3 d inhomogeneities in the upper mantle abstract the method developed by aki christofferson and husebye for determining a 3 d seismic image of the earth s interior from the travel time data obtained at a 2 d array has been applied to seventeen arrays around the world by various authors the most outstanding results from these works are that small scale lateral velocity anomalies exist in the lower crust and upper mantle everywhere studied the reality of these deep seated anomalies is supported by 1 1 significant reduction of residual variance 2 2 resolution analysis for decoupling from shallower anomalies and 3 3 error analysis for the significance of anomalies in this paper we try to strengthen the credibility of these deep seated anomalies by drawing attention to those found where they were expected namely low velocity bodies under several geothermal areas and high velocity anomalies associated with the subducting plate

frequency relationship for seismic qβ of central southern italy from accelerograms for the irpinia earthquake 1980 abstract the frequency dependence of q for seismic waves in a distance range with a maximum of 150 km from the epicentre of the irpinia earthquake of november 23 1980 has been sought using displacement spectral ratios computed from strong motion accelerograms recorded in the region the method has been applied to calculate the behaviour of q as a function of frequency in the band 0 1 25 hz and to investigate whether azimuthal variations appear in seismic q for the lithosphere in central southern italy the same result is obtained using data from stations in western south italy as using data from eastern south italy namely q f 40f hz the linear relationship suggest that apparent q depends more on the scale of heterogeneity of the lithosphere affecting reflection and scattering mechanisms than on intrinsic energy losses related to the anelasticity of the materials through which the seismic waves propagate the existence of a peak in q 1 has been investigated in the low frequency band 0 1 2 5 hz using a higher resolution power a stable result in this low q zone is not possible on the basis of the available data only in six q f profiles does an evident minimum exist between 0 2 and 1 hz while in nine cases the curves are monotonically increasing from the lowest observable frequencies a further nine cases appear of uncertain interpretation

wave scattering theory in analysis of p wave anomalies at norsar and lasa summary observed travel time and amplitude anomalies at the norsar and lasa arrays are significantly larger than the measurement errors and cannot be explained in terms of deterministic crust and upper mantle structural models for the respective siting areas in this paper the chernov theory is used in modelling the crust and upper mantle as a random medium and also to estimate to what extent such models can account for the observed anomalies we find that the random medium modelling can explain 50 60 per cent of the variance of the time and amplitude anomalies at norsar the corresponding results for lasa are 50 60 per cent and 25 per cent respectively in contrast reasonable deterministic models cannot account for even 25 per cent of this variance while the random medium model can provide a satisfactory explanation of the observational data extensive tests have revealed that the parameters characterizing the random medium cannot be uniquely determined from the data the reasons underlying this limitation are discussed

seismic codas on the earth and the moon a comparison the phenomenon of the seismic coda which is composed of seismic energy delayed by scattering is seen on both the earth and the moon on the moon the scattered coda is very large relative to body wave arrivals with a delay of the time of maximum energy whereas on earth scattered codas are relatively small and show no delay of the energy maximum in both cases the form of the coda is controlled by three distance scales the mean free path l which is the average distance seismic energy travels before it is scattered the attenuation distance x which is the average distance seismic energy travels before it is attenuated and the source receiver distance r two coda models are discussed based on these parameters a strong scattering diffusion model and a weak scattering single scattering model a discussion of the diffusion scattering model indicates that if x l 1 diffusion scattering is an appropriate model but if x l 1 single scattering is the appropriate model within the appropriate range of r a survey of the literature indicates that for the frequency range 0 5 10 hz diffusion scattering is important in lunar codas but for the frequency range 1 25 hz single scattering is important in terrestrial codas another important effect of attenuation is the elimination of scattering paths much longer than x on the moon this means that seismic energy in the coda can only propagate directly in the near surface strong scattering zone between surface sources and the seismometer for source seismometer separations of the order of x l 12 otherwise scattering is limited to regions near the source and the receiver on earth this effect probably prevents multiple scattering

attenuation of coda waves in new england abstract seismic wave attenuation was measured in new england from the time domain decay of coda wave amplitudes on narrow bandpass filtered seismograms of local earthquakes the frequency band of interest was 0 75 to 10 hz q c f was found to increase with frequency across this band but there was also a difference between the q c f values for short t t 100 sec lapse times of coda wave propagation for the short lapse time data corresponding to wave paths primarily in the upper crust q c f increases from 400 at 3 hz to 1300 at 10 hz for the large lapse time data corresponding to wave paths in the lower crust and upper mantle q c f was found to vary from 660 at 1 hz to 1500 at 10 hz if we interpret this dataset in terms of a model incorporating both scattering and anelastic attenuation we find that the mean free path of seismic waves over this frequency band is 80 km for short lapse times and 400 km for long lapse times if we assume that scattering is entirely responsible for the observed attenuation we find that the minimum mean free path for short lapse times is about 75 km over all frequencies whereas for long lapse times the minimum mean free path decreases from 400 km at 0 75 hz to 90 km at 10 hz

temporal change in coda q before the tangshan earthquake of 1976 and the haicheng earthquake of 1975 a new earthquake precursor called coda q is demonstrated for the tangshan earthquake of 1976 and for the haicheng earthquake of 1975 the precursor is based on the measurement of coda decay rate for small local earthquakes in the general area that is preparing for a major earthquake during the 3 year period preceding the tangshan earthquake the coda q was about 3 times lower than it was before or after this period a comparable change also occured at the time of the haicheng earthquake the observed change cannot be due to the change in the source parameters such as the focal depth or the source spectrum the coda q precursor appears to detect the same physical process detected by other precursors such as b value quiescence radon water quality vp vs and animal behavior but has advantages over them in its clearer physical mechanism easier sampling and better defined anomalous region

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

characteristics of coda waves central and southcentral alaska abstract code amplitude decay rates as a function of lapse time time measured from the origin time for two moderate size alaskan earthquakes are related to their known values of seismic moments this relation is then used to compute seismic moments from coda wave data for a selected group of small earthquakes located in the greater fairbanks alaska seismic zone the computed values of moment appear to be consistent with the local magnitudes next with the moment and magnitude data an empirical moment magnitude relation is obtained for central and southcentral alaska this relation is similar to those for central and northern california proposed by others computation for q values in the frequency f band 1 03 to 1 5 hz for central and southcentral alaska with local coda wave data yielded values in the range from about 160 to 290 the minimum of q f appears to be in the frequency interval from 0 5 to 1 5 hz moreover q values f 1 hz in the above range have been recently reported by others for areas in western united states having similar tectonic history as the alaskan study area

spatial distribution of coda scatterers in the crust around two active volcanoes and one active fault system in central japan inversion analysis of coda envelope abstract coda waves observed by local seismographic networks were analysed by using the inversion method presented by nishigami 1991 to estimate spatial distribution of coda scatterers in the crust first deviations of the decay curve of observed coda envelope away from a reference curve were measured for lapse times greater than about 1 5 2 0 times the s wave travel times we assume this kind of deviation is mainly caused by the non uniform distribution of scatterers in the crust next the 3 d distribution of relative scattering strength in the crust was obtained by solving the observational equation where single isotropic scattering and a spherical radiation from the source are assumed and the observational data is given by the deviation of coda envelope stated above this method was applied to two volcanic regions and one active fault region in the central part of japan in each analysis the target region with dimension of 50 160 km in horizontal and 30 80 km in depth was divided into about 1500 2000 blocks with one side of 2 10 km and 600 900 waveform traces from about 100 250 events observed at 7 38 stations were used the lapse time of coda waves analysed was taken to be as short as possible to reduce the multiple scattering effect it was in the shortest case about 3 13 s for the ontake region the result of inversion analyses showed several significant features strong scatterers were found at shallow part 0 20 km of the crust around the fukui earthquake fault a low seismicity area between active faults showed a correlation with the weak scattering area the detailed distribution of scatterers was also revealed around two active volcanoes mt ontake and mt nikko shirane the vertical distribution of strong scatterers just below the volcano from 0 to 7 km in depth and another horizontal one at a depth of 7 km were estimated in the ontake region an inclined distribution of scatterers was estimated at depths from 0 to 20 km just below mt nikko shirane the location of scatterers around these active volcanoes agreed well with that of the s wave reflectors in the crust obtained by the nmo correction analysis frequency dependence of scatterer distribution was also examined for the ontake region the horizontal distribution of scatterers at 7 km depth showed a similar pattern for frequencies between 5 and 20 hz while other smaller scale scatterers appeared to have frequency dependence

regional change of coda q in the oceanic lithosphere coda q of 22 local earthquakes recorded on islands located in young and old oceanic lithosphere areas has been measured we found that the q values at periods of from 1 to 2 seconds increase from young to old ocean lithosphere in the same way as for the continent where the intensity of current tectonic activity shows a strong negative correlation with the coda q the q values increase with frequency proportional to fn where n was found to be 0 46 0 61 with the higher values for younger oceanic lithosphere which is again similar to the continents where the active regions have higher n values

s wave attenuation in the crust in northern greece abstract the attenuation of shear waves in the crust is estimated for frequencies between 1 5 and 12 0 hz by applying a single station method based on the rate of decay of the s wave to coda wave amplitude ratio with distance the data used come from local earthquakes that occurred in the thessaloniki area northern greece during the period 1983 through 1989 and were recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki the q s values obtained are 115 244 477 and 755 for 1 5 3 0 6 0 and 12 0 hz respectively these values are very close to the coda q values estimated for the same area using the s to s single scattering model for lapse times between 30 and 100 sec but they are higher than the coda q values for lapse times between 10 and 30 sec the estimated q s is found to be strongly frequency dependent proportional to f 0 91 which is very close to the frequency dependence of the coda q

s to p scattering at the 650 km discontinuity summary a search of seismograms recorded at the warramunga seismic array wra from events occurring below the izu bonin islands shows an arrival on some but not all of the records with an onset at 25 30 s after p which is not predicted by the standard travel time tables the slowness and azimuth of the phase show that it is generated almost in line with p and the variation of arrival time with the hypocentral depth of the earthquake indicates that its origin lies on the receiver side of the source it appears in fact to be an s to p conversion at a depth of 650 700 km which is seen only when the receiver is close to a node of the p radiation pattern and an antinode for s so that its amplitude compared with that of p is at a maximum finally the duration of the phase indicates that it is not simply a refracted wave but that it has a coda of scattered arrivals from lateral heterogeneity in the neighbourhood of 650 km below the izu bonin islands

frequency dependence and spatial distribution of seismic attenuation in france experimental results and possible interpretations campillo m and plantet j l 1991 frequency dependence and spatial distribution of seismic attenuation in france experimental results and possible interpretations phys earth planet inter 67 48 64 we processed digital records from 431 earthquakes at 25 stations of the laboratoire de detection geophysique network in france we computed spectral amplitudes of pg and lg in different group velocity windows this large data set aliowed us to compute a map of mean crustal attenuation through simultaneous consideration of source amplitude site response and apparent q our inversion procedure combines an iterative reconstruction technique with an adjustment of source amplitudes and site responses at each step the stability of the result is tested with different subsets of data and the resolution is evaluated maps of apparent attenuation at frequencies between 1 5 and 10 hz were computed from pg lg and early coda of lg these results are in a good agreement with the predictions of the singie scattering model both for frequency dependence and for qs qp ratios the comparison between the attenuation anomaly found in the yariscan belt and results from a deep reflection seismic profile confirms the prominent part played by scattering in the apparent attenuation of seismic waves in the crust

estimates of q in central asia as a function of frequency and depth using the coda of locally recorded earthquakes digital recordings of microearthquake codas from shallow and intermediate depth earthquakes in the hindu kush region of afghanistan were used to determine the attenuation factors of the s wave coda qc and primary s waves q an anomalously rapid decay of the coda shortly after the s wave arrival observed also in a study of coda in central asia by rautian and khalturin 1978 seems to be due primarily to depth dependent variations in qc in particular we deduce the average qc in the crust and uppermost mantle 100 km depth is approximately four times lower than the deeper mantle 400 km depth over a wide frequency range 0 4 to 24 hz further while qc generally increases with frequency at any depth the degree of frequency dependence of qc depends on depth except at the highest frequency studied here 48 hz the magnitude of qc at a particular frequency increases with depth while its frequency dependence decreases for similar depths determinations of q and qc agree suggesting a common wave composition and attenuation mechanism for s waves and codas comparison of these determinations of qc in afghanistan with those in other parts of the world shows that the degree of frequency dependence of qc correlates with the expected regional heterogeneity such a correlation supports the prejudice that qc is primarily influenced by scattering and suggests that tectonic processes such as folding and faulting are instrumental in creating scattering environments

study of seismogram envelopes based on scattering by random inhomogeneities in the lithosphere a review abstract instead of the precise examination of individual phases in seismograms we will focus on the relation between random inhomogeneities in the lithosphere and the systematic change in seismogram envelopes recent developments in the study of high frequency seismogram envelopes are briefly reviewed the smooth amplitude decay of coda envelopes of local earthquakes first attracted seismologists interest in scattering and was investigated based on the single scattering assumption with a uniform distribution of point like scatterers subsequently the importance of multiple scattering was recognized and theoretical models were introduced as a bridge between conventional seismology and the scattering approach a hybrid model in which a large impedance contrast plane was embedded in a scattering medium was proposed for the interpretation of a reflected s phase in the coda for shallow events around a volcanic front in japan next three component seismogram envelopes of a small local earthquake were synthesized using the born approximation in inhomogeneous media the s coda is excited in all directions from the hypocenter the p coda appears even in the nodal direction of the p wave radiation mostly owing to sp scattering near the hypocenter both pseudo p and s phases appear even on the null axis these synthetic seismogram envelopes are in harmony with characteristics of observed seismogram envelopes of local earthquakes scattering due to random inhomogeneities quantitatively explains the frequency dependence of s wave attenuation from the analysis of seismogram envelopes around direct s waves of earthquakes with intermediate hypocentral distances it was recently found that the time lag of the maximum amplitude arrival from the s wave onset increased and the envelope broadened with travel distance diffraction due to slowly varying velocity inhomogeneities is modeled using the parabolic approximation and is used to explain the envelope around the s wave arrival observed at intermediate distances a nonlinear inversion of the full seismogram envelope is used for the evaluation of randomness thus the analysis of seismogram envelopes offers us useful information on the randomly inhomogeneous structure of the lithosphere complementary to the array observation analysis of individual phases

coda waves a review the analysis and interpretation of coda waves have received increasing attention since the early seventies in the past few years interest in this subject has spread worldwide and the study of high frequency seismic coda waves has become a very important seismological topic as a conclusion of the studies accomplished in this time coda waves are considered the result of scattering processes caused by heterogeneities acting on seismic waves p ands waves play a particularly important role in this interaction the process introduces an attenuation which added to the intrinsic absorption gives the observed apparent attenuation therefore coda waves constitute a thumbprint left by the heterogeneities on the seismograms coda waves offer decisive information about the mechanism of how scattering and attenuation take place this review describes coda waves in detail and summarizes the work done in this subject to 1986 the relation between coda waves and attenuation in the context of research on seismic scattering problems is stressed particular attention has been given to the application of coda waves to estimate source and medium parameters the state of the art of the temporal variations of coda wave shape and the possible use of these variations as an earthquake precursor also are presented care has been taken to introduce the statistical models used to deal with the heterogeneities responsible for scattering

some medium properties of the hohenzollerngraben swabian jura w germany inferred from qp qs analysis high quality three component records of some very low magnitude aftershocks ml 2 of the september 3 1978 swabian jura earthquake have been used to estimate the crustal ratio qp qs in this seismically active area the slopes of the p and s spectra at high frequency 20 40 hz are the basic data used in this investigation qp qs ratios depend upon the area crossed by the corresponding ray path in particular small ratios are observed for rays crossing the hohenzollerngraben this result suggests that the crystalline basement has been tectonized under the graben structure and has experienced microcracking and or grain size reduction

the effects of attenuation and site response on the spectra of microearthquakes in the northeastern caribbean abstract the spectra of microearthquakes recorded by a seismic network in the northeastern caribbean were analyzed to determine the effects of attenuation and site response on these spectra the ratios of the spectral amplitudes at 5 and 20 hz were measured for several earthquakes at different distances from a fixed receiver to estimate q for p and s waves in the crust and upper mantle the average q p determined from three stations was 380 for epicentral distances between 40 and 200 km the average q s determined from two stations was estimated at 400 spectra of earthquakes closer than 40 km to one station indicate that a high q path q 800 exists for these short distances in the island arc platform the near equivalence of q p and q s observed in this study of the upper lithosphere contrasts with estimates of anderson et al 1965 that q p 9 4 q s in the asthenosphere this finding that q p is approximately equal to q s suggests that the attenuation mechanism in the upper lithosphere differs from that in the asthenosphere the spectra of nearby microearthquakes unaffected by crustal attenuation display corner frequencies which are uniform despite large differences in the seismic moments of the events the corner frequencies of these spectra appear to be characteristic of the receiver site and insensitive to the location and moment of the earthquakes at one station the s wave corner frequency of a nearby blast was identical to the corner frequency of a magnitude 4 8 earthquake derived from the record of a strong motion accelerograph at the same site

seismic coda q and scaling law of the source spectra at the aeolian islands southern italy the model developed by aki and chouet for the coda wave generation and propagation has been used to calculate the quality factor q for the zone of the aeolian islands southern italy in the frequency range of 1 to 12 hz and the scaling properties of the seismic spectrum in the magnitude range of 0 4 to 4 7 the q found for the aeolian area has a frequency dependence of the form q qfv the absolute values of q seem to be dependent on the station and location of the seismic events confirming the strong lateral heterogeneities in the geological structure beneath the aeolian arc a temporal variation has been noted in the q calculated at vulcano station vpl in a period of 3 weeks soon after the occurrence of a main shock of ml 5 5 located near the station the scaling behavior of this sequence is similar to that obtained in two areas of california and one portion of japan with a corner frequency that remains constant with an increasing seismic moment between magnitudes 1 and 4 it differs substantially from the scaling properties of the hawaian earthquakes that show a linear pattern without an increase of the stress drop with magnitude the fact that vulcano is an active volcano seems not to influence the scaling properties of the seismic sequence localized very near it it probably indicates that the aftershocks used for calculating the scaling law are generated out of the volcanic complex lipari vulcano in a zone with a good capability of accumulating the stress

the seismic response of two dimensional sedimentary deposits with large vertical velocity gradients an extension of the aki larner technique to vertically inhomogeneous media is presented so that vertical velocity gradients may be taken into account in two dimensional models only sh waves are considered here but the theory is valid for p and sv waves as well this method is applied to investigate the seismic response of two dimensional sedimentary deposits with large velocity gradients three different cases are considered a shallow high contrast valley a deep high contrast valley and a deep low contrast valley in each case a comparison is performed with the results of a two dimensional model taking into account only homogeneous sediments and a one dimensional model taking into account the vertical inhomogeneity of sediments the presence of a large velocity gradient does not change a lot the qualitative behavior of a two dimensional deposit local surface waves and or two dimensional resonance patterns are observed as in the case of homogeneous sediments nevertheless the surface waves are much more dispersive with lower phase and group velocities and larger amplitudes only very deep valleys give rise to the development of two dimensional resonance on the other hand the amplifications obtained in such deposits may reach much larger values than those predicted with either two dimensional homogeneous models or one dimensional inhomogeneous models since these results have been obtained for realistic values of valley geometrical and mechanical considerations they should find some application in earthquake engineering or seismic microzonation studies

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

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

estimates of short period q values and seismic moments from coda waves for earthquakes of the beijing and yun nan regions of china abstract coda waves are used to determine the q value of short period waves in the beijing area and in yun nan province china and the seismic moments of the earthquakes studied for the beijing area the q 0 or 1 hz value is found to be approximately 400 with little or no indication of frequency dependence of q for frequencies near 1 hz in that region for yun nan province the q 0 value is about 180 and the data suggest that q f q 0 f 0 2 where f is wave frequency these values are in fairly good agreement with short period q estimates made for those regions by chen and nuttli 1984 on the basis of attenuation of seismic intensity values hermann9s 1980 application of aki9s 1969 coda wave theory is extended to provide simple equations for calculating master curves for coda wave studies two types of master curves provide independent estimates of q 0 and of the dependency of q on wave frequency for the data analyzed the two methods gave similar results a third type of master curves gives estimates of the seismic moments of the earthquakes studied the moments obtained by this means agree with values obtained by the conventional methods of analysis that use the spectrum of body waves or surface waves

attenuation parameters for friuli region from strong motion accelerogram spectra abstract by using the accelerometric data obtained during the heaviest earthquakes that occurred in friuli in 1976 an attempt was made to obtain a law of attenuation in the northeastern po river area as dependence on the frequency the study was carried out by comparison of power spectra of entire accelerograms at different distances in the frequency range of 0 1 to 10 hz a q value was found which was proportionally dependent on the frequency as f n with n 1 1 this result can be considered valid for that region and for distances of up to about 200 km from the epicentral area

a preliminary study of coda q in california and nevada the decay rate of local earthquake coda is characteristic of the area in which the epicenter and stations are located aki 1969 aki and chouet 1975 rautian and khalturin 1978 tsujiura 1978 aki 1980 interpreted the coda decay rate in terms of the attenuation property of s waves in the lithosphere under the area the q of s waves inferred from coda waves is called coda q recently several papers reported temporal changes in coda q prior to the occurrence of large earthquakes they are 1 the tangshan earthquake m 7 8 of 1976 and the haicheng earthquake m 7 4 of 1975 jin and aki 1986 2 three earthquakes m 8 in the kuril kamchatka region gusev and lemzikov 1985 3 the kalapana hawaii earthquake m 7 2 of 1975 wilson et al 1983 and 4 the eastern yamanashi japan earthquake m 6 0 of 8 august 1983 sato 1986 in all these cases the coda q was reported to be anomalously low before the occurrence of the earthquake however in a detailed study by chouet 1979 a strong fluctuation of coda q with time was observed in bear valley california which was not followed by a significant earthquake a recent coda q study in the adak seismic zone by scherbaum and kisslinger 1985 also did not find significant coda q changes that could be related to a mb 5 8 earthquake which occurred in the area of investigation in order to evaluate the feasibility of using coda q for earthquake prediction research in california and nevada we began a systematic study of coda q using digital waveform data from the regional microearthquake networks operated by the u s geological survey and the university of nevada

coda attenuation in the lutzow holm bay region east antarctica the frequency dependent coda qc 1 was estimated for the lutzow holm bay region east antarctica on the basis of the single scattering model and discussed together with qc 1 data of kyoto japan as an example of an active region coda waves from six shallow earthquakes observed with a local telemetry seismic network installed along the soya coast were analyzed with narrow band pass filters qc 1 for a lapse time of 20 40 s was estimated to be 0 00495 0 776 for a frequency of 4 16 hz and qc 1 for 150 210 s was 0 00335 0 926 for 1 24 hz in comparison with qc 1 data for kyoto and other regions with various tectonic conditions qc 1 in the lutzow holm bay region was characterized by large values at low frequency around 1 hz and smaller values at higher frequency from the single scattering model qc 1 suggests a strong frequency dependence of intrinsic absorption for s waves assuming that the observed qc 1 reflects scattering loss of energy and taking account of the geological conditions and the extremely low seismic activity in the east antarctic continental shield it is suggested that the frequency dependent qc 1 is attributable to large scattering loss in the lower frequency range caused by large scale heterogeneities as a result of velocity and or density perturbations

site amplification of coda waves from local earthquakes in central california the goals of this study are two fold 1 to examine the site effect of coda waves believed to be the average site effect of shear waves in order to understand its spatial and frequency dependent behavior and 2 to learn what we can about the processes that generate the coda itself we use digital data from over 90 earthquakes each recorded by a subset of some 150 stations in the coast ranges of central california between san francisco and san luis obispo results from the band 1 5 to 24 hz indicate that site amplification depends strongly on surface geology and frequency at low frequencies 1 5 to 3 0 hz changes in amplification up to a factor of 20 are observed amplification generally varies inversely with deposit age at sediment sites and is lowest at granite and franciscan basement sites at high frequencies 6 to 24 hz the pattern changes many granite sites the majority in the gabilan range exhibit increasing amplification with frequency relative to the average station this behavior differs strikingly from that observed at sediment and franciscan sites which roll off at an intermediate rate and many sediment sites adjacent to the san andreas fault zone which decay away even more rapidly with frequency these results can be explained qualitatively by appealing to variable near site impedance and attenuation however complicating phenomena such as mode excitation in valley sediments must exist at low frequencies peaked behavior at a few hard rock sites at high frequency 12 hz currently lacks explanation at a few sediment sites the low frequency excitation is so strong that the coda envelopes begin to take on different shapes this contradicts the assumption based on previous observations that the coda shape is independent of source receiver location thus some site measurements may be artificially high the working model of coda waves as body wave energy backscattered from randomly distributed inhomogeneities must be modified to include the possibility of efficient near site resonance excited by incident direct and coda wave energy

two dilatancy based models to explain coda wave precursors and p s spectral ratio abstract some coda wave precursors can be predicted by the dilatancy model others need more complicated models the first of the models proposed here takes into account the compression of the medium around the swelling dilatancy zone and explains several observed precursor properties a simple theoretical model is employed to describe anisotropic s wave absorption in a microcracked medium under shear load the second model is used to explain the radiation bursts observed in coda in the preparation period and which overlap background scattered waves this model also explains the unusually high p s energy ratio of seismic waves from shocks in preparation zones the concept of seismic emission is employed to explain these phenomena two possible modes of emission are proposed 1 1 passive radiation generated by an abrupt dilatancy drop produced by stress drop in and around the earthquake source and 2 2 active radiation stimulated by seismic waves in a preparation zone or in any other volume of the lithosphere which is in a state of changing dilatancy

scattering and attenuation abstract an extensive existence of strong small scale heterogeneity in the earth is suggested by the great variability of direct waves and remarkable stability of scattered waves both in the case of teleseismic p coda and in the case of local earthquake s coda quantitative studies of small scoale heterogeneities have been made by the following three methods a lower bound of heterogeneity in the lithosphere has been estimated by the deterministic or stochastic modeling of travel time and amplitude fluctuation of teleseismic p waves across a large aperture seismic array an upper bound of heterogeneity has been estimated by modeling the attenuation of s waves as a scattering loss due to heterogeneity these two approaches suggest the existence of heterogeneity with rms velocity fluctuations from 3 to 10 per cent the third method is based on the estimation of heterogeneity from the amplitude of coda waves we found a significant discrepancy between the result obtained by the third method and those from the first two and attribute the discrepancy to the assumption of a single scattering model adopted in the coda generation theory the need for including multiple scattering as well as for considering vector elastic waves rather than scalar waves is emphasized

q estimates along the wasatch front in utah derived from sg and lg wave amplitudes abstract this study develops estimates for the attenuation of peak vertical ground motions using a conventional least squares regression model applied to unfiltered and bandpass filtered ground motion data the input data are from 88 earthquakes 1 0 m 3 3 epicentral distance range 10 to 450 km located along the utah idaho border and propagating sg and lg waves southward to seismograph stations along the wasatch front in north central utah the regression model includes parameters to account for geometric spreading anelastic attenuation with a power law frequency dependence source size and station site effects the maximum ground motion amplitudes are derived from waves arriving about 3 sec on the average after the s wave arrivals and are interpreted to be sg in close roughly 100 km or two crustal thicknesses and lg at greater distances accordingly geometric spreading coefficients of 1 0 and 0 9 for body waves sg and 0 83 5 6 for higher mode airy phase surface waves lg are chosen for testing similarly a range of initial values of the power dependence of the attenuation 0 5 to 0 9 are also tested the suite of estimates that result from regressing the amplitude data while employing the family of fixed parameter values leads to the following q model q f 97 f 0 80 for 3 hz f 10 hz these results are important to the estimation of the seismic hazard for the study area this pronounced level of attenuation comparable to that found in california has been reported in previous investigations of the study area using psrv spectra intensity attenuation and fall off of wood anderson seismogram amplitudes

attenuation and scattering of broadband p and s waves across north america differential attenuation deltat italic measurements of teleseismic p italic and s italic waves are made in the frequency range 0 05 5 0 hz across north america using broadband seismic data from the department of energy s regional seismic test network and lawrence livermore national laboratory s basin and range network data from four events have been analyzed by first assuming frequency independent q italic the observed regional variations for deltat italic are consistent with previous studies and show greater attenuation for stations in the basin and range relative to those in shield regions of north america

interrelation between fault zone structures and earthquake processes in order to develop capabilities for predicting earthquake processes on the basis of known fault zone structures and stress conditions we need to find relations between seismogenic structures and processes in the present paper we search for the scale dependence in various earthquake phenomena with the hope to find some structures in the earth that may control the earthquake processes among these phenomena we shall focus on 1 geologic structures which play some role in nucleation and stopping of earthquake fault rupture 2 depth ranges of the brittle seismogenic zone 3 asperities and barriers distributed over a fault plane 4 source controlled f max effect 5 nonfractal behavior of creep events and 6 temporal correlation between coda q 1 and seismicity of earthquakes with magnitude characteristic to a given area our review of various scale dependent phenomena leads us to propose a working hypothesis that the temporal change in coda q 1 may reflect the activity of creep fractures near the brittle ductile transition zone

regional coda q variations in the western alps northern italy abstract to study the microseismicity of the central segment of the western alps a local temporal seismic network of six stations was installed in addition to the regional centralized network operating in the area in 3 months about 220 shocks with magnitude ranging between 1 0 and 3 8 have been analyzed and located the epicenter distribution shows a possible subdivision into seismogenetic bands this subdivision is also recognizable from the spectral characteristics of the analyzed seismic signals a study of the wave attenuation in a restricted area well covered by the local network was carried out through a coda analysis the results show strong spatial qc variations in agreement with the strong lateral heterogeneities that characterize this area in particular the brianconnais domain the crystalline massifs and the inner part of the alpine arc appear to behave as decreasing attenuation bands

coda q estimates in the mount cameroon volcanic region west africa abstract coda q qc has been determined in the mount cameroon volcanic region west africa from the decay of the amplitudes of coda waves on narrow band pass filtered seismograms of local microearthquakes in the frequency range 1 5 to 24 hz qc averages about 121 and 1745 at 1 5 hz and 24 hz respectively and has a frequency dependence of the form qc 65f for each frequency band the coda q values averaged over all the earthquakes show an insensitivity to the compoment of the ground motion considering a model incorporating both scattering and intrinsic attenuation and assuming that the attenuation is entirely due to the scattering loss a frequency independent minimum mean free path of about 38 km was found

effect of anelastic and scattering structures of the lithosphere on the shape of local earthquake coda a simple model of single acoustic scattering is used to study the dependence of the shape of local earthquake coda on the anelastic and scattering structures of the lithosphere the model is applied to the coda of earthquakes located near stone canyon central california and provides an explanation for the features observed in the data which include an interesting temporal variation in the coda shape a surficial layer with aq of 50 and thickness of 10 or 25 km underlain by a zone with aq of 1000 extending to the bottom of the lithosphere together with a scattering scale length a that varies with depthz according to the relationa 0 3 exp z 45 2 are found to constitute the simplest structure of the medium compatible with the coda data and with body and surface wave attenuation data the profile of heterogeneity sizes implies that the scattering strength increases strongly with depth a constraint required by the necessity to boost the energy of the later coda without forcing the intrinsicq to be excessively high in the uppermost mantle this constraint is viewed as an artifact of the single scattering model which overstimates the scattering coefficient due to the neglect of multiple scattering the observed temporal variation of the signal is difficult to explain by a simple change of the intrinsicq at some depth rather it is suggested that the scattering properties at depth changed with time through a variation of the fractional rms velocity fluctuation on the order of one percent

seismic responses to ridge transform subduction chile triple junction the first local seismic network established in the remote region bordering the chile triple junction monitored earthquakes at a rate of three per day with magnitudes m 0 to m 4 far smaller than any recorded previously from that region focal mechanisms were obtained by the adaptation of the relative amplitude method to local earthquakes epicentral locations define a lineament corresponding to the active segment of a subducted transform fault and events corresponding to the predicted position of a subducted ridge show extensional mechanisms with the exclusion of thrusting and trench parallel mechanisms these data suggest that oceanic spreading and seismic activity continue in the subducted ridge transform system extension in the slab influences the overlying crust giving rise to dextral transtension over the past 10 m y the locus of ridge subduction has migrated northward we postulate that the pattern through time of extension and basin development in the overlying crust has mirrored this

spatial and temporal correlation between coda q 1 and seismicity and its physical mechanism from the analysis of local earthquake coda waves recorded by the benioff short period vertical seismograph at riverside california we found a surprisingly large and systematic temporal variation in coda q 1 in the southern california during the 55 year period from 1933 to 1987 comparison of the coda q 1 variation with the b value obtained for earthquakes with m 3 occurred in the area within 180 km from riverside corresponding to the area for which q 1 is estimated by the coda method led to an extraordinary result that coda q 1 correlates positively with b value with the correlation coefficient of 0 79 the significance of correlation cannot be rejected at the confidence level of 0 974 since the data used for measuring q 1 namely the coda part of seismograms and the data used for measuring b namely the seismicity catalog are totally independent the observed correlation supports strongly the physical reality of temporal change in both coda q 1 and b value the correlation between coda q 1 and b value has been reported for several other cases but the correlation was positive in some cases and negative in others our current preferred model for explaining the observed correlation is the following aseismic creep is going on from time to time over various sizes of cracks in the ductile part and in some cases in the brittle part of lithosphere at and near the plate boundary creep activities tend to increase the crack density and coda q 1 observed in the region if the creek occurs over distributed cracks with a certain predominant scale length spatial stress concentration may enhance seismicity for earthquakes with a similar size if this characteristic size is in the lower part of the magnitude range for which the b value is estimated the enhanced seismicity will increase b on the other hand if it is in the upper part of the magnitude range it will decrease b thus we can explain the observed strong correlation between coda q 1 and b value for both positive and negative cases the existence of such a characteristic crack size in a seismic region has been supported by various observations on earthquake scaling

body wave crustal attenuation characteristics in the garhwal himalaya india we estimate frequency dependent attenuation of p and s waves in garhwal himalaya using the extended coda normalization method for the central frequencies 1 5 2 3 4 6 8 10 12 and 16 hz with earthquake hypocentral distance ranging from 27 to 200 km forty well located local earthquake waveforms were used to study the seismic attenuation characteristics of the garhwal himalaya india as recorded by eight stations operated by wadia institute of himalayan geology dehradun india from 2007 to 2012 we find frequency dependent p and s wave quality factors as defined by the relations q p 56 8f 0 91 0 002 and q s 151 8f 0 84 0 002 by fitting a power law frequency dependence model for the estimated values over the whole region both the q p and q s values indicate strong attenuation in the crust of garhwal himalaya the ratio of q s q p 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium playing an important role in seismic wave attenuation in the himalayan crust

inversion of p coda for isotropic scatterers at the yucca flat test site although many studies have addressed the statistical properties of p coda there have been few attempts to analyze coda in a deterministic framework in this analysis 1050 teleseismic p wave seismograms from 32 yucca flat explosions are inverted for the locations of any isotropic point scatterers in the source region that contribute coherent arrivals to the coda a rectangular grid of potential scattering locations is constructed around the source array and the semiblance a measure of waveform ensemble coherence for each point is computed by slant stacking the full set of seismograms at various move out velocities the potential resolution or sensitivity of the method for this data set is tested by constructing a corresponding suite of synthetic seismograms with direct arrivals plus arrivals from various point scatters and calculating the semiblance at each point on the grid the particular source station geometry produces better sensitivity near the array sensitivity is enhanced parallel to the trend of the elongated source array and diminished in the orthogonal direction stacking the data for a velocity of 2 5 km sec yields relatively high semiblance values in the central portion of the test site as well as about 10 km to the ene and moderately high semiblance valuesmore about 10 km to the wnw less

a model for attenuation and scattering in the earth s crust the mechanisms contributing to the attenuation of earthquake ground motion in the distance range of 10 to 200 km are studied with the aid of laboratory data coda waves rg attenuation strong motion attenuation measurements in the northeast united states and canada and theoretical models the frequency range 1 10 hz has been studied the relative contributions to attenuation of anelasticity of crustal rocks constant q fluid flow and scattering are evaluated scattering is found to be strong with an albedo b 0 0 8 0 9 and a scattering extinction length of 17 32 km the albedo is defined as the ratio of the total extinction length to the scattering extinction length the rg results indicate that q increases with depth in the upper kilometer or two of the crust at least in new england coda q appears to be equivalent to intrinsic anelastic q and indicates that this q increases with frequency as q q 0 f n where n is in the range of 0 2 0 9 the intrinsic attenuation in the crust can be explained by a high constant q 500 q 0 2000 and a frequency dependent mechanism most likely due to fluid effects in rocks and cracks a fluid flow attenuation model gives a frequency dependence q q 0 f0 5 similar to those determined from the analysis of coda waves of regional seismograms q is low near the surface and high in the body of the crust

temporal change in attenuation intensity before and after the eastern yamanashi earthquake of 1983 in central japan a crutal earthquake of magnitude 6 0 took place on august 8 1983 in the middle of the kanto tokai microearthquake observation network of the national research center for disaster prevention in central japan by analyzing vertical seismograms of microearthquakes occurring in a small volume in the aftershock region we measured temporal change in attenuation intensity for a period from 22 months before to 9 months after the main shock attenuation change was estimated by using two different kinds of analyses in the first analysis station magnitude calculated from the maximum amplitude at each station was compared with the average of station magnitudes deviations of station magnitude from the average magnitude at five stations in the vicinity of the aftershock area are found to have increased after the main shock compared with that before in the second analysis s coda duration from the origin time was measured and was compared with the average magnitude the increase of s coda duration for the same average magnitude is found after the main shock at two stations close to the main shock epicenter the simplest interpretation of the results is that the attenuation intensity in the upper crust in the close vicinity of the focal region decreased after the main shock for frequencies f from 2 to 20 hz qs 1 1 4 10 2f 1 since other precursors appeared in the preparation stage it is possible to interpret the change in qs 1 as a precursor the attenuation intensity would have been anomalously large before the main shock

q determined from local earthquakes in the south carolina coastal plain abstract coda q or qc is determined from the rate of coda decay in the coastal plain near charleston south carolina the mean of qc calculated from individual estmates is near 190 at 1 hz and increases to over 1650 at 10 hz a possible temporal change in qc is identified high values being associated with increased seismic activity during late 1977 temporal changes have been observed elsewhere and laboratory measurements of q under different stress states correlate high q with high stress a spatial variation in qc is identified increasing from west qc at 10 hz equal to 850 to east qc at 10 hz greater than 2100 across the coastal plain the demarcation of high to highest zones of qc is coincident with the western boundary of the innermost isoseismal of the charleston 1886 earthquake it is hypothesized that the 1886 earthquake was mislocated originally because of this spatial variation in energy attenuation that was unrecognized at that time

attenuation of coda waves in northern greece the single scattering model has been applied for the estimation of codaq values for local earthquakes that occurred in northern greece during the period 1983 1989 and recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki codaq estimations were made for four frequency bands centered at 1 5 hz 3 0 hz 6 0 hz and 12 0 hz and for the lapse time windows 10 20 sec 15 30 sec 20 45 sec 30 60 sec and 50 100 sec the codaq values obtained show a clear frequency dependence of the formq c q 0 f n whileq 0 andn depend on the lapse time window q 0 was found equal to 33 andn equal to 1 01 for the time window of 10 to 20 sec while for the other windowsq 0 increased from 60 to 129 withn being stable close to 0 75 this lapse time dependence is interpreted as due to a depth dependent attenuation the high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity in agreement with studies in other seismic regions

high frequency seismic coda and scattering in the northwest pacific data from a 1500 km linear ocean bottom hydrophone array deployment near wake island by the hawaii institute of geophysics are used to examine seismic coda and scattering in the northwest pacific two earthquakes in the kuril islands that occurred along the trend of the hydrophone array are analyzed in the distance range 2700 to 3700 km the coda of the oceanic s waves 1 5 to 20 hz display 1 a constant decay rate independent of distance and 2 an increasing coda energy falloff rate with increasing frequency both of these observations suggest that substantial scattering is not occurring in the propagation along the array the properties of the oceanic s coda are relatively stable when the propagation paths are nearly the same the observations are consistent with coda generation dominated by back scattering in the source region rather than from forward scattering along the propagation path

time space variation of seismic s wave coda attenuation qc 1 and magnitude distribution b values for the petatlan earthquake average s wave coda q qc at 6 hz and to about 10 sec after the s wave arrival shows 1 temporal variation positively correlated with the magnitude distribution parameter b for foreshocks and aftershocks of the 1979 petatlan mexico earthquake 2 spatial variation through the aftershock area positively correlated with b high qc b values at the two activity centers intermediate values in between and landward and low values toward the middle america trench which remain low for two weeks after the main shock and 3 five foreshock average qc 135 1 6 and eleven aftershock average qc 175 1 3 for the eastern asperity the b values and possibly qc values seem to correlate with the level of aftershock activity

regional wave propagation in southern california and nevada observations from a three component seismic array we present results from a study conducted to characterize regional wave propagation in southern california and nevada the data are from events whose paths sample the southern coast ranges the southern sierra nevada mountains and the southern basin and range these regional earthquake data were recorded by a small aperture three component seismic array located at the pinon flat observatory southern california the data are analyzed using a statistical array processing algorithm that provides estimates of the propagation direction frequency wavenumber and particle motion polarization characteristics of the coherent arrivals observed at the array perhaps the most striking feature shared by these data is the extent to which the p s and lg wave trains are composed of coherent forward scattered multipathed energy the nature of the p s and lg wave trains suggests that spatially anisotropic scattering plays an important role in regional wave propagation in southern california and nevada and that scattering sources are located not on elliptical shells whose foci are the source and the receiver but instead in a limited volume subparallel to the path of the direct arrivals the high amplitude coherent nature of numerous of the pg and lg coda waves suggests that strong scattering in the source zone plays an important role in shaping the pg and lg wave trains while the p s and lg wave trains for these regional events share some general characteristics they also exhibit fairly significant differences these differences illustrate the important role regional and source zone structure play in shaping the wave field and the need to account for both complex scattering and three dimensional propagation effects in regional waveform modeling the coda for these regional data do not begin to exhibit a character consistent with the random scattering model for coda generation until the arrival of the surface waves the fact that much of the surface wave coda cannot be effectively modeled as plane waves suggests that it is not the product of scattering from distant heterogeneities

lateral variation and frequency dependence of coda q in the southern part of iberia summary a method based on the coda attenuation law q qo f fo v leads to the determination of the lateral variation of coda q in the southern part of the iberian peninsula using seismograms belonging to the seismological network of the cartuja observatory located in granada the lateral variation of qo q value corresponding to a reference frequency fo of 1 hz and its frequency dependence for the 1 to 5hz frequency range are in general in agreement with coda q values for frequencies less than about 1 hz previously determined in the region under study to determine the coda q values analytical functions have been used to fit the magnification curves of the vertical component short period seismographs belonging to the cartuja network the problem is solved by using least squares techniques and non linear inversion the determined coda q values and its frequency dependence correlate well with several known geophysical parameters in the southern part of the iberian peninsula

seismic q for the lithosphere of the montenegro region yugoslavia frequency depth and time windowing effects abstract the availability of accelerometric data for the montenegro earthquake of 15th april 1979 makes it possible to investigate seismic q of the lithosphere in that region in particular its dependence on frequency on the depth reached by seismic waves and on the length of time windows in which signals are processed two different spectral methods s phase energy ratio and coda envelope decay are applied respectively to direct and scattered shear waves similar results are obtained using different portions of the recordings i e coda waves for the envelope decay fit and the s wave train with a significant duration of 10 s for the energy ratios the same apparent q q 40 f where f is the frequency expressed in hz that is found for other neighbouring central mediterranean regions e g ancona on the central italian adriatic coast valnerina in the central apennines irpinia in the southern apennines is also found for the southern yugoslavian coast in the band 1 25 hz up to a maximum range of 120 km from the focus this strong frequency dependence is probably connected with the type of small scale heterogeneity and the same geological age and level of tectonic activity peculiar to all these seismotectonic areas in order to compare the apparent q of the whole s wave train 10 s long with the intrinsic apparent q of the single direct s wave usually 1 s or less the maximum entropy method is applied in the energy spectrum computation for shorter wave trains the use of shorter time windows does not reveal any significant variation in the tendency of q to increase linearly with frequency as the length of the time window containing the sample of the s waves decreases this seems to indicate that scattering dependent q is generally inseparable from intrinsic q in the lithosphere when estimates based on variations with distance of the seismic signal spectrum are used while the type of linear growth with frequency does not seem to undergo any variations it remains of the q qf type the data show there are a considerable decrease in the coefficient of proportionality q with decreasing duration of the window of s waves analysed probably as a result of variations in seismic attenuation with depth

attenuation characteristics of coda waves in mainland gujarat india abstract the attenuation characteristics based on coda waves of mainland gujarat india have been investigated in the present study the broadband waveforms of 53 local earthquakes mw 1 1 3 3 having focal depths in the 6 0 33 6 km range recorded at five stations of mainland gujarat region has been used for the analysis the frequency dependent relationships q q0fn for coda q qc and dependency of coda q on lapse time windows have been determined for the said region the average lapse time dependent coda q relations estimated for the region are qc 87 13 f 1 01 0 06 lapse time 30 s qc 112 20 f 0 94 0 08 lapse time 40 s and qc 120 22 f 0 76 0 07 lapse time 50 s the increase in qc values with lapse time shows the depth dependence of qc as longer lapse time windows will sample larger area the observed quality factor is strongly dependent on frequency and lapse time which indicates that the upper lithosphere is more heterogeneous and seismotectonically active while the lower lithosphere is homogeneous and relatively less active a comparison of the coda q estimated for mainland gujarat region with those of nearby kachchh and saurashtra regions shows that mainland gujarat region is more heterogeneous the rate of decay of attenuation q 1 with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ the obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the mainland gujarat region where no such relations were available earlier these relations are also important for the simulation of earthquake strong ground motions in the region

time frequency analysis of seismic excitation and estimates of attenuation parameters for the friuli italy local earthquakes abstract stochastic modelling is applied to the analysis of local earthquake recordings which are usually extremely rich in random incident wave trains that are chaotically superimposed because of scattering effects in the earth s crust the presence in the seismic signal of effects connected with the scale of inhomogeneity in the lithosphere cannot be deterministically described in detail the application of a stochastic second order autoregressive model to accelerometric records for the higher magnitude m l 6 friuli earthquakes and to short period seismometric records for the aftershocks of the strong earthquake of 6 may 1976 has allowed inferences to be drawn about the spectral properties of seismic signals and the propagation mechanisms of seismic waves these inferences are based on an extremely small number of parameters of a mathematical model suitable for simultaneously describing the random sequence of scattered wave trains in the time and frequency domains useful physical information has been obtained about the dynamic characteristic correlation times and the predominant frequency of the seismic signals moreover the strength 2 e t of the innovation of the stochastic process fitting the real digital data set has been estimated from the envelopes of 2 e t the quantity heuristically used in the stochastic approach to describe seismic excitation the mean free path between successive scatterings l or the equivalent diffusivity coefficient d and turbidity g and their dependence on seismic wave frequency have been investigated for friuli using seismometric data at an epicentral distance of 20 km and earthquakes with a magnitude just under 2 mean free path estimates obtained by means of autoregressive parameters vary from 5 km for the strong interaction model to 30 km for the single scattering model furthermore by means of accelerometric records for the strongest earthquakes in friuli during may and september 1976 the dependence for the maximum of the seismic excitation on the epicentral distance r was estimated as 2 e max r with 1 94 0 13 which is in good agreement with results obtained for the same region using standard methods by means of acceleration peaks versus r lastly stochastic modelling provides a method of estimating change versus time for the predominant frequency and characteristic correlation time of narrow band digital recordings these two parameters were computed by means of autoregressive parameters in different physical situations and were found to be functions of the earthquake source the instrumentation frequency response and the earth s filtering effects

azimuthal variation of coda q in northern taiwan seismograms of local earthquakes recorded on the short period sensor of the tato station one of the sro stations near taipei northern taiwan are used to determine values of coda q qc results show the azimuthal dependence of the values of qc a correlation between the values of qc and the tectonics of the region is determined the value of qc is small in the oceanic lithosphere intermediate in the plate boundaries and large in the continental lithosphere

stress associated intrinsic and scattering attenuation from laboratory ultrasonic measurements on shales seismic attenuation is sensitive to stress induced subtle changes in the physical state of rocks in this study the stress and frequency associated attenuation is quantified through ultrasonic measurements on three differently oriented cylindrical shale samples under various axial stresses as an improvement to the single scattering model the elastic monte carlo method is employed to investigate multiple scattering attenuations by incorporating the boundary reflections and wave conversions our results show that as the axial stress increases the intrinsic attenuation decreases in all directions while the scattering attenuation decreases slightly in the direction perpendicular to the bedding but increases largely and nonlinearly in other directions these discrepancies result from different attenuation mechanisms both the intrinsic and scattering attenuation are found to be largest in the direction 45 to the bedding but least in the perpendicular direction the s wave attenuation is larger and more sensitive to stress changes than p wave attenuation due to its shorter wavelength as expected from sandstone examples the scattering attenuation in shales is significantly larger and more sensitive to stress changes than the intrinsic attenuation the frequency dependence of scattering attenuation suggests that the peak frequency with the maximum scattering attenuation is independent of axial stresses but varies in different directions of an individual rock with different heterogeneity and anisotropy scales the peak frequency of s coda is smaller and its peak scattering attenuation is larger than p coda in conclusion the stress and frequency dependence of ultrasonic attenuations in shales differ largely in various directions indicating significant anisotropy and heterogeneity

experimental study of the spectral content for shallow earthquakes twenty four seismic stations were installed for 1 month in october and november 1978 to study the seismicity and fault plane solutions of the arette region pyrenees six of these stations were three component magnetic tape recording instruments we recorded about 115 events which could be located well having magnitudes varying from 0 6 to 2 9 nineteen of these earthquakes were recorded on more than two tape recording stations spectra of a given event recorded on the three components of one station are similar but there are differences in corner frequencies or high frequency decays between stations and earthquakes we first studied q factor by assuming it is independent of frequency and that the source spectra are proportional to f 2 at high frequencies we find a strong correlation of q with hypocentral distance which can be attributed to an increase of qp from 120 to 170 and qs from 180 to 350 in the top 10 km of the crust the mean value of qs 1 6 qp the coverage of stations and quality of datas allow us to correct spectra for site amplification geometrical spreading free surface reflection and radiation pattern the mean ration of p and s wave corner frequencies for a given event is 1 43 close to that predicted by madariaga s model madariaga s model was used to calculate source parameters the highest stress drop calculated 170 80 bars is significantly higher than the mean stress drop 35 bars of all the events and was obtained for the earthquake which was located where an earthquake of magnitude 5 1 occurred 15 months later 29 february 1980 in a place where the seismicity had been below average

study of the montenegro earthquake sequence march july 1979 abstract data from more than 80 european seismic stations concerning foreshocks the main shock and aftershocks of the earthquake which occurred near the coast of montenegro on 15 april 1979 have been collected and analyzed the data have allowed the focal mechanism of the two strongest shocks to be estimated the hypocentral coordinates of more than 180 aftershocks and some foreshocks have been also computed giving the time space distribution of the sequence the shocks are mostly contained in an area about 100 km long and 30 km wide almost corresponding to the adriatic coast line of the yugoslavia albania border region the hypocentral depths although determined approximately appear to be in the order of 15 to 20 km the results have been compared with previous knowledge of the tectonics of the zone

properties of scattered elastic waves in the lithosphere of kamchatka parameters and temporal variations abstract records of near earthquakes from the shipunsky station were used to estimate s wave absorption for seven frequency bands ranging from 0 4 to 24 hz three techniques were employed and three rows of consistent estimates were obtained two of the three techniques give estimates that are independent of q anisotropic scattering was studied by observing the broadening of the s wavelet the estimates obtained show that anisotropic scatter may be significant the time variation of the coda envelope shape was studied using the records of 1 s regional seismographs three epicentral regions were chosen in the kurile kamchatka zone where m 8 earthquakes have occurred time series of the parameter which is the anomaly of the logarithmic steepness of coda envelope were constructed for vertical and horizontal channels of several stations pronounced forerunner type variations of were revealed we show that the probable cause of these variations is a qs decrease in the vicinity of impending m 8 earthquake this decrease is about 20 with a lead time of about a year the forerunner anomaly is not of the bay type and recovers 1 2 years after a large earthquake

seismic source parameters for microearthquakes of the granada basin southern spain abstract ninety five microearthquakes of the granada basin southern spain with duration magnitudes ranging from 1 3 to 3 5 moment magnitude from 0 9 to 2 5 have been spectrally analyzed with digital recordings from ten stations of the andalusian seismic network the coda q quality factor qc assumed to be frequency dependent was used instead of q for the path correction and the q adopted was equal to 9 4 qc the k parameter for site attenuation correction had values in the range of 0 02 0 05 fourier displacement spectra were calculated for p and s waves and analyzed with respect to the source model of brune 1970 1971 spectral parameters were automatically determined by the method of snoke 1987 the seismic moment ranged from 1017 to 1020 dyne cm with average m0 p to m0 s ratio of 1 02 and the source radii spanned from 0 14 to 0 40 km with average r p to r s ratio of 1 3 the seismic energy values ranged from 1 103 to 9 107 j with p to s energy ratio from 1 to 10 for about 85 of the events whereas the static stress drop varied from 0 02 to 2 6 bar the scaling relation between the seismic moment and the stress drop indicates a decrease in stress drop with decreasing seismic moment apparent stress is linearly correlated with stress drop and have on average similar values and this points out to a partial stress drop

depth dependent seismic attenuation in the granada zone southern spain abstract coda q estimates for the granada basin southern spain are obtained by analyzing earthquakes occurring within or close to the borders of this area the data set is composed of 54 earthquakes with local magnitudes ranging between 2 2 and 4 0 and with epicentral distances to the nearest station smaller than 10 km a single scattering process is assumed coda q values obtained show a clear dependence on frequency according to the relationship q q o f n where n ranges from 0 81 to 0 89 after removing the main site effects and discussing the possible multiple scattering influence the lapse time dependence is interpreted as due to attenuation variations with depth this result agrees with the variation of coda q obtained by using different sets of events with increasing hypocentral depth ranges

numerical simulations of wave propagation in heterogeneous wave guides with implications for regional wave propagation and the nature of lithospheric heterogeneity i present results from elastic finite difference simulations of regional wave propagation conducted in an effort to characterize in a statistical sense the nature of lithospheric heterogeneities required to generate scattered wave fields with characteristics consistent with those observed in regional array data in particular regional p s and lg wave trains that are comprised not of the occasional coherent deterministic phase emersed in randomly scattered coda but of a continuous succession of coherent forward scattered arrivals my modeling suggests that lithospheric heterogeneities should be parameterized using spatially anisotropic correlation functions models containing spatially isotropic heterogeneities inhibit the extent to which energy is forward scattered and trapped in the crustal wave guide and consequently produce regional wave fields whose characteristics are inconsistent with array observations models containing spatially anisotropic heterogeneities which preferentially forward scatter energy that is subsequently trapped in the crustal wave guide produce wave fields whose characteristics are consistent with regional array observations and provide intuitively appealing representations of subsurface structure

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

residence time of diffuse waves in the crust as a physical interpretation of coda q application to seismograms recorded in mexico summary we consider a simple model for elastic wave propagation in the earth s litho sphere consisting of a heterogeneous and scattering crust overlying a homogeneous mantle that is we neglect backscattering from the upper mantle this rough condition is not strictly valid everywhere but this model allows us to investigate the effects of variations of diffracting properties between crust and mantle on the coda decay the free parameters describing the wave propagation are the mean free path of the waves and the intrinsic absorption in the crust in the framework of the radiative transfer theory we treat accurately jumps in s wave speed and the mean free path at the moho without intrinsic absorption this configuration yields a synthetic coda decay 1 texp 2 ft qc a form similar to that proposed by aki chouet 1975 to parametrize the observations the exponential decay in our purely elastic model is due to the partial leakage of diffuse energy into the mantle in order to test the applicability of our model we have determined the coda q parameter qc in the 1 15 hz frequency band from data recorded at four stations in mexico in the low frequency regime around 1 hz we suggest that the energy leakage significantly affects coda q whilst at higher frequencies around 10 hz the anelastic attenuation dominates a weak intrinsic absorption expressed by a frequency independent parameter qi of about 1000 accounts satisfactorily for the observed qc values in the whole frequency range our very simple model has only two free parameters and offers an attractive alternative physical interpretation of coda q in mexico this model is sufficient to interpret the coda observations according to our model in regions where the mean free path is much larger than the crustal thickness weakly heterogeneous crust the leakage effect should be small and the observed qc will mainly be due to the intrinsic absorption on the other hand when the mean free path is of the order of the crustal thickness strongly heterogeneous crust we predict a strong sensitivity of the decay rate of the coda to the crustal thickness this dependence may be important for the interpretation of the regional variations of coda q we propose introducing a new parameter d the residence time of diffuse energy in the crust which is physically more meaningful than a quality factor to quantify the leakage effect

temporal change in coda associated with the round valley california earthquake of november 23 1984 seven thousand seismograms of small earthquakes in the mammoth lakes bishop area were used to measure values of q from the decay of the earthquake coda these measurements were compared between events that occurred before and after the round valley earthquake m 5 7 we found that in regions near the main shock epicenter measurements of coda q 1 for earthquakes that occurred after the main shock were higher than for those earthquakes that occurred prior to the main shock the opposite behavior was found for regions farther away from the main shock namely lower coda q 1 after the main shock than before measurements of coda q 1 in the long valley caldera outside of the immediate source region of the earthquake were higher than in surrounding areas before the main shock but the difference disappeared after the occurrence of the main shock this indicates that the temporal variation in coda q 1 is comparable to its spatial variation the doughnut model seismicity quiescence surrounded by a zone of activity which was invoked for explaining the precursory seismicity pattern appears to be similar with the observed coda q 1 variation associated with the round valley earthquake the observed spatial variations in coda q 1 also help to reconcile conflicting results published in previous studies of the coda q 1 precursor

modeling the seismic p coda as the response of a discrete scatterer medium abstract the seismic coda can be modeled as a composite of wavelets scattered from spherical heterogeneities embedded in an elastic medium the exact scattering response of a spherical heterogeneity is calculated for elastic waves using mie theory to generate synthetic codas a p source wavelet is defined for propagation along the ray paths from the hypocenter to the receiver via each scatterer in the model only singly scattered waves are computed along the path the wavelet is adjusted for geometric spreading intrinsic attenuation scattering response the free surface effect and instrument response the source scatterer receiver path length is used to determine the appropriate time shift for the scattered wavelet scattered wavelets are obtained individually by calculating the response and lapse time corresponding to each scatterer in the medium this is done independently for scattered p p and p s waves the individual wavelets are then time shifted and superimposed to obtain the complete coda synthetic codas were able to match the emergent p wave codas from surface explosions in alabama and the impulsive p wave arrivals from earthquakes in southeastern tennessee

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

the scattering of seismic waves through a crust and upper mantle with random lateral and vertical inhomogeneities abstract the propagation of seismic waves through earth models with slightly random lateral and vertical inhomogeneities superimposed on one composed of layers with vertical velocity gradients was investigated the maximum deviation of velocity from a mean value at a given depth and a correlation distance derived from a two dimensional smoothing filter were two parameters used to vary the amplitude and size of the velocity anomalies the resulting models show short discontinuous reflectors scattered about at various depths throughout the model and are thus in agreement with many deep seismic reflection experiments on the other hand numerical experiments using ray tracing techniques showed that the effect of the lateral and vertical velocity anomalies is to scatter the energy and break up the continuous travel time lines from vertical gradient models into travel time segments with different slopes similar to those observed in many long range seismic refraction experiments and to those resulting from layering effects in the media many of the numerical experiments which modelled the random crust produced a pg segment and a p segment with an apparent conrad discontinuity at a depth of 10 20 km this apparent depth being related to the correlation distance when a seismic wave propagates through a heterogeneous earth the amount of its energy which is converted into scattered energy will be a function of the inhomogeneous characteristics of the medium through which it has passed if a ray passes through a homogeneous earth the energy arriving at an array station should be relatively coherent whereas if the ray encounters lateral and vertical inhomogeneities its energy will be incoherent and much more complex a series of coherency measurements done on array recordings of earthquakes at various distances showed that large lateral and vertical variations in complexity exist for different ray paths through the earth with the region below the 650 km discontinuity in the mantle tending to be much simpler than the region just below the lithosphere

coda q in the eastern caribbean west indies summary coda q q has been estimated from seismograms of local earthquakes recorded on short period seismographs on some of the eastern caribbean islands of the lesser antilles arc west indies using the s s single scattering model the region was subdivided into four distinct subregions in order to investigate lateral variations in q the qc values exhibit a strong frequency dependence in the frequency band 1 5 to 16 hz with calculated coda q at 1 hz qo ranging from a minimum of 97 in the dominica area to a maximum of 145 in the leewards the degree of frequency dependence is also largest in the dominica area n 1 09 and smallest in the leewards n 0 82 although there appears to be some lateral and depth variation of both q and n in the region this variation does not seem to be very significant

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

coda q estimates in the koyna region india the coda q q c have been estimated for the koyna region of india the coda waves of 76 seismograms from thirteen local earthquakes recorded digitally in the region during july august 1996 have been analyzed for this purpose at nine central frequencies viz 1 5 2 0 3 0 4 0 6 0 8 0 12 0 16 0 and 24 0 hz using a single backscattering model all events with magnitude less than 3 fall in the epicentral distances less than 60 km and have focal depths which range from 0 86 to 9 43 km for the 30 sec coda window length the estimated q c values vary from 81 to 261 at 1 5 hz and 2088 to 3234 at 24 hz whereas the mean values of q c with the standard error vary from 148 13 5 at 1 5 hz to 2703 38 8 at 24 hz both the estimated q c values and their mean values exhibit the clear dependence on frequency in the region and a frequency dependence average attenuation relationship q c 96f 1 09 has been obtained for the region covering an approximate area of 11 500 km2 with the surfacial extent of about 120 km and depth of 60 km

scattering of p waves beneath scarlet in southern california previous studies have indicated that the crust and upper mantle beneath the caltech usgs large seismic array scarlet is extremely heterogeneous in this study chernov theory has been applied to characterize the crust and upper mantle as a random medium the data consist of travel time residuals from plane waves fit to teleseismic arrival times amplitude data were not available consistent results were obtained for events arriving from the nw sw and se and indicate a correlation distance for the inhomogeneities of 25 km and a maximum velocity perturbation of 3 26 the random medium extends to a minimum depth of 119 km although these values are similar to those obtained for other arrays they indicate that it may be improper to apply chernov theory to teleseismic p waves with dominant frequencies near 1 hz

frequency dependent attenuation characteristics of coda waves in the northwestern himalayan india region abstract digital seismogram data of 82 earthquakes from the northwestern himalayan india region recorded at different stations during 2004 2006 were analyzed to study the seismic coda wave attenuation characteristics in this region we used 132 seismic observations from local earthquakes with a hypocentral distance q c using the single isotropic scattering model these earthquakes were recorded at 20 temporary seismic stations installed in the northwestern himalayas india by the wadia institute of himalayan geology dehradun the q c values were estimated at 10 central frequencies 1 5 3 5 7 9 12 16 20 24 and 28 hz using starting lapse times of 10 20 30 40 50 and 60 s and coda window lengths of 10 20 30 40 and 50 s the q c fits the frequency dependent power law q c q 0 f n for a 10 s lapse time with a 10 s coda window length q c 47 42 f 1 012 and for a 50 s lapse time with a 50 s coda window length q c 204 1 f 0 934 q 0 q c at 1 hz varied from 47 for a 10 s lapse time and a 10 s window length to 204 for a 50 s lapse time and a 50 s window length an average frequency dependent power law fit for the study region may be given as q c 116 716 f 0 9943 the exponent of the frequency dependence law n ranged from 1 08 to 0 9 which correlates well with values obtained in other seismically and tectonically active and heterogeneous regions of the world in our study region q c increases both with respect to lapse time and frequency i e the attenuation decreases as the quality factor is inversely proportional to attenuation the low q c values or high attenuation at lower frequencies and high q c values or low attenuation at higher frequencies suggest that the heterogeneity decreases with increasing depth in our study region

a finite difference simulation of wave propagation in two dimensional random media a finite difference algorithm is used to generate synthetic seismograms for waves propagating through two dimensional random media the media have a significant component of their material properties varying randomly over length scales smaller than the seismic wavelength and are meant to approximate the heterogeneity of the crust and upper mantle the finite difference technique retains all multiply scattered and diffracted waves and also accounts for transmission losses the synthetic seismograms clearly exhibit coda and apparent attenuation caused by scattering for a medium with a white wavenumber spectrum of velocity fluctuations the coda is higher frequency than the initial pulse the apparent attenuation is greatest when the scatterer size is comparable to the seismic wavelength the spectra of the coda generally increase in frequency as the scatterers decrease in size examples demonstrate how scattering can produce spectra with broad peaks and sharp fall offs that can make the determination of the source spectra and corner frequencies of small earthquakes extremely difficult

source parameters of two ml 5 earthquakes near anza california and a comparison with an imperial valley aftershock strong motion records were used to determine the seismic moments source dimensions and stress drops for two earthquakes near the proposed anza seismic gap thatcher et al 1975 along the san jacinto fault the 25 february 1980 m l 5 5 event and the shock of 15 june 1982 m l 4 8 seismic moments determined for the two events were 2 5 10 23 and 1 1 10 23 dyne cm respectively the source radii were estimated from the displacement pulse widths using the source model of madariaga 1976 static stress drops for the 1980 and 1982 earthquakes were calculated as 110 and 100 bars respectively stress drops determined from the rms accelerations using the method of hanks and mcguire 1981 were 220 bars for the 1980 earthquake and 180 bars for the 1982 event the long period seismic moments for these events derived from regional recordings of 30 to 40 sec love waves were a factor of two to three greater than the moments estimated from the strong motion records as a comparison to the anza events source parameters were also determined from strong motion records for an immediate aftershock m l 5 0 of the 1979 imperial valley earthquake the seismic moment of this aftershock was calculated as 4 2 10 23 dyne cm and its static stress drop was 130 bars static stress drops calculated from the displacement pulse shapes for the three events studied in this paper as well as for an aftershock of the oroville earthquake reported by fletcher et al 1980 exhibit a relatively narrow range between about 100 and 180 bars this result indicates that the stress drops of the two main shocks near anza were not unusually high relative to those of certain aftershocks in other tectonic settings in california

determination of near surface attenuation with κ parameter to obtain the seismic moment stress drop source dimension and seismic energy for microearthquakes in the granada basin southern spain abstract a set of 43 microearthquakes of the granada basin with magnitude duration m d from 1 4 to 3 5 have been spectrally analysed the digital data used in this study was recorded by two short period digital seismic network five permanent stations using andalusian seismic network red sismica de andalucia rsa and three stations of a portable digital seismic network red sismica portatil rsp the displacement spectra for p and s waves were analysed with brune s j geophys res 75 1970 4997 j geophys res 76 1971 5002 source model and the spectra parameters were determined by snoke s model to correct spectra from path attenuation coda q was used for the spectra correction from near surface attenuation parameter was calculated obtaining it from acceleration spectra the values of parameter range from 0 01 to 0 04 s for p waves and from 0 006 to 0 04 s to s waves once the spectra of these attenuation effects was corrected we obtained the seismic moments that range from 5 45 10 17 dyne cm to 1 53 10 20 dyne cm the source radii are between 0 13 and 0 39 km the seismic energy ranges from 7 17 10 3 j to 1 13 10 8 j the stress drop values were below 4 bars the scaling relations between seismic moment and stress drop indicated decreasing stress drop with decreasing seismic moment