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

Abstract

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.

Envelope Widths of Volcano‐Seismic Events and Seismic Scattering Characteristics Beneath Volcanoes

“…According to finite difference full waveform simulations in von Kármántype heterogeneous structures, a = 50 m produced strong scattering effects for seismic waveforms in the 5-10-Hz frequency band (Kumagai et al, 2011;Morioka et al, 2017). This correlation distance is clearly shorter than those estimated from tectonic earthquakes in the normal crust (Takemura et al, 2009(Takemura et al, , 2016, which are estimated to be around a few kilometers. Based on the Born approximation, l m for κ = 0.5 is given as…”

Source rupture process of the 2016 central Tottori, Japan, earthquake (M JMA 6.6) inferred from strong motion waveforms

“…The large amplitude of the second wave packet in high-frequency waveforms is likely due to the dominant frequency of the waveforms from R2 being higher than that of the waveforms from R1 because of the compact fault rupture of R2. In addition, the radiation pattern of body waves, which largely affects the spatial amplitude pattern in the low frequency band, is distorted at frequencies over 1 Hz mainly due to the seismic wave scattering and diffraction within the heterogeneous crust (e.g., Liu and Helmberger 1985;Takemura et al 2016). Both of these factors lead to the reduction in the amplitude difference shown in the low frequency band; however, they are not enough to explain the larger amplitude of the second wave packet than the first one in the high-frequency waveforms at TTR005.…”

Characteristics of Shallow Low‐Frequency Earthquakes off the Kii Peninsula, Japan, in 2004 Revealed by Ocean Bottom Seismometers

“…Here, the radiation pattern is assumed to be uniform over the relatively short period of observations (Takemura et al, 2009(Takemura et al, , 2016. Here, the radiation pattern is assumed to be uniform over the relatively short period of observations (Takemura et al, 2009(Takemura et al, , 2016.…”