pollen sequence from the chilean lake district during the llanquihue glaciation in marine oxygen isotope stages 4 2 pollen stratigraphy of a core taken from a fen at fundo nueva braunau 40 17 499s 73 04 839w situated 2 km beyond the western border of llanquihue age glacial drift spans an age range from an estimated 60 000 70 000 bp to about 14 000 14 c yr bp marine oxygen isotope stages 4 2 the location at present is in the contact zone of valdivian evergreen forest and lowland deciduous beech forest early and late in the pollen record as indicated by assemblages of southern beech nothofagus dombeyi type and grass gramineae the site was located in subantarctic parkland intervening assemblages represent expansion of valdivian north patagonian evergreen forest 49 355 to about 40 000 14 c yr bp and north patagonian evergreen forest subantarctic parkland approximately 40 000 to 30 000 14 c yr bp climate over the time span was under the storm regime of the southern westerlies and apparently uninterruptedly wet when subantarctic parkland expanded cold conditions with summer temperatures estimated at 8 9 c 7 c lower than present resulted in episodes of glacier maxima climate moderated during the period of forest expansion at which time glaciers were in a state of recession contrasting with the continuously wet climate of the lake district for the period of record climate in semi arid arid subtropical chile underwent extended intervals of precipitation data from both the terrestrial and marine realm implicate the southern westerlies as the cause of intensified storm activity at lower latitudes copyright 2000 john wiley sons ltd

spectral discrimination between nts explosions and western united states earthquakes at regional distances spectral ratio disciminants are applied to 72 western united states earthquakes and 64 nts explosions recorded at four broadband seismic stations surrounding nts the ratio of the energy in the 1 to 2 and 6 to 8 hz bands for pn pg and lg is calculated and a simple distance correction applied to the data the spectral ratio appears to have potential as a disciminant at relatively small magnitudes 3 0 4 5 to 5 0 this may be due to uncertainties in the apparent source time function for explosions these complications may be due to changes in the dynamic response of the material in the near source region as a function of overburden pressure effects of secondary sources or to variations in regional phase excitation with depth

calibration of mb pn mb lg scales and transportability of the m0 mb discriminant to new tectonic regions we have developed mo mb relationships for earthquakes and explosions in central asia using regional waveform data from the chinese broadband digital station wmq regional magnitude scales mb pn and mb lg were established by 1 determining the attenuation rates of pn and lg waves 2 calibrating the mb pn against the teleseismic rob and 3 applying nuttli s method to determine m b from the lg waves seismic moments for earthquakes and explosions were obtained by applying the bolt and herraiz 1983 method calibrated using cmt moments for earthquakes and regional moment estimates of the soviet joint verification experi ment jve explosion the results show that mo mb pn relationships for central asian earthquakes and explosions are in excellent agreement with the relationships for the western united states this demonstrates that the mo r discriminant is transportable to other regions and supports theoretical claims patton and walter 1993 that mo m b are directly comparable for explosions detonated in different emplacement media successful application depends upon correcting the mb pn for the magnitude bias known to exist between the shagan river test site and the nevada test site nts in general region specific mb bias must be accounted for whenever regional mag nitude scales are calibrated against teleseismic rob as pointed out by douglas and marshall 1996 transporting mo mb lg can be problematic because attenuation rates based on coda waves or lg waves from earthquakes may not necessarily apply to lg waves from explosions and vice versa this is demonstrated for the western united states where the coda q measured from explosion data is much lower than the coda q from earthquake data we show that mb lg for earthquakes located close to nts is greatly overestimated using the q values determined from the coda of nts explosions this is apparently not a problem for lg calibration in central asia perhaps because of differences in velocity and or q structures for the two regions other important considerations are the character of lg propagation on short paths 400 km for nts explosions versus long paths 1000 kin for east kazakh explosions and the properties of coda wave spreading as a function of distance and velocity structures for different tectonic regions

source parameters from locally recorded aftershocks of the 9 january 1982 miramichi new brunswick earthquake abstract source parameters are derived from 111 locally recorded three component seismograms of 40 aftershocks magnitude 1 0 to 3 5 of the 9 january 1982 miramichi new brunswick earthquake this data set greatly expands the set of three component data recorded at small source to receiver distances in eastern north america preliminary analysis showed that some aftershock spectra were modified by strong site effects the need to understand and account for site effects when analyzing the aftershock data in terms of simple source models led to a two part data analysis first site effects were modeled as a seismic wave resonance in a thin layer 0 to 10 m of low seismic impedance glacial till over a high seismic impedance bedrock half space second we calculated source parameters from sh wave seismograms and amplitude spectra incorporating what had been learned about site resonances correcting for obvious site effects partially succeeded in reducing scatter in the source parameter determinations but some site dependent discrepancies remain seismic moments range from 1 10 18 to 5 10 20 dyne cm and corner frequencies from 5 to 45 hz brune model stress drops primarily range between 5 and 300 bars stress drop apparently increases with increasing seismic moment trends in apparent stress calculated from radiated energy and seismic moment parallel trends in stress drop corner frequencies from these locally recorded data are greater than those derived from regionally recorded l g waves for earthquakes of comparable moment this result contradicts a recently proposed m 0 4 constant source scaling law based primarily on l g data

mid and late holocene limnogeology of laguna del negro francisco northern chile and its palaeoclimatic implications lacustrine sediments from the high elevation endorheic saline lake negro francisco 27 28 s 69 14 w 4125 m provide a detailed mid and late holocene environmental history of the southern chilean altiplano mineralogy chemical composition and sedimentary facies analyses of the deposits confirm the regional significance of mid holocene aridity between 6000 and 3800 bp precipitation rates were signifi cantly lower than the c 250 mm yr 1 of today fully arid conditions were interrupted by short term moist spells with an average return period of about 200 years effective moisture increased after 3800 bp and peaked between 3000 and 2600 bp and between 2200 and 1800 bp in two phases with conditions more humid than today comparison with regional palaeodata suggest that these two late holocene humid spells were most likely related to pacific moisture sources salinity levels increased again in laguna del negro francisco after 1800 bp the onset of modern climatic conditions was a stepwise nonlinear proce

riphean basins of the central and western siberian platform abstract the siberian platform is unique by its volume of meso neoproterozoic sedimentary deposits for about one billion years 1650 650 ma several sedimentary basins were developed here resulting in the formation of several kilometers thickness of sedimentary cover the riphean mesoproterozoic lower neoproterozoic rocks are exposed mainly along platform peripheries the most complete sections are represented by several megacycles each megacycle contains terrigenous series at the base and carbonate formations in the upper part several isolated and anisochronous basins were created during the riphean on the territory of east siberia some of them were intracratonic others were developed on passive margins neoproterozoic orogeny along the platform boundaries resulted in re organization of the siberian basins with extensive faulting uplifting and erosion of the territories in eastern siberia riphean series contain large hydrocarbon accumulations the reservoirs were formed mainly due to fracturing and leaching of carbonate strata e g vugular carbonates of the pre vendian weathering crust the upper proterozoic deposits are overlain by thick clayey carbonate and saliferous carbonate series of the upper vendian and cambrian isolating them from the upper sedimentary cover the riphean basins contained thick organic rich clayey and clayey carbonate in some of them a hydrocarbon generation maximum took place at the end of the riphean the pre vendian erosion has removed a significant volume of riphean sediments during this time a majority of already formed hydrocarbon accumulations have been lost or degraded remaining riphean series have generated hydrocarbons during the paleozoic despite its complex history the riphean is still considered highly prospective with source rocks developing at multiple levels and reservoirs occurring in both carbonate and clastic rocks discoveries of new oil and gas fields in east siberia are likely but will depend on integration of detailed seismic data and a large volume of core data for the correct prognosis of riphean reservoir distribution

a 50 000 yr pollen record from chile of south american millennial scale climate instability during the last glaciation abstract high resolution 100 yr sampling interval chilean pollen data between 10 000 and 60 000 cal yr b p exhibit systematic fluctuations in subantarctic parkland development these variations are dominated by a 30 000 40 000 yr cycle similar to that in the northern hemisphere gisp2 18 o data and other climatic records both chilean and gisp2 data show oscillations in the 5000 12 000 and 1000 3000 yr period bands the coherence is however generally low and distribution of power spectra differs with the dynamics of the pollen assemblage dominated by a combination of 12 000 and 5000 yr cycles we suggest a preferential nonlinear response of chilean vegetation to climatic forcing and interhemispheric differences as possible mechanisms underlying the resemblances and dissimilarities between both records

spectral characteristics of the excitation and propagation of lg from underground nuclear explosions in central asia the nonlinear inverse method of xie 1993 is applied to analyze lg spectra from many recent underground nuclear explosions in central asia the analysis simultaneously determines lg seismic moments m0 and corner frequencies fc of events as well as path variable lg q values and their frequency dependences at 1 hz lg q at 1 hz estimated for many paths from the lop nor and balapan test sites to various broadband incorporated institution for seismology chinese digital seismic network and kyrghizstan network stations agree well with path averaged lg coda q values from previously obtained tomographic maps for eurasia this suggests that the lg q values obtained in this inversion have not been significantly affected by focusing defocusing or other effects of three dimensional structural complexities the logarithms of lg m0 values obtained in this study correlate linearly with a slope of about 1 2 with international seismological centre isc body wave magnitudes mb the linear relationship is consistent with a previous empirical relationship found between the logarithm of p wave seismic moments and isc mb values the slope of the linear relationship also suggests that the logarithm of lg m0 is a more direct measure of event size than is mb which for larger events is affected by high frequency amplitude falloff another important finding of this study is that the m0 values for the explosions scale with fc 4 rather than with fc 3 as would be expected if stress drops were constant this is consistent with previous scaling relations derived using lg from earthquake sources and suggests that the difference between lg and local s excitation by the same source types explosion or earthquake may overwhelm that between the excitation of lg by different source types a comparison between lg m0 and fc values obtained using an explosion source model with those obtained using an earthquake source model suggests that the m0 values estimated using the explosion source model are systematically lower by a factor of 0 27 than those estimated using the earthquake source model this occurs even though the data used are the same in the inversions with the two types of source model the factor of 0 27 is therefore due to the source model dependence of the m0 fc estimates the overshoot and lower spectral levels at lower frequencies in the explosion source model tend to reduce both the estimated m0 and fc values this suggests that in any nuclear monitoring program the same type of source model either an earthquake or explosion should always be used to discriminate explosions using lg the source model dependence also suggests that more effort should be made to estimate the amount of overshoot in the lg excitation caused by various source types

attenuation of multiphase surface waves in the basin and range province part i lg and lg coda summary broad band data recorded by the lawrence livermore laboratory network are used to investigate whether or not lg q and lg coda q have similar values in the basin and range province of north america in order to retrieve spectral estimates of the broad band lg and lg coda signals a hybrid method is used which retains high fidelity at lower frequencies while strongly smoothing the spectral estimates and minimizing the number of spectral points at high frequencies a stochastic approach is used to model the lg signal and ambient noise and to analyse results from two station determinations of lg q in the basin and range the effects of ambient noise frequency dependent station site response and focusing defocusing on lg q inversion are analysed it is shown that after averaging spectral ratios determined from repeated observations over four two station paths a modest site effect will not cause significant errors in the resulting lg q relation using this inversion scheme and spectral ratio estimates averaged over those paths at frequencies between 0 2 and 2 5 hz we obtain the relation qlg f 267 f 56 f0 37 0 06 for the basin and range province further constraints on lg q were obtained from lg coda which due to the natural averaging effect of scattering is insensitive to effects of focusing defocusing to investigate the validity of the single isotropic scattering model for lg coda in the basin and range province we calculated ischrons for scatterers corresponding to later lg coda signals as required by the single scattering model it is found that when significant portions of these isochrons are oceanic lg coda amplitude decay becomes irregular and abnormally slow suggesting a strong scattering reflection effect caused by the rapidly changing crustal structure along the coast applying the single isotropic scattering model to lg coda records with isochrons mostly confined to the continental crust results in q f 275 f 26 f 0 36 0 03 which is nearly identical to our qlg relation this indicates that even in a complicated geological province a joint interpretation of the dynamic properties of lg and lg coda can be successful and fruitful inconsistent lg q and coda q relations found in earlier studies in the basin and range province may be attributed to different settings of parameter trade offs different seismic phases or different dynamic properties being used

interpretation of high frequency coda at large distances stochastic modelling and method of inversion summary based on previous work a stochastic convolution model is proposed for the lg coda observed at large epicentral distances 200 km coda at these distances differ from local coda in several respects effects of various physical processes such as dispersion scattering and mode conversion on coda at large distances are discussed in detail a spectral ratio method is developed for inversion of lg coda q in which the large variance associated with inversion is greatly reduced the method is also extended to the inversion of seismic source parameters by jointly using lg and its coda we have tested the model and method exhaustively using data from two gdsn stations and found the results to be superior to other methods when those methods used only a small number of stations

lg magnitudes and yield estimates for underground novaya zemlya nuclear explosions abstract lg wave amplitudes of 30 novaya zemlya underground nuclear explosions as recorded by short period seismographs in denmark finland germany norway spitsbergen and sweden are used to determine m b lg values assuming that the m b lg versus explosion yield relation derived from nevada test site data applies to all continental areas the yields of the explosions are estimated they cover a large range of values from 2 5 to 4900 kt the largest explosion since april 1976 had an estimated yield of 145 kt the m b lg values when subtracted from the m b p values can be used to estimate the m b p bias between two test sites in this way the m b p bias between novaya zemlya and the nevada test site is estimated to be 0 20 magnitude units

lg coda q variation across eurasia and its relation to crustal evolution an extensive set of broadband and short period seismograms from regional seismic events has been used to derive a tomographic image of broad scale variations of lg coda q for most of eurasia the image indicates that lg coda q at a frequency of 1 hz varies between about 200 and 1000 lowest q values 800 are found in four regions the east european shield the siberian shield the indian shield and the southwestern and oldest portion of the altaid belt the pattern of lg coda q variation across eurasia suggests that crustal q in any region is directly proportional to the length of time that has elapsed since the most recent episode of large scale compressional tectonic activity or upper mantle heating that occurred there we interpret the low q as resulting largely from hydrothermal fluids generated by tectonic activity or heating that now reside in cracks and permeable portions of the eurasian crust crustal q increases with time after that activity as fluids are lost to the surface or absorbed by retrograde metamorphism

the riphean sedimentary basins of the eastern siberia province and their petroleum potential abstract from their location in the regional pattern of the eastern siberia province their style and their evolutionary history the riphean sedimentary basins are divided into two groups marginal cratonic and intracratonic the first group includes basins of pericratonic troughs fore deeps and marginal transverse aulacogens they are characterized by a definite division into structural stages according to both characteristics of the individual formations and interbedding of rocks with different lithology within sequences there is a complex combination of formations such as black shale and flyschlike volcanoclastic terrigenous carbonate and others the second group incorporates aulacogenic and platform intracratonic sedimentary basins the main features of aulacogen type sedimentary basin structure are due to their rift origin and style of subsequent development the early stages are marked by an alternation of volcanoclastic terrigenous and volcanoclastic carbonate rocks there is rythmic interbedding of terrigenous and terrigenous carbonate rocks up section depositional environments in sedimentary basins of platform depression have been controlled to a large extent by the structural dynamic setting of the final stages in the formation of adjacent pericratonic troughs and intracratonic aulacogens the succession consists mainly of terrigenous carbonate and carbonate terrigenous units i e products of erosion and re deposition of early riphean complexes and ancient basement distribution of particulate organic matter and its catagenetic transformation indicate rather high petroleum generating potential for the riphean regional development of high quality seals upper vendian argillaceous evaporite carbonate units and lower cambrian salts greatly favors preservation of hydrocarbon accumulation three groups of hydrocarbon reservoirs are differentiated based on structural tectonic lithologic formational and geochemical features hydrocarbon fields of considerable commercial importance have been discovered for the first time in world exploration practice in the riphean of the east siberian province these should lead to the re evaluation of the hydrocarbon potential of late proterozoic basins on other continents

the 1982 enola arkansas swarm and scaling of ground motion in the eastern united states abstract the north central arkansas swarm which began in january of 1982 and was still active as of december 1983 has produced over 30 000 events three of these events had duration magnitudes greater than 4 0 fifty three locatable events in the magnitude range 3 8 and below were recorded during the 2 1 2 weeks our 10 digital seismographs were in place the hypocentral locations are confined to a tight cluster with a radius of approximately 1 km depths range between 4 and 7 km focal mechanisms determined for 10 of the events show a combination of strike slip and normal faulting source parameters seismic moment source radius and stress drop were calculated for 48 of the events the seismic moments range from 10 18 to 10 21 dyne cm while the stress drops range from 0 2 to 60 bars acceleration spectra are band limited at the high end at 30 hz the stress drops increase with seismic moment up to 10 20 dyne cm but appear to be constant at greater moment values the arkansas source parameters are similar to other body wave source parameters determined from near source investigations of earthquakes in eastern and central north america e g new brunswick and south carolina and in california e g mammoth lakes oroville and anza but differ substantially from lg wave source parameters estimated for earthquakes in the eastern and central united states

some recent lg phase displacement spectral densities and their implications with respect to the prediction of ground motions in eastern north america abstract lg phase displacement spectral density corner periods of recent earthquakes in central new brunswick and central arkansas are used to point out a potential source of dispersion in the relative scaling of eastern north american strong motion data the corner periods of one of the central new brunswick and several of the larger central arkansas earthquakes are atypical of other events of similar magnitude and seismic moment in the region the maximum far field ground motion of an earthquake is a function of its corner period therefore strong motion data of earthquakes that exhibit atypical characteristics such as a displaced corner period are a source of dispersion in the scaling of that strong motion data if plotted as a function of magnitude or seismic moment

tomographic regionalization of crustal lg q in eastern eurasia 1 we measure q of crustal lg waves in eastern eurasia using the reliable two station methods more than 5 000 spectral ratios are collected over 594 interstation paths and are used to determine values of lg q0 and q at 1 hz and its frequency dependence over these paths these values are used to derive tomographic models of laterally varying q0 and with resolutions between 4 and 10 the q0 model contains values that vary between 100 and 900 q0 are the lowest in the tibetan plateau increase to moderate levels towards the east and north and reach maxima in the siberian and eastern europe cratons q0 values correlate well with regional tectonics most values are between 0 14 and 0 50 with a mean of 0 18 these values are lower than those obtained previously using either an lg coda q method or a method of simultaneous inversion of source spectra and q

discrimination of earthquakes and explosions in the eastern united states using regional high frequency data high frequency regional records from small earthquakes 1 3 magnitude 4 and comparable magnitude explosions are analyzed to find a reliable seismic discriminant in the eastern u s over 500 digital vertical component seismograms recorded by the new york state seismic network in the distance ranges 10 to 610 km are used mean p lg spectral ratios in the band 1 25 hz are about 0 5 and 1 25 for earthquakes and explosions respectively in the eastern united states we find that the high frequency p lg spectral amplitude ratio in the frequency band 5 25 hz is a reliable and robust discriminant for classifying these events a linear discriminant function analysis indicates that the p lg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 1 single hole instantaneous explosions and ripple fired quarry blasts have somewhat different p lg spectral ratios but as a group are distinctly different from earthquakes

lg magnitudes of selected east kazakhstan underground explosions abstract the amplitude of 1 sec period lg waves as recorded on seismograms of wwssn stations in southern asia and scandinavia are used to determine m b lg values for 62 underground nuclear explosions in the eastern portion of the east kazakhstan test site the explosions were selected to be of m b p 5 5 or greater in the period 1965 to 1985 the yields of the explosions are estimated assuming that a nevada test site derived relation between m b lg and yield for water saturated rock is also applicable to the east kazakhstan test site assuming that lateral variations in crustal structure and in depth of emplacement of the explosion do not affect m b lg values the lg data indicate that the m b p bias between the nevada test site and east kazakhstan is 0 35 magnitude units

comparison of seismic body wave and coda wave measures of q measurements of seismic attenuation q 1 can vary considerably when made from different parts of seismograms or using different techniques particularly at high frequencies these discrepancies may be methodological or may reflect earth processes to investigate this problem we compare body wave with coda q 1 results utilizing three common techniques i parametric fit to spectral decay ii coda normalization of s waves and iii coda amplitude decay with lapse time q 1 is measured from both body and coda waves beneath two mountain ranges and one platform from recordings made at seismic arrays in the caucasus and kopet dagh over paths 4 long if q is assumed frequency independent spectral decay fits show q s and q coda near 700 800 for both mountain paths and near 2100 2200 for platform paths similar values are determined with the coda normalization technique however frequency dependent parameterizations fit the data significantly better with q s 1 hz and q coda l hz near 200 300 for mountain paths and near 500 600 for platform paths lapse decay measurements are close to the frequency dependent values showing that both spectral and lapse decay methods can give similar results when q has comparable parameterizations above 6 hz coda measurements suggest some enrichment relative to body waves perhaps due to scattering but intrinsic absorption appears to dominate at lower frequencies all approaches show sharp path differences between the eurasian platform and adjacent mountains and all are capable of resolving spatial variations in q

an overview of pre devonian petroleum systems unique characteristics and elevated risks abstract the radiation of land plants at the onset of the devonian resulted in a change in the character of available biomass which in turn introduced changes to the nature of petroleum systems this study examines the nature of pre devonian petroleum systems prior to this significant evolutionary event conventional hydrocarbon resources have been associated with pre devonian petroleum systems across the globe including the neoproterozoic infracambrian huqf supergroup of the oman basin the riphean vendian sequences of east siberia the cambrian of the murzuq basin the ordovician of the tarim basin and the silurian qusaiba of saudi arabia although individual accumulations can be quite significant e g hassi messaoud has ultimate recoverable reserves of 10 billion barrels the relative importance of pre devonian derived oils is thought to be limited compared to the global conventional resource base with growing interest in unconventional resources the relative importance of these systems is expected to increase as resource plays such as the ordovician utica shale of the appalachian basin the cambrian of china and possibly the silurian of central and eastern europe develop the advanced ages of these systems result in some unique properties and amplify risks that exist in younger petroleum systems differences in the nature of the biomass contributing to pre devonian source rocks may give rise to oils that display unique geochemical characteristics for example there are some precambrian oils where c 29 steranes dominate even though land plants were absent there are also ordovician source rocks dominated by gloeocapsamorpha prisca a primitive prokaryote which yield oils containing limited amounts of c 20 components and nearly lack pristane and phytane the potential for unconventional reservoirs in pre devonian systems may also be highly dependent upon the age of the system as biological evolution influences the availability and nature of biogenic silica an important factor controlling brittleness and fracability literature has shown that biogenic silica from different sources displays varying degrees of resistance to diagenesis which allows the formation of a silica network and influences brittleness for example radiolaria present during the cambrian are more resistant to diagenesis than diatoms which did not evolve until the jurassic risks associated with preservation of hydrocarbons are also amplified in pre devonian petroleum systems many such systems have been exposed to significant thermal stresses resulting in the cracking of oil and wet gas others have had complex tectonic histories potentially resulting in the breaching of seals or changes in pvt conditions that can result in gas loss gas loss may also occur through diffusion from these older reservoirs as a result of long residence times

the petroleum potential of the riphean vendian succession of southern east siberia the siberian platform covers an area of c 4 5 million km 2 in the east siberia region of russia up to 3 5 million km 2 of which is prospective for hydrocarbons we review the archaean to neoproterozoic evolution of the siberian platform and the potential oil and gas resources of riphean vendian and infracambrian sediments the riphean was dominated by passive margin sedimentation and was intensely deformed during the baikalian orogeny vendian strata record a clastic transgressive sequence and the eventual re establishment of carbonate platform sedimen tation the late vendian early cambrian is characterized by carbonate deposition including thick salt horizons which form a regional seal hydrocarbon maturation and migration from riphean and vendian source rocks occurred during the late neoproterozoic and early palaeozoic indicating that hydrocarbon reservoirs on the siberian platform may have hosted their reserves over a remark able period of geological time despite many years of hydrocarbon exploration in east siberia many regions remain under explored and aspects of the proven hydrocarbon systems are poorly understood there are undoubtedly more major discoveries to be made in the region and the infra cambrian succession of the southern siberian platform therefore represents an irresistible target for further hydrocarbon exploration infracambrian sedimentary basins are a major source of hydrocarbons in many parts of the world including australia india pakistan oman mauri tania the usa and east siberia oil shows were noted in east siberia more than 200 years ago and since then east siberia has become a world class hydrocarbon province oil and gas in place esti mates are 4 billion barrels of oil bbbl nakashima 2004 and 38 trillion cubic feet tcf of gas ulmishek 2001a b nakashima 2004 oil in east siberia is of high quality with a density of 318api sulphur content of 0 1 1 3 and low paraf fin content c 1 poussenkova 2007 the east siberian gas reserves differ from the gas fields of west siberia in that they have a particularly high helium content 0 2 0 6 poussenkova 2007 total helium reserves in east siberia are estimated to be between 1 9 and 2 5 tcf exceeding the helium reserves of the usa which is currently the world s largest producer poussenkova 2007

modeling some empirical vertical component lg relations abstract higher mode surface wave theory is used to model the vertical component lg wave observed in eastern north america at regional distances tests of the model are made to determine whether it is capable of describing empirical spectral scaling laws spatial attenuation and peak time domain lg amplitudes it is found that a simple crustal model and a rough estimate of crustal qb are all that are required to accomplish this good results are obtained if the average crustal qp is equated to the coda q of the same frequency introduction the lg wave is a wave observed on short period seismograms of local and regional seismic events which travels with a group velocity of approximately 3 5 km sec in the central united states it is usually the largest arrival on the seismogram which makes it suitable for defining a magnitude scale nuttli 1973 herrmann and nuttli 1982 as part of developing the magnitude scale there have been many studies on the spatial attenuation of the lg wave nuttli 1973 street 1976 bollinger 1979 singh and herrmann 1982 the lg wave is usually thought of as a superposition of higher mode surface waves propagating within the crustal wave guide herrmann and nuttli 1975a b attempted to deterministically model observed lg amplitudes in terms of focal mechanism focal depth and seismic moment using surface wave techniques they were limited by their inability to compute surface wave eigenfunctions at frequencies greater than 0 5 hz however their results were encouraging harkrider 1979 drawing upon the work of apsel 1979 discovered a way to compute surface wave energy integrals of the higher modes very precisely bache

late quaternary precessional cycles of terrigenous sediment input off the norte chico chile 27 5 s and palaeoclimatic implications abstract the palaeoclimatic conditions during the last glacial maximum lgm of southern south america and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially longer palaeoclimatic records covering the late quaternary are rare a particularly sensitive area to late quaternary climatic changes is the norte chico northern chile because of its extreme climatic gradients small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments to unveil the history of shifting climatic zones in northern chile we present a sedimentological study of a marine sediment core geob 3375 1 from the continental slope off the norte chico 27 5 s sedimentological investigations include bulk and silt grain size determinations by sieving atterberg separation and detailed sedigraph analyses additionally clay mineralogical parameters were obtained by x ray diffraction methods the 14c dated core covering the time span from approximately 10 000 to 120 000 cal yr b p consists of hemipelagic sediments terrigenous sedimentological parameters reveal a strong cyclicity which is interpreted in terms of variations of sediment provenance modifications of the terrestrial weathering regimes and modes of sediment input to the ocean these interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern chile 27 5 s through the late quaternary the cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles for the palaeoclimatic signal this means that more humid conditions coincide with maxima of the precession index as e g during the lgm higher seasonal precipitation for this part of chile is most likely derived from frontal winter rain of the southern westerlies thus the data presented here favour not only an equatorward shift of this atmospheric circulation system during the lgm but also precession controlled latitudinal movements throughout the late quaternary precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the northern hemisphere monsoonal system in the atlantic ocean region

source time functions of nuclear explosions and earthquakes in central asia determined using empirical green s functions relative source time functions rstf have been estimated for four underground nuclear explosions and seven earthquakes in central asia using broadband p waveforms of nearby smaller events as empirical green s functions egf rstfs of the four explosions m sub b 5 3 to 6 5 are each dominated by a simple pulse with a source duration of 0 4 to 0 8 s rstfs for two of the explosions show a significant secondary pulse with a pulse width similar to that of the first pulse the authors conclude that the secondary phases are most likely associated with the spall slapdown phenomenon seismic moment releases by the spall phases are less than one third of those by the first explosion pulses elastic radii of the explosions are estimated to be about 0 25 to 0 5 km and stress drops of the explosion range from 13 to 52 mpa in contrast rstfs of earthquakes studied m sub b 5 5 to 6 6 typically comprise multiple source pulses with a total source duration from a few to several tens of seconds indication that the complex source process involves a fault dimension of several tens of kilometers stress drops of the earthquakes are much smaller than those of the nuclearmore explosions ranging from 0 5 to 3 5 mpa the authors study demonstrates the power of the egf method for retrieving rstfs and reveals that differences in rstfs and source parameters can be used to distinguish large nuclear explosions from moderate to large earthquakes m sub b 5 5 80 refs 11 figs 6 tabs less

integrated chronostratigraphy of the vendian system of siberia implications for a global stratigraphy integrated 13 c chemostratigraphy and sequence stratigraphy are developed for a succession of vendian strata nokhtuisk section on the southern margin of the siberian platform the carbonates exhibit secular variations in 13 c and at least three major depositional sequences that encompass the last c 20 million years

regional phase excitation and propagation in the lop nor region of central asia and implications for p lg discriminants ital pn and ital lg spectra for lop nor explosions and nearby earthquakes were analyzed for source and propagation effects using a modified inversion method of ital xie 1993 spectral analyses were performed on waveform data from incorporated research institution for seismology chinese digital seismic network kazakhstan and krgyzstan networks ital pn amplitude variations of a factor of 20 are observed across the small aperture lt 200 km kyrgyzstan network and are probably related to three dimensional moho structure close to the network comparisons of ital pn amplitudes and spectral ratios provide evidence for nonisotropic radiation pattern effects in the case of earthquakes and overshoot in explosion time histories complex source effects are born out in our inversion results 1 logarithm of seismic moment m sub 0 from ital pn and ital lg spectra scale linearly with body wave magnitude m sub b for explosions 5 0 le m sub b le 6 0 and for earthquakes 4 0 le m sub b le 5 5 2 pn m sub 0 estimates are similar to lg m sub 0 for earthquakes but are higher than lg m sub 0 for explosions 3 corner frequency f sub c scale as quarter root of m sub 0 for explosions and cube root for earthquakes 4 at the same m sub 0 level pn f sub c aremore 4 endash 5 times higher than lg f sub c for earthquakes and explosions and 5 ital pn source spectra are characterized by significant overshoot for explosions our results suggest that the cause of maximum separation between earthquake and explosion populations on plots of p lg spectral ratios which typically occurs for frequencies above explosion pn f sub c between 2 and 4 hz for explosions in this study may be related to overshoot in the reduced velocity potential copyright 1999 american geophysical union less

seismic yield determination of soviet underground nuclear explosions at the shagan river test site summary a study of p and lg based source size estimators has been conducted for 101 presumed underground nuclear explosions at the shagan river test site near semipalatinsk ussr a systematic variation in the relative patterns across the test site has been observed when comparing the p wave estimators world wide mb and ulm and the lg based observations rms lg determined from norsar and grafenberg array recordings these variations correlate well with geological features determined from satellite imagery and suggest in particular that the northeast and southwest portions of the test site divided by the chinrau fault are characterized by distinct geophysical properties a difference in m p mlg bias of as much as 0 15 magnitude units exists between these two subareas available data indicate that the mlg observations are very consistent with published yields and suggest that the magnitude yield relationship for p wave based estimators can be significantly improved by introducing regional bias corrections we have determined such corrections for three subareas of the test site and used the corrected mh and ym observations in combination with the lg data in a weighted averaging scheme to arrive at yield estimates for all events in the database for the explosion of 1988 september 14 we obtain yield estimates from the three estimators ranging from 106 to 118 kt which is consistent with the independently derived estimates of 115 122 kt quoted by sykes ekstrom 1989 a further assessment of the validity of our results would require access to independently measured yields of additional explosions

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

the stability of rms lg measurements and their potential for accurate estimation of the yields of soviet underground nuclear explosions data on underground nuclear explosions have recently become available from modern digital seismic stations installed within the soviet union and china observations of root mean square rms lg wave signals for soviet underground nuclear explosions at the shagan river test site in east kazakhstan show that the relative amplitudes of the rms signals at stations in norway the ussr and china are very similar for different explosions the standard deviation of the differences being only about 0 03 in logarithmic units i e magnitude units this is consistent with earlier observations comparing norsar and graefenberg array data and the observed scatter is significantly lower than has been reported for lg data from nevada test site explosions in view of the excellent correspondence found by nuttli 1986 and patton 1988 for lg versus yield at nevada this indicates that rms lg has a potential for yield estimation with very high accuracy at shagan river our study has shown that a selected stations in the ussr and china situated at regional distances provide a much improved signal to noise ratio of the lg phase for events at shagan river as compared to norsar array data b the scaling of rms lg amplitudes between different sized events recorded at the same single station site appears to be consistent with that of norsar indicating a remarkable degree of precision in single station measurements of lg signal c rms lg amplitude measurements for the best of these stations may be made at 1 5 to 2 0 magnitude units lower than at norsar or graefenberg allowing a much lower threshold for lg based yield determination and d the p wave detection capabilities of these single stations do not match those of the noress and arcess arrays thus teleseismic signals continue to be important for detection of small nuclear explosions our conclusion is that lg signals appear to provide an excellent basis for supplying estimates of the yields of nuclear explosions even down to below 1 kt when such signals are recorded at high quality digital in country seismic stations and when calibrated by access to independent nonseismic yield information for a few nuclear explosions at the test sites of interest in the context of monitoring a low yield threshold test ban treaty it will in addition be important to take into consideration various environmental conditions in the testing area such as the possible presence of cavities and to devise appropriate procedures for on site observations in this regard

source characterization of nevada test site explosions and western u s earthquakes using lg waves implications for regional source discrimination an investigation is made of the lg waves from 15 nuclear tests at the nevada test site nts and 25 shallow western united states earthquakes to obtain a scheme for discriminating between possible source mechanisms the data were recorded at four broadband stations operated by lawrence livermore national laboratory llnl which encircle the nts the lg wave spectra are modeled through a genetic algorithm search to find optimal values for 1 the seismic moment m o 2 the corner frequency of the amplitude spectrum f c 3 the 1 hz attenuation quality factors q o for all of the paths and 4 the frequency dependence of attenuation along the paths because the inversion solves for the path attenuation characteristics little a priori information is needed for the analysis the resulting m o and f c values are used in conjunction with the m b values as seismic discriminants the populations of earthquakes and explosions have nearly identical relationships between their moments and corner frequencies for earthquakes the relationship is log m o 16 07 2 93 log f c for the set of nts explosions using an earthquake source model the relationship is log m o 15 87 2 76 log f c a source discriminant is found however through a comparison of the moments and m b values this gives a line log m o 10 20 1 16 m b which cleanly separates the earthquake and explosion populations with earthquakes falling above and explosions below the line reliability tests examine the inverse trade off between moments and q o values noise in the lg spectra has a limited effect on the scaling relations

ice age vegetation and climate of subtropical chile abstract vegetation and climate of subtropical chile over the past 50 000 yr are reconstructed from pollen spores and other microfossils contained in a 10 7 m section of lacustrine deposits of laguna de tagua tagua 34 30 s 71 10 w controlled by 14 radiocarbon age determinations five pollen assemblages covering stratigraphic zones in the section represent plants on the upland and species inhabiting the lake basin surface pollen spectra from 58 stations approximately 30 40 s form an adjunct for interpreting past vegetation and climate from the fossil record temperature semi humid woodland of southern beech nothofagus dombeyi type and podocarp prumnopitys andina was apparently established about laguna de tagua tagua during the pleistocene contrasting existing semi arid broad sclerophyllous vegetation the woodland was extensive about the lake at the time of the last glacial maximum 25 000 14 000 yr b p and earlier 43 000 34 000 yr b p pollen from the families chenopodiaceae and amaranthaceae which characterize intervals of the pleistocene centered around 33 000 and 43 000 yr b p and the holocene suggests intervening episodes of relative aridity lake level fluctuations appear to follow the late quaternary climatic pattern implied by pollen assemblage data water in the lake was relatively high during development of southern beech podocarp woodland whereas during intervals of chenopod amaranth dominance lake levels were comparatively low excess precipitation over evaporation which during the pleistocene favored development of woodland of beech and podocarp is attributed to greater storm frequency conditions were apparently governed by strengthening of atmospheric circulation in the belt of southern westerly winds in the late glacial the temperate and more humid ice age climate with limited seasonality underwent transition to a subtropical semi arid mediterranean type that identifies the postglacial fluctuations in intensity of the southern westerlies marked by latitudinal movement of the polar front can account for past vegetation changes at laguna de tagua tagua

average seismic source parameter relations for mid plate earthquakes mid plate earthquakes which are defined as having their epicenters at least 500 km from plate margins represent a small portion of the total global seismicity however because those occurring within continental interiors are characterized by anomalously large damage areas they are of particular interest empirical mb ms and m o data are used to develop scaling relations for mid plate earthquakes from them it is found that the corner period t o2 of their far field displacement spectra varies as the one fourth power of the seismic moment which indicates that average stress drop increases as seismic moment increases by use of savage s 1972 rectangular bilateral dislocation model the derived spectra of mid plate earthquakes yield estimates of fault rupture length and width average fault displacement and source rise time as a function of seismic moment these relations show that large mid plate earthquakes such as the 1886 south carolina and 1811 and 1812 new madrid events do not require large fault rupture length

lg attenuation near the north korean border with china part ii model development from the 2006 nuclear explosion in north korea an underground nuclear explosion was set off on 9 october 2006 in north korea the event was recorded at near regional to regional distances over purely continental paths by a network of broadband seismographs located along the northern edge of the korean peninsula the event provided the first window of opportunity to make a reliable measurement of lg wave attenuation in northernmost north korea where the regional phase propagation characteristics are poorly known the results of our analysis show q0 317 14 and 0 343 0 024 in close agreement with the corresponding values obtained of late using a completely different methodology and an independent set of seismic recordings in an adjacent region to the northwest in southern jilin and in liaoning provinces in china

regional variation of lg coda q in the continental united states and its relation to crustal structure and evolution records from broadband digital stations have allowed us to map regional variations of lg coda q across almost the entire united states using a stacked ratio method we obtained estimates of q 0 lg coda q at 1 hz and its frequency dependence for 218 event station pairs those sets of estimates were inverted using a back projection method to obtain tomographic images showing regional variations of q 0 and q 0 is lowest 250 300 in the california coastal regions and the western part of the basin and range province and highest 650 750 in the northern appalachians and a portion of the central lowlands intermediate values occur in the colorado plateau 300 500 the columbia plateau 300 400 the rocky mountains 450 550 the great plains 500 650 the gulf coastal plain and the southern portion of atlantic coastal plain 400 500 and the portions of the central lowlands surrounding the high q region 500 550 the pattern of q 0 variations suggests that the united states can be divided into two large q provinces one province spans the area from the rocky mountains to the atlantic coast is tectonically stable and exhibits relatively high q 0 the other extends westward from the approximate western margin of the rocky mountains to the pacific coast is tectonically active and exhibits low q 0 the transition from high to low lg coda q in the western united states lies further to the west than does an upper mantle transition for q and electrical resistivity found in earlier studies the difference in q 0 between the western and eastern united states can be attributed to a greater amount of interstitial crustal fluids in the west regions of moderately reduced q within the stable platform often occur where there are accumulations of mesozoic and younger sediments reduced q 0 in the southeastern united states may not be due to anelasticity but may rather be explained by a gradational velocity increase at the crust mantle boundary that causes shear energy to leak into the mantle

guided wave tracking in 3 d a tool for interpreting complex regional seismograms abstract the tracking of guided wave trains by raytracing in 3 d structures can provide a means of interpreting complex seismograms at regional distances the method relies on the interpretation of lg as the constructive interference of multiple s reflections within the crust and strong scattering can be simulated by the inclusion of secondary sources this approach has been applied to californian events observed in the southwestern united states whose records at regional distances frequently exhibit an extended and complex lg coda with significant late energy arriving with group velocities of 2 5 km sec or less the general character of this energy precludes an interpretation as the result of stochastic scattering processes or dispersion in low velocity surface sediments therefore some alternative explanation needs to be sought the observed wavetrains of events from two sites in southwestern california coalinga and north baja at stations lac mnv and elk have been compared with the predictions from tracking guided wave patterns multipathing of energy by major changes in the thickness of the crustal wave guide is consistent with the extended and often pulse like nature of the lg coda examples of plausible multipathing mechanisms include reflection from the ocean continent transition scattering associated with topographic features such as the sierra nevada and resonance within the narrow corridor of baja california

the effect of 3 d structure on lg propagation patterns the method of ray diagrams based on the constructive interference of multiple s reflections gives a visual measure of the interaction of guided wavetrains with variations in crustal structure the technique is extended to 3 d heterogeneity and by representing the s ray systems in plan view through their basement reflection points a semi quantitative measure of the disruption of lg at different phase velocities can be made in addition the tilt of the ray systems can be used as an indication of the degree of interconversion between rayleigh and love wave energy two simple crustal models are examined to investigate the effects of oblique incidence and transverse topographic gradients on multiple s reflections using ray diagrams the method is then applied to several real earth models of the crust in central asia using topographic data and assuming isostasy interpretations of the ray diagrams for paths across the major tectonic features compare well with many of the observations from previous studies ruzaikan et al 1977 ni barazangi 1983 and suggest that the gross characteristics of lg propagation can be attributed to the shape of the crustal waveguide

frequency dependent attenuation in the crust beneath central france from lg waves data analysis and numerical modeling abstract the quality factor of shear waves in the crust beneath central france is evaluated by the combined use of data analysis and theoretical modeling the measurement is made from lg wave records of 18 earthquakes at 22 short period vertical seismic stations of the french seismic network the geometrical attenuation of lg waves has been calculated through a numerical simulation in a perfectly elastic model the station responses including site effects have been evaluated from lg waves and from records of the seismic noise q has been calculated for a set of 11 frequencies between 0 5 and 10 hz and has been found to be in the form q 290 f 0 52 where f is the frequency the numerical simulation leads to the interpretation of q of lg waves as the mean value of q within the crust theoretical and experimental decay of energy with distance are in very good agreement the lg waves present a different sensitivity to a low q zone whether this zone is associated with the sediments or with scattering in the lower crust the lower crust beneath central france appears from our experimental results to be associated with high values of q

the excitation of lg waves by explosions a finite difference investigation several mechanisms have been proposed to explain the excitation of the regional lg phase by explosions we examine some of these mechanisms with finite difference simulations an energy flux technique is used to analyze the synthetic signals the method is adapted from conventional array analysis techniques and gives a clear characterization of wave field intensity wave slow ness and propagation direction the vector energy flux in the model is studied instead of the scalar distribution of energy in the space time domain the cal culations show that for an explosive source in a high p wave velocity crust p wave energy cannot be effectively trapped in the crust and the nongeomet rical phase s may be the primary contributor to thelg phase for an explosive source buried in a low velocity upper crust i e where the p wave velocity is lower than the upper mantle s wave velocity part of the ps wave can be trapped in the crustal wave guide to form the lg phase the relative lg excitation de pends on the ratio between the p wave velocity in the source region and the s wave velocity in the uppermost mantle scattering effects can transfer p wave or surface wave energy into lg but the efficiency strongly depends on both the wave frequency and the characteristic size of the scatterers any source process that directly excites s waves is more efficient for generating lg than the afore mentioned mechanisms spall directly generates s wave energy and conse quently is an efficient source for lg for actual explosions all of these factors may simultaneously contribute to lg excitation determining their relative im portance and interactions requires additional observations

spectral inversion of lg from earthquakes a modified method with applications to the 1995 western texas earthquake sequence spectral inversion of lg from earthquake sources is subject to significant errors due to random and systematic deviation of the lg spectra from idealized theoretical models i present an analysis of these errors and demonstrate that their effects tend to increase with decreasing frequency and recording distance i propose modifications to the inverse method of xie 1993 to reduce these errors the modifications include a more robust q estimator and the added capability of incorporating a priori knowledge into the inversion the modified method is applied to lg spectra from the 1995 western texas earthquake mw 5 7 i measured average two station q values for selected station pairs as well as the source rise time of the mainshock with an empirical green s function approach these served as a priori knowledge for the simultaneous inversion for lg seismic moment m corner frequency fc and path q the result of the inversion indicates that lg source radiation is nearly isotropic the m and fc values estimated using lg from the mainshock and two aftershocks are typical for lg from central and eastern north american earthquakes with m scaling with fc 4 and m and fc being 3 3 1016 n m and 0 3 hz respectively for the mainshock the 1 hz lg q correlates with tectonic environments increasing from about 200 for westerly paths to above 700 for easterly paths two station q measurements suggest that as previously discovered for eurasia the frequency dependence of lg q may be variable with distance if the distance spans a wide range 103 km

yield estimates of nevada test site explosions obtained from seismic lg waves a methodology is presented for determining the yield of underground nuclear explosions from lg wave amplitudes the methodology is applied to nevada test site nts explosions for which the data from short period vertical component analog seismographs at three stations are used to develop calibration curves for unsaturated material and water saturated rock source conditions the latter curves are found to provide reasonably accurate estimates of the yields of explosions in other areas of the united states and in the french sahara suggesting that they may be applicable to all continental areas if so they also can provide an estimate of the bias of mb p magnitudes between different continental sites for example the lg data from nts explosions indicate a 0 31 0 02 magnitude unit bias between nts and eastern north america similar to the approximately 0 33 unit bias found between western and eastern north america previously by use of earthquake data

excitation and propagation of lg from earthquakes in central asia with implications for explosion earthquake discrimination broadband lg records from 52 shallow earthquakes that occurred near the balapan and lop nor nuclear test sites have been used to study spectral characteristics of the excitation and propagation of the lg phase in central asia using a source model that falls off as 2 at high frequencies and a nonlinear inversion method we simultaneously inverted for lg seismic moments m0 corner frequencies fc and path variable values of q0 and qlg at 1 hz and its power law frequency dependence the logarithms of m0 obtained using lg correlate linearly with logarithms of fc the slope being about 3 56 when all data are used and 4 04 when data were sufficient that full inversions could be performed these slopes differ only slightly from the slope of 3 83 obtained in our earlier studies using underground nuclear explosions the fc values in this study are systematically lower than those found for explosions at the same m0 level a comparison of corner frequencies and lg moment values for unknown events with the plots for known events of this study therefore provides means to discriminate between earthquakes and explosions the mb values are systematically lower for earthquakes of this study than for previously studied explosions at the same seismic moment moreover the logarithms of lg moments obtained in this study correlate linearly with a slope of 1 04 with mb values when all data are used and 1 21 when only well recorded events are used these slopes are close to the slope of 1 19 obtained for explosions the average qlg values along the paths used in this study agree well with those obtained using explosion data in central asia and with reported lg coda q values

bias in the centroid moment tensor for central asian earthquakes evidence from regional surface wave data surface waves recorded on the chinese digital seismic network cdsn station urumqi wmq are analyzed for 26 centroid moment tensor cmt earthquakes located within an epicentral distance of 1300 km applying a simple grid search method for source parameter retrieval i obtain revised estimates of the focal depth fault strike and seismic moment m sub 0 from amplitude spectra of love and rayleigh waves and compare these estimates with the cmt best double couple solutions the comparisons show that residuals are unbiased for focal depth and fault strike where population spreads are plus minus 13 km and plus minus 17 degree respectively on the other hand m sub 0 estimates are found to be biased with cmt m sub 0 larger than regional estimates by an average of 0 27 plus minus 0 04 log units the results for focal depth and strike are consistent with previous global and regional studies comparing independent estimates with cmt results recent full waveform modeling studies for central asian earthquakes support the findings of bias in m sub 0 estimates i suggest that causes for m sub 0 bias may be related to great thicknesses of continental crust in hindu kush and tien shan regions and to data censoring practices at small magnitudes m sub 0 m sub b scaling relationships for central asianmore earthquakes show better agreement with western u s scaling when m sub 0 estimates determined in this study are used copyright 1998 american geophysical union less