small mammal taphonomy at la trinchera de atapuerca burgos spain a remarkable example of taphonomic criteria used for stratigraphic correlations and palaeoenvironment interpretations abstract palaeoecological and biostratigraphical interpretations have been traditionally based on the presence in the fossil record of certain species nevertheless there are many taphonomic factors controlling the species composition and their relative abundance in a fossil site that may alter spatial and temporal correlations between the site where fossils have been found and the place where past beings were living taphonomic studies have been conducted at different sites from atapuerca ibeas cave complex this cave complex in burgos spain includes several karstic sites with extensive evidence of human activity and a complete record of vertebrate remains of the middle pleistocene as well as abundant human fossils the small mammal taphonomic analysis of one of these sites penal is explained and discussed here in detail to show the taphonomic procedure stratigraphical correlation between levels at the penal site is particularly difficult and correlations have been proposed here based on taphonomic data since 1980 a working hypothesis suggested a sedimentary connection between penal and another site named dolina presently separated by an abandoned railway cutting in order to test this hypothesis the results of penal obtained from the present study are compared to previous analysis done in dolina it is also attempted here through taphonomic comparison of these two sites to obtain a better understanding of the past context where hominids inhabited

geologic framework of the mississippian barnett shale barnett paleozoic total petroleum system bend arch fort worth basin texas this article describes the primary geologic characteristics and criteria of the barnett shale and barnett paleozoic total petroleum system tps of the fort worth basin used to define two geographic areas of the barnett shale for petroleum resource assessment from these two areas referred to as assessment units the u s geological survey estimated a mean volume of about 26 tcf of undiscovered technically recoverable hydrocarbon gas in the barnett shale the mississippian barnett shale is the primary source rock for oil and gas produced from paleozoic reservoir rocks in the bend arch fort worth basin area and is also one of the most significant gas producing formations in texas subsurface mapping from well logs and commercial databases and petroleum geochemistry demonstrate that the barnett shale is organic rich and thermally mature for hydrocarbon generation over most of the bend arch fort worth basin area in the northeastern and structurally deepest part of the fort worth basin adjacent to the muenster arch the formation is more than 1000 ft 305 m thick and interbedded with thick limestone units westward it thins rapidly over the mississippian chappel shelf to only a few tens of feet the barnett paleozoic tps is identified where thermally mature barnett shale has generated large volumes of hydrocarbons and is 1 contained within the barnett shale unconventional continuous accumulation and 2 expelled and distributed among numerous conventional clastic and carbonate rock reservoirs of paleozoic age vitrinite reflectance ro measurements show little correlation with present day burial depth contours of equal ro values measured from barnett shale and typing of produced hydrocarbons indicate significant uplift and erosion furthermore the thermal history of the formation was enhanced by hydrothermal events along the ouachita thrust front and mineral wells newark east fault system stratigraphy and thermal maturity define two gas producing assessment units for the barnett shale 1 a greater newark east fracture barrier continuous barnett shale gas assessment unit encompassing an area of optimal gas production where dense impermeable limestones enclose thick 300 ft 91 m barnett shale that is within the gas generation window ro 1 1 and 2 an extended continuous barnett shale gas assessment unit covering an area where the barnett shale is within the gas generation window but is less than 300 ft 91 m thick and either one or both of the overlying and underlying limestone barriers are absent

the importance of secondary cratering to age constraints on planetary surfaces small craters less than one kilometer diameter can be primary craters produced by impact of interplanetary debris or they can be secondary craters produced by fallback of high velocity ejecta blocks from much larger but infrequent primary impacts the prevalent assumption over recent decades has been that primaries are most abundant so most small craters are independent random events and can be used for dating however recent results from europa and mars support the early theory that distant secondaries globally dominate the number of small lunar craters this would invalidate part of production functions that have been widely used for age dating crater excavation results in higher mean ejection velocities for smaller fragments resulting in a steeper size frequency distribution for secondary craters than is produced by the same size frequency distribution of interplanetary debris this review also discusses how small craters can sometimes be used to derive meaningful age constraints

paleomagnetic age for hominid fossils at atapuerca archaeological site spain a paleomagnetic investigation at the gran dolina site excavation atapuerca spain shows that the sediments containing the recently discovered human occupation were deposited more than 780 000 years ago near the time of the matuyama brunhes boundary forty one oriented samples were obtained from 22 sites along an 18 meter section of the gran dolina karst filling the lower 16 sites displayed reversed polarity magnetizations whereas the upper six sites were normal the reversal spans the hominid finds at stratigraphic level td6 the aurora stratum and these hominid fossils are therefore the oldest in southern europe

rheological properties of water ice applications to satellites of the outer planets 1 abstract the icy moons of the outer solar system have not been quiescent bodies in part because many have a substantial water component and have experienced significant internal heating we can begin to understand the thermal evolution of the moons and the rate of viscous relaxation of surface topography because we now have good constraints on how ice in several of its polymorphic forms flows under deviatoric stress at planetary conditions details of laboratory derived flow laws for pure polycrystalline ice are reviewed in detail one of the more important questions at hand is the role of ice grain size grain size may be a dynamic quantity within the icy moons and it may or may not significantly affect rheology one recent beneficiary of revelations about grain size sensitive flow is the calculation of the rheological structure of europa s outer ice shell which may be no thicker than 20 km

barnett shale gas production fort worth basin issues and discussion newark east barnett shale field fort worth basin texas is currently the most productive gas field in texas in terms of daily production and is growing at an annual rate of more than 10 however despite the fact that the barnett play has been studied intensely by very capable geologists and engineers from several companies over a period of many years there continues to be several misunderstandings concerning fundamental factors controlling the success of the barnett play of north texas barnett gas production is poorer in areas near faults and structural flexures anticlines and synclines fractures which are most abundant in these structural settings are detrimental to barnett production open natural fractures are rare in the barnett and have little or nothing to do with barnett productivity in areas where barnett shale is thermally mature with respect to gas generation it is slightly overpressured about 0 52 psi ft 11 76 kpa m limestone beds within the barnett formation are the product of debris flows that originated on a carbonate shelf to the north of the present basin center it appears that the barnett can be used as an exploration model for other basins especially analogous basins of the ouachita trend the history of the development of the barnett reservoir in north texas provides an excellent example of how persistence can lead to success in nonconventional gas plays

liquid water and active resurfacing on europa voyager images of the jovian moon europa show a bright icy surface transected by a complex pattern of long linear fracture like markings with a slightly lower albedo1 very few impact craters are observed with sizes generally hi the range 10 20 km indicators of surface composition and texture include deep ir h2o absorption features2 uv absorption features characteristic of sulphur in a water matrix on the trailing hemisphere3 and a photometric function indicating much more homogeneous scattering than areas of equal albedo on ganymede and callisto4 europe s mean density is 3 03 g cm 3 indicating a primarily silicate composition however if the density of the silicates is the same as for io the h2o mass fraction would be 6 enough to form an outer layer of h2o 100 km thick if completely differentiated several models have been suggested for the evolution and present state of europa5 8 we present here arguments for recent resurfacing by h2o from a liquid layer based on new interpretations of recent spacecraft and earth based observations and revised theoretical calculations

investigation of microearthquake activity following an intraplate teleseismic swarm on the west flank of the southern east pacific rise between february 1991 and may 1992 33 intraplate earthquakes having body wave magnitudes between 4 3 and 6 0 were located on the west flank of the southern east pacific rise by the international seismological center seven months after the last teleseismic event we deployed four ocean bottom seismometers at the site of the teleseismic swarm one hundred and ninety two microearthquakes were located using p and s travel times of events recorded by three or more instruments during the 16 day deployment most of the microearthquakes were in a band about 30 km long and 6 km wide between and parallel to seamount chains in addition several events were distributed along a line perpendicular to the main seismicity band and parallel to the ridge axis the focal depths of the microearthquakes range from 1 to 15 km and most are between 5 and 12 km similar to the depth range of the teleseismic events hung and forsyth 1996 the composite p wave polarities indicate that the microearthquakes had a variety of focal mechanisms we developed a new grid search inversion technique that utilizes the p wave polarities and the empirically corrected ratios of p and s wave amplitudes to find the focal mechanisms of individual events within the acceptable travel time and amplitude misfits focal solutions are fairly stable normal faulting is found in the ridge parallel seismicity line the thrust and strike slip faulting in the main seismicity band is distinctly different from the exclusively normal faulting mechanisms of the teleseismic events there is no apparent depth dependence of fault types none of the existing models of the sources of stress ridge push thermoelastic stresses loading by local topographic features caldera collapse and north south extension of the pacific plate provides a satisfactory explanation for both the teleseismic swarm and microearthquakes we propose a new tectonic scenario in this scenario the lithosphere is prestressed by the cooling of the plate magma rising from the deeper mantle induces normal faulting ahead of the dike tips in the lower lithosphere which is already under extensional thermal stress producing the larger teleseismically detected events once the dikes propagate into the lithosphere the region surrounding the dikes behind the tips is compressed by the overpressure of magma depending on the geometry of the dikes the local orientations of the minimum principal stress and the local weaknesses in the lithosphere thrust or strike slip faulting the microearthquakes may occur

injection induced seismicity and fault slip potential in the fort worth basin texasinjection induced seismicity and fault slip potential in the fort worth basin texas

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

geomechanical analysis of fluid injection and seismic fault slip for the mw4 8 timpson texas earthquake sequence an earthquake sequence that culminated in a mw4 8 strike slip event near timpson east texas the largest reported earthquake to date in that region had previously been attributed to wastewater injection starting 17 months before the onset of recorded seismic activity to test if this earthquake sequence can be attributed to wastewater injection we conducted coupled poroelastic finite element simulations to assess the spatial and temporal evolution of pore pressure and stress field in the vicinity of the injection wells and to calculate the coulomb failure stress on the seismogenic fault as a function of the permeability of the injection layer fault orientation fault permeability and orientation and magnitude of the in situ stress we find that injection induced fault slip is plausible within the range of selected model input parameters with slip favored by low reservoir permeability low fault permeability and a favorable orientation of the fault relative to the in situ stress state other combinations of equally plausible input parameters predict no slip within 96 months of simulated injection under most favorable boundary conditions for fault slip fault slip occurs 7 months after the start of injection our results highlight the importance of detailed geomechanical site characterization for robust fault stability assessment prior to wastewater injection

large impact features on europa results of the galileo nominal mission the galileo orbiter examined several impact features on europa at considerably better resolution than was possible from voyager the new data allow us to describe the morphology and infer the geology of the largest impact features on europa which are probes into the crust we observe two basic types of large impact features 1 classic impact craters that grossly resemble well preserved lunar craters of similar size but are more topographically subdued e g pwyll and 2 very flat circular features that lack the basic topographic structures of impact craters such as raised rims a central depression or central peaks and which largely owe their identification as impact features to the field of secondary craters radially sprayed about them e g callanish our interpretation is that the classic craters all 30 km diameter formed entirely within a solid target at least 5 to 10 km thick that exhibited brittle behavior on time scales of the impact events some of the classic craters have a more subdued topography than fresh craters of similar size on other icy bodies such as ganymede and callisto probably due to the enhanced viscous relaxation produced by a steeper thermal gradient on europa pedestal ejecta facies on europa and ganymede may be produced by the relief flattening movement of plastically deforming but otherwise solid ice that was warm at the time of emplacement callanish and tyre do not appear to be larger and even more viscously relaxed versions of the classic craters rather they display totally different morphologies such as distinctive textures and a series of large concentric structural rings cutting impact feature related materials impact simulations suggest that the distinctive morphologies would not be produced by impact into a solid ice target but may be explained by impact into an ice layer 10 to 15 km thick overlying a low viscosity material such as water the very wide near antipodal separation of callanish and tyre imply that 10 15 km may have been the global average thickness of the rigid crust of europa when these impacts occurred the absence of detectable craters superposed on the interior deposits of callanish suggests that it is geologically young 108years hence it seems likely that our preliminary conclusions about the subsurface structure of europa apply to the current day

tracking induced seismicity in the fort worth basin a summary of the 2008 2018 north texas earthquake study catalogtracking induced seismicity in the fwb a summary of the 2008 2018 north texas earthquake study catalog

probabilistic assessment of potential fault slip related to injection induced earthquakes application to north central oklahoma usa we utilize quantitative risk assessment qra to calculate the conditional probability of slip on mapped faults in response to injection related increases in pore pressure in north central oklahoma usa where widespread injection of produced saltwater has triggered thousands of small to medium sized earthquakes in the past 7 yr the conditional probability incorporates the uncertainty in each mohr coulomb parameter stress tensor pore pressure coefficient of friction and fault orientation through qra the result is a cumulative distribution function of the pore pressure required to cause slip on each fault segment the results can be used to assess the probability of induced slip on a known fault from a given injection related pore pressure increase after dividing north central oklahoma into six study areas we invert earthquake focal plane mechanisms in each area to constrain the orientation and relative magnitude of the principal stresses the qra identifies the potential for slip on the fault that produced the m 5 6 prague earthquake in 2011 and the northeastern extension of a mapped fault associated with the m 5 1 fairview earthquake sequence that occurred in early 2016 and had the 289 striking fault of the september 2016 m 5 8 pawnee event been mapped it would have been identified as potentially active

environmental change across the early middle pleistocene transition small mammalian evidence from the trinchera dolina cave atapuerca spain t he sites of atapuerca are well known for their hominin bearing localities of early to middle pleistocene age trinchera dolina yields western europe s oldest fossil hominin the 850 ka homo antecessor and at sima de los huesos there occurs the best collection of the middle pleistocene hominin homo heidelbergensis however small mammals rodentia insectivora chiroptera and lagomorpha represent the largest number of species and greatest fossil abundance in the deposits of the atapuerca cave complex the small mammals are grouped by habitat catego ries but because the ecology of mammals is complex we base our study on the evolution of these categories throughout the sequence the assemblage distribution at the trinchera dolina site reflects landscape and environmental changes during the past million years shifts between wood land open land and moorland are indicated by the relative abundance of species based on diagnos tic elements such as first lower molars these data are combined with the distribution of large mammals pollen sediments and geological context of the trinchera dolina site from this interdis ciplinary approach we conclude that the first hominins from western europe homo antecessor lived during a warm wet and wooded interval probably corresponding to marine isotope stages 21 to 19 the transition from early to middle pleistocene at atapuerca is characterized by palaeoenvi ronmental changes recorded between levels td5 6 and td8 10 respectively the general opening of the landscape at the beginning of the middle pleistocene could have favoured the dispersal of hominins homo heidelbergensis across western europe

geology of lofn crater callisto lofn crater is a 180 km diameter impact structure in the southern cratered plains of callisto and is among the youngest features seen on the surface the lofn area was imaged by the galileo spacecraft at regional scale resolutions 875 m pixel which enable the general geology to be investigated the morphology of lofn crater suggests that 1 it is a class of impact structure intermediate between complex craters and palimpsests or 2 it formed by the impact of a projectile which fragmented before reaching the surface resulting in a shallow crater even for callisto the asymmetric pattern of the rim and ejecta deposits suggests that the impactor entered at a low angle from the northwest the albedo and other characteristics of the ejecta deposits from lofn also provide insight into the properties of the icy lithosphere and subsurface configuration at the time of impact the target for the lofn impact is inferred to have included layered materials associated with the adlinda multiring structure northwest of lofn and ejecta deposits from the heimdall crater area to the southeast the lofn impact might have penetrated through these materials into a viscous substrate of ductile ice or possibly liquid water this interpretation is consistent with models of the current interior of callisto based on geophysical information obtained from the galileo spacecraft

pedestal craters on ganymede abstract the high resolution voyager images of ganymede show a class of fresh craters 6 89 km in diameter which is distinguished by an ejecta blanket similar to those seen for some types of martian craters one hundred and eighty five were identified and studied for trends with respect to latitude longitude and terrain type no correlation of the ratio of ejecta diameter to crater diameter was found as a function of latitude or longitude and there is only a suggestion of a trend in this ratio with respect to major terrain types central peak frequency is greatest for the smaller crater diameters central pit occurrence dominates central peak occurrence at crater diameters 35 km we conclude that the ejecta morphology probably results from impact into an icy target the question of whether atmospheric ejecta particle drag contributes to ejecta blanket morphologies on planets with an atmospheric cannot be resolved entirely from the voyager images the image resolution is insufficient to show diagnostic flow features on the ejecta if they exist or to detect evidence of any other ejecta deposits which would lie beyond the pedestal predicted by some researchers to exist only on bodies with an atmosphere

dallas fort worth earthquakes coincident with activity associated with natural gas production on 31 october 2008 and the following day numerous dallas fort worth dfw residents called 911 to report experiencing several small earthquakes accompanied by loud booming noises and the shaking of walls and furniture using data recorded by regional seismic stations the usgs national earthquake information center neic located nine earthquakes with magnitudes between 2 5 and 3 0 on 16 may 2009 this scenario repeated itself as local residents felt three earthquakes and the neic located four largest magnitude 3 3 a third sequence of felt events began on 2 june 2009 approximately 65 km southwest near the city of cleburne texas but has not yet been studied in detail figure 1

induced seismicity associated with fluid injection into a deep well in youngstown ohio 1 over 109 small earthquakes mw 0 4 3 9 were detected during january 2011 to february 2012 in the youngstown ohio area where there were no known earthquakes in the past these shocks were close to a deep fluid injection well the 14 month seismicity included six felt earthquakes and culminated with a mw 3 9 shock on 31 december 2011 among the 109 shocks 12 events greater than mw 1 8 were detected by regional network and accurately relocated whereas 97 small earthquakes 0 4 mw 1 8 were detected by the waveform correlation detector accurately located earthquakes were along a subsurface fault trending ene wsw consistent with the focal mechanism of the main shock and occurred at depths 3 5 4 0 km in the precambrian basement we conclude that the recent earthquakes in youngstown ohio were induced by the fluid injection at a deep injection well due to increased pore pressure along the preexisting subsurface faults located close to the wellbore we found that the seismicity initiated at the eastern end of the subsurface fault close to the injection point and migrated toward the west away from the wellbore indicating that the expanding high fluid pressure front increased the pore pressure along its path and progressively triggered the earthquakes we observe that several periods of quiescence of seismicity follow the minima in injection volumes and pressure which may indicate that the earthquakes were directly caused by the pressure buildup and stopped when pressure dropped

the effect of viscosity on impact cratering and possible application to the icy satellites of saturn and jupiter impact experiments in newtonian fluids with a range of viscosities of 10 3 to 60 pa s demonstrate that transient crater volume and shape depth to diameter ratio depend on target viscosity as well as on gravity volume is reduced and depth to diameter ratio is increased for cratering events in which viscosity plays a dominant role in addition to being affected by target kinematic viscosity viscous scaling is most strongly influenced by projectile diameter less strongly by projectile velocity and least strongly by gravity in a planetary context viscous effects can occur for craters formed by small or slow moving impacting bodies low planetary surface densities high surface viscosities and low gravity values conditions all likely for certain impacts into the icy satellites of saturn and jupiter especially if liquid mantles were still present beneath solid crusts age dating based on crater counts and size frequency distributions for these icy bodies may have to be modified to account for the possibility that viscosity dominated craters were initially smaller and deeper than their gravity controlled counterparts

deep injection and closely monitored induced seismicity at paradox valley colorado the u s bureau of reclamation s paradox valley unit pvu extracts aquifer brine from nine shallow wells along the dolores river paradox valley in southwestern colorado and after treating high pressure injects the brine 4 3 4 8 km below the surface pvu injects at rates between 800 and 1300 l min since 1991 pvu has emplaced over 4 106 m3 of fluid and induced more than 4000 surface recorded seismic events the events are recorded on the local 15 station paradox valley seismic network the induced seismicity at paradox separates into two distinct source zones a principle zone 95 of the events asymmetrically surrounding the injection well to a maximum radial distance of 3 km and a secondary ellipsoidal zone 2 5 km long and centered 8 km northwest of the injection well the expansion of these zones has stabilized since mid 1999 about three years after the onset of continuous injection within the principal zone hypocenters align in distinct linear patterns showing at depth stratigraphy and the local wray mesa fracture and fault system the primary faults of the wray mesa system are aseismic striking subparallel to the inferred maximum principal stress direction with one or more faults probably acting as fluid conduits to the secondary seismic zone individual seismic events in both zones do not discernibly correlate with short term injection parameters however a 0 5 km2 region immediately northwest of the injection well responds to long term large scale changes in injection rate and the surpassing of a threshold injection pressure focal mechanisms of the induced events are consistent with simple double couple strike slip moments and subhorizontal extension to the northeast in addition the fault planes are consistent with principal stress directions determined from borehole breakouts more than 99 9 of the pvu seismicity is below human detection m 2 5 however approximately 15 events have been felt locally with the largest being a magnitude m 4 3 because of the m 4 3 and two earlier felt m 3 5 events and injection economics pvu changed injection strategies three times since 1996 these changes reduced seismicity from 1100 events year to as low as 60 events year

experimentation in planetary geology the reasons for conducting experimentation are as varied as the topics that are studied whether a specific parameter must be quantified or an attempt is being made to duplicate a peculiar process all experiments are unified by a common ultimate objective to provide a tangible link between theory and observation although a suitable theory is often nonexistent at the time of the experiment experimentation in planetary geology assumes particular importance because of the factors inherent in the field of study itself often enormous spatial scales timescales rivaled only by those of cosmology and the remoteness of the objects of study in addition any geoscientist who has entertained thoughts of developing a realistic mathematical model of even the simplest of processes rapidly becomes acquainted with the intimidating complexity of geological phenomena experimentation is still in many cases the only effective means of learning more about some natural mechanisms

the gran dolina site lower to middle pleistocene atapuerca burgos spain new palaeoenvironmental data based on the distribution of small mammals new palaeoenvironmental data are reported after analysing the distribution of micromammals orders rodentia insectivora chiroptera and lagomorpha in the 11 stratigraphical levels at the gran dolina site td1 td11 early to middle pleistocene atapuerca spain a continental dry and cold climate is inferred at the beginning of the succession td3 to lower td5 the fauna in the upper td5 and in td6 reflects a complex interglacial period with fluctuations in the degree of relative humidity in the lower part of td8 the presence of microtus aff ratticepoides indicates a relatively cold period finally data from upper levels td8b td10 td11 reflect another interglacial period with slight oscillations in relative moisture the different levels at gran dolina are also correlated with oxygen isotope stages ois td3 td4 and td5 may be correlated with ois 22 td6 is correlated with ois 21 lower td8 td8a is correlated with ois 18 upper td8 td8b is correlated with ois 13 or 15 td10 and td11 are correlated with ois 9 or 11

a schematic model of crater modification by gravity models are proposed to account for the formation of slump terraces central peaks peak rings and concentric rings in large impact structures crater slumping and central peak formation is attributed to the process of acoustic fluidization which endows a volume of the target surrounding the crater with a bingham plastic rheology for a short time after the impact the parameters of this bingham plastic model are remarkably constant throughout the solar system the bingham yield stress ranges from a maximum of 80 bars on mercury to a minimum of 7 bars on callisto the bingham viscosity is between 109 and 1010 p at the onset of central peak formation for all bodies studied although it appears to rise to 1011 p as crater diameter grows to a few hundred kilometers asymmetric or scarp bounded concentric rings are due to a fundamentally different process they form when the target planet s lithosphere fractures under stresses imposed by the flow of the asthenosphere toward the transient crater cavity lithosphere yield strengths of less than a few hundred bars are implied by observed ring development on the moon and callisto

morphology and origin of palimpsests on ganymede based on galileo observations palimpsests are large circular low relief impact scars on ganymede and callisto these structures were poorly understood based on voyager era analysis but high resolution galileo images allow more detailed inspection we analyze images of four ganymedean palimpsests targeted by galileo memphis and buto faculae epigeus and zakar ganymedean craters and europan ring structures are used as tools to help better understand palimpsests based on morphologic similarities from analysis of galileo images palimpsests consist of four surface units central plains an unoriented massif facies a concentric massif facies and outer deposits using as a tie point the location in these structures where secondary craters begin to appear outer deposits of palimpsests are analogous to the outer ejecta facies of craters the concentric massif facies of palimpsests are analogous to the pedestal facies of craters and the unoriented massif facies and central plains are analogous to crater interiors these analogies are supported by the presence of buried preexisting structure beneath the outer two and absence of buried structure beneath the inner two units our observations indicate that palimpsest deposits represent fluidized impact ejecta rather than cryovolcanic deposits or ancient crater interiors

analysis of the cleburne texas earthquake sequence from june 2009 to june 2010 on 9 june 2009 an graphic 1 2 8 earthquake shook cleburne texas a community not known to have previously experienced earthquakes over 50 small earthquakes followed by the end of december 2009 a temporary network of four and then five iris passcal broadband systems was deployed from june 2009 to june 2010 recording data that were used to locate 38 events with the most confident p and s arrival picks event locations were distributed along a 2 km long north northeast trend the location centroid was at 32 298 n 97 372 w and at 3 6 km depth this location is approximately 1 3 km from a saltwater disposal well that began injection in october 2007 and 3 2 km away from a second injection well that was active from september 2005 to late july 2009 focal mechanisms estimated for the best recorded events suggest a north northeast south southwest trending normal fault with a dip of 50 and a component of oblique motion rake of 80 this average solution is generally consistent with the north northeast trending extensional faults that are prevalent across parts of texas oklahoma louisiana and arkansas stress drops calculated from p and s spectra for seven different events ranged from 3 9 to 90 bars with most estimates between 40 and 50 bars typical values for intraplate earthquakes because there were no known previous earthquakes and the located events were close to the two injection wells and near the injection depth the possibility exists that earthquakes may be related to fluid injection online material tables of absolute and relative earthquake locations and a figure summarizing focal mechanism solutions 1 embed inline graphic 1 gif

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

in situ stress and active faulting in oklahoma abstract appreciable injection induced seismicity has been occurring in north central oklahoma since 2009 to better understand these earthquakes we have compiled new information on the state of stress in the state to compare it with both mapped faults and faults inferred from earthquake epicenters and focal plane mechanisms seventy five new in situ stress orientations are available from wellbores throughout the state in the north central part of the state where the induced seismicity is occurring stress orientation and relative magnitude from focal mechanism inversions show excellent agreement with the wellbore stress orientations all of the data show remarkably uniform stress directions the azimuth of s hmax the maximum horizontal stress is about n85 5 e strike slip faulting is occurring in central oklahoma with strike slip normal and normal faulting observed in northern oklahoma and southern kansas as very few of the thousands of m 2 5 earthquakes that have recently occurred are located on or near already mapped faults we utilize the stress information to interpret the likely fault planes associated with over 300 well constrained focal plane mechanisms in the vicinity of the january 2016 sequence of magnitude 4 and 5 earthquakes in the fairview oklahoma region we illustrate how knowledge of the stress field can be used to identify the faults responsible for the seismicity and better evaluate the potential hazard associated with possible future earthquakes in the area the september 2016 m w 5 8 pawnee event occurred on an unmapped n70 w trending strike slip fault expected to be active in the local stress field

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

iberian plio pleistocene biochronology micromammalian evidence for mns and elmas calibration in southwestern europe a multivariate biochronological analysis of the plio pleistocene iberian rodent fossil record is presented among more than 300 fossil sites 49 sites have been selected the ordination of the fossil sites selected from the iberian peninsula has been achieved by the appearance event ordination method after calibration of this ordination with geochronological dates at some of the localities numerical dates are proposed for all the localities studied hence mammal fossil sites non datable by other means palaeomagnetism radiometric dating etc have been dated with a relatively high degree of confidence final results allow dating of boundaries between the plio pleistocene european land mammal ages elmas or the mammal neogene mn units these boundaries agree with previous studies using magnetostratigraphical calibration of these scales copyright 2004 john wiley sons ltd

evolution of early middle miocene rodent faunas in relation to long term palaeoenvironmental changes abstract cluster and principal components analyses have been applied to the composite sequence of 59 rodent assemblages from ramblian to lower vallesian deposits in the daroca calamocha area in the calatayud teruel basin north central spain the studied record is thought to represent the interval from the late aquitanian to the end of the serravallian i e early to middle miocene from ca 22 10 5 ma ago the quantitative results are interpreted by using individual rodent taxa as environmental indicators and by extrapolating the predominant adaptive strategies of recent taxonomic groups which also seem to form natural groups on a demographic scheme french et al 1975 a general warming trend starts in the rambian early miocene and continues into the middle aragonisn early middle miocene the cooling in the middle to late aragonian boundary interval is correlated to the middle miocene cooling phase another cooling occurred around the aragonian vallesian boundary late middle miocene we relate a major increase of aridity in the beginning of the middle aragonian ca 16 5 ma to the spread of low biomass vegetation due to intensification of the subtropical belt wolfe 1985 a notable feature around the early middle aragonian boundary indicating a major shift of climatic belts is the reversal of the relationship between our relative temperature and humidity curves before the reversal we find a positive correlation after it a negative correlation around the middle to late aragonian boundary humidity increased again and a further increase of humidity is indicated by the earliest vallesian faunas our data suggest that the nature of favoured adaptive strategy amongst rodents is related in the end to the degree of climatic humidity

calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor

small mammal taphonomy of gran dolina atapuerca burgos spain abstract the middle pleistocene sequence at the atapuerca burgos complex of caves is most completely represented at gran dolina eleven stratigraphic units are distinguished seven of which contain abundant small mammal fossils these seven units are analysed in order to determine the taphonomic processes present during the accumulation of their faunal remains the fossil bones are extensively broken both before and after burial fossils from six of the units show evidence of localized pre depositional acid corrosion which occurred both before and after breakage in the upper levels there is also evidence of post depositional corrosion both from alkaline and from acid environments of deposition and in the top level some fossil bones also show evidence of weathering and root marks images of these modifications by means of the scanning electron microscope and their comparison with a large comparative data base of recent modifications from known causal agents permits the identification of the agents responsible for many of the modifications and consequently the reconstruction of the sequence of events leading to the accumulation and preservation of the fossil assemblages predators are implicated for some of the breakage and all of the pre depositional corrosion which is the result of digestion in the predators stomachs in all cases the category of predator can be identified and at three stratigraphic levels the actual species can be identified with moderate degrees of reliability post depositional corrosion is linked with observations on local acidity alkalinity of different levels and the incidence of weathering is linked with evidence for roof collapse over parts of the cave taking account of the effects of these processes particularly the selectivity resulting from predator hunting methods allows estimates to be made of the degree of bias in the faunal composition and the palaeoecology thereby indicated

a decade of induced slip on the causative fault of the 2015 mw 4 0 venus earthquake northeast johnson county texas on 7 may 2015 a mw 4 0 earthquake occurred near venus northeast johnson county texas in an area of the bend arch fort worth basin that reports long term high volume wastewater disposal and that has hosted felt earthquakes since 2009 in the weeks following the mw 4 0 earthquake we deployed a local seismic network and purchased nearby active source seismic reflection data to capture additional events characterize the causative fault and explore potential links between ongoing industry activity and seismicity hypocenter relocations of the resulting local earthquake catalog span 4 6 km depth and indicate a fault striking 230 dipping to the west consistent with a nodal plane of the mw 4 0 regional moment tensor fault plane solutions indicate normal faulting with b axes striking parallel to maximum horizontal compressive stress seismic reflection data image the reactivated basement fault penetrating the ordovician disposal layer and mississippian production layer but not displacing post lower pennsylvanian units template matching at regional seismic stations indicates that low magnitude earthquakes with similar waveforms began in april 2008 with increasing magnitude over time pressure data from five saltwater disposal wells within 5 km of the active fault indicate a disposal formation that is 0 9 4 8 mpa above hydrostatic we suggest that the injection of 28 000 000 m3 of wastewater between 2006 and 2015 at these wells led to an increase in subsurface pore fluid pressure that contributed to inducing this long lived earthquake sequence the 2015 mw 4 0 event represents the largest event in the continuing evolution of slip on the causative fault

comment iberian plio pleistocene biochronology micromammalian evidence for mns and elmas calibration in southwestern europe m hernandez fernandez b azanza and m a alvarez sierra 2004 journal of quaternary science19 605 616

earthquake hypocenters and focal mechanisms in central oklahoma reveal a complex system of reactivated subsurface strike slip faulting the sharp increase in seismicity over a broad region of central oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma in order to record the evolving seismicity in this study we apply a multiple event relocation method to produce a catalog of 3639 central oklahoma earthquakes from late 2009 through 2014 regional moment tensor rmt source parameters were determined for 195 of the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled us to determine the length depth and style of faulting occurring on reactivated subsurface fault systems results show that the majority of earthquakes occur on near vertical optimally oriented ne sw and nw se strike slip faults in the shallow crystalline basement these are necessary first order observations required to assess the potential hazards of individual faults in oklahoma

rodents and climate 1 a model for estimating past temperatures using arvicolids mammalia rodentia abstract analysis of 253 extant mammalian local faunas shows that the number of arvicoline species in each fauna is related to temperature parameters the very high correlation allows us to propose a method to estimate the temperature for fossil faunas bearing arvicoline species from temperate areas to illustrate this method mean annual temperatures were estimated for late pleistocene hungarian localities and for a sequence from the baume de gigny jura france these were compared with results obtained by other techniques multivariate analysis of rodent associations and synthetic analysis of pollen faunal and sedimentological data