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Author

Haruo Sato

Bio: Haruo Sato is an academic researcher from Tohoku University. The author has contributed to research in topics: Scattering & Seismogram. The author has an hindex of 43, co-authored 141 publications receiving 6641 citations. Previous affiliations of Haruo Sato include Showa University & Saitama Medical University.
Topics: Scattering, Seismogram, Attenuation, Coda, Wavelength


Papers
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Book
19 Dec 1997
TL;DR: In this paper, a three-component Seismogram Envelope Synthesis based on the Radiative Transfer Theory (RTT) was proposed for earthquakes using Scattering Amplitudes from the Born Approximation.
Abstract: Introduction- Heterogeneity in the Lithosphere- Phenomenological Approaches to Seismogram Envelopes in short-periods- Born approximation for Wave Scattering in Random Media- Attenuation of High-Frequency Seismic Waves- Synthesis of Three-Component Seismogram Envelopes for Earthquakes Using Scattering Amplitudes from the Born Approximation- Envelope Synthesis Based on the Radiative Transfer Theory: Multiple Scattering Models- Parabolic approximation and Envelope Synthesis based on the Markov Approximation Summary and Epilogue

890 citations

Journal ArticleDOI
TL;DR: In this paper, the elastic energy propagation in a three dimensional infinite elastic medium, in which scatterers are distributed homogeneously and randomly, is investigated by a statistical method, and a space-time distribution of the mean energy density of the scattered waves is obtained as Es(r, t)=(W 0/4πlVtr)1n((Vt+r)/(Vt-r)) for Vt≥r, where r is the distance from the source and W 0 is the total energy radiated.
Abstract: The elastic energy propagation in a three dimensional infinite elastic medium, in which scatterers are distributed homogeneously and randomly, is investigated by a statistical method. A single isotropic scattering process is investigated. The elastic medium is characterized by the wave velocity V and the distribution of the scatterers is characterized by the mean free path l. It is assumed that the elastic energy is radiated spherically from the source at a time t=0 in a short time duration. A space-time distribution of the mean energy density of the scattered waves is obtained as Es(r, t)=(W0/4πlVtr)1n((Vt+r)/(Vt-r)) for Vt≥r, where r is the distance from the source and W0 is the total energy radiated. A uniform spatial distribution is constructed far behind the wave front and near the source. The mean energy density Es is proportional to t-2 for t_??_2r/V and independent of r and W0. Several important properties of coda waves observed near the hypocenter are explained qualitatively by this solution when heterogeneities in the earth are interpreted as the scatterers and Es corresponds to the power spectrum of coda waves.

458 citations

Journal ArticleDOI
TL;DR: The field of seismic interferometry has at its foundation a shift in the way we think about the parts of the signal that are currently filtered out of most analyses as mentioned in this paper, the multiply scattered parts of seismic waveforms and background noise (whatever is recorded when no identifiable active source is emitting, and which is superimposed on all recorded data).
Abstract: Turning noise into useful data—every geophysicist's dream? And now it seems possible. The field of seismic interferometry has at its foundation a shift in the way we think about the parts of the signal that are currently filtered out of most analyses—complicated seismic codas (the multiply scattered parts of seismic waveforms) and background noise (whatever is recorded when no identifiable active source is emitting, and which is superimposed on all recorded data). Those parts of seismograms consist of waves that reflect and refract around exactly the same subsurface heterogeneities as waves excited by active sources. The key to the rapid emergence of this field of research is our new understanding of how to unravel that subsurface information from these relatively complex-looking waveforms. And the answer turned out to be rather simple. This article explains the operation of seismic interferometry and provides a few examples of its application.

374 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a method for quantifying the ratio of scattering loss to total attenuation, called seismic albedo, which can be used to calculate the losses due to scattering and intrinsic absorption.
Abstract: SUMMARY Determining 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

307 citations

Journal ArticleDOI
TL;DR: In this paper, a unified model is proposed for explaining the frequency dependence of Q−1 and the formation of velocity seismograms by a single scattering process, which is spatially characterized by the exponential autocorrelation function.
Abstract: A unified model is proposed for explaining the frequency dependence of Q−1 and the formation of velocity seismograms by a single scattering process. Adopting Birch's law and a linear correlation between P and S wave velocities, we statistically describe the inhomogeneous medium by one random fluctuation, which is spatially characterized by the exponential autocorrelation function. We calculate Q−1 for P and S waves on the basis of the Born approximation, supposing seismic waves attenuate due to scattering largely by rapidly fluctuating random structure. Resulting Qs−1 explains the observed frequency dependence well, when the mean square fractional fluctuation and the correlation distance are chosen to be 0.01 and 2 km, respectively. Nonspherical radiation due to a point shear dislocation and frequency dependent nonisotropic scattering including conversion between P and S waves complicate the seismograms. Taking those complexities into account, we synthesize the “envelopes” of three-component velocity amplitudes of P and S coda waves by summing up energy singly scattered by distributed inhomogeneities. From numerical calculations, we found that the radial component of the P coda wave is excited even in the nodal direction of the P wave radiation mostly due to SP scattering occurring near the hypocenter. The P coda waves appearing on the transverse components are a complex mixture of PP, PS, and SP scattering. The S coda waves are excited mostly due to SS scattering in all directions, and appear in all three components; their polarizations are controlled by the radiation pattern even in the later part of S coda waves.

254 citations


Cited by
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Book
25 Jan 1991
TL;DR: The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws -producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events.
Abstract: This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

3,802 citations

Journal ArticleDOI
24 Jan 2003-Science
TL;DR: This seismological example shows that diffuse waves produced by distant sources are sufficient to retrieve direct waves between two perfectly located points of observation and has potential applications in other fields.
Abstract: The late seismic coda may contain coherent information about the elastic response of Earth. We computed the correlations of the seismic codas of 101 distant earthquakes recorded at stations that were tens of kilometers apart. By stacking cross-correlation functions of codas, we found a low-frequency coherent part in the diffuse field. The extracted pulses have the polarization characteristics and group velocities expected for Rayleigh and Love waves. The set of cross-correlations has the symmetries of the surface-wave part of the Green tensor. This seismological example shows that diffuse waves produced by distant sources are sufficient to retrieve direct waves between two perfectly located points of observation. Because it relies on general properties of diffuse waves, this result has potential applications in other fields.

1,139 citations

Book
19 Dec 1997
TL;DR: In this paper, a three-component Seismogram Envelope Synthesis based on the Radiative Transfer Theory (RTT) was proposed for earthquakes using Scattering Amplitudes from the Born Approximation.
Abstract: Introduction- Heterogeneity in the Lithosphere- Phenomenological Approaches to Seismogram Envelopes in short-periods- Born approximation for Wave Scattering in Random Media- Attenuation of High-Frequency Seismic Waves- Synthesis of Three-Component Seismogram Envelopes for Earthquakes Using Scattering Amplitudes from the Born Approximation- Envelope Synthesis Based on the Radiative Transfer Theory: Multiple Scattering Models- Parabolic approximation and Envelope Synthesis based on the Markov Approximation Summary and Epilogue

890 citations

Journal ArticleDOI
TL;DR: In this article, the inverse problem of interpreting seismic reflection data can be posed with sufficient generality using the concepts of inverse theory, which consists of obtaining the Earth model for which the predicted data best fit the observed data.
Abstract: The problem of interpretation of seismic reflection data can be posed with sufficient generality using the concepts of inverse theory. In its roughest formulation, the inverse problem consists of obtaining the Earth model for which the predicted data best fit the observed data. If an adequate forward model is used, this best model will give the best images of the Earth’s interior. Three parameters are needed for describing a perfectly elastic, isotropic, Earth: the density ρ(x) and the Lame parameters λ(x) and μ(x), or the density ρ(x) and the P-wave and S-wave velocities α(x) and β(x). The choice of parameters is not neutral, in the sense that although theoretically equivalent, if they are not adequately chosen the numerical algorithms in the inversion can be inefficient. In the long (spatial) wavelengths of the model, adequate parameters are the P-wave and S-wave velocities, while in the short (spatial) wavelengths, P-wave impedance, S-wave impedance, and density are adequate. The problem of inversion o...

817 citations

Journal ArticleDOI
13 Jul 2006-Nature
TL;DR: Strong evidence is provided that these earthquakes occur on the plate interface, coincident with the inferred zone of slow slip, and the locations and characteristics of these events suggest that they are generated by shear slip during otherwise aseismic transients, rather than by fluid flow.
Abstract: Non-volcanic seismic tremor was discovered in the Nankai trough subduction zone in southwest Japan and subsequently identified in the Cascadia subduction zone. In both locations, tremor is observed to coincide temporally with large, slow slip events on the plate interface downdip of the seismogenic zone. The relationship between tremor and aseismic slip remains uncertain, however, largely owing to difficulty in constraining the source depth of tremor. In southwest Japan, a high quality borehole seismic network allows identification of coherent S-wave (and sometimes P-wave) arrivals within the tremor, whose sources are classified as low-frequency earthquakes. As low-frequency earthquakes comprise at least a portion of tremor, understanding their mechanism is critical to understanding tremor as a whole. Here, we provide strong evidence that these earthquakes occur on the plate interface, coincident with the inferred zone of slow slip. The locations and characteristics of these events suggest that they are generated by shear slip during otherwise aseismic transients, rather than by fluid flow. High pore-fluid pressure in the immediate vicinity, as implied by our estimates of seismic P- and S-wave speeds, may act to promote this transient mode of failure. Low-frequency earthquakes could potentially contribute to seismic hazard forecasting by providing a new means to monitor slow slip at depth.

773 citations