PRECISE DETECTION OF A P-WAVE IN LOW S N SIGNAL BY USING TIME-FREQUENCY REPRESENTATIONS OF A TRIAXIAL HODOGRAM/

We have developed a signal processing technique for three-component mi croseismic data that allows the precise determination of P-wave arriva l times. The method is based on a time-frequency representation of the signal that allows the evaluation of the 3-D particle motion from sei smic waves in both time and frequency domains. A spectral matrix is co nstructed using the time frequency distributions. A crosscorrelation c oefficient for the three-component signal is derived through eigenvalu e analysis of the spectral matrix. The P-wave arrival time is determin ed through a statistical test of hypotheses using the crosscorrelation coefficient. This signal processing method is evaluated using a synth etic signal and it is compared to the local stationary autoregressive method for determining P-wave arrival times. We also show that the pro posed method is capable of determining the arrival time of a synthetic P-wave to within 1 ms (five points in the discrete time series) in th e presence of a signal-to-noise ratio of -5dB. The method can detect t he arrival time of different frequency components of the P-wave, which is a possibility for the evaluation of velocity dispersion of the sei smic wave. We demonstrate the feasibility of the method further by app lying it to microseismic data from a geothermal field.