Study of the inhomogeneous structure of the earth from the analysis of scattering phenomena of broad band seismic waves

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Study of inhomogeneous structure of the earth medium is important for understanding the evolution process of the earth. We performed three seismological studies as follows : 1.Small-scale inhomogeneity of the lithosphere based on the analysis of high-frequency seismic waves : Combining the radiative transfer theory and the Markov approximation, we constructed a hybrid model for the synthesis of the whole scalar-wave envelope in 2-D random media. Extending the Markov approximation for vector wave propagation in 2-D elastic random media, we proposed a new synthesis model, which quantitatively explains envelopes synthesized by the finite difference simulation. Scattering due to random inhomogeneity well explains the peak amplitude decay and the envelope broadening observed. Strong scattering beneath Quaternary volcanoes was revealed from the envelope broadening analysis in Tohoku district. We made the depth profile of the Moho and the subducting Philippine-sea plate in Chugoku-Shikoku dis … More trict by using the receiver function method. 2.Scattering characteristics in the mantle from the analysis of ScS phase in intermediate periods : Analyzing wave envelopes around the ScS phase of regional earthquakes by using the isotropic scattering model based on PREM, we first estimated quantitatively the scattering coefficient in the mantle for periods from 4 to 10 s. 3.Envelope analysis of long period Rayleigh waves : We analyzed vertical-component seismograms of large earthquakes in long periods recorded by IRIS and F-net. The array analysis revealed that the fundamental mode Rayleigh waves dominate early lapse times but higher modes dominate as lapse time increases because of small attenuation in the lower mantle. We find that the coda attenuation factor directly represents the attenuation factor in the lower mantle. Clarifying the scattering characteristics between Rayleigh waves and body waves in random elastic half media, we established the solid base for the envelope synthesis in long periods. Less