulation becomes characterized by a zonally averaged state in which the potential vorticity at upper levels is very small outside of high latitudes the available observational data in particular the 15 m observations obtained by the viking irtm during the 1977 winter solstice global dust storm provide evidence for changes in the martian circulation that are basically like those found in the gcm in the mars gcm simulations for dusty solstice conditions an extremely intense and approximately angular momentum conserving hadley circulation is responsible for creating the low potential vorticity configuration this can be contrasted with the venus titan numerical simulations discussed by allison et al in which quasi barotropic eddies appear to be largely responsible for the existence of low potential vorticity in lower and midlatitudes at a near equinox seaso

control of the 2009 l aquila earthquake central italy by a high velocity structure a receiver function study 1 receiver functions rfs analyzed at two permanent broadband seismic stations operating in the epicentral area of the mw 6 3 2009 l aquila earthquake central italy yield insight on crustal structure along the fault rupture the harmonic decomposition of rfs highlights a subsurface structure in which both isotropic and anisotropic features are present we model the waveforms using recently developed monte carlo methods the retrieved models display a common depth structure between 10 and 40 km depth consistent with the under thrusting of the adria lithosphere underneath the apennines belt along the fault in the uppermost crust the s wave velocity structure is laterally heterogeneous right above the hypocenter we find a 4 6 km thick very high s wave velocity body vs as high as 4 2 km s that is absent in the se portion of the fault where the earthquake propagated the high vs body is coincident with the area of fewer aftershocks and is anticorrelated with the maximum slip patches of the earthquake as modeled by differential interferometric synthetic aperture radar dinsar and strong motion data we interpret this high vs body as a high strength barrier responsible for the high peak ground motion in the near field observed in the l aquila city and surroundings and for the complexity in the rupture evolution the retrieved seismic s wave velocity of this body far exceeds common vs values in the upper crust and it is more compatible with values observed in mafic basement rocks

permian triassic boundary ptb in the lower yangtze region southeastern china a new discovery of deep water archive based on organic carbon isotopic and u pb geochronological studies abstract the lower yangtze region of southeastern china is an important area for the study of permian triassic boundary ptb in this region many well known ptb sections e g meishan have been investigated widely and extensively however these sections are dominantly in shallow water settings and data from deep water areas are lacking to fill the gap we conducted a field survey recently and found a deep water ptb section with relatively continuous deposition using integrated organic carbon isotopic and u pb geochronological studies this well exposed and fresh section is located at niushan xuancheng city anhui province 90 km west of the well known meishan section which is the ptb global boundary stratotype section and point the organic carbon isotope curve of the section contains three positive excursions pcies and two negative excursions ncies which can be well correlated with other ptb sections as well as with wuchiapingian changhsingian boundary wcb sections worldwide they archive the original ptb and wcb signatures further u pb dating of magmatic zircons in volcanic ashes validates this new finding i e the ptb interval between 252 49 0 76 ma and 251 74 0 77 ma carbon isotopes of ptb sections in south china reflect the regional paleogeography the two ncies ncie 2 and ncie 3 across the ptb transition are most likely caused by widespread large scale volcanic activity in contrast the ncie 1 near the wcb is possibly related to an increase in the productivity of organic matter as a result of transgression and a change in the organic matter type from terrigenous to marine

dynamic evolution of the ediacaran ocean across the doushantuo formation south china abstract oceanic redox conditions and atmospheric oxygenation likely played a crucial role in the evolution of macroscopic multicellular eukaryotes during the early ediacaran period however the oxidation mechanism and magnitude of the ediacaran ocean atmosphere system remain controversial to constrain the oceanic redox conditions and the contemporaneous oxygenation of the atmosphere we present a comprehensive investigation of redox sensitive elements e g mo and u fe speciation and s isotopes of pyrite from the platform slope and basin sections across the doushantuo formation in south china our results suggest a redox stratified ediacaran ocean with a fluctuating chemocline from the slope to platform location across the doushantuo formation in particular euxinic intermittently euxinic conditions developed not only at the platform and slope but also in the deep basin furthermore these euxinic conditions indicate that high sulfate concentrations may have accumulated not only at the ending of the ediacaran doushantuo formation but also at the middle and beginning thus these results suggest that the extensive euxinic conditions associated with the continuous oceanic sulfate input were in response to progressive oxygenation of the atmosphere during the early ediacaran period integrated with previously published results if the dissolved organic carbon doc reservoir existed different mechanisms may be responsible for the oxidation of deep ocean in each part of the studied sections across the doushantuo formation one mechanism is oxidation by sulfate through a bacterial sulfate reduction bsr process under anoxic conditions another mechanism is oxidation by dissolved free oxygen under oxic suboxic conditions finally a dynamic evolution model of the ediacaran ocean atmosphere system across the doushantuo formation south china was suggested

periglacial landforms at the phoenix landing site and the northern plains of mars 1 we examine potentially periglacial landforms in mars orbiter camera moc and high resolution imaging science experiment hirise images at the phoenix landing site and compare them with numerical models of permafrost processes to better understand the origin nature and history of the permafrost and the surface of the northern plains of mars small scale 3 6 m polygonal patterned ground is ubiquitous throughout the phoenix landing site and northern plains larger scale 20 25 m polygonal patterns and regularly spaced 20 35 m rubble piles localized collections of rocks and boulders are also common rubble piles were previously identified as basketball terrain in moc images the small polygon networks exhibit well developed and relatively undegraded morphology and they overlay all other landforms comparison of the small polygons with a numerical model shows that their size is consistent with a thermal contraction origin on current day mars and are likely active in addition the observed polygon size is consistent with a subsurface rheology of ice cemented soil on depth scales of about 10 m the size and morphology of the larger polygonal patterns and rubble piles indicate a past episode of polygon formation and rock sorting in thermal contraction polygons while the ice table was about twice as deep as it is presently the pervasive nature of small and large polygons and the extensive sorting of surface rocks indicates that widespread overturning of the surface layer to depths of many meters has occurred in the recent geologic past this periglacial reworking has had a significant influence on the landscape at the phoenix landing site and over the martian northern plains

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

yearly comparisons of the martian polar caps 1999 2003 mars orbiter camera observations abstract the mars global surveyor mars orbiter camera wide angle cameras were used to obtain images of the north and south seasonal and residual polar caps between 1999 and 2003 wide angle red camera images were used in assembling mosaics of the north and south polar recessions and regression rates were measured and compared there are small variations in the north polar recession between 2000 and 2002 especially between l s 7 and l s 50 however there is no evidence for the plateau in the recession curves that has been observed in some prior years the south polar recession changes very little from year to year and the 2001 dust storm had little if any effect on the average cap recession that year albedo values of the geographic north pole were measured using wide angle red and blue camera images and the residual south polar cap configuration was compared between the three years observed by moc the albedo of the geographic north pole generally varies between 0 5 and 0 6 as measured from moc wide angle red camera images there were only minor variations near the edges of the residual south polar cap between the three years examined

reconstruction of paleoceanic redox conditions of the lower cambrian niutitang shales in northern guizhou upper yangtze region abstract the paleoceanic redox conditions and the vertical and spatial distribution of organic matter rich lower cambrian niutitang shales are varied in the upper yangtze region china an integrated approach including organic geochemistry major and trace elemental geochemistry and x ray diffraction xrd mineralogy was used to characterize changes in redox conditions and to determine key controls on organic matter accumulation during deposition of the lower cambrian niutitang shales a 202 m long cored well located in kaiyang county in northern guizhou china was thoroughly characterized by the integrated approach in this study vertically total organic carbon toc rich siliceous and argillaceous black shales were developed in the lower and middle niutitang formation and toc lean silty shales were found in the upper niutitang formation the toc content in the lower and middle niutitang shales ranges from 0 27 to 6 7 with an average value of 2 1 and it decreases from 0 30 to 0 11 in the upper niutitang formation shales the toc rich siliceous shales in the lower niutitang formation were characterized by high total sulfur content enrichment in redox sensitive trace elements high corg p ratios and high authigenic mo u covariation indicating they were deposited under persistent anoxic conditions most organic rich shales from the middle niutitang formation were deposited under anoxic conditions whereas a few intervals having low toc contents were deposited in a predominantly oxic depositional environment in contrast the upper niutitang formation were deposited under fully oxic conditions a combination of high primary productivity and enhanced organic preservation under euxinic water column conditions is the key control on organic matter accumulation in the lower niutitang formation shales however a coupling of redox depositional environment and terrestrial mineral dilution plays an important role in organic matter accumulation and preservation in the middle niutitang formation similar organic matter abundance distribution and carbon isotope excursion of organic matter in the sediments deposited at different depositional facies on the yangtze platform suggest regional isotopically homogenous organic carbon input due to the widespread transgressive event with deep basinal waters being transported into the shallow shelf environments at the base of the lower cambrian as a result 13corg distribution patterns can be used as a stratigraphic correlation marker in the upper yangtze region

geochemical evidence from marine carbonate for enhanced terrigenous input into seawater during the ediacaran cambrian transition in south china abstract high resolution carbon and oxygen analyses along with residue contents major and trace element concentrations were carried out for marine dolostone from a profile through the upper ediacaran to the lower cambrian strata in south china the results provide geochemical evidence for enhanced input of terrigenous material into seawater in this period four positive and four negative carbon isotope excursions are identified in this profile the first remarkably negative 13c excursion exhibits the lowest value down to 2 at the ediacaran to cambrian boundary ecb in agreement with the global 13c and stratigraphy correlation the second remarkably negative 13ccarb excursion is as low as 1 81 subsequent to a positive 13ccarb excursion as high as 1 74 in the lower cambrian the ecb position in the stratigraphic profile is constrained by carbon isotope correlations the decreases of dolostone 18o and 13c values are synchronous across the ecb suggesting a change of the seawater composition at that time the increase of residue contents is concordant with decreases of y ho ratios and 18o values for the dolostone across the ecb suggesting the increase of terrigenous input in this period the relatively smooth ree y patterns of dolostone suggest its deposition in the environment of continental platform an integrated interpretation of these geochemical data including the major and trace element concentrations mn sr and mg ca ratios and the well preserved dolostone 13c and 18o values indicates that the terrigenous material from the continental weathering is rich in nutrients and 13c depleted organic matter which would have contributed to the negative 13ccarb excursion of dolostone at the stratigraphic boundaries the strong positive 13ccarb excursion in the lower cambrian may be linked to the biological radiation with lots of organic matter buried from the seawater in this period the fall and rise of sea level during different periods in the same region may result in differential input of terrigenous materials including freshwater into marine carbonates recording the coupling between regional tectonism and paleoclimatic change on the continental platform

near fault strong motion complexity of the 2000 tottori earthquake japan from a broadband source asperity model abstract the october 6 2000 tottori earthquake that occurred in central japan was an intermediate size strike slip event that produced a very large number of near field strong motion recordings the large amount of recorded data provides a unique opportunity for investigating a source asperity model of the tottori earthquake that combined with a hybrid strong motion simulation technique is able to reproduce the observed broadband frequency near fault ground motion we investigated the optimum source asperity parameters of the tottori earthquake by applying a genetic algorithm ga inversion scheme to optimise the fitting between simulated and observed response spectra and peak ground acceleration pga values we constrained the initial model of our inversion by using the heterogeneous slip distribution obtained from a kinematic inversion of the source of previous studies we used all the observed near fault ground motions 100 m from the borehole strong motion network of japan kik net which are little affected by surficial geology site effects the calculation of broadband frequency strong ground motion 0 1 10 hz is achieved by applying a hybrid technique that combines a deterministic simulation of the wave propagation for the low frequencies and a semi stochastic modelling approach for the high frequencies for the simulation of the high frequencies we introduce a frequency dependent radiation pattern model that efficiently removes the dependence of the pattern coefficient on the azimuth and take off angle as the frequency increases the good agreement between the observed and simulated broadband ground motions shows that our inversion procedure is successful in estimating the optimum asperity parameters of the tottori earthquake and provides a good test for the strong ground motion simulation technique the ratio of background stress drop to average asperity stress drop from our inversion is nearly 50 in agreement with the theoretical asperity model of das and kostrov das s kostrov b v 1986 fracture of a single asperity on a finite fault a model for weak earthquakes earthquake source mechanics agu pp 91 96 and an empirical ratio of asperities to rupture area seismol res lett 70 1999 59 80 the simulated radiation pattern is very complex for epicentral distances within half the fault length but it approaches the radiation of a double couple point source for larger distances the rupture velocity and rise time have a significant influence on the peak ground velocity pgv distribution around the fault an increase in rupture velocity produces a similar effect on the ground motion as a reduction in rise time

the 2009 l aquila central italy mw6 3 earthquake main shock and aftershocks 1 a m w 6 3 earthquake struck on april 6 2009 the abruzzi region central italy producing vast damage in the l aquila town and surroundings in this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks the distribution of aftershocks 712 selected events with m l 2 3 and 20 with m l 4 0 defines a complex 40 km long nw trending extensional structure the main shock fault segment extends for 15 18 km and dips at 45 to the sw between 10 and 2 km depth the extent of aftershocks coincides with the surface trace of the paganica fault a poorly known normal fault that after the event has been quoted to accommodate the extension of the area we observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes

two major dust storms one mars year apart comparison from viking data the viking mars landers have been on the mars surface for over two mars years during the first year two major probably global dust storms occurred the first was unusually early compared to most previous earth based observations a major storm occurred during the second year almost precisely one year after the first storm of the first year meteorological data show roughly similar atmospheric behavior for the two early storms of particular note is the increase in amplitude of pressure oscillations probably of baroclinic origin and concurrent increases in wind speed during the build up phase of all three storms the generation of these waves appears to be a natural consequence of seasonal effects not associated with the dust storms it is suggested that baroclinic waves should they exist in the southern hemisphere during the time of dust storm generation could be an important factor in growth and development of the dust storms

high resolution organic carbon isotope stratigraphy from a slope to basinal setting on the yangtze platform south china implications for the ediacaran cambrian transition organic carbon isotope data from two slope to basinal sections across the ediacaran cambrian transition on the yangtze platform south china record secular variations in delta c 13 data supplement highly comparable organic carbon isotope profiles from time equivalent shallow shelf and slope settings no environmentally determined carbon isotope gradient across the yangtze platform is discernible suggesting that a transgressive anoxic event provided an isotopically homogenous carbon source for primary productivity that originated from the deeper part of an anoxic and or sulfidic basin c 2011 elsevier b v all rights reserved

the 1997 1998 umbria marche sequence central italy source path and site effects estimated from strong motion data recorded in the epicentral area 1 we apply a nonparametric spectral inversion scheme to calculate source spectra s wave attenuation and site transfer functions from strong motion records in the epicentral region of the 1997 1998 umbria marche seismic sequence central italy we use records from moderate size earthquakes 4 6 ml 5 9 to parameterize the spectral amplitude decay in the distance range from 5 to 40 km we find that the average quality factor q can be approximated by q f 49 f0 9 between 0 5 and 8 hz and the geometrical spreading by r 0 9 at high frequencies f 8 hz the dependence of q on frequency weakens and it takes an approximate constant value of 318 we fit the source spectra to the square model and calculate an average stress drop of 2 1 mpa the average value is consistent with the previous estimates from the weak events 1 4 ml 4 5 of the umbria marche seismic sequence the most remarkable site effects are found in correspondence of large sedimentary basins filled by alternation of sandy clayey deposits the estimated spectral parameters are used to simulate acceleration spectra recorded during several earthquakes of the umbria marche sequence both point source and finite fault effects are considered furthermore attenuation relationships for peak ground velocity and ground acceleration are estimated using synthetic data and compared to existing relationships

selection of the mars exploration rover landing sites 1 the selection of meridiani planum and gusev crater as the mars exploration rover landing sites took over 2 years involved broad participation of the science community via four open workshops and narrowed an initial 155 potential sites 80 300 30 km to four finalists based on science and safety engineering constraints important to the selection included 1 latitude 10 n 15 s for maximum solar power 2 elevation less than 1 3 km for sufficient atmosphere to slow the lander 3 low horizontal winds shear and turbulence in the last few kilometers to minimize horizontal velocity 4 low 10 m scale slopes to reduce airbag spin up and bounce 5 moderate rock abundance to reduce abrasion or strokeout of the airbags and 6 a radar reflective load bearing and trafficable surface safe for landing and roving that is not dominated by fine grained dust the evaluation of sites utilized existing as well as targeted orbital information acquired from the mars global surveyor and mars odyssey three of the final four landing sites show strong evidence for surface processes involving water and appear capable of addressing the science objectives of the missions which are to determine the aqueous climatic and geologic history of sites on mars where conditions may have been favorable to the preservation of evidence of possible prebiotic or biotic processes the evaluation of science criteria placed meridiani and gusev as the highest priority sites the evaluation of the three most critical safety criteria 10 m scale slopes rocks and winds and landing simulation results indicated that meridiani and elysium planitia are the safest sites followed by gusev and isidis planitia

martian north polar cap recession 2000 mars orbiter camera observations abstract the wide angle cameras of the mars orbiter camera moc on the mars global surveyor have recorded the 2000 recession of the seasonal co 2 cap in the north polar region from l s 330 to 90 in stark contrast to the asymmetric behavior of the south seasonal cap the seasonal north cap remains relatively circular and uniform until mid spring when the retreat reaches the circum polar dune field which is the one major nonuniformity in the cap the recession of cap edge latitude versus areocentric longitude l s is very well represented as a linear function until late spring there is no evidence for the plateau or standstill in the recession curve that has been observed in some prior years the lambert albedo of the seasonal frost deposits in the north polar region demonstrates the increase with insolation first observed by paige in 1985 increasing to approximately 0 57 at l s 40 the north polar cap near solstice visually appears smaller than that observed by moc at the start of mapping in 1999 but later images acquired in summer show the residual cap returning to its more usual shape the most likely explanation for these changes in albedo is precipitation and subsequent removal of dust on the cap as a result of frequent dust storms near the cap edge

the mw 6 3 2009 l aquila earthquake source path and site effects from spectral analysis of strong motion data summary the strong motion data of 2009 april 6 l aquila central italy earthquake mw 6 3 and of 12 aftershocks 4 1 mw 5 6 recorded by 56 stations of the italian strong motion network are spectrally analysed to estimate the source parameters the seismic attenuation and the site amplification effects the obtained source spectra for s wave have stress drop values ranging from 2 4 to 16 8 mpa being the stress drop of the main shock equal to 9 2 mpa the spectral curves describing the attenuation with distance show the presence of shoulders and bumps mainly around 50 and 150 km as consequence of significant reflected and refracted arrivals from crustal interfaces the attenuation in the first 50 km is well described by a quality factor equal to q f 59f0 56 obtained by fixing the geometrical spreading exponent to 1 finally the horizontal to vertical spectral ratio provides unreliable estimates of local site effects for those stations showing large amplifications over the vertical component of motion

multiple controls on the paleoenvironment of the early cambrian marine black shales in the sichuan basin sw china geochemical and organic carbon isotopic evidence abstract in order to understand the paleoenvironment of the early cambrian black shale deposition in the western part of the yangtze block geochemical and organic carbon isotopic studies have been performed on two wells that have drilled through the qiongzhusi formation in the central and southeastern parts of sichuan basin it shows that the lowest part of the qiongzhusi formation has high toc abundance while the middle and upper parts display relative low toc content redox sensitive element mo and trace elemental redox indices e g ni co v cr u th and v v ni suggest that the high toc layers were deposited under anoxic conditions whereas the low toc layers under relatively dysoxic oxic conditions the relationship of the enrichment factors of mo and u further shows a transition from suboxic low toc layers to euxinic high toc layers on the basis of the mo toc relationship the qiongzhusi formation black shales were deposited in a basin under moderately restricted conditions organic carbon isotopes display temporal variations in the qiongzhusi formation with a positive excursion of 13 c org values in the lower part and a continuous positive shift in the middle and upper parts all these geochemical and isotopic criteria indicate a paleoenvironmental change from bottom anoxic to middle and upper dysoxic oxic conditions for the qiongzhusi formation black shales the correlation of organic carbon isotopic data for the lower cambrian black shales in different regions of the yangtze block shows consistent positive excursion of 13 c org values in the lower part for each section this excursion can be ascribed to the widespread early cambrian transgression in the yangtze block under which black shales were deposited

three dimensional modeling of near fault ground motions with nonplanar rupture models and topography case of the 2004 parkfield earthquake 1 we study the applicability of deterministic strong ground motion simulations at very near fault distances for a subvertical strike slip fault model corresponding to the 2004 m6 parkfield california earthquake in the frequency range up to 1 hz theoretical modeling under the assumptions of a planar rupture and 1 d medium shows that as a consequence of the s wave radiation pattern the particle motion for such close stations should be almost linear in the fault normal fn direction having fault parallel fp and vertical v components of almost zero however as shown on the parkfield earthquake recordings observed particle motions are rather circular with peak velocities at fp and v components comparable to those at fn components we investigate several realistic features that could explain this controversy namely nonplanar fault realistic three dimensional 3 d medium and the topography of the area we test and quantify these hypotheses using discrete wave number and discontinuous galerkin modeling methods applying 1 d and 3 d velocity structures respectively and two nonplanar rupture models we compare the synthetic and observed particle motions and peak velocity ratios and conclude that deviations from a planar rupture geometry in reasonable bounds for the parkfield fault and the influence of topography only partially explain the behavior of the observed seismograms on the contrary the heterogeneous 3 d velocity structure significantly reduces the synthetic peak ratios to values closer to 1 and provides rather circular particle motions therefore the 3 d velocity model is crucial to obtain realistic estimates of ground motions at near fault distances and is more important than the detailed fault geometry or topography in the parkfield area

carbon isotope variability across the ediacaran yangtze platform in south china implications for a large surface to deep ocean δ13c gradient new isotope data obtained from relatively conformable carbonate rich strata of the ediacaran yangtze platform in south china reveal substantial 13 c variability in platform sections four negative 13 c anomalies with a nadir down to 8 pdb are present in the interval between the cap carbonate level 635 ma and the precambrian cambrian boundary 542 ma while in slope and basinal sections 13 c values are negative through the entire doushantuo formation 635 551 ma if these 13 c values are close to their primary seawater signature they imply a strong 10 surface to deep ocean 13 c gradient that is consistent with long term deep ocean anoxia and the presence of a large dissolved organic carbon doc reservoir the two prominent negative 13 c excursions within the doushantuo formation above the cap carbonate level are associated with shoaling and local exposure of the platform the anomalies may thus record remineralization of a large oceanic doc pool via sulfate reduction that transferred 13 c depleted carbon from the oceanic doc reservoir to the surface ocean during regression inconsistencies in ediacaran 13 c profiles globally and variations in south china in particular highlight the need for further evaluation of local departures in 13 c from an inferred average seawater signature

marine redox variations and nitrogen cycle of the early cambrian southern margin of the yangtze platform south china evidence from nitrogen and organic carbon isotopes the early cambrian is a crucial interval during which the marine environment encountered significant perturbations alongside key biological innovations the nitrogen isotopic composition of ancient sediments has the potential to record co variation between the marine ecosystem and environmental conditions here we report bulk nitrogen and organic carbon isotopic compositions accompanied by mo concentration data a proxy for redox conditions for a shelf marginal drill core section sancha and a deep basinal outcrop section yuanjia in hunan province south china for the cambrian fortunian stage variable delta n 15 bulk values 4 to 2 parts per thousand and low delta c 13 org values 35 parts per thousand to 33 from the yuanjia section indicate that anoxic waters shoaled into the photic zone with ammonia assimilation competing with anammox in the basinal area in the late cambrian stage 2 low delta n 15 bulk and delta c 13 org values together with high mo bulk concentrations delta n 15 bulk 5 to 0 parts per thousand delta c 13 org 33 5 to 31 0 parts per thousand 100 ppm mo bulk in sancha section and delta n 15 bulk 0 parts per thousand delta c 13 org similar to 33 parts per thousand 100 ppm mo bulk in yuanjia section reflect intense n 2 fixation accompanied by intermittent ammonia assimilation under expanded euxinic condition with shoaling chemocline possibly into the photic zone in the early cambrian stage 3 relatively high delta n 15 bulk values alongside positive delta c 13 org excursions at both sections indicate an increasing contribution from n 15 enriched nitrate assimilation and hence more oxic conditions shelf margin sediments from the middle and late parts of cambrian stage 3 are characterized bylaw delta n 15 bulk values similar to 0 parts per thousand being lowest in the basinal area 3 to 0 parts per thousand in combination with high mo bulk concentration 100 ppm and high mo tocbulk ratios averaging similar to 18 in deep basinal sediments these data suggest that the photic zone became anoxic again but that sulfidic conditions occurred in the basinal area only compared with stage 2 euxinia was less extensive during this interval with photosynthetic biomass dominating over chemoautotrophic biomass at both localities based on a combination of delta n 15 data from this study and published data from studies on contemporaneous sections in yunnan province and the three gorges area it is possible to reconstruct the spatial variability and temporal evolution of redox conditions in the various marine environments along the southern margin of the yangtze platform the basinal area appears to have been dominated by anoxia and intermittent euxinia in the photic zone during most of the early cambrian fortunian stage to stage 3 with the exception of more oxic conditions during early stage 3 on the platform oxygenated shallow water prevailed with the exception of the notable cambrian stage 2 anoxic event the outer shelf area experienced anoxia from stage 2 to stage 3 of the early cambrian although of possibly limited areal extent the high mo bulk concentrations and mo tocbulk ratios suggest that the south china basin was well connected with the considerably oxygenated open ocean and that the mean low delta n 15 bulk values similar to 1 6 parts per thousand from the basin may reflect generally lower delta n 15 composition for seawater nitrate in the early cambrian compared with modern value c 2015 elsevier b v all rights reserved

a composite source model for computing realistic synthetic strong ground motions a composite source model is presented for convolution with synthetic green s functions in order to synthesize strong ground motions due to a complex rupture process of a large earthquake subevents with a power law distribution of sizes are located randomly on the fault each subevent radiates a displacement pulse with the shape of a brune s pulse in the far field at a time determined by a constant rupture velocity propagating from the hypocenter thus all the input parameters have a physical basis we simulate strong ground motions for event station pairs that correspond to records obtained in mexico by the guerrero accelerograph network the synthetic accelerations velocities and displacements have realistic amplitudes durations and fourier spectra

a constant stress drop model for producing broadband synthetic seismograms comparison with the next generation attenuation relations broadband 0 1 20 hz synthetic seismograms for finite fault sources were produced for a model where stress drop is constant with seismic moment to see if they can match the magnitude dependence and distance decay of response spec tral amplitudes found in the next generation attenuation nga relations recently developed from strong motion data of crustal earthquakes in tectonically active re gions the broadband synthetics were constructed for earthquakes of m 5 5 6 5 and 7 5 by combining deterministic synthetics for plane layered models at low fre quencies with stochastic synthetics at high frequencies the stochastic portion used a source model where the brune stress drop of 100 bars is constant with seismic mo ment the deterministic synthetics were calculated using an average slip velocity and hence dynamic stress drop on the fault that is uniform with magnitude one novel aspect of this procedure is that the transition frequency between the deterministic and stochastic portions varied with magnitude so that the transition frequency is inversely related to the rise time of slip on the fault the spectral accelerations at 0 2 1 0 and 3 0 sec periods from the synthetics generally agreed with those from the set of nga relations for m 5 5 7 5 for distances of 2 100 km at distances of 100 200 km some of the nga relations for 0 2 sec spectral acceleration were substantially larger than the values of the synthetics for m 7 5 and m 6 5 earthquakes because these relations do not have a term accounting for q at 3 and 5 sec periods the synthetics for m 7 5 earth quakes generally had larger spectral accelerations than the nga relations although there was large scatter in the results from the synthetics the synthetics showed a sag in response spectra at close in distances for m 5 5 between 0 3 and 0 7 sec that is not predicted from the nga relations

uncertainties in strong ground motion prediction with finite fault synthetic seismograms an application to the 1984 m 5 7 gubbio central italy earthquake abstract this study investigates the engineering applicability of two conceptually different finite fault simulation techniques we focus our attention on two important aspects first to quantify the capability of the methods to reproduce the observed ground motion parameters peaks and integral quantities second to quantify the dependence of the strong motion parameters on the variability in the large scale kinematic definition of the source i e position of the nucleation point value of the rupture velocity and distribution of the final slip on the fault we applied an approximated simulation technique the deterministic stochastic method and a broadband technique the hybrid integral composite method to model the 1984 m w 5 7 gubbio central italy earthquake at five accelerometric stations we first optimize the position of the nucleation point and the value of the rupture velocity for three different final slip distributions on the fault by minimizing an error function in terms of acceleration response spectra in the frequency band from 1 to 9 hz we found that the best model is given by a rupture propagating at about 2 65 km sec from a hypocenter located approximately at the center of the fault in the second part of the article we calculate more than 2400 scenarios varying the kinematic source parameters at the five sites we compute the residuals distributions for the various strong motion parameters and show that their standard deviations depend on the source parameterization adopted by the two techniques furthermore we show that arias intensity ai and significant duration are characterized by the largest and smallest standard deviation respectively housner intensity is better modeled and less affected by uncertainties in the source kinematic parameters than ai the fact that the uncertainties in the kinematic model affects the variability of different ground motion parameters in different ways has to be taken into account when performing hazard assessment and earthquake engineering studies for future events

a hybrid method for calculating near source broadband seismograms application to strong motion prediction abstract we present a hybrid method for computing broadband strong motion seismograms in the near field of large earthquakes we combine complete seismograms at low frequency with ray theory seismograms at high frequency to form a composite broadband seismogram that spans the entire frequency range of interest in our approach the amplitude spectra of the two sets of synthetic seismograms are reconciled at intermediate frequencies where their domain of validity overlaps we demonstrate the method with scenario earthquakes based on the spatial random field model for complex earthquake slip j geophys res 107 b11 2002 2308 the hybrid near source broadband seismograms are useful both for detailed source modeling and for incorporating source effects into probabilistic seismic hazard analysis

marci and moc observations of the atmosphere and surface cap in the north polar region of mars abstract we used mgs moc and mro marci daily mapping images of the north polar region of mars from 16 august 2005 ls 270 to 21 may 2009 ls 270 covering portions of three consecutive martian years my 27 my 29 to observe the seasonal behavior of the polar ice cap and atmospheric phenomena the rate of cap regression was similar in my 28 and my 29 but was advanced by 3 5 of ls 7 8 sols in my 29 the spatial and temporal behaviors of dust and condensate clouds were similar in the two years and generally in accord with prior years dust storms 100 km2 were observed in all seasons with peak activity occurring at ls 10 20 from 50 n to 70 n and at ls 135 140 from 70 n to 90 n the most active quadrant was 0 90 w in my 28 shifting to 180 270 w in my 29 the majority of regional storms in both years developed in longitudes from 10 w to 60 w during late summer the larger storms obscure the north polar region in a cloud of dust that transitions to north polar hood condensate clouds around autumnal equinox changes in the distribution of perennial ice deposits especially in olympia planum were observed between the 2 years with the my 29 ice distribution being the most extensive observed to date modeling suggests that the small bright ice patches on the residual cap are not the result of slope or elevation effects rather we suggest that they are the result of local meteorological effects on ice deposition the annual darkening and brightening of peripheral areas of the residual cap around summer solstice can be explained by the sublimation of a brighter frost layer revealing an underlying darker ice rich layer that itself either sublimes to reveal brighter material below or acts as a cold trap attracting condensation of water vapor that brightens the surface an alternative explanation invokes transport and deposition of dust on the surface from the cap interior and later removal of that dust the decrease in cap albedo and accompanying increase in near surface atmospheric stability may be related to the annual minimum of polar storm activity near northern summer solstice

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

evaluating episodic hydrothermal activity in south china during the early cambrian implications for biotic evolution abstract the early cambrian 541 514 ma was a crucial interval for the evolution of life on earth popularly known as the cambrian explosion here we report the timing of changes in hydrothermal and depositional inputs as well as paleo redox state which may have influenced biogeochemical changes according to high resolution petrology fossil distributions isotopic records and inorganic geochemistry the lower cambrian of the south china can be subdivided into four intervals the lowermost cambrian zhujiaqing formation cam i the cambrian stage 2 shiyantou formation cam ii the lower part of the cambrian stage 3 yu anshan formation cam iii and the mid upper cambrian stage 3 and the middle upper part of the yu anshan formation continuing into the canglangpu formation cam iv hydrothermal events are detected during the early cam i cam ii and cam iii intervals during the early cam i and cam ii intervals these events coincided with extensive bottom water euxinia which in turn may have restricted the spread or proliferation of ediacaran fauna and small shelly fauna through the whole cam iii interval further hydrothermal events occurred concurrently with euxinic and ferruginous conditions probably within a single spatially stratified water column again plausibly restricting the spread of aerobic organisms in conjunction with the cessation of hydrothermal events and the gradual lowering of sea level during the late cam iii oxic water environments gradually spread into relatively deep water regions concurrent with the emergence of the chengjiang and qingjiang faunas these data suggest that periodic hydrothermal events may have had a significant impact on the spread radiation and extinction of macroscopic fauna during the early cambrian in south china

marine redox stratification on the earliest cambrian ca 542 529 ma yangtze platform abstract in order to explore the marine redox structure on the earliest cambrian ca 542 529 ma yangtze platform south china new fe mo c s geochemical data from the slope xugongping section for the liuchapo and the base of niutitang formation are reported here integrated fe speciation and mo abundance data from the xugongping section in combination with previously published data from slope basinal longbizui section and others suggest oxic surface waters and ferruginous deep waters coexisting with occasional mid depth euxinic waters during the fortunian stage and with widespread euxinic waters during the early stage 2 marine transgression a compilation of new and published sulfur isotope data of pyrite for the liuchapo and the base of niutitang formations presents high isotopic values mostly 10 and distinctly different spatiotemporal gradient characteristics during the fortunian stage and the beginning of the stage 2 we propose that redox stratification developed in the earliest cambrian protected basin and eustatic change and the connectivity of the protected basin with the open ocean controlled the materials supply from riverine input and open ocean reservoir and thus spatiotemporal variability of ocean chemistry

evolution of oceanic molybdenum and uranium reservoir size around the ediacaran cambrian transition evidence from western zhejiang south china abstract the cambrian explosion is one of the most fascinating episodes of diversification in the history of life however its relationship to the oxygenation of the oceans and atmosphere around the ediacaran cambrian transition is not fully understood marine inventories of redox sensitive trace elements reflect the relative balance of oxidative weathering on land and deposition in anoxic water masses and can be used to explore the evolution of oceanic and atmospheric redox conditions for this study we conducted a series of geochemical analyses on the upper lantian piyuancun and hetang formations in the chunye 1 well part of the lower yangtze block in western zhejiang iron speciation results indicate that the entire studied interval was deposited under anoxic conditions with three intervals of persistent euxinia occurring in the uppermost lantian fm the lower hetang formation fm and the upper hetang fm molybdenum mo and uranium u contents and mo toc and u toc ratios from the anoxic euxinic intervals of the chunye 1 well combined with published data from the sections in the middle and upper yangtze block suggest that the oceanic mo reservoir declined consistently from the ediacaran to cambrian stage 3 while the size of the oceanic u reservoir remained relatively constant both metals were depleted in the ocean in lower cambrian stage 4 before increasing markedly at the end of stage 4 the lack of an apparent increase in the size of the marine mo and u reservoir from the upper ediacaran to cambrian stage 3 suggests that oxic water masses did not expand until cambrian stage 4 the increase in marine mo and u availability in the upper hetang fm may have been due to the expansion of oxic water masses in the oceans associated with oxygenation of the atmosphere during cambrian stage 4 this expansion of oxic waters in the global ocean postdates the main phase of cambrian diversification suggesting that pervasive oxygenation of the ocean on a large scale was not the primary control on animal diversity following the ediacaran cambrian transition

marine carbon and sulfur cycling across the ediacaran cambrian boundary in tarim block and its implications for paleoenvironmental changes abstract the ediacaran cambrian transition was a critical period of earth history because of the coincidence among climate change bioevolution and tectonic activity the nature of carbon and sulfur cycling processes spanning the ediacaran cambrian boundary remains debatable this study considers high resolution stable isotope chemostratigraphy of the sugetbrak and yutixi sections of the keping area of the tarim basin northwestern china the sections display a pronounced negative 13ccarb shift the basal cambrian carbon isotope excursion that spans the ediacaran cambrian boundary deposits overlying the negative excursion are characterized by heavier 13ccarb values ranging from 7 8 to 4 1 the biostratigraphically calibrated 13ccarb profiles likely reflect widespread perturbation of the global oceanic carbon cycle and associated mass extinction and subsequent biological evolution the 34spy profiles of the studied sections display a wide distribution of values ranging from 16 4 to 23 8 the variable 34spy signatures of these sections are partially controlled by microbial sulfate reduction rates which are sensitive to local sulfate concentration availability of organic matter and the marine redox state the strong coupling between enhanced organic carbon and pyrite burial the appearance of cambrian type animals and a shift to a more oxidizing marine environment might suggest a temporal causality of higher oxygen levels of the atmosphere ocean realm with bio events during the ediacaran cambrian transition the development of ecosystems across the ediacaran cambrian transition may have significantly impacted the oceanic carbon and sulfur biogeochemical processes in earth s history and in turn affecting themselves

evaluation of paired carbon isotopic signals from the ediacaran doushantuo phosphorites diagenetic or primary abstract this study reports high resolution c isotopic data of carbonate carbon 13ccarb and organic carbon 13corg from the ediacaran doushantuo carbonate and phosphorite as well as from the underlying tillite of the nantuo formation from the datang mine and chuanyuandong sections for the nantuo tillite in the datang section the striking negative 13ccarb values ranging mostly from 10 to 16 with negative 18o values down to 27 2 and clear covariance between 13ccarb and 18o suggest that nearly all of the primary c and o isotopic compositions have been reset by meteoric diagenesis the near complete modification of the primary isotopic signals may be due to frequent exposure to fresh water conditions during diagenesis and the lithification of porous tillite sediment the extremely negative 13ccarb values down to 16 8 suggest the contribution of 12c enriched dissolved inorganic carbonate which originated from the remineralization of organic carbon during burial diagenesis these observations suggest that caution is needed when using tillite samples for paleoenvironmental reconstruction the correlative lower phosphorite deposits from the datang and chuanyuandong sections show clear covariance between 13ccarb and 18o although the chuanyuandong phosphorites have more negative values of 13ccarb and 18o than the datang section although most of the 18o values of the lower phosphorites may have been altered by secondary diagenetic processes the 13ccarb values of 3 5 and the 13corg values of

paleo sedimentary environment in relation to enrichment of organic matter of early cambrian black rocks of niutitang formation from xiangxi area china abstract early cambrian organic rich black rocks are extensively distributed in the southern china in this study we have discussed the relation of paleo sedimentary environments with enrichment of organic matter based on toc data we divided the niutitang formation into three parts upper middle and lower the amount of total organic carbon in the lower 1 55 wt and the upper part 1 35 wt of niutitang formation is significantly smaller than the middle part 8 0 wt which suggest initial transgression and regression stages of the sea level respectively the middle part from both sections longbizui and sancha contains higher toc content which is a clue of intense transgression stage of sea level with high bio productivity kerogen type index kti using different macerals specify the organic matter in these black rock series is mainly type i with a minor amount of type ii1 moreover these black rocks were deposited in weak to moderately restricted hydrographic conditions the heterogenic mineral composition was also observed in these black rocks including quartz clay gypsum pyrite barite dolomite and plagioclase quartz content in the middle part is relatively higher than the upper and the lower part displays a strong positive relation with toc which suggests the main source of quartz during deposition of the middle part was biogenic quartz during early cambrian period due to extension between the yangtze and the cathaysian plate the hydrothermal fluids rich in uranium vanadium molybdenum zinc barium etc from the deeper part of the earth crust and entered the ocean basin through extensional remnant fissures and cracks and due to upwelling phenomena entered to the shelf area these nutrient rich deep crustal fluids at the surface of the sea enhanced the evolution and breeding of planktons and other marine life meanwhile it upsurges the bio productivity additionally it creates bottom water hypoxia which is favourable for the preservation of organic matter in the sedimentary rocks the main factors responsible for the enrichment of organic matter in these early cambrian black rock series of niutitang formation were a hydrographic restriction hydrothermal activities and paleo redox conditions respectively

geochemistry of ediacaran cap dolostones across the yangtze platform south china implications for diagenetic modification and seawater chemistry in the aftermath of the marinoan glaciation cap dolostones of the ediacaran doushantuo formation yangtze platform south china from various palaeo water depths were studied to evaluate the extent of their diagenetic alteration and to assess temporal and spatial variations of seawater chemistry in the aftermath of the marinoan glaciation diagenetic fluid overprint is common in cap dolostone lithologies however the mobilization of trace elements and the modification of sr and o isotopic compositions are variable and were controlled by multiple stages of fluid overprint the highest 87 sr 86 sr ratios up to 0 7246 occur in cap dolostones from the palaeo slope environment at the huanglianba section whereas cap dolostones deposited in platform settings and in one of the distal basinal settings reveal 87 sr 86 sr ratios close to the proposed late neoproterozoic seawater composition 0 7077 shale normalized ree y patterns of carbonate leachates display enrichments of heavy over light ree and superchondritic y ho ratios typical of seawater however y ho ratios in the cap dolostones are always lower than modern seawater values which is interpreted to reflect dilution of the seawater signal by continent derived meltwater influx during deglaciation negative ce anomalies in carbonate leachates from platform and slope sections suggest that oxidized conditions existed in shallow marine environments shortly after the marinoan glaciation whereas positive or no resolvable ce anomalies in basin settings indicate that the latter remained anoxic redox stratification of the yangtze margin at the beginning of the ediacaran is further supported by the relative enrichment of redox sensitive trace metals in basinal sections these data may indicate moderately anoxic less than 10 m dissolved o 2 and presumably manganous conditions during the deposition of cap dolostones in the deeper realms of the yangtze basin supplementary material supplementary data for this paper are available at https doi org 10 6084 m9 figshare c 3770957

moc observations of the 2001 mars planet encircling dust storm abstract from 15 september 1997 through 21 january 2006 only a single planet encircling martian dust storm was observed by mgs moc the onset of the storm occurred on 26 june 2001 l s 184 7 earliest recorded to date it was initiated in the southern mid to low latitudes by a series of local dust storm pulses that developed along the seasonal cap edge in malea and in hellas basin l s 176 2 184 4 the initial expansion of the storm though asymmetric was very rapid in all directions 3 32 m s 1 the main direction of propagation however was to the east with the storm becoming planet encircling in the southern hemisphere on l s 192 3 several distinct centers of active dust lifting were associated with the storm with the longest persisting for 86 sols syria claritas these regional storms helped generate and sustain a dust cloud haze which reached an altitude of about 60 km and a peak opacity of dust 5 0 by l s 197 0 the cloud had encircled the entire planet between 59 0 s and 60 0 n obscuring all but the largest volcanoes the decay phase began around l s 200 4 with atmospheric dust concentrations returning to nominal seasonal low levels at l s 304 0 exponential decay time constants ranged from 30 117 sols the storm caused substantial regional albedo changes darkening and brightening as a result of the redistribution removal and deposition of a thin veneer of surface dust at least 0 1 11 1 m thick it also caused changes in meteorological phenomena i e dust storms dust devils clouds recession of the polar caps and possibly surface temperatures that persisted for just a few weeks to more than a single mars year the redistribution of dust by large annual regional storms might help explain the long period 30 years between the largest planet encircling dust storms events

ediacaran negative c isotopic excursions associated with phosphogenic events evidence from south china abstract the yangtze platform of south china preserves relatively continuous strata of the ediacaran period and has been one of the key areas to explore neoproterozoic earth history in this study high resolution carbon isotope 13c and oxygen isotope 18o data of 701 samples were reported for sedimentary rocks spanning the entire ediacaran period using a continuous drill core collected from wangji south china the c isotopic data of the doushantuo formation are consistent with previous work showing three negative 13c excursions that can be correlated intra basinally a large negative 13c excursion from 8 16 to 7 20 identified at the top of the doushantuo formation which is equivalent to the shuram negative excursion allows us to correlate the 13c profile globally in the overlying dengying formation we identified two distinct 13c intervals with an average value of 3 32 and of 0 40 respectively as well we observed a negative 13c excursion in the middle dengying formation which has not been reported previously three major negative 13c excursions two in the doushantuo formation and one in the dengying formation are tightly associated with phosphorite deposits the temporal correlation between the negative 13c excursions and the phosphorite deposits suggests a potential link between carbon and phosphorus cycling in the ediacaran oceans we argue that multiple periods of strong upwelling may have played an important role in c and p cycling in the ediacaran oceans oxidative processes of the 13c depleted dissolved organic carbon doc transported into oxic near surface waters by upwelling resulted in the negative 13c excursions and contributed to synchronous burial of abundant phosphorites in the inner shelf areas the different magnitudes of the negative 13c excursions observed in the doushantuo and dengying formations may reflect spatial changes of doc reservoir and variations of upwelling intensity and mixing processes

the vertical structure of limb hazes in the martian atmosphere abstract profiles of scattered light above the planetary limb from over 100 viking orbiter images are used to constrain the temporal and spatial behavior of earosols suspended in the martian atmosphere the data cover a wide range of seasons locations and viewing geometry providing information about the aerosol optical properties and vertical distribution the vertical resolution of the data is about 1 5 km with an absolute elevation accuracy of 1 to 4 km viking orbiter camera colibration algorithms provided reflectance accuracies to 7 absolute allowing meaningful radiometric analysis the typical atmospheric column contains one or more discrete optically thin ice like haze layers between 30 and 90 km elevation depending on season whose composition is inferred to be water ice below the detached hazes there is a continuous haze extending to the surface the continuous haze is rarely observed above 50 km and is much redder in color than the detached hazes above implying a composition that has a strong dust component the aerosol distribution exhibits a strong seasonal control inferred to be driven by the variable solar flux around the orbit of mars

nitrogen and organic carbon isotope stratigraphy of the yangtze platform during the ediacaran cambrian transition in south china abstract n and corg isotope results are presented from six sections along a west east transect in the south china basin scb covering both shallow and deeper domains in order to investigate biogeochemical cycling stratigraphic correlation and isotope systematics over the crucial ediacaran cambrian transition 15n bulk values range between 3 and 7 while 13corg values range between 21 and 39 similar isotopic trends have been identified for both these proxies across the basin although hiatuses differences in depositional setting and syn depositional bacterial fermentation may have caused some inconsistencies a trend towards negative n isotope values can be recognized above the pc c boundary in both shallow and deeper basin realms across the yangtze platform this negative 15n excursion is probably a response to photic zone anoxia and intense nitrogen fixation assimilation by diazotrophic cyanobacteria and green purple sulfur bacteria gsb and psb the xiaotan section and a composite section from the yangtze gorges area show meaningful similarities in their nitrogen isotope trends interpreted as chemocline fluctuations in the water column that testify to rapid mixing of water overlying the shallow platform using carbon isotope stratigraphy we correlate boundary strata across the platform to test the wider significance of nitrogen isotopic variations increased bioturbation and food chain complexity across the ediacaran cambrian transition probably led to more frequent variations in nitrate isotope composition and related pool dimension during the early cambrian reflecting the beginning of a new more biologically controlled era

pyrite and organic matter in phanerozoic normal marine shales data have been obtained from our own chemical analyses and from the literature for the concentrations of organic carbon c and pyrite sulfur s in over 600 samples of cambrian to recent normal marine shales normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and or indicators of bioturbation all samples were selected to minimize 1 1 loss of c and or s due to weathering at the outcrop by emphasizing the use of drill core material 2 2 analytical errors and non diagenetic effects by avoiding sediments low in c or s content such as sandstones 3 3 fe limitation of pyrite formation by avoiding limestones cherts and euxinic shales 4 4 metamorphic loss of c relative to s by avoiding rocks obviously subjected to even low grade metamorphism our results indicate that 1 there is generally a good positive linear correlation between organic c and pyrite s for normal marine shales of all ages and 2 the mean cs ratio for normal marine shales has varied over time devonian to tertiary shales exhibit mean cs weight ratios 1 8 0 5 somewhat lower than quaternary sediments meancs 2 8 this we believe is due to preferential c loss relative to s during biogenic methanogenesis plus diagenetic heating distinctly lower mean c s values for the cambrian and ordovician 0 5 0 1 cannot be explained solely in terms of diagenetic c loss and instead must represent low original ratios the low original ratios we suggest were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time because the major source of such material vascular land plants had not yet evolved this along with a possibly lower degree of bioturbation contributed to enhanced pyrite formation and preservation and thus lower early paleozoic cs ratios

stratigraphic reconstruction of the ediacaran yangtze platform margin hunan province china using a large olistolith abstract the southeast facing slope of the yangtze platform during deposition of the ediacaran doushantuo formation included several submarine slides and olistostromes of regional extent these platform margin derived slides provide windows into the contemporaneous platform margin this manuscript proposes a paleoenvironmental reconstruction and evolution of the ediacaran yangtze platform margin using facies analysis of one of these large scale slide sheets which transported shallow marine platform facies the base of the slide sheet shows dolomite chert evaporites and phosphorites lithological association with tepee structures and storm induced microbreccia dolomitised limestones with current related sedimentary structures overlie these facies thus the ediacaran yangtze platform may have evolved from a shallow rimmed platform with shallow restricted back rim basins developed on the margin to a wave dominated shallow subtidal platform sequence analysis applied to the slide sheet sediments allows relative dating of the sliding

the origin evolution and trajectory of large dust storms on mars during mars years 24 30 1999 2011 abstract mars daily global maps mdgm derived from the mars global surveyor mgs mars orbiter camera moc and mars reconnaissance orbiter mro mars color imager marci are used to study the distribution and evolution of large dust storms over the period from mars years 24 30 1999 2001 large storms are defined here as discrete dust events visible in image sequences extending over at least 5 sols mars days and where the dust covers areas beyond the origination region a total of 65 large dust storms meeting these criteria are identified during the observational period and all are observed during the l s 135 30 seasonal window dust storms originating in the northern and southern hemispheres appear to form two distinct families all but two of the storms originating in the northern hemisphere are observed in two seasonal windows at l s 180 240 and l s 305 350 while all but two of those originating in the southern hemisphere are observed during l s 135 245 none of the large dust storms originating in the northern hemisphere are observed to develop to global scale but some of them develop into large regional storms with peak area 1 10 7 km 2 and duration on the order of several weeks in comparison large dust storms originating in the southern hemisphere are typically much smaller except notably in the two cases that expanded to global scale the 2001 and 2007 global storms distinct locations of preferred storm origination emerge from the dust storm image sequences including acidalia utopia arcadia and hellas a route trajectory graph for the observed sequences is provided the routes are highly asymmetric between the two hemispheres in the south for non global dust storms the main routes are primarily oriented eastwest whereas in the north the routes are primarily north south and zonally concentrated into meridional channels in a few impressive cases storms originating in the northern hemisphere are observed to flush through acidalia and utopia across the equator and then branch in the low and mid southern latitudes the origin of the 2007 global dust storm is ambiguous from the imaging data immediately prior to the global storm a dust storm sequence from chryse is identified this storm s connection to the explosive expansion observed to start from noachis west hellas is unclear due to image coverage this paper further identifies and describes three different styles of dust storm development which we refer to as consecutive dust storms sequential activation and merging the evolution of a given dust storm sequence can exhibit different combinations of these growth styles at different stages of development dust storm sequences can overlap in time which makes them good candidate to grow into larger scale

high resolution backprojection at regional distance application to the haiti m7 0 earthquake and comparisons with finite source studies a catastrophic m w7 earthquake ruptured on 12 january 2010 on a complex fault system near port au prince haiti offshore rupture is suggested by aftershock locations and marine geophysics studies but its extent remains difficult to define using geodetic and teleseismic observations here we perform the multitaper multiple signal classification music analysis a high resolution array technique at regional distance with recordings from the venezuela national seismic network to resolve high frequency about 0 4 hz aspects of the earthquake process our results indicate westward rupture with two subevents roughly 35 km apart in comparison a lower frequency finite source inversion with fault geometry based on new geologic and aftershock data shows two slip patches with centroids 21 km apart apparent source time functions from usarray further constrain the intersubevent time delay implying a rupture speed of 3 3 km s the tips of the slip zones coincide with subevents imaged by backprojections the different subevent locations found by backprojection and source inversion suggest spatial complementarity between high and low frequency source radiation consistent with high frequency radiation originating from rupture arrest phases at the edges of main slip areas the centroid moment tensor cmt solution and a geodetic only inversion have similar moment indicating most of the moment released is captured by geodetic observations and no additional rupture is required beyond where it is imaged in our preferred model our results demonstrate the contribution of backprojections of regional seismic array data for earthquakes down to m 7 especially when incomplete coverage of seismic and geodetic data implies large uncertainties in source inversions

complexity of the mw 6 3 2009 l aquila central italy earthquake 1 multiple finite extent source inversion 1 strong ground motion recordings of the mw 6 3 2009 l aquila earthquake are analyzed by a newly proposed slip inversion technique the source model consists of multiple finite extent mufex subsources the slip amplitude rupture velocity rake and risetime are assumed constant within each subsource the size and location of the mufex subsources have to be inferred independently from other methods preferably those free of strong constraints such as constant rupture velocity over the whole fault etc here we use two published approaches satisfying such requirement the truncated singular value decomposition and the iterative multiple point source deconvolution each mufex subsource is characterized by an individual set of trial nucleation points rupture velocities and nucleation times which are grid searched for each combination of these parameters the subsources slip is determined by the least squares approach this procedure thus provides not only the best fitting model but also a whole range of acceptable models allowing for the uncertainty analysis the method is demonstrated on three synthetic tests when applied to the l aquila data both the best fitting model and the uncertainty analysis suggest that the event consisted of two major episodes one with the rupture propagating immediately after the nucleation in the updip direction the other being delayed by 3 4 s with dominant propagation toward the se along the deeper part of the fault the retrieved complexity of the rupture propagation warns against attempts to stabilize inversions by the use of a constant rupture velocity over the whole fault

the persistence of directivity in small earthquakes abstract we derive a simple inversion of peak ground acceleration pga or peak ground velocity pgv for rupture direction and rupture velocity and then test this inversion on the peak motions obtained from seven 3 5 m 4 1 earthquakes that occurred in two clusters in november 2002 and february 2003 near san ramon california these clusters were located on two orthogonal strike slip faults so that the events share the same approximate focal mechanism but not the same fault plane three earthquakes exhibit strong directivity but the other four earthquakes exhibit relatively weak directivity we use the residual pgas and pgvs from the other six events to determine station corrections for each earthquake the inferred rupture directions unambiguously identify the fault plane for the three earthquakes with strong directivity and for three of the four earthquakes with weak directivity the events with strong directivity have fast rupture velocities 0 63 v 0 87 the events with weak directivity either rupture more slowly 0 17 v 0 35 or bilaterally the simple unilateral inversion cannot distinguish between slow and bilateral ruptures adding a bilateral rupture component degrades the fit of the rupture directions to the fault planes by comparing pgas from the events with strong and weak directivity we show how an up dip rupture in small events can distort the attenuation of peak ground motion with distance when we compare the rupture directions of the earthquakes to the location of aftershocks in the two clusters we find than almost all the aftershocks of the three earthquakes with strong directivity occur within 70 of the direction of rupture

directivity effects for moderate magnitude earthquakes mw 5 6 6 0 during the 1997 umbria marche sequence central italy abstract the colfiorito mw 6 0 september 26 1997 09 40 utc and the sellano mw 5 6 october 14 1997 normal faulting earthquakes are the two strongest events of the 1997 1998 umbria marche seismic sequence central italy they provided accelerograms recorded at epicentral distances within nearly two fault lengths previous studies on these events revealed clear evidence of unilateral rupture propagation and directivity effects on the source time functions we developed an approximate procedure to correct the observed peak ground motion for the site effects and we found a systematic increase of peak ground acceleration pga and peak ground velocity pgv at sites located in the direction of the rupture propagation respect to the stations located to the backward in particular we showed that for the colfiorito earthquake the average pgv at the north west sites is 2 8 times larger than the pgv at south east sites 2 1 for pga an opposite behaviour is found during the sellano earthquake with an amplification factor of about 1 9 for pgv 1 5 for pga recorded at south east sites respect to the north west stations we explained these behaviours in terms of directivity effect by comparing recorded ground accelerations with synthetics simulated by a deterministic stochastic technique this method computes high frequency ground motions f 0 5 hz from extended faults generalizing the point source stochastic method to capture the essence of near source effects the synthetic pgas decrease with distance in agreement with the ground motion empirical predictive model available for the area and describe the azimuthal variation of recorded data in terms of source effects

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

geochronological constraints on stratigraphic correlation and oceanic oxygenation in ediacaran cambrian transition in south china the continuous late ediacaran early cambrian deep water successions of south china archive the complete evolution of seawater chemical conditions in the deep ocean during this critical time interval however the geochemical data from these poorly fossiliferous and condensed successions lack high resolution stratigraphic constraints hampering their interpretation for the spatio temporal evolution of the sweater chemistry in this time interval in this study we report a new sims and ca id tims zircon u pb age 545 76 0 66 ma total uncertainty for an ash bed at the lower liuchapo formation in the deep water longbizui section in western hunan province the new age suggests that the lower and the middle upper parts of the liuchapo formation in the deep water facies can be correlated with the lower dengying formation and the upper dengying lower zhujiaqing formations in the shallow water facies respectively this correlation implies that the correlative horizon of the ediacaran cambrian boundary in the deep water facies in south china is likely located near the base of a widespread negative 13corg excursion at the upper liuchapo formation based on our new geochronological framework the compilations of fe speciation mo and u data indicate that the deep ocean was characterized by widespread anoxic ferruginous water with intermittent euxinic water impinged on the middle lower slope in ediacaran cambrian transition and significant oxygenation events occurred in 533 520 ma the compilations do not support any significant oceanic oxygenation events in 551 535 ma

carbonate carbon isotope evolution of seawater across the ediacaran cambrian transition evidence from the keping area tarim basin nw china sedimentary rocks from the ediacaran cambrian boundary record important biological climatic and geotectonic changes during this time to date only few geochemical investigations on the upper ediacaran upper cambrian rocks in the tarim basin have been carried out here we report high resolution 13 c carb records from the penglaiba the wushi phosphorite and the dongergou sections from ediacaran cambrian series 3 in the keping area of the tarim basin the sections display several obvious 13 c carb shifts 13 c carb values increased from 3 to 6 7 across the qigebulage formation moreover a negative 13 c carb shift across the ediacaran cambrian boundary is apparent 13 c carb values decreased to a minimum of 9 8 in the wushi phosphorite section 7 7 in dongergou section and 5 4 in penglaiba section followed by a positive carbonate carbon isotopic excursion across the yuertusi formation into the middle of the overlying xiaoerbulak formation furthermore more or less invariable positive 13 c carb values characterize the middle and upper xiaoerbulak formation the most negative 13 c carb value 14 3 occurred near the base of the shayilik formation which is the absolute minimum value among the studied sections of the cambrian series 2 to cambrian series 3 transition in the world the 13 c data from keping tarim basin are in good agreement with carbon isotope profiles recorded in south china and these events may reflect the perturbation of the carbon cycle in the tarim basin during the ediacaran cambrian and the cambrian series 2 cambrian series 3 transitions

rupture history of the 2009 l aquila italy earthquake from non linear joint inversion of strong motion and gps data 1 we image the rupture history of the 2009 l aquila central italy earthquake using a nonlinear joint inversion of strong motion and gps data this earthquake ruptured a normal fault striking along the apennines axis and dipping to the sw the inferred slip distribution is heterogeneous and characterized by a small shallow slip patch located up dip from the hypocenter 9 5 km depth and a large deeper patch located southeastward the rupture velocity is larger in the up dip than in the along strike direction this difference can be partially accounted by the crustal structure which is characterized by a high velocity layer above the hypocenter and a lower velocity below the latter velocity seems to have affected the along strike propagation since the largest slip patch is located at depths between 9 and 14 km the imaged slip distribution correlates well with the on fault aftershock pattern as well as with mapped surface breakages

ree and trace element patterns from organic rich rocks of the ediacaran cambrian transitional interval abstract it has been established that important changes in the marine environment and the biosphere occurred during the cambrian however the relationships between the so called cambrian explosion and the concomitant environmental changes are not yet fully understood this study presents new geochemical data from the black shale successions from different facies belts of the yangtze platform in south china variations in the concentrations of ree and trace elements varying ce ce th u v sc and v cr ratios in kerogen as well as in bulk rocks from different depositional environments along a transect from platform to basin indicate two oxidation events which led to the oxygenation of the water column in shallow marine environments and euxinic conditions weak correlation between toc v u and mo in the deeper sea during the first oxidation event in the late terreneuvian anoxic conditions in bottom waters rapidly changed to euxinic conditions subsequently the second oxidation event during the early epoch 2 of the cambrian led to oxic suboxic conditions in deeper seawater

controls on organic matter accumulation on the early cambrian western yangtze platform south china abstract the origin of widespread organic rich shales on the early cambrian yangtze platform of nanhua basin south china has been attributed to high primary productivity to test this hypothesis we generated multiple paleoproductivity ocar and par paleoredox corg p ratios upwelling restriction coef mnef co ppm mn mo toc and cd mo ratios and terrigenous flux proxies al and unreactive fe feu for the lower cambrian niutitang formation in the outer shelf jinsha section which records a typical transition from the organic rich black shales to overlying organic lean mudstones or siltstones these new data were integrated with published paleoredox proxies iron speciation and redox sensitive trace metals for the same section our results suggest that the organic rich toc 4 6 1 8 lower member lm 0 37 m of the niutitang formation records ferruginous conditions high productivity levels and low siliciclastic fluxes and that the organic poor toc 0 1 0 1 upper member um 37 329 m was characterized by dominantly oxic conditions declining productivity levels and high siliciclastic fluxes our results suggest a redox shift from ferruginous to oxic conditions and enhanced terrigenous fluxes in response to falling sea level from the lm to the um secular variations in primary productivity and redox conditions are strongly correlated which is consistent with a positive feedback high primary productivity led to increasing water column anoxia which enhanced organic p recycling stimulating further productivity variations in primary productivity may reflect variable upwelling intensity in a semi restricted shelf setting linked to sea level changes taken together these findings suggest that a combination of primary productivity redox conditions and terrigenous fluxes driven by sea level changes played a key role in organic matter accumulation on the early cambrian western yangtze platform

a window into the complexity of the dynamic rupture of the 2011 mw 9 tohoku oki earthquake the 2011 mw 9 tohoku oki earthquake recorded by over 1000 near field stations and multiple large aperture arrays is by far the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in earthquake source dynamics here we conduct a high resolution array analysis based on recordings from the usarray and the european network the mutually consistent results from both arrays reveal rupture complexity with unprecedented resolution involving phases of diverse rupture speed and intermittent high frequency bursts within slow speed phases which suggests spatially heterogeneous material properties the earthquake initially propagates down dip with a slow initiation phase followed by sustained propagation at speeds of 3 km s the rupture then slows down to 1 5 km s for 60 seconds a rich sequence of bursts is generated along the down dip rim of this slow and roughly circular rupture front before the end of the slow phase an extremely fast rupture front detaches at about 5 km s towards the north finally a rupture front propagates towards the south running at about 2 5 km s for over 100 km key features of the rupture process are confirmed by the strong motion data recorded by k net and kik net the energetic high frequency radiation episodes within a slow rupture phase suggests a patchy image of the brittle ductile transition zone composed of discrete brittle asperities within a ductile matrix the high frequency is generated mainly at the down dip edge of the principal slip regions constrained by geodesy suggesting a variation along dip of the mechanical properties of the mega thrust fault or their spatial heterogeneity that affects rise time

martian dust storm activity near the mars 2020 candidate landing sites mro marci observations from mars years 28 34 abstract mro marci daily global mapping images from 16 november 2006 ls 111 4 through 15 july 2017 ls 33 5 covering portions of seven consecutive martian years my 28 my 34 were used in a survey of dust storm activity within 2000 km radius of the final three candidate sites for the 2020 mars rover mission columbia hills at 14 59 s 175 53 e north east syrtis at 17 89 n 77 16 e and jezero at 18 39 n 77 54 e a total of 1321 dust storms 1228 local 93 regional were observed storms were observed in all seasons but showed distinct seasonal trends columbia hills monitoring area experienced eastward traversing polar hood seasonal cap edge storms during southern autumn and winter with a gradual transition during southern spring to northern hemisphere storms along the elysium and arcadia amazonis tracks with winter dominated by the northern hemisphere storms syrtis sitess were dominated by cap edge storms during northern spring transitioning to subtropical syrtis major and north of hellas basin storms in both hemispheres during northern summer with autumn bringing continued storm activity in the southern subtropics and increased activity along the utopia cross equatorial storm track followed in winter by a transition back to north polar hood seasonal cap edge storms peak storm frequency occurs during autumn for the syrtis sites and winter for columbia hills site during the entry descent and landing edl season ls 345 25 the daily probability of dust storm activity at the landing sites ranged from 1 6 for the columbia hills to 3 2 for syrtis sites for edl sol ls 6 storm probabilities drop to approximately 0 0 for columbia hills and ranged from 0 6 1 2 for the other sites indicating that storms are of minimum concern for edl

carbon isotopic evolution of the terminal neoproterozoic and early cambrian evidence from the yangtze platform south china profound geotectonic climatic and biological changes occurred during the terminal neoproterozoic and its transition into the early cambrian these changes are reflected in temporal variations of the carbon isotopic composition of seawater recorded in a sedimentary succession on china s yangtze platform however in addition to secular changes in carbon isotopes the studied succession reflects additional variations in accordance with the deposition in different sedimentary facies ranging from shallow water platformal to deeper water basinal settings likely a consequence of incorporation of variable amounts of 13 c depleted

spatiotemporal evolution and causes of marine euxinia in the early cambrian nanhua basin south china abstract marine redox conditions and their dynamic variations in the early cambrian are thought to have strongly influenced the evolution of early animals however the patterns and mechanisms of contemporaneous marine redox variation remain poorly understood the nanhua basin south china was a failed rift basin located between the yangtze block nw margin and cathaysia block se margin in the early cambrian in this study we conducted a comprehensive study of marine redox conditions sulfur cycling and chemical weathering intensity of source areas for the lower cambrian shales of the qingxi formation in the basinal shimensuidao section which was geographically close to the cathaysia block we integrated these results with previously published data from the nearby silikou section as well as the coeval inner shelf xiaotan upper slope daotuo lower slope longbizui and basinal zhalagou sections where were closer to the yangtze block at shimensuidao iron species and redox sensitive trace element data suggest dominantly euxinic conditions for the organic rich black shale interval lower member lm and variable redox conditions oxic ferruginous euxinic for the overlying organic lean shales upper member um of the qingxi formation integrated redox results show a similar lessening of euxinic conditions from lm to um across the entire basin and that euxinia developed along both the yangtze and cathaysia basin margins but it was mainly in upper slope areas e g daotuo on the yangtze margin and reached basinal areas e g silikou and shimensuidao on the cathaysia margin a decline of 34spy from lm to um was observed at shimensuidao and other sections which can be explained by decreasing microbial sulfate reduction rates due to decreasing organic availability and increasing riverine sulfate flux at study sections lower 34spy values in shallow marine relative to deep marine areas suggest increased terrestrial sulfate availability to the shallower sites chemical index of alteration cia values at shimensuidao are uniformly high for both the lm ciacorr1 82 5 0 4 ciacorr2 88 6 0 5 and um ciacorr1 80 2 2 3 ciacorr2 86 2 2 5 compared with the low to moderate values at daotuo ciacorr2 61 9 3 9 for lm 71 3 4 8 for um this pattern is consistent with intense chemical weathering of source areas on the cathaysia block and weaker chemical weathering of source areas on the yangtze block based on these observations we propose that strong chemical weathering of the cathaysia block led to regionally high terrigenous sulfate fluxes resulting in expansion of mid depth euxinia into deep basinal areas on the cathaysia margin of the nanhua basin in contrast weak chemical weathering of the yangtze block yielded lower terrigenous sulfate fluxes limiting euxinia to upper slope areas on the yangtze margin of the basin weaker euxinia during um deposition may have been due to its decreasing organic availability and or small seawater sulfate reservoir caused by persistent euxinic consumption during lm deposition our results highlight the complex controls and the key role of continental weathering and resulting terrigenous sulfate fluxes in marine euxinic variations in early cambrian marginal seas providing new insights into the co evolution of continents oceans and early animals