Study On Application Of Wavelet Transform In Compressing Seismic Data And Picking The Onset Time Of Seismic Phase

The lossless compression of seismic data was studied on the basis of the integer wavelet transform, which was based on the theoretical analysis of the Lifting scheme and the Laurent polyphase matrix representation. To the traditional code method like the HUFFMAN code, the ARITH code, the RUN-LENGTH code and the LZW code, except the RUN-LENGTH code, it was found that the compression ratio was largely increased by wavelet transform. And it was also found the compression ration of the LZW code is the highest and the effect of the wavelet transform is the best. Comparing to the Steim-1 code and Steim-2 code of the standard exchange format of the seismic data, the compression ratio based on the wavelet transform is much higher than on steim-1 and little higher than on steim-2. The compression results of the noise data and the actual observation seismic data show that the compression code on the basis of the wavelet transform is better than the other kinds of compression code. The wavelet function affects the compression ratio to some extent, the compression results of noise data told us the compression ratio of the biorthogonal wavelet function CDF, is best, while to the result of the observation seismic data, it shows the compression ratios of the CRF(13,7) and SWE(13,7) biorthogonal wavelet function are better.Based on the biorthogonal wavelet function merit, it is studied the lossy compression of seismic data and the influence of the reconstruction error on the calculation of the basic earthquake parameters. According to the influence of the coefficient length of wavelet transform filter group and the size of decomposition level on the S/N(the ratio of signal and noise) and RMSE(the root of mean square error), it is believed that the S/N is higher and RMSE is smaller at the condition that the compression ratio is lager than 10 and the decomposition level of bior (3,7) is 5, where bior(3,7) is B-spline biorthogonal wavelet, and 3 is the coefficient length of the reconstruction filter and 7 is the coefficient length of the decomposition filter. From the compression results of the seismic data as the given example, it is known when the compression ratio is in the range 0~40, the signal reconstruction error has little affect on calculating the magnitude and the epicenter distance of the earthquake event, even can be neglected. The analysis of the reconstruction signal frequency spectrum and the phase indicates the change of the frequency spectrum and phase increase with the increase of the compression ratio. Specially, when the compression ratio is approximately larger than 26, their changes are much obvious. The compression results of many earthquake event data show the changes, which include the magnitude, picking onset time of the P wave and S wave of the reconstruction signals, are smaller at the compress ratio 10.5, 21 and 30.5 respectively, and the error of the seismic magnitude and epicenter distance is at the reasonable scope. The compression results of the given example also told us that the change of the S/N and the RMSE has a relatively flat region, and it was thought the compression ratio is quite ideal in this region.On the basis of wavelet transform, it was studied the method of picking onset time of seismic phase and proposed a new method for constructing the characteristic function. According to the frequency features of the P wave and the S wave, we think that the wavelet decomposition coefficient at the smaller scale is corresponding to the noise and should be omitted when calculating the characteristic function. Studying on the local earthquake and remote earthquake, the results show the precision of picking onset time of P phase is higher for the new characteristic function than the other traditional ones. The result also indicated near to theonset of the P wave, the gradient of the new characteristic function increases and the corresponding abscissa axis scope is narrower, so it is benefit to picking P phase onset time. From result tested by the real earthquake event data, it was found the...