seismic anisotropy and velocity structure beneath the southern half of the iberian peninsula travel times of 11 612 pn arrivals collected from 7675 earthquakes are inverted to image the uppermost mantle velocity and anisotropy structure beneath the southern half of the iberian peninsula and surrounding regions pn phases are routinely identified and picked for epicentral distances from 200 to 1200 km the method used in this study allows simultaneous imaging of variations of pn velocity and anisotropy the results show an average uppermost mantle velocity beneath the study area of 8 0 km s the peninsular area covered by the iberian massif is characterized by high pn velocity as expected in tectonically stable regions indicating areas of the hercynian belt that have not recently been reactivated the margins of the iberian peninsula have undergone a great number of recent tectonic events and are characterized by a pronouncedly low pn velocity as is common in areas greatly affected by recent tectonic and magmatic activity our model indicates that the betic crustal root might be underlined by a negative anomaly beneath the southeastern iberian peninsula in the atlantic ocean we find a sharp variation in the uppermost mantle velocities that coincides with the structural complexity of the european and african plate boundary in the gulf of cadiz our results show a very pronounced low velocity anomaly offshore from cape san vicente whereas high velocities are distributed along the coast in the gulf of cadiz in the alboran sea and northern morocco the direction of the fastest pn velocity found is almost parallel to the africa eurasia plate convergence vector northwest southeast whereas to the north this direction is almost parallel to the main trend of the betic cordillera i e east west in its central part and north south in the curvature of the arc of gibraltar this suggests that a significant portion of the uppermost mantle has been involved in the orogenic deformation that produced the arcuate structure of the betic cordillera however we assume that the neogene extension had no major influence on a lithospheric scale in the alboran sea our results also show a quite complex pattern of anisotropy in the southwest iberian lithospheric mantle since the relationship between the direction of fastest pn velocity and major hercynian tectonic trends cannot be directly established 2004 elsevier b v all rights reserved

seismic response of fractures by numerical simulation summary fractures occur on a wide range of scales and are important in the study of hydrocarbon reservoirs seismic simulation by finite difference modelling using an equivalent medium method can devise the elastic parameters of a cell intersected by a fracture as those of a medium with an equivalent seismic response numerical experiments confirm that diffractions from the fracture tips are a strong component of the total wavefield however a comparison of boxcar linear angular and elliptic tapering suggests that there is little dependence on shape because the energy involved in a single diffraction is much lower than the incident energy an open fluid filled fracture has stronger effect on the wavefield than the wet and dry multiple crack models because an open fracture would have a stronger dissimilarity to the background rock the density of microcracks within a fracture also has strong effect on the seismic response however the properties of those cracks are not significant to the overall seismic response considering a distribution of a large number of fractures even when the overall density of fractures is held constant longer fractures attenuate seismic energy more than smaller ones for the orientation effect fractures oriented in the direction of propagation seem to affect the wavefield more than those perpendicular because of the incident wave striking the fracture at an angle greater than the critical angle experiments on clustering of the fractures indicate that although clusters which are large compared to the wavelength may attenuate and shield more than for a uniform distribution smaller ones in fact attenuate less because of the healing effect these are important results when trying to characterize the fracture properties including density clustering size and orientation of a fractured reservoir from field seismic data

poisson s ratio and porosity at coso geothermal area california high resolution three dimensional compressional and shear wave velocity models derived from microearthquake traveltimes are used to map the distribution of poisson s ratio and porosity at coso geothermal area inyo county california spatial resolution of the three dimensional poisson s ratio and porosity distributions is estimated to be 0 5 km horizontally and 0 8 km vertically model uncertainties 1 in the interior and 2 3 around the edge of the model are estimated by a jackknife method we use perturbations of r vp vs ratio and vp vs product to derive distributions of poisson s ratio and porosity which are then used to constrain and delineate possible zones of intense heat fracture accumulation and fluid saturation poisson s ratio at coso ranges from 0 15 to 0 35 with an average of 0 224 lower than the crustal average of 0 25 high poisson s ratios are more extensive in shallower depths 1 5 km while lower poisson s ratios are found in the deeper section 1 5 3 0 km of the target area two major features with low poisson s ratio are identified at geothermal production depth 1 3 km around stations s2 s6 and s1 s3 s4 the two low features are separated by a northwest southeast trending high belt with variable width of 1 3 km a high body is found around s2 and s6 and extends down in depth a circular low belt corresponding to the high belt is located around s2 s6 and is linked to a previously reported structure in vs tomography this low highly porous belt is probably a horizontal conduit reservoir of geothermal fluid a vertical low and high channel beneath triangle s1 s3 s4 corresponds to a high attenuation dome like feature we propose an upwell and spread magma intrusion model for the last major magmatism in the coso region the magmatic upwelling is centered in the s1 s3 s4 area the model predicts potential geothermal resources to the south and west of triangle s1 s3 s4 based on local faulting patterns

ice water pits upon the yellow river delta plain abstract the erosion circular pit is a common sedimentary structure but its genesis is complex many erosion pits occur on the yellow river delta plain with some formed by ice water erosion the ice water pits are generally circular or semi circular in cross section and are typically 2 40 cm across and 2 20 cm in depth we identify four types of pits on the basis of their origin i pits that formed by liquefaction and tight arrangement ii pits that formed by spattering iii pits that formed by lateral leakage and iv pits that formed by bottom leakage the formation of the ice water pits is likely a function of many complex variables including frequent runoff channel structure ice run and fine sediment size the example of ice water pits from the yellow river delta plain offers a useful frame of reference for the interpretation of formation conditions and environment significances of some circular pits pot or pothole in ancient rocks

geochemistry of thermal springs alhama de granada southern spain abstract the waters of the thermal springs at alhama de granada vary in temperature between 27 and 45 c temporal changes in the composition of the principal spring banos viejos indicate that a small degree of mixing may occur between deep thermal waters and shallow groundwater slight compositional variations also occur between the various thermal springs in the study area these spatial variations are due to the different local hydrodynamic conditions in the springs towards the north in less hydraulically transmissive rocks cooling of the rising water is more noticeable as are ion exchange and processes of so 4 reduction the chemical composition of the water is related to the dissolution of evaporites so 4 and cl salts carbonates and silicates and to the possible existence of sources of s within the rock estimates of the mean residence times have been obtained based on 14 c dic and t the state of thermodynamic equilibrium at the spring discharge was calculated using the solmineq 88 program the results indicate that all the samples are supersaturated with respect to quartz chalcedony cristobalite calcite aragonite and dolomite and undersaturated with respect to gypsum anhydrite and halite the use of different geothermometers and modelling of saturation indices for quartz albite and anhydrite indicate temperatures of about 110 c

air discharge pits on the yellow river delta plain abstract a large number of air discharge pits varying in size and shape are developed on the yellow river delta their planar cross sections are circular sub circular elongated and frequently irregular and their spatial configurations may be in form of a shallow dish to root like or other extremely irregular shapes they range in diameter from less than 1 cm to over 60 cm and their depth varies from less than 1 mm to more than 20 cm they most commonly occur individually or in groups on the point bar our investigation indicates that the occurrence of the air discharge pits is closely associated with the unique hydrological channel and hydrodynamic conditions caused by the intermittent flow interruptions of the yellow river and the fine sediments typical of the river course during a yellow river flow interruption an underground air saturation zone in the dry layer of the riverbed may be formed due to the lowering of the ground water level when flooding originates from the up stream section of the yellow river the water quickly inundates the channel and rapidly submerges the extremely dry river bed and point bar as a result due to the blocking effect caused by the silty sand and mud preferential percolation occurs along the outer edge of the point bar and levee trapping air in the process the resulting air pocket and pressure capsule are enclosed in the air saturation zone providing the source material required for the subsequent formation of air discharge pits the trapped air may also form a high pressure capsule caused by the slow downward percolation of the river water the differential relatively lower pressure on the point bar permits the trapped air to escape provided the air is discharged in a shallow body of water

late mississippian bryozoan microbial build ups on a drowned karst terrain port au port peninsula western newfoundland bryozoan and microbial carbonate build ups occur within the late mississippian mid visean codroy group on the port au port peninsula western newfoundland build ups formed only adjacent to a rocky cliffed shoreline filling narrow submerged palaeovalleys of a well developed late devonian early mississippian karst terrain the nearshore setting was a stressed environment as indicated by 1 the absence of normal marine biota such as corals echinoderms and calcareous algae 2 high numbers and low species diversity of dominant taxa bryozoans brachiopods and microbial communities and 3 abundant plant bearing siliciclastics deposited by the episodic influx of fresh water from adjacent uplands build up development was terminated by meramec time due to falling sea level and seaward progradation of terrestrial sediments preserved structural and constructional fabrics within the build ups include 1 thickets of bryozoans and microbial microthrombolites structurally enhanced by probable marine mg calcite and aragonite cements 2 multigeneration internal sediment and 3 small colonies of serpulid worms and terebratulid brachiopods submarine cementation within the build ups appears to have been abundant during arrested sedimentation whereas intermound sediments carbonates and siliciclastics were lithified only during burial diagenesis shallow burial fracturing stylolitization sulphide and sulphate mineralization and precipitation of phreatic iron poor calcite cement occurred during burial diagenesis codroy build ups are distinct from the more common mississippian mud mounds their internal characteristics and the geologic setting are more like other late palaeozoic and holocene bryozoan rich build ups

evidence of episodic fluid gas and sediment venting on the northern gulf of mexico continental slope surficial sediments and sea floor features of the northern gulf of mexico continental slope record dramatic episodic venting and slower seepage of formation fluids brines crude oil gases and fine grained sediments faults activated by massive sediment input during periods of plio pleistocene falling to low sea levels accompanied by compensating salt movement provide avenues of vertical transport to the continental slope surface many of these faults cut thick sedimentary sequences that frequently contain geopressured zones which provide the driving force for fluid and gas expulsion flux rate and fluid characteristics are interpreted as important determinants of modern sea floor geology and biology qualitatively under conditions of rapid flux of sediment rich fluids mud volcanoes up to 1 km wide and 50 m high and extensive sheets of extruded mud result these sediments contain old and displaced microfaunas muds are frequently extruded with large volumes of crude oil and gas both biogenic and thermogenic in water depths greater than approximately 500 m rapid to moderate vertical flux of hydrocarbon gases and fluids results in the construction of relief features composed of gas hydrates ejected mud and authigenic carbonates areas with near surface hydrates frequently support complex chemosynthetic communities with associated hardgrounds containing calcareous remains of mussels clams and associated gastropods slow flux seeps promotes the formation of 13 c depleted carbonate hardgrounds stacked carbonate slabs and moundlike carbonate buildups frequently 20 m relief barite along with carbonate has been found in areas where rapid flux of sediment carrying fluids has waned in the recent past and mineral rich brines are now being ejected crests chimneys and cones of these minerals are found in such settings both recent numerical simulations of fluid release from geopressured zones and direct observations at the sea floor support a pattern of episodic venting short term episodes of venting are probably regulated by fault movement perhaps controlled by local salt adjustment destabilization of gas hydrates by oceanographic processes also causes short term episodic gas expulsion these events occur with interannual to intra annual frequencies longer gas hydrate stabilization destabilization cycles in continental margin settings are forced by hydrostatic loading and unloading at the frequency of sea level change radiometric dating suggests that other long term episodes of venting and major venting expulsion events are also probably modulated by sea level change time scales of thousands of years in response to low stand sedimentary loading results of this summary of vent seep related phenomena suggest that sediment input from the shelf margin associated with cyclic plio pleistocene falling to low sea level periods followed by major listic fault and salt adjustments to a new sediment load have activated venting seepage throughout this period and perhaps longer

dehydration induced damage and deformation in gypsum and implications for subduction zone processes 1 experimental heating tests were performed on volterra gypsum to study the micromechanical consequences of the dehydration reaction the experimental conditions were drained at 5 mpa fluid pressure and confining pressures ranging from 15 to 55 mpa one test was performed with a constantly applied differential stress of 30 mpa the reaction is marked by 1 a porosity increase and homogeneous compaction 2 a swarm of acoustic emissions 3 a large decrease in p and s wave velocities and 4 a decrease in vp vs ratio wave velocity data are interpreted in terms of crack density and pore aspect ratio which modeling pores as spheroids is estimated at around 0 05 crack like spheroid complementary tests performed in an environmental scanning electron microscope indicate that cracks first form inside the gypsum grains and are oriented preferentially along the crystal structure of gypsum most of the visible porosity appears at later stages when grains shrink and grain boundaries open extrapolation of our data to serpentinites in subduction zones suggest that the signature of dehydrating rocks in seismic tomography could be a low apparent poisson s ratio although this interpretation may be masked by anisotropy development due to preexisting crystal preferred orientation and or deformation induced cracking the large compaction and the absence of strain localization in the deformation test suggests that dehydrating rocks maybe seen as soft inclusions and could thus induce ruptures in the surrounding nonreacting rocks

deep biological communities in the subduction zone of japan from bottom photographs taken during nautile dives in the kaiko project abstract twenty seven dives of the submersible nautile in the subduction zone around japan conducted in the french japanese project kaiko proved that fairly luxuriant benthic communities dominated by deep sea giant clams of the genus calyptogena family vesicomyidae were consistently present on the accretionary prism at abyssal depths benthic communities characterized by three hitherto undescribed bivalves of the genus calyptogena were found between depths of about 3800 and 4020 m at the mouth of tenryu canyon and at the top of basement swell of the zenisu ridge both situated in the eastern nankai subduction zone sporadic but discrete patches of organisms characterized by one more undescribed bivalve belonging to the genus calyptogena were observed and collected between depths of 5130 and 5960 m on the landward wall of the japan and kouriles trenches photographic inventories were prepared semiquantitatively using each series of bottom photographs taken in these areas with bow cameras of the submersible nautile observations on the sporadic but dense distribution of the clams and other characteristic associated organisms match well with the scheme that communities sustained by chemosynthetic energy sources can be present at connate water seepages in subduction zones these are to date the deepest record of benthic communities supposedly associated with chemosynthetic processes

3 d seismic structure of kii peninsula in southwest japan evidence for slab dehydration in the forearc abstract kii peninsula is located in the forearc region of southwest japan and has distinct structural and tectonic features characterized by high seismicity in the crust and the subducting philippine sea slab high surface heat flow high 3he 4he isotopic ratio and a local change in the geometry of the subducting slab we have tried to determine detailed 3 d p and s wave velocity structures of this region using a large number of high quality arrival time data recorded by dense seismic networks on the japan islands from the obtained seismic velocities we further estimated 3 d distributions of poisson ratio crack density saturation rate and porosity parameter in the study area our results show significant heterogeneities in the crust and upper mantle wedge characterized by low seismic velocities high poisson ratio high values of crack density saturation rate and porosity these results suggest the existence of fluids in the crust and mantle wedge resulting from the dehydration of the subducting philippine sea slab which can explain the observed geophysical and geochemical features in kii peninsula

why did ancient chemosynthetic seep and vent assemblages occur in shallower water than they do today cold seep communities have relatively low diversity are dominated by one or two taxa present in high density and high biomass in comparison with the surrounding fauna and are restricted to aphotic habitats their associated heterotrophic fauna are usually distinctive from the fauna of their surroundings in contrast a more commonplace chemoautotrophically based community occurs in shallow photic habitats the associated heterotrophic fauna includes many of the species typical of the surrounding communities and typically dominates abundance whereas the species with chemoautotrophic symbionts dominate biomass all modern seep assemblages are deeper than 550 m many fossil seep assemblages occurred in water as shallow as the mid shelf 200 m in contrast communities where species with chemoautotrophic symbionts are biomass dominants but not numerical dominants are common in shallow waters at present but rarely reported in the geological record we suggest that the absence of cold seep communities on the continental shelf presently is due to a combination of predation and competitive exclusion by primary consumers limiting the presence of species dependent on chemoautotrophic symbionts we suggest that cold seep assemblages are more common at shelf depths in the fossil record for two reasons a the biases of preservation have accentuated their distribution by transforming communities where species with chemoautotrophic symbionts dominate by biomass but not numerically into cold seep appearing assemblages b the importance of predation pressure and oligotrophy has varied with decreased predation pressure accompanying increased oligotrophy favoring cold seep communities we suggest that the paucity of shallow water assemblages with species harboring chemoautotrophic symbionts as biomass dominants in the fossil record is based on the reliance of paleoecological analysis on numerical abundance data when energy flow analyses are required to identify these assemblages the distinctiveness of the fossil seep assemblage is intensified by taphonomic processes that bias the assemblage against small individuals and epifaunal species so that diversity declines the small heterotrophic component of the assemblage is significantly reduced and the epifaunal component is minimized the final assemblage is usually dominated by the better preserved large infaunal clams which perchance are also the species with chemoautotrophic symbionts in contrast preservation does not enhance the distinctiveness of these chemoautotroph harboring species in shallow water

comment on a metamodel for crustal magmatism phase equilibria of giant ignimbrites by s j fowler and f j spera the generation and evolution of giant supereruptionforming magma bodies is a contentious topic that has prompted much recent work much of which has appeared in this journal in a recent paper fowler spera 2010 summarize the state of the discussion and disagreement in very useful terms on one side bindeman valley 2001 and bindeman et al 2008 using evidence from geochronology and oxygen isotope geochemistry of yellowstone zircons argue in favor of a selfcannibalization crustal melting origin of large volumes of low do rhyolites on the other side bachmann bergantz 2004 2008 emphasize the challenges posed by heat flow constraints to an upper crustal melting scenario and advocate step wise crystal fractionation of mafic parental magmas interestingly fowler spera 2010 use phase equilibria information derived from melts simulations to place themselves in a more extreme position and suggest that single step fractional crystallization from mafic parental magmas is sufficient to explain the origin and evolution of giant bodies of rhyolitic magma there are many critical assumptions in the treatment of fowler spera 2010 that need careful scrutiny but we concentrate on those that we feel better equipped to address we focus on the evolution of the bishop magma body and we comment on 1 the compatibility of the proposed scenario with existing evidence from minerals melt inclusions and pumice from the bishop tuff and 2 the estimates for the longevity of the bishop magma body derived from heat balance considerations it seems significant to point out that the model proposed by fowler spera 2010 is essentially a transposition of the model they developed for the evolution of the campanian ignimbrite using similar methods fowler et al 2007 however there are significant differences between the trachyte phonolite system characteristic of the campanian ignimbrite and the high silica rhyolite systems discussed by fowler spera 2010 probably cognizant of some of the difficulties in transposing their model from one type of system to another fowler spera 2010 present what they call a metamodel an abstract construct that is useful to understand the generation and evolution of large volumes of high silica rhyolite by doing so they purposely distance themselves from the details of the various magmatic systems and focus on the first order features of the geochemical evolution of the systems of interest importantly they postulate evolution from parental mafic intermediate magmas erupted in the same regions and with similar ages to the high silica rhyolites and carry forward the exercise of seeking inconsistencies between modeled evolutionary paths and data for the natural systems

internal triggering of volcanic eruptions tracking overpressure regimes for giant magma bodies abstract understanding silicic eruption triggers is paramount for deciphering explosive volcanism and its potential societal hazards here we use phase equilibria modeling to determine the potential role of internal triggering wherein magmas naturally evolve to a state in which eruption is inevitable in rhyolitic magma bodies whole rock compositions from five large to super sized rhyolitic deposits are modeled using rhyolite melts by running simulations with varying water contents we can track crystallization and bubble exsolution during magma solidification we use simulations with variable enthalpy and fixed pressure for the five compositions the interplay between bubble exsolution and crystallization can lead to an increase in the system volume which can lead to magma overpressurization we find that internal triggering is possible for high silica rhyolite magmas crystallizing at pressures below 300 mpa 50 wt which makes magma immobile high silica rhyolite eruptions from such depths would require external triggering but examples are scarce or entirely absent calculated crystallinities at which the critical overpressure threshold is reached compare favorably with observed crystal contents in natural samples for many systems suggesting that internal evolution plays a critical role in triggering eruptions systems in which fluid saturation happens late relative to crystallization or in which degassing is effective can delay or avoid internal triggering we argue that priming by crystallization and bubble exsolution is critical for magma eruption and external triggering serves simply as the final blow rather than being the driving force of explosive rhyolitic eruptions

the 1995 kobe earthquake seismic image of the source zone and its implications for the rupture nucleation in order to understand what may have triggered the 1995 kobe japan earthquake and how the rupture proceeded after initiation we determined high resolution three dimensional 3 d p and s wave velocity and poisson s ratio structures in the kobe epicentral area and relocated the aftershocks with the obtained 3 d velocity model we used 64 337 p and 49 200 s wave high quality arrival times from 3634 kobe aftershocks and local microearthquakes recorded by both permanent seismic networks and portable stations that were set up following the kobe mainshock significant velocity variations of up to 6 are revealed in the aftershock area we found that areas with high aftershock activity are generally associated with low poisson s ratio which may be the strong and competent parts of the fault zone and were apt to generate aftershocks the kobe mainshock hypocenter is located in a distinctive zone characterized by low p and s wave velocities and a high poisson s ratio this anomaly exists in the depth range of 16 to 21 km and extends 15 to 20 km laterally this anomaly may be due to a fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake our interpretation has been supported by many pieces of evidence from hydrological geochemical seismological and geophysical investigations conducted at the kobe earthquake region

fluid participation in deep fault zones evidence from geological geochemical and 18o 16o relations fluid incursion into fault zones and their deeper level counterparts brittle ductile shear zones is examined in a number of different crustal environments at the grenville front translation was accommodated along two mylonite zones and an associated boundary fault the high mz ii and low temperature mz i mylonite zones formed at 580 to 640 c and 430 to 490 c respectively in the presence of fluids of metamorphic orgin indigenous to the immediate rocks a population of posttectonic quartz veins occupying brittle fractures were precipitated from fluids with extremely negative 18o at 200 to 300 c the water may have been derived from downwards penetration into fault zones of low 18o precipitation on a mountain range induced by continental collision with uplift accommodated at deep levels by the mylonite zones coupled with rebound on the boundary faults at lagoa real brazil archaean gneisses overlie proterozoic sediments along thrust surfaces and contain brittle ductile shear zones locally occupied by uranium deposits following deformation at 500 to 540 c in the presence of metamorphic fluids and under conditions of low water to rock ratio shear zones underwent local intense oxidation and desilicification all minerals undergo a shift of 10 indicating discharge of meteoric water recharged formation brines in the underlying proterozoic sediments up through the archaean gneisses during overthrusting about 1000 km3 of solutions passed through these structures at yellow knife a series of large scale shear zones developed by brittle ductile mechanisms involving volume dilation with migration of 5 wt volatiles into the shear zone from surrounding metabasalts this early deformation involved no departures in redox state or whole rock 18o from background states of fe2 fe 0 72 and 7 to 7 5 respectively attesting to conditions of low water rock shear zones subsequently acted as high permeability conduits for pulsed discharge of 9 km3 of reduced metamorphic hydrothermal fluids at 360 450 c the west bay fault a late major transcurrent structure contains massive bull quartz that grew at 200 300 c from fluids of 2 to 6 possibly formation brines in general flow regimes in these fault and shear zones follow a sequence from conditions of high temperature and pressure with locally derived fluids at low water to rock ratios during initiation of the structures to high fluxes of reduced formation or metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs later in the tectonic evolution and at shallower crustal levels there was incursion of oxidizing fluids from near surface reservoirs into the faults

seismic waves in rocks with fluids and fractures seismic wave propagation through the earth is often stronglyaffected by the presence of fractures when these fractures are filledwith fluids oil gas water co2 etc the type and state of the fluid liquid or gas can make a large difference in the response of theseismic waves this paper summarizes recent work on methods ofdeconstructing the effects of fractures and any fluids within thesefractures on seismic wave propagation as observed in reflection seismicdata one method explored here is thomsen s weak anisotropy approximationfor wave moveout since fractures often induce elastic anisotropy due tononuniform crack orientation statistics another method makes use ofsome very convenient fracture parameters introduced previously thatpermit a relatively simple deconstruction of the elastic and wavepropagation behavior in terms of a small number of fracture parameters whenever this is appropriate as is certainly the case for small crackdensities then the quantitative effects of fluids on thesecrack influence parameters are shown to be directly related to skempton scoefficient b of undrained poroelasticity where b typically ranges from0 to 1 in particular the rigorous result obtained for the low crackdensity limit is that the crack influence parameters are multiplied by afactor 1 b for undrained systems it is also shown how fractureanisotropy affects rayleigh wave speed and how measured rayleigh wavespeeds can be used to infer shear wave speed of the fractured medium higher crack density results are also presented by incorporating recentsimulation data on such cracked systems

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

ecologie des pseudobiohermes des terres noires jurassiques lies a paleo sources sous marines le site oxfordien de beauvoisin drome bassin du sud est france abstract pseudobioherms are fossiliferous calcareous bodies well exposed within jurassic calcareous shales of se france their genesis is unknown oxfordian psedobioherms of the outcrop of beauvoisin are studied here several kinds of results show that they are probably built at vent of submarine springs in a bathyal environment among their related fauna bivalves are thriving they show some remarkable analogies morphology growth distribution with some typical bivalves of recent springs hydrothermal vents or cold seeps like calyptogena isotopic composition of their shell exhibits a highly positive 13c and emphasizes this resemblance this suggests a chemosynthetic food supply through a bacterial symbiosis the whole fauna microfauna and macrofauna was inventoried within pseudobioherms and their close and far environment a comparative paleoecological study has been carried out to evaluate the faunal anomaly shown by a selected pseudobioherm two contemporaneous sections one close to this pseudobioherm and one other in a distant area without pseudobioherms have been studied in detail all taphonomic disturbances which are able to alter data have been carefully studied the paleobiocoenose suggests a slightly higher environmental stability because of an additional food supply within an environment usually less favorable it also suggests some permanency of spring activity the impact of the supposed springs on the benthic fauna is localized and slightly preserved through fossil fauna it mainly expresses itself in bivalves and organisms able to eat them crustacean cephalopods considering these various observations and after a critical comparison with characteristics and geological setting of recent submarine springs a model is suggested to understand the highly original paleo ecosystem of pseudobioherms

structural heterogeneity in northeast japan and its implications for the genesis of the 2004 and 2007 niigata earthquakes abstract we utilized 188 766 p wave and 179 328 s wave high quality arrival time data from 14 666 local earthquakes to determine the three dimensional 3d seismic velocity v p v s v p v s ratio crack density e and bulk velocity v structures in and around the source areas of the 2004 and 2007 niigata earthquakes japan meteorological agency magnitude m j 6 8 in japan in order to understand the generation mechanisms of the niigata mainshocks the aftershock hypocenters were relocated by applying the double difference location method simultaneously with the tomographic inversion indicating a complicated fault system that includes not only two parallel dominant faults dipping to the northeast but also some conjugate faults crossing the niigata mainshock hypocenters in general high velocity v p v s with low e at 11 km depth is visible in the southeastern part of this area in contrast to anomalous low velocity with high crack density in the northwestern part along the niigata kobe tectonic zone nktz these characteristics of the velocity and crack density are consistent with the spatial distribution of active faults along the nktz the surface geological features that indurated pre neogene rock outcrops were observed in the southeastern area whereas deep sedimentary basins were observed on the opposite side low v p and low v s zones with high v p v s anomalies were imaged in and or under the source areas showing agreement with those revealed by previous studies all the features of the velocity and v p v s structures together with the images of the crack density and bulk velocity suggest the presence of fluids under the source areas such fluids might have weakened the mechanical strength of the fault zone of the source areas thus triggering the 2004 and 2007 niigata earthquakes our present study together with other recent tomographic images reveals that fluids penetrated into the source rocks from the lower crust and uppermost mantle as a result of dehydration of the subducting pacific slab and thus may play a key role in the genesis of these large crustal earthquakes

melt inclusion shapes timekeepers of short lived giant magma bodies geology v 43 no 11 p 947 950 1 doi 10 1130 g37021 1 in the third paragraph of the methods section the following equation was incorrect t d ti l 2 4 the correct version of the equation is t l 2 4 d ti 1 lookup volpage 43 947

regional metamorphic dehydration and seismic hazard we use a one dimensional model of coupled heat transport fluid transport porosity feedback and metamorphism to investigate how dehydration reactions proceeding during burial of hydrous rocks in the footwall of thrusts or the hanging wall of normal faults may influence the temporal evolution of pore fluid pressure pf based on a new interpretation of existing kinetic data for the dehydration of model serpentinite we advance the hypothesis that pf buildup to tensile failure may be possible within decades of the onset of dehydration in low permeability metamorphic rocks of the middle crust this model contrasts with both 1 typical earthquake nucleation models which involve preexisting fluids that play a passive role responding to tectonic stresses rather than generating them and 2 conventional treatments of pf generation based on equilibrium thermodynamics and constant rates of dehydration which require 10 106 years to produce significant pf increases our results suggest that repeated cycles dehydration induced seismicity are plausible in low permeability areas of the mid crust and can be sustained throughout an orogenic episode if fresh hydrous minerals descend into the metamorphic zone along the downgoing face of a thrust or normal fault system

time averaging taphonomy and their impact on paleocommunity reconstruction death assemblages in texas bays the death assemblages in upper copano bay and upper laguna madre texas were compared with the living communities as sampled over a two year period in order to determine how taphonomy and time averaging affect paleocommunity reconstruction the living and death assemblages were compared using taxonomic composition numerical abundance diversity biomass and trophic and habitat proportions taxonomic composition particularly adult taxonomic composition and the biomass of the death assemblage more accurately reflect the characteristics of the living community than do numerical abundance and other community attributes based upon numerical abundance such as diversity taxonomic composition and biomass are less modified by taphonomy and time averaging because they are temporally more persistent characteristics of the community community and paleocommunity attributes are not equivalent because the paleocommunity is described using time averaged data ecological theory must be supplanted by paleoecological theory that takes into account this temporal component

p and s velocity structure of the yellowstone volcanic field from local earthquake and controlled source tomography the three dimensional p and s velocity from vp vs ratios distribution and improved hypocenters for the yellowstone volcanic field have been determined from inversion of first arrival times from 7942 local earthquakes and 16 controlled source explosions the p velocity model has an rms residual of 0 09 s whereas the vp vs ratio model calculated from 511 earthquakes has an rms residual of 0 29 s high p and s velocities outside the yellowstone caldera represent thermally undisturbed basement and sedimentary rocks a caldera wide 15 decrease from regional p velocities at depths of 6 to 12 km is coincident with a 60 mgal gravity anomaly and is interpreted as a hot subsolidus granitic batholith with a quasi plastic rheology localized 30 reductions from regional seismic velocities and higher vp vs ratios 8 km beneath yellowstone s resurgent domes are interpreted as partial melts and vestigial magma systems associated with youthful less than 2 ma silicic volcanism additional low seismic velocities and vp vs ratios and a 20 mgal gravity low less than 4 km beneath the northeast caldera rim are interpreted as a hydrothermal fracture zone thermally driven by underlying partial melt hypocenters relocated with the three dimensional p velocity model show subparallel alignment with nw se trending postcaldera volcanic vents and normal faults northwest of the caldera focal depths of relocated earthquakes decrease from more than 11 km outside the caldera to less than 6 km within the caldera reflecting thinning and heating of the seismogenic crust

basement structure of the granada basin betic cordilleras southern spain abstract the analysis and interpretation of geophysical data gravity and seismic reflection has facilitated the definition of the granada basin structure the reflector showing the contact between the betic subbetic basement and the neogene quaternary sedimentary filling has been identified mapping of the basement in two and three dimensions is presented the presence of four important depocenters genil chimeneas cubillas and granada has been determined these troughs are limited by ridge areas through important sets of fractures in some cases the accumulation of neogene quaternary sediments reaches a thickness exceeding 3 km as in the genii and cubillas depocenters the mapping of the most important fractures affecting the basement has been achieved defining four systems that have influenced and conditioned the genesis and late evolution of the granada basin the directions of the most important groups of fractures are ne sw n70w to e w n45w and n10 30e

crack density and saturation rate in the 1995 kobe earthquake region we have estimated the 3 d distribution of crack density parameter and saturation rate in the 1995 kobe earthquake region by applying a crack theory to values of seismic velocity and poisson s ratio obtained from seismic tomography our results show that and exhibit considerable heterogeneity higher and exist in the kobe fault zone in particular at the mainshock hypocenter high areas are generally consistent with high areas but high areas have a much wider distribution indicating that microcracks exist in more localized areas while fluids are permeating through wider areas in the crust a significant discrepancy between and exists beneath osaka bay where is low while is high is generally high beneath seas but low beneath land areas osaka bay and the present sea land distribution in southwest japan have existed for 2 millions years this period is long enough for the sea water to permeate down to the deep crust through the active faults that would have been ruptured during many earthquakes cycles

early carboniferous low temperature hydrothermal vent communities from newfoundland living vent communities dependent on microbial chemosynthesis rather than photosynthesis were discovered only in the 1970s1 since then six fossil vent communities have been identified they range in age from early carboniferous to early tertiary2 7 here we describe fossil tubes an abundant low diversity fauna and sulphide mineralization in 340 myr old carboniferous carbonate mounds in newfoundland fig 1a these features together with evidence for microbial activity point to the existence of a seventh chemosynthetic community clustered around low temperature hydrothermal vents the remarkable preservation of this newfoundland community allows a direct comparison to be made with the composition and structure of modern vent communities

3 d crustal structure of the extensional granada basin in the convergent boundary between the eurasian and african plates three dimensional p and s wave velocity models of the crust under the granada basin in southern spain are obtained with a spatial resolution of 5 km in the horizontal direction and 2 to 4 km in depth we used a total of 15407 p and 13704 s wave high quality arrival times from 2889 local earthquakes recorded by both permanent seismic networks and portable stations deployed in the area the computed p and s wave velocities were used to obtain three dimensional distributions of poisson s ratio r and the porosity parameter vpvs the 3 d velocity images show strong lateral heterogeneities in the region significant velocity variations up to 7 in p and s velocities are revealed in the crust below the granada basin at shallow depth high velocity anomalies are generally associated with mesozoic basement while the low velocity anomalies are related to the neogene sedimentary rocks the south southeastern part of the granada basin exhibits high r values in the shallowest layers which may be associated with saturated and unconsolidated sediments in the same area vpvs is high outside the basin indicating low porosity of the mesozoic basement a low velocity zone at 18 km depth is found and interpreted as a weak ductile crust transition that is related to the cut off depth of the seismic activity in the lower crust at 34 km depth a clear slow vp and vs anomalous zone may indicate variations in lithology and or with the rigidity of the lower crust rocks d 2002 elsevier science b v all rights reserved

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

phase equilibria constraints on the chemical and physical evolution of the campanian ignimbrite the campanian ignimbrite is a 4200 km trachyte phonolite pyroclastic deposit that erupted at 39 3 0 1ka within the campi flegrei west of naples italy here we test the hypothesis that campanian ignimbrite magma was derived by isobaric crystal fractionation of a parental basaltic trachyandesitic melt that reacted and came into local equilibrium with small amounts 5 10 wt of crustal rock skarns and foid syenites during crystallization comparison of observed crystal and magma compositions with results of phase equilibria assimilation fractionation simulations melts is generally very good oxygen fugacity was approximately buffered along qfm 1 where qfm is the quartz fayalite magnetite buffer during isobaric fractionation at 0 15 gpa 6 km depth the parental melt reconstructed from melt inclusion and host clinopyroxene compositions is found to be basaltic trachyandesite liquid 51 1 wt sio2 9 3 wt mgo 3 wt h2o a significant feature of phase equilibria simulations is the existence of a pseudo invariant temperature 883 8c at which the fraction of melt remaining in the system decreases abruptly from 0 5 to50 1 crystallization at the pseudo invariant point leads to abrupt changes in the composition properties density dissolved water content and physical state viscosity volume fraction fluid of melt and magma a dramatic decrease in melt viscosity from 1700 pa s to 200 pa s coupled with a change in the volume fraction of water in magma from 0 1 to 0 8 and a dramatic decrease in melt and magma density acted as a destabilizing eruption trigger thermal models suggest a timescale of 200 kyr from the beginning of fractionation until eruption leading to an apparent rate of evolved magma generation of about 10 3 km year in situ crystallization and crystal settling in density stratified regions as well as in convectively mixed less evolved subjacent magma operate rapidly enough to match this apparent volumetric rate of evolved magma production

modern analogues to middle ordovician sedimentary mounds and washout depressions abstract mounds and depressions containing dense fossil accumulations occur in a bed of middle ordovician age in the upper ottawa valley canada the appearance of these relict seabed features is similar to modern features containing dense accumulations of live species in the north sea it is suggested that the middle ordovician fossil accumulations relied on a similar local upward flux of minerals and nourishment as north sea communities which live in areas where sediments contain light hydrocarbon gases if further petrological and sedimentological studies on the middle ordovician deposits could confirm such a relationship then it would be the first time relict or fossil pockmarks were found in the sedimentary column

tomography of the source area of the 1995 kobe earthquake evidence for fluids at the hypocenter seismic tomography revealed a low seismic velocity 5 and high poisson s ratio 6 anomaly covering about 300 square kilometers at the hypocenter of the 17 january 1995 magnitude 7 2 kobe earthquake in japan this anomaly may be due to an overpressurized fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake

recent and present day stresses in the granada basin betic cordilleras example of a late miocene present day extensional basin in a convergent plate boundary the diffuse convergent boundary between the eurasian and african plates in the western mediterranean is associated with a seismicity zone more than 300 km wide although the two plates are converging nw se the betic and rif cordilleras contain extensional structures that have been active since the miocene the extensional tectonics in the region which occurred simultaneously with the uplift of the cordillera have been analyzed in the southeastern sector of the late miocene to recent granada basin using earthquake focal mechanisms the determination of paleostresses from the study of the orientation and kinematics of microfaults and the study of the major structures both the geological surface data and the focal mechanisms indicate present day regional conditions of ne sw extension with triaxial to prolate stress ellipsoids however the stress field is heterogeneous with local variations in stress over time with different stresses sometimes even acting simultaneously in adjacent areas the most frequent changes consist of pluridirectional or ne sw extension favored by the prolate character of the stress ellipsoids and nw se subhorizontal compression favored by the regional tectonic setting strike slip faults are scarce even though they are the most likely structure to be expected in a region with sw ne extension and nw se compression seismicity is concentrated in the upper crust and may correspond to the activity of low to high angle normal faults similar to the surface faults although they can not be correlated with them the lower cutoff of this seismicity probably coincides with the 300 c isotherm and suggests a low thermal gradient for the region present day regional stresses have 1 vertical at the surface but in depth plunge toward the sw

geologic evolution of the betic cordilleras in the western mediterranean miocene to the present abstract the betic cordilleras were formed during the eo meso and neo alpine evolution of the western mediterranean area during the neo alpine stage the northward subduction of the african plate took place and the algerian provencal basin opened with the creation of oceanic floor associated space problems produced the expulsion and extensive stretching of the internal zones to the west which in turn disrupted and deformed the external zones of the betic and rif cordilleras these occurrences essentially took place in the burdigalian and continued with diminished intensity into the middle miocene following the suturing of the transcurrent contact between the internal and external zones important n60 90 e and nw se faults occurred the betic cordilleras are characterized as having been deformed by regional horizontal shortening compression oriented wnw ese or nw se which gradually rotated to the nnw sse in the late miocene when its most important intramontane neogene basins were formed the alboran basin with a thinned continental crust was formed as a western prolongation of the opening of the algerian provencal basin with its basic features already apparent in the burdigalian the volcanism present in the southeast of the betic cordilleras and in northeast morocco crossing the alboran basin is mainly late miocene in age it is linked to fracturing and exhibits chemistry related to the different thickness of the crust

origin and evolution of silicic magmatism at yellowstone based on ion microprobe analysis of isotopically zoned zircons the origin of large volume yellowstone ignimbrites and smallervolume intra caldera lavas requires shallow remelting of enormous volumes of variably o depleted volcanic and sub volcanic rocks altered by hydrothermal activity zircons provide probes of these processes as they preserve older ages and inherited do values this study presents a high resolution oxygen isotope examination of volcanism at yellowstone using ion microprobe analysis with an average precision of 0 2o and a 10 mm spot size we report 357 analyses of cores and rims of zircons and isotope profiles of 142 single zircons in 11 units that represent majoryellowstone ignimbrites and post caldera lavas many zircons from these samples were previously dated in the same spots by sensitive high resolution ion microprobe shrimp and all zircons were analyzed for oxygen isotope ratios in bulk as a function of grain size by laser fluorination we additionally report oxygen isotope analyses of quartz crystals in three units the results of this work provide the following new observations 1 most zircons from post caldera low do lavas are zoned with higher do values and highly variable u pb ages in the cores that suggest inheritance from pre caldera rocks exposed on the surface 2 many of the higher do zircon cores in these lavas have u pb zircon crystallization ages that postdate caldera formation but pre date the eruption age by 10 20 kyr and represent inheritance of unexposed post caldera sub volcanic units that have do similar to the lava creek tuff 3 young and voluminous 0 25 0 1ma intra caldera lavas which represent the latest volcanic activity atyellowstone contain zircons with both high do and lowdo cores surrounded by an intermediate do rim this implies inheritance of a variety of rocks from high do pre caldera and low do post caldera units followed by residence in a common intermediate do melt prior to eruption 4 major ignimbrites of huckleberry ridge and to a lesser extent the lava creek and mesa falls tuffs contain zoned zircons with lower do zircon cores suggesting that melting and zircon inheritance from the lowdo hydrothermally altered carapace was an important process during formation of these large magma bodies prior to caldera collapse 5 the do zoning in the majority of zircon core rim interfaces is step like rather than smoothly inflected suggesting that processes of solution reprecipitation were more important than intracrystalline oxygen diffusion concave downward zircon crystal size distributions support dissolution of the smaller crystals and growth of rims on larger crystals this study suggests that silicic magmatism atyellowstone proceeded via rapid shallow level remelting of earlier erupted and hydrothermally alteredyellowstone source rocks and that pulses of basaltic magma provided the heat for melting each postcaldera yellowstone lava represents an independent homogenized magma batch that was generated rapidly by remelting of source rocks of various ages and do values the commonly held model of a single large volume super solidus mushy state magma chamber that is periodically reactivated and produces rhyolitic offspring is not supported by our data rather the source rocks for theyellowstone volcanism were cooled below the solidus hydrothermally altered by heated meteoric waters that caused low do values and then remelted in distinct pockets by intrusion of basic magmas each packet of new melt inherited zircons that retained older age and do values this interpretation may have significance for interpreting seismic data for crustal low velocity zones in which magma mush and solidified areas experiencing hydrothermal circulation occur side by side new basalt intrusions into this solidifying batholith are required to form the youngest volcanic rocks that erupted as independent rhyolitic magmas we also suggest that the lava creek tuff

v p v s and lithology published laboratory investigations suggest an association exists between the ratio of seismic compressional and shear wave velocities vp vs and sedimentary rock lithology comparisons of some theoretical models with these laboratory studies suggest that crack or pore geometry has a stronger effect on observed vp vs values than elastic constants of the minerals comprising the matrix further it can be inferred that the observed association between lithology and vp vs is a result of an association between lithology and distribution of pore and crack shapes direct observation of crack shapes for a variety of lithologies is a next step in strengthening these inferences the present study reviews the empirical relations between vp vs and lithology and examines two published theoretical models of cracked elastic media the models suggest that seismic velocities of sandstones may be controlled by cracks and pores with aspect ratios in the range of 10 1 to 1 dolomite in the range of 10 2 to 10 1 and dens

sedimentary mounds and washout depressions from the middle ordovician limestone ottawa valley canada abstract small elliptical mounds and depressions about 1 m long occur on and within a bed of fine grained middle ordovician limestone in the ottawa valley canada both the mounds and the bottoms of the depressions contain abundant fossils in contrast to the surrounding bed which is essentially barren the mounds and depressions formed in the outer and deepest part of a quiet tropical marine lagoon behind a carbonate bank where bottom conditions were normally anoxic an unusually diverse and abundant fauna lived on the bottom just prior to deposition of the bed containing the mounds and depressions indicating an abnormally high oxygen concentration at the sediment water interface at the time as bottom conditions deteriorated many of the species survived only on the mounds which had fo med by the trapping and holding of sediment by large branching bryozoans the suspension feeding fauna that flourished on the mounds slightly above the barren sea floor implies a location at the interface between the oxygenated normal sea water and a bottom lens of anoxic water of somewhat higher salinity the depressions are washout features that formed when sediment was eroded from the mounds

seismic anisotropy of the shallow crust in the umbria marche italy region abstract small magnitude earthquake data recorded during the 1997 umbria marche italy seismic crisis have been used to study the shear wave splitting in the central apennine using the method of diagonalization of the covariance matrix a set of 1234 s waves impinging the earth at an angle less than the critical angle has been selected the cross correlation method was used to estimate the splitting time between the two horizontal s components and the direction of the symmetry axis of the anisotropic structure a further analysis based on visual inspection of corrected traces allowed us to estimate the anisotropic parameters for 884 s waves an average splitting time 32 3 4 ms has been estimated splitting times do not generally show a clear pattern with distance which is an indication of possible spatial variations of seismic anisotropy a minimum 2 km depth of the anisotropic layer is estimated the trend of normalized splitting time vs depth roughly indicates a maximum 4 5 km depth of the anisotropic layer the distribution of the fast symmetry axis indicates a main symmetry axis oriented along the direction of the maximum compressive stress in the area and a secondary symmetry axis almost orthogonal to the first one the stereographic plots of fast axis direction seem exclude a depth dependence of anisotropic parameters a clear spatial correlation between the directions of the fast symmetry axes at the considered stations and the orientations of the nearest fault systems and thrust fronts is found which confirms the spatial variability in the anisotropic properties of the area as inferred by the analysis of splitting times based also on previous studies results are interpreted in terms of the extensive dilatancy anisotropy eda model the estimated crack density is always smaller than the critical coalescence value enforcing the hypothesis that fluid filled separated crack systems control the polarization of s waves

seismological evidence for magmatic and hydrothermal structure in long valley caldera from local earthquake attenuation and velocity tomography we compare the results of six different tomographic inversions for the three dimensional seismic attenuation and velocity structure in long valley caldera california in order to constrain interpretations on the location and character of magmatic and geothermal structure in the caldera crust p and s wave amplitudes and arrival times obtained in previous studies from seismograms of local earthquakes recorded on vertical and three component seismographis were inverted for q sv 1 q sh 1 q s 1 q p 1 and v p v s in the upper 9 km of teh caldera crust detailed comparisons of the results of the inversions suggest significant locations of high temperatures and perhaps magma and hydrothermal zones in the caldera a region of low q s with locally variable q p and v p v s is imaged in the 7 9 km depth range beneath the resurgent dome overlying and adjacent to this anomaly are significant low q p and low v p v s anomalies as well as smaller zones of low q s and high v p v s together these suggest zones of high temperature magma below and adjacent to zones of supercritical hydrothermal fluids at 4 5 km depth along the southern rim of the caldera just east of mammoth mountain a significant anomaly with relatively low q p and relatively low v p v s is imaged and is interpreted as a supercritical hydrothermal zone poorly resolved relatively low q p and relatively high v p v s are seen at 4 5 km depth beneath the inyo craters suggesting possible high temperatures and perhaps magma because of lack of data in the individual inversions the resultant images have spatially variable error and resolution however by comparing multiple images of different seismic parameters we have improved our ability to determine the significance of an constrain interpretation of seismic structure anomalies

high resolution seismic imaging of an active fault in the eastern guadalquivir basin betic cordillera southern spain abstract we calculated the high resolution seismic velocity poisson s ratio crack density and saturation ratio structures in and around the source areas of the torreperogil seismic series october 2012 april 2013 this seismic series characterized by a large number of low magnitude below mw 3 7 or md 3 9 and very shallow microearthquakes took place in the guadalquivir basin a large flexural foreland basin with a linear ene wsw trending bounded to the north by the iberian massif and to the south by the betic cordillera and filled from a middle miocene to plio quaternary sedimentary sequence in the upper layers of the crust strong low velocity anomalies are extensively distributed under the central zone which together with high poisson s ratio and crack density values may correspond to rocks which are less likely to fracture perhaps due to the accumulation of tectonic and seismic stress 93 of the earthquakes occurred at depths of up to 8 km which could indicate that the base of the seismogenic zone lies at this depth the seismic series was concentrated in layers of strong structural heterogeneities in the boundary area between low and high anomalies which were likely to generate earthquakes due to differential strain accumulation beneath the region the high velocity areas are also considered to be strong yet brittle parts of the fault zone which may generate earthquakes at depths of between 5 km and 9 km by contrast low velocity areas are less prone to fracture allowing seismic slippage to take place from 2 to 4 km depth the best estimate of the depth of the main shock m blg 3 9 is 7 6 km which could tend to nucleate at the base of the seismogenic zone at the fault end on the boundary between a low velocity zone to the east and a high velocity zone to the west indicating the fault plane which separates both areas laterally assuming that this seismic contrast is one of the main torreperogil faults it could imply that stress has accumulated in an existing fault zone with lateral heterogeneity in velocity

v p v s from mode converted p sv reflections p sv reflections are generated by a compressional wave source and result from p waves that are converted to shear sv waves upon reflection recording both the p and sv components yields compressional and shear data simultaneously verifying that the easily detected events really are p sv reflections is accomplished by noting the good correlation of surface cdp data with vertical seismic profile vsp reflections stacking velocities from p sv cdp gathers determine the vpvs product when source to receiver offset is less than the depth of the reflector but data from synthetic models show that p sv reflections are nonhyperbolic for shallow reflections or when source to receiver offset is too large shear velocity vs can be calculated from p sv reflections by one of two techniques comparison of stacked section p p and p sv reflection times or by using the p p and p sv stacking velocities unfortunately most p sv reflections on a p sv seismic section do not necessarily originate from exactly the same dep

a fossil hydrothermal worm assemblage from the tynagh lead zinc deposit in ireland fossil hydrothermal chimneys were first discovered at silvermines1 ireland subsequent discoveries of fossils associated with mounds and chimneys in sulphide deposits within the ophiolite complexes of cyprus2 and oman3 prove that life forms similar to those colonising active vents on the east pacific rise4 7 were extant 100 myr ago around ridge crest hot springs here i report the discovery of 350 myr old worm like fossils recovered from pyrite chimneys associated with sedimentary exhalative mineralization at tynagh ireland this find suggests that even older examples of life existing at seafloor hot springs may be awaiting discovery