propagation characteristics of lg across the tibetan plateau abstract we present the results of a study on the propagation of lg within the tibetan plateau we analyze over 1200 seismograms for lg propagation from 185 local and regional earthquakes recorded at distances from 150 to 2000 km 52 of which are located within the tibetan plateau although the propagation of lg has been observed across most of asia lg has not been observed for paths crossing the tibetan plateau we analyze paths that cross the plateau boundaries and paths contained entirely within the tibetan plateau lg is generated within the tibetan plateau and can propagate to epicentral distances of at least 600 km for events located outside of the tibetan plateau lg is either absent or severely diminished for paths that cross both the himalayan and kunlun ranges confirming that the margins of the plateau weaken lg transmission based on the observations from our qualitative analysis we invert lg amplitudes for event station paths that are confined to the tibetan plateau to estimate the quality factor q the inversion yields a frequency dependent q function q f 366 37 f 0 45 0 06 0 5 f 16 h z similar observations in other areas indicate that frequency dependent apparent q within the tibetan plateau is well below that expected for a typical continental interior instead it has a frequency dependence that is characteristic of a tectonically active region

source radiation invariant property of local and near regional shear wave coda application to source scaling for the mw 5 9 wells nevada sequence 1 this study documents another unique property of local and regional shear wave coda that scattering in the earth s crust averages out source heterogeneities such as focal mechanism and directivity we consider two recent events which exhibited significant source directivity the first an mw 4 2 oakland hills california strike slip event on july 20 2007 resulted in uncharacteristically large amounts of damage in the montclair and south berkeley neighborhoods along strike and north west of the hypocenter but almost no damage to the south east the second event the mw 5 9 wells nevada dip slip event of february 21 2008 was well recorded by the earthscope transportable array usarray and determined to exhibit south west directivity we conclude with an example of corner frequency fc estimates from the wells sequence which showcase the coda s low variance and find that scaling is non self similar suggesting a change in dynamics between the mainshock and aftershocks

local magnitude tomography in california lateral variation in crustal attenuation of california is calculated by inverting 25 330 synthetic wood anderson amplitudes from the california integrated seismic network cisn for site source and path effects two dimensional attenuation q or 1 q is derived from the path term which is calculated via an iterative least squares inversion that also solves for perturbations to the site and source terms source terms agree well with initial cisn m l s and site terms agree well with a prior regression analysis q ranges from low attenuation at 0 001 q 1000 to high attenuation at 0 015 q 66 with an average of 0 07 q 143 the average q is consistent with an amplitude decay function log a for california when q is combined with a simple geometrical spreading rate attenuation in california is consistent with the tectonic structure of california with low attenuation in the sierra batholith and high attenuation at the geysers at long valley and in the salton trough possibly due to geothermal effects also path terms are an order of magnitude smaller than site and source terms suggesting that they are not as important in correcting for m l

lithospheric waveguide beneath the midwestern united states massive low velocity zone in the lower crust variations in seismic velocities are essential in developing a better understanding of continental plate tectonics fortunately the usarray has provided an excellent set of regional phases from the recent m5 6 oklahoma earthquake 6 november 2011 table 1 that can be used for such studies its strike slip mechanism produced an extraordinary set of tangential recordings extending to the northern edge of the usarray the crossover of the crustal slow s to the faster s n phase is well observed s ms has a critical distance of around 2 and its first multiple sms 2 reaches critical angle near a distance of about 4 and so on until s ms n merges with the stronger crustal love waves these waveforms are modeled in the period band of 2 100 s by assuming a simple three layer crust and a two layer mantle which allows a grid search approach our results favor a 15 km thick low velocity zone lvz in the lower crust with an average shear velocity of less than 3 6 km s the short period lg waves s waves at periods of 0 5 2 s travel with velocities near 3 5 km s and decay with distance faster than high frequency s n 5 0 hz which travels at a velocity of 4 6 km s and persists to large distances although these short period waveforms are not modeled their amplitude and travel times can be explained by adding a small velocity jump just below the moho with essentially no attenuation p n is equally strong but is complicated by the interference produced by the depth phase sp but well modeled the p velocities appear normal with no definitive lvz while these observations of s n and p n are common beneath most cratons the lower crustal lvz appears to be anomalous and maybe indicative of hydrous processes possibly caused by the descending farallon slab

earthquake spectra and near source attenuation in the cascadia subduction zone f 1 for slow events and as f 2 for fast earthquakes we show that at least in cascadia wave propagation effects likely control spectral decay rates above 2 hz we use seismograms from multiple small aperture arrays to estimate the spectral decay rates of near source spectra of 37 small events and find strong correlation between source location and decay rate the decay rates 1 vary overall by an amount in excess of that inferred to distinguish slow sources from fast earthquakes 2 are indistinguishable for sources separated by a few tens of km or less and 3 separate into two populations that correlate with propagation through and outside a low velocity zone imaged tomographically we find that some events repeat as is characteristic of low frequency earthquakes lfes but have spectra similar to those of non repeating earthquakes we also find no correlation between spectral decay rates and rates of ambient tremor activity these results suggest that earthquakes near the plate boundary at least in cascadia do not distinctly separate into slow and fast classes and correctly accounting for propagation effects is necessary to characterize sources

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

application of regional phase amplitude tomography to seismic verification we have applied tomographic techniques to amplitude data to quantify regional phase path effects for use in source discrimination studies tomography complements interpolation kriging methods by extending our ability to apply path corrections into regions devoid of calibration events as well as raising levels of confidence in the corrections because of their more physical basis our tomography technique solves for resolvable combinations of attenuation source generation site and spreading terms first difference regularization is used to remove singularities and reduce noise effects in initial tests the technique was applied to a data set of 1488 1 0 hz p g l g amplitude ratios from 13 stations for paths inside a 30 by 40 box covering western china and surrounding regions tomography reduced variance 60 relative to the power law distance correction traditionally applied to amplitude ratios relative p g l g attenuation varied with geologic region with low values in tibet intermediate values in basins and high values for platforms and older crust spatial patterns were consistent with previous path effect studies in asia especially local earthquake coda q relative spreading was consistent with expected values for p g and l g relative site terms were similar to one another yet some tradeoff with attenuation was evident tomography residuals followed systematic trends with distance which may result from the evolution from direct to coda phases focusing model tradeoff or data windowing effects examination of the residuals using a kriging interpolator showed coherent geographical variations indicating unmodeled path effects the residual patterns often follow geological boundaries which could result from attenuating zones or minor blockages that are too thin to be resolved or that have anisotropic effect on regional phases these results will guide efforts to reparameterize tomography models to more effectively represent regional wave attenuation and blockage the interpolated residuals also can be combined with predictions of the tomographic model to account for path effects in discrimination studies on a station by station basis

seismic lg wave q tomography in and around northeast china 1 we investigate regional variations in the lg wave quality factor q in northeast china and its vicinity with a tomographic method digital seismic data recorded at 20 broadband stations from 125 regional events are used to extract lg wave spectra tomographic inversions are independently conducted at 58 discrete frequencies distributed log evenly between 0 05 and 10 0 hz we simultaneously invert for the lg wave q distribution and source spectra at individual frequencies without using any a priori assumption about the frequency dependence of the q model and source function the best spatial resolution is approximately 1 1 in well covered areas for frequencies between 0 4 and 2 0 hz the lg q shows significant regional variations and an apparent relationship with regional geology we use a statistical method to investigate the regional variations of lg q and their frequency dependence the average q0 1 hz lg q in the entire investigated region is 414 sedimentary basins are usually characterized by lower average q0 values from 155 to 391 while volcanic mountain areas have relatively high average q0 values from 630 to 675 lg q generally increases with increasing frequency however the frequency dependence has complex nonlinear features on a double logarithmic scale indicating that the commonly adopted power law relationship may be oversimplified in a broad frequency band the frequency dependence varies in different geological areas with larger variations seen at lower frequencies

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

ml amplitude tomography in north china we have selected 10 899 m l amplitude readings from 1732 events re corded by 91 stations as reported in the annual bulletin of chinese earthquakes abce and have used tomographic imaging to estimate the lateral variations of the quality factor q0 q at 1 hz within the crust of northern china estimated q0 values vary from 115 to 715 with an average of 415 q0 values are consistent with tectonic and topographic structure in eastern china q0 is low in the active tectonic regions having many faults such as the shanxi and yinchuan grabens bohai bay and tanlu fault zone and is high in the stable ordos craton q0 values are low in several topographically low lying areas such as the north china taikang hefei jianghan subei yellow sea and songliao basins whereas it is high in mountainous and uplift regions exhibiting surface expressions of crystalline basement rocks the yinshan yanshan taihang qinlin dabie and wuyi mountains and luxi and jiaoliao uplifts quality factor estimates are also consistent with pn and sn velocity patterns high velocity values in general correspond with high q0 and low velocity values with low q0 this is consistent with a common temperature influence in the crust and uppermost mantle

amplitude tomography of lg waves in xinjiang and its adjacent regions amplitude tomography of lg waves at frequencies from 1 to 5 hz are investigated in this work to reveal the lateral attenuation heterogeneities of the study area the xinjiang uygur autonomous region of china and its adjacent regions by using a large set of broadband seismic waveform data first we inverted the average q lg at each of 10 frequencies from 0 5 to 5 hz then the study area was divided into evenly spaced 1 1 grid cells after conducting both a checkerboard test and a resolution test finally the high resolution q lg tomographic images at the 10 frequencies were obtained the moment magnitudes of the events and the site terms of the stations we used were obtained simultaneously the attenuation pattern of q lg at each frequency shows obvious lateral heterogeneities in xinjiang and its adjacent regions which are coincident with the geological features of the area the tarim basin and the middle and the eastern part of the southern tian shan belong to high q regions the northeastern margin of the pamir plateau the northwestern margin of the tibetan plateau the western part of the southern tian shan and northern tian shan are prominent low q areas the attenuation pattern of lg waves shows that large scale tectonic boundaries zones with rapid topographic or crustal thickness gradient are in good accordance with the boundaries of the high and low q lg most of the historical strong earthquakes occurred on the interior or edge of low q lg areas

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

effect of low q sediments and crustal q on lg attenuation in the united states q values for lg and its coda exhibit significant lateral variations across the united states some of which correlate with known variations in the thickness of shallow sedimentary layers the possibility that all variations in lg attenuation are caused by changes in the thickness of shallow sediments is investigated by computing multi mode synthetic seismograms for crustal models with various thicknesses of low q sediments using crustal velocity and q models obtained in previous studies and reasonable values for the thicknesses and intrinsic q values of sediments in several regions we find that the variation of lg q values between the appalachian and rocky mountains can easily be produced by varying accumulations of sandstone and shale of mesozoic age and younger by contrast throughout most of the western united states neither the low lg q values which have been observed nor the regional variation of those values can be explained by accumulations of low q sediments instead their explanation appears to require low and laterally varying values of q in the crystalline crust

attenuation of lg in the western us using the usarray 1 the unprecedented breadth and density of the usarray allows us to resolve lateral variations of 1 hz lg attenuation to 0 5 degrees over much of the western united states we collected over 31 000 lg amplitudes from 547 events and 408 stations of the initial usarray footprint two dimensional tomographic inversion yielded q ranging from 60 to 550 with a variance reduction of 47 relative to the best fit constant q model q 155 q is low over most of the region with lowest values associated with recent volcanic activity and active shear zones high q is found in older stable crust notably the colorado and columbia plateaus while smaller islands of high q are associated with batholiths including the sierra nevada peninsular and bitterroot ranges the western mojave and okanogan highlands as well as other areas of competent crust such as the harcuvar range and two topographically bounded blocks in the basin and range

a novel technique for measuring lg attenuation results from eastern canada between 1 to 10 hz spectral amplitudes of regionally recorded lg waves are studied in detail between 0 6 and 10 hz using vertical component velocity seismograms of the eastern canada telemetered network stations and a supplementary seismic research observatory type station at glen almond gac quebec we find that the site responses vary among these stations by more than a factor of 3 within the frequency range of interest furthermore they are found to be strongly frequency dependent consequently it is essential that they be taken into consideration in studies of lg wave attenuation and lg source spectra of regionally recorded seismic events we present a new method of measuring interstation surface wave attenuation which is closely related to the conventional two station method while retaining all the desirable features of the conventional two station method the new technique which we will call the reversed two station method allows simple direct one parameter determination of the lg wave attenuation from sparse spectral data in a manner unaffected by station site effects and associated instrument error the reversed two station method is successfully tested over weakly attenuating short 53 to 210 km interstation paths in eastern canada a difficult experimental condition by normal standards the lg attenuation coefficient 0 6 to 10 hz in eastern canada is found to be frequency dependent and of the form f 0 0008 f 0 81 km 1 at higher frequencies the lg attenuation appears to be essentially frequency independent this latter finding is preliminarily interpreted as evidence that regionally recorded lg waves in the canadian shield are as in the case of lg waves propagating through the structurally complex appalachian province contaminated by the high frequency coda of sn waves the lg contamination over the shield paths becomes severe starting at 14 hz twice the frequency above which the lg signal propagating over the appalachian province becomes completely dominated by non lg arrivals

attenuation of crustal waves across the alpine range we present observational evidence of an anomalous propagation of lg waves across the south western part of the alpine range and we use numerical simulations to model these observations we consider a set of 48 earthquakes which occurred in switzerland northern italy and southeastern france and were recorded by the french laboratoire de detection et de geophysique and northwest italian istituto geofisico di genova seismic networks while the amplitude of the pn phase is stable throughout the region studied lg wave amplitude undergoes strong variations we map this anomaly in lg wave propagation by dividing the region into a grid and attributing to each cell a value equal to the mean value of the lg pn amplitude ratios computed for all the paths which cross this cell the image obtained shows that the extinction of lg waves occurs in a limited region of the western alps which corresponds to the zone of highest positive bouguer anomaly this zone located to the east of the high peaks of the massifs cristallins externes does not correspond either to the region of the highest topographies or to the one of the deepest moho at a frequency of 2 hz the crustal waves that cross this anomalous region have amplitudes divided by more than 10 with respect to waves that propagate along other paths in order to investigate the cause of the anomaly we perform numerical simulations of sh wave propagation through a model of the western alps which includes the main characteristics of the geological structure our results indicate that the geometrical effect of the lateral variations of the medium does not account entirely for the actual vanishing of crustal waves the simulation predicts a decay of the amplitude by only a factor between 2 and 3 the introduction of corrugation in the interface shapes further adds to the decay however other sources of attenuation such as anelasticity or severe heterogeneity must be invoked to explain fully the observations

strong lg attenuation in the tibetan plateau the widespread existence of strong lg attenuation in the tibetan plateau is further demonstrated by analysis of lg spectra on many paths within the plateau and quantitative estimates of the lg attenuation from low frequency lg signals for new localized path geometries strong path length dependent shifts of the lg spectra to lower corner frequencies with increasing distance are observed across the plateau consistent with a low regional average 1 hz lg attenuation value q 0 of about 125 there are clearly lateral variations within the plateau found in this and other recent studies with localized areas having q 0 values of 60 90 low enough to eliminate high frequency lg energy over path lengths of just several hundred kilometers while some localized areas may have higher q 0 values of up to 147 or higher a q 0 value of 103 is found in south central tibet compatible with recent work by others for higher frequencies on very localized scales and values from 83 to 147 are found in eastern tibet the lowest q 0 estimates found in tibet tend to be in areas for which there is evidence of volcanism and or partial melting within the crust however the strong regional attenuation may have a contribution from scattering by small scale crustal heterogeneity the strong lg attenuation in tibet gives a new constraint for understanding the tectonic development of the plateau and presents challenges to seismic monitoring of the region for possible clandestine nuclear tests

evaluation of nga west2 and chinese ground motion prediction equations for developing seismic hazard maps of mainland chinaevaluation of nga west2 and chinese gmpes for developing seismic hazard maps of mainland china

extracting surface wave attenuation from seismic noise using correlation of the coda of correlation 1 extracting surface wave travel time information from the cross correlation cc of seismic ambient noise has been a great success and remains fast growing however it is still challenging to exploit the amplitude content of the noise cc although spatial average is able to constrain somewhat meaningful attenuation using noise cc amplitudes clear bias is observed when spatially varying attenuation is estimated with the traditional noise cc calculation methods perhaps the key lies in the development of novel techniques that can mitigate the effect of the uneven distribution of natural noise sources in this paper we propose a new method to use the correlation of the coda of correlation of noise c3 for amplitude measurement we examine the ability of the method to retrieve surface wave attenuation using data from selected line array stations of the usarray by comparing c3 derived attenuation coefficients with those estimated from earthquake data we demonstrate that c3 effectively reduces bias and allows for more reliable attenuation estimates from noise this is probably because of the fact that the coda of noise correlation contains more diffused noise energy and thus the c3 processing effectively makes the noise source distribution more homogeneous when selecting auxiliary stations for c3 calculation we find that stations closer to noise sources near the coast tend to yield better signal to noise ratios we suggest to preprocess noise data using a transient removal and temporal flattening method to mitigate the effect of temporal fluctuation of the noise source intensity and to retain relative amplitudes in this study we focus our analysis on 18 s measurements

pg attenuation tomography within the northern middle east abstract a seismic attenuation map of regional phase pg is constructed for the northern middle east using two station frequency dependent q measurements and seismic attenuation tomography pg is widely used in source discrimination but its attenuation behavior is not well understood we investigate the functional form of the geometrical spreading of pg for both uniform and more complex seismic velocity structures we find that there is significant trade off between attenuation and geometrical spreading of pg and we quantify this trade off to interpret the observed pg attenuation in the middle east the northern middle east attenuation tomographic images show significant lateral q pg variations which may be caused by lateral variations of crustal rheology if intrinsic attenuation dominates the seismic attenuation mechanism of this region we observe very large variations in the q pg model such as low q pg within the anatolian plate and high q pg within much of the stable arabian plate the low q pg anomalies generally coincide with active fault systems or quaternary volcanisms in order to perform a systematic comparison with lg propagation we have also updated the q lg map of zor et al 2007 these two new maps provide estimates for crustal q pg and q lg for the northern middle east

analytical solutions of velocity profile in flow through submerged vegetation with variable frontal width abstract flow within vegetation is one of the main driving forces for material exchange and energy transfer in wetland systems impacted by vegetation the flow velocity profile illustrates distortions to the classic logarithmic velocity profile and has attracted much attention among researchers different from analytical models of velocity distribution in literature which is mainly suitable for vegetation with uniform frontal width this paper establishes new analytical solutions of the velocity profile for vegetation such as shrub and sedge that have a variable frontal width in the vertical direction a new shape function is proposed under these conditions in which the frontal width exhibits a gradual increase in the vertical direction from bottom up in the vegetation along with different closure models for eddy viscosity in the vegetation layer and surface layer analytical solutions of the velocity profile are derived from the momentum equations good agreement between calculated and measured data shows our analytical model is effective in predicting velocity profiles

lateral variation of lg wave propagation in southern mexico 1 in this study we investigated lateral variation of lg wave propagation in southern mexico from recordings of 92 crustal earthquakes along 591 travel paths the efficiency of lg propagation was measured in terms of lgto pn spectral ratio it was found that lgpropagation is inefficient for travel paths through the gulf of mexico coastal plains and the gulf of tehuantepec areas with thick layers of sediments an average lg quality factor qlg as a function of frequency for southern mexico was estimated for the efficient lg travel paths the relation obtained for qlg in the frequency range 1 6 8 hz is qlg f 204 f0 85 the lateral variation of qlg 1was solved as a mixed determined inverse tomography problem separately for each frequency in which a spatial smoothness constraint was imposed and a priori information was added in poorly covered regions the spatial resolution obtained was about 200 km it was found that the trans mexican volcanic belt the gulf of mexico coastal plains and the area east of 94 w are characterized by lower than average qlgvalues i e higher attenuation high qlg values were obtained for the mixteco oaxaca terranes while for the guerrero terrane values similar to the average were obtained the results show a correlation between qlg and crustal structure and provide valuable information on lateral variation of qlg which is needed for reliable prediction of ground motion during future earthquakes

a back projection method for imaging large scale lateral variations of lg coda q with application to continental africa summary a new method is developed which uses back projection tomography to regionalize large scale lateral variations of coda q for lg waves which have traversed long continental paths successful use of this method requires precise and stable single trace measurements of lg coda q xie nuttli 1988 the method converges rapidly and requires minimal computer storage it also allows quantitative estimation of resolution and error in imaging lateral variations of coda q the spatial resolution of this method is limited by the uneven spatial coverage of the data base by our limited knowledge of lg coda generation and by the trade off between the stability and the spatial resolution of the coda q inversion the method is applied to a large set of digital lg coda data from africa where large scale lateral variations of lg coda q are found to correlate well with major tectonic features most of africa is stable and like other stable regions has relatively high coda q values the lowest values of coda q are associated with the african rift system other regions of low q values include the atlas mountains and cape fold belt regions of mesozoic and younger deformation the lateral variation of frequency dependence of lg coda q correlates in most regions with that of q at 1 hz our analysis of the spatial resolution of this method indicates that the resolving power of lg coda q imaging is comparable to that of velocity tomography using long period surface waves using empirical approaches we estimate that uncertainties in lg coda q and its power law frequency dependence parameter are less than about 60 and about 0 2 respectively for most of africa

accounting for lateral variations of the upper mantle gradient in pn tomography studies 1 the effect of an upper mantle velocity gradient on regional arrival times has been approximated by a cubic distance term which can be extended to two dimensions for use in tomographic studies to demonstrate this we add a laterally varying upper mantle gradient to the standard pn time term tomography technique and apply to a data set from asia compiled using ground truth event location criteria we observe strong lateral variations in the gradient ranging from 0 001 to 0 003 s 1 with high gradients associated with the tethys convergence zone the gradient patterns may reflect lateral variations in the thermal gradient of the mantle lid variance reduction is 63 with respect to pn tomography without gradients adding gradients allows the use of longer path lengths improving velocity image definition in high gradient regions with sparse station distribution such as tibet

1 hz lg q tomography in central asia we have applied tomographic techniques to a data set of over 1700 regional distance lg amplitudes from 12 stations for paths inside a 30 by 40 region of central asia our purpose is to create high resolution path correction maps for use in regional distance source discrimination and magnitude determination as well as to study lg propagation characteristics in one of the most heterogeneous portions of the earth for 1 0 hz data tomography reduced variance 33 relative to a best fit uniform q model lgq varied with geologic region with low values in tibet the tien shan and the pamir range q 200 to 400 intermediate values in basins such as the tarim q 500 and high values for platforms and older crust q 800 the relatively efficient propagation across the tarim differs from the poor propagation that is generally observed across sedimentary basins

northern california seismic attenuation 3d qp and qs models the geological complexity of northern california and its accreted terranes produces pronounced regional variations in the attenuation 1 q of earthquake waves using local earthquakes 3d q p and q s models have been obtained for this region that includes the san andreas fault system the great valley the sierra nevada batholith and the gorda subduction volcanic system path attenuation t values were determined from p and s spectra of 959 spatially distributed earthquakes magnitude 2 5 6 0 using 1254 stations from northern california earthquake data center networks and mendocino and sierra nevada temporary arrays the t data were used in q inversions using existing 3d velocity models and basic 10 km node spacing uneven data coverage was accommodated with linking nodes into larger areas for useful q images across the 3d volume results at shallow depth show very low q in the sacramento delta the eureka area and parts of the san francisco bay area in the brittle crust low q tends to be associated with regions of fault zones and microearthquakes in the ductile lower crust low q is observed below fault zones with large cumulative displacement and inferred grain size reduction with apparent broad ductile shear zones across the fault system in the coast ranges underlying active arc volcanoes low q features are apparent below 20 km depth under the long valley caldera two distinct partial melt features at 3 and 15 km depth are inferred moderately high q is associated with sierra nevada and salinian igneous rocks whereas the franciscan subduction complex shows moderately low q prominent high q relates to the great valley ophiolite the pattern of path specific attenuation rate from 3d q is generally similar to the pattern of psuedospectral acceleration residuals for the south napa earthquake indicating that it may be beneficial to incorporate 3d q models into future ground motion prediction equations for northern california online material figures of q p and q s resolution and station delays for t and table of q p v p q s and v s

attenuation tomography of the yellow sea korean peninsula from coda source normalized and direct lg amplitudes we invert for regional attenuation of the crustal phase lg in the yellow sea korean peninsula yskp using three different amplitude attenuation tomography methods the first method solves for source site and path attenuation the second method uses a scaling relationship to set the initial source amplitude and interpret the source term after inversion the third method implements a coda derived source spectral correction by comparing methods with slightly different assumptions we are able to make a more realistic assessment of the uncertainties in the resulting attenuation maps than is obtainable through formal error analysis alone we compare the site source and path terms produced by each method and comment on attenuation which correlates well with tectonic and topographic features in the region source terms correlate well with each other and with magnitude site terms are similar except for two stations that are located in a region that has the greatest difference in path term which demonstrates the site path trade off another region of path term difference has the fewest crossing paths where the tomography method employing the coda derived spectral correction may perform more accurately since it is not as susceptible to the source path trade off the bohai bay basin an area of extension is a region of high attenuation and regions of low attenuation occur along topographic highs located in the da xin an ling and changbai mountains and mount taishan

bayesian lg attenuation tomography applied to eastern asia bayesian attenuation tomography tarantola 1987 is being used to refine existing lg attenuation models in eastern asia the advantages of a bayesian approach to tomography are that large scale and high resolution tomographic models available from other well accepted studies can be used as prior background models the resulting refined tomographic model will blend into these prior background models moreover the uncertainties are well established in a bayesian framework we assume a general linear gaussian least squares model where the covariance matrix is partitioned into data and prior model components uncertain data are naturally down weighted and model components with small errors will be subject to little change amplitude tomography provides only an approximation to the propagation effects a seismic wave may experience for example phase blockage can occur over relatively short distances in the absence of any anelastic effects station centric kriged amplitude correction surfaces on top of the tomographic models may assist in identifying blocked paths because a signal to noise criterion is used to select amplitudes for the inversion the data are left censored and the resulting q 0 models will be biased high we examine the utility of a maximum likelihood data augmentation method to the left censored data problem schafer 1997 in this case we can only measure an upper bound to measured amplitudes on the basis of prephase noise data augmentation is used to impute the missing data values with their conditional expectation based on the relationship of amplitudes with other completely observed variables we have initially chosen a bivariate gaussian model for filling in missing amplitudes based on the relationship between amplitude and prephase noise we apply the technique to eastern asia for lg signals at 1 hz using data from 1651 earthquakes recorded at 12 stations tomographic patterns correlate well with those expected from geophysical considerations e g high attenuation in tibet and low attenuation up into the stable regions of kazakhstan many of the large cratonic basins surrounding the tibet plateau e g tarim junggar show reduced attenuation consistent with the hypothesis that they represent regions of stronger lithosphere data augmentation tends to increase attenuation in tibet particularly western tibet and the cratonic basins to the north of but not to the east of tibet in addition the resulting models are much smoother than models that do not account for censoring

strong crustal heterogeneity in the bolivian altiplano as suggested by attenuation of lg waves using the seismological data of four temporary networks installed across the andes of bolivia and chile between 1990 and 1995 we study the amplitudes of the lg phase for 45 regional events located at crustal depths this analysis reveals that lg is strongly attenuated for most of the ray paths crossing the altiplano independent of the azimuth of propagation to map the anomalies and evaluate their frequency dependence we conduct a regionalization of the crustal average qs factor using a damped least squares inversion technique in the frequency range 0 6 5 hz the resulting maps delineate regions with contrasting values of apparent attenuation the altiplano is characterized by strong attenuation with an average qs of 100 at 1 hz whereas the cordilleras are regions of weaker attenuation the frequency dependence of qs is investigated in an attempt to separate the source of the apparent attenuation into scattering and anelastic absorption within the hypothesis of a weak frequency dependence of the intrinsic q we show that at 1 hz scattering plays a major part in the attenuation of lg waves whereas at 4 hz both mechanisms are of equal importance these results indicate that the attenuation of lg waves in the altiplano is due more to scattering by small scale heterogeneities than to a high percentage 1 of partial melt involving a large part of the crust

frequency dependent lg attenuation in the indian platform we use seismograms from regional earthquakes recorded on digital seismographs in peninsular india to determine the frequency dependent q of lg for the indian platform we measure lg attenuation by determining the decay of spectral amplitudes with distance the available data suggest some spatial variation in attenuation but a much denser ray path coverage would be required to validate such observations we therefore combine all the measurements of overlapping regions that span both the shield and intervening terranes to obtain an average value of attenuation for the indian platform lg q 665 10 with the frequency exponent n 0 67 0 03 this average value of lg attenuation for the indian platform is similar to the average for other stable regions of the globe

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

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

amplitude ratio tomography for regional phase q 1 we image regional seismic phase attenuation q by extending amplitude ratio techniques which are widely used to determine average q within a sampled region to obtain laterally varying q structure using tomographic techniques the method assumes that source radiation is isotropic and that the amplitude ratios can be modeled by a two dimensional q map and relative site terms application to 2286 1 hz lg amplitudes from 816 events recorded at 35 central and east asia stations yields a misfit of 0 09 log10 units a variance reduction of 73 relative to the uniform q model that best fits the data and laterally varying q from 100 to 1000 with patterns closely following regional geology the image is resolved on average to 2 5 with resolution peaking at 1 5 in the best covered areas which is remarkable given the sparse station geometry employed the high resolution results from the dense distribution of earthquake sources and is aided by the increased confidence in source locations provided by merging catalogs from many different agencies

crustal attenuation within the turkish plateau and surrounding regions the lateral variations of seismic attenuation in the crust of turkey and surrounding regions have been imaged from the inversion of interstation lg q measurements this study develops the first tomographic model for lg q 0 in this region that model is consistent with previous more qualitative lg attenuation models that showed inefficient or blocked lg across the eurasian arabian plate boundary in general the northern arabian platform has low to normal lg q 0 values 250 350 whereas high q 0 values 670 800 occur in the southern arabian plate additionally we have found a dramatic decrease in lg q 0 across the bitlis suture the plate boundary between the arabian and eurasian plates beneath the turkish plateau our high to moderate lg attenuation values q 0 100 200 probably originates from both scattering and intrinsic attenuation due to the tectonic complexity and the widespread young volcanics in the region we conclude that the lowest q 0 values for the east anatolian plateau 70 100 and the portion of western turkey around the menderes massif 60 150 are probably caused by intrinsic attenuation we find low to normal lg q 0 values 150 300 beneath the part of the taurus mountains in western anatolia these higher values may be related to the nature of the crust in the tauride mountain belt we also mapped the lateral variations in lg and observed a fairly consistent negative correlation between and lg q 0 in the northern middle east

a preliminary study of regional seismic discrimination in central asia with emphasis on western china abstract in support of a comprehensive test ban treaty we have started to evaluate regional seismic event discrimination capabilities for central asia emphasizing western china we have measured noise and signal levels of over 260 earthquakes and 26 underground nuclear explosions recorded at the broadband digital station wmq in western china and over 120 earthquakes and five nuclear explosions at station aak in kyrgyzstan the explosions are from the kazakh test site kts and lop nor china the earthquakes are mostly from northwest china event magnitudes measured as either m b or m l range between 2 5 and 6 5 and maximum event station distance is about 1700 km we formed phase spectral cross spectral short period long period and long period ratios to test many possible event discriminants all ratios were corrected for distance effects before forming ratio versus magnitude discrimination plots the most consistent discriminants for separating earthquakes from explosions are p s phase ratios for frequencies above 3 to 4 hz p wave f 1 hz to rayleigh wave 0 03 hz f p s ratios separation between earthquakes and explosions increases with frequency and for the p r ratios separation increases with increasing p frequency the p 3 to 6 hz s 0 75 to 1 5 hz cross spectral ratios also separate earthquakes and explosions these cross spectral ratios may prove quite useful because due to weak high frequency l g signals from explosions the high frequency p l g ratio sometimes cannot be evaluated but the p 3 to 6 hz l g 0 75 to 1 5 hz can be evaluated successfully p spectral ratios 3 to 6 hz 0 75 to 1 5 hz also separate earthquakes and explosions but not quite as consistently as the p s ratios however p spectral ratios may prove useful in cases where path effects block or highly attenuate s n and l g waves rendering the p s ratios unavailable in contrast to nevada test site nts events the l g 3 to 6 hz 0 75 to 1 5 hz spectral ratio does not separate earthquakes and nuclear explosions in central asia this observation may be a source effect as asian explosions are thought to be detonated in highly lithified rocks below the water table while most of the smaller m b for station aak the short period spectral and cross spectral ratios identify a few earthquakes not recorded at wmq from the north pamir region that plot with the lop nor explosions the waveforms from these earthquakes lack surface waves and a distinct l g phase these events which we interpret as having occurred in a subducted slab do separate from the explosions on high frequency f 4 hz p s discrimination plots for station wmq long period r l rayleigh wave love wave ratios separate kts explosions and asian earthquakes however r l ratios fail to identify the large lop nor explosions recorded at station aak because the love waves are as large as the rayleigh waves suggesting that strong tectonic release occurs with these explosions because we have examined only one path at a single station for these explosions source radiation pattern may be influencing this observation

low δ18o rocks in the belomorian belt nw russia and scourie dikes nw scotland a record of ancient meteoric water captured by the early paleoproterozoic global mafic magmatism abstract the 2 45 2 38 ga intrusions and their host rocks in the belomorian belt of nw russia and the scourie dikes of the lewisian complex in nw scotland are marked by extremely low 18o values their isotope signatures reflect high temperature exchange between rocks and low 18o meteoric waters representing a record of active hydrologic cycle early in the earth s history here we explore triple oxygen and hydrogen isotope systematics d 18o and 17o of these rocks to evaluate the isotope composition of meteoric water the new occurrences from belomorian belt range in 18o from 14 to 2 combined with previously reported data ranging between 27 and 3 the low 18o rocks are traced across 500 km of the belomorian belt based on spatial distribution of the values hydrothermal alteration driven by the emplacement of the mafic intrusions is the most consistent explanation for the low 18o values recorded in the belomorian belt the 17o systematics reveals contribution of distinct meteoric waters with 18o of 38 and 9 recorded at different localities across the belt we also present new data for the 2 41 2 38 ga scourie dikes with the lowest 18o value of 2 5 recorded in the amphiboles of loch na h dike unlike the belomorian belt the low 18o signature of scourie dikes requires igneous incorporation of low 18o hydrothermally altered rocks through contamination of mantle derived melts the 17o data analyzed at the loch na h dike reveals that the incorporated material experienced water rock interaction with meteoric water that had 18o of 35 10 the exact mechanism for incorporation of such low 18o rocks in the mafic scourie dike melts is equivocal and could involve subduction or assimilation of low 18o hydrothermally altered mafic rocks these reconstructed isotope compositions of meteoric waters are diverse and comparable to the modern day precipitation of high latitude regions e g greenland 18o 35 and precipitation of mid latitude regions 9 possibly reflecting spatial 18o gradients resulted from an active hydrologic cycle during the cold climate of the early paleoproterozoic as depicted by previous isotope enabled global circulation models of snowball earth state

amplitude corrections for regional seismic discriminants a fundamental problem associated with event identification lies in deriving corrections that remove path and earthquake source effects on regional phase amplitudes used to construct discriminants our goal is to derive a set of physically based corrections that are independent of magnitude and distance and amenable to multivariate discrimination by extending the technique described in taylor and hartse 1998 for a given station and source region a number of well recorded earthquakes is used to estimate source and path corrections the source model assumes a simple brune 1970 earthquake source that has been extended to handle non constant stress drop the discrimination power in using corrected amplitudes lies in the assumption that the earthquake model will provide a poor fit to the signals from an explosion the propagation model consists of a frequency independent geometrical spreading and frequency dependent power law q a grid search is performed simultaneously at each station for all recorded regional phases over stress drop geometrical spreading and frequency dependent q to find a suite of good fitting models that remove the dependence on m b and distance seismic moments can either be set to pre determined values or estimated through inversion and are tied to m b through two additional coefficients we also solve for frequency dependent site phase excitation terms once a set of corrections is derived effects of source scaling and distance as a function of frequency are applied to amplitudes from new events prior to forming discrimination ratios thus all the corrections are tied to just m b or m 0 and distance and can be applied very rapidly in an operational setting moreover phase amplitude residuals as a function of frequency can be spatially interpolated e g using kriging and used to construct a correction surface for each phase and frequency the spatial corrections from the correction surfaces can then be applied to the corrected amplitudes based only on the event location the correction parameters and correction surfaces can be developed offline and entered into an online database for pipeline processing providing multivariate normal corrected amplitudes for event identification examples are shown using events from western china recorded at the station makz