Method for identifying Doppler effect in earthquake by using wavelet transform

Abstract

The invention discloses a method for identifying Doppler effect in earthquake by using wavelet transform, and belongs to the field of earthquake engineering. According to the principle, seismic records in the initial period of a seismic station are selected for wavelet transformation, and seismic waves are superposed at a high-frequency part in front of fault sliding, so that the high-frequency amplitude of a wavelet spectrum is increased. A plurality of stations located in the direction perpendicular to a certain seismic fault are selected, along with increase of epicentral distances, wavelet spectrum high-frequency amplitudes of the stations are rapidly reduced, and wavelet spectrum low-frequency amplitudes are obviously larger than the wavelet spectrum high-frequency amplitudes when the epicentral distances are increased to a certain extent, which indicates that in the direction, a medium plays a main role in high-frequency absorption attenuation of seismic waves, and no Doppler effect occurs; and a plurality of stations in front of the sliding of the seismic fault are selected, and the invention finds that the high-frequency amplitude of the wavelet spectrum is obviously greater than the low-frequency amplitude of the wavelet spectrum along with the increase of the epicentral distance, which indicates that although the absorption attenuation effect of a medium on seismic waves exists, the Doppler effect enables the high-frequency amplitude of the wavelet spectrum to be increased. The method is clear in theory and has practical value.

Description

technical field [0001] The invention belongs to the field of earthquake engineering, and in particular relates to a method for identifying the Doppler effect in earthquakes. Background technique [0002] The Doppler effect will be produced when the earthquake fault slips. Zhuo Yuru et al. and Douglas A, et al. confirmed the existence of the Doppler effect in the process of earthquake occurrence by using the distribution of the first arrival frequency of the seismic P wave around the earthquake fault. The above method is very clear and accurate in theory. For earthquakes with high fault slip velocity, the Doppler effect is obvious, so the frequency difference of the first arrival of P waves received at different azimuths is large, and it is easy to judge the existence of the Doppler effect; If the slip velocity of the seismic fault is small, the Doppler effect will cause little difference in the first arrival of the P wave of the seismic wave in different azimuths, and it is ...

AI Technical Summary

Problems solved by technology

[0012] Morlet put forward the theory of wavelet transform in 1974, which inherited the idea of ​​localization of short-time Fourier transform, and overcomes the disadvantage that the size of the Fourier transform window cannot change with the frequency of the wave, and provides a "wavelet transform" that can change with frequency. The time-frequency window, referred to as the "time-frequency" window, enables the wavelet transform to perform localized analysis on the time domain and the frequency domain, rather than the Fourier transform that can only perform global analysis. Carry out multi-scale refinement, and finally achieve time refinement processing at the high frequency of the signal, and frequency refinement processing at the low frequency of the signal, and gradually adapt to the requirements of high-quality analysis of the time-frequency signal, which can highlight all the details of the signal and solve the problem of The Fourier transform only considers the global change of the signal, does not have the ability of global analysis, and cannot analyze the shortcomings of non-stationary signals such as earthquakes.

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