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Haruo Sato - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Three-Component Seismogram Envelopes of a Small Earthquake
Seismic Wave Propagation and Scattering in the Heterogeneous Earth : Second Edition, 2011Co-Authors: Haruo Sato, Michael Fehler, Takuto MaedaAbstract:The initial direction of motion of the P-wave, the amplitudes of the direct P- and S-waves, and the high-frequency character of the P- and S-coda envelopes on all three components of motion from a local microearthquake are influenced by the angle between the fault plane and the receiver and the scattering characteristics of the lithosphere. To better understand the effects of scattering on recorded regional Seismograms, we desire a method to synthesize three-component Seismogram envelopes for realistic earthquake sources in an inhomogeneous medium. The simplest way to synthesize Seismograms is to sum up all waves scattered by distributed heterogeneities in the time domain. It is easier to synthesize the MS envelope by adding the power of scattered waves. Assuming the complete incoherence of scattered waves, Malin (1980) synthesized the MS acoustic-wave envelope by summing up scattered wave power. Extending the method of summing up single scattered energy, we will present a way to synthesize three-component Seismogram envelopes resulting from realistic earthquake sources in an infinite random medium, where S-wave polarization is carefully treated (Sato 1984a).
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synthesis of three component Seismogram envelopes for earthquakes using scattering amplitudes from the born approximation
2009Co-Authors: Haruo Sato, Michael FehlerAbstract:Figure 2.29 shows that the initial direction of motion of the P-wave, the amplitudes of the direct P- and S-waves, and the high-frequency character of the P- and S-coda envelopes on all three components of motion from a local microearthquake are influenced by the angle between the fault plane and the receiver and the scattering characteristics of the lithosphere. To better understand the effects of scattering on recorded regional Seismograms, we desire a method to synthesize threecomponent Seismogram envelopes for realistic earthquake sources in an inhomogeneous medium. The simplest way to synthesize Seismograms is to sum up all waves scattered by distributed heterogeneities in the time domain. Craig et al. [1991] synthesized the high-frequency Seismograms of a local explosion by summing up all singly scattered waves from distributed spherical obstacles; however, this method needs detailed information about the scatterers and considerable computational work.
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three component Seismogram envelope synthesis in randomly inhomogeneous semi infinite media based on the single scattering approximation
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Kazuo Yoshimoto, Haruo Sato, Masakazu OhtakeAbstract:Abstract We present a method for synthesizing three-component Seismogram envelopes of local earthquake in a randomly inhomogeneous semi-infinite medium. The method extends the single scattering model of Sato [Sato, H., 1984. Attenuation and envelope formation of three-component Seismograms of small local earthquakes in randomly inhomogeneous lithosphere. J. Geophys. Res. 89: 1221–1241.] by incorporating the effects of a free surface, frequency-dependent non-spherical radiation from a double-couple point source, and non-isotropic scattering including wave-type conversion. We synthesize Seismogram envelopes—the root-mean-square (rms) amplitude of Seismograms—at a receiver located on the free surface by dividing an inhomogeneous medium into many small cells and summing the energy of scattered waves from the cells on the isochronal scattering shells of different scattering modes for a given lapse time. Our main focus is the free surface effect, which alters the shape of isochronal scattering shells and the amplitudes of incident waves. Synthesizing three-component Seismogram envelopes for different source-receiver configurations, we find that these effects on Seismogram envelopes are not negligible and are pronounced at early S coda. P coda envelope shape is not very sensitive to free-surface incorporation because of dominant SP scattered waves which come from the source direction.
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short wavelength crustal heterogeneities in the nikko area central japan revealed from the three component Seismogram envelope analysis
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Kazuo Yoshimoto, Haruo Sato, Masakazu OhtakeAbstract:Abstract The short-wavelength crustal heterogeneity is investigated in the Nikko area (Central Japan), using a three-component Seismogram envelope analysis applied to small local earthquakes. We stochastically model fluctuations in crustal density and seismic wave velocities by using an exponential auto-correlation function. The model parameters are correlation length a and root mean square (rms) fractional fluctuation strength e. Free surface and non-spherical source radiation effects are incorporated in the synthesis of three-component Seismogram envelopes. We use 149 short-period Seismograms recorded by array stations from 10 local earthquakes with magnitudes 1 ∼ 2 and epicentral distances less than 15 km. A best fit minimum residual between observed and synthetic envelopes in the frequency band of 8 ∼ 16 Hz gives e 2 a ⋍ 8 × 10 −6 m −1 . With the additional information on the strength of direct wave attenuation and the excitation of coda waves at low frequencies, we estimate that a = 300 ∼ 800 m and e = 5 ∼ 8%. This strong heterogeneity and short correlation length probably reflect the geological condition of the Nikko area which is located in the vicinity of the volcanic front.
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regional differences of random inhomogeneities around the volcanic front in the kanto tokai area japan revealed from the broadening of s wave Seismogram envelopes
Journal of Geophysical Research, 1995Co-Authors: Kazushige Obara, Haruo SatoAbstract:Broadening of Seismogram envelopes around direct S waves of deep earthquakes that occurred in a lithospheric slab reveals random inhomogeneities in the upper mantle and crust. Regional differences in the character of envelope broadening were studied in relation to the volcanic front in the central part of Japan. A total of 58 earthquakes that occurred along the subducting Pacific plate ranging from 80 to 500 km in depth were observed at 73 stations of the Kanto-Tokai seismic observation network and used in this analysis. Time lags of the maximum peak arrival and the half-maximum arrival were measured from the onset of the direct S wave on root-mean-squared traces of horizontal component Seismograms in frequency bands of 1, 2, 4, and 8 Hz. The envelope broadening is weak at stations located along the coastline of the Pacific Ocean, however, the dependence of time lags on the hypocentral distance and frequency becomes strong at stations near the volcanic front. Moreover, the time lags become very long with increasing hypocentral distances and frequencies west of the volcanic front. This broadening of the Seismogram envelope can be interpreted as the effect of the diffraction and multiple forward scattering on the seismic wave propagation through random inhomogeneities. The parabolic approximation is applied to simulate the envelope broadening when the correlation distance of velocity inhomogeneities is longer than the seismic wavelength. The numerical simulation indicates that the dependence of the envelope broadening on the travel distance and frequency depends greatly on the type of the autocorrelation function for the randomness. By comparing the observed frequency dependence of the envelope broadening with the result of the numerical simulation, the type of the autocorrelation function was estimated to be close to Gaussian at stations east of the volcanic front and close to exponential west of the volcanic front. The regional difference in the randomness on both sides of the volcanic front might reflect the difference in the short-wavelength component inhomogeneities.
Masakazu Ohtake - One of the best experts on this subject based on the ideXlab platform.
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three component Seismogram envelope synthesis in randomly inhomogeneous semi infinite media based on the single scattering approximation
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Kazuo Yoshimoto, Haruo Sato, Masakazu OhtakeAbstract:Abstract We present a method for synthesizing three-component Seismogram envelopes of local earthquake in a randomly inhomogeneous semi-infinite medium. The method extends the single scattering model of Sato [Sato, H., 1984. Attenuation and envelope formation of three-component Seismograms of small local earthquakes in randomly inhomogeneous lithosphere. J. Geophys. Res. 89: 1221–1241.] by incorporating the effects of a free surface, frequency-dependent non-spherical radiation from a double-couple point source, and non-isotropic scattering including wave-type conversion. We synthesize Seismogram envelopes—the root-mean-square (rms) amplitude of Seismograms—at a receiver located on the free surface by dividing an inhomogeneous medium into many small cells and summing the energy of scattered waves from the cells on the isochronal scattering shells of different scattering modes for a given lapse time. Our main focus is the free surface effect, which alters the shape of isochronal scattering shells and the amplitudes of incident waves. Synthesizing three-component Seismogram envelopes for different source-receiver configurations, we find that these effects on Seismogram envelopes are not negligible and are pronounced at early S coda. P coda envelope shape is not very sensitive to free-surface incorporation because of dominant SP scattered waves which come from the source direction.
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short wavelength crustal heterogeneities in the nikko area central japan revealed from the three component Seismogram envelope analysis
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Kazuo Yoshimoto, Haruo Sato, Masakazu OhtakeAbstract:Abstract The short-wavelength crustal heterogeneity is investigated in the Nikko area (Central Japan), using a three-component Seismogram envelope analysis applied to small local earthquakes. We stochastically model fluctuations in crustal density and seismic wave velocities by using an exponential auto-correlation function. The model parameters are correlation length a and root mean square (rms) fractional fluctuation strength e. Free surface and non-spherical source radiation effects are incorporated in the synthesis of three-component Seismogram envelopes. We use 149 short-period Seismograms recorded by array stations from 10 local earthquakes with magnitudes 1 ∼ 2 and epicentral distances less than 15 km. A best fit minimum residual between observed and synthetic envelopes in the frequency band of 8 ∼ 16 Hz gives e 2 a ⋍ 8 × 10 −6 m −1 . With the additional information on the strength of direct wave attenuation and the excitation of coda waves at low frequencies, we estimate that a = 300 ∼ 800 m and e = 5 ∼ 8%. This strong heterogeneity and short correlation length probably reflect the geological condition of the Nikko area which is located in the vicinity of the volcanic front.
Kazushige Obara - One of the best experts on this subject based on the ideXlab platform.
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constraining the source location of the 30 may 2015 mw 7 9 bonin deep focus earthquake using Seismogram envelopes of high frequency p waveforms occurrence of deep focus earthquake at the bottom of a subducting slab
Geophysical Research Letters, 2016Co-Authors: Shunsuke Takemura, Takuto Maeda, Takashi Furumura, Kazushige ObaraAbstract:In this study, the source location of the 30 May 2015 (Mw 7.9) deep-focus Bonin earthquake was constrained using P wave Seismograms recorded across Japan. We focus on propagation characteristics of high-frequency P wave. Deep-focus intraslab earthquakes typically show spindle-shaped Seismogram envelopes with peak delays of several seconds and subsequent long-duration coda waves; however, both the main shock and aftershock of the 2015 Bonin event exhibited pulse-like P wave propagations with high apparent velocities (~12.2 km/s). Such P wave propagation features were reproduced by finite-difference method simulations of seismic wave propagation in the case of slab-bottom source. The pulse-like P wave Seismogram envelopes observed from the 2015 Bonin earthquake show that its source was located at the bottom of the Pacific slab at a depth of ~680 km, rather than within its middle or upper regions.
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regional differences of random inhomogeneities around the volcanic front in the kanto tokai area japan revealed from the broadening of s wave Seismogram envelopes
Journal of Geophysical Research, 1995Co-Authors: Kazushige Obara, Haruo SatoAbstract:Broadening of Seismogram envelopes around direct S waves of deep earthquakes that occurred in a lithospheric slab reveals random inhomogeneities in the upper mantle and crust. Regional differences in the character of envelope broadening were studied in relation to the volcanic front in the central part of Japan. A total of 58 earthquakes that occurred along the subducting Pacific plate ranging from 80 to 500 km in depth were observed at 73 stations of the Kanto-Tokai seismic observation network and used in this analysis. Time lags of the maximum peak arrival and the half-maximum arrival were measured from the onset of the direct S wave on root-mean-squared traces of horizontal component Seismograms in frequency bands of 1, 2, 4, and 8 Hz. The envelope broadening is weak at stations located along the coastline of the Pacific Ocean, however, the dependence of time lags on the hypocentral distance and frequency becomes strong at stations near the volcanic front. Moreover, the time lags become very long with increasing hypocentral distances and frequencies west of the volcanic front. This broadening of the Seismogram envelope can be interpreted as the effect of the diffraction and multiple forward scattering on the seismic wave propagation through random inhomogeneities. The parabolic approximation is applied to simulate the envelope broadening when the correlation distance of velocity inhomogeneities is longer than the seismic wavelength. The numerical simulation indicates that the dependence of the envelope broadening on the travel distance and frequency depends greatly on the type of the autocorrelation function for the randomness. By comparing the observed frequency dependence of the envelope broadening with the result of the numerical simulation, the type of the autocorrelation function was estimated to be close to Gaussian at stations east of the volcanic front and close to exponential west of the volcanic front. The regional difference in the randomness on both sides of the volcanic front might reflect the difference in the short-wavelength component inhomogeneities.
Kristel Carolina Meza Fajardo - One of the best experts on this subject based on the ideXlab platform.
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Identification of Surface Waves Generated in a Sedimentary Basin in Japan
2019Co-Authors: Kristel Carolina Meza Fajardo, Hideo Aochi, Apostolos PapageorgiouAbstract:Recent events have allowed the observation of the effects of long-period motions on large-scale structures in Japan, and their devastating consequences. In this work we investigate the generation of surface waves in the basin of Nagoya (Nobi plain) in Japan, from Seismograms of the K-net network, including recordings of the Mw 9.0 2011 Tohoku earthquake. The sur-face waves are identified by their polarization characteristics when the Seismogram is repre-sented in the time-frequency space via the S-Transform. We adopt the “Normalized Inner Product” (NIP) as criterion to quantify the polarization features of the different train waves, since the NIP can be considered as the time-frequency counterpart of correlation. We then ap-ply filters based on the NIP to the S-Transform to isolate and extract the identified surface waves. With this procedure we provide the direction of propagation of the identified wa-vetrains, and then evaluate their mechanisms of generation.
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Identification and Extraction of Surface Waves from Three-Component Seismograms Based on the Normalized Inner Product
Bulletin of the Seismological Society of America, 2015Co-Authors: Kristel Carolina Meza Fajardo, Apostolos S Papageorgiou, Jean François SemblatAbstract:Identification of different wave types in a Seismogram is an important step for the understanding of wave propagation phenomena. Because in most Seismograms, different types of waves with different frequencies may appear simultaneously, separation of waves is more effectively achieved when a time-frequency analysis is performed. In this work, we propose a new time-frequency analysis procedure to identify and extract Rayleigh and Love waves from three-component Seismograms. Exploiting the advantage of the absolute phase preservation by the Stockwell transform, we construct time-frequency filters to extract waves based on the normalized inner product (NIP). Because the NIP is the time-frequency counterpart of the correlation, Rayleigh and Love waves can be identified depending on the NIP between the Stockwell transforms of the horizontal and vertical displacement components. The novelty and advantage of the proposed procedure is that it does not require specifying a priori the direction of propagation of the surface waves, but instead such direction is determined. Furthermore, it is shown that the NIP is a more stable parameter in the time-frequency domain when compared to the instantaneous reciprocal ellipticity, and thus it avoids smoothing (and with it, altering) the data. The procedure has been successfully tested with real signals, specifically to extract Rayleigh and Love waves from Seismograms of one aftershock of the 1999 Chi-Chi earthquake. With the proposed procedure, we found different directions of propagation for retrograde and prograde Rayleigh waves, which might suggest that they are generated by different mechanism.
Kazuo Yoshimoto - One of the best experts on this subject based on the ideXlab platform.
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three component Seismogram envelope synthesis in randomly inhomogeneous semi infinite media based on the single scattering approximation
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Kazuo Yoshimoto, Haruo Sato, Masakazu OhtakeAbstract:Abstract We present a method for synthesizing three-component Seismogram envelopes of local earthquake in a randomly inhomogeneous semi-infinite medium. The method extends the single scattering model of Sato [Sato, H., 1984. Attenuation and envelope formation of three-component Seismograms of small local earthquakes in randomly inhomogeneous lithosphere. J. Geophys. Res. 89: 1221–1241.] by incorporating the effects of a free surface, frequency-dependent non-spherical radiation from a double-couple point source, and non-isotropic scattering including wave-type conversion. We synthesize Seismogram envelopes—the root-mean-square (rms) amplitude of Seismograms—at a receiver located on the free surface by dividing an inhomogeneous medium into many small cells and summing the energy of scattered waves from the cells on the isochronal scattering shells of different scattering modes for a given lapse time. Our main focus is the free surface effect, which alters the shape of isochronal scattering shells and the amplitudes of incident waves. Synthesizing three-component Seismogram envelopes for different source-receiver configurations, we find that these effects on Seismogram envelopes are not negligible and are pronounced at early S coda. P coda envelope shape is not very sensitive to free-surface incorporation because of dominant SP scattered waves which come from the source direction.
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short wavelength crustal heterogeneities in the nikko area central japan revealed from the three component Seismogram envelope analysis
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Kazuo Yoshimoto, Haruo Sato, Masakazu OhtakeAbstract:Abstract The short-wavelength crustal heterogeneity is investigated in the Nikko area (Central Japan), using a three-component Seismogram envelope analysis applied to small local earthquakes. We stochastically model fluctuations in crustal density and seismic wave velocities by using an exponential auto-correlation function. The model parameters are correlation length a and root mean square (rms) fractional fluctuation strength e. Free surface and non-spherical source radiation effects are incorporated in the synthesis of three-component Seismogram envelopes. We use 149 short-period Seismograms recorded by array stations from 10 local earthquakes with magnitudes 1 ∼ 2 and epicentral distances less than 15 km. A best fit minimum residual between observed and synthetic envelopes in the frequency band of 8 ∼ 16 Hz gives e 2 a ⋍ 8 × 10 −6 m −1 . With the additional information on the strength of direct wave attenuation and the excitation of coda waves at low frequencies, we estimate that a = 300 ∼ 800 m and e = 5 ∼ 8%. This strong heterogeneity and short correlation length probably reflect the geological condition of the Nikko area which is located in the vicinity of the volcanic front.
