HR: 09:30h
AN: S51B-07    [PDF]
TI: Average Dissipation Spectrum and Waveform Characteristics of Deep Low-frequency Earthquakes
AU: * Takeo, M
EM: takeo@eri.u-tokyo.ac.jp
AF: Earthq. Res. Inst., Univ. Tokyo, 1-1-1, Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AU: Ueda, H
EM: bono@eri.u-tokyo.ac.jp
AF: Earthq. Res. Inst., Univ. Tokyo, 1-1-1, Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AU: Matsuura, M
AF: Infor. Sci. Tech., Univ. Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo, 113-0033 Japan
AU: Okabe, Y
AF: Infor. Sci. Tech., Univ. Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo, 113-0033 Japan
AB: It is well known in regions operating dense seismic networks that the depths of almost all inland earthquakes are shallower than 15 km. However, anomalously deep events with depths ranging 20 km to 40 km have been observed beneath the Japan Island, and they have lower dominant frequencies for both P and S waves than corner frequencies expected from those magnitudes. These events are termed deep low-frequency earthquakes (DLF). Using high-density high-gain seismic data in Japan, it makes clear that DLF occur not only beneath the volcanic front but also beneath source regions of large inland earthquakes. Sometimes, DLF are characterized by large and long tailing coda parts of S-wave, and these waves represent the time evolution of DLF's source process directly. Based on the theory of KM2O-Langevin equation, we propose a new method to represent characteristics of coda parts of DLF. The most advantage of this theory is free from a prior information about data when the data satisfies stationarity, and we can deduce an stochastic difference equation producing the data without any parametric models before data analysis. If a specific physical process continues to excite seismic waves, it will be expected that the similar dissipation terms are obtained from the seismic waveforms. We propose a new algorithm to get an average KM2O-Langevin matrix function (LMav(X)) for plural local time series. Applying this method to the large and long tailing coda parts of S-waves excited by DLF on July 11, 2001, we calculate LMav(X) and get the linear difference equations using these dissipation matrices. The time series predicted by these difference equations can explain the dominant frequencies and the waveforms of DLF well. The fluctuation matrices of LMav(X) seem to be corresponding to the excitation of DLF. Using the inverse z-transformation, we solve the linear difference equations to obtain the discrete dominant frequencies with those attenuation factors and magnitudes. We term these quantities average dissipation spectra. We calculated the average dissipation spectrum of DLF on July 11, recorded at NIB, GJOH, and ANIH. The dominant frequencies and the attenuation factors at NIB, GJOH, and ANIH are (1.55 Hz, -0.37), (1.58 Hz, -0.31), and (1.59 Hz, -0.26), respectively. The frequencies and the attenuation factors with the second large magnitude also show the similar values each other. These results indicate that the average dissipation spectrum is useful method to reveal characteristics of long tailing coda parts excited by DLF.
DE: 7215 Earthquake parameters
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting