Application of scattering theory to P-wave amplitude fluctuations in the crust

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The effects of the short-wavelength heterogeneity of the crustal structure on predicted ground motion at periods of 1 s and longer were investigated by conducting three-dimensional finite-difference simulations using a detailed realistic velocity model of the Kanto region of Japan. The short-wavelength heterogeneity of the media within the upper crust was randomly modeled using the exponential-type autocorrelation function where the velocity standard deviation was set to 5%. Combinations of heterogeneous media with various correlation lengths and point source models with various depths and durations were considered in order to investigate the variability of the predicted ground motion and the sensitivity to the parameters. The effects of random heterogeneity on the simulated ground motion appeared as a result of changes in the amplitude and phase of both the direct waves and later phases, as well as the spectral peaks of the response spectra. Ground-motion variability, in terms of peak ground velocity (PGV) and velocity response spectra (Sv), was evaluated using the residual, or the difference in logarithm of PGV and Sv between the ground motion computed with and without random heterogeneity. While the residual averaged over the surface of the computed area was almost negligible in the studied period range, the variability of the residual was found to increase with distance and to be larger for point sources with shorter durations. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Section: Spatial Variability Of Ground Motionmentioning

confidence: 99%

Section: Spatial Variability Of Ground Motionmentioning

confidence: 99%

Effects of random 3D upper crustal heterogeneity on long-period (≥ 1 s) ground-motion simulations

Iwaki¹,

Maeda²,

Morikawa³

et al. 2018

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“…1c, d (λ P and λ S , respectively) were calculated by using the central frequencies of each band and seismic velocities in the crust. Observed amplitudes are scattered around master attenuation curves, reflecting the effects of non-isotropic source radiation and fluctuation of amplitude due to small-scale velocity inhomogeneity along propagation path (e.g., Hoshiba 2000; Yoshimoto et al 2015).…”

Section: Apparent Radiation Pattern For Crustal Earthquakesmentioning

confidence: 99%

Prediction of maximum P- and S-wave amplitude distributions incorporating frequency- and distance-dependent characteristics of the observed apparent radiation patterns

Takemura

Kobayashi

Yoshimoto

2016

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Frequency-dependent model of the apparent radiation pattern has been extensively incorporated into engineering and scientific applications for high-frequency seismic waves, but distance-dependent properties have not yet been fully taken into account. We investigated the unified characteristics of frequency and distance dependences in both apparent P-and S-wave radiation patterns during local crustal earthquakes. Observed distortions of the apparent Pand S-wave radiation patterns could be simply modeled by using a function of the normalized hypocentral distance, which is a product of the wave number and hypocentral distance. This behavior suggests that major cause of distortion of the apparent radiation pattern is seismic wave scattering and diffraction within the heterogeneous crust. On the basis of observed normalized hypocentral distance dependency, we proposed a method for prediction of spatial distributions of maximum P-and S-wave amplitudes. Our method incorporating normalized hypocentral distance dependence of the apparent radiation pattern reproduced the observed spatial distributions of maximum P-and S-wave amplitudes over a wide frequency and distance ranges successfully.

“…Analysis of coda waves can thus lead to detailed views of seismic structure and provide valuable information on the dynamics and evolution of the Earth (e.g., Kubanza et al 2006). To explore the stochastic properties of these small-scale heterogeneities in the crust and upper mantle, for several decades, direct and coda waves propagating in the random media have been intensively studied based on both theoretical and numerical methods (e.g., Aki 1973;Scherbaum and Sato 1991;Gusev and Abubakirov 1999;Kubanza et al 2007;Takahashi et al 2009;Carcolé and Sato 2010;Yoshimoto et al 2015;Eulenfeld and Wegler 2017;Emoto and Sato 2018).…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, spatial variations of lithospheric heterogeneity have been globally established to correlate with tectonic settings based on Markov approximation (e.g., Kubanza et al 2006Kubanza et al , 2007. Besides the theoretical methods, numerical simulations of scattered waves propagating in random medium using finite difference methods have been conducted to determine the statistical parameters of random heterogeneities (e.g., Frankel and Clayton 1986;Yoshimoto et al 2015;Emoto et al 2017;Takemura et al 2017) and effects on ground motions (e.g., Hartzell et al 2010;Imperatori and Mai 2013;Savran and Olsen 2019). These studies have demonstrated various random models within the Earth's lithosphere and revealed significantly variable regional randomnesses from the shallow crust to uppermost mantle (Kubanza et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Small-scale scattering heterogeneities beneath the northern Tien Shan from the teleseismic P wavefield

Huang

2020

In order to investigate the small-scale scattering heterogeneities underneath the northern Tien Shan, we analyze the P wavefield from teleseismic events. By using the teleseismic fluctuation method, we separate the total wavefield into coherent and fluctuating parts in the frequency band of 0.1-8.0 Hz. Subsequently, we investigate the scattering characteristics by analyzing the frequency-dependent intensities of the coherent and fluctuating wavefield between 0.3 and 2.5 Hz. We further constrain the velocity perturbations and correlation lengths by modeling the P-wave coda envelope with the Monte Carlo simulation. Strong scattering heterogeneities are revealed beneath the northern Tien Shan. The preferred scattering model can be described as a ~ 55-to 130-km-thick randomly heterogeneous layer with velocity perturbations of 6-9% and correlation lengths on the order of 0.4 km. We attribute these small-scale scatterers to isolated melt pockets from the upwelling hot mantle materials.