attenuation of high frequency seismic waves in eastern iran we investigated the frequency dependent attenuation of the crust in eastern iran by analysis data from 132 local earthquakes having focal depths in the range of 5 25 km we estimated the quality factor of coda waves q c and body waves q p and q s in the frequency band of 1 5 24 hz by applying the single backscattering theory of s coda envelopes and the extended coda normalization method respectively considering records from recent earthquakes rigan m w 6 5 2010 12 20 goharan m w 6 2 2013 5 11 and sirch m w 5 5 2013 1 21 the estimated values of q c q p and q s vary from 151 49 63 6 and 93 14 at 1 5 hz to 1 994 124 945 84 and 1 520 123 at 24 hz respectively the average frequency dependent relationships q q o f n estimated for the region are q c 108 10 f 0 96 0 01 q p 50 5 f 1 01 0 04 and q s 75 6 f 1 03 0 06 these results evidenced a frequency dependence of the quality factors q c q p and q s as commonly observed in tectonically active zones characterized by a high degree of heterogeneity and the low value of q indicated an attenuative crust beneath the entire region

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

moho geometry and upper mantle images of northeast india 1 images of the crust and mantle beneath northeast india obtained by 2d migration of 1000 broadband p receiver functions clearly trace a northward dipping moho from the himalayan foredeep reaching depths up to 50 km further north beneath the himalayan convergence zone also these images reveal presence of largely coherent 410 km and 660 km discontinuities that conform to the iasp91 model marginal variations in the depth of the 410 km interface are observed that appear region specific the thickness of the mantle transition zone does not deviate significantly from a global average of 250 km interestingly our results reveal consistent presence of a signal from an interface around 300 km origin of such a boundary known as x discontinuity and unrelated to the lehmann discontinuity is discussed possible presence of the x discontinuity from the indian region is reported here for the first time

temporal variations of qc 1 and b values associated to the december 2000 january 2001 volcanic activity at the popocatepetl volcano mexico abstract we correlated temporal variations of coda attenuation q c 1 at 6 hz and b values with the 11 december 2000 23 january 2001 major eruptive activity at the popocatepetl volcano mexico we interpreted a total of 225 volcanic earthquakes with magnitudes between 1 9 and 3 3 located between 2 and 8 km from the summit of the volcano and registered from january 1999 to june 2001 q c 1 was estimated using a single scattering model and values of b were obtained applying the method of maximum likelihood our results indicate that from january 1999 to march 2000 period 1 q c 1 varied within the same range without significant changes then values of q c 1 steadily decreased during april mid december 2000 period 2 from about mid december 2000 onset of the major volcanic activity up to february 2001 period 3 q c 1 sharply increased reaching its peak value from march to june 2001 period 4 q c 1 decreased and increased in response to the post eruptive phase of dome formation and destruction process that took place during periods 2 and 3 average b values behaved opposite to the q c 1 trend within period 2 when q c 1 decreased b slowly increased at the start of period 3 b reached its peak value and returned to low values by the end of this time interval we associate the temporal changes of the two analyzed parameters to variations of pressure and or the variation in the degree of saturation of pore fluids that took place before during and after the major eruption during periods 2 and 3 q c 1 correlated negatively with b with a correlation coefficient of 0 61 and 0 83 respectively the significance of correlation cannot be rejected at the confidence level of 0 975 our observations may have important implications for future prediction studies of large eruptions at the popocatepetl volcano

qc qβ qi and qs attenuation parameters in the umbria marche italy region the attenuation of coda and s waves has been inferred for the umbria marche region central italy using seismic waveforms collected during the 1997 seismic crisis the selected dataset is composed of 343 small magnitude 1 4 ml 4 2 earthquakes recorded at a temporary array composed of 23 seismic stations the sato 1977 method based on the assumption of single isotropic scattering has been used to infer qc considering three different lapse times 20 30 and 40 s the coda normalization method aki 1980 has been used to infer q both qc and q show a clear frequency dependence with a different frequency dependent parameter the frequency dependence of qc is comparable with that previously found in the same area and around it using the method of wennerberg 1993 intrinsic and scattering attenuation have been separated intrinsic attenuation is found to be close to coda attenuation and dominates over scattering dissipation coda q increases with increasing lapse time but at a rate smaller than that observed in other areas of the earth coda and intrinsic attenuation in the umbria marche region are very high compared to other seismic active regions of the earth the retrieved high values of intrinsic attenuation may be explained in terms of the previously hypothesized fluid pressurized regime of the crust in the central apennines miller et al 2004

progressive infilling of a kimberlite pipe at diavik northwest territories canada insights from volcanic facies architecture textures and granulometry abstract processes responsible for the formation of crater facies kimberlite remain poorly understood because there are few occurrences of well preserved deposits new open pit exposures of the a154n kimberlite pipe at diavik in the lac de gras region of the northwest territories canada reveal well preserved crater facies deposits here we describe the geometries structures and componentry of deposits from the uppermost 130 m of the a154n pipe we then interpret the processes responsible for their emplacement on the basis of these characteristics the base of the section features a poorly sorted primary massive volcaniclastic kimberlite deposit mvk1 grading upward into a better sorted and weakly stratified volcaniclastic kimberlite deposit mvk2 which is itself overlain by 45 m of stratified volcaniclastic kimberlite svk the mvk svk contact is sharp and marks an abrupt transition from sustained eruption of pyroclastic kimberlite to episodic sedimentation from collapse of an unstable volcanic edifice into the open crater the svk deposit is overlain dis conformably by a poorly to well sorted diffusely bedded and graded pyroclastic kimberlite pk1 and pk2 that erupted from another younger kimberlite volcano the pk deposits show a variety of textures supporting a pyroclastic origin including vesiculated juvenile pyroclasts a grain and clast supported fabric and the absence of mud size particles in the matrix vertical clast size grading over 40 50 m and the absence of bedding in the pk2 suggest hydraulic sorting during en masse deposition of pyroclastic kimberlite into a deep water column granulometric analysis shows the pk2 deposit was originally transported as a pyroclastic density current that was sourced from one of the many adjacent pipes in the diavik area and inundated the a154n pipe these observations have implications for kimberlite volcanic processes and grade distribution

separation of intrinsic and scattering seismic attenuation in the southern apennine zone italy summary scattered waves observed at the seismographs of the national italy s seismic network have been used to investigate the intrinsic dissipation and scattering properties of the lithosphere under the southern apennines italy first we investigate the coda q properties then we apply the mltw analysis in the hypothesis of velocity and scattering coefficient constant with depth and finally we interpret these results with the aid of numerical simulations in a medium with depth dependent velocity and scattering coefficient results obtained in the hypothesis of a uniform model show that a low scattering q 1 and a relatively higher intrinsic q 1 characterize the lithosphere of the southern apennines numerical simulations of the seismogram energy envelopes were performed hypothesizing a strongly scattering crust and trasparent upper mantle both with reasonable intrinsic dissipation coefficients in these symplifying assumptions the theoretical curves calculated for the homogeneous model fit to the synthetic envelopes with scattering attenuation coefficients always greater than the synthetic values this results lead to the consideration that scattering q 1 obtained using mltw analysis under the assumption of uniform medium are overestimated the values of the scattering q 1 estimated for apennines at low frequency 1 2 hz in the hypothesis of uniform medium are of the same order of those obtained in several areas around the world the estimates obtained for frequencies ranging from 2 to 12 hz are very low if compared with those obtained in the same hypothesis for other areas around the world coda q 1 closely resembles intrinsic q 1

response of monsoonal temperate glaciers to global warming since the little ice age abstract monsoonal temperate glaciers in china mainly occur in the southeastern part of qinghai tibetan plateau they constitute an area of 13203 2 km2 accounting for 22 2 of china s total glaciated area such glaciers are extremely sensitive to climatic warming due to their unique characters an inconsiderable rise in air temperature may lead to a significant rise in ela and a large shrinkage in glacier area since the maximum of the little ice age 17th century the mean temperature of monsoonal temperate glaciers in china has increased by 0 8 c and the glacier area has decreased by 3921 2 km2 an amount equivalent to 30 of the modern glacier area it is predicted that by the year 2100 the temperature in the monsoonal temperate glaciers of china will rise by 2 1 c the glacier area will decrease by 75 approximately 9900 km2 if the precipitation decreases the retreat of the glaciers will be even faster but the area reduction percentage of the glaciers will not exceed 80 this will no doubt pose a serious threat to the water resources and environment in these regions

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

coda wave attenuation for three regions of georgia sakartvelo using local earthquakes abstract seventy two local earthquakes were analyzed and the quality factor q c was calculated for three regions of georgia using the single scattering model in the frequency range of 1 32 hz standard international association of seismology and physics of the earth s interior iaspei routines for the coda q c determination have been used the coda window varied from 35 to 45 s and the lapse time was up to 63 s the epicenter distances and the focal depths of the earthquakes were up to 50 km and 20 km respectively local magnitudes ranged from 1 7 to 4 1 these earthquakes were recorded by three digital seismic stations equipped with broadband guralp cmg40t seismometers the q c values show strong frequency dependence for three regions the value of q c at frequency 1 hz varies from 35 1 5 3 to 83 8 2 and the frequency parameter n increases from 0 890 0 062 to 1 095 0 056 depending on the model of the coda generation and the considered region observed q c values reflect the average attenuation property of the whole crust beneath each region and are correlated with the seismicity pattern and geology in the studied regions

estimation of coda wave attenuation in the east anatolia fault zone turkey in this study the attenuation of coda waves qc f has been estimated for different lapse times and frequencies in the east anatolian fault zone eafz in turkey using a single back scattering model of s coda envelopes the data include 255 earthquakes recorded by ten stations the frequency dependent qc values are estimated at central frequencies of 1 5 3 6 8 12 and 18 hz using 20 30 40 s lapse time windows along this fault zone the frequency dependent qc obtained for all data and lapse time is qc 57 5f0 82 the entire study area is divided into six subregions according to the magnitude of the earthquakes and the location of the fault segments the estimated average frequency dependent relation for all lapse times are q text c left text i right 3 4 3f 0 9 3 for bingol karliova erzincan triple junction q text c left text ii right 56 3f 0 71 for bingol lake hazar segment q text c left text iii right 68 5f 0 75 for lake hazar sincik segment q text c left text iv right 72 5f 0 78 hazar sincik and celikhan golbasi faults q text c left text v right 59 7f 0 87 for kahramanmaras triple junction and q text c left text vi right 67 4f 0 94 for amanos range and karasu basin the lowest qc is determined between bingol and malatya the highest qc value is along amanos range in addition qc values are calculated for each regions at different lapse times the average qc value of the study region varies from 53 11 at 1 5 hz to 498 41 at 18 hz for 20 s lapse time window as its variation is from 116 11 at 1 5 hz to 749 75 at 18 hz of central frequency for 40 s lapse time window the increase of qc with lapse times changes from one subregion to another along the fault zone the rate of increment is significantly higher in bingol karliova erzincan triple junction than in the other subregions this rapid increase of low qc values in the junction reaches the general attenuation characteristics of the fault at 40 s lapse time finally the low q0 and high n values can be attributed to the energy loss as a result of the heterogeneity and activity along the fault zone the increase of qc with frequency lapse time may be related to heterogeneity decreases with depth the rapid increase of qc with depth in bingol karliova erzincan triple junction may be interpreted that the effect of the northern anatolian fault zone is effective in the upper crust is not so deep compared to eafz

empirical attenuation of ground motion spectral amplitudes in southeastern canada and the northeastern united states a database of 1700 digital seismograms from 186 earthquakes of mag nitude mn 2 5 5 6 that occurred in southeastern canada and the northeastern united states from 1990 to 2003 was compiled maximum likelihood regression analysis of the database was performed to determine a model for the attenuation of fourier spectral amplitudes for the shear window for the vertical and horizontal component of motion for frequencies from 0 2 to 20 hz fourier amplitudes follow a hinged trilinear attenuation model fourier spectral amplitudes decay as r 1 3 where r is hypocentral distance within 70 km of the source there is a transition zone from 70 to 140 km as the direct waves are joined by strong postcritical reflections where the attenuation is described as r 0 2 spectral amplitudes actually increase with distance in this range for low frequencies beyond 140 km the attenuation is well described by r 0 5 corresponding to geometric spreading in two dimensions the associated model for the regional quality factor for frequencies greater than 1 hz can be ex pressed as q 893f 032 q can be better modeled over a wider frequency range 0 2 20 hz by a polynomial expression log q 3 052 0 393 log f 0 945 log f 2 0 327 log f 3 the polynomial expression accommodates the observation that q values are at a minimum about 1000 near 1 hz and rise at both lower and higher frequencies correction factors for the spectral amplitude model that describe the effects of focal depth on the amplitudes and their attenuation are developed using the subset of events with known focal depth the attenuation model is similar to that determined from an earlier study with more limited data atkinson and mereu 1992 but the enlarged database indicates more rapid near source amplitude decay and higher q the attenuation model is used to play back attenuation effects to determine the apparent source spectrum for each earthquake in the database and hence determine moment magnitude m and brune stress drop the events have moment magnitude in the range from 2 5 to 5 stress drop increases with moment magnitude for events of m 4 3 then appears to attain a relatively constant level in the range from 100 to 200 bars for the larger events as previously noted in atkinson 1993b the results of this study provide a useful framework for improving regional ground motion relations in eastern north america they further our understanding of attenuation in the region through analysis of an enlarged ground motion database in particular the inclusion of the three component broadband data gathered over the last decade allows extension of attenuation models to both horizontal and vertical components over a broad frequency range 0 2 20 hz

attenuation of high frequency seismic waves in northeast india summary we studied attenuation of s and coda waves their frequency and lapse time dependencies in northeast india in the frequency range of 1 24 hz we adopted theories of both single and multiple scattering to bandpass filtered seismograms to fit coda envelopes to estimate q for coda waves qc and q for s waves qs at five central frequencies of 1 5 3 6 12 and 24 hz the selected data set consists of 182 seismograms recorded at ten seismic stations within epicentral distance of 22 300 km in the local magnitude range of 2 5 5 2 we found that with the increase in lapse time window from 40 to 60 s q0 qc at 1 hz increases from 213 to 278 while the frequency dependent coefficient n decreases from 0 89 to 0 79 both qc and qs increase with frequency the average value of qs obtained by using coda normalization method for ne india has the power law form of 96 8 21 5 f 1 03 0 04 in 1 24 hz we adopted energy flux model efm and diffusion model for the multiple scattered wave energy in three dimensions the results show that the contribution of multiple scattering dominates for longer lapse time close to or larger than mean free time of about 60 s the estimates of qc are overestimated at longer lapse time by neglecting the effects of multiple scattering some discrepancies have been observed between the theoretical predictions and the observations the difference could be due to the approximation of the uniform medium especially at large hypocentral distances increase in qc with lapse time can be explained as the result of the depth dependent attenuation properties and multiple scattering effect

large and great earthquakes in the shillong plateau assam valley area of northeast india region pop up and transverse tectonics abstract the tectonic model of the shillong plateau and assam valley in the northeast india region the source area for the 1897 great earthquake ms 8 7 and for the four 1869 1923 1930 and 1943 large earthquakes m 7 0 is examined using the high precision data of a 20 station broadband seismic network about 300 selected earthquakes m 3 0 recorded during 2001 2009 are analysed to study the seismicity and fault plane solutions the dominating thrust reverse faulting earthquakes in the western plateau may be explained by the proposed pop up tectonics between two active boundary faults the oldham brahmaputra fault to the north and the dapsi dauki thrust to the south though the northern boundary fault is debated the more intense normal and strike slip faulting earthquakes in the eastern plateau mikir massif and in the assam valley on the other hand are well explained by transverse tectonics at the long and deep rooted kopili fault that cuts across the himalaya and caused the 2009 bhutan earthquake mw 6 3 it is conjectured that the complex tectonics of the shillong plateau and transverse tectonics at the kopili fault make the region vulnerable for impending large earthquake s

3 d seismic structure of the northeast india region and its implications for local and regional tectonics abstract in this study we attempted to estimate 3 d p wave velocity structure of northeast india region using the first arrival data of local earthquakes that were recorded by about 77 temporary permanent local seismic stations the data set the published bulletins include 3494 p wave travel times and 3064 s p travel times from 980 local earthquakes that were located with a minimum of six observations the located earthquakes having a travel time root mean square rms residual 0 49 s and azimuthal gap 180 are selected to compute a 1 d velocity model for the region which is used as initial model for the subsequent 3 d inversions our results demonstrate that the computed 3 d velocity model has significantly improved hypocenter locations of the selected 980 earthquakes by reducing the rms error 0 06 by about 88 with respect to that by the 1 d velocity model the reconstructed p wave velocity v p structure with relocated events reveal strong heterogeneity in lateral as well as in vertical direction corresponding to the local and regional geology tectonics of the region high v p is mapped beneath the shillong plateau mikir hills and in the vicinity of indo burma ranges at shallower crust v p structure is imaged between the shillong plateau and mikir hills at 20 km depth which corresponds to the kopili fault the kopili fault system extends down to 30 km depth as evidenced by the low v p a high v p is imaged below the mikir hills at 40 km depth which is possibly the stress concentrator for high seismic activity along the kopili fault particularly at the fault end the bengal basin south of the shillong plateau is identified as a low v p zone extending down to a depth of about 20 km that indicates the thick alluvium sediments

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

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

variation of seismic coda wave attenuation in the garhwal region northwestern himalaya seismic coda wave attenuation q text c 1 characteristics in the garhwal region northwestern himalaya is studied using 113 short period vertical component seismic observations from local events with hypocentral distance less than 250 km and magnitude range between 1 0 to 4 0 they are located mainly in the vicinity of the main boundary thrust mbt and the main central thrust mct which are well defined tectonic discontinuities in the himalayas coda wave attenuation q text c 1 is estimated using the single isotropic scattering method at central frequencies 1 5 3 5 7 9 12 16 20 24 and 28 hz using several starting lapse times and coda window lengths for the analysis results show that the q text c 1 values are frequency dependent in the considered frequency range and they fit the frequency power law q text c 1 left f right q 0 1 f n the q0 qc at 1 hz estimates vary from about 50 for a 10 s lapse time and 10 s window length to about 350 for a 60 s lapse time and 60 s window length combination the exponent of the frequency dependence law n ranges from 1 2 to 0 7 however it is greater than 0 8 in general which correlates well with the values obtained in other seismically and tectonically active and highly heterogeneous regions the attenuation in the garhwal region is found to be lower than the qc 1 values obtained for other seismically active regions of the world however it is comparable to other regions of india the spatial variation of coda attenuation indicates that the level of heterogeneity decreases with increasing depth the variation of coda attenuation has been estimated for different lapse time and window length combinations to observe the effect with depth and it indicates that the upper lithosphere is more active seismically as compared to the lower lithosphere and the heterogeneity decreases with increasing depth

spatial distribution of scattering loss and intrinsic absorption of short period s waves in the lithosphere of japan on the basis of the multiple lapse time window analysis of hi net data summary propagation of short period s waves through the crust is strongly controlled by scattering loss and intrinsic absorption scattering loss controls the shape of the seismic envelope and the spatial distribution of the energy while intrinsic absorption produces an exponential decay as a function of time which is independent of the coordinates since both parameters have a different effect it is possible to compute them by means of the multiple lapse time window analysis mltwa in this paper high resolution maps of japan for both seismic s wave attenuation parameters are obtained by using the mltwa with data provided by the hi net seismic network the maps show strong regional variation of the parameters the variations depend mainly on the tectonic setting of each region and volcanism mechanisms in the scattering loss maps in the 1 2 hz map there is a very different behaviour between the northeast stronger scattering loss and the southwest much weaker scattering loss in the northeast of japan areas with strong scattering loss correspond mainly to the location of the volcanic arcs in southwest japan chugoku region and the west side of kii peninsula show strong scattering levels for the 4 8 hz and higher frequency bands in hokkaido strong scattering loss and intrinsic absorption can be observed for the lower frequency bands in the sendai plain we find strong scattering loss for all the frequency bands under all these areas low velocity anomalies have been detected in previous works in tohoku area the east side shows lower intrinsic attenuation than the west side this characteristic seems to extend to the southern part of hokkaido and to central japan in kanto area the values of intrinsic absorption are lower than in the surrounding areas but in the region around the itoigawa shizuoka tectonic line and in its western side strong absorption areas are observed the behaviour of each area for intrinsic absorption is similar to the behaviour observed in the q 1c maps the mltwa is based on the hypothesis of multiple isotropic scattering in a medium with the homogeneous distribution of scattering mean free path and intrinsic absorption although these hypotheses are very simple the results are very informative on the characteristics of each region and show the usefulness of studying the properties of scattered seismic waves in the understanding of the properties of the crust

attenuation of short period seismic waves at mt vesuvius italy we analysed short period seismograms from about 250 very local events recorded by a network of high dynamic range short period seismic stations deployed on mt vesuvius to estimate the site corrected short period seismic attenuation we calculated qc 1 the inverse of the quality factor for coda waves for short lapse times 12 s and qp 1 and qs 1 the inverse of the direct body wave quality factors for p and s waves follow ing shallow ray paths we used the single scattering assumption to fit the amplitude envelopes of the coda at different frequency bands obtaining a qc 1 slowly varying with frequency similar to values measured for other volcanoes at the same lapse time site corrected qp 1 and qs 1 were estimated using the frequency decay method for both p and s waves in two frequency bands 1 6 hz and 15 24 hz results show that qp 1 is 0 028 in both frequency bands and qs 1 is 0 015 and 0 017 at low and high frequencies respectively almost independent of the frequency and that the value of qp 1 is about twice that of qs 1 as measured worldwide a check was made by measuring the broadening of the first p wave pulse with station source distance finding qp 1 0 024 using the independent estimates of qc 1 and qs 1 we separated the intrinsic from the scattering quality factor at mt vesuvius obtaining a high scattering and a low intrinsi c q 1 as already observed for other volcanoes this result confirms the hypothesis of the predominant role of the scattering phenomena with respect to the intrinsic dissipation in the seismogram formation for volcanic earthquakes

intrinsic and scattering attenuation in the crust of the abu dabbab area in the eastern desert of egypt abstract fifty five microearthquakes recorded by a digital temporary seismic network in the abu dabbab area in the eastern desert of egypt were used to estimate the direct s wave q coda q c intrinsic q i and scattering quality factors q s sato s sato h 1977 single scattering assumption was used to fit the amplitude envelopes of the coda at seven central frequency bands 1 5 3 6 9 12 18 and 24 hz obtaining a q c varying with frequency as generally observed in tectonically active areas lapse time dependence was also studied for the area with the coda waves analyzed at window lengths ranging from 10 to 40 s starting from the onset of the s wave arrival the direct s wave q was estimated using the coda normalization method aki k 1980a the frequency dependence of q was investigated for the direct s waves and coda waves results show a low quality factor and a high frequency parameter indicating that the upper lithosphere of the abu dabbab area is seismically active and heterogeneous using the independent estimates of q c and q the intrinsic quality factor q i was separated from the scattering quality factor the results suggest that intrinsic dissipation plays a predominant role with respect to scattering phenomena in the area the obtained q values seem closer to those reported by analyzing volcano tectonic earthquakes this finding reflects that the cause of abu dabbab earthquake swarms might be igneous activity where the magma is ascending through joints or serpentinized joints that are dewatering

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

the attenuation mechanism of seismic waves in northwestern himalayas summary we analysed local earthquake waveforms recorded on a broad band seismic network in northwestern himalayas to compute the intrinsic and scattered attenuation parameters from coda waves similar to other tectonically active and heterogeneous regions attenuation frequency relation for western himalaya is q 1 113 7 f 1 01 0 05 where qc is the coda q parameter intrinsic q 1 and scattering q 1 attenuations was separated using qc and direct s wave q data qd it is observed that estimated q 1 is close to q 1 and both of them are much larger than q 1 suggesting that coda decay is predominantly caused by intrinsic attenuation at higher frequencies both the attenuation parameters qc and qd are similar indicating that coda is predominantly composed of back scattered s waves at these frequencies

a precursorlike change in coda excitation before the western nagano earthquake ms 6 8 of 1984 in central japan temporal variations of coda duration were studied in relation to a crustal earthquake september 14 1984 which took place near the nw corner of the kanto tokai microearthquake observation network of the national research center for disaster prevention in japan vertical seismograms recorded at station ger close to the main shock epicenter 24 km between february 1982 and december 1984 were analyzed a precursorlike change was found in the relation between coda duration and average magnitude for 185 earthquakes which occurred in a small volume in the middle of the aftershock region the average magnitude is the arithmetic mean of station magnitudes which are calculated from the maximum amplitudes of direct waves coda durations for earthquakes of the same average magnitude were significantly longer during the 16 month period preceding the main shock than those before and after this period with a confidence level of 99 9 the increase in coda durations was about 3 s on average in this period the coda duration anomaly was significant for lapse time shorter than 30 s which corresponds to a travel radius less than 50 km although no clear temporal change was found in the residuals of station magnitude measured at ger from average magnitude an attenuation change in the preevent period can not be ruled out due to the large scatter of data crack formation however is the most plausible mechanism for an increase in scattering intensity around the focal region in the stress accumulation stage and is consistent with other precursory observations clusters of cracks in the heterogeneous earth medium might be big enough to scatter high frequency seismic waves even though each individual crack may be very small

attenuation of coda waves in the garhwal himalaya india abstract q c estimates have been obtained by analysing coda waves of seven local earthquakes recorded in the garhwal himalaya the earthquakes have their epicentral distances within 100 km focal depths up to 20 km with 2 4 m l 4 9 q c values have been computed at central frequencies of 1 5 3 0 6 0 12 0 and 18 0 hz for different earthquake stations falling in the lapse time window of 30 60 s using a single backscattering model the mean value of q c shows a dependence on frequency varying from 206 at 1 5 hz to 2090 at 18 hz the frequency dependence average q c relationship q c q 0 f n has been obtained for the region as q c 126 f 0 95 which indicates that attenuation at higher frequencies is less pronounced q c values estimated for the region represent the average attenuation properties for a surface area of about 20 000 km 2 in a circular shape with a radius of about 80 km assuming single backscattering

stability of coda q in the region of parkfield california view from the u s geological survey parkfield dense seismograph array many investigators have proposed that changes in the rate at which the coda decays may be an intermediate term precursor to moderate to large earthquakes parkfield california on the san andreas fault is a promising location for studying premonitory changes in coda q qc because a large earthquake is likely to occur there we have investigated qc using recordings from the u s geological survey parkfield dense seismograph array which is a digital array with 14 triaxial sensors and an aperture of about 1 km for each earthquake we can measure qc from up to 42 recordings their average is more stable than the measurement from a single station using clustered seismicity we have developed criteria for selecting events and reducing scatter in the measurement the qc value determined from a seismogram depends on the position and length of the analysis window thus qc should always be measured from the same length window starting at the same lapse time regardless of the source location in addition the band limited signal to noise ratio at the end of the analysis window is important qc determined in two frequency bands 4 8 hz and 8 16 hz from a tight cluster of 26 events which occurred between december 1989 and january 1994 has not changed despite m 4 7 and m 4 6 events in october 1992 and november 1993 qc measured from local events 60 km in three frequency bands shows larger scatter but has also not changed during this period for monitoring qc observations should include array averaged measurements from a single lapse time because qc measurements made using an analysis window that starts at a constant multiple of the s wave lapse time depend on epicentral distance a procedure combining the evaluation of the time and distance dependences of qc also gives stable observations

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

intrinsic and scattering attenuation of the mt fuji region japan summary mount fuji is the focus of intense study because of its potential hazard signaled by seismic geologic and historical activity based on extensive seismic data recorded in the vicinity of mt fuji coda quality factor q 1c using a single scattering model hypothesis and intrinsic and scattering quality factor q 1i and q 1s using the multiple lapse time window mltw method were measured to focus the study on the magmatic structure below mt fuji the data were separated into two groups a near fuji region of rays traversing an area with radius 5 km around the summit r 20 km this classification shows the largest discrepancy of q 1c at a range of sampling volumes corresponding to overlapped sampling depth of about 80 km further the spatial division shows significant difference of q 1i and q 1s at hypocentral distance of 80 km the large difference of q 1s in bandwidths 2 4 and 4 8 hz indicates lithospheric heterogeneity beneath mt fuji with a characteristic heterogeneity scale length of about 1 km the results have a small error range due to the large data sample showing that all q 1 values in the near fuji area are greater than those of the far fuji area and q 1i for both the near and far fuji areas is higher than q 1s at high frequencies the q 1i and q 1s values for far fuji are in the range of values for typical non volcanic areas the q 1i values of the near fuji area are lower than those of other volcanic areas considered where as values of q 1s are not the low q 1i for the volcanic region of near fuji suggests that the magmatic activity indicated by percent partial melt in the vicinity of mt fuji is not as active as hot spot volcanoes such as kilauea hawaii

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

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

the effects of attenuation and site on the spectra of microearthquakes in the shillong region of northeast india microearthquake spectra from the shillong region are analyzed to observe the effect of attenuation and site on these spectra the spectral ratio method is utilized to estimate the q values for both p and s waves in the subsurface layer wherein the ratio of spectral amplitudes at lower and higher frequencies are taken into consideration for three stations at varying epicentral distances average estimates of qp and qs are 178 and 195 the ratio of qs to qp is estimated to be greater than 1 in major parts of the shillong area which can be related to the dry crust prevailing in the shillong region typically the variation in corner frequencies for these spectra is inferred to be characteristic of the site simultaneously observations from spectral content of local earthquakes recorded at two different stations with respect to the reference site yield greater amplification of incoming seismic signals in the frequency range of 2 5 hz which is found to be well supported by the existing local lithology pertinent to that region