modification and preservation of environmental signals in speleothems speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system however the climatological meaning of many speleothem records cannot be interpreted unequivocally this is particularly so for more subtle shifts and shorter time periods but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward

duality of magmatism in the plutonic sequence of the sumail nappe oman abstract detailed field mapping of the crustal sequence in several areas of the sumail ophiolite nappe mainly in the fizh the salahi and the haylayn blocks and comparisons with other well studied areas have shown that the crustal sequence was constructed by two distinct although nearly contemporaneous magmatic series the first a gabbroic series was emplaced during the accretion stage at an oceanic spreading centre which formed the layered gabbro unit the high level isotropic gabbro unit and their by products the sheeted dyke complex and the lower extrusives fine grained homogeneous planar laminated gabbros commonly occur at the top of the layered gabbro sequence in some specific areas wadi haymiliyah and wadi rajmi these are strongly differentiated fe ti rich gabbronorites and norites which coincide with large scale discontinuities within the plutonic sequence interpreted as axial discontinuities of the spreading magma chambers the second series an ultramafic wehrlitic series is locally rooted in the upper mantle i e the impregnated dunitic transition zone this has intruded the whole crustal sequence up to the pillow lavas countless discordant and concordant wehrlitic bodies intruded the plutonic sequence making up 20 40 of it in volume we describe the various settings and forms of these intrusions which were largely underestimated in previous studies we also describe their mineralogy and textures and show with chemical and mineralogical arguments that these bodies evolved as relatively closed systems independently from each other we infer from the study of the contacts that the gabbros were still hot and consolidated just at the moment of the wehrlitic intrusion at the base of the crust however indications of immiscibility between gabbros and wehrlites are common suggesting that both magmatic series were quite contemporaneous the wehrlites are commonly isotropic and may exhibit an internal layering of the dunite wehrlite clinopyroxenite type sometimes appearing at the upper or lower margins of the intrusions in this case the ultramafic layered cumulates show lobate intrusive contacts with the adjacent layered gabbros these plagioclase free ultramafic layered cumulates therefore are not interbedded within the gabbro cumulates but actually belong to the wehrlitic intrusive series picritic dykes radiating from the uppermost intrusions can be traced up to the upper extrusives which are for the main part cogenetic with the wehrlites the time of this second magmatic event coincides with the cessation of the accretion process and with the beginning of the intraoceanic detachment of the ophiolite at the spreading centre we believe that the compressive regime that initiated the detachment acted as an efficient filter press and helped the extraction and ascent of the wehrlitic magmas towards the uppermost levels of the crust

characterization of hyperalkaline fluids produced by low temperature serpentinization of mantle peridotites in the oman and ligurian ophiolites a regional survey of alkaline springs in oman and ligurian ophiolites shows that the alkaline water compositions significantly vary from one ophiolite to the other and within the same ophiolite the first order correlation between the na and k and cl concentrations points to fluid compositions only partly due to evaporation the scatter around the evaporation line implies that na and cl may not be conservative during the alteration of the ultramafic rocks mg is almost entirely depleted at ph 10 5 as a result of serpentine formation within the ultramafic body and of brucite and minor hydrotalcite precipitation at the springs ca accumulates in the high ph fluids and is consumed by ca carbonate formation at the springs by mixing with river waters or by the co2 supply from the atmosphere thermodynamic calculations show that brucite saturation is reached at ph values around 10 5 which triggers major changes in the water composition the waters evolve from a quartz saturated low ph continental environment to a brucite dominated high ph serpentinizing system at low temperature the highest water salinities are found in springs located along the basal thrust plane of the ophiolite the highest al concentrations are found in some springs located on the crustal side of the mantle crust boundary this poses the question of the hydrologic pathways and of the role of the mineralogical composition of the altered formations key points new temperature and composition of the alkaline waters brucite formation at ph 10 5 triggers major chemical and mineralogical changes relationship between the water compositions and the hydrologic pathways

the volcanic stratigraphy and petrogenesis of the oman ophiolite complex the volcanic stratigraphy and trace element geochemistry of the oman ophiolite complex indicate a multistage magmatic origin comprising 1 magmatism due to sea floor spreading in a marginal basin 2 magmatism associated with discrete submarine volcanic centres or seamounts 3 magmatism associated with crustal uplift and rifting and 4 magmatism associated with continent arc collision trace element petrogenetic modelling is used to investigate the nature of the mantle source region and the partial melting and fractional crystallization history for each magmatic event the petrogenetic pathway for the sea floor spreading lavas requires a high degree of melting of a mantle that was depleted in incompatible elements prior to subduction but subsequently selectively enriched in certain elements mostly lil elements and h2o from an underlying subduction zone it also requires magma mixing in an open system magma chamber prior to eruption the seamount lavas were probably derived by a similar degree of partial melting of a similar source but fractional crystallization was restricted to smaller high level magma chambers the rifting lavas were derived from a mantle source that was more depleted than the seamount lavas prior to subduction but which was later modified by a larger subduction zone component the syn collision lavas were however derived from an enriched mantle source which probably underlay the passive continental margin rather than the marginal basin complex results such as these may provide considerable insight into the petrogenetic changes accompanying the transitions from spreading to arc volcanism in a supra subduction zone setting

seafloor geomorphology of the sw barents sea and its glaci dynamic implications abstract three dimensional 3d reflection seismic imaging techniques provide a unique means of identifying large scale submarine geomorphic features produced by former ice sheets we have used such techniques to image the geomorphology of the sw barents sea but using a dense grid of 2d seismic covering a 240 000 2 km large study area supplemented with 3d seismic from selected areas the study area is located at the convergence of ice flow from the former fennoscandian barents sea and svalbard ice sheets the morphology of the major cross shelf troughs is characterized by elongated ridge groove features interpreted to be glacial bedforms produced by fast flowing grounded glaciers mega scale glacial lineations have been grouped into distinct flow sets related to three specific ice flow events these events document the last glacial maximum lgm and two readvances during deglaciation of specific interest is a detailed and well preserved set of seafloor imprints in the bjornoyrenna trough which acted as the main pathway for ice streams draining the surrounding ice sheets the geomorphic features indicate that bjornoyrenna hosted six separate ice stream lobes that diverged fan like at their margins but were not all active simultaneously an end moraine zone 68 km wide up to 85 m high and 300 km long filled the whole width of this major glacial trough as a result of high sediment flux within sub ice stream deformable beds the imprint of this ice stream system can be followed on our seabed images for 500 km however detailed geomorphologic elements demonstrate that these imprints reflect time transgressive behaviour and do not indicate the length or width of single ice streams the seismic derived seafloor geomorphology demonstrates that the barents sea ice behaved in a much more dynamic way during the last glaciation than previously assumed with major shifts between ice originating from the fennoscandian spitsbergen and barents sea ice sheets

hot spring systems geobiology abiotic and biotic influences on travertine formation at mammoth hot springs yellowstone national park usa multiple abiotic and biotic factors combine in nature to influence the formation of calcium carbonate limestone deposits systems geobiology studies of how micro organisms respond to or sometimes even control the coupled effects of environmental change and mineralization will permit more accurate interpretation of the fossil record of ancient microbial life mammoth hot springs in yellowstone national park usa serves as a natural laboratory for tracking how the dynamic interplay of physical chemical and biological factors come together to form hot spring limestone called travertine systematic downstream correlations occur at mammoth hot springs between travertine deposition geomorphology crystalline structure and geochemistry microbial communities mat morphology pigmentation and phylogenetic and metabolic diversity and spring water conditions temperature ph geochemistry and flow field based microscale and mesoscale experimentation indicates that microbes directly influence travertine growth rate and crystalline structure at the macroscale time lapse field photography and numerical modelling suggest that travertine terrace geomorphology is influenced strongly by hydrology heat dispersion and geochemistry these results from mammoth hot springs allow establishment of a conceptual framework across broad spatial and temporal scales in which to track how multiple geological and biological factors combine to control caco3 crystal precipitation and the resulting formation of travertine deposits

seasonal variations in sr mg and p in modern speleothems grotta di ernesto italy sub annual variations in trace element chemistry and luminescence have recently been demonstrated from speleothems and offer the potential of high resolution palaeoclimatic proxies however no studies have yet examined microscopic trace element variations in relation to modern cave conditions in this study the spatial variations in trace element sr mg and p concentrations in speleothems a stalagmite and a soda straw stalactite from the alpine ernesto cave temperature 6 6 0 1 c in a forested catchment in ne italy have been studied using secondary ion mass spectrometry sims and compared with environmental parameters and waters in the modern cave an annual lamination exists in the stalagmite and soda straw stalactite in the form of clear calcite with narrow visible layers which are uv fluorescent and interpreted to contain soil derived humic fulvic acids washed into the cave during autumn rains microanalyses were undertaken of seven annual laminae probably deposited during the 1960s in the stalagmite and seven laminae in the 1990s for the stalactite the analysis results show that sr consistently has a trough and p a peak centred on the inclusion rich layer mg shows mainly a negative covariation with sr in laminae formed in the 1990s but a positive covariation in the stalagmite formed in 1960s the spatial scale of the main geochemical variations is the same as that of annual laminae of inclusion poor and inclusion rich couplets mass balance arguments are used to show that the p is inorganic in form and presumably occurs as individual phosphate ions within the calcite most drip waters show limited chemical variations but a summer peak in trace elements in 1995 and a decrease in mg ca in the following winter are notable more pronounced covariations in mg ca and sr ca are shown by a site with highly variable drip rates where ratios increase at slow drip rates the strongest seasonal variations are found in pool waters where ratios increase reflecting significant ca removal from the water into the calcite during the winter in response to seasonal pco2 variations in cave air thus the cave waters compositions tend to reflect climate conditions such that mg ca and sr ca are tentatively interpreted to be higher when climate conditions are dry combining results from the speleothems and cave water along with the behaviour of each trace species mg ca variations in the speleothems are considered to reflect their variation in the cave waters whereas sr incorporation is also dependent on precipitation rate in this case mainly controlled by temporal variations in pco2 in the cave and conceivably also by inhibitors such as phosphate p adsorption a fraction of which is subsequently incorporated within calcite depends on aqueous phosphate concentration and water flux both of which should increase during the autumn therefore multiple trace element profiles in speleothems reflect multiple aspects of environment seasonality and conditions and hence a calibration against weather records is desirable to establish their palaeoclimatological meaning the strong annual variation of trace elements and particularly p can provide chronological markers for high resolution studies of other climate proxies such as stable isotopes

intrinsic and extrinsic controls of spatial and temporal variations in modern fluvial tufa sedimentation a thirteen year record from a semi arid environment sedimentological and hydrochemical parameters of the river piedra north east spain were monitored every six months from 1999 to 2012 at 24 sites at which tablets were installed all along the river the river water is of hco3 so4 ca type and is notably influenced by inputs from upstream karstic springs tufa deposition was first detected 8 km downstream of these springs and greatly increased from there primarily along the steeper stretch i e within the monasterio de piedra natural park then deposition decreased through the most downstream stretch with smaller ground water inputs the spatial evolution of the tufa thickness with parallel variations of pwp plummer wigley parkhurst rates was thus determined by the river water pco2 which was controlled by ground water inputs and by the river bed slope five fluvial subenvironments and seven sedimentary facies were characterized the water flow conditions are the primary factor responsible for the distinct deposition rates of facies mainly through co2 outgassing stromatolites and moss tufa and alga tufa had the highest rates whereas loose tufa formed in slow flowing water and tufa of spray areas had thinner deposition a six month pattern in the deposition rate was detected through thickness measurements that pattern was parallel to the seasonal pwp rates the increased deposition during warm periods spring and summer mean 5 08 mm compared with cool periods autumn and winter mean 2 77 mm is linked chiefly to temperature which controlled the seasonal changes in the physico chemical and biological processes this finding is supported by a principal components analysis seasonal variations of insolation and day duration also contributed to such a deposition pattern large discharge events which provoked erosion of tufa deposits and dilution of water caused the reversal of the seasonal deposition rate pattern stromatolites are likely to preserve the most complete sedimentary record although tufas are a potentially sensitive record of climate related parameters erosion is an intrinsic process that may overwhelm the effects of such parameters this issue should be considered in palaeoclimatic studies based on the tufa record particularly in semi arid conditions

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

30 000 years of hydrothermal activity at the lost city vent field strontium carbon and oxygen isotope data and radiocarbon ages document at least 30 000 years of hydrothermal activity driven by serpentinization reactions at lost city serpentinization beneath this off axis field is estimated to occur at a minimum rate of 1 2 10 4 cubic kilometers per year the access of seawater to relatively cool fresh peridotite coupled with faulting volumetric expansion and mass wasting processes are crucial to sustain such systems the amount of heat produced by serpentinization of peridotite massifs typical of slow and ultraslow spreading environments has the potential to drive lost city type systems for hundreds of thousands possibly millions of years

tectonic setting for the genesis of oceanic plagiogranites evidence from a paleo spreading structure in the oman ophiolite abstract in the oman ophiolite detailed structural and lithological mapping of the 60 45 km maqsad area has revealed several plagiogranite intrusions ranging from metre scale dykes to hectometre scale bodies these plagiogranites are spatially related to kilometre scale mafic plutons displaying generally pegmatitic textures and locally deformed in amphibolite facies conditions along shear zones up to a few hundred metres thick isotope data demonstrate the mantle origin of these pegmatites and plagiogranites nd ranges from 6 3 to 9 9 and has an average value 26 samples of 8 1 within the field of present day morbs and similar to the average nd 7 8 of the oman ophiolite primary igneous sequence these intrusions are not restricted to a given structural level their paleovertical extent exceeds 5 6 km from 2 km below the moho up to the base of the sheeted dyke complex their modal composition evolves up section from predominantly pyroxenites and gabbro norites in the mantle harzburgites to gabbro norites diorites and quartz diorites at crustal level petrography whole rock and mineral chemistry show that this vertical succession of lithologies can be simply explained by low pressure fractional crystallization of a hydrated basaltic melt plagiogranites although more abundant at upper crustal level are not restricted to this horizon plagioclase composition in plagiogranites presents a remarkable evolution with paleodepth from highly calcic 70 95 an in the mantle section intermediate and highly scattered in the lower crust 10 85 an to quite sodic at upper crustal level 5 20 an highly calcic plagioclases in quartz bearing rocks is a puzzling character inconsistent with fractional crystallization even if high degrees of fractional crystallization of a hydrated basaltic melt remain the simplest way to account for the chemistry of the upper crustal plagiogranites processes such as fluid induced remelting or assimilation of country rocks must be invoked to account for the chemistry and field characteristics of the deeper plagiogranites mantle and crustal structures in the maqsad area indicate that the pegmatites and plagiogranites emplaced in an ocean ridge setting when a mantle diapir soaked with basaltic melt intruded a cool hydrothermally altered lithosphere they were eventually transposed in an off axis setting as the ascension of the diapir progressed up to moho level it is concluded that the formation of large volumes of buoyant leucocratic rocks is possible at ocean ridges provided periods of amagmatic spreading are long enough to induce the growth and alteration of an axial lithospheric lid this is likely more frequent at slow spreading centres where mantle upwelling is discontinuous in space and time

a multidisciplinary approach to understanding carbonate deposition under tectonically controlled hydrothermal circulation a case study from a recent travertine mound in the euganean hydrothermal system northern italy a multidisciplinary study was carried out on an upper pleistocene travertine mound montirone hill abano terme south of padova veneto italy with the aim of developing a comprehensive understanding of the processes interacting in structurally controlled thermal springs and the consequent deposition of thermal limestones the sedimentology geochemistry structural characteristics and hydrogeology of the mound which is associated with the euganean geothermal field and the related complex structural framework of the schio vicenza fault system were investigated a palaeo environmental model of the deposit has been reconstructed clarifying the connection between the travertine deposition and the regional structural setting calcium rich thermal waters rose from spring orifices estimated temperature from 54 c to 61 c based on geochemical calculations and produced a mound made of coalescent shield like bodies the dominant lime mudstone facies resulted from the accumulation of lime mud at the bottom of shallow crater like basins located on top of stacked cones soft sediment deformations affecting the lime mud sediment were most probably produced by the recurrent uprising of gas bubbles the overlying crystalline crusts were deposited on the flanks of the mound by waters overflowing from the vents with laminar flux a deep hydrothermal circuit with a long period of water rock interaction is supported by geochemical analyses furthermore a local extensional regime enhancing the migration of thermal fluids to the surface is inferred based on the results of the structural analysis carried out on the fault fracture mesh that affects the mound these results corroborate the well established relation among travertine deposits hydrothermal systems and fault systems and substantiate the structurally controlled conceptual model of the euganean hydrothermal system suggesting that both the thermal and the fault systems were active at least since 34 ka

large kinetic isotope effects in modern speleothems the application of stable isotopes in speleothem records requires an understanding of the extent to which speleothem calcite isotopic compositions refl ect the compositions of the cave waters from which they precipitate to test for equilibrium precipitation modern speleothem calcite was grown on glass plates so that the carbon and oxygen isotope composition of the calcite and the water from which it precipitated could be directly compared the plates were placed on the tops of three actively growing stalagmites that occupy a 1 m 2 area in harrison s cave barbados west indies only some of the plate 13 c values and none of the plate 18 o values correspond to equilibrium values indicating signifi cant kinetic isotope effects during speleothem calcite growth we investigate herein mechanisms that may account for the kinetic isotope effects on each plate speleothem calcite was deposited with distinct 18 o and 13 c compositions that increase progressively away from the growth axis with up to 6 6 13 c and 1 7 18 o enrichments the positive 13 c

controls on trace element sr mg compositions of carbonate cave waters implications for speleothem climatic records abstract at two caves clamouse s france and ernesto ne italy cave drip and pool waters were collected and sampled at intervals over a 2 3 year period mg ca and sr ca concentration ratios corrected for marine aerosols are compared with those of bedrocks and in some cases aqueous leachates of soils and weathered bedrocks cave waters do not lie along mixing lines between calcite and dolomite of bedrock carbonate but typically show enhanced and covarying mg ca and sr ca four factors are considered as controlling processes 1 the much faster dissolution rate of calcite than dolomite allows for the possibility of increase of mg ca if water rock contact times are increased during drier conditions a theoretical model is shown to be comparable to experimental leachates 2 prior calcite precipitation along a flow path is a powerful mechanism for generating enhanced and covarying mg ca and sr ca ratios this mechanism requires the solution to lose co 2 into pores or caverns 3 incongruent dolomite dissolution has only limited potential and is best regarded as two separate processes of dolomite dissolution and calcite precipitation 4 selective leaching of mg and sr with respect to ca is shown to be important in leachates from ernesto where it appears to be a phenomenon of calcite dissolution in general selective leaching can occur whenever ca is sequestered into precipitates due to freezing or drying of soils or if there is derivation of excess sr and mg from non carbonate species the ernesto cave has abundant water supply which in the main chamber is derived from a reservoir with year round constant p co 2 of around 10 2 4 and no evidence of calcite precipitation in the karst above the cave two distinct but overlying trends of enhanced and covarying mg ca and sr ca away from the locus of bedrock compositions are due to calcite precipitation within the cave and at a variable drip site due to enhanced selective leaching at slow drip rates mg enhancement in the first chamber is due to a more dolomitic bedrock and longer residence times the clamouse site has a less abundant water supply and presents geochemical evidence of prior calcite precipitation both in the cave and in overlying porous dolomite dedolomitized limestone bedrock initial p co 2 values as high as 10 1 are inferred experimental incubations of clamouse soils which generated enhanced p co 2 and precipitated caco 3 had compositions similar to the karst waters calcite precipitation is inferred to be enhanced in drier conditions hydrological controls on cave water chemistry imply that the trace element chemistry of speleothems may be interpretable in palaeohydrological terms drier conditions tends to promote not only longer mean residence times enhancing dolomite dissolution and hence mg ca but also enhances degassing and calcite precipitation leading to increased mg ca and sr ca

two mathematical models of mg and sr partitioning into solution during incongruent calcite dissolution implications for dripwater and speleothem studies abstract positive correlation between sr ca and mg ca in cave dripwaters and speleothem is often attributed to prior calcite precipitation pcp where exclusion of mg and sr from calcite precipitated upstream of the dripwater speleothem site results in enrichment in the mg ca and sr ca ratios of residual effluent modelling predicts that pcp will produce a straight line correlation in graphs of ln sr ca vs ln mg ca with a theoretical slope that is given by kd sr 1 kd mg 1 calculated to be 0 88 0 13 regardless of rock or absolute dripwater composition sinclair et al submitted for publication while this makes the correlation slope potentially diagnostic for pcp mg and sr are also preferentially released from calcite during incongruent calcite dissolution icd and it is possible that icd produces a similar correlation between ln sr ca and ln mg ca to examine this possibility mathematical formulations for two different mechanisms of icd are presented model 1 simulates net dissolution as a dynamic kinetic process where forward and reverse reactions compete dissolution is congruent but ions are fractionated by a simultaneous reverse reaction where new calcite forms with sr ca and mg ca ratios that are determined by the solution composition and kd sr and kd mg model 2 simulates leaching of mg and sr from a fresh calcite surface by tracking the dissolution of a thin layer where high ion mobility allows the calcite to maintain a homogenous composition controlled by kd sr and kd mg in both models generalised kinetic equations are used in the derivations meaning that the results are not specific to a particular kinetic model in both models of icd the mathematics predict that under conditions that may prevail during dissolution of limestone the correlation between ln sr ca and ln mg ca is approximately linear with a slope given by kd sr 1 kd mg 1 thus this property is not specific to just pcp however for both pcp and icd this slope is universal expected to occur regardless of kinetics and the absolute composition of solution or host rock a correlation slope of 0 88 in either karst waters or speleothem is therefore diagnostic for calcite water interaction

uniform california earthquake rupture forecast version 2 ucerf 2 the 2007 working group on california earthquake probabilities wgcep 2007 presents the uniform california earthquake rupture forecast version 2 ucerf 2 this model comprises a time independent poisson process earthquake rate model developed jointly with the national seismic hazard mapping program and a time dependent earthquake probability model based on recent earthquake rates and stress renewal statistics conditioned on the date of last event the models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular extensible open seismic hazard analysis framework the rate model satisfies integrating measures of deformation across the plate boundary zone and is consistent with historical seismicity data an overprediction of earthquake rates found at intermediate magnitudes 6 5 m 7 0 in previous models has been reduced to within the 95 confidence bounds of the historical earthquake catalog a logic tree with 480 branches represents the epistemic uncertainties of the full time dependent model the mean ucerf 2 time dependent probability of one or more m 6 7 earthquakes in the california region during the next 30 yr is 99 7 this probability decreases to 46 for m 7 5 and to 4 5 for m 8 0 these probabilities do not include the cascadia subduction zone largely north of california for which the estimated 30 yr m 8 0 time dependent probability is 10 the m 6 7 probabilities on major strike slip faults are consistent with the wgcep 2003 study in the san francisco bay area and the wgcep 1995 study in southern california except for significantly lower estimates along the san jacinto and elsinore faults owing to provisions for larger multisegment ruptures important model limitations are discussed

pleistocene glacial history of the nw european continental margin abstract in this paper new and previously published data on the pleistocene glacial impact on the nw european margin from ireland to svalbard between c 48 n 80 n are compiled the morphology of the glaciated part of the european margin strongly reflects repeated occurrence of fast moving ice streams creating numerous glacial troughs channels that are separated by shallow bank areas end moraines have been identified at several locations on the shelf suggesting shelf edge glaciation along the major part of the margin during the last glacial maximum deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55 n and northwards whereas the margin to the south of this is characterised by the presence of submarine canyons glaciation curves based primarily on information from the glacial fed fan systems that depict the pleistocene trends in extent of glaciations along the margin have been compiled these curves suggest that extensive shelf glaciations started around svalbard at 1 6 1 3 ma while repeated periods of shelf edge glaciations on the uk margin started with mis 12 c 0 45 ma the available evidence for mis 2 suggest that shelf edge glaciation for the whole margin was reached between c 28 and 22 14 c ka bp and maximum positions after this were more limited in some regions north sea and lofoten the last glacial advance on the margin has been dated to 15 13 5 14 c ka bp and by c 13 14 c ka bp the shelf areas were completely deglaciated the younger dryas loch lomond advance reached the coastal areas in only a few regions

isotope study of moisture sources recharge areas and groundwater flow paths within the eastern batinah coastal plain sultanate of oman oxygen and hydrogen isotope analyses of rainfall samples collected on the eastern batinah coastal plain of northern oman between 1995 and 1998 indicate two different principal water vapor sources for precipitation in the area a northern mediterranean source and a southern indian ocean source as a result two new local meteoric water lines were defined for the study area isotopic analyses of groundwater samples from over 200 springs and wells indicate that the main source of water to the batinah coastal alluvial aquifer is high altitude rainfall from the adjacent jabal akhdar mountains originating from a combination of northern and southern moisture sources the groundwater recharged at high altitude forms two plumes of water which is depleted in the heavy isotopes 18o and 2h and stretches from the mountains across the coastal plain to the sea thereby retaining a chemical homogeneity horizontally and vertically down to a depth exceeding 300 m in contrast in areas adjacent to these two plumes the alluvial aquifer is geochemically stratified near the coast saline intrusion results in abrupt changes in chloride concentrations and isotope values

speleothem evidence from oman for continental pluvial events during interglacial periods growth periods and stable isotope analyses of speleothems from hoti cave in northern oman provide a record of continental pluvial periods extending back over the past four of earth s glacial interglacial cycles rapid speleothem growth occurred during the early to middle holocene 6 10 5 ka b p 78 82 ka b p 120 135 ka b p 180 200 ka b p and 300 325 ka b p the speleothem calcite deposited during each of these episodes is highly depleted in 18 o compared to modern speleothems the d 18 o values for calcite deposited within pluvial periods generally fall in the range of 24 to 28 relative to the vienna peedee belemnite standard whereas modern speleothems range from 21 to 23 the growth and isotopic records indicate that during peak interglacial periods the limit of the monsoon rainfall was shifted far north of its present location and each pluvial period was coincident with an interglacial stage of the marine oxygen isotope record the association of continental pluvial periods with peak interglacial conditions suggests that glacial boundary conditions and not changes in solar radiation are the primary control on continental wetness on glacial interglacial time scales

origins of elements building travertine and tufa new perspectives provided by isotopic and geochemical tracers fluid rock interaction represents a major process in the formation of calcitic or aragonitic travertine and tufa catt in most cases catt is associated to limestone dissolution somewhere along the hydrogeological pathway however a wide array of other substratum basalts rhyolites carbonatites ultramafics granites dolomites evaporites can act as potential source of elements involved in the formation of catt this study reports on the evaluation of potential geochemical tracers linking catt to their substratum and unravelling the origin of elements a large database was established from available literature data as well as new data acquired in the frame of this study for a set of modern to recent catt ligurian ophiolites italy the chaine des puys limagne graben and paris basin france reunion island indian ocean jebel oust tunisia four most reliable tracing methods are identified 1 13c and 18o cross plot allows distinguishing epigean min 13c 27 2 max 13c 0 9 mean 13c 12 3 for n 314 from hypogean systems min 13c 4 max 13c 11 7 mean 13c 2 87 for n 198 very low 13c values 4 associated to negative 13c values are specifically indicative of an ultramafic source rock 2 barium and strontium cross plot helps to discriminate different groups of source rocks amongst the hypogean catt i source rocks composed of mixed limestones evaporites and dolomites are characterised by low barium 400 ppm contents ii mafic and granitic source rocks are undifferentiated and display similar barium from 15 to 930 ppm and high strontium 200 ppm contents iii the carbonatite group is characterised by its exceptional high barium and strontium values in epigean catt a pure limestone source rock usually relates to very low barium and strontium contents 50 ppm 3 relatively high beryllium content 30 ppm in catt seems to indicate a pure granitoid source 4 high chromium concentrations 20 ppm are systematically documented in modern catt located on an ultramafic substratum the definition of diagnostic compositional fields for actively forming or recently formed catt is influenced by many factors including water composition water temperature dissolved gas composition and concentration biological activity position in the sedimentary body and early diagenesis in addition to substratum lithology however the results of this study illustrate that despite these many factors the combined use of ba sr be cr 13c and 18o may be valuable to discriminate the rock lithology prevailing in the hydrogeological or palaeo hydrogeological reservoir of catt

travertines associated with hyperalkaline springs evaluation as a proxy for paleoenvironmental conditions and sequestration of atmospheric co2 abstract travertine are found in ophiolite massifs in association with bicarbonate depleted hyperalkaline spring waters ph up to 11 9 in contrast with most continental carbonates e g travertine tufa speleothems that precipitate from calcium bicarbonate enriched waters here travertines formed from bicarbonate depleted hyperalkaline spring water were subjected to a multidisciplinary and multi scale approach to evaluate their potential as proxies of past climatic records and sequestration of atmospheric co 2 two mechanisms of calcium carbonate precipitation were apparent 1 hydration hydroxylation reaction due to the mixing of hyperalkaline and surface runoff waters or 2 dissolution of atmospheric co 2 g into hyperalkaline waters for two sites the bulk chemical signature of travertines mg ca and sr wt are consistent with prior calcite precipitation pcp processes and thus likely records the environmental conditions at the time of their formation however for the third site the trace element concentrations in the various carbonate fabrics indicate some recrystallization constant 18 o values indicate that hydration and hydroxylation reactions completely buffer the oxygen isotope composition of the water equilibrium state from which a paleo temperature can be estimated in contrast 13 c values reflect potential carbon sources either from surface runoff waters or atmospheric co 2 within the framework of continental carbonate calcium carbonate formation in bicarbonate depleted hyperalkaline environments results in a linear and positive co variation of 18 o and 13 c values and defines a unique and distinctive stable isotope field on a 18 o 13 c plot in contrast to carbonates formed in more typical bicarbonate enriched environments moreover the combined variations in 18 o 13 c and 87 sr 86 sr between laminae document the changes in the paleo activity of hyperalkaline spring and surface runoff waters on the time scale of formation the 87 sr 86 sr ratio represents a tracer for quantifying surface runoff water contribution furthermore the amount of co 2 sequestrated in travertine has been estimated following different scenarios of formation the calculated co 2 sequestrated for these deposits ranges from 9 kgco 2 yr 1 to 522 kgco 2 yr 1

computational tools for relaxing the fault segmentation in probabilistic seismic hazard modelling in complex fault systems use of faults in seismic hazard models allows us to capture the recurrence of large magnitude events and therefore improve the reliability of probabilistic seismic hazard assessment psha in the past decades fault segmentation provided an important framework for quantifying fault based psha recent complex coseismic ruptures e g 2010 mw 7 1 canterbury 2012 mw 8 6 sumatra 2016 mw 7 8 kaik ura 2016 mw 6 5 central italy have shown the need to consider different possible combinations of rupture scenarios in psha here we present two new methodologies that model rates of ruptures along complex fault systems one based on a floating rupture approach fresh and another one based on assumed rupture scenarios sunfish they represent alternatives to a recently proposed approach sherifs and further step to overcome the segmented and un segmented approaches commonly used in psha in europe differences among sherifs sunfish and fresh are related to the way slip rate rupture geometries and magnitude frequency distributions are modelled to quantify the differences between these three methodologies we compared psha results based on geometries and slip rates of a fault system located in northeastern italy assuming a given maximum magnitude and the same seismic moment rate target differences up to 20 30 in the peak ground acceleration at 2 and 10 in 50 years are observed finally we show that the three methodologies are able to solve for the long term rate of ruptures with resulting psha that reflect the fault system geometry and slip rates without any assumption on segment boundaries using fault based approaches in psha requires collecting as much local geological information as possible now that multi fault rupture approaches are available simplifying assumptions often made to model complex fault systems uniform slip rate segmentation hypothesis are no longer necessary on the other hand local data collection should be strongly encouraged to better characterize the actual fault slip rate variability and the complex 3d geometries

coseismic slip vectors of 24 august and 30 october 2016 earthquakes in central italy oblique slip and regional kinematic implications after 24 august and 30 october 2016 central italy earthquakes mw 6 0 and 6 5 respectively photogrammetry and geodetic survey were performed at various sites along a 6 km long portion of the rupturing monte vettore fault system providing very high resolution georeferenced 3 d point clouds and imagery of the 24 august rupture and a data set of bedrock fault scarp before after the 30 october earthquake the maximum coseismic displacement for both events occurs near scoglio dell aquila with an average normal dip slip of 22 4 and 184 6 cm respectively coseismic slip vectors and meter scale corrugation axis are oriented n280 10 on the n140 striking main vettore fault involving oblique normal slip with a right lateral component and n205 10 on n170 fault strands implying oblique normal slip with a left lateral component we quantify the near field coseismic displacements of the monte vettore fault for the 30 october event the footwall has been translated horizontally by 42 2 cm toward the ene and uplifted by 11 2 cm the hangingwall has moved horizontally by 26 2 cm toward the nw in a direction parallel to the fault plane and subsided by 116 2 cm the fault geometry and our determined surface coseismic slip vectors are mechanically compatible with a 3 n65 15 this stress regime is consistent with the 30 october 2016 focal mechanism and the relative motion between the adriatic microplate and the tyrrhenian coastal region the 30 october surface rupture results from seismic slip at depth and thus has a tectonic origin

origin of hydrogen nitrogen gas seeps oman six gas samples were collected from five thermal springs in the semail nappe ophiolite and the calcareous calcite and dolomite hajar formation northern oman the3he 4he 4he 20ne 40ar 36ar and38ar 36ar ratios chemical compositions h2 n2 co2 ch4 o2 ar and he and stable isotope compositions dh2 dh2o 13cco2 13cch4 and 15nn2 are reported samples from the ophiolite region are significantly anoxic with major constituents of h2 ch4 and n2 while those from calcite and dolomite regions are ordinary gas seeps consisting of n2 co2 and or o2 the former h2 rich gas is characterized by relatively high3he 4he ratio 0 4 0 8 ratm with low he content 300 ppm slight radiogenic40ar 36ar ratio high n2 ar ratio 77 97 and low 15nn2 value 0 observed dh2 value of 536 in h2 rich gas is distinguished from the literature value of 699 in the ophiolite region giving discrepant isotope formation temperatures

chemical and 13c 12c and 18o 16o isotope evolution of alkaline drainage waters and the precipitation of calcite carbon and o isotope ratios demonstrate that calcite precipitating from alkaline tunnel drainage waters has formed by two distinct chemical mechanisms calcium carbonate sulfate ground water dissolves portlandite preferentially this leads to an increase of ca2 ph and the co32 hco3 ratio so that calcite is precipitated the c content of this calcite is a mixture of c from soil co2 and the dissolved limestone resulting in 13c 13 pdb the o isotope composition 18o 24 smow corresponds to thequilibrium fractionation between calcite and water the precipitation continues as atmospheric co2 is absorbed by the alkaline solutions in this type of calcite the c isotope composition 13c 25 pdb is controlled by the individual reaction rate constants for the hydroxylation of 13co2 and 12co2 the o isotope composition 18o 11 smow is a mixture of the compositions of atmospheric co2 and oh the isotope compositions may be used in order to evaluate the proportions of the two different mechanisms of calcite precipitation other mechanisms which cause chemical changes of the ground water are the formation of ettringite from initially unhydrated c3a phases and the formation of brucite precipitation and dissolution rates for the various solids range from 10 3 to 10 4 kg d m2

sources and cycling of carbon in continental serpentinite hosted alkaline springs in the voltri massif italy abstract active serpentinization systems are abundant on present day earth and are of increasing interest because water rock reactions lead to alkaline ca oh fluids that have the potential to sequester co 2 and form reduced chemical species e g ch 4 and h 2 that can support chemolithoautotrophy we present a study of alkaline ph 10 12 springs in the voltri massif italy that focuses on the sources and cycling of inorganic carbon in the basement rocks the interacting fluids and the resulting surface carbonate deposits most springs are located in mantle rocks that underwent varying degrees of ocean floor serpentinization and incorporation of carbon as carbonate and organic carbon in the jurassic which is preserved during subsequent subduction and uplift onto the continent the springs are fed by meteoric water that evolves into alkaline ca rich spring waters that have 2 3 times higher ca concentrations than the adjacent rivers our study is consistent with previous reaction path modeling and identifies the formation of clay minerals in serpentinites that have been altered by alkaline fluids these strongly altered basement rocks contain up to 2 wt c in the shallow subsurface also documented by the presence of late calcite veins concentrations of dissolved inorganic carbon dic of the alkaline fluids are generally low 13 c dic is between 24 2 and 1 3 we argue that the concentrations and isotopic composition of the dic in the alkaline waters provide evidence for 1 the precipitation of calcium carbonate under closed system conditions with respect to atmospheric co 2 and 2 removal of dic by microbial activity in the subsurface late stage uptake of atmospheric co 2 in the shallow subsurface or at the exit sites subsequent to water rock microbe interactions in the basement result in fluids with lower ph and ca and enrichment in dic and 13 c at the surface interaction of the high ph ca oh fluids with atmospheric co 2 causes precipitation of carbonates as travertines or crusts on the basement rocks storing co 2 as calcium carbonate carbonate precipitation at the exit sites is strongly dominated by kinetic processes leading to carbon and oxygen isotope compositions as low as 27 2 and 18 7 respectively with increasing distance from the springs the 13 c and 18 o content of the carbonate increases and the fluid ph changes towards neutral our study shows that surficial carbonate precipitation plays a subordinate role in carbon sequestration but that the evolution from mg hco 3 spring waters to ca oh waters removes significant amounts of carbon presumably in the subsurface we calculate that the serpentinites have the capacity to sequester up to 0 50 to 2 05 10 9 mol carbon per year and conclude that they can take up significantly more co 2 than they currently contain

mineralogical assemblages forming at hyperalkaline warm springs hosted on ultramafic rocks a case study of oman and ligurian ophiolites 1 we report on the mineralogical assemblages found in the hyperalkaline springs hosted on liguria and oman ophiolites based on exhaustive x ray diffraction and scanning electron microprobe analyses in liguria hyperalkaline springs produce a thin brownish calcite precipitate that covers the bedrock due to the concomitant atmospheric co2 uptake and neutralization of the hyperalkaline waters no brucite and portlandite minerals are observed the discharge of alkaline waters in oman ophiolite forms white orange precipitates calcium carbonate minerals calcite and or aragonite are the most abundant and ubiquitous precipitates and are produced by the same mechanism as in liguria this process is observed as a thin surface crust made of rhombohedral calcite morphological features of aragonite vary from needle bouquet dumbbell spheroidal like habitus according to the origin of carbon temperature and ionic composition of the hyperalkaline springs and the biochemical and organic compounds brucite is observed both at hyperalkaline springs located at the thrust plane and at the paleo moho the varying mixing proportions between the surface runoff waters and the hyperalkaline ones control brucite precipitation the layered double hydroxide minerals occur solely in the vicinity of hyperalkaline springs emerging within the bedded gabbros finally the dominant mineralogical associations we found in oman ca bearing carbonates and brucite in a serpentinizing environment driven by the meteoric waters are surprisingly the same as those observed at the lost city hydrothermal site in a totally marine environment

fault based earthquake rupture forecast in central italy remarks after the l aquila mw 6 3 event abstract in 2006 we published an earthquake hazard model called lassci layered seismogenic source model in central italy in october 2008 we began to update the model for use in 5 and 10 year forecasts the lassci 2006 model is supported by good fault based definitions of seismogenic sources and simple physically motivated models of earthquake occurrence the lassci 2009 model has been improved by revision of the error propagation assumptions and increased accuracy of the earthquake probabilities the 6 april 2009 earthquake that struck l aquila occurred on the model fault having the highest probability of occurrence in the 2009 revised lassci forecast it is therefore consistent with our model assumptions furthermore peak ground accelerations were in reasonable agreement with the values having 90 probability of not being exceeded in 50 yr in the revised 2009 model the aggregate probability of having a maximum sized event in the next 5 yr on at least one of the neighboring sources less than 25 km distance away decreases in l aquila from 10 to 7 after the earthquake occurrence but still remains a maximum there along the central apennines the lassci models 2006 and 2009 featuring characteristic fault sources and time dependence seem to be suitable for guidance in reconstruction and seismic retrofit in the central appenines

chemical and stable isotope composition of recent hot water travertines and associated thermal waters from egerszalok hungary depositional facies and non equilibrium fractionation abstract combined petrographical mineralogical geochemical and stable isotope analyses were conducted on an actively forming egerszalok travertine mound to determine the factors that govern carbonate precipitation and thus influence the use of travertines in paleoclimate reconstruction stable isotope analyses of oxygen carbon and hydrogen demonstrate both biological and abiological factors to control travertine deposition processes of morphology related outgassing had major effects upon isotopic composition continuous co 2 degassing and temperature change of the thermal water between the spring orifice and distal parts of the system caused stable carbon and oxygen isotope compositions of the precipitating travertines to increase from 2 7 to 4 3 relative to v pdb and from 10 5 to 14 7 relative to v smow respectively the travertines at the spring orifice t 67 c are composed of almost pure calcite with a 13 c value of 2 7 relative to v pdb enabling classification as intermediate between thermometeogene and thermogene in lower temperature water away from the spring orifice various amounts of aragonite 5 35 with higher sr concentrations precipitate from solution this phenomenon is exceptional in hot spring carbonate deposits and could be explained by fast carbonate precipitation due to the morphology related outgassing oxygen and hydrogen isotope measurements of the thermal water confirmed evaporation to be causing limited kinetic isotope fractionation however 18 o values of the travertine do show isotope shifts away from the equilibrium fractionation curve which is most probably related to the rapid calcite precipitation and transportation along the flow path our data closely follow the temperature 18 o calcite water relationship observed for other travertine localities this is slightly displaced from the experimental curve and determines an empirical travertine curve our study shows that this shift may result in an approximately 8 c difference in paleotemperature calculations depending upon which fractionation curve is used

recurrent large earthquakes in a fault region what can be inferred from small and intermediate events we present a renewal model for the recurrence of large earthquakes in a fault zone consisting of a major fault and surrounding smaller faults with gutenberg richter type seismicity represented by seismic moment release drawn from a truncated power law distribution the recurrence times of characteristic earthquakes for the major fault are explored it is continuously loaded plate motion and undergoes positive and negative fluctuations due to adjacent smaller faults with a large number n eq of such changes between two major earthquakes because the distribution has a finite variance in the limit n eq the central limit theorem implies that the recurrence times follow a brownian passage time bpt distribution this allows us to calculate individual recurrence time distributions for specific fault zones without tuning free parameters the mean recurrence time can be estimated from geological or paleoseismic data and the standard deviation is determined from the frequency size distribution namely the richter b value of an earthquake catalog the approach is demonstrated for the parkfield segment of the san andreas fault in california as well as for a long simulation of a numerical fault model assuming power law distributed earthquake magnitudes up to the size of the recurrent parkfield event m 6 we find a coefficient of variation that is higher than the value obtained by a direct fit of the bpt distribution to seven large earthquakes we argue that the bpt distribution is a reasonable choice for seismic hazard assessment because it governs not only brownian motion with drift but also models with power law statistics for the recurrence of large earthquakes in an asymptotic limit finally we find that the condition b 1 separates two regimes in the first b 1 it is greater

seasonal trace element and stable isotope variations in a chinese speleothem the potential for high resolution paleomonsoon reconstruction abstract we report the presence of clear annual cycles in trace element mg ca sr ca ba ca and u ca and stable isotope 18o and 13c composition in an annually banded stalagmite from heshang cave hubei province china 30 44 n 110 42 e through a combination of micromilling and in situ analysis la mc icpms we measured geochemical variations across 16 annual growth bands to assess their potential as seasonal resolution paleomonsoon proxies to facilitate comparison with modern climatic and environmental data we created composite annual cycles for each proxy by stacking 6 well defined years speleothem 18o variations 10 8 to 8 5 are controlled by seasonal variations in temperature and drip water 18o which lead to maximum values during may around the time of summer monsoon onset this provides a chronological marker which can be used to constrain the timing of the other geochemical cycles the composite cycles reveal a strong positive correlation between mg ca sr ca ba ca and 13c values in the micromilled section r2 0 65 0 98 with minimum values occurring around may maximum u ca values occur at the same time we present simple models which show that these correlations as well as the observed ranges of mg ca 14 1 to 22 4 mmol mol sr ca 0 2 to 0 4 mmol mol and 13c 12 5 to 10 7 may be fully explained by progressive co2 degassing and calcite precipitation from an initially saturated solution using realistic initial conditions for heshang cave t 18 c mg casolution 0 84 mol mol sr casolution 0 69 mmol mol 13ctdic 16 75 we find that the observed relationships can be produced by using dmg 0 016 and dsr 0 30 within the range of expected values the model suggests that the fraction of ca removed from the solution ranges from 0 to 30 to produce the observed seasonal cycles this variation may be due to two related processes which occur during drier periods 1 increased prior precipitation of calcite in the epikarst or on the cave ceiling and or 2 a greater degree of co2 degassing and calcite precipitation on stalagmite surfaces when drip rates are lower both mechanisms would have the effect of enriching speleothem mg ca sr ca ba ca and 13c values during drier periods past variations in heshang carbonate chemistry may therefore be useful as seasonal resolution proxies for past rainfall

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

layered seismogenic source model and probabilistic seismic hazard analyses in central italy we defined a seismogenic model for central italy based on three layers of sources and computed the relative seismic hazard maps one layer is constituted by individual structures liable to generate major earthquakes m 5 5 we defined them as seismogenic boxes by using geological information in terms of plan projec tion of active faults the seismicity rates associated with an individual source are based on the geometry and kinematics of the fault the recurrence model is controlled by the earthquake source association and when possible we defined the occurrence time of the last major event using it in a time dependent approach another layer is given by the instrumental seismicity analysis of the past two decades which allows us to evaluate the background seismicity m 5 5 using a sliding window selec tion of events we defined a model of regular adjacent cells of variable a and b values of the gutenberg richter relation the last layer utilizes all the instrumental earth quakes and the historical events not correlated to known structures 4 5 m 6 by separating them into seismotectonic provinces shaped on a geological structural basis the seismic hazard computations first use this layered model in a traditional probabilistic scheme the results indicate a narrow belt of peak ground acceleration pga higher than 0 30g with standard deviation in attenuation functions in the axial part of the apennine chain with a maximum spot of pga 0 40g southeast of the area damaged by the 1997 1998 umbria marche sequence pga expected not to be exceeded in 50 years at 90 probability level the background seismicity gives a nonnegligible contribution to the hazard at least for first damage levels then a simplified time dependent hypothesis has been introduced for the individual sources alone computing the conditional probability of occurrence of characteristic earth quakes for each source by brownian passage time distributions adopting equivalent fictitious seismicity rates we obtained maps referring to the next 50 years by using traditional codes these results show that the contribution of the recently active sources vanishes and the most hazardous sites are now located south of l aquila and in the sulmona area we consider that the methodology and results obtained are useful for seismic risk reduction strategies

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

carbonation rates of peridotite in the samail ophiolite sultanate of oman constrained through 14c dating and stable isotopes abstract detailed 14 c dating as well as stable c and o isotope analyses were conducted on carbonates formed during alteration of the peridotite layer of the samail ophiolite sultanate of oman 14 c results obtained in this and previous studies indicate that surface travertines range in age from modern to 45 000 yr bp indicating long term deposition and preservation travertine deposition rates in two localities were 0 1 to 0 3 mm yr between 30 000 and 45 000 yr bp using an estimate of total travertine area this would result in a maximum of 1000 to 3000 m 3 yr of travertine being deposited throughout the ophiolite during this time period this travertine deposition would have sequestered a maximum of 1 to 3 10 6 kg co 2 yr ca rich carbonate veins that are associated with the surface travertine deposits have ages ranging from 4000 to 36 000 yr bp average 15 000 yr bp mg rich carbonate veins exposed in outcrops have ages ranging from 8000 to 45 000 yr bp average 35 000 yr bp detailed sampling from numerous locations 3 locations in this study and 10 locations in the previous studies indicates that no carbonate veins from the natural peridotite weathering surface are older than the 50 000 yr bp dating limit of 14 c however 14 c dating of mg rich carbonate veins from three roadcut exposures qafeefah fanja and al wuqbah indicates that a significant number of roadcut veins are 14 c dead 50 000 yr bp a location weighted average indicates that 40 of veins sampled at the three roadcuts are 14 c dead an average including veins sampled at both roadcuts and outcrops indicates that overall 8 of mg rich carbonate veins are 14 c dead mg rich carbonate veins are estimated to sequester on the order of 10 7 kg co 2 yr throughout the ophiolite

automatic processing of high rate high density multibeam echosounder data 1 multibeam echosounders mbes are currently the best way to determine the bathymetry of large regions of the seabed with high accuracy they are becoming the standard instrument for hydrographic surveying and are also used in geological studies mineral exploration and scientific investigation of the earth s crustal deformations and life cycle the significantly increased data density provided by an mbes has significant advantages in accurately delineating the morphology of the seabed but comes with the attendant disadvantage of having to handle and process a much greater volume of data current data processing approaches typically involve computer aided human inspection of all data with time consuming and subjective assessment of all data points as data rates increase with each new generation of instrument and required turn around times decrease manual approaches become unwieldy and automatic methods of processing essential we propose a new method for automatically processing mbes data that attempts to address concerns of efficiency objectivity robustness and accuracy the method attributes each sounding with an estimate of vertical and horizontal error and then uses a model of information propagation to transfer information about the depth from each sounding to its local neighborhood embedded in the survey area are estimation nodes that aim to determine the true depth at an absolutely defined location along with its associated uncertainty as soon as soundings are made available the nodes independently assimilate propagated information to form depth hypotheses which are then tracked and updated on line as more data is gathered consequently we can extract at any time a current best estimate for all nodes plus co located uncertainties and other metrics the method can assimilate data from multiple surveys multiple instruments or repeated passes of the same instrument in real time as data is being gathered the data assimilation scheme is sufficiently robust to deal with typical survey echosounder errors robustness is improved by pre conditioning the data and allowing the depth model to be incrementally defined a model monitoring scheme ensures that inconsistent data are maintained as separate but internally consistent depth hypotheses a disambiguation of these competing hypotheses is only carried out when required by the user the algorithm has a low memory footprint runs faster than data can currently be gathered and is suitable for real time use we call this algorithm cube combined uncertainty and bathymetry estimator we illustrate cube on two data sets gathered in shallow water with different instruments and for different purposes we show that the algorithm is robust to even gross failure modes and reliably processes the vast majority of the data in both cases we confirm that the estimates made by cube are statistically similar to those generated by hand

controls on aragonite and calcite precipitation in hot spring travertines at chemurkeu lake bogoria kenya subfossil travertines precipitated around hot spring orifices at chemurkeu on the western shore of lake bogoria kenya are composed of calcite aragonite and minor dolomite aragonite crystal beds which form 5 10 of the travertine by volume are formed of large pseudohexagonal prisms whereas the calcite crystal beds are composed mainly of feather dendrites dolomite is only found between aragonite crystals boundaries between aragonite and calcite crystals commonly display evidence of dissolution but there is no evidence to indicate that calcite formed by inversion of aragonite or that the dolomite replaced the aragonite thus the aragonite calcite and dolomite are each treated as primary precipitates reticulate gelatinous coatings with a high si and mg content cover most external and internal surfaces of the aragonite and calcite crystals the travertines may have formed under more humid conditions than today when the spring waters contained more ca2 the physiochemical conditions at the mo

present activity and seismogenic potential of a low angle normal fault system citta di castello italy constraints from surface geology seismic reflection data and seismicity abstract we present new constraints on an active low angle normal fault system in the citta di castello sansepolcro basin csb of the northern apennines of italy new field data from the geological survey of the carta geologica d italia carg project define the surface geometry of the normal fault system and lead to an interpretation of the crop 03 deep crust seismic reflection profile castiglion fiorentino urbania segment with particular attention paid to the geometry of the plio quaternary extensional structures surface and sub surface geological data are integrated with instrumental and historical seismicity in order to define the seismotectonics of the area low angle east dipping reflectors are the seismic expression of the well known altotiberina fault af a regional extensional detachment on which both east and west dipping high angle faults bounding the csb sole out the af breakaway zone is located 10 km west of the csb within the extensional allochthon synthetic east dipping planes prevail displacement along the af is 4 5 km which agrees with the cumulative offset due to its synthetic splays the evolution of the csb has mainly been controlled by the east dipping fault system at least since early pleistocene time this system is still active and responsible for the seismicity of the area a low level of seismic activity was recorded instrumentally within the csb but several damaging earthquakes have occurred in historical times the instrumental seismicity and the intensity data points of the largest historical earthquakes 5 events with maximum mcs intensity of ix to ix x allow us to propose two main seismogenic structures the monte santa maria tiberina mmax 5 9 and citta di castello mmax up to 6 5 normal faults both are synthetic splays of the af detachment dipping to the ne at moderate 45 50 to low 25 30 angles and cutting the upper crust up to the surface this study suggests that low angle normal faults at least with dips of 25 30 may be seismogenic

diversity and origin of quartz cements in continental carbonates example from the lower cretaceous rift deposits of the south atlantic margin abstract silica precipitation in continental carbonates is a common process occurring during sedimentation and diagenesis the lower cretaceous rift deposits of the south atlantic equatorial margin which are intensively explored by petroleum companies provide good examples of such silicifications in carbonates exhibiting a wide diversity of petrographic habit of early to late quartz cements in order to understand the palaeoenvironmental and diagenetic conditions leading to this diversity we integrated detailed petrography of diagenetic sequences and quartz habit with 18oquartz measurements by sims of individual cements observed in samples from the offshore and onshore basins of the west african margin the petrographic description highlights the omnipresence of early fibrous microquartz cements exhibiting either length fast or length slow habit in addition to laminated microquartz and micro or mega quartz forms amongst the isotopic analysis the 18oquartz data show that length slow cements are generally strongly enriched in 18o 18oquartz ranging from 31 to 37 smow whereas length fast forms show less elevated values 25 c and

changing moisture sources over the last 330 000 years in northern oman from fluid inclusion evidence in speleothems speleothems from hoti cave in northern oman provide a record of continental pluvial periods over the last 330 000 yr periods of rapid speleothem deposition occurred from 6000 to 10 500 78 000 to 82 000 120 000 to 135 000 180 000 to 200 000 and 300 000 to 330 000 yr ago with little or no growth during the intervening periods during each of these five pluvial periods d values of water extracted from speleothem fluid inclusions dfi are between 60 and 20 vsmow and 18o values of speleothem calcite 18oc are between 12 and 4 to vpdb these values are much more negative than modern rainfall for d or modern stalagmites for 18o previous work on the isotopic composition of rainfall in oman has shown that northern and southern moisture sources are isotopically distinct combined measurements of the d values of fluid inclusion water with calculated 18o values from peak interglacial speleothems indicate that groundwater was predominantly recharged by the southern indian ocean moisture source when the monsoon rainfall belt moved northward and reached northern oman during each of these periods

hydrogen generation from mantle source rocks in oman hydrogen gas associated with ca2 oh rich alkaline groundwaters ph 10 12 is at present emanating from ultramafic rocks of the oman ophiolite isotopic and chemical evidence indicates that hydrogen is formed by low temperature redox reactions in a closed groundwater environment this is normally a cryptic process in the hydrosphere but is fortuitously revealed by the unusual hydrogeological conditions in oman where atmospheric oxygen is totally assimilated it is suggested that hydrogen generation in mantle source rocks at depth and in the early archaean surface environment may be more widespread than has hitherto been realised

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

uncertainty in strain rate from field measurements of the geometry rates and kinematics of active normal faults implications for seismic hazard assessment abstract multiple measurements of the geometry kinematics and rates of slip across the auletta fault campania italy are presented and we use these to determine 1 the spatial resolution of field measurements needed to accurately calculate a representative strain rate 2 what aspects of the geometry and kinematics would introduce uncertainty with regard to the strain rate if not measured in the field we find that the magnitude of the post last glacial maximum throw across the fault varies along strike if such variations are unnoticed different values for a representative strain rate hence different results in seismic hazard calculations would be produced to demonstrate this we progressively degrade our dataset calculating the implied strain rate at each step excluding measurements can alter strain rate results beyond 1 uncertainty thus we urge caution when using only one measurement of slip rate for calculating hazard we investigate the effect of approximating the throw profile along the fault with boxcar and triangular distributions and show that this can underestimate or overestimate the strain rate with results in the range of 72 237 of our most detailed strain rate calculation we discuss how improved understanding of the potential implied errors in strain rate calculations from field structural data should be implemented in seismic hazard calculations

geochemistry of high ph waters from serpentinites of the gruppo di voltri genova italy and reaction path modeling of co2 sequestration in serpentinite aquifers abstract the large number of geochemical data gathered on the gruppo di voltri springs confirm that progressive interaction of meteoric waters with ultramafic rocks variably affected by serpentinization leads initially to the formation of mg hco3 waters when the system is open to co2 and na hco3 and ca oh type water upon further interaction with the rock under highly reducing closed system conditions with respect to co2 as indicated by 3h data these high ph waters have had long residence times underground in deep aquifers hosted by serpentinitic rocks these waters are the only available evidence of the presence of such deep aquifers high pressure injection of co2 into these deep aquifers was simulated by reaction path modeling results indicate that this is a feasible methodology to reduce the inputs of anthropogenic co2 into the atmosphere serpentinitic rocks have a high capacity for co2 sequestration mainly through formation of carbonate minerals dissolution of serpentinitic rocks and precipitation of magnesite and silica minerals occurs naturally in areas of high terrestrial co2 fluxes such as in southern tuscany corroborating the feasibility of this methodology of co2 sequestration however this process causes a progressive decrease in the porosity of the aquifer at least under closed system conditions these side effects must be carefully evaluated by means of further laboratory tests and field activities

the role of viscoelastic stress transfer in long term earthquake cascades insights after the central italy 2016 2017 seismic sequence central italy is characterized by a network of active faults that interact in a complex manner coseismic coulomb stress changes have been invoked by several authors to explain the concentration of moderate to strong earthquakes in this region but none has considered the time dependent viscoelastic relaxation of the lower crust and upper mantle as a possible additional source of stress changes at a regional scale here starting from the 1915 m w 6 9 0 2 fucino earthquake we calculated the coseismic plus postseismic coulomb failure stress changes cfs due to eight moderate to strong earthquakes that have struck central italy in the last century and culminated with the 2016 2017 sequence results from this modeling coupled with some synthetic tests simulating normal fault earthquakes with different magnitudes allowed us to highlight the importance of postseismic processes in particular the viscoelastic stress transfer due to events of m w 6 5 can modify the spatial distribution of cfs on a centennial timescale and therefore trigger events at larger distances in addition using these results we identified other earthquake clusters in the historical catalogue last 618 years which like the 1915 2017 series were potentially modulated by both coseismic and postseismic processes finally considering our calculations combined with historical and paleoseismological data we suggest that several faults in central italy may be at present close to failure

possible microbial effects on stable carbon isotopes in hot spring travertines recent and older early holocene to pleistocene hot spring travertine carbonates from central italy have two distinctive macrofabrics crystalline crusts and shrubs crystalline crusts are laminated slope deposits that formed abiotically following co 2 degassing from spring water the formation of shrub travertine irregular dendritic precipitates from pool environments is controversial and has been attributed to both abiotic and microbial processes oxygen isotope variation in our travertines can be explained by abiotic processes mainly co 2 degassing in contrast our carbon isotope data cannot be wholly explained by abiotic co 2 degassing invoked in earlier studies because photosynthesis is known to preferentially remove 12 c leaving ambient waters enriched in 13 c this fractionation should be recorded in delta 13 c values of microbially influenced travertine our shrub carbon isotope values are between 0 5 per thousand and 6 0 per thousand larger than values for associated abiotic precipitates and this difference is probably caused by microbial activity these isotope data support previous visual evidence that some shrub fabrics are microbially influenced

the magnitude distribution of declustered earthquakes in southern california abstract the binned distribution densities of magnitudes in both the complete and the declustered catalogs of earthquakes in the southern california region have two significantly different branches with crossover magnitude near m 4 8 in the case of declustered earthquakes the b values on the two branches differ significantly from each other by a factor of about two the absence of self similarity across a broad range of magnitudes in the distribution of declustered earthquakes is an argument against the application of an assumption of scale independence to models of main shock earthquake occurrence and in turn to the use of such models to justify the assertion that earthquakes are unpredictable the presumption of scale independence for complete local earthquake catalogs is attributable not to a universal process of self organization leading to future large earthquakes but to the universality of the process that produces aftershocks which dominate complete catalogs

submarine glacial landforms record late pleistocene ice sheet dynamics inner hebrides scotland we use 7000 km2 of high resolution swath bathymetry data to describe and map the submarine glacial geomorphology and reconstruct late pleistocene ice sheet flow configurations and retreat dynamics within the inner hebrides western scotland frequently dominated by outcrops of structurally complex bedrock the seabed also comprises numerous assemblages of well preserved glacigenic landforms typical of grounded ice sheet flow and punctuated ice margin retreat the occurrence and character of the glacially streamlined landforms is controlled in part by the shallow geology and topography however these factors alone cannot account for the location orientation and configuration of the observed landforms we attribute the distribution of these elongate streamlined landforms to the onset zone of the former hebrides ice stream his part of a major ice stream system that drained 5 10 of the last british irish ice sheet biis we suggest this geomorphic signature represents the transition from slow sheet flow to streaming flow as ice accelerated out from an environment characterized by numerous bedrock obstacles e g islands headlands towards the smooth sediment dominated shelf the majority of streamlined landforms associated with the his indicate ice sheet flow to the southwest with regional scale topography clearly playing a major role in governing the configuration of flow during maximal glacial conditions 29 23 ka we infer that the his merged with the north channel malin shelf ice stream to form a composite ice stream system that ultimately reached the continental shelf edge at the barra donegal trough mouth fan taken collectively however the pattern of landforms now preserved at seabed e g convergent flow indicators cross cutting flow sets is more indicative of a thinning ice mass undergoing reorganization during overall ice sheet retreat during latter stages of late weischselian glaciation suites of moraines overprinting the streamlined landforms suggest partial stabilization of the his prior to the ice sheet retreating to more isolated topographically confined troughs and basins retreat from the shelf towards and back into the inner hebrides may have been rapid due the prevalence of overdeepened troughs within the near shore fjord like troughs and deeps basin aligned streamlined landforms indicate the subsequent flow of thinner topographically partitioned ice masses and overprinted moraines record further ice margin retreat potentially along tide water margins this work provides the first geomorphological constraints for this large marine influenced sector of the former biis we also shed new light on the glacial geomorphic record found at the transition from terrestrial to marine continental shelf settings and examine the interplay between substrate geology bed topography bathymetry and grounding line positions relationships which are important for characterizing contemporary marine ice sheet margins

do static stress changes of a moderate magnitude earthquake significantly modify the regional seismic hazard hints from the l aquila 2009 normal faulting earthquake mw 6 3 central italy we investigated the coulomb stress changes in the active faults surrounding a moderate magnitude normal faulting earthquake 2009 l aquila mw 6 3 and the associated variations in the expected ground motion on regional probabilistic seismic hazard maps we show that the static stress variations can locally increase the seismic hazard by modifying the expected mean recurrence time on neighbouring faults by up to 290 years with associated variations in the probability of occurrence of the maximum expected earthquake of up to 2 our findings suggest that the increase in seismic hazard on neighbouring faults following moderate magnitude earthquakes is probably not sufficient to necessitate systematic upgrades of regional probabilistic seismic hazard maps but must be considered to better address and schedule strategies for local scale mitigation of seismic risk

rates of geodetic deformation across active faults in southern italy abstract active deformation in southern italy is accommodated by a distributed number of faults with low moderate slip rates outcropping extensional faults and mostly blind transcurrent faults are mapped within a western or axial and an eastern domain respectively we use a combination of continuous 2001 00 2011 84 and episodic 1995 68 2010 79 gnss observations to firstly estimate the geodetic deformation rate on 32 faults geodetic results were successively compared with geological displacement estimates in agreement with seismological and geological information a net spatial segregation emerges between the extensional axial belt and the eastern domain where strike slip faults are geodetically active although uncertainties are at times large average displacement rates show broadly consistent patterns within both domains a longitudinal gradient in extension rate is observed for the axial fault array with two sectors of higher magnitude 0 8 1 7 mm yr for individual faults this result is consistent with geological observations and supports the notion that extension occurs in discrete patches faults of the eastern domain have lower few 0 1 to 1 2 mm yr strike slip rates and an eastward decreasing extensional component but significant geodetic displacement is detected in areas lacking clear evidence of activity few faults with 1 2 mm yr extension rate are locally found in the eastern domain but based on their limited length and on inconsistency with seismology and geology they are considered as due to deep seated gravitational spreading for crustal faults although geodetic slip and moment rates are larger than geological rates the broad trend of long to short term rates is similar indicating the feasibility of geodetic analysis to contribute estimating fault slip rate and testing tectonic models in the region whereas the western domain extension is thought to be controlled by potential energy related to the tyrrhenian moho uplift beneath the apennines strike slip in the east is related to shear on inherited faults within the adriatic crust

a mutually consistent seismic hazard source model for southern california abstract a previous attempt to integrate geological geodetic and observed seismicity data into a probabilistic hazard source model predicted a rate of magnitude 6 to 7 earthquakes significantly greater than that observed historically one explanation was that the discrepancy or apparent earthquake deficit is an artifact of the upper magnitude limit built into the model this was controversial however because removing the discrepancy required earthquakes larger than are seen in the geological record and larger than implied from empirical relationships between fault dimension and magnitude although several articles have addressed this issue an alternative integrated source model without an apparent deficit has not yet appeared we present a simple geologically based approach for constructing such a model that agrees well with the historical record and does not invoke any unsubstantiated phenomena the following factors are found to be influential the b value and minimum magnitude applied to gutenberg richter seismicity the percentage of moment released in characteristic earthquakes a round off error in the moment magnitude definition bias due to historical catalog incompleteness careful adherence to the conservation of seismic moment rate uncertainty in magnitude estimates obtained from empirical regressions allowing multi segment ruptures cascades and the time dependence of recurrence rates the previous apparent deficit is shown to have resulted from a combination of these factors none alone caused the problem nor solves it the model presented here is relatively robust with respect to these factors

a 20 ka sediment record from the hajar mountain range in n oman and its implication for detecting arid humid periods on the southeastern arabian peninsula abstract playa like sediments from the hajar mountain range in northern oman 22 83 n 59 00 e 1050 m asl document variations of the paleoenvironmental and paleoclimate conditions over the last 20 ka based on high resolution sediment sampling and their osl dating sedimentation rates were calculated and used as a proxy for paleorainfall the results show that the glacial to lateglacial was characterized by arid conditions with a following transitional period of even less rainfall at 10 5 ka sedimentation rates increases abruptly indicating the onset of the early holocene humid period ehhp rainfall reaches its maximum at 9 8 ka ehhp 2 and a decreasing sedimentation rate after 8 ka characterizes the arid period of the middle to late holocene variations of the hydrological regime are associated with the intensity of the boreal summer indian monsoon and its related position of the itcz for the onset of the ehhp a northerly shift of the itcz is postulated thus confirming earlier results from the southern arabian peninsula

reconstruction of water temperature ph and flux of ancient hot springs from travertine depositional facies an extensive data set of the physical and chemical attributes of two modern hot springs in the mammoth hot springs complex of yellowstone national park wyoming u s a yields a strong correlation between travertine depositional facies and the temperature ph and flux of the hot spring water from which the travertine precipitated because advection dominates in these hot spring drainage systems we quantify variability between and within springs in order to construct a hydrologic model that defines the primary flow path in the context of key macroscopic travertine accumulation patterns this model based on 343 in situ triplicate measurements provides the basis for the use of travertine facies models to quantitatively reconstruct hot spring aqueous temperature ph and flux solely from precipitated travertine as an example reconstruction we deduce that previously described pleistocene apron and channel facies travertine quarry deposits from central italy precipitated from hot spring waters with a ph of 6 86 6 0 19 and a temperature of 65 4 6 3 6uc

controls on bedrock bedform development beneath the uummannaq ice stream onset zone west greenland this paper investigates the controls on the formation of subglacially eroded bedrock bedforms beneath the topographically confined region upstream of the uummannaq ice stream uis during the last glacial cycle palaeoglaciological conditions are believed to have been similar for all sites in the study characterised by thick fast flowing ice moving over a rigid bedrock bed classic bedrock bedforms indicative of glacially eroded terrain were mapped including p forms roches moutonnees and whalebacks bedform long axes and plucked face orientations display close correlation parallel and perpendicular to palaeo ice flow directions inferred from striae measurements across all sites elongation ratios length to width varied by an order of magnitude between 0 8 1 and 8 4 1 bedform properties length height width and long axis orientation from four subsample areas form morphometrically distinct populations despite their close proximity and hypothesised similarity in palaeoglaciological conditions variations in lithology and geological structures e g joint frequency joint dip joint orientation bedding plane thickness and bedding plane dip provide lines of geological weakness which focus the glacial erosion in turn controlling bedform geometries determining the relationship s between bedding plane dip relative to palaeo ice flow and bedform shape relative length amplitude and wavelength has important ramifications for understanding subglacial bed roughness cavity formation and likely erosion style quarrying and or abrasion at the ice bed interface this paper demonstrates a direct link between bedrock bedform geometries and geological structure and emphasises the need to understand bedrock bedform characteristics when reconstructing palaeoglaciological conditions

seismic slip history of the pizzalto fault central apennines italy using in situ produced 36cl cosmic ray exposure dating and rare earth element concentrations morphological and geological observations reveal that most apenninic faults are highly segmented and that the majority of the fault segments are less than 10 km long although these faults have undergone numerous paleoseismological investigations quantitative data remain crucially lacking for a large number of fault segments because such data are essential to understanding how these faults have ruptured and interacted in the past and how they might behave in the future we investigated the holocene seismic history of the pizzalto normal fault a 13 km long fault segment belonging to the pizzalto rotella aremogna fault system in the apennines we collected 44 samples from the pizzalto fault plane exhumed during the holocene and analyzed the 36cl and rare earth element ree contents together the 36cl and ree concentrations show that at least six events have exhumed 4 4 m of the fault scarp between 3 and 1 ka with slip per event values ranging from 0 3 to 1 2 m no major events have been detected over the last 1 kyr the rotella aremogna pizzalto fault system has a clustered earthquake behavior with a mean recurrence time of 1 2 kyr and a low to moderate probability ranging from 4 to 26 of earthquake occurrence over the next 50 years

magnesium and strontium systematics in tropical speleothems from the western pacific abstract we present bulk average sr and mg data for 13 speleothems from different locations in the western equatorial pacific guam solomon islands and vanuatu these data plot on a single straight line in a graph of ln sr ca vs ln mg ca with a slope of 0 9 a 22 000 year record of sr and mg in one of these samples from guam also plots with the same slope suggesting that the process partitioning mg and sr within the guam speleothem is the same as the one that partitions mg and sr between the different pacific speleothems we rule out temperature growth rate detrital phases and sea spray as likely mechanisms for this correlation we construct mathematical models of limestone diagenesis and show that this cannot explain the slope of the correlation our favoured explanation for the correlation is calcite water interaction in the form of prior calcite precipitation pcp and or incongruent calcite dissolution icd we present a formal mathematical model of pcp and prove that the slope of a graph of ln sr ca and ln mg ca is given by kd sr 1 kd mg 1 a similar equation is derived for icd in a companion paper sinclair 2011 using published values for kdsr and kdmg this slope is calculated to be 0 88 in excellent agreement with our observations because the slope is independent of solution and host limestone composition it can be used to diagnose calcite water interaction in individual cave water studies where host rock composition is unknown or in speleothems for which no field drip water data or host rock geochemistry exists approximately half of published drip and speleothem mg sr studies plot within error of this slope we hypothesize that the overall trend in our pacific speleothem data results from the individual dripwater systems evolving from a roughly similar initial rock composition set by late quaternary reef limestone in the guam speleothem the broad peak in mg and sr centred on the early mid holocene reflects a change in hydrology rainfall with the most likely scenario being that dry conditions prevailed on guam at this time

the calcareous tufa in the tadrart acacus mt sw fezzan libya an early holocene palaeoclimate archive in the central sahara article i nfo the palaeoclimatic signi cance of calcareous tufa deposits found in the presently hyperarid tadrart acacus massif central sahara sw libya is discussed on the basis of u th datings stable isotope analyses and the regional hydrogeological context these deposits formed mostly between c 9600 and 8100 yr bp the isotopic signature 18 o and 13 c of this tufa indicates that the water forming these carbonates originated as isotopically depleted rainwater as a result of the northward expansion of the sw african monsoon system during the early holocene carbonate sedimentation in the tadrart acacus decreased shortly before c 8000 yr bp attributed to a drop in precipitation in the course of the well known 8 2 kyr event a correlation between tufa development and climate change in n and e africa and in the mediterranean basin during the early holocene is discussed the effect of early holocene climate change on both the landscape and the dwellers living in the tadrart acacus region is also evaluated

effect of time dependence on probabilistic seismic hazard maps and deaggregation for the central apennines italy abstract we produce probabilistic seismic hazard assessments for the central apennines italy using time dependent models that are characterized using a brownian passage time recurrence model using aperiodicity parameters of 0 3 0 5 and 0 7 we examine the sensitivity of the probabilistic ground motion and its deaggregation to these parameters for the seismic source model we incorporate both smoothed historical seismicity over the area and geological information on faults we use the maximum magnitude model for the fault sources together with a uniform probability of rupture along the fault floating fault model to model fictitious faults to account for earthquakes that cannot be correlated with known geologic structural segmentation we show maps for peak ground acceleration pga and 1 0 hz spectral acceleration sa 1 on rock having 10 probability of exceedence in 50 yr we produce maps to compare the separate contributions of smoothed seismicity and fault components in addition we construct maps that show sensitivity of the hazard for different parameters and the poisson model for the poisson model the addition of fault sources to the smoothed seismicity raises the hazard by 50 at locations where the smoothed seismicity contributes the highest hazard and up to 100 at locations where the hazard from smoothed seismicity is low for the strongest aperiodicity parameter smallest the hazard may further increase 60 80 or more or may decrease by as much as 20 depending on the recency of the last event on the fault that dominates the hazard at a given site in order to present the most likely earthquake magnitude and or the most likely source site distance for scenario studies we deaggregate the seismic hazard for sa 1 and pga for two important cities rome and l aquila for pga both locations show the predominance of local sources having magnitudes of about 5 3 and 6 5 respectively for sa 1 at a site in rome there is significant contribution from local smoothed seismicity and an additional contribution from the more distant apennine faults having magnitude around 6 8 for l aquila the predominant sources remain local in order to show the variety of impact of different values we also obtained deaggregations for another three sites in general as decreases periodicity increases the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates this effect is strongest for the long period 1 sec ground motions

the 2009 l aquila earthquake central italy a source mechanism and implications for seismic hazard an edited version of this paper was published by agu copyright 2009 american geophysical union

annual trace element cycles in calcite aragonite speleothems evidence of drought in the western mediterranean 1200 1100 yr bp each of two calcitic stalagmites from grotte de clamouse herault southern france displays a discrete aragonite layer dated at around 1100 yr bp the layer of fanning aragonite ray crystals is immediately preceded by calcite with mg and sr compositions that are uniquely high for the past 3 kyr trace element compositions close to the boundary between original aragonite and calcite are consistent with quasi equilibrium partitioning of trace elements between the phases study of modern dripwaters demonstrates that pronounced covariation of mg ca and sr ca ratios in dripwater occurs owing to large amounts of calcite precipitation upflow of the drips that fed the stalagmites trace element to ca ratios are enhanced during seasonally dry periods ion microprobe data demonstrate a pronounced covariation of trace elements including mg and sr in calcite and sr u and ba in aragonite the mean peak spacing is close to the long term mean of annual growth rates determined by differences in u series ages and so the trace element peaks are interpreted as annual the trace element chemistry of the stalagmites on annual to inter annual scales thus directly reflects the amounts of prior calcite precipitation interpreted as an index of aridity the longer term context is a multi decadal period of aridity 1200 1100 yr bp possibly correlated with an analogous episode in central america the arid period culminated in the nucleation of aragonite but within a decade was followed by a return to precursor conditions copyright 2005 john wiley sons ltd

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

reply to comment on layered seismogenic source model and probabilistic seismic hazard analyses in central italy by b pace l peruzza g lavecchia and p boncio by w marzocchi we greatly appreciate the interest in and feedback onour article we will address the comments in the next par agraphs following the comment points our article is not a novel or new approach toquantifyingthe recurrence behavior and seismic hazard of faults in italy fault recurrence behavior has been addressed previously innortheastern italy e g papoulia and slejko 1992 slejkoand rebez 2000 southern italy peruzza

travertine distinctive depositional fabrics of carbonates from thermal spring systems the terrestrial limestones forming at the emergence of thermal springs show a variety of unusual depositional facies the specific lithological and petrological features of these deposits have few counterparts in the marine and continental karst related carbonates but they are typical of the epigean limestone that has been quarried since antiquity in the surroundings of tivoli rome under the name of travertine where it is still forming in hydro geothermal fields linked to extensional tectonics the physicochemical hydrodynamic and geological conditions specific to the tivoli thermal spring system imply hypersaturated alkaline sulphate warm to hot waters upwelling from springs fed through open fractures faults in extensional and or volcanic regimes these features together with the hydrodynamic behaviour of the water flows running from the vents control the petrogenetic features of the travertine a well bedded mostly finely laminated porous but quite compact limestone the results of a detailed comparative petrological analysis carried out on the lithofacies of travertine limestones and of those observed during formation within numerous active thermal spring fields provide the elements required for an exhaustive textural classification of the travertine lithofacies which has not yet been described systematically according to the genetic processes and fabrics the thermal deposits that originate from such hypersaturated alkaline sulphate warm to hot waters can be subdivided into abiotic crystalline crusts microbially mediated crusts microbialites and granular deposits mostly represented by small accumulations of lime mudstone some of the granular deposits and the microbialites are only partially comparable with analogous sediments forming on tidal flats sabkhas or other continental sites however the facies association of crystalline crusts and laminar curled microbialites has no counterpart in the marine realm the widespread presence of thermophile bacteria and sulphobacteria and the general absence of autochthonous eukaryote organisms unable to live in poisonous sulphate waters are also undeniable evidence of their thermal origin

what controls the location of ice streams ice streams influence ice sheet mass balance and stability but key aspects of their behaviour remain poorly understood this paper reviews and discusses one very important aspect what controls their location in an ice sheet seven potential controls on ice stream location are identified from the literature topographic focusing topographic steps macro scale bed roughness calving margins subglacial geology geothermal heat flux and subglacial meltwater routing for each control the theoretical basis for its link to rapid ice flow is introduced followed by discussion of the evidence of its influence on the location of both contemporary and palaeo ice streams based on this new synthesis topographic focusing subglacial geology meltwater routing and calving margins appear to be most commonly associated with fast ice flow it is clear that rather than a single control however there exist a number of potential controls of varying influence we propose a hierarchy of factors with those occurring at the top of the hierarchy exerting a stronger influence on ice stream location and where present beneath an ice sheet are very likely to be associated with fast flow those factors occurring lower down the hierarchy are less commonly associated with ice streaming but appear to be influential in the absence of more common controls in such a hierarchy topographic focusing in the presence of a calving margin is the primary control in the absence of this ice streams will preferentially occur in areas with favourable subglacial meltwater routing and subglacial geology in the absence of these bed roughness geothermal heat flux and topographic steps may promote ice streaming significantly the primary controls on a given ice stream location are likely to influence its spatial and temporal dynamics ice streams governed by the presence of meltwater routing and or calving processes might exhibit more variable behaviour because these controls can vary over relatively short time scales compared to controls that vary over longer time scales e g geothermal heat flux subglacial roughness geology and topography identifying the controls on ice stream location is therefore of paramount importance when understanding ice stream longevity and their past and future activity