influence of the lower crustal structure on the early coda of regional seismograms we use synthetic seismograms for a flat layered earth model to study the influence of the widely observed strong reflectivity of the lower crust on the propagation of seismic regional phases the lower crustal layering induces a clear increase in the duration of the pg and lg phases on both the vertical and radial components beyond the group velocity of their terminations in a model with a homogeneous lower crust the transverse component is weakly affected the amplitude and the spectral content of the early lg coda are strongly dependent on the distribution of layer thicknesses the predominance of the low frequency components below 2 hz observed in the lg coda of real data is correctly accounted for with 1 km thick layers in the lower crust from particle motions at various depths and the analysis of the dispersion curves of normal modes we hypothesize that the late arrivals result from the interaction of plate type disturbances of the high impedance layers these waves leak energy in the mantle at a low rate this mode of generation of the coda waves explains the puzzling observation that the spreading coefficient of lg seems to be applicable to the early coda of regional seismograms the study of the influence of the lamellae on the average q factor of the continental crust shows that the lower crust layering does not account for the observed low values of the apparent qs another origin is needed for this strong attenuation for example scattering by randomly distributed heterogeneities

recent climatic significance of chemical signals in a shallow firn core from an alpine glacier in the south asia monsoon region abstract there are 19 sub tropical temperate glaciers on mount yulong the southernmost currently glacier covered area in eurasia controlled by the south western monsoon climate in the summer of 1999 a firn core 10 10 m long extending down to glacier ice was recovered in the accumulation area of the largest glacier baishui no 1 periodic variations of climatic signals above 7 8 m depth were apparent and net accumulation of four years was identified by the annual oscillations of isotopic and ionic composition the boundaries of annual accumulation were confirmed by higher values of electrical conductivity and ph and by dirty refreezing ice layers at the levels of summer surfaces calculated mean annual net accumulation from 1994 95 to 1997 98 was about 900 mm water equivalent the amplitude of isotopic variations in the profile decreased with increasing depth and isotopic homogenization occurred below 7 8 m as a result of meltwater percolation variations of 18 o above 7 8 m showed an approximate correlation with the winter climatic trend at lijiang station 25 km away concentrations of ca 2 and mg 2 were much higher than those of na and k indicating that the air masses for precipitation were mainly from a continental source and that the core material accumulated during the winter period the close correspondence of cl and na indicated their common origin the decreasing trend of na cl ratios with increasing depth further reflects a progressive homogenization process caused by meltwater percolation concentrations of so 4 2 and no 3 in the core are quite low the mean annual net accumulation in the core and the estimated ablation indicate that the average annual precipitation above the glacier s equilibrium line is 2400 3100 mm but this needs to be confirmed by long term observation of mass balance

frequency dependent seismic attenuation in the eastern united states as observed from the 2011 central virginia earthquake and aftershock sequence abstract ground shaking due to earthquakes in the eastern united states eus is felt at significantly greater distances than in the western united states wus and for some earthquakes it has been shown to display a strong preferential direction shaking intensity variation can be due to propagation path effects source directivity and or site amplification in this paper we use s and lg waves recorded from the 2011 central virginia earthquake and aftershock sequence in the central virginia seismic zone to quantify attenuation as frequency dependent q f in support of observations based on shaking intensity we observe high q values in the eus relative to previous studies in the wus with especially efficient propagation along the structural trend of the appalachian mountains our analysis of q f quantifies the path effects of the northeast trending felt distribution previously inferred from the u s geological survey usgs did you feel it data historic intensity data and the asymmetrical distribution of rockfalls and landslides

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

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

lithospheric extension and the opening of the red sea sediment basalt relationships in yemen this paper analyses new field and radiometric age data on the timing of extension sedimentation and magmatism related to the opening of the red sea the first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine tawilah formation of cretaceous to early tertiary age the first indication of magmatism is the eruption of alkaline basalts 43 5 21 2 ma on to marine and non marine sandstones of lower to middle tertiary age the lack of an angular unconformity at the sediment basalt contact over a period of 25 myr corroborates a diachronous relationship between the tawilah sandstones and the yemen volcanics these data also indicate that the onset of volcanism in yemen was in the eocene as is the case in ethiopia and saudi arabia a passive rifting model is supported by early extension and sedimentation followed by syn and post tectonic magmatism

the evolution and environmental significance of glaciochemistry during the ablation period in the north of tibetan plateau china in order to explore the glaciochemistry of shiyi glacier in the central qilian mountains a total of 142 samples have been collected for fresh snow surface snow snowpit and meltwater from july 2012 to november 2013 the results indicated cations dominated the glaciochemistry especially the high ca2 concentration relatively high cl and na concentrations were mainly contributed by desert dust aerosols and the atmospheric aerosols from warm water bodies such as the black caspian and aral seas the analysis also confirmed the chemical ions in fresh snow are mainly contributed by atmospheric wet deposition surface snow is mainly influenced by dry deposition and snowpits are influenced by both atmospheric deposition and leaching process while meltwater is influenced by water rock interactions the profile of ionic concentration in the snowpit became more smoothed during ablation period owing to the influence of leaching the elution sequence of the snowpit in the shiyi glacier was so42 k ca2 mg2 na cl no3 the chemical concentrations for meltwater are mainly influenced by water dilution and soil thawing the ions in snow in the central qilian mountains showed relatively lower concentrations than in the western qilian mountains tianshan mountains and altai mountains it was closer to balance than in glaciers in the central tibetan plateau but was higher than in the southern tibetan plateau different ionic sources and dissolution process had caused the differences of chemical composition for fresh snow surface snow snowpit and meltwater and these chemical compositions reflected the atmospheric background values in the northern tibetan plateau c 2014 elsevier ltd and inqua all rights reserved

association between atmospheric circulation patterns and firn ice core records from the inilchek glacierized area central tien shan asia 1 glacioclimatological research in the central tien shan was performed in the summers of 1998 and 1999 on the south inilchek glacier at 5100 5460 m a 14 36 m firn ice core and snow samples were collected and used for stratigraphic isotopic and chemical analyses the firn ice core and snow records were related to snow pit measurements at an event scale and to meteorological data and synoptic indices of atmospheric circulation at annual and seasonal scales linear relationships between the seasonal air temperature and seasonal isotopic composition in accumulated precipitation were established changes in the 18o air temperature relationship in major ion concentration and in the ratios between chemical species were used to identify different sources of moisture and investigate changes in atmospheric circulation patterns precipitation over the central tien shan is characterized by the lowest ionic content among the tien shan glaciers and indicates its mainly marine origin in seasons of minimum precipitation autumn and winter water vapor was derived from the arid and semiarid regions in central eurasia and contributed annual maximal solute content to snow accumulation in tien shan the lowest content of major ions was observed in spring and summer layers which represent maximum seasonal accumulation when moisture originates over the atlantic ocean and mediterranean and black seas

crustal and upper mantle structure of peninsular india and source parameters of the 21 may 1997 jabalpur earthquake mw 5 8 results from a new regional broadband network abstract in the past two years a permanent network of 10 broadband seismographs has become operational in the indian peninsular shield region in this article we analyze the data recorded by this network with two goals 1 to lay ground for a quick estimation of source parameters of future earthquakes in the region and 2 to estimate the source parameters of the destructive jabalpur earthquake of 21 may 1997 mw 5 8 which occurred within the network toward these goals we measure rayleigh and love wave group velocity dispersion curves in the period range of 10 to 75 sec and invert these curves to estimate the crustal and the upper mantle structure below the indian shield region our best model consists of a two layer crust the upper layer is 14 km thick with a shear wave velocity v s of 3 55 km sec the corresponding values for the lower layer are 25 km and 3 85 km sec v s for the upper mantle is 4 65 km sec based on this structure we perform a moment tensor mt inversion of the bandpassed 0 05 0 02 hz seismograms of the jabalpur earthquake the best fit is obtained for a source located at a depth of 42 km with a seismic moment m 0 of 7 7 10 24 dyne cm and a focal mechanism with strike 61 dip 64 and rake 74 these source parameters are similar to those previously reported in the literature demonstrating that a routine mt inversion of moderate and large indian penisular earthquakes is now possible a careful examination of the seismograms and modeling of the two closest records reveal that the jabalpur earthquake nucleated in the lower crust at a depth of 36 km it consisted of two subevents separated in time by 0 65 sec with the second subevent located 2 km above the first one the total source duration was 1 4 sec

estimation of ground motion variability in the central and eastern united states using deterministic physics based syntheticsestimation of ground motion variability in the ceus using deterministic physics based synthetics

ground motion simulations of 1811 1812 new madrid earthquakes central united states we performed a suite of numerical simulations based on the 1811 1812 new madrid seismic zone nmsz earthquakes which demonstrate the importance of 3d geologic structure and rupture directivity on the ground motion response throughout a broad region of the central united states cus for these events our simulation set consists of 20 hypothetical earthquakes located along two faults associated with the current seismicity trends in the nmsz the hypothetical scenarios range in magnitude from m 7 0 to 7 7 and consider various epicenters slip distributions and rupture characterization approaches the low frequency component of our simulations was computed deterministically up to a frequency of 1 hz using a regional 3d seismic velocity model and was combined with higher frequency motions calculated for a 1d medium to generate broadband synthetics 0 40 hz in some cases for strike slip earthquakes located on the southwest northeast striking nmsz axial arm of seismicity our simulations show 2 10 s period energy channeling along the trend of the reelfoot rift and focusing strong shaking northeast toward paducah kentucky and evansville indiana and southwest toward little rock arkansas these waveguide effects are further accentuated by rupture directivity such that an event with a western epicenter creates strong amplification toward the northeast whereas an eastern epicenter creates strong amplification toward the southwest these effects are not as prevalent for simulations on the reverse mechanism reelfoot fault and large peak ground velocities 40 cm s are typically confined to the near source region along the up dip projection of the fault nonetheless these basin response and rupture directivity effects have a significant impact on the pattern and level of the estimated intensities which leads to additional uncertainty not previously considered in magnitude estimates of the 1811 1812 sequence based only on historical reports the region covered by our simulation domain encompasses a large portion of the cus centered on the nmsz including several major metropolitan areas based on our simulations more than eight million people living and working near the nmsz would experience potentially damaging ground motion and modified mercalli intensities ranging from vi to viii if a repeat of the 1811 1812 earthquakes occurred today moreover the duration of strong ground shaking in the greater memphis metropolitan area could last from 30 to more than 60 s depending on the magnitude and epicenter online material tables of 1d velocity models used to generate the high frequency synthetics and figures of source models and peak ground motion synthetics

magnitudes and locations of the 1811 1812 new madrid missouri and the 1886 charleston south carolina earthquakes we estimate locations and moment magnitudes m and their uncertainties for the three largest events in the 1811 1812 sequence near new madrid missouri and for the 1 september 1886 event near charleston south carolina the intensity magnitude m i our preferred estimate of m is 7 6 for the 16 december 1811 event that occurred in the new madrid seismic zone nmsz on the bootheel lineament or on the blytheville seismic zone m i is 7 5 for the 23 january 1812 event for a location on the new madrid north zone of the nmsz and 7 8 for the 7 february 1812 event that occurred on the reelfoot blind thrust of the nmsz our preferred locations for these events are located on those nmsz segments preferred by johnston and schweig 1996 our estimates of m are 0 1 0 4 m units less than those of johnston 1996b and 0 3 0 5 m units greater than those of hough et al 2000 m i is 6 9 for the 1 september 1886 event for a location at the summerville middleton place cluster of recent small earthquakes located about 30 km northwest of charleston

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

changes in ionic and oxygen isotopic composition of the snow firn pack at baishui glacier no 1 southeastern tibetan plateau to properly interpret climatic and environmental information recorded in ice cores retrieved in the temperate glacier region the post depositional processes especially the meltwater percolation need to be well understood from late april to mid july 2006 two successive snow pits site p1 located at 4 750 m a s l in the ablation zone and site p2 at 4 900 m a s l in the accumulation area at baishui glacier no 1 mt yulong southeastern tibetan plateau were excavated changes in soluble ions k na ca2 mg2 cl no3 and so4 2 and stable oxygen isotopes 18o in the snow pits were investigated before the melting period soluble ions and 18o exhibit pronounced seasonal variations with high values in the upper snow firn layer accumulated in winter spring season and relatively low values in the lower firn layer deposited in summer season reflecting seasonal shift in the indian summer monsoon and winter westerlies over the region during the melting period most ions in the upper snow firn layer were leached with different efficiencies although no significant changes in ion concentrations in the lower firn layer were observed the impurities in the upper snow firn layer could be eluted down into the lower firn layer however the pre melting isotopic stratigraphy remained relatively unchanged during the observation period indicating that the influence of meltwater percolation on stable isotopes is less significant than that on soluble ions this understanding is crucial for the interpretation of ice core records in the monsoon temperate glacier region

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

frequency dependent lg q within the continental united states frequency dependent crustal attenuation 1 q is determined for seven distinct physiographic tectonic regions of the continental united states using high quality lg waveforms recorded on broadband stations in the frequency band 0 5 to 16 hz lg attenuation is determined from time domain amplitude measurements in one octave frequency bands centered on the frequencies 0 75 1 0 3 0 6 0 and 12 0 hz modeling errors are determined using a delete j jackknife resampling technique the frequency dependent quality factor is modeled in the form of q q 0 f regions were initially selected based on tectonic provinces but were eventually limited and adjusted to maximize ray path coverage in each area earthquake data was recorded on several different networks and constrained to events occurring within the crust m b 3 5 in size a singular value decomposition inversion technique was applied to the data to simultaneously solve for source and receiver terms along with q for each region at specific frequencies the lowest crustal q was observed in northern and southern california where q is described by the functions q 152 37 f 0 72 0 16 and q 105 26 f 0 67 0 16 respectively the basin and range province pacific northwest and rocky mountain states also display lower q and a strong frequency dependence characterized by the functions q 200 40 f 0 68 0 12 q 152 49 f 0 76 0 18 and q 166 37 f 0 61 0 14 respectively in contrast in the central and northeast united states q functions are q 640 225 f 0 344 0 22 and q 650 143 f 0 36 0 14 respectively show a high crustal q and a weaker frequency dependence these results improve upon previous lg modeling by subdividing the united states into smaller distinct tectonic regions and using significantly more data that provide improved constraints on frequency dependent attenuation and errors a detailed attenuation map of the continental united states can provide significant input into hazard map mitigation both scattering and intrinsic attenuation mechanisms are likely to play a comparable role in the frequency range considered in the study

soluble ionic and oxygen isotopic compositions of a shallow firn profile baishui glacier no 1 southeastern tibetan plateau in the summer of 2004 a firn profile 18 3m long extending down to glacier ice was recovered in the accumulation area of the largest glacier baishui no 1 on yulong mountain the southernmost glacier covered area in mainland eurasia multivariate empirical orthogonal function eof and statistical correlation analyses of major ion data from the profile demonstrate that three distinct types of ionic material contribute to the chemical characteristics of firn in this monsoonal region material of marine origin which is transported by the indian southwest monsoon crustal materials which come from local sources and anthropogenic pollutants which are produced by industrial and agricultural activities in south asia although the influence of post depositional processes on the seasonal isotopic and soluble ionic compositions is significant dust layers in the firn profile are clearly visible due to the effects of meltwater percolation the dust layers generally coincide with latesummer snow surfaces we therefore use the dust layers combined with the seasonal variations of electrical conductivity ec ca and mg to establish a depth age scale for the firn profile the reconstructed net accumulation has a significant negative correlation with the temperature at lijiang whereas the correlation between the net accumulation and the precipitation amount at lijiang is weak although the do time series of the firn profile was modified significantly by meltwater percolation the correlation between annual mean do values and the indian southwest monsoon index wsi1 is significant this result suggests that do records from monsoon influenced temperate glaciers can provide a valuable record of past variations of the indian southwest monsoon

modification of three ice core δ18o records from an area of high melt stable oxygen isotope ratios d 18 o of three shallow ice cores extending back to 1963 from urumqi glacier no 1 at the headwater of urumqi river tien shan northwest china were used to test the relationship between d 18 o and contemporaneous surface air temperature ta the ice cores were dated using the seasonal stable isotopic signals and seven insoluble particulate activity horizons associated with known nuclear tests although a strong positive relationship exists between d 18 oi n precipitation and ta at our study site this relationship is not preserved between the annually averaged ice core d 18 o records and the local temperature due to post depositional modification these results indicate that the processes forming the ice core chemical records in areas of high melt must be understood before the d 18 o record can be confidently interpreted as a climatic indicator

modified frequency wavenumber algorithm for regional seismograms using filon s quadrature modelling of lg waves in eastern north america summary the main focus of this study is to develop an efficient frequency wavenumber code to synthesize high frequency say 10 hz regional seismograms up to a distance of more than 1000 km in a medium consisting of a large number of crustal layers and investigate effects of regional waveguides on lg waves in this newly developed code the frequency wavenumber response is evaluated by using the filon s quadrature at high frequency and the polynomial approximation of bessei s functions implementing trapezoidal integration at low frequency this has reduced the computation time by several folds compared to the time needed for the trapezoidal integration using this algorithm both broad band seismograms at harvard and short period ectn eastern canadian telemetered network seismograms from 1988 november 25 saguenay earthquake were successfully modelled a moment magnitude of 5 9 was used initially an average waveguide was calibrated to successfully excite the regional pnl and snl waves at hrv its near surface structure constrained by matching the recorded frequency content the crust mantle transition zone was constrained by modelling the strength of the broad band snl waves consisting of sn ssmsnsmssms and ssmssms phases relative to the initial pnl waves the model was modified to consist of thin layers with an alternating high and low velocity distribution to match the high frequency ectn lg waves observed from 300 to 600 km away in addition the effect of a near surface irregular receiver structure on the duration of lg waves was also investigated by convolving its response with the regional lg seismograms initial study suggests this method as viable for modelling the entire lg waves including the coda numerical studies suggest that the shapes and peak amplitudes on lg seismograms depend more strongly on the source depth anelasticity and crustal waveguide than do the pnl seismograms

seasonal variability of ionic concentrations in surface snow and elution processes in snow firn packs at the pgpi site on urumqi glacier no 1 eastern tien shan china to investigate the effects of both non meltwater and meltwater related post depositional processes on chemical species within the snow firn pack a research program the program for glacier processes investigation was initiated in july 2002 by the tien shan glaciological station chinese academy of sciences the seasonal variability of the ionic concentrations in surface snow samples and ion elution behavior in the snow firn pack were assessed from surface samples collected year round and 1011 samples collected from a snow pit at weekly intervals from september 2003 through september 2004 the results indicate that elevated ionic concentrations in spring and summer result from asian dust storm derived aerosol input and other aerosols entrained in precipitation potential sources of these chemical species are explored using correlation and factor analyses the elution sequence through the snow firn pack was determined to be so4 2 c a 2 n a n o3 c l k m g 2 n h4 the elution of ions at the sampling site was found to be driven primarily by air temperature and became evident when a diurnal mean temperature of 3 68c was attained at 0 38c all of the year round new ionic input was leached from the snow

physical changes in the lithosphere associated with thermal relaxation after rifting we define the terms modem rift and paleorift with respect to the thermal state of the lithosphere the former being rifted lithosphere not in thermal equilibrium and the latter being thermally stabilized rifted lithosphere a comparison of the physical characteristics of modern rifts with paleorifts shows that they share many of the same geomorphic structural and magmatic features but have important differences in their geophysical signatures using a simple model for the thermal relaxation of the lithosphere in the transition from modern rift to paleorift we show that differences in upper mantle seismic velocities and density surface heat flow thermal structure and curie point depth and magnetotelluric properties of the lithosphere between modern and paleorifts can be explained by lithospheric cooling cooling alone cannot explain the complex subsidence histories associated with and following rifting however nor the presence of high velocity crustal layers and sometimes thickened crust in paleorifts these features can be explained by consideration of lithospheric flexural strength and magmatic thickening of the crust associated with rifting we speculate that the anomalous upper mantle beneath many modern rifts may be associated with the process of magmatic thickening of the rifted crust

simulation of earthquake ground motions in the eastern united states using deterministic physics based and site based stochastic approaches abstract earthquake ground motion recordings are scarce in the central and eastern united states ceus for large magnitude events and at close distances we use two different simulation approaches a deterministic physics based method and a site based stochastic method to simulate ground motions over a wide range of magnitudes drawing on previous results for the modeling of recordings from the 2011 m w 5 8 mineral virginia earthquake and using the 2001 m w 7 6 bhuj india earthquake as a tectonic analog for a large magnitude ceus event we are able to calibrate the two simulation methods over this magnitude range both models show a good fit to the mineral and bhuj observations from 0 1 to 10 hz model parameters are then adjusted to obtain simulations for m w 6 5 7 0 and 7 6 events in the ceus our simulations are compared with the 2014 u s geological survey weighted combination of existing ground motion prediction equations in the ceus the physics based simulations show comparable response spectral amplitudes and a fairly similar attenuation with distance the site based stochastic simulations suggest a slightly faster attenuation of the response spectral amplitudes with distance for larger magnitude events and as a result slightly lower amplitudes at distances greater than 200 km both models are plausible alternatives and given the few available data points in the ceus can be used to represent the epistemic uncertainty in modeling of postulated ceus large magnitude events

some comments on climatic reconstructions from ice cores drilled in areas of high melt poor consideration has been given in many arctic circum polar ice core studies to the effect of summer snow melt on chemistry stable isotope concentrations and time scales many of these corps are drilled close to the firn line where melt is intense some come from below the firn line where accumulation is solely in the form of super imposed ice in all cases seasonal signals are reduced or removed and in some time gaps develop during periods of excessive melting which situate the drill site in the ablation zone consequently cross correlations of assumed synchronous events among the cores are invalid so that time scales along the same cores differ between authors by factors of over 2 many so called climatic signals are imaginary rather than real by reference to published analyses of cores from the superimposed ice zone on devon ice cap koerner 1970 and meighen ice cap koerner and paterson 1974 it is shown how melt affects all the normally well established ice core proxies and leads to their misinterpretation despite these limitations the cores can give valuable low resolution records for all or part of the holocene they show that the thermal maximum in the circum polar arctic occurred in the early holocene this maximum effected negative balances on all the ice caps and removed the smaller ones cooler conditions in the second half of the holocene have caused the regrowth of these same ice caps

why the new madrid earthquakes are m 7 8 and the charleston earthquake is m 7 estimates of magnitudes of large historical earthquakes are an essential input to and can seriously affect seismic hazard estimates the earthquake intensity observations modified mercalli intensities mmi and assigned magnitudes m of the 1811 1812 new madrid events have been reinterpreted several times in the last decade and have been a source of controversy in making seismic hazard estimates in the central united states observations support the concept that the larger the earthquake the greater the maximum felt distance for the same crustal attenuation and local soil conditions magnitude should be the main influence on intensity values at large distances we apply this concept by comparing the mean mmi at distances of 600 1200 km for each of the four largest new madrid 1811 1812 earthquakes the 1886 charleston south carolina earthquake the 1929 m 7 2 grand banks earthquake and the 2001 m 7 6 bhuj india earthquake we fit the intensity observations using the form mmi a c dist 0 8 log dist to better define intensity attenuation in eastern north america ena the intensity attenuation in cratonic india differs from ena and is corrected to ena using both the above estimate and published intensity relations we evaluate source marine geophysical q and stress drop information as well as a 1929 milne shaw record at chicago to confirm that the 1929 grand banks earthquake occurred in ena crust our direct comparison of mean intensities beyond 600 km suggests m 7 5 7 3 7 7 and 6 9 for the three new madrid 1811 1812 mainshocks and the largest aftershock and m 7 0 for the 1886 charleston south carolina earthquake with an estimated uncertainty of 0 3 units at the 95 confidence level based on a monte carlo analysis our mean new madrid and charleston mainshock magnitudes are similar to those of bakun and hopper 2004 and are much higher than those of hough and page 2011 for new madrid online material tables of mean modified mercalli intensity for 800 1200 and 600 1000 km distance ranges and figures of least squares fit for all intensity measures used and for frequency dependent q in easternmost canada

structure of yemeni miocene dike swarms and emplacement of coeval granite plutons abstract dike swarms in the yemeni sector of the eastern margin of the red sea basin have been mapped and sampled the greatest concentration of mafic dikes occurs along the tihama coastal escarpment zone less profuse swarms lace the plateau interior the escarpment zone also hosts microgranitic dike swarms related to a chain of closely spaced miocene granite plutons dolerite irruption overlapped in time and space with this plutonism southern red sea basin evolution commenced with flood basalt eruptions upon the late proterozoic arabian craton subsequent continental rifting and crustal fissuring focussed dike swarms along a zone of coeval anatectic granites that largely blocked further flood basalt eruption immediately following this crustal fissuring diking episode severe crustal stretching and thinning led to block faulting and tilting eventually rupture near the rift axis initiated sea floor spreading the resulting crust beneath the outer parts of the red sea basin is new igneous material that has generated two layer neo continental crust

geology and palaeontology of the late miocene middle awash valley afar rift ethiopia the middle awash study area of ethiopia s afar rift has yielded abundant vertebrate fossils 10 000 including several hominid taxa1 2 3 4 the study area contains a long sedimentary record spanning late miocene 5 3 11 2 myr ago to holocene times exposed in a unique tectonic and volcanic transition zone between the main ethiopian rift mer and the afar rift sediments along the western afar rift margin in the middle awash provide a unique window on the late miocene of ethiopia these deposits have now yielded the earliest hominids described in an accompanying paper5 and dated here to between 5 54 and 5 77 myr these geological and palaeobiological data from the middle awash provide fresh perspectives on hominid origins and early evolution here we show that these earliest hominids derive from relatively wet and wooded environments that were modulated by tectonic volcanic climatic and geomorphic processes a similar wooded habitat also has been suggested for the 6 0 myr hominoid fossils recently recovered from lukeino kenya6 these findings require fundamental reassessment of models that invoke a significant role for global climatic change and or savannah habitat in the origin of hominids

strong influence of water vapor source dynamics on stable isotopes in precipitation observed in southern meghalaya ne india to calibrate 18o time series from speleothems in the eastern indian summer monsoon ism region of india and to understand the moisture regime over the northern bay of bengal bob we analyze the 18o and d of rainwater collected in 2007 and 2008 near cherrapunji india d values range from 18 5 to 144 4 while 18o varies between 0 8 and 18 8 the local meteoric water line lmwl is found to be indistinguishable from the global meteoric water line gmwl late ism september october rainfall exhibits lowest 18o and d values with little relationship to the local precipitation amount there is a trend to lighter isotope values over the course of the ism but it does not correlate with the patterns of temperature and rainfall amount 18o and d time series have to be interpreted with caution in terms of the amount effect in this subtropical region we find that the temporal trend in 18o reflects increasing transport distance during the ism isotopic changes in the northern bob surface waters during late ism and vapor re equilibration with rain droplets using an isotope box model for surface ocean waters we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern bob temporal variations in this source can contribute up to 25 of the observed changes in stable isotopes of precipitation in ne india to delineate other moisture sources we use backward trajectory computations and find a strong correlation between source region and isotopic composition palaeoclimatic stable isotope time series from northeast indian speleothems likely reflect changes in moisture source and transport pathway as well as the isotopic composition of the bob surface water all of which in turn reflect ism strength stalagmite records from the region can therefore be interpreted as integrated measures of the ism strength

the e greenland rifted continental margin an examination of the coastal flexure the structure of the e greenland coastal flexure a major structure developed during continental break up is interpreted on the basis of field observations an earlier model which involves normal inland dipping antithetic faulting and seaward rotation of fault blocks is confirmed and amplified this model requires that regional dips are very much less than dips measured on bedding planes thus leading to considerably reduced thicknesses for the tertiary volcanic succession in e greenland detailed mapping confirms the validity of these thickness estimates and leads to the conclusion that the volcanic extrusion rate was similar to that of present day iceland thus obviating the need for special mechanisms of magma generation comparable structures occur in other regions of continental break up and voluminous basalt discharge and it is suggested that the flexure developed by collapse of the attenuated crust subsequent to the massive extrusion of plateau basalts

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

analysis of peak ground motion in terms of a model of inhomogeneous faulting measurements of peak ground velocity v and acceleration a for earthquakes and mine tremors with local magnitudes ranging from 0 8 to 6 4 have been analyzed in terms of a model of inhomogeneous faulting the fault model involves the failure of a circular asperity of radius ri surrounded by a previously faulted annular region of outer radius r0 the failure of the asperity results in seismic radiation with a characteristic frequency proportional to 1 ri followed by lower frequency radiation proportional to 1 r0 as static equilibrium is regained over the larger region for r0 ri 1 both v and a are associated primarily with the failure of the asperity but also depend on the large scale source parameters specifically v r0 r 0 10 r0 ri 0 15 and a r 0 30 r0 ri 2 0 45 where is the shear wave velocity is the overall stress drop is the modulus of rigidity and is density the terms involving r0 ri correspond to the high frequency radiation associated with the failure of the asperity and the other terms indicate the peak parameters due to the broad scale readjustment observations of peak ground motion for events with seismic moments ranging from 5 1016 to 1026 dyn cm indicate that r0 ri is normally in the range of 1 10 and appears to be independent of earthquake size the inhomogeneous fault model also yields convenient expressions for the small scale displacement and stress drop of the asperity failure as well as for the level of regional stress available to cause slip

a new asymptotic method for the modeling of near field accelerograms we study high frequency radiation from a dislocation model of rupture propagation at the earthquake source we demonstrate that in this case all the radiation emanates from the rupture front and by a change of variables that at any instant of time the high frequency waves reaching an observer come from a line on the fault plane that we call isochrone an asymptotic approximation to near source velocity and acceleration is obtained that involves a simple integration along the isochrones for every time step it is shown that wave front discontinuities critical or stopping phases are radiated every time an isochrone becomes tangent to a barrier this leads to what we call the critical ray approximation which is given in a closed form the previous results are compared with discrete wavenumber synthetics obtained by bouchon 1982 for the gilroy 6 recording of the coyote lake earthquake of 1980 the fit between the asymptotic and full numerical method is extremely good the critical ray approximation permits the identification of different phases in bouchon s synthetics and the prediction of the behavior of the signal in the vicinity of their arrival time

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

significant motions between gps sites in the new madrid region implications for seismic hazard position time series from global positioning system gps stations in the new madrid region were differenced to determine the relative motions between sta tions uncertainties in rates were estimated using a three component noise model con sisting of white flicker and random walk noise following the methodology of langbein 2004 significant motions of 0 37 0 07 one standard error mm yr were found between sites ptgvand stle for which the baseline crosses the inferred deep portion of the reelfoot fault baselines between stle and three other sites also show significant motion site mcty adjacent to stle also exhibits significant motion with respect to ptgv these motions are consistent with a model of interseismic slip of about 4 mm yr on the reelfoot fault at depths between 12 and 20 km if constant over time this rate of slip produces sufficient slip for an m 7 3 earthquake on the shallow portion of the reelfoot fault using the geologically derived recurrence time of 500 years this model assumes that the shallow portion of the fault has been pre viously loaded by the intraplate stress a gps site near little rock arkansas shows significant southward motion of 0 3 0 4 mm yr 0 08 mm yr relative to three sites to the north indicating strain consistent with focal mechanisms of earthquake swarms in northern arkansas

dips of normal faults in british coal measures and other sedimentary sequences fault dip measurements n 3291 from 122 faults in british coalfields are presented two classes of normal fault are recognized a gently dipping 55 post coalification tectonic faults formed at depths of about 2 5 km which comprise 90 of the faults analysed dip data from the steeply dipping faults are variable standard deviation 9 both on single faults and between faults and 70 is a better approximation of fault dip than the commonly accepted value of 60 data on tectonic normal faults with comparable depths of formation using the modified griffith fracture criterion the dips of faults at varying depths up to 4 km are calculated for both unsaturated dry and saturated rocks the dips of normal faults are expected to vary from 90 at the surface to 60 at 3 4 km and this variation is consistent with the limited field data available the coalfield data are consistent with fault formation at standard hydrostatic pore fluid pressures at depths of about 2 5 km below depths of a few kilometres normal faults are expected to flatten out gradually to a dip of 45 but such flattening is not necessarily an indication of an underlying detachment

isotopic measurements of precipitation on central asian glaciers southeastern tibet northern himalayas central tien shan the glacial regions of central asia considered in our study are influenced by tropical monsoons and western extratropical cyclones isotopic 18o and d data were obtained over 3 years in three climatic regions gongga massif of southeastern tibet windward slope of summer monsoon xixibangma massif on the northern slope of the himalayas leeward of summer monsoon and the massifs of pobeda khan tengry in the central tien shan exposed to western airstreams the survey reported here provides information from atmospheric precipitation snow pits and a 23 m ice core the significant differences of oxygen isotopic ratios from 25 1 per mil to 9 5 per mil indicate that the indian and pacific oceans as well as the atlantic ocean are sources of moisture on the northern slope of the himalayas and southeastern tibet sharply changing isotopic ratios in precipitation corresponded to changing wind direction and were associated with different sources of air masses on the northern slope of the himalayas and southeastern tibet steady isotopic ratios in atmospheric precipitation and the absence of changing 18o composition in a 23 m ice core suggest only one source of moisture in central tien shan the relatively heavier oxygen isotopic ratios in atmospheric precipitation and ice core indicate the moisture from which the precipitation was derived originated over the caspian or mediterranean seas within the eurasian continent air masses developed over the atlantic ocean advance farther than those from the pacific and indian oceans

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

modification of lower crust by continental rift magmatism we document a systematic inverse relationship between the volume of erupted volcanic rocks associated with continental rifts and the seismic compressional wave velocity contrast across the moho this relationship is interpreted as evidence that magmatism significantly modifies the composition s of the lower crust and upper mantle during rifting processes the relationship is not influenced by the current thermal state of the lithosphere being observed for both modern rifts rio grande kenya rhine and paleorifts oslo and may also characterize continental flood basalt provinces columbia river and snake river plain the trend is reconciled by igneous and metamorphic processes that collectively modify the lower crust to more mafic bulk compositions resulting in higher compressional velocities and that decrease the density of the residual mantle resulting in lower compressional velocities these results support the view that most mantle derived magma in continental rift settings is trapped in the crust

nature of the crust under afar new igneous not thinned continental abstract thinned continental crust is considered absent from beneath afar except for isolated remnants such as comprise the danakil block the ethiopian plateau sialic crust thins abruptly across the plateau afar margin to abut new igneous crust under afar generated during the early development of the red sea basin analyses of stretching and sea floor spreading amounts elsewhere in the red sea and gulf of aden basins are employed to support this concept the dual layering of the afar crust and the similarity of p wave velocities in these layers to velocities in sialic crust lead to the proposal that new continental crust can be generated at magmatic rift zones

crustal extension in the oslo graben se norway a method incorporating magmatism and erosion abstract three methods for determining crustal extension were examined for use in the late paleozoic oslo graben of southeast norway 1 1 analysis of faults and dikes 2 2 volume budget isostasy 3 3 analysis of crustal thickness distribution assuming constant crustal volume during extension these methods were found not to be suitable mainly due to rift age and magmatism instead a new integrated model which combines the effect of moho contours volumes of mantle injecta and erosion was used volumes of intracrustal mantle injecta are found from a model combining data on upper crustal felsic magmatic rocks with petrological and gravity inversion models for the vestfold graben segment in the south this implies twice the stretching estimate as compared to stretching derived from moho contours alone and two to three times the estimate from an inadequate set of fault and dike information the batholiths mark zones of high crustal thinning and magmatism was most likely caused by a combination of a thermal anomaly and lithospheric stretching

ratios of mg2 na in snowpack and an ice core at austfonna ice cap svalbard as an indicator of seasonal melting snowpack and ice core samples were collected from the dome of austfonna ice cap svalbard in the spring of both 1998 and 1999 the samples were analyzed for anions cations ph liquid electrical conductivity and oxygen isotopes concentrations of chemical components in snowpack with a history of melting were much lower than those in unmelted snowpack there was a clear difference between mg 2 na ratios previously in melted snowpack 0 011 0 02 and in unmelted snowpack 0 11 0 02 we propose that the mg 2 na ratio can be used as an indicator of whether or not firn or bubbly ice in the austfonna ice core has experienced melt percolation the mg 2 na ratio indicates that firn or bubbly ice prior to ad 1920 was much less affected by melt percolation than firn or bubbly ice formed after 1920

source and site response study of the 2008 mount carmel illinois earthquake abstract two separate inversions are performed using the ground motion data from the 2008 mount carmel illinois earthquake one uses aftershocks as empirical green s functions to determine a finite fault slip distribution the second uses mainshock ground motion spectra to calculate source path and site response parameters the slip inversion reveals a prominent asperity at the hypocenter with an area of approximately 6 km 2 moment of m w 5 20 and stress drop of about 100 bars considering all major and minor slip the total moment is m w 5 45 the rupture velocity is not resolvable due to the small source area after fixing the geometric spreading the source path and site parameter inversion yields a similar moment of m w 5 26 and a corner frequency of 0 89 hz which also give a stress drop of approximately 100 bars our combined geometric and anelastic attenuation function q f r b 1137 f 0 12 r 0 94 fits the regional spectral amplitudes where the data is more plentiful as well as previously derived attenuation relationships site response spectra show prominent resonant frequencies that correlate with the thickness of mississippi river sediments and mississippi embayment deposits in addition higher frequency resonance peaks are observed that most likely represent higher mode resonances and resonances from shallower structure

chemistry of snow deposited during the summer monsoon and in the winter season at baishui glacier no 1 yulong mountain china the glaciers on yulong mountain 5596 m a s l china are the southernmost in mainland eurasia the largest is baishui glacier no 1 up to 90 of the annual precipitation there falls in summer when warm moisture rich air masses associated with the southwest monsoon reach the area from the indian ocean the winter climate is influenced by air masses with a continental origin and by the southern branch of the westerlies the snow that accumulates on baishui glacier no 1 includes marine aerosols associated with the summer monsoon and dust brought in winter from central west asia africa or the thar desert area studies in may 2006 at two sites one in the accumulation area 4900 m and one in the ablation area 4750 m revealed differences between the ionic composition of the snow that had accumulated in the 2005 06 winter and that of the snow which had been deposited during the preceding summer monsoon differences in the chemistry of the summer accumulated snow at the two sites probably reflected local differences in ablation and elution rates rather than differences in ion supplies differences in the chemistry of the winter accumulated snow may reflect the influence of up valley winds which bring more crustal material to the lower site

the stable isotope evolution in shiyi glacier system during the ablation period in the north of tibetan plateau china in order to firstly explore the stable isotope evolution of shiyi glacier system in the central qilian mountains a total of 167 samples have been collected from newly deposited snow surface snow snowpits meltwater and glacier fed river water from july 2012 to november 2013 the results indicated that only the newly deposited snow in 23 november 2013 showed a significant altitude effect whereas surface snow had a reverse altitude effect owing to evaporation and sublimation in summer 2012 and 2013 the d

spatial and seasonal variation of major ions in himalayan snow and ice a source consideration abstract the spatial and temporal variation of major ions ca2 mg2 na k nh 4 so 4 2 no 3 and cl in himalayan snow and ice is investigated by using two snow pits from the east rongbuk glacier 28 01 n 86 58 e 6500 m a s l one snow pit from the nangpai gosum glacier 28 03 n 86 39 e 5700 m a s l one snow pit from the gyabrag glacier 28 11 n 86 38 e 6303 m a s l and three ice cores from the sentik 35 59 n 75 58 e 4908 m a s l dasuopu 28 33 n 85 44 e 7000 m a s l and east rongbuk 27 59 n 86 55 e 6450 m a s l glaciers respectively in general the major ions show a significant seasonal variation with high concentrations during the non monsoon pre monsoon and post monsoon season and relatively low concentrations during the monsoon season monsoon precipitation with high local regional dust loading related to summer circulation is possibly responsible for the high concentrations occurring sporadically during the monsoon season the crest of the himalayas is an effective barrier to the spatial distribution of na cl and nh 4 concentrations but not to the major ions associated with dust influx e g ca2 and mg2 atmospheric backward trajectories from the hysplit 4 model used in identifying chemical species sourcing suggest that the major ions in the himalayan snow and ice come mainly from the thar desert located in the north india as well as west asia or even the distant sahara desert in the north africa during the winter and spring seasons this is different from the conventionally assumed arid and semi arid regions of the central asia factors such as different vapor sources due to atmospheric circulation patterns and geographical features e g altitude topography may contribute to the differences in major ionic concentrations between the western and eastern himalayas

toward a consistent model for strain accrual and release for the new madrid seismic zone central united states 1 at the heart of the conundrum of seismogenesis in the new madrid seismic zone is the apparently substantial discrepancy between low strain rate and high recent seismic moment release in this study we revisit the magnitudes of the four principal 1811 1812 earthquakes using intensity values determined from individual assessments from four experts using these values and the grid search method of bakun and wentworth 1997 we estimate magnitudes around 7 0 for all four events values that are significantly lower than previously published magnitude estimates based on macroseismic intensities we further show that the strain rate predicted from postglacial rebound is sufficient to produce a sequence with the moment release of one mmax6 8 every 500 years a rate that is much lower than previous estimates of late holocene moment release however mw6 8 is at the low end of the uncertainty range inferred from analysis of intensities for the largest 1811 1812 event we show that mw6 8 is also a reasonable value for the largest main shock given a plausible rupture scenario one can also construct a range of consistent models that permit a somewhat higher mmax with a longer average recurrence rate it is thus possible to reconcile predicted strain and seismic moment release rates with alternative models one in which 1811 1812 sequences occur every 500 years with the largest events being mmax 6 8 or one in which sequences occur on average less frequently with mmax of 7 0 both models predict that the late holocene rate of activity will continue for the next few to 10 thousand years

source spectra of great earthquakes teleseismic constraints on rupture process and strong motion short period body waves recorded at teleseismic distances from great earthquakes provide information about source rupture processes and strong motions first we examine mostly wwssn records of 19 earthquakes of moment magnitude m w of 6 5 to 9 5 four parameters are measured from the short period p wave train the maximum amplitude the period at maximum amplitude the time between the first arrival and when the maximum amplitude is attained and coda length an extension m b of the teleseismic magnitude m b is defined using the maximum amplitude of the entire short period p wave rather than the amplitude achieved in the first few p wave cycles a least squares fit to the data yields the following relationship between m b and m w m b 0 53 m w 2 70 for m w 6 5 to 9 5 the time from the first arrival until the maximum amplitude is achieved and the coda length are roughly proportional to m w but are further interpreted by a simple asperity model of the rupture process these data support that short period waves are on average generated preferentially in the same regions of the fault plane as long period waves with periods of 10 to 50 sec we analyze the spectra of short and intermediate period teleseismic gdsn records for seven earthquakes with m w s of 6 4 to 7 8 and hand digitized short period wwssn records of the 1971 san fernando earthquake significant differences exist between the spectra of different events due partly to variations in tectonic setting or seismic coupling using the digital data we also investigate the relationship between time domain amplitude and spectral amplitude for short period p waves from our empirical relation between spectral amplitude and time domain amplitude we estimate the spectral amplitudes implied by the m b data we compare our results to the 2 and gusev spectral models neither model can completely represent the data nevertheless we consider the 2 model a useful reference model for comparing different events the average source spectrum of six large events with m w 7 4 to 7 8 does not have the spectral structure suggested by gusev an application to strong motion modeling is presented in which a 1971 san fernando teleseismic short period record is summed up to simulate teleseismic records produced by five great earthquakes the summation procedure matches the moment of the event to be simulated and includes rupture propagation fault plane roughness and randomness the m b data provide an important constraint on the summation procedures thus constrained this summation procedure can be more confidently used with near field strong motion records as green s functions to predict strong motions from great earthquakes

oxygen isotopes in glacier river water austre okstindbreen okstindan norway there is no discernible river discharge from austre okstindbreen norway in winter any water formed by basal melting is likely to be stored in isolated cavities or sediments at the bed in summer a baseflow component of discharge relatively depleted of 18 o is diluted by water more enriched in 18 o glacier ice meltwater with a high 18 o value passes rapidly through channelized systems and emerges in the glacier river within a few hours headward extension of the systems in late summer may tap water stored within the glacier since the previous summer s close down stored water also is released during early melt season events when the low capacity drainage systems cannot accommodate inputs the high 18 o value indicates that the probable source of the released water is glacier ice or low altitude snowfall stratigraphic variations of 18 o values resulting from changing weather conditions characterize the accumulating winter snowpack during the melt season the mean 18 o value of the residual pack rises the water leaving it depleted of 18 o passes slowly through the glacier smoothing out variations of supply 18 o values of rain vary between and within events and their effect on glacier river 18 o values is unpredictable

the morton black hypothesis for the thinning of continental crust revisited in western afar abstract geological observations along the western margin of afar show that the morton black model in which thinning of upper continental crust at a nascent continental margin is accomplished through block faulting and tilting is not wholly applicable rather dikes are concentrated into swarms suggestive of important direct dilatation faults are concentrated into sets within which no block tilting steeper than 45g is observed therefore attenuation of the afar margins requires a significant role for processes other than block tilting and in some margin sectors the transition from continental to neo oceanic crust may be relatively abrupt

a review of the origins of subparallel ridges and troughs generalized morphological predictions from terrestrial models the morphologies of ridges and troughs on earth and the processes involved in their formation are reviewed for application to sets of subparallel ridges and troughs on outer planet satellites we consider tension fracturing normal faulting thrust faulting buckle folding strike slip tectonism fissure eruption wall diapirism surface folding of a flow and near surface laccolithic intrusion the landform characteristics and geologic associations predicted of each process are generalized to be independent of planet specific parameters we find that the combinations of landforms derived from each process are unique making each distinguishable in the idealized case morphological parameters most diagnostic of formational process are ridge and trough cross sectional shape termination style and incipient character the characteristics described are useful in constraining the origin of ridge and trough terrains observed in voyager images and will aid in analysis of high resolution images from the galileo and cassini spacecraft

the earthquake potential of the new madrid seismic zone the fault system responsible for new madrid seismicity has generated temporally clustered very large earthquakes in a d 900 100 years and a d 1450 150 years as well as in 1811 1812 given the uncertainties in dating liquefaction features the time between the past three new madrid events may be as short as 200 years and as long as 800 years with an average of 500 years this advance in understanding the late holocene history of the new madrid seismic zone and thus the contemporary tectonic behavior of the associated fault system was made through studies of hundreds of earthquake induced liquefaction features at more than 250 sites across the new madrid region we have found evidence that prehistoric sand blows like those that formed during the 1811 1812 earthquakes are probably com pound structures resulting from multiple earthquakes closely clustered in time or earthquake sequences from the spatial distribution and size of sand blows and their sedimentary units we infer the source zones and estimate the magnitudes of earth quakes within each sequence and thereby characterize the detailed behavior of the fault system it appears that fault rupture was complex and that the central branch of the seismic zone produced very large earthquakes during the a d 900 and a d 1450 events as well as in 1811 1812 on the basis of a minimum recurrence rate of 200 years we are now entering the period during which the next 1811 1812 type event could occur

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

geologie und bau des sithonia ophioliths chalkidiki ne griechenland anmerkungen zur bildung ozeanischer krusten der oberjurassische sithonia ophiolith der chalkidiki ne griechenland bietet die moglichkeit die an der bildung fossiler ozeanischer krusten beteiligten prozesse ausfuhrlich zu untersuchen

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

the seismic radiation from composite models of faulting abstract the failure of an asperity i e the dynamic rupture of a small fault area with finite stress drop surrounded by a broken or weak fault area which has no stress drop but which slips after the asperity fails is proposed as a model for the rupture process of a subevent in a composite earthquake the rupture area of the composite earthquake surrounding the subevent is modeled by the weak fault area surrounding the asperity in the subevent model the resulting seismic moment of the subevent is proportional to the stress drop and the rupture area of the subevent as well as the radius of the composite earthaquake by setting the stress drops of the asperity models equal to the dynamic stress drops of the subevents the composite earthquake can be modeled as the sum of a set of subevents which cover the rupture area of the composite earthquake the scaling of the high and low frequency radiation from composite earthquakes composed of asperities is commensurate with generally observed spectral scaling laws in contrast to composite earthquakes composed of cracks or smaller earthquakes a simple filtering strategy is proposed for filtering the waveforms radiated by cracks to approximate the waveforms radiated by asperities the p and s waves radiated by an m l 5 2 earthquake which occurred on 9 may 1983 at coalinga california are simulated using the p and s waves radiated by an m l 3 6 aftershock the aftershock waveforms are first filtered to approximate the radiation from asperities with the appropriate rupture areas and then the waveforms of 12 asperity subevents are summed together to simulate the waveforms and spectra of the composite earthquake

mechanisms of seismic attenuation in the crust scattering and anelasticity in new york state south africa and southern california the envelopes of high frequency seismograms from earthquakes in new york state south africa and southern california are analyzed to determine how much of the observed attenuation of shear waves in the crust is caused by anelasticity and how much is produced by scattering from small scale heterogeneities for seismograms from new york and south africa there is a systematic enrichment of high frequency energy that develops in the coda relative to the direct s or l sub g waves the author uses the growth with source receiver distance of the high frequency energy in the coda relative to the direct wave to estimate the scattering attenuation of the crust and the relative time decay of high frequency energy in the coda to determine the anelastic attenuation using the estimate of l sub g wave q as a constraint he finds that the scattering q in the crust of new york is either independent of frequency or increases with frequency f slower than f sup 0 3 a similar analysis for south africa indicates that scattering is the major cause of the observed s wave attenuation of high frequency energy 30 hz at local distances 100 km for southern california the extent of the scattering attenuation is unclear from the data more although the relatively steep coda decay of southern california implies that anelastic attenuation is stronger there than in new york or south africa for southern california and new york state the 3 hz coda q taken from the late coda 50 110 s is comparable to the l sub g wave q however the 3 hz coda q for south africa over these lapse times is about 5 times the estimated l sub g wave q for all three areas the frequency dependence of the coda q does not match the frequency dependence of the s wave q and for new york and south africa it changes with lapse time less

rupture process of the 26 january 2001 mw 7 6 bhuj india earthquake from teleseismic broadband data we investigate the rupture process of the 26 january 2001 bhuj india m w 7 6 earthquake through inversion of teleseismic broadband body waves this earthquake ranks as one of the most important recent events due to its occurrence within a stable continental interior where such events are rare the bhuj earthquake occurred on a moderately dipping blind thrust fault within an ancient failed rift about 70 of the seismic moment released in the earthquake was confined to a very small area 375 km2 surrounding the hypocenter and at depths below 12 km the static stress drop of the bhuj earthquake is anomalously high 20 mpa the source time history of the event indicates very rapid onset to the moment release and most likely high slip velocities within the deep asperity this suggests that some of the damage near the epicenter may have been caused by anomalously high frequency ground motions the teleseismic data also indicate the presence of a second area of large slip in the shallow part of the bhuj fault although the depth extent of this shallow large slip area is not resolved comparisons of the predicted ground motions with observed intensities suggest that substantial slip occurred in the upper 10 km of the fault in order to explain the distribution of high intensities to the west and northwest of the fault the upper surface layers near the bhuj fault consist of unconsolidated low rigidity sediments and alluvium the upper 10 km of the bhuj fault may therefore be in a conditionally stable region that normally deforms through aseismic creep and can sustain seismic rupture only when dynamically stressed by rupture of the high strength deep asperity we suggest that this deep asperity may be related to a lithologic anomaly of ultramafic composition

tectonic rotations in extensional regimes and their paleomagnetic consequences for oceanic basalts paleomagnetic samples of many deep sea drilling project dsdp basalts have shallower inclinations than would be inferred from the paleolatitude at which the basalts were extruded at mid ocean ridges rather than arising from peculiarities of the geomagnetic field the anomalous magnetic directions may result from tectonic rotations along the listric normal faults which often characterize extensional tectonic regimes several lines of evidence support this conclusion observations of the basin and range province an extensional tectonic regime occurring in continental crust observations of the troodos complex cyprus an oceanic extensional tectonic regime now exposed on land and analysis of possible fault patterns associated with the magma chambers postulated to occur at some mid oceanic ridges the tectonic rotations resulting from movement along the listric normal faults occur about a horizontal axis generally perpendicular to the extension direction and typically amount to 30 to 50 although rotations as large as 70 to 90 are not uncommon the paleomagnetic consequences of these rotations can be calculated for dsdp basalts if the original strike and latitude of a ridge are known at four dsdp sites for which adequate data are available namely sites 319 332 410 and 417 rotations ranging from 50 to 70 are required to explain the paleomagnetic results if the original strike and location of the ridge are not known as is the case for most of the older parts of the pacific ocean the paleomagnetic data and the inferred rotation determine a relationship between possible ridge strikes and locations this information combined with a similar but independent relationship derived from the marine magnetic anomalies puts severe constraints on the original strike and location of the ridge

tibetan plateau summer monsoon northward extent revealed by measurements of water stable isotopes a program of individual precipitation events and river water sampling and of water isotopic measurements d 18o was carried out during summer 1996 along a northeast southwest transect of the tibetan plateau the spatial distribution of both 18o and deuterium excess d d 8 18o of the precipitation reveals three distinct regions simulations with a simple isotopic model and seasonal isotopic variations measured at two extreme south and north locations support our interpretation in terms of different summer moisture origins 1 south of the himalayan mountains the moisture provided by the indian monsoon has been recycled over the indian peninsula 2 between the himalayas and the tanggula mountains the oceanic moisture is directly transported from the bay of bengal along the brahmaptra river valley 3 north of the tanggula mountains the moisture is not provided by the monsoon anymore but by continental water recycling

novel type of crust produced during continental rifting a normal oceanic crust cannot be generated after continental crust splitting of rifts filled by a thick pile of young sediments the magma released by the rising mantle is trapped mainly in these sediments as basalts sills and plugs the sediments are themselves metamorphosed by the heat flux from the underlying mantle a metasedimentary crust is formed in direct contact with an abnormal mantle vp 7 5 km s l produced by partial serpentinization