thermochronometry reveals headward propagation of erosion in an alpine landscape glacial erosion of mountain ranges produces spectacular alpine landscapes and by linking climate with tectonics influences a broad array of geophysical phenomena although the resultant landforms are easily identified the timing and spatial pattern of topographic adjustment to pleistocene glaciations remain poorly known we investigated topographic evolution in the archetypal glacial landscape of fiordland new zealand using u th he thermochronometry we find that erosion during the past 2 million years removed the entire pre pleistocene landscape and fundamentally reshaped the topography erosion focused on steep valley segments and propagated from trunk valleys toward the heads of drainage basins a behavior expected if subglacial erosion rate depends on ice sliding velocity the fiordland landscape illustrates complex effects of climate on earth s surface morphology

the sedimentary expression of oceanic anoxic event 1b in the north atlantic abstract the aptian albian oceanic anoxic event 1b contains the record of severalperturbations in the global carbon cycle and multiple black shale levels particularly in the western tethys the local lithological expression of anoceanic anoxic event depends on palaeogeographical and depositional settingas well as on regional palaeoclimate marine sediments at a particular locationmay therefore be more or less organic rich or not at all and they may consistof different lithologies in most studies however much of the lithologicalvariability associated with oceanic anoxic events is left unaccounted for and thus the exact processes leading to the enrichment of organic matter in thesemarine sediments and their subsequent preservation in the geological recordare unknown this study focuses on the local sedimentary processes behindthe deposition of organic rich sediments at deep sea drilling project site 545and ocean drilling program sites 1049 and 1276 in the north atlantic duringoceanic anoxic event 1b although speci cally dealing with the sedimentsdeposited during this particular event at these localities it is expected that thesame processes were responsible for determining the exact sedimentaryproducts at localities in similar settings as well as during other similar eventsin the mesozoic here it is shown that the deposition of organic richsediments during oceanic anoxic event 1b was a consequence of theenhanced productivity favoured by upwelling and by riverine nutrientinput or aeolian fertilization of the euphotic zone depending ongeographical location slope instability processes resulted in the transfer ofpart of these organic rich sediments from the shelf to deep sea depocentres asmud laden organic rich turbidites especially in the northern north atlantic the so called black shales are much more varied than their name implies the end product of sedimentation during an oceanic anoxic event at aparticular location is commonly the result of several equi nal processes actingon a local scale rather than the direct result of basinal or even globalmechanisms keywords aptian albian kilian event north atlantic oae 1b oceandrilling program oceanic anoxic event paquier event

earthquake ground motion estimation using strong motion records a review of equations for the estimation of peak ground acceleration and response spectral ordinates abstract engineering seismology is the link between earth sciences and engineering the main input of engineering seismology in engineering design are loading conditions which must satisfy certain conditions regarding their level and frequency of occurrence during the lifetime of a structure one method for estimating these loading conditions is through equations based on strong ground motion recorded during previous earthquakes these equations have a handful of independent parameters such as magnitude and source to site distance and a dependent parameter such as peak ground acceleration pga or spectral acceleration and the coefficients in the equation are usually found by regression analysis this review examines such equations in terms of data selection accelerogram processing techniques of the strong motion records used to construct the equations the characterisation of earthquake source travel path and local site used and regression techniques employed to find the final equations it is found that little agreement has been reached in the past 30 years of ground motion estimation relation studies workers have chosen their techniques based on the available data which varies greatly with geographical region also it is noted that there is a need to include more independent parameters into ground motion estimation equations if the large uncertainties associated with such equations are to be significantly reduced the data required to do this is unfortunately scarce

zircon 4he 3he thermochronometry abstract multiple thermochronometric methods are often required to constrain time continuous rock exhumation for studying tectonic processes or development of km scale topography at earth s surface here we explore 4he 3he thermochronometry of zircon as a method for constraining continuous time temperature t t paths of individual samples through a temperature range that is complementary to methods such as 40ar 39ar thermochronometry of k feldspar and 4he 3he thermochronometry of apatite for different cooling rates and diffusion domain size the temperature sensitivity of zircon 4he 3he thermochronometry ranges from slightly less than 100 c to slightly greater than 250 c a typical sample provides continuous thermal constraints over 100 c within that range outside these temperatures 4he in zircon will either be quantitatively retained or completely lost by volume diffusion as proof of concept we present stepwise release 4he 3he spectra and associated u and th concentration maps measured by laser ablation icp ms analysis of individual crystal aliquots of fish canyon tuff fct zircon and of a more complex setting in the sierra nevada batholith that experienced reheating from a proximal basaltic intrusion the little devil s postpile ldp the fct zircon 4he 3he release spectra are consistent with a 4he spatial distribution dominated by alpha ejection from crystal surfaces the spatial distributions of u and th measured in the same crystals do not substantially influence 4he 3he release spectra that are predicted for the known thermal history even when incorporating spatially variable diffusivity due to accumulation of radiation damage conversely the ldp 4he 3he release spectra are strongly influenced by the observed parent nuclide zonation a three dimensional 3d numerical model of 4he production and diffusion which incorporates crystal geometry u and th zonation and spatially variable he diffusion kinetics substantially improves the fit between measured and modeled 4he 3he release spectra for the independently known thermal history of the sample we conclude that zircon 4he 3he thermochronometry provides accurate thermal constraints through geologic time but certain applications of this technique may require 3d numerical modeling approaches

equivalent point source modeling of moderate to large magnitude earthquakes and associated ground motion saturation effects we modeled the source and attenuation attributes of well recorded m6 earthquakes based on the equivalent point source approach with the goal of determin ing how to treat ground motion saturation effects within this context we consider ground motions as originating from an equivalent point source and mimic finite fault effects by treating the motion as emanating from a virtual point not a real point on the fault rupture such that ground motions are correctly predicted at close distances this is achieved by using an effective distance metric r d 2 h 2 0 5 in which drup is the closest distance to the rupture and h is a pseudodepth term that accounts for sat uration effects we found that the distance saturation effect is magnitude dependent extending to further distances with increasing magnitude for earthquakes of m 6 we model the saturation term as logh 1 72 0 43 m with a standard deviation of 0 19 in log10 units based on the values obtained from the study earthquakes the apparent source spectra of most m6 earthquakes can be modeled using a simple brune point source model for a few of the m6 earthquakes notably those in california we observed a spectral sag at intermediate frequencies for such earth quakes a two corner point source model provides a better match than the brune model we conclude that an equivalent point source model based on the effective distance concept can successfully predict the average ground motions from m6 earthquakes over a wide distance range including close distances 20 km

cosmogenic 3 he in hematite and goethite from brazilian canga duricrust demonstrates the extreme stability of these surfaces helium isotopes were measured in hematite and goethite samples from several lateritiric duricrusts canga developed on banded iron formations these samples uniformly have high 3 he concentrations which must arise from long periods of cosmic ray exposure from coexisting phases from the quadrilatero ferrifero in east central brazil we determined the ratio of cosmogenic 3 he in hematite to that of 21 ne in quartz to be 3 96 0 19 combined with best current estimates of the 21 ne production rate in quartz this ratio implies a sea level high latitude slhl 3 he production rate in hematite of 68 1 8 1 atoms g yr from the chemical composition we estimate the 3 he production rate in goethite to be 5 higher we use these production rate estimates to interpret 3 he concentrations measured in goethite and hematite from a 10 m depth profile collected from a surface canga in carajas in the amazon basin of brazil we find that the carajas canga has experienced a very low rate of surface erosion 0 16 0 54 m myr over at least the last few millions of years this iron rich canga surface is remarkably resistant to erosion despite its location in a wet tropical environment details of the depth profile suggest that despite its stability the canga has also been internally dynamic translocation of material solution and reprecipitation over million year timescales

hybrid empirical ground motion prediction equations for eastern north america using nga models and updated seismological parameters in the field of earthquake engineering ground motion prediction models are frequently used to estimate the peak ground acceleration pga and the pseudos pectral acceleration psa in regions of the world where ground motion recordings are plentiful such as western north america wna the ground motion prediction equations are obtained using empirical methods in other regions such as eastern north america ena with insufficient ground motion data alternative methods must be used to develop ground motion prediction equations gmpes the hybrid empiri cal method is one such method used to develop ground motion prediction equations in areas with sparse ground motions this method employs the stochastic simulation method to adjust empirical gmpes developed for a region with abundant strong motion recordings in order to estimate strong motion parameters in a region with a sparse database the adjustments take into account differences in the earthquake source wave propagation and site response characteristics between the two regions in this study a hybrid empirical method is used to develop a new gmpe for ena using five new ground motion prediction models developed by the pacific earthquake engineering research center peer for wna a new ena gmpe is derived for a magnitude range of 5 to 8 and closest distances to the fault rupture up to 1000 km ground motion prediction equations are developed for the response spectra pseudoacceleration 5 damped and the pga for hard rock sites in ena the resulting ground motion prediction model developed in this study is compared with two ena ground motion models used in the 2008 national seismic hazard maps as well as with available observed data for ena

hypocenter locations in finite source rupture models we use a database of more than 80 finite source rupture models for more than 50 earthquakes m w 4 1 8 1 with different faulting styles occurring in both tectonic and subduction environments to analyze the location of the hypocenter within the fault and to consider the correlation between hypocenter location and regions of large slip rupture in strike slip and crustal dip slip earthquakes tends to nucleate in the deeper sections of the fault subduction earthquakes do not show this tendency ratios of the hypocentral slip to either the average or the maximum slip show that rupture can nucleate at locations with any level of relative displacement rupture nucleates in regions of very large slip d 2 3 d max in only 16 of the events in regions of large slip 1 3 d max d d max in 35 of the events and in regions of low slip d 1 3 d max in 48 of the events these percentages significantly exceed the percentages of fault area with very large 7 and large 28 slip ruptures that nucleate in regions of low slip however tend to nucleate close to regions of large slip and encounter a zone of very large slip within half the total rupture length applying several statistical tests we conclude that hypocenters are not randomly located on a fault but are located either within or close to regions of large slip

source parameters of earthquakes in eastern and western north america based on finite fault modeling the ground motion from large earthquakes is often predicted based on finite fault modeling in which the fault plane is discretized into small independently rupturing subfaults the radiation from all subfaults is summed at the observation point despite the success of the method in matching observed ground motion char acteristics the physical interpretation of the subfaults has remained largely unclear and a rationale for the choice of the subfault attributes has been lacking two key parameters the subfault size and the maximum slip velocity on the fault govern the amplitude of the source spectrum at intermediate and high frequencies respec tively we determined these key source parameters on an event by event basis for all well recorded moderate to large earthquakes in western north america wna by fitting simulated to observed response spectra we compare the values of these source parameters with those obtained previously for eastern north america ena and the michoacan mexico earthquakes a total of 26 modeled events we find that the characteristic subevent size increases linearly with moment mag nitude in an apparently deterministic manner the subevent size relationship obtained for wna is not statistically different from that obtained for ena in both regions the subevent size follows the trend of log dl 2 0 4 m 4 m 8 where dl is the subfault size in km this trend agrees well with independent studies by somerville et al 1999 and aki 1992 in which the characteristic size of the patches asperities or barriers on earthquake faults was determined these results indi cate that large earthquakes should be viewed as a sequence of smaller events that comprise the large rupture interestingly the characteristic size of these constituent small events appears to be directly related to the size of the overall rupture the slip velocities determined for all 26 earthquakes vary in a narrow range from about 0 25 to 0 60 m sec with a mean of 0 40 m sec and standard deviation of 0 09 m sec the slip velocities for the ena events are distributed randomly over this range while those for the wna region appear to exhibit a decreasing trend with increasing magnitude our results indicate that a generic region independent earthquake source model for engineering prediction of strong ground motions can be developed

u and th zonation in fish canyon tuff zircons implications for a zircon u th he standard the inability to accurately determine the distribution of u and th in zircon crystals analysed using u th he is a major source of error and limits the confidence in subsequent data interpretation the fish canyon tuff fct zircon standard shows u th he age reproducibility in excess of 10 we have tested the extent to which this is due to u and th zonation using a combination of cathodoluminescence and ion probe analysis of a population of fct zircons primarily we find that fct zircons exhibit extreme u and th zonation and the population has large inter crystalline variability furthermore the net cathodoluminescence intensity from the fct zircons is negatively correlated with u and th concentration allowing cathodoluminescence emission to be used as a proxy for u and th zonation this correlation was exploited to constrain the u and th zonation within the crystal population and to show that the poor age reproducibility of the fct zircons is consistent with the observed zonation

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

incorporating 3 d parent nuclide zonation for apatite 4he 3he thermochronometry an example from the appalachian mountains the ability to constrain km scale exhumation with apatite 4he 3he thermochronometry is well established and the technique has been applied to a range of tectonic and geomorphic problems however multiple sources of uncertainty in specific crystal characteristics limit the applicability of the method especially when geologic problems require identifying small perturbations in a cooling path here we present new 4he 3he thermochronometric data from the appalachian mountains which indicate significant parent nuclide zonation in an apatite crystal using la icpms measurements of u and th in the same crystal we design a 3 d model of the crystal to explore the effects of intra crystal variability in radiation damage accumulation we describe a numerical approach to solve the 3 d production diffusion equation using our numerical model and a previously determined time temperature path for this part of the appalachians we find excellent agreement between predicted and observed 4he 3he spectra our results confirm this time temperature path and highlight that for complex u and th zonation patterns 3 d numerical models are required to infer an accurate time temperature history in addition our results provide independent and novel evidence for a radiation damage control on diffusivity the ability to exploit intra crystal differences in 4he diffusivity i e temperature sensitivity greatly increases the potential to infer complex thermal histories

the influence of burial heating on the u th he system in apatite grand canyon case study article history thermochronological data can constrain the cooling paths of rocks exhumed through the uppermost 1 2 km of earth s crust and have thus been pivotal in illuminating topographic development over timescales 0 1 ma however in some cases different methods have led to conflicting conclusions about timing of valley scale exhumation here we investigate the case of western grand canyon usa where different thermochronological datasets have been interpreted to record very different timings of canyon incision 70 ma versus 5 ma we present a method to assess key assumptions in these constraints and demonstrate that burial heating conditions of basement rocks in the mesozoic can result in incomplete annealing of radiation damage in apatite in turn this has a dramatic effect on the temperature sensitivity of the apatite u th he system and its ability to record post burial exhumation the possibility of incomplete annealing resolves the apparent conflict in time temperature paths inferred over the last 70 ma although it requires temperatures during burial that are lower than predicted by apatite fission track data a refinement of parameters that prescribe the kinetics of damage annealing and related control on 4 he diffusivity in apatite would account for this discrepancy specifically if alpha recoil damage anneals at a lower rate than fission tracks at a given temperature these effects will be important for any application of the apatite u th he system in geologic settings that experienced prolonged residence 10 ma between 50 150 c the approaches developed here provide means to assess these effects

ground motion prediction equations for eastern north america from a referenced empirical approach implications for epistemic uncertainty abstract i outline a referenced empirical approach to the development of ground motion prediction equations gmpes the technique is illustrated by using it to develop gmpes for eastern north america ena the approach combines the ena ground motion database with the empirical prediction equations of boore and atkinson 2008 for the reference region of western north america wna the referenced empirical approach provides gmpes for ena that are in agreement with regional ground motion observations while being constrained to follow the overall scaling behavior of ground motion that is observed in better instrumented active tectonic regions they are presented as an alternative to the commonly used stochastic ground motion relations for ena the motivation of the article is not to supplant stochastic gmpes but is rather to consider other approaches that might shed light on their epistemic uncertainty differences between the referenced empirical gmpes of this study and the stochastic gmpes of atkinson and boore 2006 along with inconsistencies between both of these studies and inferences based on intensity observations suggest that uncertainty in median enagmpes is about a factor of 1 5 2 for m 5 at distances from 10 to 70 km uncertainty is greater than a factor of 2 for large events m 7 at distances within 10 km of the source it may be that saturation effects not modeled in the stochastic predictions but inferred from observations in other regions cause overestimation of near source amplitudes from large events in atkinson and boore 2006 on the other hand these saturation effects cannot be directly verified in ena data differences in predictions according to the approach taken are also significant at distances from 40 to 150 km due to uncertainty in the shape of the attenuation function that will be realized in future earthquakes

improved spatial resolution of elemental maps through inversion of la icp ms data laser ablation inductively coupled plasma mass spectrometry la icp ms provides the spatial distribution of elements within crystals and therefore can constrain the rates of geological processes spatial resolution of la icp ms is limited by the requirement to ablate sufficient material to surpass the detection limit of the instrument too little material and the concentration cannot be measured too much material from the same spatial location and the possibility of depth dependent variations in concentration increases because of this requirement and typical analytical setup this commonly places a lower bound on the diameter of an ablation spot size of approximately 20 m for elements with ppm concentration here we present a means to achieve sub spot size resolution using inverse methods we discretize the space sampled in an analysis into pixels and note that the average concentration of the pixels sampled by a spot equals the measured concentration as multiple overlapping spots sample some of the same pixels we can combine discrete expressions for each spot as a system of linear equations through linear inversion with smoothness constraints we can solve for unknown pixel concentrations we highlight this approach with two natural examples in which diffusive processes are important magmatic ascent speeds and u th he noble gas thermochronometry in these examples accurate results require that the true concentration gradients can be recovered from la icp ms data we show that the ability to infer rapid rates of magma ascent is improved from months to weeks and that we are able to interpret previously un interpretable thermochronometric data

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

quantifying the diffusion kinetics and spatial distributions of radiogenic 4he in minerals containing proton induced 3he apatite titanite and olivine samples were bombarded with a 150 mev proton beam to produce 10 8 atoms mg of spallation 3he high precision stepped heating experiments were then performed in which the artificial 3he and for apatite and titanite the natural radiogenic 4he were measured to characterize the diffusive behavior of each isotope helium 3 diffusion coefficients are in excellent agreement with concurrently and or previously determined he diffusion coefficients for each mineral our results indicate that proton induced 3he is uniformly distributed and that radiation damage associated with a proton fluence of 5 x 10 14 protons cm 2 does not cause noticeable changes in 4he diffusion behavior in at least apatite and titanite proton induced 3he can therefore be used to establish he diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural 4he distribution is inhomogeneous in addition step heating 4he 3he analysis of a mineral with a uniform synthetic 3he concentration provides a means by which a natural 4he distribution can be determined

empirical stochastic ground motion prediction for eastern north america an alternative approach based on a hybrid empirical model is utilized to predict the ground motion relationship for eastern north america ena in this approach a stochastic model is first used to derive modification factors from the ground motions in western north america wna to the ground motions in ena the ground motion parameters are then estimated to develop an empirical attenuation relationship for ena using empirical ground motion relationships from wna w e develop an empirical stochastic source model for both regions to obtain ground mo tions at different magnitude distance range of interest at short distances r 30 km and large magnitudes mw 6 4 an equivalent point source model is carried out to consider the effect of finite fault modeling on the ground motion parameters source focal depth and brune stress drop are assumed to be magnitude dependent we choose three well defined empirical attenuation relationships for wna to com pare the empirical ground motion processes between the two regions a composite functional attenuation form is defined and in turn a nonlinear regression analysis is performed by using a genetic algorithm ga for a wide range of magnitudes and distances to develop an empirical attenuation relationship from the stochastic ground motion estimates in ena the empirical stochastic attenuation relationship for hor izontal peak ground acceleration and spectral acceleration are applicable to earth quakes of mw 5 0 8 2 at distances of up to 1000 km the resulting attenuation model developed in this study is compared with those used in the 2002 national seismic hazard maps derived in the 2003 electric power research institute studies and re corded in ena the comparison of the results to the other attenuation functions and the available ena data show a reasonable agreement for the ena ground motions

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

low temperature anisotropic diffusion of helium in zircon implications for zircon u th he thermochronometry abstract in the last decade the zircon u th he zhe thermochronometer has been applied to a variety of geologic problems although bulk diffusion coefficients for he in zircon are available from laboratory step heating experiments little is known about the diffusion mechanism s and their dependence on the crystallographic structure of zircon here we investigate the diffusion of he in perfectly crystalline zircon using atomistic simulation methods that provide insights into the structural pathways of he migration in zircon empirical force fields and quantum mechanical calculations reveal that the energy barriers for he diffusion are strongly dependent on structure the most favorable pathway for he diffusion is the 0 0 1 direction through the open channels parallel to the c axis e 001 13 4 kj mol 1 activation energy for tracer diffusion of a he atom along 0 0 1 in contrast energy barriers are higher in other directions where narrower channels for he diffusion are identified such as 1 0 0 1 0 1 and 1 1 0 e of 44 8 101 7 and 421 3 kj mol 1 respectively molecular dynamics simulations are in agreement with these results and provide additional insight in the diffusion mechanisms along different crystallographic directions as well as the temperature dependence below the closure temperature of he in zircon t c 180 c reiners p w spell t l nicolescu s and zanetti k a 2004 zircon u th he thermochronometry he diffusion and comparisons with ar 40 ar 39 dating geochim cosmochim acta 68 1857 1887 diffusion is anisotropic as he moves preferentially along the 0 0 1 direction and calculated tracer diffusivities along the two most favorable directions differ by approximately five orders of magnitude d 001 d 100 10 5 at t 25 c above this temperature he atoms start to hop between adjacent 0 0 1 channels along 1 0 0 and 0 1 0 directions perpendicular to the c axis the diffusion along 1 0 0 and 0 1 0 is thermally activated such that at higher temperatures he diffusion in zircon becomes nearly isotropic d 001 d 100 10 at t 580 c these results suggest that the anisotropic nature of he diffusion at temperatures near the closure temperature should be considered in future diffusivity experiments furthermore care should be taken when making geologic interpretations e g exhumation rates timing of cooling etc from this thermochronometer until the effects of anisotropic diffusion on bulk ages and closure temperature estimates are better quantified

a spatial random field model to characterize complexity in earthquake slip 1 finite fault source inversions reveal the spatial complexity of earthquake slip over the fault plane we develop a stochastic characterization of earthquake slip complexity based on published finite source rupture models in which we model the distribution of slip as a spatial random field the model most consistent with the data follows a von karman autocorrelation function acf for which the correlation lengths a increase with source dimension for earthquakes with large fault aspect ratios we observe substantial differences of the correlation length in the along strike a x and downdip a z directions increasing correlation length with increasing magnitude can be understood using concepts of dynamic rupture propagation the power spectrum of the slip distribution can also be well described with a power law decay i e a fractal distribution in which the fractal dimension d remains scale invariant with a median value d 2 29 0 23 while the comer wave number k c which is inversely proportional to source size decreases with earthquake magnitude accounting for larger slip patches for large magnitude events our stochastic slip model can be used to generate realizations of scenario earthquakes for near source ground motion simulations

the attenuation of fourier amplitudes for rock sites in eastern north america we develop an empirical model of the decay of fourier amplitudes for earthquakes of m 3 6 recorded on rock sites in eastern north america and discuss its implications for source parameters attenuation at distances from 10 to 500 km may be adequately described using a bilinear model with a geometric spreading of 1 r 1 3 to a transition distance of 50 km with a geometric spreading of 1 r 0 5 at greater distances for low frequencies and distances less than 50 km the effective geometric spreading given by the model is perturbed using a frequency and hypocentral depth dependent factor defined in such a way as to increase amplitudes at lower frequencies near the epicenter but leave the 1 km source amplitudes unchanged the associated anelastic attenuation is determined for each event with an average value being given by a regional quality factor of q 525f 0 45 this model provides a match on aver age between the known seismic moment of events and the inferred low frequency spectral amplitudes at r 1 km obtained by correcting for the attenuation model the inferred brune stress parameters from the high frequency source terms are about 600 bars 60 mpa on average for events of m 4 5

diffusion of helium in radiation damaged zircon abstract diffusion of helium was characterized in natural zircon that had been implanted with kr at a range of energies to simulate the effects of alpha recoil in natural radiation damage polished slabs of zircon oriented either normal or parallel to c were implanted with kr ions at a series of energies to produce a damaged region 1 m in thickness then implanted with 100 kev 3he at a dose of 1 1015 3he cm2 which placed the 3he within the region damaged by the kr ion implantation the implanted zircons were annealed isothermally in pt capsules in 1 atm furnaces at temperatures ranging from 51 to 252 c and times ranging from 15 min to 3 weeks 3he distributions following experiments were measured with nuclear reaction analysis using the reaction 3he d p 4he for diffusion in zircon normal to c we obtain the following arrhenius relation d 1 7 10 8 exp 71 2 kj mol 1 rt m2 sec 1 this activation energy for diffusion is about half of the value for he diffusion in zircon from the same sample locality but without kr implantation measured with an otherwise similar experimental and analytical approach cherniak et al 2009 he diffusivities in the kr implanted material are also significantly faster further he diffusivities normal and parallel to c in the kr implanted zircon are similar in contrast to the marked diffusional anisotropy with differences of two orders of magnitude for diffusion normal and parallel to c observed for he diffusion in this zircon in samples not implanted with kr these data indicate that heavily damaged zircon will have very limited retentivity of helium only those zircons larger than a few hundred m will have mean closure temperatures exceeding typical earth surface temperatures mean closure temperatures for he in highly damaged zircon will be about 200 c lower than those for relatively undamaged zircon at 200 c equivalent amounts of he will be lost from severely damaged zircon at a rate about a million times faster than from relatively undamaged zircon for retentivity of he comparable to that for low damage zircon at 200 c the severely damaged zircon would require residence temperatures of 10 c

is apatite u th zonation information necessary for accurate interpretation of apatite u th he thermochronometry data abstract new u th and ce concentration maps were acquired by la icpms for 70 apatites from 18 cratonic basement samples from the canadian shield to characterize the nature and variability in apatite u th zonation all apatites are zoned in effective u concentration eu with 80 exhibiting modest zoning that varies from a factor of 1 2 to 2 4 zonation patterns include those with a general eu decrease from core to rim 25 a core to rim eu increase 35 and patchy or irregularly shaped eu distributions 40 most samples consist of individual apatites with markedly different and opposing eu profiles cathodoluminescence cl images were obtained for 258 apatites in 25 samples comparison of eu and cl patterns reveals no consistent relationships suggesting that cl is not a reliable proxy for apatite eu zonation we explore the implications of eu zonation for the interpretation of apatite u th he ahe data by comparing the age predictions for representative and endmember apatite eu profiles with those for unzoned apatites we focus on thermal histories that should magnify eu zonation effects including slow monotonic cooling extended he partial retention zone heprz residence and protracted reheating and cooling application of incorrect ejection correction f t factors different he concentration gradients and variable intracrystalline retentivity due to heterogeneous radiation damage may cause the ahe dates for zoned and unzoned apatites to differ in our dataset the magnitude of the f t effect is by simulating zoned apatite suites from representative and endmember samples we find that eu zoning adds modest age dispersion to most samples the commonly opposing eu profiles for individual apatites in most samples have different effects on the predicted age and partially cancel each other out to reduce the predicted age difference at the sample level higher predicted age differences between zoned and unzoned samples generally correlate with greater sample scatter the age deviations generally fall within the 15 uncertainty range that we commonly apply for sample ahe dates except in unusual circumstances it appears unlikely that the unzoned apatite assumption will lead to misinterpretation of ahe datasets thus precluding the need to routinely acquire apatite eu zonation information as part of ahe dating studies

thermal history of an early paleozoic epithermal deposit constraints from 40ar 39ar and u th he thermochronology at zhengguang eastern central asian orogenic belt abstract the zhengguang epithermal au zn deposit located in heilongjiang province ne china is an early paleozoic intermediate sulfidation epithermal deposit which is adjacent to the duobaoshan and tongshan porphyry cu deposits in the duobaoshan magmatic arc eastern central asian orogenic belt caob our new 40ar 39ar dating presents plateau ages of 276 9 1 2 ma mswd 1 5 for adularia and 265 7 1 2 ma mswd 3 5 for illite these ages are clearly younger than the mineralization age of zhengguang 480 ma and therefore represent a post ore event which reset the adularia and illite argon systems the resetting event could be related to post collision of xing an block and songliao xilinhot block the weighted mean of zircon u th he ages zhe and apatite u th he ages ahe from the same dacite porphyry with illite dating sample are 192 10 ma mswd 2 2 and 98 8 5 3 ma mswd 2 1 respectively the zhe age 190 ma indicates a tectonothermal resetting event possibly related to the development of tongshan fault whereas the ahe age 100 ma likely reflects 3 km deep burial at zhengguang the intra sample variations of u th he ages for zircon grains are mainly due to radiation damage while those for apatite are unknown we argue that the post ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the paleo pacific plate could facilitate burial and preservation of the epithermal and by inference porphyry deposits in ne china considering the complex collisional and amalgamation history in this area we believe that there is exploration potential for ancient porphyry and epithermal deposits within the eastern section of the caob

sedimentation of lithogenic particles in the deep ocean abstract investigation of lithogenic particles collected by sediment traps in open ocean stations revealed that the sediment flux increased linearly with depth in the water column this rate of increase decreased with distance of the station from the continent it was largest at the panama basin station and almost negligible at the e hawaii abyssal plain station at the panama basin station smectite flux increased with depth we suggest that smectite resuspended from bottom sediments of the continental slope west of the sediment trap station is advected by easterly deep currents and the suspended particles are then possibly entrapped by large settling particles on the other hand the flux of hemipelagic clay particles kaolinite and chlorite was nearly constant at all depths this can be explained by incorporation of these particles in fecal pellets which then settle from the surface water at the demerara abyssal basin station flux of illite and chlorite particles increased with depth and the flux of smectite was constant a sudden increase of the flux of illite and chlorite was observed near the bottom traps at the sohm abyssal plain station the flux of quartz and feldspar was 10 to 15 of the clay flux

tracking the evolution of large volume silicic magma reservoirs from assembly to supereruption the most voluminous silicic volcanic eruptions in the geological past were associated with caldera collapses above giant silicic magma reservoirs the thermal evolution of these subcaldera magma reservoirs controls the volume of eruptible magma and eruptive style here we combine high precision zircon u pb geochronology trace element analyses of the same mineral grains and mass balance modeling of zircon trace element compositions allowing us to track the thermal and chemical evolution of the oligocene fish canyon tuff magma reservoir colorado united states as a function of absolute time systematic compositional variations in u pb dated zircons record 440 k y of magma evolution an early phase of volumetric growth was followed by a period of cooling and crystallization during which the fish canyon magma approached complete solidifi cation subsequent remelting due to underplated andesitic recharge magmas began 219 45 k y prior to eruption and led to the generation of 5000 km3 of eruptible crystal rich 45 vol dacite age equivalent but compositionally different zircons in an andesite enclave from late erupted fish canyon tuff tie the growth and thermal evolution of the upper crustal reservoir to a lower crustal magma processing zone our results demonstrate that the combination of high precision dating and trace element analyses of accessory zircons can reveal invaluable information about the chemical and thermal histories of silicic magmatic systems and provides critical input parameters for fl uid dynamic modeling

a euxinic southern north atlantic ocean during the cenomanian turonian oceanic anoxic event abstract during mid cretaceous times large amounts of organic carbon corg became sequestered in black shales possibly due to oceanic anoxic events characterized by the development of an extended oxygen minimum zone omz here we provide the first direct evidence for an open ocean omz in the cenomanian turonian c t southern north atlantic and in fact show that the base of the photic zone was euxinic as revealed by molecular fossils from photosynthetic green sulfur bacteria in c t black shales this together with evidence for bottom water anoxia and accumulation of redox sensitive trace metals and hydrogen rich organic matter indicates a continuously euxinic water column concurrent with the high corg accumulation rates which are 15 150 times greater in the southern than in the northern north atlantic and the low biological productivity this suggests that preservation controlled the accumulation of corg in c t black shales

westernmost grand canyon incision testing thermochronometric resolution the timing of carving of grand canyon has been debated for over 100 years with competing endmember hypotheses advocating for either a 70 ma old or 6 ma young grand canyon several geological constraints appear to support a young canyon model but thermochronometric measures of cooling history and corresponding estimates of landscape evolution have been in debate in particular 4he 3he thermochronometric data record the distribution of radiogenic 4he from the 238u 235u and 232th decay series within an individual apatite crystal and thus are highly sensitive to the thermal history corresponding to landscape evolution however there are several complicating factors that make interpreting such data challenging in geologic scenarios involving reheating here we analyze new data that provide measures of the cooling of basement rocks at the base of westernmost grand canyon and use these data as a testbed for exploring the resolving power and limitations of 4he 3he data in general we explore a range of thermal histories and find that these data are most consistent with a young grand canyon a problem with the recovered thermal history however is that burial temperatures are under predicted based on sedimentological evidence a solution to this problem is to increase the resistance of alpha recoil damage to annealing thus modifying he diffusion kinetics allowing for higher temperatures throughout the thermal history this limitation in quantifying radiation damage and hence crystal retentivity introduces non uniqueness to interpreting time temperature paths in rocks that resided in the apatite helium partial retention zone for long durations another source of non uniqueness is due to unknown u and th distributions within crystals we show that for highly zoned with a decrease in effective u of 20 ppm over the outer 80 of the radius of the crystal the 4he 3he data could be consistent with an old canyon model to reduce this non uniqueness we obtain u and th zonation information for separate crystals from the same rock sample through la icp ms analysis the observed u and th distributions are relatively uniform and not strongly zoned thus supporting a young canyon model interpretation of the 4he 3he data furthermore we show that for the mapped zonation the difference between predicted 4he 3he data for a uniform crystal and a 3d model of the crystal are minimal highlighting that zonation is unlikely to lead us to falsely infer an old grand canyon

impact thermochronology and the age of haughton impact structure canada 1 most successful efforts to determine the ages of impact events are based on the isotope geochronology of crystalline or glassy impact melts studies of impact sites on earth show that many form without significant melt production meaning that traditional geochronologic approaches can yield unsatisfying results we describe here an alternative approach based on theoretical calculations that even brief thermal events related to impact can reset the isotopic systematics of unmelted target rocks thermochronometers based on the production of radiogenic 4he in accessory minerals are particularly amenable to complete resetting by impact and should yield robust impact ages if helium systematics are not further disturbed during post impact thermal events we illustrate the utility of this method through a presentation of a new zircon u th he date for the haughton impact structure canada of 23 5 2 0 ma

empirical attenuation of ground motion spectral amplitudes in southeastern canada and the northeastern united states a database of 1700 digital seismograms from 186 earthquakes of mag nitude mn 2 5 5 6 that occurred in southeastern canada and the northeastern united states from 1990 to 2003 was compiled maximum likelihood regression analysis of the database was performed to determine a model for the attenuation of fourier spectral amplitudes for the shear window for the vertical and horizontal component of motion for frequencies from 0 2 to 20 hz fourier amplitudes follow a hinged trilinear attenuation model fourier spectral amplitudes decay as r 1 3 where r is hypocentral distance within 70 km of the source there is a transition zone from 70 to 140 km as the direct waves are joined by strong postcritical reflections where the attenuation is described as r 0 2 spectral amplitudes actually increase with distance in this range for low frequencies beyond 140 km the attenuation is well described by r 0 5 corresponding to geometric spreading in two dimensions the associated model for the regional quality factor for frequencies greater than 1 hz can be ex pressed as q 893f 032 q can be better modeled over a wider frequency range 0 2 20 hz by a polynomial expression log q 3 052 0 393 log f 0 945 log f 2 0 327 log f 3 the polynomial expression accommodates the observation that q values are at a minimum about 1000 near 1 hz and rise at both lower and higher frequencies correction factors for the spectral amplitude model that describe the effects of focal depth on the amplitudes and their attenuation are developed using the subset of events with known focal depth the attenuation model is similar to that determined from an earlier study with more limited data atkinson and mereu 1992 but the enlarged database indicates more rapid near source amplitude decay and higher q the attenuation model is used to play back attenuation effects to determine the apparent source spectrum for each earthquake in the database and hence determine moment magnitude m and brune stress drop the events have moment magnitude in the range from 2 5 to 5 stress drop increases with moment magnitude for events of m 4 3 then appears to attain a relatively constant level in the range from 100 to 200 bars for the larger events as previously noted in atkinson 1993b the results of this study provide a useful framework for improving regional ground motion relations in eastern north america they further our understanding of attenuation in the region through analysis of an enlarged ground motion database in particular the inclusion of the three component broadband data gathered over the last decade allows extension of attenuation models to both horizontal and vertical components over a broad frequency range 0 2 20 hz

simulating strong motions of large earthquakes using recordings of small earthquakes the loma prieta mainshock as a test case abstract a simple method is developed for predicting ground motions for future large earthquakes for specific sites by summing and filtering recordings of adjacent small earthquakes this method is tested by simulating strong motion records for the loma prieta earthquake m 7 0 using aftershocks m 3 7 to 4 0 recorded at the same sites i use an asperity rupture model where the rms stress drop averaged over the fault plane is constant with moment the observed spectra indicate that stress drop remains constant from the m 3 aftershocks up to the m 7 mainshock about six orders of magnitude in seismic moment each simulation sums the seismogram of one aftershock with time delays appropriate for propagating rupture and incorporates directivity and site response the simulation scales the spectrum in accordance with a constant stress drop 2 source model in this procedure the high frequency energy of the aftershock sum above the corner frequency of the aftershock is not reduced when it is convolved with the mainshock slip velocity function unlike most previous methods of summation for most cases the spectra 0 6 to 20 hz peak accelerations and durations of the simulated mainshock records are in good agreement with the observed strong motion records even though only one aftershock waveform was used in each simulation this agreement indicates that the response of these soil sites is essentially linear for accelerations up to about 0 3 g the summed aftershock records display the same site dependent values of f max as the mainshock records implying that f max is a site effect rather than a property of the mainshock rupture process

evaluation of ground motion models for usgs seismic hazard forecasts induced and tectonic earthquakes in the central and eastern united statesevaluation of gmms for usgs seismic hazard forecasts

4he 3he thermochronometry using classical diffusion theory we present a mathematical technique for the determination of 4he concentration profiles in minerals this approach should prove useful for constraining the low temperature cooling histories of individual samples and for correcting u th he ages for partial diffusive loss the calculation assumes that the mineral of interest contains an artificially produced and uniform distribution of 3he obtained by proton irradiation shuster et al earth planet sci lett 217 2004 19 32 in minerals devoid of natural helium this isotope allows measurement of he diffusion coefficients in minerals with measurable radiogenic he it permits determination of 4he profiles arising during ingrowth and diffusion in nature the 4he profile can be extracted from stepwise degassing experiments in which the 4he 3he ratio is measured the evolution of the 4he 3he ratio as a function of cumulative 3he released can be compared with forward models to constrain the shape of the profile alternatively we present a linear inversion that can be used to directly solve for the unknown 4he distribution the inversion incorporates a standard regularization technique to filter the influence of random measurement errors on the solution using either approach we show that stepwise degassing data can yield robust and high resolution information on the 4he profile profiles of radiogenic he are a sensitive function of the time temperate t t path that a cooling sample experienced thus by step heating a proton irradiated sample it is possible to restrict the sample s acceptable t t paths the sensitivity of this approach was explored by forward modeling 4he profiles resulting from a range of realistic t t paths using apatite as an example results indicate that 4he profiles provide rich information on t t paths especially when the profiles are coupled with u th he cooling ages on the same sample samples that experienced only moderate diffusive loss have 4he concentration profiles that are rounded at the edge but uniform in the core of the diffusion domain such profiles can be identified by nearly invariant 4he 3he ratios after the first few to few tens of percent of 3he have been extracted by step heating we show how such data can be used to correct u th he ages for partial diffusive loss

a composite source model for computing realistic synthetic strong ground motions a composite source model is presented for convolution with synthetic green s functions in order to synthesize strong ground motions due to a complex rupture process of a large earthquake subevents with a power law distribution of sizes are located randomly on the fault each subevent radiates a displacement pulse with the shape of a brune s pulse in the far field at a time determined by a constant rupture velocity propagating from the hypocenter thus all the input parameters have a physical basis we simulate strong ground motions for event station pairs that correspond to records obtained in mexico by the guerrero accelerograph network the synthetic accelerations velocities and displacements have realistic amplitudes durations and fourier spectra

the provenance of low calcic black shales the elemental concentration of sedimentary rocks depends on the varying reactivity of each element as it goes from the source through weathering deposition diagenesis lithification and even low rank metamorphism however non reactive components of detrital particles ideally are characteristic of the original igneous source and thus are useful in provenance studies to determine the source of detrital granitic and volcanic components of low calcic 1 caco3 marine black shales the concentrations of apparently non reactive i e unaffected by diagenetic redox and or low rank metamorphic processes trace elements were examined using standard trace element discrimination diagrams developed for igneous rocks the chemical data was obtained by neutron activation analyses of about 200 stratigraphically well documented black shale samples from the cambrian through the jurassic a la th sc ternary diagram distinguishes among contributions from the upper and bulk continental crust and the oceanic crust taylor and mclennan 1985 all the low calcic black shales cluster within the region of the upper crust th hf co ternary diagrams also are commonly used to distinguish among the upper and bulk continental crust and the oceanic crust taylor and mclennan 1985 as co is redox sensitive in black shale environments it was necessary to substitute an immobile element i e example rb in the diagram with this substitution of black shales all cluster in the region of the upper continental crust to determine the provenance of the granitic component pearce et al 1984 plots of ta vs yb and rb vs yb ta shows a cluster at the junction of the boundaries separating the volcanic arc granite vag syn collision granite syn colg and within plate granite wpg fields the majority fall within the vag field there are no occurrences of ocean ridge granite org the minimal contribution of basalts to marine black shales is confirmed by the ternary wood diagram th hf 3 ta wood et al 1979 the black shales plot in a cluster in a high th region outside the various basalt fields which suggests contribution from the continental crust

a constant stress drop model for producing broadband synthetic seismograms comparison with the next generation attenuation relations broadband 0 1 20 hz synthetic seismograms for finite fault sources were produced for a model where stress drop is constant with seismic moment to see if they can match the magnitude dependence and distance decay of response spec tral amplitudes found in the next generation attenuation nga relations recently developed from strong motion data of crustal earthquakes in tectonically active re gions the broadband synthetics were constructed for earthquakes of m 5 5 6 5 and 7 5 by combining deterministic synthetics for plane layered models at low fre quencies with stochastic synthetics at high frequencies the stochastic portion used a source model where the brune stress drop of 100 bars is constant with seismic mo ment the deterministic synthetics were calculated using an average slip velocity and hence dynamic stress drop on the fault that is uniform with magnitude one novel aspect of this procedure is that the transition frequency between the deterministic and stochastic portions varied with magnitude so that the transition frequency is inversely related to the rise time of slip on the fault the spectral accelerations at 0 2 1 0 and 3 0 sec periods from the synthetics generally agreed with those from the set of nga relations for m 5 5 7 5 for distances of 2 100 km at distances of 100 200 km some of the nga relations for 0 2 sec spectral acceleration were substantially larger than the values of the synthetics for m 7 5 and m 6 5 earthquakes because these relations do not have a term accounting for q at 3 and 5 sec periods the synthetics for m 7 5 earth quakes generally had larger spectral accelerations than the nga relations although there was large scatter in the results from the synthetics the synthetics showed a sag in response spectra at close in distances for m 5 5 between 0 3 and 0 7 sec that is not predicted from the nga relations

earthquake ground motion prediction equations for eastern north america new earthquake ground motion relations for hard rock and soil sites in eastern north america ena including estimates of their aleatory uncertainty vari ability have been developed based on a stochastic finite fault model the model incorporates new information obtained from ena seismographic data gathered over the past 10 years including three component broadband data that provide new in formation on ena source and path effects our new prediction equations are similar to the previous ground motion prediction equations of atkinson and boore 1995 which were based on a stochastic point source model the main difference is that high frequency amplitudes f 5 hz are less than previously predicted by about a factor of 1 6 within 100 km because of a slightly lower average stress parameter 140 bars versus 180 bars and a steeper near source attenuation at frequencies less than 5 hz the predicted ground motions from the new equations are generally within 25 of those predicted by atkinson and boore 1995 the prediction equations agree well with available ena ground motion data as evidenced by near zero average residuals within a factor of 1 2 for all frequencies and the lack of any significant residual trends with distance however there is a tendency to positive residuals for moderate events at high frequencies in the distance range from 30 to 100 km by as much as a factor of 2 this indicates epistemic uncertainty in the prediction model the positive residuals for moderate events at 100 km could be eliminated by an increased stress parameter at the cost of producing negative residuals in other magnitude distance ranges adjustment factors to the equations are provided that may be used to model this effect

evaluation of models for earthquake source spectra in eastern north america there have been several relations proposed in the last few years to describe the amplitudes of ground motion in eastern north america ena these relations differ significantly in their assumptions concerning the amplitude and shape of the spectrum of energy radiated from the earthquake source in this article we compare ground motions predicted for these source models against the sparse ena ground motion database the source models evaluated include the two comer models of boatwright and choy 1992 atkinson 1993a haddon 1996 and joyner 1997a b and the one comer model of brune as independently implemented by frankel et al 1996 and by toro et al 1997 the database includes data from ena mainshocks of m 4 and historical ena earthquakes of m 5 5 for a total of 110 records from 11 events of 4 m 7 3 all recorded on rock we also include 24 available rock records from 4 large earthquakes in other intraplate regions con clusions are checked to determine whether they are sensitive to the addition of these non ena data the atkinson source model as implemented in the ground motion relations of atkinson and boore 1995 is the only model that provides unbiased ground motion predictions over the entire period band of interest from 0 1 to 10 sec the source models of frankel et al 1996 toro et al 1997 and joyner 1997a b all provide unbiased ground motion estimates in the period range from 0 1 to 0 5 sec but over estimate motions at periods of 1 to 10 sec the haddon 1996 source model over predicts motions at all periods by factors of 2 to 10 these conclusions do not change significantly if data from non ena intraplate regions are excluded although the ten dency of all models toward overprediction of long period amplitudes becomes more pronounced the tendency of most proposed ena source models to overestimate long period motions is further confirmed by an evaluation of the relationship between ms a measure of the spectrum at 20 sec period and moment magnitude a worldwide catalog of shallow continental earthquakes triep and sykes 1996 is compared to the ms m relations implied by each of the source models the atldnson source model is consistent with these data while other proposed ena models overpredict the average ms for a given m the implications of mmi data from historical earthquakes are also addressed by exploiting the correlation between felt area and high frequency source spectral level high frequency spectral amplitudes as specified by the atkinson and boore 1995 frankel et al 1996 toro et al 1997 and joyner 1997a b source models equal or exceed the levels inferred from the felt areas of most of the large ena events with the noteable exception of the saguenay earthquake by contrast high frequency spectral amplitudes specified by the haddon 1996 source model agree with the felt area of the saguenay earthquake but overpredict the felt areas of nearly all other large events in general models that fit the saguenay data be it intensity data strong ground motion data regional seismographic data or teleseismic data will not fit the data from the remaining earthquakes a source model derived from the california database suitably modified for re gional differences in crustal properties is also evaluated this model is not signifi

diffusion of helium in zircon and apatite abstract diffusion of helium has been characterized in natural zircon and apatite polished slabs of zircon and apatite oriented either normal or parallel to c were implanted with 100 kev 3he at a dose of 5 1015 3 he cm2 diffusion experiments on implanted zircon and apatite were run in pt capsules in 1 atm furnaces 3he distributions following experiments were measured with nuclear reaction analysis using the reaction 3he d p 4he for diffusion in zircon we obtain the following arrhenius relations d c 2 3 10 7 exp 146 11 kj mol 1 r t m 2 s 1 d c 1 7 10 5 exp 148 17 kj mol 1 r t m 2 s 1 although activation energies for diffusion normal and parallel to c are comparable there is marked diffusional anisotropy with diffusion parallel to c nearly 2 orders of magnitude faster than transport normal to c these diffusivities bracket the range of values determined for he diffusion in zircon in bulk release experiments although the role of anisotropy could not be directly evaluated in those measurements in apatite the following arrhenius relation was obtained over the temperature range of 148 449 c for diffusion normal to c d 2 10 10 6 exp 117 6 kj mol 1 r t m 2 s 1 in contrast to zircon apatite shows little evidence of anisotropy he diffusivities obtained in this study fall about an order of magnitude lower than diffusivities measured through bulk release of he through step heating and within an order of magnitude of determinations where ion implantation was used to introduce helium and he distributions measured with elastic recoil detection since the diffusion of he in zircon exhibits such pronounced anisotropy helium diffusional loss and closure cannot be modeled with simple spherical geometries and the assumption of isotropic diffusion a finite element code cylmod has recently been created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients we present some applications of the code in evaluating helium lost from zircon grains as a function of grain size and length to diameter ratios and consider the effects of shape anisotropy where diffusion is isotropic as in the case of apatite but shapes of crystal grains or fragments may depart significantly from spherical geometry

tethyan mediterranean organic carbon rich sediments from mesozoic black shales to sapropels the jurassic to holocene record of black shale deposition in the tethys mediterranean region is unrivalled by that of any other ocean basin either in land sections or drill cores the term black shale is used here broadly for sediments with elevated organic carbon concentrations 1 including the pliocene to recent sapropels most of the black shales are devoid of benthonic organisms are laminated and were deposited in distinct rhythms during periods when the deep waters of the ocean basins were anoxic or dysoxic the tethyan black shale records have become essential in studies of the transfer of organic carbon into the sediment record and for astronomical tuning and geological time scales these records have been central in understanding climate control on ocean dynamics and biogeochemical cycles the mesozoic black shales were deposited within well defined time envelopes of around 0 5 to 1 myr these black shales which were confined to certain chronostratigraphic intervals in the jurassic and cretaceous were recognized as expressions of global oceanic anoxic events in the mid 1970s and subsequently named after prominent researchers bonarelli selli goguel the black shale episodes were dated by biostratigraphic methods and by high resolution chemostratigraphy and cyclostratigraphy mesozoic black shales are now interpreted as the oceanographic expression of major perturbations of the global carbon cycle and climate research into younger pliocene to pleistocene sedimentary cycles including black shales termed sapropels exposed in land sections or found in pelagic and hemipelagic marine sediment cores of late quaternary age started in the 1950s main threads pursued from this end of the record were the climatic control of oceanic processes that permitted the development of highly detailed and precise time scales tuned to the astronomical clock of insolation changes palaeoclimate evolution of the circum mediterranean area and biogeochemical dynamics in anoxic basins after 50 years of intensive research the tethyan and mediterranean black shales remain subjects of fascination in earth science tracing the origins and building upon recent progress the current hypotheses on their formation are reviewed here it is a panorama of complex interplays between global and regional tectonics climate dynamics during both ice house and greenhouse states of global and regional climate oceanographic responses to these climate changes and biogeochemical adaptations that were all needed to shape an extraordinary archive of global change in the absence of human activity

an empirical study of earthquake source spectra for california earthquakes we generalize source path and site effects for california earthquakes as functions of magnitude and distance based on regression analysis of 1000 fourier acceleration spectra from 43 california earthquakes in the moment magnitude range from 4 4 to 7 4 recorded at rupture distances from 1 to 200 km empirically derived source spectra for california earthquakes are generally inconsistent with the spectral shape implied by a brune omega squared point source model this is manifested by magnitude and frequency dependence of the brune model parameters for ex ample the brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at m5 5 to a value near 50 bars at m7 5 at frequencies below 1 hz though source spectra have much lower spectral ampli tudes than predicted by the brune point source model for these values of stress this discrepancy grows with increasing magnitude finite fault simulations indicate that this is a consequence of the breakdown of the validity of the point source approxi mation for large ruptures a stochastic finite fault model in which the fault is dis cretized as a number of subfaults each of which is represented by a brune omega squared point source correctly matches the observed spectral shapes and amplitudes the spectral decay parameter kappa representing average near surface attenuation of high frequency motion at rock sites increases with increasing magnitude from values near 0 035 sec at m5 5 to 0 050 sec at m7 5 magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical california sites subjected to strong ground motion comparisons of our empirical source spectra for california to corresponding spec tra for eastern north america suggest that the spectral amplitudes are similar in the two regions for low frequency motions f 2 hz for m5 5 f 0 5 hz for m7 5 for equivalent crustal conditions the eastern events appear to have enhanced high frequency near source amplitudes relative to the california events this is particularly pronounced for large magnitude earthquakes

alternative hybrid empirical ground motion model for central and eastern north america using hybrid simulations and nga west2 models abstract an alternative hybrid empirical ground motion model for central and eastern north america cena is proposed the new ground motion model gmm is developed for the average horizontal components rotd50 of peak ground acceleration peak ground velocity and 5 damped pseudospectral accelerations at 0 01 10 s spectral periods hybrid empirical estimates are derived using the regional modification factors between two regions host and target along with empirical gmms from the host region the regional adjustment factors are ratios of the intensity measures from the generated synthetics in the host western north america wna and target cena regions in this study the recent updated empirical gmms developed by the pacific earthquake engineering research center for the next generation attenuation west2 nga west2 project bozorgnia et al 2014 are incorporated we used a broadband simulation technique proposed by the authors shahjouei and pezeshk 2015a to generate synthetics for both the wna and cena regions in which the high frequency and low frequency parts of synthetics are calculated through a stochastic finite fault method and kinematic source models along with the deterministic wave propagation respectively the updated seismological and geological parameters are deployed in simulations the new ground motion model is developed as part of the nga east research project considering multiple shaking scenarios that characterize the magnitude in the m 5 0 8 0 range the proposed gmm represents the level of ground shaking in the distance range of 2 1000 km and are developed for the reference rock site condition with v s 30 3 km s in cena the results are compared with some other existing models in the region in addition a comprehensive residual analysis is performed using the recorded earthquakes available in the nga east database

canyon incision and knickpoint propagation recorded by apatite 4he 3he thermochronometry abstract in many regions of the world deeply incised canyons demonstrate the net effects of physical processes active at earth s surface in response to surface uplift low temperature thermochronometry can constrain the timing and rates of bedrock incision which is necessary for relating canyon incision to surface uplift over geological timescales we analyzed four samples from the cotahuasi ocona canyon system in southwest peru using 4 he 3 he thermochronometry and we present a new inversion model to identify continuous low temperature cooling histories that are consistent with the observed data derived cooling histories limit the onset of fluvial incision to 13 to 8 ma this is in agreement with previously reported interpretations based on a three dimensional thermal model interpolation to a much larger set of conventional apatite u th he ages however because 4 he 3 he thermochronometry constrains an independent cooling history for each sample the results also permit testing of landscape evolution models with greater spatial variability in exhumation compared to those models that can be tested by a geographically scattered set of conventional u th he ages the different cooling histories of the four samples require asynchronous incision along at least part of the canyon system that is best explained by headward propagation of fluvial incision by knickpoint migration

u pb zircon and titanite systematics of the fish canyon tuff an assessment of high precision u pb geochronology and its application to young volcanic rocks a large data set of single and multi grain zircon and titanite analyses from a sample of the oligocene fish canyon tuff fct a voluminous ash flow from the san juan mountains of colorado and widely used 40ar 39ar geochronological standard has been used to evaluate the influence of various sources of analytical and geological uncertainty on the calculated age of this tuff by the isotope dilution u pb zircon method twenty three single zircon grains and seven small multi grain fractions of the fct yield an inverse variance weighted mean 206pb 238u date of 28 402 0 023 ma 2 mswd 0 93 and a slightly older weighted mean 207pb 235u date of 28 529 0 030 ma mswd 0 74 which are insensitive to common pb corrections initial 230th disequilibria calculated from a newly measured th u 2 2 for fct pumice shards indicate th deficiency for these zircons its correction brings the weighted mean 206pb 238u date to 28 478 0 024 mswd 0 97 minimizing the discordance of the fct zircon analyses these calculations culminate in concordia ages ludwig 1998 for the crystallization of the fct zircons of 28 476 0 029 ma mswd 1 50 without propagating decay constant errors or 28 498 0 035 ma mswd 1 03 with propagated decay constant errors these results are in close agreement with a previous single grain 206pb 238u zircon date of 28 41 0 05 ma for the fct oberli et al 1990 however they do not corroborate the discordia lower intercept date of 27 52 0 09 put forth by lanphere and baadsgard 2001 the 28 476 0 064 ma concordia age for fct zircons including systematic decay constant errors and uncertainty in pb u tracer calibration is substantially older than all published 40ar 39ar sanidine ages which range from 27 5 to 28 05 ma lanphere and baadsgaard 1997 renne et al 1998 a lengthy period 400 k y of zircon residence in the magma chamber before eruption is commonly called upon to explain the age discrepancy however fct titanite which may remain open to pb diffusive exchange until quenching upon eruption yield a minimum 230th disequilibrium corrected weighted mean 206pb 238u age of 28 395 0 049 ma 0 078 with tracer uncertainty weakening residence time arguments and supporting recent calls for re evaluation of the 40k decay constant and the accepted ages for commonly used 40ar 39ar mineral standards the fct zircon concordia age also provides an empirical constraint on the decay constants of the u isotopes indicating the relative accuracy of the currently accepted decay constants to within the original counting statistic errors of jaffey et al 1971

variable helium diffusion characteristics in fluorite abstract precise analysis of the diffusion characteristics of helium in fluorite is crucial for establishing the new fluorite u th sm he thermochronometer fhe which potentially provides a powerful tool for dating ore deposits unsuitable for the application of conventional geochronometers incremental helium outgassing experiments performed on fluorites derived from a spectrum of geological environments suggest a thermally activated volume diffusion mechanism the diffusion behaviour is highly variable and the parameters range between log d 0 a 2 0 30 0 27 7 27 0 46 s 1 and e a 96 3 5 182 3 8 kj mol despite the fact that the caf 2 content of natural fluorites in most cases exceeds 99 weight percent the closure temperature t c of the fluorite u th sm he thermochronometer as calculated from these diffusion parameters varies between 46 14 c and 169 9 c considering a 125 m fragment size here we establish that minor substitutions of calcium by rare earth elements and yttrium ree y and related charge compensation by sodium fluorine oxygen and or vacancies in the fluorite crystal lattice have a significant impact on the diffusivity of helium in the mineral with increasing ree y concentrations f vacancies are reduced and key diffusion pathways are narrowed consequently a higher closure temperature is to be expected an empirical case study confirms this variability two fluorite samples from the same deposit horni krupka czech republic with ca 170 c and ca 43 c t c yield highly different u th sm he ages of 290 10 ma and 79 10 ma respectively accordingly the fluorite sample with the high t c could have quantitatively retained helium since the formation of the fluorite bearing ores in the permian despite subsequent mesozoic burial and associated regional hydrothermal heating in contrast the fluorite with the low t c yields a late cretaceous age close to the apatite fission track aft and apatite u th he ages ahe from the same locality remarkably thermal modelling of fhe yields comparable results to the well established modelling based on aft and ahe

time scale controversy accurate orbital calibration of the early paleogene 1 timing is crucial to understanding the causes and consequences of events in earth history the calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating uncertainties in the computations of earth s orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 ma attempts to construct a robust astronomically tuned time scale for the early paleogene by integrating radioisotopic and astronomical dating are only partially consistent here using the new la2010 and la2011 orbital solutions we present the first accurate astronomically calibrated time scale for the early paleogene 47 65 ma uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the fish canyon standard comparison with geological data confirms the stability of the new la2011 solution back to 54 ma subsequent anchoring of floating chronologies to the la2011 solution using the very long eccentricity nodes provides an absolute age of 55 530 0 05 ma for the onset of the paleocene eocene thermal maximum petm 54 850 0 05 ma for the early eocene ash 17 and 65 250 0 06 ma for the k pg boundary the new astrochronology presented here indicates that the intercalibration and synchronization of u pb and 40ar 39ar radioisotopic geochronology is much more challenging than previously thought

radiation damage control on apatite u th he dates from the grand canyon region colorado plateau individual detrital apatite grains from the esplanade coconino and moenkopi formations in the grand canyon region of the colorado plateau yield u th he dates from 104 to 5 ma the range of dates within each unit far exceeds analytical uncertainty but correlates with both he concentration he and effective u concentration eu these dates are all signifi cantly younger than the sandstone units indicating partial to complete he loss following deposition recently published laboratory diffusion data suggest that he retentivity in apatite increases with radiation damage forward models predict that the consequences of this effect will be manifested most clearly as a correlation between u th he dates and the he and eu in suites of apatites that 1 are characterized by a large span of eu and 2 had thermal histories in which suffi cient time elapsed for the apatite he diffusion kinetics to diverge prior to reheating and partial resetting apatites in the sedimentary units investigated fi t these cri teria using geologically reasonable deposition burial and unroofi ng histories simulations that include the effect of radiation damage on apatite he retentivity can reproduce the observed distributions of apatite dates and correlations with parent and daughter concentrations these results suggest that a span of u th he dates positively correlated with eu may provide important information regarding a sample s thermal history

enhanced preservation of marine derived organic matter in cenomanian black shales from the southern angola basin black shales possessing high concentrations of organic carbon1 were deposited in many parts of the proto south atlantic ocean during the cretaceous period2 the way such sediments accumulated is not fully understood but is likely to have occurred through a combination of low oxygen availability and abundant supply of organic matter thin centimetre thick layers of black shales are commonly interbedded with thicker layers of organic carbon deficient green claystones as found in strata of aptian to coniacian age at deep sea drilling project dsdp site 530 in the southern angola basin3 and elsewhere these differences in carbon content and colour reflect the conditions of deposition and possibly variations in the supply of organic matter4 5 we have compared using organic geochemical methods the compositions of organic matter in three pairs of closely bedded black and green cenomanian claystones obtained from site 530 kerogen analyses and distributions of biological markers show that the organic matter of the black shales is more marine and better preserved than that of the green claystones

determination of stress parameters for eight well recorded earthquakes in eastern north america we determined the stress parameter for the eight earthquakes stud ied by atkinson and boore 2006 using an updated dataset and a revised point source stochastic model that captures the effect of a finite fault we consider four geometrical spreading functions ranging from 1 r at all distances to two or three part functions the values are sensitive to the rate of geometrical spreading at close distances with 1 r 1 3 spreading implying much higher than models with 1 r spreading the important difference in ground motions of most engineering con cern however arises not from whether the geometrical spreading is 1 r 1 3 or 1 r at close distances but from whether a region of flat or increasing geometrical spreading at intermediate distances is present as long as is constrained by data that are largely at distances of 100 km 800 km the simple 1 r model fits the sparse data for the eight events as well as do more complex models determined from larger datasets where the larger datasets were used in our previous ground motion predic tion equations this suggests that uncertainty in attenuation rates is an important com ponent of epistemic uncertainty in ground motion modeling for the attenuation model used by atkinson and boore 2006 the average value of from the point source model ranges from 180 bars to 250 bars depending on whether or not the stress parameter from the 1988 saguenay earthquake is included in the average we also find that for a given earthquake is sensitive to its moment magnitude m with a change of 0 1 magnitude units producing a factor of 1 3 change in the derived

reference rock site condition for central and eastern north america abstract the reference rock site condition has two important applications for ground motion prediction in the stable continental region of central and eastern north america cena 1 it represents the site condition for which ground motions are computed using semiempirical ground motion prediction equations in addition 2 it represents the site condition to which site amplification factors which are used to modify ground motion intensity measures for softer site condition are referenced i e site amplification is unity for reference rock we define reference rock by its shear s and compression p wave velocities as well as a site attenuation parameter 0 which is used in stochastic ground motion simulation methods prior definitions of reference rock conditions in cena were based mostly on indirect large scale crustal velocity inversions and judgment we compile and interpret a unique database of direct velocity measurements to develop criteria for assessing the presence of reference rock site condition based on measured seismic velocities and their gradient with respect to depth we apply the criteria to available profiles and perform rigorous statistical analysis from which we recommend s and p wave velocities of 3000 and 5500 m s respectively for the reference rock condition we recommend that for practical applications use ranges of reference s and p wave velocities of 2700 3300 m s and 5000 6100 m s respectively the ranges are based on a 5 change in amplification using quarter wavelength theory we do not find evidence for regional dependence of the reference velocities which are derived principally from three general geographic regions 1 atlantic coast 2 continental interior and 3 appalachian mountains our data do not provide reference velocities for the gulf coast region the recommended velocity compatible reference rock site kappa is 0 006 s

the cenomanian turonian anoxic event in europe an organic geochemical study received 14 october 1988 revised 14august 1989 accepted 31 august 1989 thirty two sediment samples mainly black shales from cenomanian turonian organic rich sequences in europe and tunisia were examined by organic geochemical techniques the results of molecular analyses indicate that all the black shales are dominated by marine derived organic matter from both algal and bacterial sources with only a minor terrestrial component oxygen deficient conditions prevailed during the deposition of the black shales although interbedded non laminated organic lean horizons indicate that oxygen deficiency was intermittent at some sites the presence of 17cx h 18c h 211 h 28 30 bisnorhopane in some black shale samples from shallow shelf areas may be evidence for severely oxygen depleted conditions possibly in association with upwelling and an oxygen minimum layer overall the organic geochemical data are in agreement with a depositional model whereby an oxygen minimum layer developed in response to high surface productivity this oxygen minimum layer may have extended over a considerable thickness of the water column 1000 m in some areas we report the first observation of an a ring methylated c29 hopane namely methyl 17e h 18 h 211 h 28 30 bisnorhopane the environmental significance of this compound cannot yet be assessed although in the sample in which it occurs the direct parallel between the carbon number distribution of the hopanes and that of the methylhopanes suggests either that they have the same biological origin or that methylation of hopanoids may have occurred possibly during diagenesis

ground motion amplification at rock sites across canada as determined from the horizontal to vertical component ratio we determine the frequency dependent amplification inherent in hard rock sites across canada under the assumption that it can be estimated from the ratio of the horizontal to vertical h v components of ground motion the use of h v as an estimate of amplification was originally proposed by nakamura 1989 for microtremors and then generalized to earthquake ground motions by lermo and chavez garcia 1993 the h v method was applied to a fourier spectra database compiled from 424 earthquakes of magnitude greater than or equal to 2 recorded on 32 three component stations of the canadian national seismograph network cnsn all sited on rock shear wave velocity 1500 m sec in each case we analyzed the s wave portion of the seismograms including the direct s and other strong s phases such as lg the average amplification h v for rock sites does not vary significantly across the country it is weakly frequency dependent increasing from a factor near unity at 0 5 hz to a maximum in the range from 1 2 to 1 6 at 10 hz this amplification is consistent with what would be expected from a gradual decrease in shear wave velocity as the seismic waves approach the surface due to factors such as near surface weathering the interpretation of the h v ratio as a measure of site response is consistent with the general geological conditions of the recording sites in particular the 5 hz h v ratio can be correlated with local geological conditions the central canada sites have the lowest estimated site amplification this is consistent with competent hard rock site conditions with high near surface shear wave velocities there are two stations that show anomalous h v ratios that suggest significant local site effects these are edm near edmonton which may be influenced by topographic amplification and a61 a station in the charlevoix seismic zone

sedimentation and accumulation of organic carbon in the angola basin and on walvis ridge preliminary results of deep sea drilling project leg 75 leg 75 investigated two periods of accumulation of sediments rich in organic matter in the upper cretaceous section more than 200 beds of gray or black shale and mudstone rich in organic carbon as much as 18 are intercalated within a sequence of red and green mudstones that contain less than 1 organic carbon the black shale beds are 1 to 62 cm thick and constitute less than 10 of the section in the 20 cores in which they were recovered both turbiditic and pelagic processes were involved in the deposition of these black shale beds a combination of factors including increased productivity and warm saline bottom waters probably resulted in a delicate balance between oxic and anoxic conditions that periodically favored the accumulation and preservation of organic matter in the basinal sediments the pliocene pleistocene sediments are thoroughly bioturbated and there is no evidence of persisting anoxia in the overlying water in spite of the high organic carbon content of the sediments these two different periods of accumulation of organic matter both resulted in significant concentration of organic carbon 2 maximum 18 but the pliocene pleistocene sediments contain the greater mass of organic carbon per unit volume of the solid sediment