regional variation and frequency dependence of qβ in the crust of the united states approximate lg attenuation coefficient values are determined for paths in eastern north america at periods between 2 and 4 sec where no data were previously available these new data together with reported values at a period of 1 sec are consistent with values predicted by a frequency dependentent q of the crust in which q varies as 0 2 the new data are inconsistent with values which would be predicted by models having prominent maxima or minima in q 1 within the period range 1 to 5 sec lg attenuation coefficients were computed for the frequency independent crustal q models of cheng and mitchell 1981 for the basin and range province and colorado plateau of the western united states the predicted values at 1 sec for the colorado plateau and basin and range province are about twice as large and three times as large respectively as those predicted for the eastern united states recently reported values of q for 1 sec lg in those regions are consistent with the attenuation coefficients and q values of lg predicted by the colorado plateau and basin and range province models a model with a small degree of frequency dependence of q would be consistent but is not required by the data

seismic attenuation in northeastern sonora mexico we studied the attenuation of local and regional earthquake body waves recorded by the seismic network of northeastern sonora mexico red sismica del noreste de sonora resnes the source station paths of the selected data set cover the epicentral region of the may 1887 m w 7 5 sonora earthquake we used the best located earthquakes recorded by resnes between 2003 and 2004 to analyze the spectral amplitude decay of body waves with hypocentral distance the database consists of 44 earthquakes with magnitudes between 1 8 and 3 2 and hypocentral distances between 25 and 150 km we calculated fourier spectral amplitudes from more than 400 records and defined attenuation functions with a nonparametric model by inverting the observed spectral amplitudes at 23 individual frequencies between 0 4 and 63 1 hz we determined regional attenuation curves based on events located more than 100 km northwest of the center of the network and local curves based on earthquakes located near the fault zone that ruptured in the 1887 earthquake the obtained attenuation curves indicate that the spectral amplitudes decay faster in the area of the 1887 rupture than in the surrounding region to analyze the possible sources of attenuation we parameterized the attenuation functions considering three terms one that accounts for geometrical spreading another one for anelastic attenuation and a third for near surface attenuation we found the s wave quality factor q to be similar in both the general region and near the 1887 rupture however in the region of the 1887 rupture the near surface attenuation exceeds the regional average finally in the region of the 1887 rupture the nonparametric attenuation functions and the estimates of q indicate that at between 0 6 and 63 1 hz p waves attenuate more than s waves q p 20 8 f 1 1 whereas q s 83 8 f 0 9

timeseries of polar water properties in fram strait 1 timeseries of temperature and salinity of polar water in the east greenland current egc and on the east greenland shelf at 79 n are presented the observations in the egc are made in the 45 74 dbar layer carrying liquid freshwater from the arctic ocean to subarctic seas the properties on the outer fringe of the egc are dominated by shifts of the position of the east greenland front egf in the inner part of the egc and on the shelf the seasonal cycle of the properties are dominated by the annual cycle of sea ice freezing and melting comparing the observations with the world ocean atlas woa and other climatologies demonstrates that the climatologies in the egc and on the shelf at 79 n are poor due to poor data coverage

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

comparative analysis of teleseismic p coda and lg waves from underground nuclear explosions in eurasia this study has investigated the characteristics of p coda and lg waves recorded at the norsar and graefenberg arrays from presumed nuclear explosions in western russia lg waves were found to be more energetic relative to the preceding coda in the mid band frequency range 0 2 to 1 0 hz recorded on the broadband graefenberg instruments than in the high frequency band 0 6 to 3 0 hz at either array comparison of the log rms coda envelopes at the two arrays revealed that the early high frequency p coda at norsar is stronger relative to lg than at graefenberg also the amplitudes of p waves and early p coda waves within 55 sec after p recorded at the centers of the norsar subarrays are positively correlated indicating the effect of focusing defocusing on the p and coda waves however for subarrays which cluster spatially there is an inverse correlation which seems to be due to scattering attenuation suggesting that much of the early p coda is generated by local p wave scattering beneath the norsar array also the norsar coda envelopes flatten between about 219 and 352 sec after p whereas the graefenberg coda decays monitonically from the p wave out to the sn and lg arrival times the standard deviation across the norsar array of the log rms amplitudes of lg and s coda phases are higher by about 0 05 to 0 06 magnitude units than those of p coda phases these differences are probably related to differential site and propagation path effects on p s and lg waves in the p coda the flattening of the norsar coda envelopes appears to be a burst of energy not associated with any known regional phases the burst may be caused by forward scattering of lg to p waves along the path between the source and norsar based on a regional travel time curve for western russia the start and end time of the coda flattening is consistent with lg to p scattering in the distance range of 23 to 29 from norsar which brackets the ural mountains the lg propagation path from the source region to graefenberg does not appear to traverse the ural mountains which may explain why the coda flattening is not observed at graefenberg

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

a study of p waves from nevada test site explosions near source information from teleseismic observations spectral analyses of short period p arrivals on teleseismic recordings of nuclear explosions at yucca flats and pahute mesa regions of the nevada test site seem to provide explosion source medium information the spectral ratio p p coda on short period vertical component records at norsar shows significant correlation with explosion medium velocity for a given yield spectrum of the initial p waves from an explosion within a high velocity medium is richer in high frequencies as compared to that for p waves from an explosion within a low velocity medium the spectra of p codas on the other hand are considerably less sensitive to the near source velocity differences from one shot to another so that the spectral ratio p p coda is diagnostic of the shot medium velocity relative insensitivity of the p coda spectra and amplitudes to the overburden velocity is perhaps due to several factors including an effective source function controlled by average properties of rock within a fairly large nonlinear region around the shot point the study provides valuable insight into effects of the shot medium on the spectra and amplitudes of compressional arrivals and offers the exciting possibility of extracting near source information from teleseismic observations

a study of ground motion attenuation in the southern great basin nevada california using several techniques for estimates of qs log a 0 and coda q as a first step in the assessment of the earthquake hazard in the southern great basin of nevada california this study evaluates the attenuation of peak vertical ground motions using a number of different regression models applied to unfiltered and band pass filtered ground motion data these data are concentrated in the distance range 10 250 km the regression models include parameters to account for geometric spreading anelastic attenuation with a power law frequency dependence source size and station site effects we find that the data are most consistent with an essentially frequency independent q and a geometric spreading coefficient less than 1 0 regressions are also performed on vertical component peak amplitudes reexpressed as pseudo wood anderson peak amplitude estimates pwa permitting comparison with earlier work that used wood anderson wa data from california both of these results show that q values in this region are high relative to california having values in the range 700 900 over the frequency band 1 10 hz comparison of ml magnitudes from stations brk and pas for earthquakes in the southern great basin shows that these two stations report magnitudes with differences that are distance dependent this bias suggests that the richter log a0 curve appropriate to california is too steep for earthquakes occurring in southern nevada a result implicitly supporting our finding that q values are higher than those in california the pwa attenuation functions derived from our data also indicate that local magnitudes reported by california observatories for earthquakes in this region may be overestimated by as much as 0 8 magnitude units in some cases both of these results will have an effect on the assessment of the earthquake hazard in this region the robustness of our regression technique to extract the correct geometric spreading coefficient n and anelastic attenuation q is tested by applying the technique to simulated data computed with given n and q values using a stochastic modeling technique we generate suites of seismograms for the distance range 10 200 km and for both wa and short period vertical component seismometers regressions on the peak amplitudes from these records show that our regression model extracts values of n and q approximately equal to the input values for either low q california attenuation or high q southern nevada attenuation regressions on stochastically modeled wa and pwa amplitudes also provides a method of evaluating differences in magnitudes from wa and pwa amplitudes due to recording instrument response characteristics alone these results indicate a difference between mlwa and mlpwa equal to 0 15 magnitude units which we term the residual instrument correction in contrast to the peak amplitude results coda q determinations using the single scatterer theory indicate that qc values are dependent on source type and are proportional to p where p 0 8 to 1 0 this result suggests that a difference exists between attenuation mechanisms for direct waves and backscattered waves in this region

the effect of crustal structure on the regional phases pg and lg at the nevada test site the effect of local structure on the characteristics of the regional phases pg and lg was investigated by analyzing events at epicentral distances less than 10 from the nevada test site the stations used are on markedly different geological structures three on granitic intrusions two on pahute mesa a feature overlaying a buried volcanic caldera and finally four on yucca flats a deep alluvial valley the crustal effect on amplitudes is quite significant for both lg and pg yucca flats gives amplitudes as much as a full order of magnitude higher than the stations on granite while pahute mesa stations are 0 7 0 8 magnitude units higher in amplitude than the granite sites besides gross amplitude effects the local crust also induces prolonged ringing at yucca flats resulting in the lengthening of the signal wave trains the observed site amplification effects show no clear dependence on the azimuths of arrivals indicating that the phenomenon is due to local structures and is not caused by lateral refraction of surface wave modes the observed amplification is similar in magnitude for the vertical component of both pg and lg thus not affecting the pg lg amplitude ratio a possible discriminant between earthquakes and explosions at regional distances finite difference theoretical simulations using two dimensional models of the yucca basin reproduce in a qualitative sense the ringing effect observed at the yucca flats any attempt at matching characteristics of pg and lg with synthetic seismograms computed for laterally homogeneous layered structures is apt to lead to false conclusions about the source and path properties unless the recording sites used are carefully chosen for small crustal effects

numerical modelling of sh lg waves in and near continental margins summary the effect of transition regions between continental and oceanic structures on the propagation of l waves from continental sources is examined in particular the attenuation due to variations in layer thickness in such transition regions is calculated and explained for a suite of simple models the measured attenuation due tq the geometry of the transition regions between the oceanic and continental structures within a partially oceanic path with source and receiver in a continental structure is at most a factor of four for frequencies from 0 01 to 1 hz this is inadequate to explain the observed extinction of l along such paths this extinction has previously been attributed to the effects of the transition region geometry the method used to calculate the results presented in this study is developed and its validity and accuracy are demonstrated propagator matrix seismograms are coupled into a finite element calculation to produce hybrid teleseismic sh mode sum seismograms these hybrid synthetics can be determined for paths including any regional transition zone or other heterogeneity that exists as part of a longer mostly plane layered path numerical results presented for a suite of transition models show distinct trends in each of the regions through which the wavefield passes the wavefield passes through a continent ocean transition region then a region of oceanic structure and finally through an ocean continent transition region when an l wavefront passes through a continent ocean transition the amplitude and coda duration of the l wave at the surface both increase at the same time much of the modal l energy previously trapped in the continental crust is able to escape from the lower crust into the subcrustal layers as body waves the magnitude of both these effects increases as the length of the transition region increases when the wavefront passes through the region of oceanic structure further energy escapes from the crustal layer and produces a decrease in l amplitude at the surface the rate of amplitude decrease is maximum near the transition region and decreases with distance from it when the wavefield passes through the oceancontinent transition region a rapid decrease in the l amplitude at the surface of the crust results the energy previously trapped in the oceanic crustal layer spreads throughout the thickening crustal layer some of the body wave phases produced when the wavefield passes through the continent ocean transition region are incident on the continental crust in the ocean continent transition region these waves are predominantly transmitted back into the crust the other body wave phases reach depths below the depth of the base of the continental crust before reaching the ocean continent transition and thus escape from the system

analysis of near source contributions to early p wave coda for underground explosions i waveform complexity a data set of more than 1600 teleseismic short period p waves from 46 nuclear explosions is analyzed to establish near source contributions to the first 15 sec of the p signals the near source components are isolated by event to event comparisons of first cycle magnitudes rms amplitudes in the first 5 and next 10 sec of the wave forms and energy temporal centroid measurements events from the nevada amchitka and novaya zemlya test sites are analyzed separately to characterize overall source region variations event averaged waveform complexity variations between explosions within a given site are tested for dependence on source strength burial depth location within the site and tectonic release azimuthal patterns of the individual event complexity anomalies are used to discriminate between possible near source influences for events at pahute mesa a strong azimuthal amplitude pattern in both the direct p waves and the p coda for all of the events is produced principally by deep mantle variations defocusing by a high velocity anomaly in the crust and uppermost mantle beneath the site has a stronger effect on the direct p signals than on the early p coda resulting in a systematic spatially varying relative pattern

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

multi mode analysis of rayleigh type lg part 2 application to southern california and the northwestern sierra nevada the uc diagram technique described in the companion paper part 1 is applied to nine sets of lg phases recorded through the cedar system in southern california and two sets of lg phases recorded along the northwestern margin of the sierra nevada a clear image of the signal is obtained in time frequency wavenumber space and we discuss in particular observations at 2 5 sec period for events 200 to 300 km outside the profiles from the gross features of uc diagrams we conclude that a representation of lg as a single coherent multi mode wave train is oversimplified in the case of southern california but is more appropriate for the sierra block in southern california peaks observed at group velocities smaller than 3 2 km sec are not predicted by realistic crustal models of the area and are probably due to lateral heterogeneities effects such as mode conversion and multipathing on the other hand for group velocities between 3 2 and 3 6 km sec peaks observed in either area can generally be interpreted in terms of overtones excited at the source and propagating through spatially averaged structures although care must be taken to monitor the stability of the algorithm on actual short period records

measurement of frequency dependent lg attenuation in the great basin measurement of the spatial decay of spectral amplitudes of the higher mode seismic surface wave train lg indicates that in the great basin the apparent seismic quality factor q is a function of frequency observations along a 300 km profile recording of a nuclear explosion yield the function q 206 0 68 over the band 0 3 10 0 hz similar analysis using numerous recordings of earthquakes along paths which provide a good average sampling of the great basin crust gives q 214 15 0 54 0 09 for 0 3 5 0 hz if the crustal sampling by lg energy from nuclear explosions surface sources is primarily in the shallow crust as has been suggested then these results indicate a greater frequency dependence of apparent q there than at depth

a scattering model to explain seismic q observations in the lithosphere between 1 and 30 hz observations of lithospheric q for shear waves in the range 1 30 hz reported in the literature are examined using a scattering model consisting of randomly distributed spheres for the single scattering approximation i have assumed 1 q 1 q sub i gv omega where q sub i is the intrinsic q due to anelasticity v is the velocity of shear waves omega is angular frequency and g is the turbidity g is taken as a constant in this paper since g integral n a sigmada where n a da is the number of scattering spheres of radius a unit volume and sigma is the scattering cross section for a sphere this suggests that geometrical scattering dominates this will be true for ka 1 where k is wavenumber based on this criterion and the observation that q is large i e g small at a frequency of 0 05 hz a is of the order of magnitude 1 10 km fits of observations of shear wave q from japan and central asia indicate that q sub i 2000 500 for the lithosphere of both regions g 0 01 km for the japan observations and g 0 005 km sup 1 for central asia

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

trace metal concentration and partitioning in the first 1 5 m of hydrothermal vent plumes along the mid atlantic ridge tag snakepit and rainbow abstract to determine the significance of metal fluxes from hydrothermal vents understanding the speciation reactivity and possible transformations of metals and metal sulfides within the hydrothermal plume is critical in this study we measure the concentration and partitioning of trace metals fe mn cu cd co pb ni and sulfide phases within the first 1 5 m of the rising plume at three vent fields tag snakepit and rainbow along the mid atlantic ridge a hcl hno3 leaching method was used to differentiate metals present in metal mono sulfides from those in pyrite and chalcopyrite at all three vent sites mn and fe are primarily in the

magnitude the relation of ml to mblg abstract the m blg magnitude developed by nuttli 1973 for the central united states is adapted to other regions of the world by incorporating a specific term for the spatial coefficient of anelastic attenuation using region specific values m blg values are determined for earthquakes occurring near the wwssn stations bks gsc and dug a comparison of the m blg values with published m l magnitudes shows that these two magnitude scales are essentially equivalent between magnitudes 3 to 5 because of this observation we now have a direct way of comparing eastern and western united states earthquake sizes for the purpose of adapting western strong motion data bases to the east and also for understanding teleseismic magnitude biases

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

analysis of near source contributions to early p wave coda for underground explosions ii frequency dependence an analysis of dispersion in more than 1600 teleseismic short period p waves from 46 underground explosions has established that near source effects are responsible for systematic frequency dependent variations observed in the first 15 sec of the p signals explosions from the nevada amchitka and novaya zemlya test sites exhibit a common magnitude dependence of the dispersive behavior with smaller events having relatively enriched low frequency 0 4 to 0 8 hz energy in the coda for the nevada and amchitka sites the larger events have relatively enhanced high frequency 0 8 to 1 1 hz energy in the coda as well which may actually be a consequence of diminished high frequency content of the direct arrivals the dispersive behavior also correlates well with known source depths for the nevada test site and amchitka events and with estimated pp delay times for the novaya zemlya events indicating that burial depth and or explosion size are important factors pahute mesa tests show a secondary dependence on position in the site with centrally located events having stronger dispersion as well as more pronounced slowly varying azimuthal patterns in the frequency dependence stations at azimuths to the north northeast from the mesa have particularly strong dispersion for centrally located events the spatial and azimuthal variations for pahute mesa events do not appear to be the result of aftershock radiation as suggested by douglas 1984 but instead are associated with frequency dependent defocusing and scattering from a high velocity structure beneath the test site some of the dispersion from novaya zemlya events appears to result from deep path properties however the strong magnitude depth dependence for all of the test sites indicates that very near source conditions have the strongest influence on the frequency dependence a likely explanation for the dispersive behavior is a combination of relatively enhanced surface wave excitation and scattering for shallower events and frequencydependent defocusing for sites overlying anomalous high velocity structures as is the case for both pahute mesa and amchitka

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

a local magnitude scale for the western great basin eastern sierra nevada from synthetic wood anderson seismograms abstract we have computed synthetic wood anderson seismograms for over 1100 arrivals at 10 three component broadband digital stations in the unr western great basin eastern sierra nevada network these represent all the available records from local earthquakes over magnitude 3 5 between 1990 and june of 1993 plus selected events of smaller magnitude there were 77 events ranging in magnitude from 2 2 to 5 9 including four events over magnitude 5 the distances considered ranged from 15 to 600 km with the best represented range being from 30 to 450 km we invert these measurements to determine distance and station corrections appropriate for a local magnitude scale constrained by richter9s original definition that an earthquake of m l 3 will cause a 1 mm zero to peak deflection of the wood anderson seismogram at 100 km from the epicenter the results between 30 and 450 km were essentially independent of choice of curve fitting parameters in the 30 to 500 km distance region the smooth distance correction curves were very similar to that determined by richter 1958 which is still used for southern california earthquakes we propose to use richter9s distance correction curve in reporting amplitude magnitudes from our digital network