Sliding speed calculation of the Wenchuan earthquake fault using the Doppler effect

Currently, the fault sliding speed functions or source-time functions used in theoretical seismogram calculations have only produced theoretical results; that is, the results of the fault speed-time functions have been obtained only from theoretical studies, and have not been validated using the measured data. This paper significantly improves the method for calculating fault sliding speed using the Doppler effect, from the following four perspectives. First, the paper theoretically demonstrates how to confirm that the seismic waves received in some frequency bands by two different receivers are emitted by the same source. Second, the paper proposes a method to determine the similarity of seismic waves received by two different receivers in some frequency bands; it applies the relative change at the two receivers in Fourier amplitude standard deviation in some frequency bands, and determines that similar seismic waves are emitted by the same frequency bands. Third, to eliminate the interference of reflected and refracted waves, this study uses fault sliding time S-wave records for data processing. Finally, the paper replaces the long-time Fourier transform with short-time Fourier transform to enhance the positioning accuracy of fault sliding times. Based on these perspectives, the paper systematically summarizes a general methodology for calculating the fault sliding speed using the Doppler effect. This method is employed to calculate the fault sliding speed of the Wenchuan earthquake; the calculations reveal that there is a general correlation between the fault sliding speeds of the Wenchuan earthquake and the seismic moment changes. The results confirm that the sliding speed of the Wenchuan earthquake fault possesses the characteristics of abrupt change, whereby a sudden increase in the sliding speed is followed by a rapid decrease. Generally, the sliding speed is not fast, and sometimes, no sliding occurs. There are obvious differences from the currently used sliding speed functions, such as the Haskell function, bell-shaped function, exponential function, and triangular function. To determine the fault sliding speed using the Doppler effect, only the earthquake records and locations of the epicenter and receivers are required, instead of using unknown crust parameters. In short, the proposed calculation method has clear physical meaning, and the required parameters are easier to obtain.