the valencia trough coda q abstract the coda q method has been applied to a set of earthquakes located in the mediterranean region between the iberian peninsula and the balearic islands the valencia trough and recorded at the short period seismographic station of ebro ebr located in roquetes tarragona to obtain the anelastic quality factor q of coda waves the applied method uses a set of master curves taking into account the frequency dependence of the coda q values to determine the master curves used to obtain the coda q values non linear inversion techniques have been applied to the short period instruments the coda q values and the frequency dependence obtained for the region seem to indicate that the southern part of the valencia trough tends to attenuate the seismic energy in the same manner as the betic system and the northern part seems to present higher q values than the southern one this fact may indicate different q structures in both regions a good correlation is observed among the obtained coda q values their frequency dependence and known coda q values and l g wave attenuation in the coastal region of the mediterranean sea

an inversion of lg wave attenuation and site response in the north china region a joint inversion method for determining the lg wave attenuation along the propagation path and site response based on seismic spectral ratios was developed and applied to invert the lg wave attenuation and site response in the north china region is related to the quality factor q by f uq where u is the velocity waveform data of 200 earthquakes during 2006 2008 with m l 1 7 5 5 in the area of 38 41 n 114 120 e were selected for this study more than 1500 three component records chosen from 81 stations on the basis of the signal to noise ratio were used in the inversion the waveform data were processed in the frequency range of 1 6 hz with an interval of 0 2 hz the results indicate that there is remarkable heterogeneity in lg wave attenuation in the study area we divided the area into four regions according to the lg wave propagation paths lower values are found in the tectonic mountain region higher values occur in the tectonic basin region and moderate values are found for the propagation paths passing through both the mountain and basin regions on the vertical component was found to be frequency dependent and in the form graphic 1 and graphic 2 for propagation paths in the mountain and basin regions respectively and graphic 3 and graphic 4 for paths passing through both mountain and basin regions with seismic ray direction from the mountain to the basin and vise versa respectively the absolute quality factor q ranges from 125 to 306 the response of rock sites is smooth and flat and less than five at low frequency while that for soil sites is higher than for rock sites for soil sites the amplification of low frequency waves is higher than that for high frequency waves for both site response and attenuation no significant differences were observed between different components online material source parameters of the studied earthquakes 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif

2d kernel based imaging of coda q space variations in the gargano promontory southern italy abstract crustal seismic attenuation in the gargano promontory southern italy was inferred by analyzing coda waves of about one hundred small magnitude earthquakes recorded by the otrions local seismic network coda attenuation qc was computed using the sato 1977 model i e the assumption of single back scattering at different lapse times and at different frequencies average qc is comparable with the same quantity measured in the adjacent area of the umbria marche region central italy a recent kernel based imaging technique for qc was then applied and the results evidence a well confined zone located south west of the investigated area showing a sharp qc anomaly while qc cannot be directly related to the physical properties of the propagation medium its spatially dependent modeling allows an interpretation in the light of other geophysical and geological information our results were then interpreted following the two extreme hypotheses according to which qc could be representative of the effect of only intrinsic attenuation or of only scattering from the heterogeneities both the hypothesis correlate with the observation of anomalies in several geophysical parameters such as heat flow magnetic field gravity density seismic velocity in the southwestern gargano moreover the qc images support the results obtained in a recent study that shows clear variations in the rheological properties of the gargano the results obtained at local scale confirm and detail previous regional scale studies on attenuation and highlight for the first time the presence of a positive qc anomaly in the south western part of the gargano promontory

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

intrinsic and scattering attenuation in western india from aftershocks of the 26 january 2001 kachchh earthquake abstract 176 vertical component short period observations from aftershocks of the mw 7 7 26 january 2001 kachchh earthquake are used to estimate seismic wave attenuation in western india using uniform and two layer models the magnitudes mw of the earthquakes are less than 4 5 with depths less than 46 km and hypocentral distances up to 110 km the studied frequencies are between 1 and 30 hz two seismic wave attenuation factors intrinsic absorption qi 1 and scattering attenuation qs 1 are estimated using the multiple lapse time window method which compares time integrated seismic wave energies with synthetic coda wave envelopes for a multiple isotropic scattering model we first assume spatial uniformity of qi 1 qs 1 and s wave velocity a second approach extends the multiple scattering hypothesis to media consisting of several layers characterized by vertically varying scattering coefficient g intrinsic absorption strength h density of the media and shear wave velocity structure the predicted coda envelopes are computed using monte carlo simulation results show that under the assumption of spatial uniformity scattering attenuation is greater than intrinsic absorption only for the lowest frequency band 1 to 2 hz whereas intrinsic absorption is predominant in the attenuation process at higher frequencies 2 to 30 hz the values of q obtained range from qt 118 qi 246 and qs 227 at 1 5 hz to qt 4000 qi 4600 and qs 33 300 at 28 hz center frequencies being qt 1 a measure of total attenuation results also show that qi 1 qs 1 and qt 1 decrease proportional to f two rates of decay are clearly observed for the low 1 to 6 hz and high 6 to 30 hz frequency ranges values of are estimated as 2 07 0 05 and 0 44 0 09 for total attenuation 1 52 0 21 and 0 48 0 09 for intrinsic absorption and 3 63 0 07 and 0 06 0 08 for scattering attenuation for the low and high frequency ranges respectively despite the lower resolution in deriving the attenuation parameters for a two layered crust we find that scattering attenuation is comparable to or smaller than the intrinsic absorption in the crust whereas intrinsic absorption dominates in the mantle also for a crustal layer of thickness 42 km intrinsic absorption and scattering estimates in the crust are lower and greater than those of the mantle respectively

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

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

attenuation of coda waves in western mexico using local seismicity coda waves are an important instrument to study the elastic properties of the lithosphere the attenuation of coda waves in western mexico is analyzed using seismograms recorded during the mapping of the rivera subduction zone experiment the coda wave attenuation is measured by means of q within the single backscattering model and the single isotropic scattering model schemes the frequency dependence of q is analyzed using the power fit formulation q f q f the resulting q q and are then used to study the seismic attenuation properties in western mexico we compare our results with the crustal structure by means of the surface geology seismic activity crustal thickness and p wave velocity patterns in the study area there is a poor correlation of the attenuation parameters with such crustal features however an analysis of the variations of the p wave velocity shows that the seismic attenuation parameters correlate to some extent with seismic velocity variations previously noted in the study area where low attenuation and weak frequency dependence correlate with low velocity variation

a frequency dependent relation of coda q c for koyna warna region india attenuation properties of the lithosphere around the koyna warna seismic zone is studied by estimating the coda q c from 30 local earthquakes of magnitude varying from 1 5 to 3 8 an average lapse time of 65 sec used in the single scattering model sampled a circular area with an average radius of 114 km the estimated q c values show a frequency dependent relation q c 169 f0 77 and range from 169 at i hz to 1565 at 18 hz a comparison of worldwide q studies reveals that for a large frequency range the q for active regions is low as compared to that for stable regions however south carolina and norway are exceptions in that their q is low in the low frequency range while new england and north iberia are exceptions as they have a q value similar to that for active regions like spain turkey italy and garhwal himalaya stih in the higher frequency range in contrast to this the q for the koyna warna area which belongs to a stable region is low in the entire frequency range as compared to the stable regions and similar to the active stih regions

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

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

seismic wave attenuation associated with crustal faults in the new madrid seismic zone the attenuation of upper crustal seismic waves that are refracted with a velocity of about 6 kilometers per second varies greatly among profiles in the area of the new madrid seismic zone in the central mississippi valley the waves that have the strongest attenuation pass through the seismic trend along the axis of the reelfoot rift in the area of the blytheville arch defocusing of the waves in a low velocity zone and or seismic scattering and absorption could cause the attenuation these effects are most likely associated with the highly deformed rocks along the arch consequently strong seismic wave attenuation may be a useful criterion for identifying seismogenic fault zones

s wave coda q from 3 to 20 hz and p wave q for foreshocks and aftershocks of the petatlan earthquake in order to understand better the variations of mechanical properties close to the source and the failure process in the upper portion of the crust in a geologically very young subduction zone the seismic s wave coda qc from 3 to 20 hz and p wave half pulse width qp from 6 to 12 hz were determined for selected foreshocks and aftershocks of the 1979 petatlan mexico ms 7 6 earthquake to limit the region being sampled the quality factor of s coda qc was obtained from the first 10 s following the s onset qc exhibited a strong spatial temporal and frequency dependence and in the small foreshock portion of the aftershock area qc and to a lesser extent qp were significantly lower before the mainshock than afterward the frequency dependence n in qc qo n was practically constant for aftershocks in four different regions n 1 32 0 03 and for foreshocks n 1 43 0 07 only in one peripheral region station pair did we find a significantly different n n 0 97 0 09 our observations indicate that qc and perhaps the frequency dependence n are sensitive to the physical property changes in the source region and might be useful as predictors of large earthquakes in a shallow subduction zone environment

postseismic rebound in fault step overs caused by pore fluid flow near field strain induced by large crustal earthquakes results in changes in pore fluid pressure that dissipate with time and produce surface deformation synthetic aperture radar sar interferometry revealed several centimeters of postseismic uplift in pull apart structures and subsidence in a compressive jog along the landers california 1992 earthquake surface rupture with a relaxation time of 270 45 days such a postseismic rebound may be explained by the transition of the poisson s ratio of the deformed volumes of rock from undrained to drained conditions as pore fluid flow allows pore pressure to return to hydrostatic equilibrium

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 area of el chichon volcano chiapas mexico abstract coda wave attenuation is investigated using the single scattering approximation on analog records from stations of a telemetered network situated close to el chichon volcano in southern mexico as well as from temporary stations deployed during 1982 the single scattering model was applied to the envelope of coda waves to characterize the coda decay rate we obtained values of q c which according to the filter settings of the seismographs and the average period measured in the traces correspond to frequencies of about 1 3 0 3 hz results indicate apparently larger attenuation than observed with similar techniques in other regions of mexico including the mexican volcanic belt within the limitation imposed by the data the spatial distribution of coda q with respect to the volcanic edifice was investigated for paths sampling the near vicinity of the volcano a value of approximately q c 30 was obtained the highest attenuation results are obtained for volumes with a slight e w tendency with q c values of 28 and 25 respectively the location of a gravity high as well as microseismic activity correlates well with this result which is interpreted as due to the probable presence of an intrusive magma body lower attenuation is obtained for volumes sampling deeper than the moho reaching a value of q c 87 suggesting that rocks below this boundary play a major role in controlling the overall attenuation of paths traversed by coda waves the results also suggest a decrease in attenuation towards the south and north possibly reflecting a decrease in magmatic processes in both of these directions

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

spatial variations of seismic attenuation in the north west of iranian plateau from analysis of coda waves abstract in this study spatial variation of coda wave attenuation in the north western nw iranian plateau is explored using local earthquakes single backscattering method is used to map the spatial variations of coda q qc using 14 969 earthquakes which are recorded digitally by sixteen permanent stations observed spatial attenuation maps are well correlated with geological setting of study area north west of iranian plateau is dominated with high attenuation which is well correlated with quaternary deposits as well as the sahnad sabalan volcanic zone and tabriz fault these observation is in accordance with numerous 2d velocity tomograms which have shown very low velocity in the nw iran the region characterized by volcanic structures exhibits mainly higher seismic attenuation than the surrounding regions whereas paleo tethys basin in the eastern part of covered area are categorized by smaller attenuation than the other zone our observation shows good correlation with reported lower crustal low velocity region beneath the sahand and sabalan volcanos the sahand and sabalan volcanoes are very large structures and they dominate the pliocene quaternary magmatic landscape of nw iran in addition our observation has clearly shown existence of a probable fault zone trending in ne sw direction between tabriz city and urmia lake which is consistent with the trend of meizoseismal zone of the deh khareqan modern azarshahr earthquake m 6 8 in 1641

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

modeling of strong motion data in northeastern india q stress drop and site amplification abstract in this article point source seismological model is used to model the available strong motion accelerograms in northeastern india key seismic parameters such as quality factor q value kappa factor 0 site amplification and stress drop are derived from the strong motion data a total of 111 three component records coming from seven earthquakes with magnitudes ranging from m w 5 2 to 7 2 are used in obtaining the source and path parameters the q value of the indo burma tectonic domain which is a subduction zone is obtained as 431 f 0 7 for the bengal basin shillong plateau region the quality factor is estimated as 224 f 0 93 the kappa factors for vertical and horizontal components are obtained as 0 013 and 0 033 for soft rock type sites for firm ground sites 0 is estimated as 0 025 for vertical and 0 041 for horizontal components respectively the site amplification functions for soft rock and firm ground conditions are found from the horizontal to vertical ratio the obtained stress drops of the seven events lie between 128 and 282 bars the source parameters obtained in this study provide a useful framework for working out ground motion relations in northeastern india

coda q in the charlevoix quebec region lapse time dependence and spatial and temporal comparisons coda q is determined in the seismically active charlevoix region quebec using 34 earthquakes recorded on the six station charlevoix local telemetered network for comparison an average value of coda q for southeastern canada is determined from 32 events that occur over a much larger region at lapse times of 20 to 40 sec coda q at 1 hz q at charlevoix and for southeastern canada is 91 4 and 125 10 respectively at a 40 to 80 sec lapse time it is 200 3 and 305 15 respectively the lower q value at charlevoix in comparison with other parts of southeastern canada is in agreement with jin and aki s 1988 finding that q is lower in the vicinity of large earthquakes no statistically significant temporal change in coda q at charlevoix is observed over the 11 yr of data studied a variation of as little as 15 would be statistically apparent ongoing monitoring of coda q in the area is planned using the local network in order to investigate any temporal changes prior to future large earthquakes coda q is found to increase with lapse time lapse time is defined as time elapsed after the origin time this dependence could be due to any of the following nonzero source receiver distance nonisotropic scattering scattering from below the crust multiple scattering or increase of q with depth or with distance from both source and receiver

attenuation of lg waves in the new madrid seismic zone of the central united states using the coda normalization method abstract unique properties of coda waves are employed to evaluate the frequency dependent quality factor of lg waves using the coda normalization method in the new madrid seismic zone of the central united states instrument and site responses are eliminated and source functions are isolated to construct the inversion problem for this purpose we used 121 seismograms from 37 events with moment magnitudes m ranging from 2 5 to 5 2 and hypocentral distances from 120 to 440 km recorded by 11 broadband stations a singular value decomposition svd algorithm is used to extract q values from the data while the geometric spreading exponent is assumed to be a constant inversion results are then fitted with a power law equation from 3 to 12 hz to derive the frequency dependent quality factor function the final results of the analysis are q v lg f 410 38 f 0 49 0 05 for the vertical component and q h lg f 390 26 f 0 56 0 04 for the horizontal component where the term after sign represents one standard error for stations within the mississippi embayment with an average sediment depth of 1 km around the memphis metropolitan area estimation of quality factor using the coda normalization method is not well constrained at low frequencies f

using pkikp coda to determine inner core structure 2 determination of qc 1 despite the similar and rather uniform composition of two components of the core the solid inner part presents a much larger attenuation compared to the liquid outer part more over several authors have reported evidence of scattered seismic energy coming from the inner core ic this implies that the ic has lateral variations in structure or composition with a scale length from one to tens of kilometers these seismic scatterers could be caused by changes in crystal grain size variations in the orientation of anisotropy or the presence of partial melt and or impurities this work pursues the characterization of inner core scattering ics using a global data set of high frequency pkikp waveforms recorded at short period small aperture seismic arrays we apply a methodology used in the study of heterogeneities in the crust and upper mantle that consists of curve fitting of the observed scattered energy with a standard model along with a stripping technique to isolate the pkikp coda from the rest e g p pcp and pp codas from the observed pkikp codas we found an average qc 500 for the inner core reflecting a scattering attenuation at least comparable to the intrinsic attenuation we found a geographical dependence in the observations of pkikp coda with most of them coming from the pacific ocean and asia and relatively few observations coming from the atlantic ocean the simplest explanation is that the ics has a quasi hemispherical variation similar to other properties such as p wave velocity jump at the inner core boundary attenuation in the upper ic strength of anisotropy and or thickness of an overlaying isotropic layer this phenomenon is probably related to the solidification texturing of iron crystals showing hemispherical differences in the growth of the inner core

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

dependence of coda attenuation on frequency and lapse time in central greece the dependence of coda attenuationq c on frequency and lapse time was studied data from small local earthquakes recorded at three stations vmr vsi and vfi of the volnet network operating in central greece were used q c was estimated by applying the single scattering model to bandpass filtered seismograms over a frequency range of 1 to 12 hz analysis was performed every 10 s until the end on overlapping time windows q c is found to depend on frequencyf in hz according to a power law q c q0f n observedq0 ranges from 30 to 100 and the powern ranges from 0 90 to 0 70 q0 increases andn decreases with lapse time increasing a strong dependence ofq c on lapse time was also found in the frequency range of 1 to 8 hz and at a short lapse time q c values were found to be similar for all three stations on the other hand at the longest analyzed time window 50 s the estimatedq c values show a discrepancy which is more obvious at a higher frequency band the scattering coefficient around the central station vsi is found to range from 0 029 to 0 0041 km 1 q c from the single scattering model andq s from the amplitude ratio of directs to coda waves for the vsi station are similar we believe dependence of coda attenuationq c on frequency and lapse time is caused by a combination of geotectonic features and depth variation asq s

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

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

lapse time and frequency dependent attenuation characteristics of kumaun himalaya abstract we have analyzed local earthquake data set consists of 84 well located events recorded by a digital seismic network in the kumaun himalaya region during 2004 2007 to study seismic attenuation characteristics of the region single back scattering assumption is used to estimate coda q q c values of the region at frequency range of 1 5 3 6 8 12 and 18 hz for different lapse time window length the values of q c show a ubiquitous observation of frequency dependence and follow a substantially similar trend as observed in other tectonically active parts of the himalaya the lapse time dependencies of coda waves are investigated which reveal that by increasing lapse time window from 20 to 50 s q 0 q c at 1 hz increases from 64 2 to 230 19 while frequency dependent parameter n decreases from 1 08 to 0 81 increase in q c with lapse time indicates decrease in heterogeneity with depth the observed values of q 0 and n infer that the medium beneath the study area is highly heterogeneous and tectonically very active the variation of q c with lapse time at 1 5 hz follow a similar pattern with the theoretically predicted values of gusev 1995 although the frequency parameter n does not match with the model it may suggest that the turbidity decays rapidly with depth for the kumaun himalaya our results are comparable with those obtained from tectonically active regions in the world

regional and local factors in attenuation modelling hong kong case study seismic attenuation behaviour is controlled by a large number of wave modification mechanisms the characteristics of some of these mechanisms are specific to a local area whilst the remainder can be generalised to the entire seismic region factors representing these mechanisms are often not resolved a new attenuation modelling approach is demonstrated in this paper using hong kong as a case study to evaluate individual regional and local wave modification factors shear wave velocity swv information for the four prevalent geological formations found in hong kong was first obtained a at shallow depths from instrumented boreholes b at depths of up to 100 200 m from measurements using the microtremor spatial auto correlation spac technique c at depths of up to 1 5 km from the monitoring of quarry blasts and d at depths from 1 5 to 8 km in the hard basement rock layers from results of seismological refraction surveys the upper crust amplification factor calculated from the four modelled rock swv profiles was then combined with predicted attenuation parameters to determine the upper crust modification factor filter function incorporating the local wave modification characteristics associated with hong kong geological formations such functions may then be combined with the regional attenuation characteristics in that part of the south china region a seismic attenuation model was developed by combining the upper crust modification factor with the regional source function of intra plate earthquakes based on stochastic simulations the ground shaking model developed from the presented methodology is supported by the comparison with macro seismic data of seven historical earthquake events affecting hong kong

regional variation of coda q in kopili fault zone of northeast india and its implications abstract kopili fault has been experiencing higher seismic and tectonic activity during the recent years these kind of active tectonics can be inspected by examining coda wave attenuation and its dependence with frequency exploiting single back scattering model we have endeavored to measure coda q and its associated parameters such as frequency dependent factor n and attenuation coefficient covering seven lapse time windows spanning from 30 to 90 s and central frequencies 1 5 3 5 6 9 and 12 hz the average estimated values of qc increase s with frequency and lapse time window from 114 at frequency 1 5 hz to 1563 at frequency 12 hz for 30 s window length and from 305 at frequency 1 5 hz to 2135 at frequency 12 hz for 90 s window length the values of q0 and n are also estimated for the entire kopili fault zone for this study region the q0 values vary from 62 to 348 and n varies from 0 57 to 1 51 within the frequency range 1 5 to 12 hz furthermore depth variation of attenuation of this region reveals that there is velocity anomaly at depth 210 220 km as there arises sharp changes in and n which are supported by available data reported by other researcher for this region finally we have tried to separate the intrinsic and scattering attenuation for this area it is observed that the entire region is dominated by mainly scattering attenuation but we can see an increase in intrinsic attenuation with depths in two stations namely tzr and bkd furthermore the obtained results are comparable with the available global data

coda q estimates in the andaman islands using local earthquakes the attenuation property of andaman island has been investigated analyzing coda waves from 57 local earthquakes in the magnitude range of 2 0 4 9 using the single backscattering model these earthquakes waveforms recorded on five broadband seismographs sited over the island from north to south during nov 2003 to march 2004 have been used to calculate the frequency dependent coda q q c applying the time domain coda decay method the coda q computed at central frequencies from 0 5 12 hz and five lapse time windows from 40 to 80 s progressively increases from 105 f 0 88 in the north andaman to 135 f 0 79 in the south andaman with an average of 119 f 0 80 the average q c values vary from 75 42 at 0 5 hz to 697 54 at 12 hz central frequency for 40 s lapse time window while for 80 s lapse time window its variation is from 117 38 at 0 5 hz to 1256 115 at 12 hz the q c estimated at different lapse times manifests a significant variation from 122f 0 75 to 174f 0 73 corresponding to lapse time window lengths of 40 and 80 s respectively the variation of q c with frequency lapse time and also with the location of seismograph reflects the marked structural and compositional inhomogeneity with depth along the andaman islands these observations are well correlated with the seismicity pattern and distinct high angle subduction beneath the island

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

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

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

estimation of coda wave attenuation for the national capital region delhi india using local earthquakes attenuation of seismic waves is very essential for the study of earthquake source parameters and also for ground motion simulations and this is important for the seismic hazard estimation of a region the digital data acquired by 16 short period seismic stations of the delhi telemetric network for 55 earthquakes of magnitude 1 5 to 4 2 which occurred within an epicentral distance of 100 km in an area around delhi have been used to estimate the coda attenuation qc using the single backscattering model the seismograms have been analyzed at 10 central frequencies the frequency dependence average attenuation relationship qc 142f1 04 has been attained four lapse time windows from 20 to 50 seconds duration with a difference of 10 seconds have been analyzed to study the lapse time dependence of qc the qc values show that frequency dependence exponent n remains similar at all the lapse time window lengths while the change in q0 values is significant change in q0 with larger lapsetime reflects the rate of homogeneity at the depth the variation of qc indicates a definitive trend from west to east in accordance with the geology of the region

coda wave seismic structure beneath the indian ocean region and its implications to seismotectonics and structural heterogeneity abstract the indian ocean region is one of the challenging areas for seismological research because of its complex seismotectonic settings and intricate structural heterogeneity prevails beneath the indian ocean region in order to address the problem we attempted to determine the attenuation structure for the indian ocean region using coda wave generation by single backscattering model in this study the central frequency of interest has been considered between 1 5 and 12 0 hz with lapse time window ltw of 20 30 40 50 and 60 s measured from the origin time of the earthquake we obtained the attenuation relation for different seismotectonic zones associated with varying estimate of attenuation parameters spreading zone qc spz 171f1 10 subduction zone qc sz 220f0 961 triple point junction qc tpj 156f1 15 prominent faults of indian ocean region qc pfioz 197f0 99 and volcanic and hotspot qc vz hs 209f0 97 we estimated average frequency dependent attenuation parameters of q0 that varies as 156 32 q0 220 33 with corresponding variability in frequency parameter as 0 96 0 05 1 15 0 09 at 40 s ltw for the entire indian ocean region suggesting that the entire indian ocean is seismo tectonically highly active and is attributed to the nature and extent of attenuation due to varying amount of structural heterogeneity in different tectonic zones characterized by the occurrence of earthquakes of varying strengths in the seismically active tectonic zones of the region we found that the triple junction rtj is associated with low qc and high attenuation because of deposition of a variety of sediments at the rtj which is in unison to the geological mapping of the region we observed that our estimated attenuation model is comparable that of the aleutian islands the adak seismic zone at low frequency 5 hz and to the philippine sea subduction zone petukhin at higher frequency range 5 hz which is very much correlative to seismo tectonic settings we infer that our assimilated attenuation model has potential to provide information on intricate seismotectonics and seismogenesis for computing earthquake source parameters and earthquake hazards that may be useful for assimilating detailed seismic velocity structure beneath the indian ocean region

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

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

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

spatial and temporal correlation between coda q and seismicity in china a map of coda q at 1 hz q was constructed for china by analyzing more than 1000 seismograms from 80 seismic stations distributed throughout china the resultant contour map of q shows a strong correlation with the epicenters of historic great earthquakes in china the high q regions are devoid of the epicenters and the low q regions are full of them a remarkably linear relation was found between the logarithm of coda q and the maximum earthquake within the area sampled by coda waves radius of about 150 km from each station when we consider earthquakes which occurred from 1700 to present roughly speaking if q is 1000 m max is about 4 and if q is 100 m max is about 8 this relation will be very useful for siting critical facilities such as nuclear power plants and waste disposal sites we also found evidence in support of the migration of low q region coincident with the well known migration of high seismicity region over the distance of several hundred kilometers during the period of several hundred years if the migration is due to a diffusion process the diffusion constant is of the order of 100 km2 yr which agrees very well with those associated with the aftershock migration fluid injection and vp vs anomaly comparison of coda q with q1 estimated from the intensity data shows that they agree very well for q1 150 supporting the validity of the s to s single backscattering model for coda waves for q1 150 however coda q becomes constant independent of q1 this behavior is qualitatively consistent with numerical experiments of frankel and clayton and suggests that coda q may be measuring the intrinsic q of about 150 for these regions where q1 150 this limiting coda q value may depend on regions because coda q lower than 100 has been observed in some active regions in this study and also coda q as low as 30 to 40 has been reported in california mexico and italy

estimates of magnitudes and short period wave attenuation of chinese earthquakes from modified mercalli intensity data abstract intensity data for chinese earthquakes are used to estimate the body wave magnitude m b of selected historical earthquakes and to estimate q 0 the 1 sec period q value of lg waves for various geographical areas of china in order to derive the necessary empirical relation between the intensity distribution and m b data are used from recent earthquakes for which instrumentally obtained m b values as well as isoseismal maps are available average q o values are approximately 175 for the mountainous regions of southwest china 550 for southeastern china and 150 for taiwan these values agree qualitatively with those obtained by evernden 1983 and chen et al 1983 who utilized a different method of analysis of the intensity data

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 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

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

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

significance of agglutinate mounds on lava flows associated with monogenetic cones an example at sunset crater northern arizona large mounds of welded pyroclasts and rootless flows on top of mafic lava flows associated with symmetrical scoria cones may be evidence for breaching and subsequent restoration of the cones textures and bedding structures of the agglutinate mounds are distinctly different from those of hornitos and indicate deposition proximal to a major explosive vent breaching of a cone armored by an agglutinate carapace may cause the welded deposits to collapse onto the emerging lava which then rafts them away renewed or continued strombolian eruptions from the vent can restore the symmetry of the cone and conceal the disrupted structure rafted agglutinate mounds on the bonito lava flow at sunset crater a symmetrical holocene scoria cone in northern arizona extend in a belt from near the base of the cone toward the northwest the direction the lava flowed eye witness accounts of the eruption at paricutin mexico in 1943 record breaching and restoration events similar to the one inferred to have occurred at sunset crater and demonstrate that symmetrical monogenetic cones may have complicated histories

mapping of coda wave attenuation and its frequency dependency over eastern indian shield the study area comprises two tectonic blocks namely the chotanagpur microplate and the singhbhum microplate waveform data of 112 local earthquakes of magnitude mw 2 5 were considered for the present analysis coda q qc for each event at eight different central frequencies 1 14 hz and four different coda windows was estimated using back projection algorithm the average q0 qc at 1 hz and exponent values were regionalized by projecting each value in selected square grid of dimension 0 1 0 1 back projection algorithm was used for inversion of qc and the final values were computed after ten iterations when the residual error was reduced to acceptable level inversion was stabilized by a nine point spatial smoothening gaussian filter to compute the qc values for each frequency and subsequently combined values of q0 and were also computed the final power law equation of the coda wave attenuation for the concerned region was found to be qc 336 38 16 50 f 0 83 0 036 q0 varies from 180 to 255 270 to 360 297 to 386 and 340 to 420 and vary from 0 9 to 1 02 0 79 to 0 89 0 79 to 0 88 and 0 79 to 0 86 for 30 35 40 and 45 s coda windows increase in q0 and decrease in values with increase of coda window length shows the depth dependency of seismic wave attenuation at 1 hz frequency the central part surrounding the receiver lying at the junction of the chotanagpur and the singhbhum tectonic provinces documents lower q0 and higher values and presumably caused by more heterogeneities present in the area the higher concentration of lower magnitude earthquakes in this area support this observation the mapping values of attenuation can be utilized for hazard assessment of the area

lateral variations of lg coda q in southern mexico broad band digital three component data recorded at unm a geoscope station were used to estimate lg coda q for 34 medium size 3 9 m b 6 3 earthquakes with travel paths laying in different geological provinces of southern mexico in an effort to establish the possible existence of geological structures acting as wave guides and or travel paths of low attenuation between the pacific coast and the valley of mexico the stacked spectral ratio method proposed by xie and nuttli 1988 was chosen for computing the coda q the variation range of q 0 q at 1 hz and the frequency dependence parameter estimates averaged on the frequency interval of 0 5 to 2 hz for the regions and the three components considered are i guerrero region 173 q 0 182 and 0 6 q 0 0 7 ii oaxaca region 183 q 0 198 and 0 6 q 0 0 8 iii michoacan jalisco region 187 q 0 204 and 0 7 q 0 0 8 and iv eastern portion of the transmexican volcanic belt tmvb 313 q 0 335 and 0 9 the results show a very high coda q for the tmvb as compared to other regions of southern mexico this unexpected result is difficult to reconcile with the geophysical characteristics of the tmvb e g low seismicity high volcanic activity and high heat flow typical of a highly attenuating low q region visual inspection of seismograms indicates that for earthquakes with seismic waves traveling along the tmvb the amplitude decay of lg coda is anomalously slow as compared to other earthquakes in southern mexico thus it seems that the high q value found does not entirely reflect the attenuation characteristics of the tmvb but it is probably contaminated by a wave guide effect this phenomenon produces an enhancement in the time duration of the lg wave trains travelling along this geological structure this result is important to establish the role played by the transmission medium in the extremely long duration of ground motion observed during the september 19 1985 michoacan earthquake the overall spatial distribution of coda q values indicates that events with focus in the michoacan jalisco and oaxaca regions yield slightly higher values than those from guerrero this feature is more pronounced for the horizontal component of coda q a slight dependence of average coda q 1 on earthquake focal depth is observed in the frequency range of 0 2 to 1 0 hz approximately on the horizontal component deeper h 50 km events yield lower values of q 1 than shallower events for frequencies higher than 1 0 hz no clear dependence of q 1 on focal depth is observed however due to the estimates uncertainties this result is not clearly established

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

anomalous character of the coda envelopes on mt vesuvius explained in terms of depth dependent q summary many observations made on volcanic areas showed that a non uniform distribution of coda wave energy is present between regions with differing geological structures this observation was carried out in la reunion and interpreted by aki and ferrazzini as due to a trapping process of the scattered waves in the volcanic cone named by these authors as coda localization the same properties were found in mt vesuvius examining codas from shots fired for active tomography in this paper we experimentally check whether the scattered wave field produced by local vt earthquakes is inhomogeneous as found for codas from shots in the same volcano we examine the log plot of s wave direct amplitude normalized for the coda amplitude at a given lapse time coda normalization for all the recording stations and the site transfer functions calculated for the same stations using both the direct s wave spectra and the coda wave spectra results show that the log normalized amplitude increases with distance the opposite of what commonly observed in non volcanic zones this effect may be caused by an effective inhomogeneity of the scattering wave field or in different words by a total q increasing with depth