S U M M A R YDifferential waveform analysis provides an excellent tool for studying the attenuation properties of the top of the inner core. W e analyse 108 P K P ( B C ) versus P K P ( D F ) waveforms from Global Digital Seismograph Network (GDSN) verticalcomponent seismograms to constrain the frequency and depth dependency of Qa in this region. W e use both frequency-and time-domain techniques. In the timedomain method, the BC phase is mapped onto the DF phase using an attenuation band operator. T h e mapping operator is parameterized by the upper and lower cut-off frequencies of the absorption band, the time shift required to align these two phases, and t*, the integrated effect of Q;' in the top of the inner core. In the frequency-domain analysis, multitaper spectral estimation is used to compute the complex spectrum of the two phases. T h e shape of the amplitude spectrum of the spectral ratio between these two phases gives an estimate of en.Similar results are obtained from frequency-and time-domain analysis but the Qa obtained from frequency-domain analysis is approximately 20 per cent greater than the value obtained from time-domain analysis. W e prefer the frequency-domain results since they are not affected by the presence of noise at higher frequencies.Apparent Qa values exhibit considerable scatter with no clear frequency or depth dependence. W e find that the average value of Qa in the t o p of the inner core is about 360 which is consistent with previous body wave studies but differs by a factor of two from values obtained from studies of the decay of free oscillations.

We analyze several thousand high-quality, globally recorded $S-$ (Q•) in the upper m•ntle. We use • multit•per frequency domain technique to measure •ttenu•tion, p•r•meterized by • t* operator, •nd implement • robust estimation technique to compute t* •nd its v•ri•nce. The differential w•veform technique minimizes the effect of f•ctors such •s finite source duration •nd structural complexity near the source •nd receiver so the differential SS-S w•veforms •re m•inly sensitive to the she•r •ttenu•tion in the upper m•ntle under the SS bounce point. We use seismograms recorded •t r•nges of 45 ø to 100 ø •nd compute the SS-S differential t* from the broadening of the SS w•veform relative to the Hilbert transform of the S w•veform. A c•reful choice of fitting windows •11ows us to reduce the biasing effects of interfering phases which c•n •ffect t* by up to 0.5 s. The t* residuals (with respect to preliminary reference E•rth model (PREM)) v•ry by •1.5 s with •n •ver•ge of • 0.24 s. Our study suggests •n •ver•ge Q• v•lue of 112 (most of the l•ter•l v•ri•tions of Q• •re within 30% of this v•lue) in the top 400 km of the m•ntle, slightly lower th•n the PREM v•lue of 128. There is • qualitative correlation of t* residual with tectonic region with distinctly higher •ttenu•tion observed under young oceans compared to platforms •nd shields. Also, the l•ter•l v•ri•tions of the residuals •re similar in trend to those observed in studies of the •ttenu•tion of ScS multiples. At long w•velengths, the Q• m•p shows • modest correlation with she•r w•ve •ttenu•tion m•ps computed from surface w•ve •n•lyses •nd with the p•tterns of l•ter•l v•ri•tions of she•r velocities •t certain upper-m•ntle depths predicted by the model S16B30. The correlation with the velocity model is highest •t 300-500 km depth indicating that there m•y be • contribution to long-w•velength •ttenu•tion from relatively deep regions. Formal inversion for •n upper m•ntle Q• model shows that while l•ter•l resolution is quite good, depth resolution is poor •s might be expected. Better depth resolution must •w•it combined body w•ve •nd surface w•ve inversions. (the ratio of the temperature to the melting temperature) than are seismic velocities [e.g., $ato et al., 1989], which means that the elastic moduli in Earth are frequency dependent. Because of this, Karato [1993] has shown that anelasticity can significantly affect the apparent relative temperature derivatives of seismic velocities and three-dimensional (3-D) variations in attenuation would inevitably lead to 3-D variations in these derivatives. This could have a significant impact on the construction of seismic tomographic models. Physical dispersion becomes even more important when seismic data with different characteristic frequencies are used in the construction of Earth models, a point which has been known since the mid !970s [Liu eta!., 1976; Anderson and Given, 1982]. 22,273 22,274 BHATTACHARYYA ET AL.: UPPER MANTLE ATTENUATIONIdeally, seismologists would solve simultaneously for the elastic and anelastic pr...

SUMMARYRecently developed three-dimensional global seismic-velocity models have demonstrated location improvements through independent regional and teleseismic travel-time calibration. Concurrently, a large set of high quality ground truth (GT) events with location accuracies 10 km or better (GT0-GT10) has been collected for Europe, the Medite rranean, North Africa, the Middle East, and Western Eurasia. In this study, we validate event location improvements using this new data set by applying the regional and teleseismic modelbased travel-time calibrations (independently and jointly) to demons trate that significant improvements can be achieved using 3D global models for locating small events with sparse network data. Besides relocating events using all station arrivals, a subset of the GT events was also relocated using controlled station geom etries generated from a "constrained bootstrapping" technique. The advantages of this approach include: (1) generating simulated sparse networks (Simulated Sparse Network Bulletin or SSNB), (2) increasing the statistical power of the tests, (3) reducing the effect of correlated errors to ensure valid 90% error ellipse coverage statistics, and (4) measuring location bias due to un-modeled three-dim ensional (3D) Earth structures.With respect to the GT events, we compared event relocations, with and without t raveltime calibrations, considering statistics of mislocation, error ellipse area, 90% coverage, origin time bias, origin time errors, and misfit. Relocations of more than 1000 GT0-GT10 reference events show significant reductions in location bias and uncertainty. Pn and/or P calibration reduces mislocation for between 60% and 70% of the events. Joint regional Pn and teleseismic P travel-time calibration provided the largest location improvements, and approximately achieved GT5 accuracy levels. Due to correlated 3 errors, calibrated event locations using large numbers of stations have deficient 90% error ellipse coverage. However, the coverages derived from the model errors are appropriate for sparse regional and teleseismic networks. This validation effort demonstrates that the global model-based travel-time calibrations of Pn and teleseismic P travel-time reduce both location bias and uncertainty over wide areas.

We construct and evaluate a new three-dimensional model of crust and upper mantle structure in Western Eurasia and North Africa (WENA) extending to 700 km depth and having 1°p arameterization. The model is compiled in an a priori fashion entirely from existing geophysical literature, specifically, combining two regionalized crustal models with a high-resolution global sediment model and a global upper mantle model. The resulting WENA1.0 model consists of 24 layers: water, three sediment layers, upper, middle, and lower crust, uppermost mantle, and 16 additional upper mantle layers. Each of the layers is specified by its depth, compressional and shear velocity, density, and attenuation (quality factors, Q P and Q S ). The model is tested by comparing the model predictions with geophysical observations including: crustal thickness, surface wave group and phase velocities, upper mantle P n velocities, receiver functions, P-wave travel times, waveform characteristics, regional 1-D velocities, and Bouguer gravity. We find generally good agreement between WENA1.0 model predictions and empirical observations for a wide variety of independent data sets. We believe this model is representative of our current knowledge of crust and upper mantle structure in the WENA region and can successfully be used to model the propagation characteristics of regional seismic waveform data. The WENA1.0 model will continue to evolve as new data are incorporated into future validations and any new deficiencies in the model are identified. Eventually this a priori model will serve as the initial starting model for a multiple data set tomographic inversion for structure of the Eurasian continent.

[1] Simultaneous infrasonic, visual, and ocean-bottom pressure sensor observations of large swells on the island of Kauai and small to medium-sized surf on the island of Hawaii yielded a clear relationship between breaking wave height and low-frequency atmospheric sound amplitudes in the 1 -20 Hz frequency range. These experiments confirmed that infrasound can be generated by barreling waves as well as by waves crashing against rocky shorelines and exposed ledges. As will be demonstrated in a companion paper, breaking wave period may also be extracted from infrasound data. The results of these experiments demonstrate that low-frequency sound may be used for real-time estimates of the amplitude, period, and spatial distribution of surf in the littoral zone, with a potential application to the identification of breaking wave types.

Infrasound arrays in the Pacific and Indian oceans that are part of the International Monitoring System (IMS) of the Comprehensive Nuclear Test Ban Treaty (CTBT) recorded distinct signatures associated with the 26 December 2004 Sumatra earthquake (M/9, http://earthquake.usgs.gov/) and tsunami. Although the radiation of infrasound from large continental earthquakes is established [e.g., Le Pichon et al., 2003], the results presented in the present article indicate that islands undergoing significant surface displacements from submarine earthquakes can produce infrasound. Far more intriguing is the possibility that the initiation and propagation of a tsunami may produce low‐frequency sound near the source as well as along coastlines and basins. Since distant sound effectively propagates at ˜300 m/s and tsunamis propagate at ˜200 m/s, precursory sound could potentially be used as a discriminant for tsunami genesis.

The temporal and spatial distribution of seismicity in the Coso Range, the Coso geothermal field, and the Indian Wells Valley region of southeast-central California are discussed in this paper. An analysis of fault-related seismicity in the region led us to conclude that the Little Lake fault and the Airport Lake fault are the most significant seismogenic zones. The faulting pattern clearly demarcates the region as a transition between the San Andreas-type strike-slip regime to the west and the Basin and Range extension regime to the east. We present the spatial and temporal variations in seismicity immediately following significant earthquakes in nearby regions from 1983 to 1999 with special emphasis on larger earthquakes (M Ն 5) in 1995-1998. The Ridgecrest earthquakes of 1995 show a complicated faulting pattern as the rupture changed from normal slip to right slip at depth. The interrelationships between the Coso Range earthquakes of 1996 and 1998 are presented as a set of conjugate events. Analysis of earthquake source mechanisms shows evidence for lateral variations in the faulting pattern in southeast-central California. Earthquake focal mechanisms are used to estimate local stress orientation within the Coso geothermal field. We have identified a boundary between a transpressional regime and a transtensional regime inside the field that correlates with observed spatial variations of heat flow and seismic attenuation, velocity, and anisotropy.Bhattacharyya, J.

We present a regionalized crustal model of Western Eurasia, WEA. The model is constructed using results from published studies and maps of geological and geophysical parameters in this region, and was developed in conjunction with the updated regionalization of Middle East and North Africa by Walter et al. [2000]. As this is the first realization of our Eurasian modeling effort, we have limited ourselves to only twelve broad regions. Particular attention has been given to identifying the boundaries for each region. The main use of this model will be to assist in monitoring the Comprehensive Nuclear Test Ban Treaty (CTBT). Specifically, this model will help us to calibrate and predict the travel time and amplitudes of various regional seismic phases and to locate events accurately. Our model based approach allows us to readily calibrate both the seismic and the aseismic parts of western Eurasia. Each region is specified by an onedimensional model of compressional and shear velocities, densities and layer thicknesses.Further improvements to this model will involve, but not be limited to, increasing the spatial coverage toward the east and west of Eurasia, identify sub-regions based on their distinct physical properties and the use of new and improved body wave and surface wave datasets. In the future, we expect to use this model and its successors to be the baseline model for calibration techniques, e.g., kriging, to improve our capability to detect, locate and discriminate different seismic events in Eurasia.2