geochemistry of eolian dust and its elemental contribution to lake qinghai sediment abstract located at the midpoint of the asian airborne dust corridor lake qinghai receives substantial dust annually which may impact the biogeochemical cycles of the system in order to determine quantitatively the flux and chemical contributions of dust to lake qinghai sediment dust samples were collected monthly at two sites surrounding the lake from june 2009 to may 2011 the results demonstrate similar chemical compositions of dust samples to the local loess implying strong representativeness of regional dust the average dust deposition flux is 265 7 55 0 g m 2 a constituting 56 6 11 7 of the modern sediment approximating to previous estimates 65 contributions of dust derived elements in the sediment differ substantially with a minimum of 16 7 for sr and a maximum of 83 9 for cu among these elements the contribution of lithophile elements na al k ti mn fe and rb is close to that of the bulk dust the contributions of mobile elements mg ca and sr are low only 16 7 sr 26 1 mg whereas potentially harmful metals cu zn and pb have high contributions 70 3 83 9 seasonal variations of elemental inputs indicate that springtime contributions dominate the annual dust fluxes for all elements into the sediment in agreement with the high dust flux in spring these observations not only quantify the contribution of dust to the sediment of lake qinghai but also highlight the important role of dust in the accumulation of various elements in the sediment especially for potentially harmful metals

selection of earthquake scaling relationships for seismic hazard analysis a fundamentally important but typically abbreviated component of seismic hazard analysis is the selection of earthquake scaling relationships these are typically regressions of historical earthquake datasets in which magnitude is estimated from parameters such as fault rupture length and area the mix of historical data from different tectonic environments and the different forms of the regression equations can result in large differences in magnitude estimates for a given fault rupture length or area we compile a worldwide set of regressions and make a first order shortlisting of regressions according to their relevance to a range of tectonic regimes plate tectonic setting and fault slip type in existence around the world regression relevance is based largely on the geographical distribution age and quantity quality of earthquake data used to develop them our compilation is limited to regressions of magnitude or seismic moment on fault rupture area or length and our shortlisted regressions show a large magnitude range up to a full magnitude unit for a given rupture length or area across the various tectonic regimes these large differences in magnitude estimates underline the importance of choosing regressions carefully for seismic hazard application in different tectonic environments

controls on the basinwide architecture of late miocene messinian evaporites on the levant margin eastern mediterranean abstract interpretation of 2d and 3d seismic data from the levant margin eastern mediterranean has revealed the complex depositional and structural setting of the basinwide late miocene messinian evaporites the data set covers a total area of 20 000 km2 permitting a semi regional investigation of the thick up to 1 8 km evaporitic wedge the sequential analysis of time structure maps isochron maps and seismic cross sections highlighted the main morphological and structural features characterizing the pre syn and post evaporitic levant margin this approach provided insights on the impact of local vs regional factors in governing the distribution of the messinian salinity crisis in the region two regional features have been recognized as the most significant controlling factors for the architecture of the messinian evaporites firstly a series of anticlines of the syrian arc foldbelt acted as a structural barrier indirectly governing the overall landward extension of the evaporites secondly submarine canyons active in the area at least since the oligocene afiq el arish and ashdod canyons represented preferential sites of erosion and deposition of evaporites our results document therefore the importance of the deep seated structures and relict drainage for the architecture of the messinian evaporites on the levant margin the new insights provided can be additionally used to infer the original depositional geometry of the evaporites in the study area and as an analogue in other mediterranean areas where 3d seismic is not available yet and sub salt imaging is limited

seasonal contributions of catchment weathering and eolian dust to river water chemistry northeastern tibetan plateau chemical and sr isotopic constraints relative to winter it is noticeable that both the lowest and the highest 87 sr 86 sr values of the buha river waters occurred in the monsoon season indicating a sensitive response of carbonate versus silicate weathering sources to hydrological forcing on a seasonal basis a significant decrease in na cation together with lower sr isotope ratios is consistent with a greater proportion of carbonate weathering relative to silicate weathering in the early monsoon season high temperature and increased rainfall during the peak of the monsoon facilitate an increased proportion of ions derived from silicates partly from groundwaters to river water in other seasons elemental and 87 sr 86 sr ratios vary much less indicating a constant ratio of silicate to carbonate weathering consistent with limited variation in discharge our results highlight that in a semiarid region where climatic conditions vary seasonally in addition to silicate and carbonate contributions supply from eolian dust may also play a significant role in controlling seasonal variations in chemistry of river waters

holocene climatic changes revealed by aeolian deposits from the qinghai lake area northeastern qinghai tibetan plateau and possible forcing mechanisms previous palaeoclimatic studies in the northeastern qinghai tibetan plateau netp during the holocene mainly using lake sediments have deepened our understanding of the climatic system in this remote region the timing and forcing mechanisms of climatic change in this region are still controversial however aeolian sand and silt deposits which are widely distributed in the netp can be readily dated by optically stimulated luminescence osl techniques and reveal the sensitive response of the landscape to climatic change in this study aeolian sand and loess at six sites around qinghai lake were studied to reconstruct millennial scale climatic changes during the holocene multiproxy data along with 24 osl age determinations show that low effective moisture and aeolian activity occurred at c 13 ka 10 9 1 ka and 8 9 7 8 ka periods of greater effective moisture may have occurred at 11 ka and 9 ka and there is evidence for a previously undocumented wet climate at 4 3 ka these results show that mi

revisiting clay sized mineral and elemental records of the silicate weathering history in the northern tibetan plateau during the late cenozoic the role of aeolian dust

lg wave propagation in a laterally varying crust and the distribution of the apparent quality factor in central france the aim of this study is to evaluate the sensitix ity of lg waves to lateral changes of the earth s structure considering a simple model of uplift of the moho numerical simulations show that the geometrical attenuation of lg is not much affected by a smooth anomaly of the moho depth on the other hand the passing of the lg wave through the region of the moho uplift results in a clear deterioration of the wave shapes which confirms the occurrence of mode conversions the presence of an overlying sedimentary basin causes a local amplification of lg above the basin itself and the appearance behind the basin of a secondary surface wave guided in the sediments the effect of the basin on the lg wave is found to be reasonably taken into account by applying a local amplification function to the data we use a data set consisting of records of lg phases in france to test the conclusions of our numerical study the mapping of the apparent quality factor computed from lg at different frequencies confirms the interpretation of the strong attenuation of s waves around i hz in terms of scattering and shows the weak sensitivity of the amplitude of lg to smooth changes in the depth of the moho

characterization of the composition of dust fallout and identification of dust sources in arid and semiarid north china abstract a source analysis to characterize the composition of dust fallout in arid and semiarid north china an important source area of dust for east asia was performed monthly samples were obtained from april 2001 to march 2002 at 29 sites in sandy and gobi deserts steppes and loess areas and the following elements were analyzed ce co cs eu fe hf lu nd rb sc ta tb th as la na sb sm u yb al ca mg mn ti and v although the dust compositions differed it was difficult to determine the potential dust source areas based solely on the elemental fingerprints of the dust principal components analysis showed that at most sites sm sc la ce eu and th were most strongly correlated r 0 7 with other elements whereas crustal elements such as al fe and ti were only strongly correlated with the other elements at a few sites of the 26 elements that we analyzed maybe only sb was representative of anthropogenic pollution but pollutant sources were unclear because at most sites in different months the crustal derived elements and those derived from anthropogenic pollutants always appeared synchronously creating difficulties and high uncertainties in source identification

high altitude aeolian research on the tibetan plateau aeolian processes and their role in desertification have been studied extensively at low elevations but have been rarely studied at high elevations in areas such as the tibetan plateau where aeolian processes were active in the geologic past and remain active today in this review we summarize research that improves our understanding of aeolian processes on the tibetan plateau including the distribution characteristics and provenance of aeolian sediments the history of aeolian activity aeolian geomorphology and wind driven land degradation contemporary aeolian processes primarily occur in dry basins in wide river valleys on lakeshores on mountain slopes and on gravel pavements sediment characteristics suggest a local origin and provide interesting contrasts with those of china s loess plateau the history of aeolian activity and its paleoclimatic implications reconstructed based on aeolian archives is short mostly since the late glacial and shows wide regional differences aeolian geomorphology is simple and suggests short formation time wind driven land degradation is less severe than previously thought driven by different factors in different areas and exhibited complex interactions with freeze thaw processes aeolian research has been conducted within the general framework of aeolian science but addresses issues specific to the tibetan plateau that arise due to the low air temperature low air density and the presence of a cryosphere we propose six priorities for future research aeolian physics the effect of freeze thaw cycles comparisons with other areas regional differences effects of wind driven land degradation and integrated observation and monitoring

fluxes of al fe ti mn pb cd zn ni cu and as in monthly bulk deposition over the pyrenees sw europe the influence of meteorology on the atmospheric component of trace element cycles and its implications for high mountain lakes 1 the atmospheric bulk wet plus dry deposition of trace elements was measured monthly at lake redon 2240 m above sea level central pyrenees spain in 2004 2006 aluminum ti fe mn and as were part of the dust carried from the iberian peninsula and north africa these elements presented low enrichment factors and occurred except mn as particles lead zn cd and cu showed a polluting character their enrichment factors were clearly above those that can be caused by natural fractionation processes and they were found in a variable though always large proportion as soluble forms nickel had intermediate properties suggesting a balance of both natural and polluting sources temporal variations of trace element deposition were related to the prevailing meteorological conditions deposition of dust pb ni and cd was higher during the year in which a larger proportion of precipitation came from the iberian peninsula north africa and followed low altitude trajectories on a seasonal scale deposition of dust and pb was similarly related to southern air masses occurring during june november possible changes in the general atmospheric circulation patterns as a result of climate change may cause a shift in the proportion of air masses coming from different locations and hence in the fluxes of the elements received by the catchments such atmospheric fluxes have caused high concentrations of several trace elements in pyrenean lake sediments at a level which may be of ecotoxicological relevance

eustatic implications of late miocene depositional sequences in the melilla basin northeastern morocco abstract the age 5 78 ma or lower chron c3r of the major drawdown of the paleo mediterranean sea during the messinian salinity crisis has been established by combining results from stratigraphy paleontology magnetostratigraphy and argon dating for a late miocene sedimentary succession in the melilla basin ne morocco this event is inferred from a marine to continental series of carbonate and siliciclastic rocks that record the end of messinian marine deposition in the melilla basin and presumably marks the final isolation of the paleo mediterranean sea the evidence from the melilla basin is approximately coeval with an increase in benthic foraminiferal 18 o values from a deep marine section in the bou regreg valley nw morocco hodell et al 1994 this increase suggests that a glacio eustatic lowering of sea level at least contributed to the final closure of the mediterranean during the messinian salinity crisis the marine to continental succession onlaps a carbonate complex that contains evidence for multiple relative sea level changes leading up to the main drawdown from bottom to top the carbonate complex is composed of 1 an onlapping ramp 2 a prograding bioclastic platform 3 a prograding and locally downstepping porites reef complex and 4 a topography draping sequence composed of grainstones porites reefs and stromatolites terminal carbonate complex of esteban 1979 the transgressive ramp correlates to relatively low values of benthic foraminiferal 18 o values from a tortonian to lower messinian section at bou regreg hodell et al 1994 this correlation indicates at least in part a link between rising sea level and a reduction in global ice volume during deposition of the ramp a major fall in relative sea level 60 m occurred near the demise of the reef complex during chron c3n 1n at 5 95 0 10 ma this signals the initiation of drawdown and changing environmental conditions in the melilla basin a marginal basin and perhaps the entire paleo mediterranean sea a megabreccia interpreted as forming by solution collapse of evaporites on the basin margin of the reef complex occurs at the base of the terminal carbonate complex updip a major subaerial unconformity separates the reef complex and terminal carbonate complex evaporite deposition likely occurred during this exposure event and has been dated at 5 82 0 02 ma near the base of chron c3r we contend that these evaporites restricted to the shallow melilla basin are related to the continuation of the initial stage of the major drawdown of the paleo mediterranean sea

calibration of the mdco dust collector and of four versions of the inverted frisbee dust deposition sampler abstract wind tunnel experiments were conducted to determine the efficiency of sediment samplers designed to measure the deposition of aeolian dust efficiency was ascertained relative to a water surface which was considered the best alternative for simulating a perfectly absorbent surface two types of samplers were studied the marble dust collector mdco and the inverted frisbee sampler four versions of the latter catcher were tested an empty frisbee an empty frisbee surrounded by an aerodynamic flow deflector ring a frisbee filled with glass marbles and a frisbee filled with glass marbles and surrounded by a flow deflector ring efficiency was ascertained for five wind velocities range 1 5 m s 1 and eight grain size classes range 10 89 m the efficiency of dust deposition catchers diminishes rapidly as the wind speed increases it also diminishes as the particles caught become coarser adding a flow deflector ring to a catcher substantially improves the catcher s efficiency by up to 100 in some cases the addition of glass marbles to a catcher on the other hand does not seem to increase the efficiency at least not at wind velocities inferior to the deflation threshold for higher velocities the marbles protect the settled particles from resuspension keeping them in the catcher the following five parameters determine the accumulation of aeolian dust in a catcher the horizontal dust flux the weight of the particles atmospheric turbulence resuspension and the dust shadow effect created by the catcher the final accumulation flux depends on the combination of these parameters the catchers tested in this study belong to the best catchers currently in use in earth science and have been the subject of various aerodynamic studies to improve their efficiency nevertheless the catching efficiency remains low in the order of 20 40 for wind speeds above 2 m s 1 other catchers suffer from the same low efficiencies there is thus evidence to believe that dust deposition rates published in the aeolian literature and obtained by collecting the sediment in a catcher largely underestimate the true deposition the errors are considerable of the order of 100 and more a reconsideration of the literature data on aeolian dust deposition measured by catchers is therefore required

pinning points a method providing quantitative constraints on relative sea level history abstract quantitative constraints on the history of relative sea level allow for a better understanding of the controls on depositional sequence development the constraints are provided by pinning point curves plots of ancient relative sea level elevations pinning points versus time constructing a pinning point curve requires identification of ancient stratigraphic positions of sea level through interpretation of facies and surfaces formed at sea level then their ancient relative elevations are determined through reconstructing aspects of ancient paleotopography upper miocene strata from las negras southeastern spain preserve paleotopography contain ancient surfaces of subaerial exposure and contain facies deposited near sea level the pinning point curve illustrates a complex relative sea level history with large and small scale relative sea level fluctuations defined by 31 pinning points

late miocene stable isotope stratigraphy of se atlantic odp site 1085 relation to messinian events abstract high resolution benthic oxygen isotope and xrf fe and ca records from site 1085 drilled in the mid cape basin odp leg 175 are used to investigate global climate changes during the late miocene in relation to messinian geological events the cyclic fluctuations of the time series at site 1085 enable us to establish a reliable chronology for the time interval 7 3 4 7 ma spectral analysis of the 18o record indicates that the 41 kyr period of orbital obliquity dominates the late miocene record a global climate record was extracted from the oxygen isotopic composition of benthic foraminifera both long and short term variabilities in the climate record are discussed in terms of sea level and deep water temperature changes the time interval 7 3 6 25 ma characterized by low amplitude 18o variations is followed by a period marked by maximum in the 18o values 6 25 5 57 ma at about 5 56 ma a rapid decrease in 18o values is documented that may reflect a warming of deep water temperature associated with a global warming period comparison between the timing of the oceanic isotope events and the chronology of the mediterranean salinity crisis suggest that global eustatic processes were not essential in the mediterranean salinity crisis history from our data we infer that the global warmth documented in the early mid pliocene probably started during the late miocene at 5 55 ma at the same time the onset of evaporite deposition in the central basin of the mediterranean sea took place sharp changes in the sedimentation rates mainly driven by terrigenous input at this site are observed during the messinian stage

attenuation of multiphase surface waves in the basin and range province part i lg and lg coda summary broad band data recorded by the lawrence livermore laboratory network are used to investigate whether or not lg q and lg coda q have similar values in the basin and range province of north america in order to retrieve spectral estimates of the broad band lg and lg coda signals a hybrid method is used which retains high fidelity at lower frequencies while strongly smoothing the spectral estimates and minimizing the number of spectral points at high frequencies a stochastic approach is used to model the lg signal and ambient noise and to analyse results from two station determinations of lg q in the basin and range the effects of ambient noise frequency dependent station site response and focusing defocusing on lg q inversion are analysed it is shown that after averaging spectral ratios determined from repeated observations over four two station paths a modest site effect will not cause significant errors in the resulting lg q relation using this inversion scheme and spectral ratio estimates averaged over those paths at frequencies between 0 2 and 2 5 hz we obtain the relation qlg f 267 f 56 f0 37 0 06 for the basin and range province further constraints on lg q were obtained from lg coda which due to the natural averaging effect of scattering is insensitive to effects of focusing defocusing to investigate the validity of the single isotropic scattering model for lg coda in the basin and range province we calculated ischrons for scatterers corresponding to later lg coda signals as required by the single scattering model it is found that when significant portions of these isochrons are oceanic lg coda amplitude decay becomes irregular and abnormally slow suggesting a strong scattering reflection effect caused by the rapidly changing crustal structure along the coast applying the single isotropic scattering model to lg coda records with isochrons mostly confined to the continental crust results in q f 275 f 26 f 0 36 0 03 which is nearly identical to our qlg relation this indicates that even in a complicated geological province a joint interpretation of the dynamic properties of lg and lg coda can be successful and fruitful inconsistent lg q and coda q relations found in earlier studies in the basin and range province may be attributed to different settings of parameter trade offs different seismic phases or different dynamic properties being used

sources and flux of trace elements in river water collected from the lake qinghai catchment ne tibetan plateau river waters play a significant role in supplying naturally and anthropogenically derived materials to lake qinghai northeastern tibetan plateau to define the sources and controlling processes for river water chemistry within the lake qinghai catchment high precision icp ms trace element concentrations were measured in water samples collected from the buha river weekly in 2007 and from other major rivers in the post monsoon late october 2006 and monsoon late july 2007 seasons the distributions of trace elements vary in time and space with distinct seasonal patterns the primary flux in the buha river is higher tds and dissolved al b cr li mo rb sr and u during springtime than those during other seasons and is attributed to the inputs derived from both rock weathering and atmospheric processes among these elements the fluxes of dissolved cr b and rb are strongly influenced by eolian dust input the fluxes of dissolved li mo sr and u are also influenced by weathering processes reflecting the sensitivity of chemical weathering to monsoon conditions the anthropogenic sources appear to be the dominant contribution to potentially harmful metals ni cu co zn and pb with high fluxes at onset of the main discharge pulses due at least partially to a runoff washout effect for other major rivers except for ba concentrations of trace elements are higher in the monsoon than in the post monsoon season a total of 38 5 3 1 tons of potentially harmful elements are transported into the lake annually despite human activities within the catchment being limited nearly all river water samples contain dissolved trace elements below the world health organization guidelines for drinking water with the exception of as and b in the daotang river water samples collected in late july probably mobilized from underlying lacustrine sediments

the nile deep sea fan an example of interacting sedimentation salt tectonics and inherited subsalt paleotopographic features abstract structural analysis of the nile deep sea fan ndsf indicates that post miocene deformation is largely controlled by down slope movement above a messinian salt layer in contrast to other similar systems the ndsf shows significant lateral asymmetry and three distinct provinces can be recognized regional variations in salt thickness and base salt geometry within the system have led to the presence of structures typical of both gravity gliding and gravity spreading trends of structures within the western and central parts of the ndsf are consistent with forming due to gravity gliding processes this pattern contrasts with that in the eastern ndsf that seem to be much more consistent with deformation due to gravity spreading observed differences in structural style across the ndsf can be related directly to the paleomorphological evolution of the nile cone during messinian time which is perhaps partly related to features that have been inherited from early mesozoic evolution of the north egypt passive margin in the east part of the ndsf the structural evolution has been significantly influenced by the proximity of eratosthenes seamount this large topographic buttress has served to both limit and deflect northeastward allochthonous advance of the messinian evaporites and has thus severely complicated deformation of the overlying plio quaternary sedimentary cover within the broad corridor that runs nnw sse and cuts obliquely across the modern bathymetry of the nile cone

interpretation of high frequency coda at large distances stochastic modelling and method of inversion summary based on previous work a stochastic convolution model is proposed for the lg coda observed at large epicentral distances 200 km coda at these distances differ from local coda in several respects effects of various physical processes such as dispersion scattering and mode conversion on coda at large distances are discussed in detail a spectral ratio method is developed for inversion of lg coda q in which the large variance associated with inversion is greatly reduced the method is also extended to the inversion of seismic source parameters by jointly using lg and its coda we have tested the model and method exhaustively using data from two gdsn stations and found the results to be superior to other methods when those methods used only a small number of stations

lake qinghai sediment geochemistry linked to hydroclimate variability since the last glacial abstract geochemistry of basin sediments from semi arid regions is valuable to understand past hydroclimatic changes here we investigate the links of sedimentary geochemistry rb sr ca zr toc and caco 3 carbonate mineralogy and ostracod shell 18 o of lake qinghai a basin proximal to major dust production centers at mid latitudes of the northern hemisphere to changes in depositional conditions and hydroclimate during the past 32 ka surface lacustrine sediments are characterized by low rb high sr low rb sr high caco 3 and high ca zr values in contrast to the chemical compositions of eolian loess high rb low sr high rb sr low caco 3 and low ca zr a direct comparison of soluble ca and sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in lake qinghai are dominated by authigenic aragonite formed under ca 2 limited water conditions and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons late may to september our high resolution down core records show that sediments during the last glacial 32 19 8 ka had high rb low sr low caco 3 and low ca zr indicating eolian dust loess accumulation in a desiccated basin under dry glacial conditions further supported by grain size and pollen results this type of sedimentation was maintained during the last deglacial 19 8 11 5 ka but interrupted by episodic lacustrine precipitates with high sr high caco 3 high ca zr and low rb at 11 5 ka sedimentary rb sr ca zr caco 3 and toc show dramatic and permanent changes implying an abrupt shift in the atmospheric circulation at the onset of the holocene in the lake qinghai region lacustrine precipitates have persisted throughout the holocene with a maximum during the early to mid holocene 10 5 8 0 ka since 8 0 ka the gradual and significant decreases in aragonite and sr accumulations in tandem with increasing dust deposit and more positive ostracod 18 o may be linked to a weakening of asian summer monsoons during the mid to late holocene overall our records appear to show a high sensitivity of sediment development and geochemistry in lake qinghai to the regional hydroclimate changes since the last glacial

toward a geochemical mass balance of major elements in lake qinghai ne tibetan plateau a significant role of atmospheric deposition abstract sediments in lake qinghai archive important information about past environmental changes in order to faithfully interpret the sediment records and constrain the elemental cycles it is critical to trace various sources of sediments in the lake the results show that the elemental input output budgets are imbalanced for most major elements between riverine fluxes and mass accumulation rate mar of lake qinghai sediments a realistic model must include contributions of dry wet atmospheric deposition that allow the major element mass balance for the lake to be defined the budget estimation is based on mass balances of si and al which are relatively immobile and carried to the lake via particulate forms estimated annual budget of dry atmospheric deposition is 1 3 0 3 103 kt a accounting for 65 of the total inputs to the lake sediments assuming local loess within the catchment as a candidate for dry atmospheric deposition to the lake the resultant flux of 300 45 g m2 a falls within the flux average of the desert area 400 g m2 a and the loess plateau 250 g m2 a consistent with the geographical setting of lake qinghai the role of atmospheric deposition would be more significant if wet deposition via rainfall and snow were taken into account this highlights the potential importance of dust as a significant source for sediment preservation flux for other catchments worldwide the results also indicate that nearly all ca input was preserved in the lake sediments under modern conditions consistent with ca2 supersaturation of the lake water

plate waves and the 1980 huajuapan de leon mexico earthquake abstract we propose two alternate structural models featuring a dipping oceanic plate in the subduction zone of southwestern mexico based on the relocation by the master event method of 77 aftershocks of the 1980 huajuapan mexico earthquake recorded by the mexican continental aperture seismic network resmac the aftershock locations roughly define the rupture surface of the main event as a normal fault dipping towards the continent the rupture involved a thickness of about 25 km in the top of the subducted plate these results are consistent with the fault plane solution both models feature a waveguide in the top of the subducted plate which may account for the large relative amplitudes of plate waves relative to direct waves at all stations and the large high frequency content observed at a station on the coast compared with stations inland

hardened subtidal stromatolites bahamas hardened high relief stromatolites have been discovered along the margins of some bahamian platforms they occur in high energy tidal oolitic sand environments in waters ranging in depth from about 1 to 5 meters physical stress produced by actively migrating bed forms of oolitic sand appears to exclude grazing gastropods and subsequent community successions permitting stromatolite growth

late orogenic doming in the eastern betic cordilleras final exhumation of the nevado filabride complex and its relation to basin genesis the geometry timing and kinematics of late orogenic extension in the betic cordilleras pose the problem of a decoupling of upper crustal and lower crustal deformation regimes perpendicular directions of extension in metamorphic domes and nearby sedimentary basins remain unexplained this paper puts kinematic constraints on the final exhumation of the nevado filabride complex focusing on the formation of metamorphic domes and their relations with the adjacent basins structural fabrics and kinematic indicators below the main shear zones as well as their relations with both published changing metamorphic p t conditions and geochronological data were studied our approach describes 1 a consistent top to the west shear parallel to dome axes of during d2 i e during decompression with distributed ductile flow and the onset of strain localization along major shear zones 2 further strain localization along the major shear zones under greenschist facies conditions during d3 leading to s c mylonites formation accompanied with a rock strong thickness reduction 3 the divergence of shear direction on either limbs of domes during d3 showing the appearance of the dome geometry and 4 a local evolution toward n s brittle extension d4 in the upper plate and formation of sedimentary basins continuous ductile to brittle top to the west shear is compatible with the slab retreat hypothesis from the miocene the formation of domes which adds gravitational forces responsible for the final stages of exhumation is thus characterized by important kinematics changes necessary to explain coeval n s opened basins later from the upper tortonian a contractional event d5 amplified the earlier domal structures forming the present north vergent folds

reconstruction of the paleoenvironmental changes around the miocene pliocene boundary along a west east transect across the mediterranean abstract in order to reconstruct the environmental changes at the end of the messinian salinity crisis a multidisciplinary study has been carried out with a high sampling resolution of the late messinian early zanclean zone mpl 1 sediments along a west east mediterranean transect the studied examples comprise sections from southern spain vera almanzora balearic basin odp site 975 tyrrhenian basin odp site 974 sicily eraclea minoa zakynthos kalamaki corfu aghios stefanos crete aghios vlasis previously analyzed sections from the levantine basin cyprus and odp sites 968 and 969 are used for comparison the sections have been correlated using planktonic foraminiferal assemblages sedimentological and stable isotope variations and compared to the astronomical cyclicity defined in the miocene pliocene boundary stratotype of eraclea minoa sicily variations of caco3 content stable isotopes of carbonates 18o 13c and foraminiferal assemblages indicate similar environmental transition at the miocene pliocene boundary in all of the investigated sections the latest messinian deposits are barren of fossils or characterized by only reworked planktonic foraminifers except for the sporadic presence of ammonia tepida brackish or lacustrine ostracods and brackish mollusks typical of the lago mare facies the oxygen and carbon isotopic compositions of carbonates usually exhibit large variations with dominantly low values indicating freshwater dilution the earliest pliocene mpl 1 cycle 1 shows a rapid and progressive increase of the 18o values which indicates the restoration of marine conditions after the lago mare event normal marine environments were definitely established and stabilized at the top of cycle 1 these data confirm that the inflow of marine waters occurred contemporaneously within the whole mediterranean at the base of pliocene although stable marine conditions occurred only about 20 kyrs later

source characteristics and propagation effects of the puebla mexico earthquake of 15 june 1999 the analysis of arrival times indicates that the focus of the 15 june 1999 20 42 utc 6 3 m b 6 5 m s 7 0 m w puebla mexico earthquake is located at 18 15 n and 97 52 w and is 68 km deep in the contact region between the continental american and the cocos subducting plate first motion data and regional and teleseismic waveform modeling indicate that the main rupture occurred as normal faulting along a fault striking n64 w and dipping approximately 42 toward the north northeast the aftershock activity though scarce is concentrated mainly toward the west of the mainshock three successive subevents are necessary to fit observed and synthetic waveforms the location in space and time of subevents indicates that the rupture started as a small release at 76 km deep and then propagated toward the northwest releasing most of the seismic energy at 73 km deep teleseismic spectral analysis indicates that the total seismic moment release was 2 0 1019 n m and the mainshock fault length is of the order of 18 km with a stress drop of 15 bars the source time function consisted of three sources with a total duration of 10 sec recorded acceleration amplitudes of the mainshock show a clear enhancement that can be up to eight times higher toward the northwest of the epicenter in the frequency range from 0 06 hz to 6 0 hz compared with the opposite direction the distribution of reported seismic intensity also shows this feature the directivity effect cannot be fully explained by the orientation of the fault neither by the rupture propagation direction therefore we investigate the possibility that the directivity could be due to a regional propagation effect by analyzing the lg coda decay of the mainshock the average frequency dependent q lg quality factor for the vertical component in the frequency range from 0 2 hz to 2 hz was q lg f 200 12 f 0 60 0 17 and q lg f 202 7 f 0 53 0 09 for paths toward the northwest and southeast of the epicenter respectively the resulting average factor q o and do not show significant azimuthal fluctuations therefore variations of crustal attenuation properties cannot explain the notable extent of felt area and observed damage northwest of the epicenter probably the presence to the north of the transmexican volcanic belt has played an important role in the enhancement of low frequency seismic signals

the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition abstract the deposition of aeolian or windblown dust is widely recognized as an important physical and chemical flux to ecosystems dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients there have been many studies that characterize the physical and chemical composition of dust however few studies have synthesized these observations in order to examine patterns geochemical fluxes we have compiled observations of dust deposition rates particle size distributions psd mineralogy and bulk elemental and organic chemistry the rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m 2 yr 1 sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions when compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales the distance from the source region that dust is deposited also influences the particle size distributions mineralogy and chemical composition of dust however more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns on average the concentrations of most major elements si al fe mg ca k in aeolian dust tend to be similar 20 to the composition of the upper continental crust ucc but there is substantial variability from sample to sample in contrast some elements tend to be depleted na or enriched ti in dust likely as a result of soil weathering processes prior to dust emissions trace elements especially heavy metals are consistently enriched in dust relative to the ucc ecologically important nutrients such as n and p are also present in dust deposition the geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions we calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition these estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models

late ordovician early silurian continental collisional orogeny in southern mexico and its bearing on gondwana laurentia connections new zircon and monazite u pb data tectonic mapping and petrologic studies in key units of the acatlan complex show a previously undocumented phase of continental collision orogeny of late ordovician early silurian age in southern mexico the event involved the partial eclogitization of oceanic lithosphere and continental crust which traveled westward more than 200 km over siliciclastic metasedimentary rocks of the trench forearc of an opposing continental margin the overriding eastern margin was the oaxaquia microplate attached to gondwana and the western overridden margin is considered to have been the eastern margin of laurentia this event which we name the acatecan orogeny was roughly synchronous with the possible closure of iapetus along the appalachian margin which involved according to current models either the docking of peri gondwanan terranes such as avalonia and carolina or the direct collision between gondwana and laurentia the permanence of oaxaquia in northwestern gondwana until the end of the silurian as suggested by tremadocian to silurian marine faunas in the cover of oaxaquia is more consistent with the direct collision of gondwana and laurentia at the end of the ordovician forming the acatlan complex between

on the nature of regional seismic phases iii the influence of crustal heterogeneity on the wavefield for subduction earthquakes the 1985 michoacan and 1995 copala guerrero mexico earthquakes summary the most prominent feature of the regional seismic wavefield from about 150 to over 1000 km is usually the lg phase this arrival represents trapped s wave propagation within the crust as a superposition of multiple reflections and its amplitude is quite sensitive to the lateral variation in the crust along a propagation path in an environment where the events occur in a subduction zone such as the western coast of mexico quite complex influences on the character of the regional wavefield arise from the presence of the subduction zone the great 1985 michoacan earthquake mw 8 1 which occurred in the mexican subduction zone was one of the most destructive earthquakes in modern history and its notable character was that at mexico city located over 350 km from the epicentre there was strong ground shaking almost comparable to that in the epicentral region that lasted for several minutes considerable effort has been expended to explain the origin of the unusual observed waves that caused the severe damage in the capital city during the destructive earthquake the nature of the propagation process in this region can be understood in part by using the detailed strong motion records from the 1995 copala guerrero mw 7 4 earthquake near the coast to the south of mexico city which also had an enhanced amplitude in the valley of mexico numerical modelling of both p and s seismic waves in 2 d and 3 d heterogeneous crustal models for western mexico using the pseudospectral method provides direct insight into the nature of the propagation processes through the use of sequences of snapshots of the wavefield and synthetic seismograms at the surface a comparison of different models allows the influences of different aspects of the structure to be isolated 2 d and 3 d modelling of the 1985 michoacan and 1995 copala earthquakes clearly demonstrates that the origin of the long duration of strong ground shaking comes from the sn and lg wave trains these s wave arrivals are produced efficiently from shallow subduction earthquakes and are strongly enhanced during their propagation within the laterally heterogeneous waveguide produced by the subduction of the cocos plate beneath the mexican mainland the amplitude and duration of the lg coda is also strongly reinforced by transmission through the mexican volcanic belt from the amplification of s waves in the low velocity surficial layer associated withs to p conversions in the volcanic zone the further amplification of the large and long lg wave train impinging on the shallow structure in the basin of mexico city with very soft soil underlain by nearly rigid bedrock with a strong impedance contrast gives rise to the destructive strong ground shaking from the mexican subduction earthquakes

late cenozoic climate changes in china s western interior a review of research on lake qinghai and comparison with other records abstract we review late cenozoic climate and environment changes in the western interior of china with an emphasis on lacustrine records from lake qinghai widespread deposition of red clay in the marginal basins of the tibetan plateau indicates that the asian monsoon system was initially established by 8 ma when the plateau reached a threshold altitude subsequent strengthening of the winter monsoon along with the establishment of the northern hemisphere ice sheets reflects a long term trend of global cooling the few cores from the tibetan plateau that reach back a million years suggest that they record the mid pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles during terminations i and ii strengthening of the summer monsoon in china s interior was delayed compared with sea level and insolation records and it did not reach the western tibetan plateau and the tarim basin lacustrine carbonate 18 o records reveal no climatic anomaly during mis3 so that high terraces interpreted as evidence for extremely high lake levels during mis3 remain an enigma following the last glacial maximum lsm several lines of evidence from lake qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr bp which was followed by a brief cold reversal possibly corresponding to the younger dryas event in the north atlantic region maximum warming occurred about 10 000 cal yr bp accompanied by increased monsoon precipitation in the eastern tibetan plateau superimposed on this general pattern are small amplitude centennial scale oscillations during the holocene warmer than present climate conditions terminated about 4000 cal yr bp progressive lowering of the water level in lake qinghai during the last half century is mainly a result of negative precipitation evaporation balance within the context of global warming

seasonally chemical weathering and co2 consumption flux of lake qinghai river system in the northeastern tibetan plateau the major cation and anion compositions of waters from the lake qinghai river system lqrs in the northeastern tibetan plateau were measured the waters were collected seasonally from five main rivers during pre monsoon late may monsoon late july and post monsoon middle october the lqrs waters are all very alkaline and have high concentrations of tds total dissolved solids compared to rivers draining the himalayas and the southeastern tibetan plateau seasonal variations in the water chemistry show that except the daotang river the tds concentration is high in october and low in july in the lqrs waters the forward models were used to quantify the input of three main rivers buha river shaliu river and hargai river from rain halite carbonates and silicates the results suggest that 1 atmospheric input is the first important source for the waters of the buha river and the shaliu river contributing 36 57 of the total dissolved cations 2 carbonate weathering input and atmospheric input have equal contribution to the hargai river water 3 carbonate weathering has higher contribution to these rivers than silicate weathering and 4 halite is also important source for the buha river the daotang river water is dominated by halite input owing to its underlying old lacustrine sediments the water compositions of the heima river are controlled by carbonate weathering and rainfall input in monsoon season and groundwater input may be important in pre monsoon and post monsoon seasons after being corrected the atmospheric input average co2 drawdown via silicate weathering in the lqrs is 35 103 mol km2 per year with highest in monsoon season lower than himalayas and periphery of tibetan plateau rivers but higher than some rivers draining shields

geochemical and isotopic characteristics of shallow groundwater within the lake qinghai catchment ne tibetan plateau abstract major ions isotopic ratios of strontium 87 sr 86 sr hydrogen d and oxygen 18 o of groundwater samples were analyzed to decipher spatial variation controlling factors solute sources and the recharge source of shallow groundwaters within the lake qinghai catchment shallow groundwaters in this area are slightly alkaline with 97 being fresh water of good quality though there are high concentrations of nitrate and sulfide in buha and lakeside groundwaters most of the shallow groundwaters are of the ca 2 hco 3 type whereas part of groundwaters surrounding the lake ls belongs to the na cl type as lake water qhl groundwater geochemistry is controlled by regional lithological association ion exchange and mineral precipitation the dissolved sr concentrations and 87 sr 86 sr ratios vary from 1 0 to 15 6 mol l and from 0 709859 to 0 715779 respectively the first quantitative calculation in groundwater using a forward model shows that 40 of dissolved sr is from carbonate weathering 33 from evaporite dissolution 17 from silicate weathering and the remainder from atmospheric input for the whole catchment carbonate weathering dominates groundwater geochemistry in shaliu sl hargai hg and buha bh samples while evaporite dissolution dominates ls and daotang dt samples d and 18 o data show that rain water is the major recharge source of both river water and shallow groundwater within the lake qinghai catchment qinghai lake water is characterized by buha type water but its sr geochemistry is different from the shallow groundwater due to carbonate precipitation although shallow groundwater contributes 5 of the dissolved sr to the qhl groundwater must be taken into account when the chemistry and budget of lake water are characterized

late miocene events in the mediterranean as recorded by carbonate evaporice relations the messinian stage in the mediterranean region is known mainly because of a major evaporitic event whose causes and global implications are still under discussion correlations between basinal evaporite bearing series and marginal carbonate platforms allow for improvement of the classical depostional models especially concerning the eustatic control of the environmental changes in the mediterranean these changes were controlled by the interplay of aperiodic and periodic factors 1 tectonics related to the relative motions of the african and eurasian plates and resultant linear increase in the basin restriction 2 sea level fluctuations that alternately aggravated the restriction or allowed marine replenishment and 3 climatic fluctuations that controlled the level of the mediterranean during stages of isolation the messinian sedimentary succession reflects a typical sequence of progressive isolation marine marls yields laminites yields transitional deposits yields evaporites yields lacustrine deposits the first stage of the so called salinity crisis was characterized by a mediterranean lowstand that resulted in erosion of former platforms and deposition of the lower evaporites during the next stage sea level rose tb3 3 cycle high enough to temporarily replenish the basin cyclic upper evaporites with development of stromatolite rich deposits finally the uppermost messinian freshwater to brackish lacustrine deposits reflect both themore cessation of sea water input maximum tectonic isolation low sea level and freshwater input related to increasing runoff less

abnormal rb sr ratio in lacustrine sediments of qaidam basin ne qinghai tibetan plateau a significant role of aeolian dust input abstract the rb sr ratio is an important indicator of weathering intensity in both lacustrine and loess sediments because of the inertness of the rb element and the activity of the sr element during the weathering process generally the environmental interpretation of rb sr ratio proxy in lacustrine sediments is contrary to that in the loess paleosol sequence it shows a negative correlation between the rb sr ratio and chemical weathering intensity in lacustrine sediments but shows a positive pattern in the loess paleosol sequence however in this study we investigated the rb sr ratio of a lacustrine core isl1a from qarhan salt lake qsl in eastern qaidam basin qb and found the rb sr ratio indicated a positive correlation with regional precipitation this pattern is similar to that of the loess paleosol sequence rather than the lacustrine sediments according to grain size statistics and the comparison of rb sr ratio with other proxies halite and calcite contents grain size and f values of grain size discriminant function we preliminarily proposed that the abundant input of aeolian materials transported by the strong northwest wind cause these unexpected rb sr ratio fluctuations in the isl1a core the comparison between background rb and sr elemental data of relevant regions and these of the core indicated the aeolian origin of rb sr ratio in the lacustrine sediments and the rb and sr elemental composition probably represents the geochemical characteristics of the dust source area the sr nd isotopic composition indicates that the erosive paleo lake strata in western qb could be the origin of aeolian materials in lacustrine sediments in the qsl as well as the loess deposits in dulan county qinghai lake basin and xining basin the regional correlation between proxies of the isl1a core and other aeolian records also supports the aeolian origin of detrital input in the core finally we propose that the origin of the detrital input must be distinguished before the rb sr ratio is applied as a weathering intensity proxy in lacustrine sediments especially in arid basins

geometry and state of stress of the wadati benioff zone in the gulf of tehuantepec mexico 1 data recorded in the gulf of tehuantepec and published moment tensor solutions were used to infer the geometry of the wadati benioff zone w b zone and the stress distribution of the subducted cocos plate from northwest to southeast the subducted slab gently increases its dip bends up at depths of the order of 100 km and about 240 km inland from the trench then unbends and increases its dip toward the southeast below chiapas contour lines of equal depth at 50 and 100 km show a significant contortion of the w b zone west of the isthmus of tehuantepec and coincide with significant changes in the topographic features of the crust we calculated a vp vs ratio of 1 75 for the whole area and a moho depth in the gulf of tehuantepec of 28 5 3 5 km near the trench along the coupling zone t axes of interplate and intraplate earthquakes are oblique to the interface and parallel to the dip direction of the subducted plate respectively at depths greater than 50 km the t axes are roughly horizontal best fit stresses using the gephart and forsyth 1984 code resulted in the following variation of the minimum stresses t axes from northwest to southeast as plunge azimuth 3 40 37 to 3 28 72 then to 3 11 54 and finally to 3 27 35 we also analyzed recordings from the 30 september 1999 oaxaca earthquake mw 7 5 and its aftershocks we inferred an approximate fault area of 80 by 30 km inside the subducted cocos plate

measurements of dust deposition in gansu province china 1986 2000 abstract dust samples collected monthly for 15 years from 50 urban sites in 10 cities in gansu province china provide information on modern rates of dust deposition in the desert and gobi areas and in the loess plateau dust deposition is highest during spring months and lowest during autumn months in both the desert and gobi areas and the loess plateau there is a significant positive correlation between dust deposition and dust event and an inverse correlation between dust deposition and precipitation the 15 year mean maximums in the desert and gobi areas and the loess plateau are 498 64 and 327 02 t km 2 year 1 respectively and the mean minimums are 290 22 and 180 86 t km 2 year 1 respectively drought may have a widespread major influence on the modern rates of the dust deposition

iterative deconvolution of complex body waves from great earthquakes the tokachi oki earthquake of 1968 abstract a method of body wave inversion is developed in an attempt to extract the information about asperities or barriers in a fault zone a sequence of point sources each being characterized with the seismic moment the onset time and the location are iteratively derived from observed records at multi stations where the two dimensional extent of the source location is taken into account a modification is made of the iterative method of kikuchi and kanamori on the formulation of inversion procedure to facilitate the computation using this method we analyse long period p waves of the tokachi oki earthquake of 1968 mw 8 2 and obtain several significant subevents with time durations of 10 s their spatio temporal distribution shows that the rupture process consists of three characteristic stages a a stage of introductory rupture b a stage of main rupture and c a stage of aftershocks the main rupture takes place in the form of clustering around a few sites of the fault plane the largest subevent occurs in the northwestern corner the stress drop associated with this event is estimated to be 200 bars one order of magnitude higher than the stress drop averaged over the entire fault plane the sum of the seismic moments of the individual subevents amounts to 2 3 1028 dyn cm which approximately coincides with the one estimated from the analysis of long period surface waves this implies that the source of the tokachi oki earthquake consists of several major subevents with time durations of 10 s in addition to other minor subevents

moment tensor and rupture model for the 1949 olympia washington earthquake and scaling relations for cascadia and global intraslab earthquakes we reanalyzed the 13 april 1949 olympia washington earthquake by using digitized records and first motion polarities from long period seismograms the moment tensor mechanism is normal faulting with a down dip trending t axis similar in style to other cascadia intraslab earthquakes the total seismic moment is 1 3 1026 dyne cm m w 6 7 and the hypocenter depth is 60 km additional inverse modeling for the kinematic rupture process assuming the steeply east dipping fault plane from the moment tensor resulted in a slightly higher total moment of 1 9 1026 dyne cm m w 6 8 the earthquake ruptured to the south with at least two subevents the combined area of asperities and seismic moment for the 1949 earthquake was compiled with those from the 1965 seattle tacoma and the 2001 nisqually earthquakes and with those from japan and mexico to develop a source scaling relation separate from shallow global strike slip earthquakes we infer that deeper intraslab earthquakes have a significantly smaller combined area of asperities than those compiled for shallower strike slip earthquakes with the same seismic moment this difference in rupture area leads to a 3 to 5 fold increase in stress drop for earthquakes with seismic moments between 1024 and 1028 dyne cm

position of the disastrous 1999 puebla earthquake in the seismotectonic pattern of mexico the location of the 1999 puebla earthquake shows that this earthquake belongs to the class of disastrous intraplate earthquakes generated by fracturing of the continental lithosphere caused by the process of subduction this is obvious from the vertical section across the middle american wadati benioff zone and from its position in the revised seismically active los azufres rio salado fracture zone delineated in the continental lithosphere of the north american plate

weathering sr fluxes and controls on water chemistry in the lake qinghai catchment ne tibetan plateau strontium sr concentrations and isotopic ratios have been measured in a series of water and rock samples from most of the major tributaries of the lake qinghai basin on the north eastern tibetan plateau dissolved sr and 87sr 86sr show ranges of 488 12 240 nmol l and 0 710497 0 716977 respectively these data together with measurements of major cations and anions in rivers and their tributaries and various lithologies of the catchment were used to determine the contributions of sr and its isotopic expense to rivers and lakes our results demonstrate that the chemical components and 87sr 86sr ratios of the alkaline waters are derived from mixing of carbonate and silicate sources with the former contributing 72 18 dissolved sr to rivers the difference in tributary compositions stems from the lithology of different river systems and low weathering intensity under a semi arid condition variation in 87sr 86sr ratios places constraint on the sr isotopic compositions of the main tributaries surrounding lake qinghai the water chemistry of the buha river the largest river within the catchment underlain by the late paleozoic marine limestone and sandstones dominates sr isotopic composition of the lake water being buffered by the waters from the other rivers and probably by groundwater however the characteristic chemical composition of the lake itself differs remarkably from the rivers which can be attributed to precipitation of authigenic carbonates low magnesium calcite aragonite and dolomite though this does not impact the sr isotope signature which may remain a faithful indicator in paleo records regarding the potential role of groundwater input within the lake qinghai systems in the water budget and water chemistry we have also determined the sr concentration and 87sr s6sr ratio of groundwater from diverse environments this has allowed us to further constrain the sr isotope systematic of this source a steady state calculation gives an estimate for the groundwater flux of 0 19 0 03 108 m3 yr accounting for about 8 of contemporary lake sr budget copyright 2010 john wiley sons ltd

shape of the subducted rivera and cocos plates in southern mexico seismic and tectonic implications the geometry of the subducted rivera and cocos plates beneath the north american plate in southern mexico was determined based on the accurately located hypocenters of local and teleseismic earthquakes the hypocenters of the teleseisms were relocated and the focal depths of 21 events were constrained using a body wave inversion scheme the suduction in southern mexico may be approximated as a subhorizontal slab bounded at the edges by the steep subduction geometry of the cocos plate beneath the caribbean plate to the east and of the rivera plate beneath north america to the west the dip of the interplate contact geometry is constant to a depth of 30 km and lateral changes in the dip of the subducted plate are only observed once it is decoupled from the overriding plate on the basis of the seismicity the focal mechanisms and the geometry of the downgoing slab southern mexico may be segmented into four regions 1 the jalisco region to the west where the rivera plate subducts at a steep angle that resembles the geometry of the cocos plate beneath the caribbean plate in central america 2 the michoacan region where the dip angle of the cocos plate decreases gradually toward the southeast 3 the guerrero oaxaca region bounded approximately by the onshore projection of the orozco and o gorman fracture zones where the subducted slab is almost subhorizontal and underplates the upper continental plate for about 250 km and 4 the southern oaxaca and chiapas region in southeastern mexico where the dip of the subduction gradually increases to a steeper subduction in central america these drastic changes in dip do not appear to take place on tear faults suggesting that smooth contortions accommodate these changes in geometry the inferred 80 and 100 km depth contours of the subducted slab lie beneath the southern front of the trans mexican volcanic belt suggesting it is directly related to the subduction thus the observed nonparallelism with the middle american trench is apparently due to the changing geometry of the rivera and cocos plates beneath the north american plate in southern mexico and not to zones of weakness in the crust of the north american plate as some authors have suggested

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

source spectra of great earthquakes teleseismic constraints on rupture process and strong motion short period body waves recorded at teleseismic distances from great earthquakes provide information about source rupture processes and strong motions first we examine mostly wwssn records of 19 earthquakes of moment magnitude m w of 6 5 to 9 5 four parameters are measured from the short period p wave train the maximum amplitude the period at maximum amplitude the time between the first arrival and when the maximum amplitude is attained and coda length an extension m b of the teleseismic magnitude m b is defined using the maximum amplitude of the entire short period p wave rather than the amplitude achieved in the first few p wave cycles a least squares fit to the data yields the following relationship between m b and m w m b 0 53 m w 2 70 for m w 6 5 to 9 5 the time from the first arrival until the maximum amplitude is achieved and the coda length are roughly proportional to m w but are further interpreted by a simple asperity model of the rupture process these data support that short period waves are on average generated preferentially in the same regions of the fault plane as long period waves with periods of 10 to 50 sec we analyze the spectra of short and intermediate period teleseismic gdsn records for seven earthquakes with m w s of 6 4 to 7 8 and hand digitized short period wwssn records of the 1971 san fernando earthquake significant differences exist between the spectra of different events due partly to variations in tectonic setting or seismic coupling using the digital data we also investigate the relationship between time domain amplitude and spectral amplitude for short period p waves from our empirical relation between spectral amplitude and time domain amplitude we estimate the spectral amplitudes implied by the m b data we compare our results to the 2 and gusev spectral models neither model can completely represent the data nevertheless we consider the 2 model a useful reference model for comparing different events the average source spectrum of six large events with m w 7 4 to 7 8 does not have the spectral structure suggested by gusev an application to strong motion modeling is presented in which a 1971 san fernando teleseismic short period record is summed up to simulate teleseismic records produced by five great earthquakes the summation procedure matches the moment of the event to be simulated and includes rupture propagation fault plane roughness and randomness the m b data provide an important constraint on the summation procedures thus constrained this summation procedure can be more confidently used with near field strong motion records as green s functions to predict strong motions from great earthquakes

the role of atmospheric deposition in the biogeochemistry of the mediterranean sea abstract estimates of atmospheric inputs to the mediterranean and some coastal areas are reviewed and uncertainities in these estimates considered both the magnitude and the mineralogical composition of atmospheric dust inputs indicate that eolian deposition is an important 50 or even dominant 80 contribution to sediments in the offshore waters of the entire mediterranean basin model data for trace metals and nutrients indicate that the atmosphere delivers more than half the lead and nitrogen one third of total phosphorus and 10 of the zinc entering the entire basin measured data in sub basins such as the north western mediterranean and northern adriatic indicate an even greater proportions of atmospheric versus riverine inputs when dissolved fluxes are compared the form most likely to impinge on surface water biogeochemical cycles the atmosphere is found to be 5 to 50 times more important than rivers for dissolved zinc and 15 to 30 times more important for lead fluxes neglecting co limitation by other nutrients new production supported by atmospheric nitrogen deposition ranges from 2 4 g c m 2 yr 1 whereas atmospheric phosphorus deposition appears to support less than 1 g c m 2 yr 1 in spite of the apparently small contribution of atmospheric deposition to overall production in the basin it has been suggested that certain episodic phytoplankton blooms are triggered by atmospheric deposition of n p or fe future studies are needed to clarify the extent and causal links between these episodic blooms and atmospheric oceanographic forcing functions a scientific program aimed at elucidating the possible biogeochemical effects of saharan outbreaks in the mediterranean through direct sampling of the ocean and atmosphere before and after such events is therefore highly recommended

messinian climate change and erosional destruction of the central european alps at the end of the miocene the european alps ceased outward expansion and tectonic uplift and exhumation shifted into the orogen interior this shift is consistent with a change from orogenic construction to orogenic destruction reflecting an increase in the ratio of erosional flux to accretionary flux the coincidence of this change with an increase in sediment yield from the alps suggests a climate driven increase in erosional flux the timing of deformation and sediment release from the southern alps indicates that the tectonic change occurred synchronous with the last phase of the messinian salinity crisis we attribute the increase in erosional flux to a climatic shift to wetter conditions throughout europe likely augmented by the base level fall that occurred during the mediterranean dessication this climate change is represented in the stratigraphic record by the lago mare deposits of the mediterranean salinity crisis

techniques to measure the dry aeolian deposition of dust in arid and semi arid landscapes a comparative study in west niger seven techniques designed to measure the dry aeolian deposition of dust on a desert surface were tested during field experiments in niger central west africa deposition fluxes were measured during eight periods of 3 4 days each experimental techniques tested were the mdco marble dust collector method the frisbee method the glass plate method optical analysis of dust deposited on glass surfaces using particle imaging software the soil surface method deposition on a simulated desert floor and the capyr capteur pyramidal method theoretical techniques tested were the inferential method and the combination method gradient method extended with a deposition term for coarse dust particles the results obtained by the mdco frisbee inferential and combination methods could be directly compared by converting the data to identical standard conditions deposition on a water surface producing no resuspension the results obtained by the other methods glass plate soil surface capyr were compared relatively the study shows that the crude unconverted deposition fluxes of the five experimental techniques were similar while the crude deposition fluxes calculated by the two theoretical techniques were substantially higher of the order of four to five times as high as for the experimental techniques recalculation of the data to identical environmental conditions the standard water surface resulted in nearly identical deposition fluxes for the mdco frisbee inferential and combination techniques although the latter two still had slightly higher values but the differences remained small the measurements illustrate the need to include a grain shape factor in theoretical dust deposition models without such a factor theoretical models overestimate the deposition the paper also discusses the advantages and disadvantages of the techniques tested copyright 2007 john wiley sons ltd

mediterranean messinian salinity crisis constraints from a coeval marginal basin sorbas southeastern spain abstract the extent timing and effects of late miocene desiccation and evaporite deposition in the mediterranean sea remain controversial marginal basins containing messinian 5 3 7 1 ma sequences now exposed onland supplement information from the deep mediterranean but have evaporites of a variety of ages some of these messinian evaporites pre date and others post date deep desiccation none appears to be exactly coeval with those of the deep mediterranean in the betic cordillera of southern spain basins e g granada basin far from the present day mediterranean lost connection with the mediterranean due to uplift 1 ma before the salinity crisis and have marine evaporites of early not late messinian age in contrast basins such as the sorbas basin in southeastern spain adjacent to the present day mediterranean record events directly reflecting the course of the salinity crisis the sorbas basin retained marine connection with the western mediterranean up until evaporative drawdown in the mid messinian and was rapidly reflooded immediately afterwards the sorbas messinian sequence is up to 320 m thick it is complete and normal marine except for an incised basinwide erosion surface overlain by a 130 m thick gypsum deposit we propose that this surface marks the interval of deep desiccation of the adjacent mediterranean basin erosion occurred shortly after 5 9 ma and the irregular unconformity has relief of at least 240 m confirming mediterranean drawdown significantly below the atlantic level sorbas gypsum deposits overlie the unconformity and are intercalated with marls estimated at 5 5 ma containing normal marine messinian biotas these gypsum deposits therefore post date deep desiccation and formed in a silled basin immediately following marine reflooding they mark the end of the salinity crisis and are overlain by 70 m of normal marine sediments containing unreworked foraminifers of latest messinian age this succession demonstrates that the salinity crisis occurred faster and was completed sooner than previously believed it took place within 0 4 ma time scale of berggren et al 1995b is 0 2 ma on the time scale of baksi 1993 and was completed before the end of the messinian this corrects previous views that the salinity crisis continued until the early pliocene there is no evidence in the sorbas basin for brackish lago mare conditions and the normal marine biotas that directly precede and follow drawdown rebut earlier suggestions of prolonged salinity effects

lateral variations of lg coda q in southern mexico broad band digital three component data recorded at unm a geoscope station were used to estimate lg coda q for 34 medium size 3 9 m b 6 3 earthquakes with travel paths laying in different geological provinces of southern mexico in an effort to establish the possible existence of geological structures acting as wave guides and or travel paths of low attenuation between the pacific coast and the valley of mexico the stacked spectral ratio method proposed by xie and nuttli 1988 was chosen for computing the coda q the variation range of q 0 q at 1 hz and the frequency dependence parameter estimates averaged on the frequency interval of 0 5 to 2 hz for the regions and the three components considered are i guerrero region 173 q 0 182 and 0 6 q 0 0 7 ii oaxaca region 183 q 0 198 and 0 6 q 0 0 8 iii michoacan jalisco region 187 q 0 204 and 0 7 q 0 0 8 and iv eastern portion of the transmexican volcanic belt tmvb 313 q 0 335 and 0 9 the results show a very high coda q for the tmvb as compared to other regions of southern mexico this unexpected result is difficult to reconcile with the geophysical characteristics of the tmvb e g low seismicity high volcanic activity and high heat flow typical of a highly attenuating low q region visual inspection of seismograms indicates that for earthquakes with seismic waves traveling along the tmvb the amplitude decay of lg coda is anomalously slow as compared to other earthquakes in southern mexico thus it seems that the high q value found does not entirely reflect the attenuation characteristics of the tmvb but it is probably contaminated by a wave guide effect this phenomenon produces an enhancement in the time duration of the lg wave trains travelling along this geological structure this result is important to establish the role played by the transmission medium in the extremely long duration of ground motion observed during the september 19 1985 michoacan earthquake the overall spatial distribution of coda q values indicates that events with focus in the michoacan jalisco and oaxaca regions yield slightly higher values than those from guerrero this feature is more pronounced for the horizontal component of coda q a slight dependence of average coda q 1 on earthquake focal depth is observed in the frequency range of 0 2 to 1 0 hz approximately on the horizontal component deeper h 50 km events yield lower values of q 1 than shallower events for frequencies higher than 1 0 hz no clear dependence of q 1 on focal depth is observed however due to the estimates uncertainties this result is not clearly established

geochemistry of dust aerosol over the eastern pamirs abstract the pamirs are situated in the inner part of the asian continent a region which plays a critical role in asian dust emission and transport this study measured the elemental composition of atmospheric dust aerosol samples collected during the period between july 2004 and april 2006 at mt muztagata eastern pamirs at a high altitude 38 17 n 75 01 e 4430 m the muztagata aerosol samples show ca al 0 7 and fe al 0 7 ratios that are distinguishable from those from other sites the la th ratios averaging 2 30 2 36 and th u ratios averaging 2 75 3 11 indicate typical eolian deposition the dust aerosol samples have very similar rare earth element ree patterns with relative enrichment of light ree a slight depletion of heavy ree and a strongly negative europium anomaly eu values averaging 0 65 the muztagata dust shows homogeneity of composition during the sampling period with minor variations due to seasonal effects and possible different air mass suggesting the possibility of a well mixed atmospheric background dust on a regional scale the zonal westerlies dominate and the longitude circulations are relatively very weak for dust transport dynamics in the pamirs and tien shan regions our results demonstrate a distinct difference in elemental composition between dust over the eastern pamirs and that over inilchek central tien shan indicating that the asian dust emission regions have great variations in their chemical properties and provide a better constraint on the climatic impact of asian dust

structure and evolution of a messinian mixed carbonate siliciclastic platform the role of evaporites sorbas basin south east spain the sorbas member is a late messinian complex sedimentary system that formed immediately following deposition of the messinian evaporites in the sorbas basin south east spain this work describes the sequence architecture and facies organization of a continuous kilometre long alluvial fan to open platform transect near the village of cariatiz in the north east of the basin the post evaporitic cariatiz platform was a mixed carbonate siliciclastic system composed of four intermediate frequency fifth order depositional sequences depositional sequences 1 to 4 arranged in an overall prograding trend the intense fracturing and brecciation of these deposits is attributed to the deformation and dissolution of an evaporite body measuring several tens of metres in thickness the four sequences display significant spatial temporal variability in both architecture and facies distribution with two main phases i depositional sequences 1 and 2 are ooid and oobioclastic dominated and show normal marine faunas and ii depositional sequences 3 and 4 show a higher siliciclastic contribution and are microbialite dominated these important changes are interpreted as modifications of the primary controlling factors following an initial 70 m drowning possibly linked to increased oceanic input depositional sequences 1 to 3 were controlled mainly by eustatic variations and inherited topography their progradation destabilized the evaporite body near the end of the depositional sequence 2 period during the second phase depositional sequences 3 and 4 recorded a progressive restriction of the sorbas basin related to a 30 to 40 m fall in water level that was driven mainly by regional factors these regional factors were dissolution and gravity induced deformation of the evaporites and correlative evaporative fluid circulation associated with the contrasted arid humid regional climate that respectively controlled sequence geometry and fluctuating water salinity which caused a microbialite bloom