constraints on mantle viscosity and laurentide ice sheet evolution from pluvial paleolake shorelines in the western united states abstract the deformation pattern of the paleoshorelines of extinct lake bonneville were among the first features to indicate that earth s interior responds viscoelastically to changes in surface loads gilbert 1885 here we revisit and extend this classic study of isostatic rebound with updated lake chronologies for lake bonneville and lake lahontan as well as revised elevation datasets of shoreline features the first order domal pattern in the shoreline elevations can be explained by rebound associated with the removal of the lake load we employ an iterative scheme to calculate the viscoelastic lake rebound which accounts for the deformation of the solid earth and gravity field to calculate a lake load that is consistent with the load deformed paleotopography we find that the domal deformation requires a regional earth structure that exhibits a thin elastic thickness of the lithosphere 15 25 km and low sublithospheric maxwell viscosity 10 19 pa s after correcting for rebound due to the lake load shoreline feature elevations reveal a statistically significant northward dipping trend we attribute this trend to continent scale deformation caused by the ice peripheral bulge of the laurentide ice sheet and take advantage of the position of these lakes on the distal flank of the peripheral bulge to provide new insights on mantle viscosity and laurentide ice sheet reconstructions we perform ice loading calculations to quantify the deformation of the solid earth gravity field and rotation axis that is caused by the growth and demise of the laurentide ice sheet we test three different ice reconstructions paired with a suite of viscosity profiles and confirm that the revealed trend can be explained by deformation associated with the laurentide ice sheet when low viscosities below the asthenosphere are adopted we obtain best fits to shoreline data using ice models that do not have the majority of ice in the eastern sectors of the laurentide ice sheet with the caveat that this result can be affected by lateral variations in viscosity we show that pluvial lakes in the western united states can place valuable constraints on the laurentide ice sheet the shape of its peripheral bulge and the underlying mantle viscosity

environmental perturbations caused by the impacts of asteroids and comets we review the major impact associated mechanisms proposed to cause extinctions at the cretaceous tertiary geological boundary we then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions but we also stress that there are many uncertainties we conclude that impacts with energies less than about 10 mt are a negligible hazard for impacts with energies above 10 mt and below about 104 mt i e impact frequencies less than one in 6 104 years corresponding to comets and asteroids with diameters smaller than about 400 m and 650 m respectively blast damage earthquakes and fires should be important on a scale of 104 or 105 km which corresponds to the area damaged in many natural disasters of recent history however tsunami excited by marine impacts could be more damaging flooding a kilometer of coastal plain over entire ocean basins in the energy range of 104 105 mt intervals up to 3 105 years corresponding to comets and asteroids with diameters up to 850 m and 1 4 km respectively water vapor injections and ozone loss become significant on the global scale in our nominal model such an impact does not inject enough submicrometer dust into the stratosphere to produce major adverse effects but if a higher fraction of pulverized rock than we think likely reaches the stratosphere stratospheric dust causing global cooling would also be important in this energy range thus 105 mt is a lower limit where damage might occur beyond the experience of human history the energy range from 105 to 106 mt intervals up to 2 106 years corresponding to comets and asteroids up to 1 8 and 3 km diameter is transitional between regional and global effects stratospheric dust sulfates released from within impacting asteroids and soot from extensive wild fires sparked by thermal radiation from the impact can produce climatologically significant global optical depths of the order of 10 moreover the ejecta plumes of these impacts may produce enough no from shock heated air to destroy the ozone shield between 106 and 107 mt intervals up to 1 5 107 years corresponding to comets and asteroids up to 4 and 6 5 km diameter dust and sulfate levels would be high enough to reduce light levels below those necessary for photosynthesis ballistic ejecta reentering the atmosphere as shooting stars would set fires over regions exceeding 107 km and the resulting smoke would reduce light levels even further at energies above 107 mt blast and earthquake damage reach the regional scale 106 km tsunami cresting to 100 m and flooding 20 km inland could sweep the coastal zones of one of the world s ocean basins fires would be set globally light levels may drop so low from the smoke dust and sulfate as to make vision impossible at energies approaching 109 mt 108 years the ocean surface waters may be acidified globally by sulfur from the interiors of comets and asteroids the cretaceous tertiary impact in particular struck evaporate substrates that very likely generated a dense widespread sulfate aerosol layer with consequent climatic effects the combination of all of these physical effects would surely represent a devastating stress on the global biosphere

integrated seismic hazard analysis of the wasatch front utah we examined the combined effects of different sources that influence earthquake hazard of the populated wasatch front utah we first evaluated the fault stress interaction of the two largest historic earthquakes of the intermountain seismic belt isb the 1959 hebgen lake montana m s 7 5 and the 1983 borah peak idaho m s 7 3 earthquakes which experienced multisegment normal faulting ruptures estimates of the static stress change for these events revealed an increase in coulomb failure stress in areas of extended aftershocks these observations suggested that fault stress analysis is applicable in evaluating the spatial distribution of aftershocks after large normal faulting earthquakes in the same extensional stress regime of the eastern basin range including the wasatch front utah which encompasses the 370 km long wasatch fault and surrounding faults on the basis of this result we applied the modeling technique to the historically seismically quiescent wasatch fault and examined the relation between the pattern of stress change and the space time distribution of paleoearthquakes ages and locations of the wasatch fault paleoseismic data imply 17 single segment or 11 multisegment ruptures in the past 5 6 kyr we prefer the multisegment model because almost all of the large historical normal faulting earthquakes in the isb were multisegment fitting the along fault displacements by an analytic half ellipse function provides a first order distribution of the displacement over an entire rupture length and allows new estimates of fault slip rates and seismic moment with these data we also estimated the occurrence rate of m w 6 6 wasatch paleoearthquakes and showed that the rate was about three times higher than that inferred by the historical seismicity this result along with new information from a megatrench on the wasatch fault near salt lake city that revealed no scarp forming earthquakes between ca 9 0 and 15 5 ka suggests that large wasatch fault events in the past 5 6 kyr may be clustered the recurrence rate of large earthquakes estimated by the geodetic measured strain on the other hand is three to four times higher than that estimated by the long term fault slip rate this difference together with the observation of a low regional strain rate from historical seismicity suggests that cumulative aseismic deformation may be significant on the wasatch fault we also examined a major consideration for along strike segmentation namely how stress contagion could affect the probability of failure of adjacent faults including paleoearthquake derived fault slip rates global positioning system derived geodetic moment rates and the effect of stress contagion in the earthquake hazard estimation for a specific location in the salt lake valley revealed an increase in the annual frequency of peak ground acceleration 0 25 g by a factor of 1 4 4 0 and 5 4 respectively compared with that derived from historical seismicity only manuscript received 31 may 2001

fireball passes and nothing burns the role of thermal radiation in the cretaceous tertiary event evidence from the charcoal record of north america high soot contents have been reported in cretaceous tertiary k t sedimentary rocks leading to the suggestion that the amount of thermal power delivered from the chicxulub impact was sufficient to have ignited wildfires soot cannot be used to indicate fire location however as soot from one large fire could spread globally sources other than biomass burning could also yield soot charcoal in nonmarine sedimentary rocks here quantified in situ in polished blocks provides a unique tool to record the distribution of wildfires and therefore assess the extent of any thermal radiation associated with the impact at chicxulub the k t and lowermost tertiary sedimentary rocks of six nonmarine sequences colorado to saskatchewan contain no charcoal or below background levels of charcoal and a significant quantity of noncharred organic materials revealing that there was no distinctive wildfire across the north american continent related to the k t event this finding indicates that the k t impact cannot have delivered a peak irradiance of 95 kw m 2 of thermal power to the atmosphere and 19 kw m 2 to the ground therefore the thermal power delivered from the impact to north america did not have the destructive potential previously predicted high amounts of thermal radiation were not responsible for the environmental perturbations or extinctions associated with the k t event

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

holocene vertical displacement on the central segments of the wasatch fault zone utah compiled per event vertical displacement observations from 17 paleoseismic sites along the six central segments of the wasatch fault zone wfz highlight possible biases and trends in displacement along the fault the displacement data are consistent with a model of characteristic type slip but anomalous and variable displacements indicate that significant natural variability in displacement occurs when combined into a composite distribution of displacement 79 of the data fit within a displacement envelope that shows displacement decreasing in a half ellipse shape from 1 4 3 5 m near the segment centers to 0 6 2 5 m near the ends additionally displacements normalized by the distance from the segment centers to ends decrease from means of 2 0 3 0 m near the segment centers to 1 3 1 9 m near the ends consistent with characteristic type slip termination although several paleoseismic sites exhibit repeated similar displacements the data are sparse and both low valued 0 5 0 8 m and high valued 4 2 4 7 m outliers suggest complex strain release possibly resulting from segment interaction and or noncharacteristic events although a global normal fault type surface rupture length srl average displacement regression underpredicts observed wfz displacements the largest displacements per segment correspond well with a srl maximum displacement regression this correlation as well as moderate variability in srl and displacement based moment magnitude suggests that the anomalous displacements represent the intrinsic variability in characteristic displacement per segment thus minor variations to the characteristic slip model to account for exceptional upper and lower bound displacements e g a hybrid characteristic variable slip model may be appropriate for the wfz additional paleoseismic data are necessary to address data gaps and biases to facilitate more robust tests of earthquake slip models and to reduce uncertainty in srl displacement and magnitude

constraints on the thermal energy released from the chicxulub impactor new evidence from multi method charcoal analysis it has been suggested by various workers that an extraterrestrial impact at the k t boundary delivered sufficient thermal power to ignite globally extensive wildfires numerous models have sought to predict the amount of thermal power released by the impact but none have considered the distribution of wildfire indicators in k t rocks probably the most distinctive product from combustion of biomass is charcoal the abundance of charcoal across the k t boundary at eight non marine sites in north america stretching from colorado in the south to saskatchewan in the north is recorded using three separate methods that allow quantitative analyses of microscopic to macroscopic charcoal particles this study not only provides the first extensive study of charcoals across the k t boundary but also uses the presence or absence of charred material to predict the extent and severity of the thermal pulse released by the k t impact across the area predicted to have suffered the most extreme environmental effects the k t rocks contain on average between four and eight times according to the method used less charcoal than the cretaceous rock record and non charred plant remains are abundant in the k t rocks the below background charcoal abundance and the high proportion of noncharred material in the k t and lowermost tertiary rocks across the western interior of north america suggest that there were no significant wildfires in this area associated with the k t event although soot and polyaromatic hydrocarbons pahs have been reported in the k t rocks we suggest that the soot morphology and pah types are more consistent with a source from the vaporization of hydrocarbons rather than biomass for spontaneous ignition of vegetation temperatures 545 c are necessary whereas smouldering will begin at 325 c the below background levels of charcoal in the k t rocks allow the ground temperatures following the k t impact to be constrained to between no more than 545 c at any point and not above 325 c for any significant period this implies a maximum irradiance of 2 at the ground surface and that no more than 6 kw m 2 of thermal power was delivered to the ground for more than a few hours therefore our results show that the fossil record indicates that the impact at chixculub did not generate sufficient thermal power to ignite extensive wildfires

holocene paleoseismicity temporal clustering and probabilities of future large m 7 earthquakes on the wasatch fault zone utah the chronology of m 7 paleoearthquakes on the central five segments of the wasatch fault zone wfz is one of the best dated in the world and contains 16 earthquakes in the past 5600 years with an average repeat time of 350 years repeat times for individual segments vary by a factor of 2 and range from about 1200 to 2600 years four of the central five segments ruptured between 620 30 and 1230 60 calendar years b p the remaining segment brigham city segment has not ruptured in the past 2120 100 years comparison of the wfz space time diagram of paleoearthquakes with synthetic paleoseismic histories indicates that the observed temporal clusters and gaps have about an equal probability depending on model assumptions of reflecting random coincidence as opposed to intersegment contagion regional seismicity suggests that for exposure times of 50 and 100 years the probability for an earthquake of m 7 anywhere within the wasatch front region based on a poisson model is 0 16 and 0 30 respectively a fault specific wfz model predicts 50 and 100 year probabilities for an m 7 earthquake on the wfz itself based on a poisson model as 0 13 and 0 25 respectively in contrast segment specific earthquake probabilities that assume quasi periodic recurrence behavior on the weber provo and nephi segments are less 0 01 0 07 in 100 years than the regional or fault specific estimates 0 25 0 30 in 100 years due to the short elapsed times compared to average recurrence intervals on those segments the brigham city and salt lake city segments however have time dependent probabilities that approach or exceed the regional and fault specific probabilities for the salt lake city segment these elevated probabilities are due to the elapsed time being approximately equal to the average late holocene recurrence time for the brigham city segment the elapsed time is significantly longer than the segment specific late holocene recurrence time

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

n2o record spanning the penultimate deglaciation from the vostok ice core nitrous oxide n2o is an important atmospheric trace gas whose concentration is determined by numerous sources and sinks over the past 200 years n2o has increased by 17 3 due primarily to increased anthropogenic emissions over the last glacial interglacial transition data from ice cores show that n2o increased by 35 this increase may be related to increased terrestrial n2o emissions resulting from a global climate amelioration here i describe a new dry extraction technique for measuring the elemental and isotopic composition of n2o in ice core samples results from a shallow gisp ii ice core spanning the last 200 years provide an estimate for the preanthropogenic n2o concentration of 266 4 ppb in addition 11 ice samples from the last interglacial period show fairly uniform n2o values 269 9 ppb during the penultimate glacial period 131 160 ka n2o concentrations of air trapped in the glacier fluctuated between 190 ppb and 320 ppb while co2 and ch4 concentrations were relatively low and stable two local n2o maxima were observed during the penultimate glacial period that actually exceeded normal interglacial n2o values 265 ppb the maxima were located in portions of the core which exhibit both elevated dust concentrations and elevated bacterial counts the 15n and 18o of n2o in this portion of the vostok core were 15 higher and 12 lower than during the warm eemian period respectively the isotopic data and coincidence between the elevated n2o concentrations and the high bacterial counts may be related to in situ n2o production by bacteria the lower 18o values are consistent with the isotopic composition of n2o produced by in situ nitrification

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

raman spectroscopy of gaseous inclusions in edml ice core first results microbubbles measurements of n2 o2 ratios inside individual air bubbles in various depths of the edml ice core are presented here the small bubbles diameter below 200 m in deeper ice are signi cantly enriched in o2 compared to the larger bubbles the n2 o2 ratios show a systematic dependence on bubble size which is not the case for bubbles in shallower ice this is interpreted as an e ect of pressure relaxation during storage of the cores

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

integration of paleoseismic data from multiple sites to develop an objective earthquake chronology application to the weber segment of the wasatch fault zone utah we present a method to evaluate and integrate paleoseismic data from multiple sites into a single objective measure of earthquake timing and recurrence on discrete segments of active faults we apply this method to the weber segment ws of the wasatch fault zone using data from four fault trench studies completed between 1981 and 2009 after systematically reevaluating the stratigraphic and chro nologic data from each trench site we constructed time stratigraphic oxcal models that yield site probability density functions pdfs of the times of individual earth quakes we next qualitatively correlated the site pdfs into a segment wide earthquake chronology which is supported by overlapping site pdfs large per event displace ments and prominent segment boundaries for each segment wide earthquake we computed the product of the site pdf probabilities in common time bins which emphasizes the overlap in the site earthquake times and gives more weight to the narrowest best defined pdfs the product method yields smaller earthquake timing uncertainties compared to taking the mean of the site pdfs but is best suited to earth quakes constrained by broad overlapping site pdfs we calculated segment wide earthquake recurrence intervals and uncertainties using a monte carlo model five surface faulting earthquakes occurred on the ws at about 5 9 4 5 3 1 1 1 and 0 6 ka with the exception of the 1 1 ka event we used the product method to define the earthquake times the revised ws chronology yields a mean recurrence interval of 1 3 kyr 0 7 1 9 kyr estimated two sigma 2 range based on interevent recurrence these data help clarify the paleoearthquake history of the ws including the important question of the timing and rupture extent of the most recent earthquake and are essential to the improvement of earthquake probability assessments for the wasatch front region

using noble gas ratios to determine the origin of ground ice abstract argon krypton and xenon have different solubilities in water meaning their ratios in water are different from those in atmospheric air this characteristic is used in a novel method to distinguish between ice bodies which originate from the compaction of snow i e buried snow banks glacial ice vs ice which forms from the freezing of groundwater i e pingo ice ice which forms from the compaction of snow has gas ratios similar to atmospheric air while ice which forms from the freezing of liquid water is expected to have gas ratios similar to air equilibrated water this analysis has been conducted using a spike dilution noble gas line with gas extraction conducted on line samples were mixed with an aliquot of rare noble gases while being melted then extracted gases are purified and cryogenically separated samples have been analysed from glacial ice buried snow bank ice intrusive ice wedge ice cave ice and two unknown ice bodies ice bodies which have formed from different processes have different gas ratios relative to their formation processes

reevaluation of holocene faulting at the kaysville site weber segment of the wasatch fault zone utah the 1978 kaysville utah trench excavated by swan and others 1980 across a large graben of the weber segment of the wasatch fault zone was reexcavated in 1988 to reevaluate the timing and nature of holocene faulting relogging of the trench reveals evidence for five or six faulting events younger than the provo phase of lake bonneville circa 13 000 14c years b p geometric reconstruction of net vertical offset in the last three events suggests a variation in coseismic vertical displacement at this site ranging from a net of 1 4 3 4 m per event the three latest faulting events occurred at shortly before 0 6 0 8 ka 2 8 0 7 ka and circa 3 8 7 9 ka earlier events cannot be directly dated because older graben fill sediments yielded thermoluminescence ages older than the time of deposition and some scarp derived colluvial wedges beneath the trench floor were not exposed the two younger faulting events we recognize at kaysville correlate reasonably well with faulting events on the same segment 25 km north near east ogden utah at circa 0 8 1 2 ka and 2 5 3 0 ka forman and others 1991 whereas the earlier kaysville event is significantly older than the earliest 3 5 4 0 ka event dated at east ogden the 3 5 4 0 ka ground rupture recognized at east ogden may have died out at a subsegment boundary between the two trench sites within the 61 km long weber segment

global fire at the cretaceous tertiary boundary cretaceous tertiary k t boundary clays from five sites in europe and new zealand are 102 104 fold enriched in elemental c mainly soot which is isotopically uniform and apparently comes from a single global fire the soot layer coincides with the ir layer suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled

metamorphism of stratified firn at dome fuji antarctica a mechanism for local insolation modulation of gas transport conditions during bubble close off 1 the evolution of the structure of a 112 59 m long firn core recovered at dome fuji east antarctica was investigated in order to improve understanding of firn densification and bubble formation processes which are important for interpreting local insolation proxies used for astronomical dating of deep ice cores using selected samples we measured physical properties including 1 the relative dielectric permittivities in both the vertical and horizontal planes 2 the bulk density at a resolution of millimeters 3 the three dimensional geometric structure of pore space and 4 crystal orientation fabrics we found that the firn at dome fuji contains horizontal strata with thicknesses of several centimeters near the surface of the ice sheet these strata are characterized by contrasting bulk density earlier field studies suggest that summer insolation causes densification of surface firn down to 30 m density maxima exhibited a clear positive correlation with the strength of structural anisotropy and c axis clustering around the vertical in contrast the correlation is negative in deeper firn confirming previous findings that initially less dense firn became denser than initially dense firn in addition numerous examples of textures indicating that deformation preferentially occurred in weaker layers were found moreover the initially dense firn layers were more permeable for air near the bottom of firn we propose a model linking firn properties with conditions for the gas transport processes near the bottom of firn the model explains how stronger insolation can lead to bulk ice with a lower o2 n2 ratio and smaller total gas content

evidence from high resolution topography for multiple earthquakes on high slip to length fault scarps the bilila mtakataka fault malawi geomorphological features such as fault scarps and stream knickpoints are indicators of recent fault activity determining whether these features formed during a single earthquake or over multiple earthquakes cycles has important implications for the interpretation of the size and frequency of past events here we focus on the bilila mtakataka fault malawi where the 20 m high fault scarps exceed the height expected from a single earthquake rupture we use a high resolution digital elevation model 1 m to identify complexity in the fault scarp and knickpoints in river profiles of 39 selected scarp profiles 20 showed evidence of either multi scarps or composite scarps and of the seven selected river and stream profiles five showed evidence for multiple knickpoints a near uniform distribution of vertical offsets on the sub scarps suggests they were formed by separate earthquakes these independent methods agree that at least two earthquakes have occurred with an average vertical offset per event of 10 and 12 m this contrasts earlier studies which proposed that this scarp formed during a single event and demonstrates the importance of high resolution topographic data for understanding tectonic geomorphology we use a one dimensional diffusion model of scarp degradation to demonstrate how fault splays form multi scarps and estimate the diffusion age t of the bilila mtakataka fault scarp to be 48 m25 m2 corresponding to 6400 4000 years since formation we calculate that a continuous rupture would equate to a mw 7 8 0 3 earthquake greater than the largest seismic event previously recorded in east africa

orbital tuning chronology for the vostok climate record supported by trapped gas composition abstract we present data on the o2 n2 ratios of trapped gas samples for the entire length of the vostok climate record as in other cores o2 n2 ratios in these samples are less than the atmospheric ratio by a small and variable amount because o2 is selectively excluded during the gas trapping process and because o2 is also preferentially lost in poorly preserved core samples samples younger than 150 ka have large and variable o2 depletions samples older than 200 ka have o2 n2 ratios that replicate well and vary smoothly with depth we plot o2 n2 ratios of well replicated samples older than 160 ka using a chronology derived by matching the 18o of paleoatmospheric o2 18oatm to northern hemisphere june insolation on this timescale o2 n2 varies coherently with local 78 s summertime insolation based on time series analysis of the o2 n2 record and the dynamics of snow metamorphism at the surface we conclude that summertime insolation influences physical properties of ice grains that control the degree of o2 exclusion during bubble closeoff o2 n2 in vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core we show that the 18oatm chronology supported by the coincidence of o2 n2 ratios with insolation is also compatible with recent radiometric dating of corals from high sea stands we further successfully test the 18oatm tuning chronology by showing that it predicts a chronology for the gisp2 core which is essentially indistinguishable from the standard gisp2 chronology and therefore in excellent agreement with the radiometric chronology of hulu cave china an accurate chronology for the vostok ice core is now in place

k pg extinction reevaluation of the heat fire hypothesis 1 the global debris layer created by the end cretaceous impact at chicxulub contained enough soot to indicate that the entire terrestrial biosphere had burned preliminary modeling showed that the reentry of ejecta would have caused a global infrared ir pulse sufficient to ignite global fires within a few hours of the chicxulub impact this heat pulse and subsequent fires explain the terrestrial survival patterns in the earliest paleocene because all the surviving species were plausibly able to take shelter from heat and fire underground or in water however new models of the global ir heat pulse as well as the absence of charcoal and the presence of noncharred organic matter have been said to be inconsistent with the idea of global fires that could have caused the extinctions it was suggested that the soot in the debris layer originated from the impact site itself because the morphology of the soot the chain length of polycyclic aromatic hydrocarbons and the presence of carbon cenospheres were said to be inconsistent with burning the terrestrial biosphere these assertions either are incorrect or have alternate explanations that are consistent with global firestorms we show that the apparent charcoal depletion in the cretaceous paleogene layer has been misinterpreted due to the failure to correct properly for sediment deposition rates we also show that the mass of soot potentially released from the impact site is far too low to supply the observed soot however global firestorms are consistent with both data and physical modeling

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

the attenuation of fast atmospheric ch4 variations recorded in polar ice cores 1 to reconstruct fast atmospheric trace gas variations from polar ice cores it has to be considered that their amplitudes are attenuated during the enclosure process in the ice relevant processes for the attenuation are the molecular diffusion in the open pores of the firn column and the gradual bubble close off in the depth of the transition from firn to ice these processes depend mainly on temperature and accumulation rate and lead e g to a strong attenuation for cold sites with low accumulation rates with a diffusion and enclosure model it is possible to calculate the attenuation for a single event and to compare ice core records from different sites we investigate the atmospheric methane ch4 variation during the cold event 8200 years ago and calculate that its amplitude as recorded in the epica dome c ice core is attenuated to a magnitude between 34 and 59

holocene behavior of the brigham city segment implications for forecasting the next large magnitude earthquake on the wasatch fault zone utah the brigham city segment bcs the northernmost holocene active segment of the wasatch fault zone wfz is considered a likely location for the next big earthquake in northern utah we refine the timing of the last four surface rupturing m w 7 earthquakes at several sites near brigham city be1 2430 250 be2 3490 180 be3 4510 530 and be4 graphic 1 b p and calculate mean recurrence intervals 1060 1500 yr that are greatly exceeded by the elapsed time 2500 yr since the most recent surface rupturing earthquake mre an additional rupture observed at the pearsons canyon site pc1 graphic 2 b p near the southern segment boundary is probably spillover rupture from a large earthquake on the adjacent weber segment our seismic moment calculations show that the pc1 rupture reduced accumulated moment on the bcs about 22 a value that may have been enough to postpone the next large earthquake however our calculations suggest that the segment currently has accumulated more than twice the moment accumulated in the three previous earthquake cycles so we suspect that additional interactions with the adjacent weber segment contributed to the long elapse time since the mre on the bcs our moment calculations indicate that the next earthquake is not only overdue but could be larger than the previous four earthquakes displacement data show higher rates of latest quaternary slip 1 3 mm yr along the southern two thirds of the segment the northern third likely has experienced fewer or smaller ruptures which suggests to us that most earthquakes initiate at the southern segment boundary online material cross sections age estimates evaluation of box elder delta earthquake chronology code for oxcal models trench logs sources of surface offset data and description of call fort gravel pit fault exposures 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

the age of the air in the firn and the ice at summit greenland in the framework of the eurocore drilling project 1989 at summit central greenland air samples were collected from a drill hole in the firn at several depth levels the samples have been analyzed for 85kr co2 ch4 cfc s f 11 and f 12 contents and for the isotopic composition of nitrogen and oxygen the measured data are compared with the results of a diffusion model co2 for example takes 12 years with a standard deviation of 7 5 years to diffuse from the surface to the firn ice transition under the present climatic conditions at summit the difference between the age of the ice and the mean age of the occluded air is approximately 210 years an enrichment of the heavier isotopes due to separation by gravity has been observed molecular diffusion alone suffices to explain the observed concentration trends in the firn column we can however not exclude the existence of a convective zone below the surface we have also measured the density and closed porosity along the firn core that has been retrieved when drilling the hole the porosity data reveal that the air is occluded into bubbles mainly between 65 and 80 m corresponding to densities of 790 and 830 kg m3 respectively

evaluation of wasatch fault segmentation and slip rates using lake bonneville shorelines 1 analysis of lake bonneville shorelines using lidar digital elevation data challenges accepted models of wasatch fault deformation since the late pleistocene while footwall deformation of the weber segment of the wasatch fault is consistent with back rotation of the footwall block and greatest displacement rate toward the center of the segment shorelines along the footwall of the salt lake city segment decrease in elevation toward the interior and are highest at the segment boundaries an opposite pattern of footwall deformation than predicted for boundaries arresting or strongly inhibiting displacement during earthquakes the spatial pattern of footwall rebound implies that some of the proposed persistent fault segment boundaries do not stop earthquake ruptures that originate on adjacent fault segments nor constrain ruptures initiated within the salt lake city segment net vertical fault displacement at the boundary between the salt lake and provo segments is 16 20 m over the past 16 3 18 5 ka corresponding to a vertical displacement rate of 0 8 1 2 mm yr a net fault slip rate of 2 0 2 8 mm yr and horizontal extension rate of 1 8 2 6 mm yr on the 25 west southwest dipping fault that forms the southern salt lake city segment boundary shoreline analysis suggests isostatic rebound caused by a drop in lake level was concentrated during a relatively short 2000 year time period following the bonneville flood at 16 ka lidar derived topography in conjunction with robust geomorphic datums improves our ability to map deformation associated with lithospheric flexure and faulting while demonstrating the limitation of lacustrine shorelines in this type of analysis

chronology of the vostok ice core constrained by o2 n2 ratios of occluded air and its implication for the vostok climate records abstract we present a timescale for the vostok ice core that is derived by orbitally tuning to o 2 n 2 ratios in occluded air for depths deeper than 1550 m 112 ka and by gas correlation to the gisp2 chronology for the section shallower than 1422 m 2 exclusion and hence the o 2 n 2 ratio in trapped gases the newly derived o 2 n 2 chronology is consistent with absolutely dated speleothem records the o 2 n 2 chronology differs from previously published orbital tuning chronologies ch 4 and 18 o atm by up to 6 kyr and from the original gt4 chronology by up to 15 kyr the difference between the o 2 n 2 chronology and the 18 o atm chronology varies in time with strong signals centered at 1 100 and 1 41 kyr 1 the ages for the last four glacial terminations in vostok correspond to high obliquity 23 7 at terminations midpoints they also correspond with decreasing precession index corresponding to increasing boreal summer insolation the vostok temperature record boreal summer insolation and the rate of change of the specmap property reflecting planktonic foram 18 o with respect to time are highly coherent at precession and obliquity periods these three properties vary almost synchronously with the possibility that vostok temperature lags behind the other two our new timescale supports the widespread view that boreal summer insolation played an important role in glacial interglacial cycles

late pleistocene record of off fault deformation and vertical slip rates from the wasatch fault zone utah implications for fault segmentation from lake bonneville shorelines

modeling the formation of the k pg boundary layer abstract in this paper we investigate the formation of the cretaceous paleogene k pg boundary layer through numerical modeling the k pg layer is widely agreed to be composed of meteoritic material and target rock from the chicxulub impact site that has been ejected around the globe and mixed with local material during final deposition the observed composition and thickness of the k pg boundary layer changes with azimuth and distance from the impact site we have run a suite of numerical simulations to investigate whether we can replicate the observational data with a focus on the distal k pg layer and the impact glasses at proximal sites such as beloc haiti previous models of the k pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination here we attempt to model the entire process from impact to the arrival of the ejecta around the globe our models replicate the observed ejecta thickness at proximal sites and the modeled ejecta is composed of sediments and silicate basement rocks in agreement with observational data models that use a 45 impact angle are able to replicate the total ejecta and iridium volume at distal sites and the majority of the ejecta is composed of meteorite and target sediments sub vertical impacts generate too little iridium and oblique impacts of 30 degrees generate too much however in contrast to observations models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance and are unable to transport shocked minerals quartz and zircon from the chicxulub basement rocks around the globe we suggest that much of the k pg ejecta is transported non ballistically and that the most plausible mechanism is through re distribution from a hot expanding atmosphere the results are important for future investigations of the environmental effects of the chicxulub impact

modeling the holocene slip history of the wasatch fault utah coseismic and postseismic coulomb stress changes and implications for paleoseismicity and seismic hazard

delta15n measurements as a calibration tool for the paleothermometer and gas ice age differences a case study for the 8200 b p event on grip ice isotopic composition measurement on atmospheric nitrogen 15n trapped in ice cores is established as a gravitational enrichment indicator recently it was discovered that thermal diffusion has a significant influence on this parameter during periods of large temperature fluctuations severinghaus et al 1998 here we present results for the 8200 b p event the largest temperature excursion during the holocene which underpin this view and extend it to medium range temperature changes the thermal diffusion component is about one third of the gravitational enrichment for this event the shortness of this cooling event does not significantly affect the gravitational enrichment as documented by rather constant close off depths therefore the 15n residuals can be directly used to estimate temperature changes hence calibrating the paleothermometer since our 15n record can resolve temperature variations as short as a few decades it complements the calibration technique of borehole temperature measurements for which the resolution decreases rapidly with increasing age we obtained a relation 18oice temperature of 0 30 0 11 k which agrees nicely with the temporal dependence for cold periods about 0 30 k and is significantly lower than today s greenland spatial relation 0 67 k this corresponds to a range of the surface temperature shift for the 8200 b p event in central greenland between 5 4 and 11 7 k with a best estimate of 7 4 k by matching the 15n variations with 18oice variations we estimate the mean gas ice age difference to be 209 15 years which is in good agreement with model estimates

4 1 5 c abrupt warming 11 270 yr ago identified from trapped air in greenland ice nitrogen and argon isotopes in air trapped in a greenland ice core gisp2 show two prominent peaks in the interval 11 800 10 800 b p which indicate two large abrupt warming events the first abrupt warming 10 4 c is the widely documented event at the end of the younger dryas here we report on the second abrupt warming 4 1 5 c which occurred at the end of a short lived cooler interval known as the preboreal oscillation 11 270 30 b p a rapid snow accumulation increase suggests that the climatic transition may have occurred within a few years the character of the preboreal oscillation and the subsequent abrupt warming is similar to the dansgaard oeschger d o events in the last glacial period suggestive of a common mechanism but different from another large climate change at 8 200 b p in which cooling was abrupt but subsequent warming was gradual the large abrupt warming at 11 270 b p may be considered to be the final d o event prior to the arrival of the present stable and warm epoch

o2 n2 ratios of occluded air in the gisp2 ice core 1 we present and discuss the record of o2 n2 ratios in air occluded in the gisp2 ice core retrieved from summit greenland in this study we examine results for 601 samples from 331 depths measured by 1994 and 92 samples from 46 depths newly measured in 2006 poorly replicated samples samples with no replicates and samples falling more than three standard deviations from the mean of each o2 n2 data set are excluded from the analysis the majority of poorly replicated samples are from the depth zone associated with the transition between gas in bubbles and gas present as clathrate hydrates we found that the o2 n2 ratio of samples is depleted by an average value of 7 3 during 11 years of storage at 35 c o2 n2 ratios measured at various times were corrected for depletion during storage and combined to form a single data set the stacked gisp2 o2 n2 record shows strong spectral power at the orbital frequencies and o2 n2 is in antiphase with local summer insolation this observation is consistent with the earlier findings for the vostok and dome fuji ice cores from east antarctica it validates previous conclusions that fractionation during bubble close off depends on ice grain properties set at the surface by solar insolation in addition the gisp2 o2 n2 record shows millennial duration signals that are in phase with the local temperature record of rapid climate change the exact mechanisms by which local summer insolation induces orbital variability in o2 n2 and by which temperature or related properties induce high frequency signals in o2 n2 remain to be identified

revisiting wildfires at the k pg boundary 1 the discovery of large amounts of soot in clays deposited at the cretaceous paleogene k pg boundary and linked to the 65 ma chicxulub impact crater led to the hypothesis that major wildfires were a consequence of the asteroid impact subsequently several lines of evidence including the lack of charcoal in north american sites were used to argue against global wildfires close to the impact site fires are likely to be directly ignited by the impact fireball whereas globally they could be ignited by radiation from the reentry of hypervelocity ejecta to date models of the latter have yet to take into account that ejection and thus the emission of thermal radiation is asymmetric and dependent on impact angle here we model 1 the impact and ejection of material 2 the ballistic continuation of ejecta around a spherical earth and 3 the thermal pulse delivered to the earth s surface when ejecta reenters the atmosphere we find that thermal pulses in the downrange direction are sufficient to ignite flora several thousand kilometers from chicxulub whereas pulses at most sites in the uprange direction are too low to ignite even the most susceptible plant matter our analyses and models suggest some fires were ignited by the impact fireball and ejecta reentry but that the nonuniform distribution of thermal radiation across the surface of the earth is inconsistent with the ignition of fires globally as a direct and immediate result of the chicxulub impact instead we propose that the desiccation of flora by ejecta reentry as well as the effects of postimpact global cooling darkness left much of the terrestrial flora prone to fires and that the volume of soot in the global k pg layer is explained by a combination of syn and postimpact wildfires

geophysical characterization of the chicxulub impact crater 1 geophysical data indicate that the 65 5 million years ago chicxulub impact structure is a multi ring basin with three sets of semicontinuous arcuate ring faults and a topographic peak ring pr slump blocks define a terrace zone which steps down from the inner rim into the annular trough fault blocks underlie the pr which exhibits variable relief due to target asymmetries the central structural uplift is 10 km and the moho is displaced by 1 2 km the working hypothesis for the formation of chicxulub is a 50 km radius transient cavity lined with melt and impact breccia formed within 10 s of the impact and within minutes weakened rebounding crust rose kilometers above the surface the transient crater rim underwent localized deformation and collapsed into large slump blocks resulting in a inner rim at 70 85 km radius and outer ring faults at 70 130 km radius the overheightened structural uplift collapsed outward buried the inner slump blocks and formed the pr most of the impact melt was ultimately emplaced as a coherent 3 km thick melt sheet within the central basin that shallows within the inner regions of the pr smaller pockets of melt flowed into the annular trough subsequently slope collapse ejecta ground surge and tsunami waves infilled the annular trough and annular basin with sediments up to 3 km and 900 m thick respectively testing this working hypothesis requires direct observation of the impactites within and adjacent to the pr and central basin

estimating surface rupture length and magnitude of paleoearthquakes from point measurements of rupture displacement we present a method to estimate paleomagnitude and rupture extent from measurements of displacement at a single point on a fault the variability of historic ruptures is summarized in a histogram of normalized slip then scaled to give the probability of finding a given displacement within a rupture for any magnitude considered the histogram can be inverted assuming any magnitude earthquake is as likely as another yielding probability density functions of magnitude and rupture length for any given displacement measurement to improve these distributions we include a term to account for the probability that the earthquake would cause ground rupture and two alternative distributions of earthquake magnitude the gutenberg richter magnitude distribution predicts shorter rupture lengths and smaller magnitudes than does a uniform distribution where any magnitude earthquake is considered equally likely longer ruptures and larger magnitudes than the uniform model are predicted by an alternative magnitude distribution designed to return site average displacement this model is a generalization of the characteristic earthquake model and reasonably describes paleoseismic findings on the southern san andreas fault where slip is accommodated by average displacements of a few meters and earthquake recurrence times of 100 250 years our results should increase the value of paleoseismic displacement measurements for hazard assessment in particular they quantify probability estimates of earthquake magnitude and rupture length where point observations of rupture displacement are available and so can contribute to probabilistic seismic hazard analyses online material rupture profiles used to sample rupture variability

survival in the first hours of the cenozoic for several hours following the chicxulub impact the entire earth was bathed with intense infrared radiation from ballistically reentering ejecta the global heat pulse would have killed unsheltered organisms directly and ignited fires at places where adequate fuel was available sheltering underground within natural cavities or in water would have been a necessary but not always sufficient condition for survival survival through sheltering from an initial thermal pulse is not adequately considered in literature about cretaceous tertiary nonmarine extinctions we compare predicted intense short term thermal effects with what is known about the fossil record of nonmarine vertebrates and suggest that paleontological evidence of survival is compatible with theoretical results from bolide physics

relationship between impact crater size and severity of related extinction episodes abstract how large must an extraterrestrial impact be to cause a peak episode of increased extinctions of life impact energies 3 107 mt tnt associated with terrestrial impact craters with final diameters 100 km seem to be required to generate significant widespread climatic effects from sub micron dust and soot in the atmosphere leading to a distinct extinction episode 15 extinction of marine genera impacts creating craters smaller than 100 km in final diameter in the 106 to 107 mt tnt range are capable of mostly regional destruction with minimal impact on global climate or biota these results are supported by the fact that the ages of the four known 100 km diameter craters of the last 260 my popigai chicxulub morokweng and manicouagan are all correlative with times of documented extinction episodes whereas smaller craters are not the largest crater the 180 km diameter chicxulub crater a 108 mt tnt event is associated with the more severe major mass extinction event 45 extinction of genera at the end of the cretaceous the percent species extinctions show a significant linear relationship with final crater diameter and impact energy the very large chicxulub impact lies close to the predicted curve of percent extinction versus impact crater diameter and energy but the low angle of impact an unusual composition of the target area with thick sediments rich in carbonates sulfates and organic material and a large excavated transient crater may have led to the generation of unusually large amounts of co2 widely distributed dust soot and sulfate aerosols and a uniquely severe impact related environmental disaster chicxulub may thus be the only large body impact associated with a major mass extinction in the phanerozoic target sensitivity may apply to large impacts into ocean crust having only a thin cover of organic poor and carbonate poor pelagic sediments and thus even large oceanic impacts which are still unknown may not produce enough dust soot and aerosols to cause environmental crises leading to global extinction peaks above background levels

evidence for molecular size dependent gas fractionation in firn air derived from noble gases oxygen and nitrogen measurements we present elemental and isotopic measurements of noble gases he ne ar kr and xe oxygen and nitrogen of firn air from two sites the first set of samples was taken in 1998 at the summit of the devon ice cap in the eastern part of devon island the second set was taken in 2001 at ngrip location north greenland he and ne are heavily enriched relative to ar with respect to the atmosphere in the air near the close off depth at around 50 70 m the enrichment increases with depth and reaches the maximum value in the deepest samples just above the zone of impermeable ice where no free air could be extracted anymore similarly elemental ratios of o2 n2 o 2 ar and ar n2 are increasing with depth in contrast but in line with expectations isotopic ratios of 15 n 14 n 18 o 16 o and 36 ar 40 ar show no significant enrichment near the close off depth the observed isotopic ratios in the firn air column can be explained within the uncertainty ranges by the well known processes of gravitational enrichment and thermal diffusion to explain the elemental ratios however an additional fractionation process during bubble inclusion has to be considered we implemented this additional process into our firn air model the fractionation factors were found by fitting model profiles to the data we found a very similar close off fractionation behavior for the different molecules at both sites for smaller gas species mainly he and ne the fractionation factors are linearly correlated to the molecule size whereas for diameters greater than about 3 6 a the fractionation seems to be significantly smaller or even negligible an explanation for this size dependent fractionation process could be gas diffusion through the ice lattice

variability of displacement at a point implications for earthquake size distribution and rupture hazard on faults abstract to investigate the nature of earthquake magnitude distributions on faults we compare the interevent variability of surface displacement at a point on a fault from a composite global data set of paleoseismic observations with the variability expected from two prevailing magnitude frequency distributions the truncated exponential model and the characteristic earthquake model we use forward modeling to predict the coefficient of variation cv for the alternative earthquake distributions incorporating factors that would effect observations of displacement at a site the characteristic earthquake model with a characteristic magnitude range of 0 25 produces cv values consistent with the data cv 0 5 only if the variability for a given earthquake magnitude is small this condition implies that rupture patterns on a fault are stable in keeping with the concept behind the model this constraint also bears upon fault rupture hazard analysis which for lack of point specific information has used global scaling relations to infer variability in average displacement for a given size earthquake exponential distributions of earthquakes from m 5 to the maximum magnitude give rise to cv values that are significantly larger than the empirical constraint a version of the model truncated at m 7 however yields values consistent with a larger cv 0 6 determined for small displacement sites although this result allows for a difference in the magnitude distribution of smaller surface rupturing earthquakes it may reflect in part less stability in the displacement profile of smaller ruptures and or the tails of larger ruptures online material global surface displacement data and identified sources of uncertainty

natural and anthropogenic changes in atmospheric co2 over the last 1000 years from air in antarctic ice and firn a record of atmospheric co2 mixing ratios from 1006 a d to 1978 a d has been produced by analysing the air enclosed in three ice cores from law dome antarctica the enclosed air has unparalleled age resolution and extends into recent decades because of the high rate of snow accumulation at the ice core sites the co2 data overlap with the record from direct atmospheric measurements for up to 20 years the effects of diffusion in the firn on the co2 mixing ratio and age of the ice core air were determined by analyzing air sampled from the surface down to the bubble close off depth the uncertainty of the ice core co2 mixing ratios is 1 2 ppm 1 preindustrial co2 mixing ratios were in the range 275 284 ppm with the lower levels during 1550 1800 a d probably as a result of colder global climate natural co2 variations of this magnitude make it inappropriate to refer to a single preindustrial co2 level major co2 growth occurred over the industrial period except during 1935 1945 a d when co2 mixing ratios stabilized or decreased slightly probably as a result of natural variations of the carbon cycle on a decadal timescale

an experimental assessment of the ignition of forest fuels by the thermal pulse generated by the cretaceous palaeogene impact at chicxulub a large extraterrestrial body hit the yucatan peninsula at the end of the cretaceous period models suggest that a substantial amount of thermal radiation was delivered to the earth s surface by the impact leading to the suggestion that it was capable of igniting extensive wildfires and contributed to the end cretaceous extinctions we have reproduced in the laboratory the most intense impact induced heat fluxes estimated to have reached different points on the earth s surface using a fire propagation apparatus and investigated the ignition potential of forest fuels the experiments indicate that dry litter can ignite but live fuels typically do not suggesting that any ignition caused by impact induced thermal radiation would have been strongly regional dependent the intense but short lived pulse downrange and at proximal and intermedi ate distances from the impact is insufficient to ignite live fuel however the less intense but longer lasting thermal pulse at distal locations may have ignited areas of live fuels because plants and ecosystems are generally resistant to single localized fire events we conclude that any fires ignited by impact induced thermal radiation cannot be directly responsible for plant extinctions implying that heat stress is only part of the end cretaceous story received 3 july 2014 revised 10 october 2014 accepted 10 october 2014

on the potential of coupling air content and o2 n2 from trapped airfor establishing an ice core chronology tuned on local insolation the potential to access an ice core chronology tuned on local insolation has been demonstrated for the first time in the work of m bender 2002 linking the variations of o2 n2 ratios in the air trapped in the vostok ice with local 78 s summertime insolation more recently it has been shown that the long term changes in air content v recorded in ice from the high antarctic plateau are also dominantly imprinted by the local summer insolation raynaud et al 2007 this paper presents a new v record from vostok which is compared with the published vostok o2 n2 record for the same period of time 160 390 ka bp by using the same spectral analysis methods the spectral differences between the two properties and the possible mechanisms linking them with insolation through the surface snow structure and the close off processes are discussed the main result of our study is that the two experimentally independent local insolation proxies lead to absolute orbital timescales which agree together within less than 1 ka on average this result strongly adds credibility to the total content and the o2 to n2 ratio of the air trapped in ice as reliable and complementary tools for accurate dating of existing and future deep ice cores

self shielding of thermal radiation by chicxulub impact ejecta firestorm or fizzle as hypervelocity ejecta from the chicxulub yucatan mexico impact fell back to earth the surface may have received a deadly dose of thermal radiation sufficient to ignite global wildfires using a two phase fluid flow code which includes ejecta and air opacities in a radiative transfer calculation we modeled the atmospheric reentry of spherules arriving at distal sites the models predict a pulse of thermal radiation at the surface peaking at 5 15 kw m 2 analogous to an oven set on broil 260 c previous calculations which ignored spherule opacity yielded 10 kw m 2 sustained over 20 min and such an extended pulse is thought to be required for wood ignition however the new modeling suggests that fluxes only exceed the solar norm for 30 min and are only 5 kw m 2 for a few minutes previous models failed to consider the self shielding effect of settling spherules which block an increasing proportion of downward thermal radiation emitted by the later arriving spherules such self shielding may have prevented widespread wildfire ignition although the thermal pulse may have been sufficient to ignite localized fires and kill fauna lacking temporary shelter an opaque cap of submicron dust in the upper atmosphere could however override the self shielding effect

fault segmentation new concepts from the wasatch fault zone utah usa the question of whether structural segment boundaries along multisegment normal faults such as the wasatch fault zone wfz act as persistent barriers to rupture is critical to seismic hazard analyses we synthesized late holocene paleoseismic data from 20 trench sites along the central wfz to evaluate earthquake rupture length and fault segmentation for the youngest 3 ka and best constrained earthquakes differences in earthquake timing across prominent primary segment boundaries especially for the most recent earthquakes on the north central wfz are consistent with segment controlled ruptures however broadly constrained earthquake times dissimilar event times along the segments the presence of smaller scale subsegment boundaries and areas of complex faulting permit partial segment and multisegment e g spillover ruptures that are shorter 20 40 km or longer 60 100 km than the primary segment lengths 35 59 km we report a segmented wfz model that includes 24 earthquakes since 7 ka and yields mean estimates of recurrence 1 1 1 3 kyr and vertical slip rate 1 3 2 0 mm yr for the segments however additional rupture scenarios that include segment boundary spatial uncertainties floating earthquakes and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length we compare the central wfz to paleoseismic and historical surface ruptures in the basin and range province and central italian apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures our comparison also suggests that the probabilities of shorter and longer ruptures on the wfz need to be investigated

impact ejecta emplacement on terrestrial planets abstract impact cratering is one of the most fundamental processes responsible for shaping the surfaces of solid planetary bodies one of the principal characteristics of impact events is the formation and emplacement of ejecta deposits an understanding of which is critical for planetary exploration current models of ejecta emplacement however do not account for several important observations of ejecta deposits on the terrestrial planets in particular the presence of more than one layer of ejecta furthermore there is also no universal model for the origin and emplacement of ejecta on different planetary bodies we present a unifying working hypothesis for the origin and emplacement of ejecta on the terrestrial planets in which the ejecta are emplaced in a multi stage process the generation of the continuous ejecta blanket occurs during the excavation stage of cratering via the conventional ballistic sedimentation and radial flow model this is followed by the emplacement of more melt rich ground hugging flows the surface melt flow phase during the terminal stages of crater excavation and the modification stage of crater formation minor fallback occurs during the final stages of crater formation several factors will affect the final morphology and character of ejecta deposits the volatile content and cohesiveness of the uppermost target rocks will significantly affect the runout distance of the ballistically emplaced continuous ejecta blanket with impact angle also influencing the overall geometry of the deposits e g the production of the characteristic butterfly pattern seen in very oblique impacts ejecta deposited during the surface melt flow stage is influenced by several factors most importantly planetary gravity surface temperature and the physical properties of the target rocks topography and angle of impact play important roles in determining the final distribution of surface melt flow ejecta deposits with respect to the source crater this working hypothesis of ballistic sedimentation and surface melt flow provides a framework in which observations of ejecta at impact craters can be compared and placed in the context of the respective terrestrial planets

a method for precise measurement of argon 40 36 and krypton argon ratios in trapped air in polar ice with applications to past firn thickness and abrupt climate change in greenland and at siple dome antarctica we describe a method for measuring the 40ar 36ar ratio and the 84kr 36ar ratio in air from bubbles trapped in ice cores these ratios can provide constraints on the past thickness of the firn layer at the ice core site and on the magnitude of past rapid temperature variations when combined with measured 15n 14n both variables contribute to paleoclimatic studies and ultimately to the understanding of the controls on earth s climate the overall precision of the 40ar 36ar method 1 standard error of the mean is 0 012 for a sample analyzed in duplicate corresponding to 0 6 m in reconstructed firn thickness we use conventional dynamic isotope ratio mass spectrometry with minor modifications and special gas handling techniques designed to avoid fractionation about 100 g of ice is used for a duplicate pair of analyses an example of the technique applied to the gisp2 ice core yields an estimate of 11 3k of abrupt warming at the end of the last glacial period 15 000 years ago the krypton argon ratio can provide a diagnostic of argon leakage out of the bubbles which may happen naturally during bubble close off or artifactually if samples are warmed near the freezing point during core retrieval or storage argon leakage may fractionate the remaining 40ar 36ar ratio by 0 007 per change in 84kr 36ar introducing a possible bias in reconstructed firn thickness of about 2 m if thermal diffusion is not accounted for or 6 m if thermal diffusion effects are quantified with measured 15n 14n reproducibility of 84kr 36ar measured in air is about 0 2 1 standard error of the mean but is about 1 for ice core samples ice core samples are systematically enriched in 84kr 36ar relative to atmosphere by 5 probably reflecting preferential size dependent exclusion of the smaller argon atom during bubble entrapment recent results from the siple dome ice core reveal two climate events during the last deglaciation including an 18 m reduction in firn thickness associated with an abrupt warming at sometime between 18 and 22 kyr bp and a partial or total removal of the firn during an ablation event at 15 3 kyr bp

tsunami backwash deposits with chicxulub impact ejecta and dinosaur remains from the cretaceous palaeogene boundary in the la popa basin mexico the la popa basin in north eastern mexico features outstanding continuous three dimensional exposures of the cretaceous palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks in the area to the south east of the el papalote diapir the cretaceous palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper maastrichtian sand siltstones with soft sediment deformation and liquefaction structures the basal unit 1 is an up to 8 m thick chaotic carbonate rich bed that discontinuously fills incised gutters and channels besides abundant silicic and carbonate ejecta spherules from the chicxulub impact unit 1 includes large sandstone boulders and abundant shallow water debris for example mud clasts algae bivalve shells gastropod shells and vertebrate remains unit 1 is conformably overlain by unit 2 distal to the diapir unit 2 consists of a centimetre to decimetre thick conglomeratic coarse bioclast and spherule bearing sandstone bed closer to the diapir unit 2 becomes a metre thick series of four to eight conglomeratic to fine grained graded sandstone beds rich in shell debris and ejecta spherules unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre event depositional regime the sedimentary characteristics of the cretaceous palaeogene deposit including its erosive base its sheet like geometry the presence of multiple graded beds evidence for upper flow regime conditions and the absence of bioturbation support an origin by a short term multiphase depositional event the occurrence of soft sediment deformation structures for example liquefaction below the cretaceous palaeogene deposit suggests that earthquakes were the first to occur at la popa then shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta rich hyperconcentrated density flows unit 1 subsequently a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple graded bedding structures of unit 2 the specific depositional sequence and the fe mg rich as well as si k rich composition of the ejecta spherules both provide a critical link to the well known deep marine cretaceous palaeogene boundary sites in the adjacent burgos basin in north eastern mexico moreover the pulse like input of chicxulub ejecta material at the base of the event deposit allows for correlation with other cretaceous palaeogene boundary sites in the gulf of mexico and the atlantic as well as in central and northern america the presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with chicxulub ejecta material these findings indicate that dinosaurs lived in the area during the latest maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well

onset of deglacial warming in west antarctica driven by local orbital forcing an annually resolved ice core record from west antarctica indicates that warming driven by local insolation resulting from sea ice decline began in that region about 2 000 years before warming in east antarctica reconciling two alternative explanations for deglacial warming in the southern hemisphere

on the use of δ18oatm for ice core dating abstract deep ice core chronologies have been improved over the past years through the addition of new age constraints however dating methods are still associated with large uncertainties for ice cores from the east antarctic plateau where layer counting is not possible indeed an uncertainty up to 6 ka is associated with aicc2012 chronology of epica dome c edc ice core which mostly arises from uncertainty on the delay between changes recorded in 18oatm and in june 21st insolation variations at 65 n used for ice core orbital dating consequently we need to enhance the knowledge of this delay to improve ice core chronologies we present new high resolution edc 18oatm record 153 374 ka and o2 n2 measurements 163 332 ka performed on well stored ice to provide continuous records of 18oatm and o2 n2 between 100 and 800 ka the comparison of 18oatm with the 18ocalcite from east asian speleothems shows that both signals present similar orbital and millennial variabilities which may represent shifts in the intertropical convergence zone position themselves associated with heinrich events we thus propose to use the 18ocalcite as target for 18oatm orbital dating such a tuning method improves the ice core chronology of the last glacial inception compared to aicc2012 by reconciling ngrip and mid latitude climatic records it is especially marked during dansgaard oeschger 25 where the proposed chronology is 2 2 ka older than aicc2012 this 18oatm 18ocalcite alignment method applied between 100 and 640 ka improves the edc ice core chronology especially over mis 11 and leads to lower ice age uncertainties compared to aicc2012

16 c rapid temperature variation in central greenland 70 000 years ago variations in the29n2 28n2 ratio of air bubbles trapped in polar ice cores and their relation to variations of the 18o 16o of the ice allow past surface temperature variations and ice age gas age differences to be determined high resolution measurements of29n2 28n2 in dansgaard oeschger event 19 around 70 000 years before the present in ice from central greenland show that at the beginning of the event the ice age gas age difference was 1090 100 years with the use of a combined firn densification temperature and gas diffusion model the 18oice temperature coefficient was determined to be 0 42 0 05 per mil per kelvin this coefficient implies a mean surface temperature change of 16 0 kelvin between 14 3 and 18 1 kelvin which differs substantially from values derived from borehole temperatures and modern spatial 18oice surface temperature correlations

holocene carbon cycle dynamics based on co2 trapped in ice at taylor dome antarctica a high resolution ice core record of atmospheric co2 concentration over the holocene epoch shows that the global carbon cycle has not been in steady state during the past 11 000 years analysis of the co2 concentration and carbon stable isotope records using a one dimensional carbon cycle model uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial scale changes of atmospheric co2 concentrations

on the impact of impurities on the densification of polar firn abstract understanding polar firn densification is crucial for reconstructing the age of greenhouse gas concentrations extracted from ice cores and for the interpretation of air in ice as a dating tool or as a climate proxy firn densification is generally modeled as a steady burial and sintering process of defined layers where the structure of the layering is maintained along the whole firn and ice column however available high resolution density data as well as firn air samples question this picture and point to a lack of understanding of firn densification based on analysis of high resolution density and calcium concentration records from antarctic and greenland ice cores we show for the first time that also impurities may have a significant impact on the densification analysis of firn cores shows a correlation between density and the calcium ion ca concentration and this correlation increases with depth the existence of this relationship is independent of the local climatic conditions at the core sites analyzed the strong positive correlation between the density and the logarithm of ca concentration indicates that impurities induce softening and lead to faster densification over a wide range of concentrations in one core the impurity effect manifests itself so strongly that the density develops a seasonal cycle closely following the seasonal cycle of ca our results clearly show that the structure of the firn layering changes with depth and suggest that the increased variability in density observed in deep firn recently described as a universal feature of polar firn may arise from the influence of ca and or other impurities the impurity effect is likely to have direct implications on our understanding of glacial firn densification and on glacial gas age estimates

thermal fractionation of air in polar firn by seasonal temperature gradients 1 air withdrawn from the top 5 15 m of the polar snowpack firn shows anomalous enrichment of heavy gases during summer including inert gases following earlier work we ascribe this to thermal diffusion the tendency of a gas mixture to separate in a temperature gradient with heavier molecules migrating toward colder regions summer warmth creates a temperature gradient in the top few meters of the firn due to the thermal inertia of the underlying firn and causes gas fractionation by thermal diffusion here we explore and quantify this process further in order to 1 correct for bias caused by thermal diffusion in firn air and ice core air isotope records 2 help calibrate a new technique for measuring temperature change in ice core gas records based on thermal diffusion severinghaus et al 1998 and 3 address whether air in polar snow convects during winter and if so whether it creates a rectification of seasonality that could bias the ice core record we sampled air at 2 m depth intervals from the top 15 m of the firn at two antarctic sites siple dome and south pole including a winter sampling at the pole we analyzed 15n 14n 40ar 36ar 40ar 38ar 18o 16o of o2 o2 n2 84kr 36ar and 132xe 36ar the results show the expected pattern of fractionation and match a gas diffusion model based on first principles to within 30 although absolute values of thermal diffusion sensitivities cannot be determined from the data with precision relative values of different gas pairs may at siple dome 40ar 4 is 66 2 as sensitive to thermal diffusion as 15n in agreement with laboratory calibration 18o 2 is 83 3 and 84kr 48 is 33 3 as sensitive as 15n the corresponding figures for summer south pole are 64 2 81 3 and 34 3 accounting for atmospheric change the figure for o2 n2 4 is 90 3 at siple dome winter south pole shows a strong depletion of heavy gases as expected however the data do not fit the model well in the deeper part of the profile and yield a systematic drift with depth in relative thermal diffusion sensitivities except for kr constant at 34 4 suggesting the action of some other process that is not currently understood no evidence for wintertime convection or a rectifier effect is seen

co2 and o2 n2 variations in and just below the bubble clathrate transformation zone of antarctic ice cores co2 measurements on the epica european project for ice coring in antarctica dml ice core in depth levels just below the bubble ice clathrate ice transformation zone 1230 2240 m depth were performed in the youngest part 1230 1600 m they reveal variations of up to 25 ppmv around the mean atmospheric concentration within centimetres corresponding to a snow deposition interval of a few years similar results are found at corresponding depth regions of the dome c and the talos dome ice cores since we can exclude all hitherto known processes altering the concentration of co2 in ice cores we present a hypothesis about spatial fractionation of air components related to episodically increasing clathrate formation followed by diffusion processes from bubbles to clathrates this hypothesis is supported by optical line scan observations and by o2 n2 measurements at the same depth where strong co2 variations are detected below the clathrate formation zone this small scale fractionation process is slowly smoothed out most likely by diffusion regaining the initial mean atmospheric concentration although this process compromises the representativeness of a single co2 measurement on small ice samples in the clathrate formation zone of an ice core it does not affect the mean atmospheric co2 concentration if co2 values are averaged over a sufficiently long depth scale 10 cm in case of the epica dml ice core

severity of ocean acidification following the end cretaceous asteroid impact ammonites went extinct at the time of the end cretaceous asteroid impact as did more than 90 of species of calcium carbonate shelled plankton coccolithophores and foraminifera comparable groups not possessing calcium carbonate shells were less severely affected raising the possibility that ocean acidification as a side effect of the collision might have been responsible for the apparent selectivity of the extinctions we investigated whether ocean acidification could have caused the disappearance of the calcifying organisms in a first detailed modelling study we simulated several possible mechanisms from impact to seawater acidification our results suggest that acidification was most probably not the cause of the extinctions

effects of molecular diffusion on trapped gas composition in polar ice cores abstract enrichment of nitrogen gas has been found from gas analyses of ice cores retrieved from deep parts of antarctica neither climate change nor gas loss through ice cracks explain the enrichment in order to investigate the mechanism of the gas composition change we develop a model of gas loss caused by molecular diffusion from clathrate hydrates toward the ice core surface through ice crystal we apply the model to interpret the data on the gas composition change in the dome fuji ice core during the storage for 3 years at 248 k the mass transfer coefficients determined using the model are 1 4 10 9 and 4 3 10 9 m s 1 at 248 k for n2 and o2 respectively the difference in the coefficient between n2 and o2 causes the change in the o2 n2 ratio of the trapped gas in the ice core during the storage during the storage period of 1000 days at 248 k the o2 n2 ratio changes from 9 9 to 20 5 the effect of the gas loss decreases as the storage temperature decreases the results have important implications for the accurate reconstructions of the paleo atmosphere from polar ice cores

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

physics of crustal fracturing and chert dike formation triggered by asteroid impact 3 26 ga barberton greenstone belt south africa archean asteroid impacts reflected in the presence of spherule beds in the 3 2 3 5 ga barberton greenstone belt bgb south africa generated extreme seismic waves spherule bed s2 provides a field example it locally lies at the contact between the onverwacht and fig tree groups in the bgb which formed as a result of the impact of asteroid possibly 50 km diameter scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site where they widely damaged onverwacht rocks over much of the bgb lithified sediments near the top of the onverwacht group failed with opening mode fractures the underlying volcanic sequence then failed with normal faults and opening mode fractures surficial unlithified sediments liquefied and behaved as a fluid these liquefied sediments and some impact produced spherules filled near surface fractures today represented by swarms of chert dikes strong impact related tsunamis then swept the seafloor p waves and rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves the duration of extreme shaking was also far longer probably hundreds of seconds than that from strong earthquakes dynamic strains of 10 3 occurred from the surface and downward throughout the lithosphere shaking weakened the onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open mode fractures coast parallel opening mode fractures on the fore arc coast of chile formed as a result of megathrust events are the closest modern analogs it is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the onverwacht rocks

quantification of rapid temperature change during do event 12 and phasing with methane inferred from air isotopic measurements the description of rapid climatic changes during the last glacial period at high northern latitudes has been largely documented through greenland ice cores that are unique climatic and environmental records however greenland ice isotopic records are biased temperature proxies and it is still a matter of debate whether changes in the high latitudes lead or lag rapid changes elsewhere we focus here on the study of the mid glacial dansgaard oeschger event 12 45 ky bp associated to a large d 18 oice change in the grip greenland ice core project ice core we use combined measurements of ch4 d 15 n and d 40 ar in entrapped air associated with a recently developed firn densification and heat diffusion model to infer i the phasing between methane and temperature increases and ii the amplitude of the temperature change our method enables us to overcome the difficulty linked with rapid accumulation change in quantifying the temperature change we obtain a 12f2 5 8c temperature increase at the beginning of do event 12 thus confirming that the conventional use of water isotopes in the greenland ice cores largely underestimates the actual amplitude of rapid temperature change in central greenland in agreement with previous studies methane and temperature increase are in phase at the sampling resolution of that part of our profile 90 years d 2004 elsevier b v all rights reserved

fractionation of gases in polar ice during bubble close off new constraints from firn air ne kr and xe observations gas ratios in air withdrawn from polar firn snowpack show systematic enrichments of ne n2 o 2 n2 and ar n2 in the firn ice transition region where bubbles are closing off air from the bubbles in polar ice is correspondingly depleted in these ratios after accounting for gravitational effects gas in the bubbles becomes fractionated during the process of bubble close off and fractionation may continue as ice cores are stored prior to analysis we present results from firn air studies at south pole and siple dome antarctica which add ne kr and xe measurements to the suite of observations ne o2 and ar appear to be preferentially excluded from the shrinking and occluding bubbles and these gases therefore accumulate in the residual firn air creating a progressive enrichment with time and depth in firn air early sealing of gases by thin horizontal impermeable layers into a nondiffusive zone or lock in zone greatly enhances this enrichment a simple model of the bubble close off fractionation and lock in zone enrichment fits the data adequately the model presumes that fractionation is caused by selective permeation of gas through the ice lattice from slightly overpressured bubbles the effect appears to be size dependent because ne o2 and ar have smaller effective molecular diameters than n2 and fractionation increases strongly with decreasing size ne is fractionated 34 2 times more than o2 in south pole firn air and reaches an enrichment of 90 in the deepest sample the large atoms kr and xe do not appear to be fractionated by this process despite the large size difference between the two gases suggesting a threshold atomic diameter of 3 6a above which the probability becomes very small that the gas will escape from the bubble these findings have implications for ice core and firn air studies that use gas ratios to infer paleotemperature chronology and past atmospheric composition

characterization of intrabasin faulting and deformation for earthquake hazards in southern utah valley utah from high resolution seismic imaging we conducted active and passive seismic imaging investigations along a 5 6 km long east west transect ending at the mapped trace of the wasatch fault in southern utah valley using two dimensional 2d p wave seismic reflection data we imaged basin deformation and faulting to a depth of 1 4 km and developed a detailed interval velocity model for prestack depth migration and 2d ground motion simulations passive source microtremor data acquired at two sites along the seismic reflection transect resolve s wave velocities of approximately 200 m s at the surface to about 900 m s at 160 m depth and confirm a substantial thickening of low velocity material westward into the valley from the p wave reflection profile we interpret shallow 100 600 m bedrock deformation extending from the surface trace of the wasatch fault to roughly 1 5 km west into the valley the bedrock deformation is caused by multiple interpreted fault splays displacing fault blocks downward to the west of the range front further west in the valley the p wave data reveal subhorizontal horizons from approximately 90 to 900 m depth that vary in thickness and whose dip increases with depth eastward toward the wasatch fault another inferred fault about 4 km west of the mapped wasatch fault displaces horizons within the valley to as shallow as 100 m depth the overall deformational pattern imaged in our data is consistent with the wasatch fault migrating eastward through time and with the abandonment of earlier synextensional faults as part of the evolution of an inferred 20 km wide half graben structure within utah valley finite difference 2d modeling suggests the imaged subsurface basin geometry can cause fourfold variation in peak ground velocity over distances of 300 m

combustion of fossil organic matter at the cretaceous paleogene k p boundary recognition of elevated concentrations of aciniform soot in cretaceous paleogene k p boundary sediments worldwide led to the hypothesis that global scale forest wildfires could have been generated by the k p boundary bolide impact and might have contributed directly to the extinction event the wildfires are estimated to have injected 10 13 t of co 2 into the atmosphere resulting in an interval of greenhouse warming yet minimal amounts of charred plant remains and abundant noncharred material occur in various k p boundary locations across north america this refutes the inference that wildfires occurred on a global scale and requires an alternative explanation for the aciniform soot here we describe significant concentrations of carbon cenospheres in k p boundary sediments from new zealand denmark and canada carbon cenospheres are thought to derive solely from incomplete combustion of pulverized coal or fuel oil droplets which suggests that the impact may have combusted organic rich target crust the chicxulub impact crater is located adjacent to the cantarell oil reservoir one of the most productive oil fields on earth this indicates that abundance of organic carbon in the chicxulub target crust was likely to have been above global mean values but even if we discount chicxulub9s organic rich locality the global mean crustal abundance for fossil organic matter is more than adequate to account for observed concentrations of both carbon cenospheres and aciniform soot therefore making the global wildfire hypothesis unnecessary

synchronous ruptures along a major graben forming fault system wasatch and west valley fault zones utah abstract the salt lake city segment slcs of the wasatch fault zone and the antithetic west valley fault zone wvfz form a large holocene active intrabasin graben in northern salt lake valley utah we integrate previous paleoseismic data with new data from recent trench investigations and compare earthquake timing and displacement for both the master and antithetic faults of this major graben forming system to address whether the wvfz ruptures simultaneously with the slcs or is a separate independent source of earthquakes nine slcs surface faulting earthquakes postdate the lake bonneville highstand 18 ka however the record is most complete since 14 ka yielding latest pleistocene and holocene mean recurrence estimates of 1 5 ky and 1 3 1 6 ky respectively six post bonneville highstand wvfz earthquakes yield a mean recurrence of 2 0 3 6 ky however we consider the wvfz earthquake record incomplete because of distributed faulting and limited paleoseismic data five of six wvfz earthquakes have mean and 2 times that are very similar to those of slcs earthquakes wvfz earthquake w5 lacks an apparent temporal correlation with an slcs earthquake but occurred during a period for which the slcs chronology may be incomplete mean wvfz per event vertical displacement 0 5 m is 26 42 of that for the slcs 1 2 1 9 m consistent with that predicted by previous mechanical modeling of antithetic faulting triggered by slip on a listric master fault we conclude that large wvfz earthquakes are likely synchronous with or triggered shortly after slcs surface faulting earthquakes although earthquake timing uncertainties preclude determining an unequivocal coseismic link between the wvfz and slcs structural models suggest a high likelihood for synchronous rupture these results have important implications for forecasting earthquake probabilities in complex normal faulting environments

estimating prehistoric earthquake magnitude from point measurements of surface rupture abstract we have developed a method for estimating the magnitude of prehistoric earthquakes using displacement data that usually can be collected from paleoseismic investigations this method is necessary because essentially all current magnitude estimates for prehistoric events rely on determining the total length of coseismic surface rupture which is rarely measurable or rely on segmentation scenarios for which uncertainties cannot be quantified although surface rupture length is a better predictor of magnitude than displacement for historic earthquakes paleoseismic investigations are better at providing measurements of the amount of displacement at a site along a fault the key to our method is to incorporate the variability in displacement observed in 14 modern events which allows a formal uncertainty in magnitude to be assigned to prehistoric ruptures we show how multiple measurements along a preserved fraction of a rupture can be combined to reduce the uncertainty in the estimate of magnitude our analysis shows that uncertainty asymptotically approaches the natural variability of ruptures so 5 to 10 displacement measurements are sufficient to characterize paleomagnitude we conclude that sampling of scarps with lengths of even 10 of the original rupture can provide magnitude values that reasonably estimate the earthquake tests of the method using randomly sampled data from the 1992 m w 7 3 landers and 1954 m s 6 8 dixie valley earthquakes provide close approximations of the actual magnitudes

mechanisms of subglacial groundwater recharge as derived from noble gas 14c and stable isotopic data abstract noble gas stable isotope and 14c data from samples collected along groundwater flow path within a confined paleozoic aquifer in northeastern wisconsin usa are used to deduce the effect of the laurentide ice sheet lis on the underlying groundwater and its recharge dynamics during the last glacial maximum the investigated area was near the center of the green bay lobe of the lis 14c ages that extend to 26 k a and low 18o derived temperatures during the time that the lis was present indicate that aquifer recharge continued when ice covered the area 18o values as low as 17 5 and 2h values as low as 127 7 indicate that a significant portion of aquifer recharge was derived from glacial meltwater that maintained its glacial isotopic signature during melting and subsequent recharge noble gas temperatures that remain above freezing at a constant 3 c unusually high excess air ne values and noble gas fractionation patterns indicate that recharge occurred across a very dynamic water table located within the ice sheet this englacial hydrologic system experienced recharge heads of as much as 7 8 m evidence for direct recharge of basal meltwater into the aquifer is not seen to the authors knowledge this is the first time that noble gas and isotope tracers have been used to deduce the provenance of aquifer water beneath continental ice sheets

dogtails versus rainbows synthetic earthquake rupture models as an aid in interpreting geological data geologists have been collecting for decades information from historical and paleoearthquakes that could contribute to the formulation of a big picture of the earthquake engine observations of large earthquake ruptures unfortunately are always going to be spotty in space and time so the extent to which geological information succeeds in contributing to a grander view of earthquakes is going to be borne not only by the quantity and quality of data collected but also by the means by which it is interpreted this article tries to understand geological data more fully through carefully tailored computer simulations of fault ruptures dogtails and rainbows are two types of fault rupture terminations that can be recognized in the field and can be interpreted through these models rainbows are concave down ruptures that indicate complete stress drop and characteristic slip rainbow terminations usually coincide with fault ends or strong segment boundaries dogtails are concave up ruptures that indicate incomplete stress drop and noncharacteristic slip dogtail terminations can happen anywhere along a fault or fault segment the surface slip pattern of the magnitude 6 6 1979 imperial valley california earthquake shows both dogtail and rainbow terminations the rainbow confirms the presence of a strong fault segment boundary 6 km north of the international border that had been suggested by sieh 1996 the dogtail implies that the displacement observed in 1979 is not characteristic by combining paleoseismic information with the surface slip patterns from this event and the magnitude 7 1 1940 imperial valley earthquake i develop a quantitative imperial fault model with northern central and southern segments possessing 50 110 and 50 bar strength respectively both the 1940 and 1979 events caused 1 m amplitude dogtailed ruptures of the northern segment however characteristic slip of the segment is more likely to be about 3 m to illustrate the full spectrum of potential rupture modes models were run forward in time to generate a 2000 year rupture encyclopedia even with well constrained segmentation and strengths modest changes in two friction law parameters produce several plausible histories further discrimination awaits analysis of the extensive paleoseismic record that geologists believe exists in the shore deposits of the intermittent lakes of the salton trough

argon and nitrogen isotopes of trapped air in the gisp2 ice core during the holocene epoch 0 11 500 b p methodology and implications for gas loss processes argon and nitrogen isotopes of air in polar ice cores provide constraints on past temperature and firn thickness with relevance to past climate we developed a method to simultaneously measure nitrogen and argon isotopes in trapped air from the same sample of polar ice this method reduces the time required for analysis allowing large numbers of measurements we applied this method to the entire holocene sequence of the gisp2 ice core 82 37 1692 22 m with a 10 20 year sampling interval 670 depths d 40 ar and d 15 n show elevated values in the oldest part of the dataset consistent with a thicker firn layer and increased temperature gradient in the firn due to the legacy of the abrupt warming at the end of the younger dryas interval and the gradual warming during the preboreal interval 11 5 10 0 ka the preboreal oscillation and the 8 2k event are clearly recorded the data show remarkable stability after the 8 2k event available data suggests that post coring gas loss involves two distinct types of fractionation first smaller molecules with less than a certain threshold size leak through the ice lattice with little isotopic fractionation second gas composition changes via gas loss through microcracks which induces isotopic fractionation these two gas loss processes can explain most trends in our data and in other ice core records 2008 elsevier ltd all rights reserved