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S U M M A R YDetermining the relative amount of attenuation caused by scattering and intrinsic absorption is important to the understanding of wave propagation and attenuation in the heterogeneous lithosphere. A recently developed model based on radiative transfer theory provides a method for quantifying the ratio of scattering loss to total attenuation, which is called seismic albedo. The basic assumption of this model is that the medium is composed of a uniform distribution of isotropic scatterers. The method is based on a theoretical result showing that the variation with sourcereceiver distance in the seismic energy integrated over time is directly related to albedo and total attenuation, Q;'. We introduce an improvement in the previously used method which results in more reliable estimates of seismic albedo and Q;', which can be used to calculate the losses due to scattering and intrinsic absorption. We call our new method multiple lapse-time window analysis. The improvement is based on the observation that the relationship between integrated energy and distance is strongly dependent on the time duration over which energy is integrated. We show that parameters describing media attenuation can be estimated from measurements of two ratios from the integrated energy versus distance relations compiled using two time windows for integration. One ratio is the energy integrated from 0 to 15 s after the S-wave arrival observed at 50 km source-receiver distance divided by the energy in the same time interval observed at 150 km distance. The second ratio is the energy integrated from 0 to 15 s observed at 150 km divided by that from 30 to 100 s observed at the same source-receiver distance.Integrated energy calculated for many source-receiver pairs may be corrected for relative site amplification and relative source amplitude determined using the coda-wave method. These corrections allow us to use data from many sourcereceiver pairs to find a well-constrained energy versus distance relation. Site amplifications relative to a reference station are calculated for three frequency bands by determining the ratio of the spectral amplitude in each band at one station for a 10s time window to that at the reference station in the same 10s time window. Ratios are calculated for many 10s time windows for each of 10 events. For each station, we found little scatter in the ratios among the windows and events used. The average of all the ratios obtained for each station was taken to be the site amplification relative to the reference station.We applied the multiple lapse-time window analysis method and source-site correction procedures to data from the Kanto-Tokai region of Japan and found that intrinsic attenuation Q;' is larger than scattering attenuation Q;' over three frequency bands; 1-2, 2-4, and 4-8Hz. We found that estimates of coda-wave attenuation Q,' made using the coda-wave decay method, are similar to the 787 788 M. Fehler et al intrinsic attenuation Q;' for the frequency range of 2-8Hz. We were unable to fit data for ...

A new method recently developed by Hoshiba et al. [1991] was used to separate the effects of scattering Q-1 and intrinsic Q-1 from an analysis of the S wave and its coda in Hawaii, Long Valley, and central California. Unlike the method of Wu [ 1985], which involves integration of the entire S wave energy, the new method relies on the integration of the S wave energy for three successive time windows as a function of hypocentral distance. Using the fundamental separability of source, site, and path effects for coda waves, we normalized the energy in each window for many events recorded at many stations to a common site and source. We plotted the geometric spreading-corrected normalized energy as a function of hypocentral distance. The data for all three time windows were then simultaneously fit to Monte Carlo simulations assuming isotropic body wave scattering in a medium of randomly and uniformly distributed scatterers and uniform intrinsic Q-1. In general, for frequencies less than or equal to 6.0 Hz, scattering Q-1 was greater than intrinsic Q-l, whereas above 6.0 Hz the opposite was true. Model fitting was quite good for frequencies greater than or equal to 6.0 Hz at all distances, despite the model's simplicity. The small range in energy values for any particular time window demonstrates that the site effect can be effectively stripped away using the coda method. Though the model fitting generally worked for 1.5 and 3.0 Hz, the model has difficulty in fitting the whole distance range simultaneously, especially at short distances. Despite the poor fit at low frequency, the results generally support that in all three regions the scattering Q-1 is strongly frequency dependent, decreasing proportional to frequency or faster, whereas intrinsic Q-1 is considerably less frequency dependent. This suggests that the scale length of heterogeneity responsible for scattering is at least comparable to the wavelength for the lowest frequencies studied, of the order of a few kilometers. The lithosphere studied in all three regions can be characterized as a random medium with velocity fluetuarion characterized by exponential or Gaussian autocorrelation functions which predict scattering Paper number 91JB03094. 0148-0227/92/91 JB-03094505.00 Q-1 decreasing proportional to frequency or faster. For all frequencies the observed coda Q-1 is intermediate between the total Q-1 and expected coda Q-1 in contrast with theoretical results for an idealized case of uniform distribution of scatterers and homogeneous absorption which predict that coda Q-1 should be close to the intrinsic Q-1. We will discuss possible causes for this discrepancy. Soc., 82, 57-80, 1985. Wu, R. S., and K. Aki, Multiple scattering and energy transfer of seismic waves --Separation of scattering effect from intrinsic attenuation, II, Application of the theory to Hindu Kush region, Pure At)t)l. Geophys., 128, 49-80, 1988. Zeng, Y., F. Su, andS[. Aki, Scattering wave energy propagation in a medium with randomly distributed isotropic scatterers, 1, Theory, J. Geoph...

Two seismic wave attenuation factors,

When an earthquake occurs, a certain amount of time elapses before destructive seismic energy hits nearby population centers. Though this time is measured on the order of seconds, depending on the proximity of the rupture to a given city or town, a new public safety program in Japan is taking advantage of the fact that seismic energy travels slower than electronic communication.In this program, the Japan Meteorological Agency (JMA) rapidly determines the hypocenter (earthquake epicenter and focal depth) and magnitude of the earthquake by using real-time data from stations near the hypocenter. The distribution of strong ground shaking is anticipated quickly, and then the information is delivered immediately to government officials, representatives from various industries, members of the news media, and individuals before strong ground shaking reaches them. For example, on receiving the warning, the control room of a railway company can send an emergency notice to all train drivers to stop their trains immediately, elevators in buildings can be triggered to stop at the nearest floor and open their doors automatically, and surgeons can temporarily suspend their surgical operations to avoid risk to patients on operating tables.This innovative new service, called Earthquake Early Warning (EEW), started nationwide in Japan and became fully operational in October 2007. This service is definitely different from earthquake prediction. Although it is currently impossible to be aware of earthquakes before their occurrence (earthquake prediction), EEW operates with the assumption that it is possible to warn people located at a certain distance from the hypocenter before strong ground shaking reaches them.Even though the interval between the delivery of EEWs and the time when strong shaking reaches people is relatively short (counted in seconds), EEWs can be a useful and powerful tool for mitigating an earthquake disaster by giving people enough time to take appropriate safety measures in advance of strong shaking. Determining Hypocentral Parameters and Anticipating Seismic IntensityEarthquakes occur when stressed rock moves through brittle rupture. Two types of seismic waves are radiated from the hypocenter: One is the P wave, which travels at about 7 kilometers per second, and the other is the S wave, which travels at about 4 kilometers per second.EEW technology not only takes advantage of the relatively slow velocity of the seismic waves as compared with instantaneous electronic communication, but it also uses the difference in arrival time between P and S waves. The S wave is slower than the P wave, but the amplitude of the S wave is usually 3-10 times larger than that of the P wave. This generally means that stronger shaking is observed along the S wave.The hypocenter and magnitude of an earthquake are determined as quickly as possible using only early parts of the P waves at a few stations close to the hypocenter. Using information about the hypocenter and magnitude, the arrival time of the S waves and seismic intensit...