evidence for stability in coda q associated with the egion central greece earthquake of 15 june 1995 one hundred seventy two seismograms recorded at one seismological station located close to the source region of the egion ms 6 2 15 june 1995 earthquake were used to measure values of q from the decay of the earthquake coda the collected data were compared between events that occurred before and after the main event the analysis showed no significant temporal variation in the value of coda q for the region

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

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

stability of coda wave attenuation during the loma prieta california earthquake sequence the loma prieta california earthquake occurred in a densely instrumented region with a history of microearthquake recording beginning more than a decade before the october 1989 mainshock this affords an unprecedented opportunity to detect changes in seismic wave propagation in the earth s crust associated with a major earthquake in this study we use pairs of nearly identical earthquakes doublets to search for temporal changes of coda attenuation in the vicinity of the loma prieta earthquake we analyze 21 earthquake doublets recorded from 1978 to 1991 that span the preseismic coseismic and postseismic intervals and measure the change in coda q using a running window ratio of the doublet spectral amplitudes in three frequency bands from 2 to 15 hz this method provides an estimate of changes in coda q that is insensitive to other factors that influence coda amplitudes our observations place an upper bound of about 5 on preseismic coseismic and postseismic changes of coda q in the epicentral region of the loma prieta earthquake even at this low level the changes are neither spatially coherent nor correlated between adjacent frequency bands the only hint of a signal is in the preseismic data where there is a possible precursory increase in coda q of approximately 5 in the two years before the mainshock the stability of coda q throughout the loma prieta sequence is in sharp contrast to other studies that have reported much larger precursory changes in coda q for other earthquakes

interaction of seismic waves with a viscous liquid layer abstract the interaction of seismic waves with a layer filled with a viscous fluid is studied this study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a hot dry rock geothermal energy system we compute transmission and reflection coefficients for p sv and sh waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half spaces we find that coefficients for sh waves at normal incidence can be written in terms of two dimensionless parameters one of these parameters i is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid the other dimensionless parameter d is a measure of the amount of energy the sh wave loses during one pass through the fluid layer we find that the amplitude of the sh wave transmitted through the fluid layer is equal to the amplitude of the incident sh wave if i is nearly 1 and d is small as d increases energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes if i is not nearly 1 some energy is reflected by the fluid layer three dimensionless parameters are required for solution for the case of p waves normally incident on the fluid layer one parameter r is the ratio of the bulk modulus to effective shear modulus of the fluid the second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is d we find that the value of r is a good measure of the importance of fluid viscosity on the propagation of p waves through the fluid detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non normal incidence finally reflection and transmission coefficients are computed for p and sv waves incident at arbitrary angle on a viscous fluid layer physical properties of fluid and rock are chosen to be those thought appropriate for the los alamos national laboratory hot dry rock geothermal test site located at fenton hill new mexico

evoluton of polygonal fracture patterns in lava flows cooling induced fractures also known as columnar joints divide basaltic lava flows into prismatic columns with polygonal cross sections the regularity and symmetry of the fracture patterns have long fascinated naturalists in view of the recent selection of two candidate nuclear waste sites in areas where polygonally fractured volcanic rocks are located a better understanding of the fracture patterns is required field data indicate that the tetragonal networks at flow surfaces evolve systematically to hexagonal networks as the joints grow inward during solidification of lava this evolution occurs by the gradual change of most orthogonal intersections to nonorthogonal intersections of about 120 degrees the surface features and intersection geometries of columnar joints show that joint segments at any given level form sequentially yet harmoniously

differential analysis of coda q using similar microearthquakes in seismic gaps part 1 techniques and application to seismograms recorded in the anza seismic gap abstract a large but conflicting literature exists that suggests that the scattering properties of the earth in seismogenic areas may be temporally variable and that this variability could be correlated with the nucleation times of moderate to large earthquakes to search for temporal variations in coda q in the vicinity of an expected moderate earthquake nucleation region along the san jacinto fault zone pairs and clusters of earthquakes recorded by the anza seismic network between 1982 and 1992 are examined to minimize differences arising from path and source variability only the most similar examples of microearthquake wave fields are intercompared to assess coda q differences between similar microearthquake signals we search for systematic temporal changes in moving window spectral amplitude ratios for a single scattering coda model with an envelope decay function of the form t m e ft qc the relationship between the natural log amplitude spectral ratio and q 1 q 1 c 2 q 1 c 1 is linear i e ln r f t ft q 1 f w f where w f is a time independent relative source term to obtain robust uncertainty estimates of q 1 f and w f we utilize multi taper spectral analysis coupled with a nonparametric monte carlo confidence interval estimation procedure for the most similar events in the anza region coda cross correlation values of approximately 0 7 for 16 sec of coda we find that coda q as a function of time is stable at a typical 1 resolution of only between 25 and 50 of the reference coda q value for the area even in the best constrained frequency bands comparison of similar microearthquake coda signals with both short and long temporal separations indicates that all of this variability can be reasonably attributed to random fluctuations in the coda that are driven by source variability and is not indicative of any systematic temporal variability in coda q to obtain estimates of relative coda q that are more precise than this level the spectral ratio analysis technique requires significantly more similar earthquakes than are produced by seismogenic processes in the anza region such earthquakes have been observed to occur in other regions of the san andreas fault system and are analyzed in antolik et al 1996

a temporal change in coda wave attenuation observed during an eruption of mount st helens during the past few years there have been numerous reports of changes in coda wave attenuation occurring before major earthquakes these observations are important because they may provide insight into stress related structural changes taking place in the focal region prior to the occurrence of large earthquakes the results of these studies led us to suspect that temporal changes in coda wave attenuation might also accompany volcanic eruptions by measuring power decay envelopes for earthquakes at mount st helens recorded before during and after an eruption that took place during september 3 6 1981 we found that coda q sup 1 for frequencies between 6 and 30 hz was 20 30 higher before the eruption than after the change is attributed to an increase in the density of open microcracks in the rock associated with inflation of the volcano prior to the eruption q sup 1 was found to be only weakly dependent on frequency and displayed a slight peak near 10 hz the weak frequency dependence is attributed to the dominance of intrinsic attenuation over scattering attenuation since it is generally accepted that intrinsic attenuation is constant with frequency whereas scattering attenuation decreases strongly at higher frequencies the weak frequency dependence of q sup 1 more at mount st helens contrasts with results reported for studies in nonvolcanic regions the peak in q sup 1 near 10 hz at mount st helens is attributed to the scale length of heterogeneity responsible for generating backscattered waves results for nonvolcanic regions have shown this peak to occur near 0 5 hz thus a smaller scale length of heterogeneity is required to explain the 10 hz peak at mount st helens copyright american geophysical union 1988 less

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

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

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

origins of amplitude variations in seismic doublets source or attenuation process summary accurate estimates of spectral ratios of two doublets i e similar seismic events occurring along the san andreas fault in the hollister region have been computed using a cross spectral method both events of each doublet occurred within a 24 hr interval although both waveforms of a doublet are remarkably similar computed spectral ratios exhibit strong but steady variations with frequency in the first arrivals the attenuation process can explain neither the sign nor the order of magnitude of these variations on the contrary they are closely related to the source mechanism we show that the slope computed from the linear and coherent part of the spectral ratio is an estimation of the variation in the apparent rupture duration between the two events one doublet exhibits an azimuthal distribution of the spectral ratio variations that is interpreted as the result of a change in the position of the hypocentres relative to the rupture area for this doublet location of hypocentres varies only from 10 to 30 per cent of the source length this points out that small changes in rupture kinematics can lead to significant variations in the spectral ratio of earthquake doublets i e in the amplitude of each event for the other doublet the variations are related to a change in source length we also have computed spectral ratios all along the seismograms using a moving window technique when an azimuthal distribution of the spectral ratio is observed in the first arrivals we notice a decrease of the spectral ratio all along the seismograms the doublet with strong but non azimuthal variations of the spectral ratio in the first arrivals does not indicate such a decrease of the spectral ratio along the seismogram this implies that the variations of the coda decay are related not only to temporal or spatial changes of attenuation but also to source parameters these variations have the same order of magnitude as those provoked by a temporal change in coda q of 10 per cent they can occult time changes of spectral ratio for instance in case the attenuation in the crust would vary before a strong earthquake

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

complexities in high frequency seismic waveforms due to three dimensional structure in the new madrid seismic zone effects of three dimensional structure on 2 to 10 hz seismic signals in the new madrid seismic zone nmsz are investigated using waveforms from similar microearthquakes that occurred near ridgely tennessee slowness power spectral sps analysis is used to study the plane wave composition of p s and coda waves the observed sps at four stations suggest that the early s coda is composed mainly of wavelets leaving the source with slownesses of the direct s wave at greater lapse times coda is increasingly affected by random scattering sps observed on the vertical components and or near the s wave nodes are more comlplex due to practical limitations of the algorithm p coda and early s coda at a fifth station located southwest of the junction show the most complex sps analysis of that complexity together with waveform synthetics and travel time analysis strongly suggests that scattering multipathing due to source zone velocity heterogeneities occurs near the path probably due to dilatancy occurring southwest of the ridgely junction or due to internal fault zone complexities coda q when averaged over three components show no station variations we infer that 1 coda at 1 hz is mainly caused by scattering in the sedimentary layer where q is frequency independent 2 at higher frequencies the coda contains an increasing amount of scattered body waves and 3 the source radiation pattern and path variable scattering multipathing effects in early coda do not affect coda q

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

baylike and continuous variations of the relative level of the late coda during 24 years of observation on kamchatka the relative amplitude levels of backscattered shear waves coda of local earthquakes as expressed in coda magnitude residuals were studied for nine kamchatka seismograph stations coda magnitudes were determined from coda amplitudes measured on three component photograph records of 1 2 s period displacement recording between 1 and 10 hz instruments a coda magnitude scale was specially designed for this study it is rather precise with a standard deviation of about 0 15 for log amplitudes measured at any single station at each station for each event we compute the station magnitude residual i e station magnitude averaged over three components minus network average magnitude station corrections for each station and component were determined and included in the procedure time series of coda magnitude residuals including 500 1000 events for each station for the 24 year period of observations 1967 1990 show moderate but statistically significant oscillations around a constant level superposed on this background two prominent anomalies are revealed one at station kbg of 3 years duration preceded two m 8 shallow earthquakes within 100 km from the station another at station aph of 1 5 years duration preceded a major volume of 2 5 km3 fissure volcanic eruption within a 70 km distance from the station no other comparable shallow earthquakes or eruptions took place on kamchatka during this period the sign and the amplitude of the anomalies indicate a possible 30 increase of s wave attenuation in the lithosphere under the stations

predictive mapping of soil landscape relationships in the arid southwest united states abstract multi scale geospatial and absolute variation of surface and near surface soil physical and chemical properties can be mapped and quantified by coupling digital soil mapping techniques with high resolution remote sensing products the goal of this research was to advance data driven digital soil mapping techniques by developing an approach that can integrate multi scale digital surface topography and reflectance derived remote sensing products and characterize multi scale soil landscape relations of quaternary alluvial and eolian deposits the study area spanned the arid landscape encompassed by the barry m goldwater range west bmgrw which is administered by the marine corps air station yuma in southwestern arizona usa an iterative principal component analysis ipca was implemented for lidar elevation and landsat etm derived soil predictors termed environmental covariates principal components that characterize 95 of covariate space variability were then integrated and classified using an isodata iterative self organizing data unsupervised technique the classified map was further segmented into polygons based on a region growing algorithm yielding multi scale maps of soil landscape relations that were compared with maps of soil landforms identified from aerial photographs satellite images and field observation the approach identified and mapped the spatial variability of soil landscape relationships in alluvial and eolian deposits and illustrated the applicability of coupling covariate selection and integration by ipca isodata classification of integrated data layers and image segmentation for effective spatial prediction of soil landscape characteristics the approach developed here is data driven applicable for multi scale mapping allows incorporation of a wide variety of covariates and maps spatially homogenous soil landscape units that are necessary for hydrologic models land and ecosystem management decisions and hazard assessment

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

properties of seismic wave scattering around water injection well at fenton hill hot dry rock geothermal site to determine the scattering properties of microcracks created by water injection in hot dry rock a method for analyzing trajectory ellipsoids of seismic particle motions has been applied lengths and directions of three principal axes of trajectory ellipsoids were calculated and a distribution of the shape of these ellipsoids suggests existence of a strong scattering region around the injection point this strong scattering has an anisotropic property presumably due to microcrack orientation in the original rock

coda q before the 1983 hawaii ms 6 6 earthquake abstract coda q values were derived for more than 300 microearthquakes that occurred in a 6 yr period before the 16 november 1983 kaoiki hawaii earthquake m s 6 6 the sources were located within a 14 16 km rectangular region surrounding the main shock epicenter and most of them occurred at depths between 5 and 10 km digital recordings from three stations at epicentral distances ranging from 0 to 18 km were used coda q was calculated from the amplitude decay rate of the s wave coda in nine frequency bands from 4 5 to 27 hz the average q of the nw part of the studied area is about 15 per cent higher than that of the se part these two subregions also showed differences in seismicity b value and microearthquake source mechanisms in the high q volume the b value was 1 0 and the rate of earthquakes per unit volume was about 50 per cent of the rate in the low q volume where b 1 3 one interpretation of these observations is that more extensive faulting in the se kaoiki fault zone leads to lower q higher b value and a higher seismicity rate during the 5 to 6 yr before the mainshock the 1 yr average q values were stable no significant q change could be identified as a precursor to the main shock