Determining S-Wave Arrival Times for Microseismic Monitoring in Tunnels Based on Instantaneous Phase Difference of Sensors.

Accurately ascertaining the S-wave arrival times of microseismic signals is crucial for improving the accuracy with which microseismic events can be located. However, the first arrival of an S-wave is often overlapped by the P-wave which can make it difficult to accurately determine the arrival time of the S-wave in tunnels. Therefore, an accurate method for determining the S-wave arrival time of microseismic signals in tunnels is urgently needed. In this paper, a novel method is proposed based on the instantaneous phase difference intensity (IPDI) of the S-wave between two microseismic sensors. The peaks in the IPDI directly indicate the first breaking of an S-wave thus allowing the arrival time of the S-wave to be identified. Tests using synthetic signals verify that the IPDI method can correctly determine the arrival time of an S-wave when the first break of the S-wave is overlapped by the P-wave. The IPDI method was further applied to microseismic monitoring in a deeply buried tunnel in the Jinping II hydropower station in China. The IPDI peaks were found to successfully highlight the arrival of S-waves that could not be determined manually. The location accuracy of rockburst and microseismic events was thus significantly improved using the new IPDI method. Highlights: A novel index (IPDI) is introduced to highlight the first break of microseismic S-wave based on the instantaneous phase of sensors. The IPDI method can identify the S-wave arrival time even in near-field MS monitoring cases where S- and P waves overlap. The IPDI-picked S-wave arrival time substantially improves the MS location accuracy. [ABSTRACT FROM AUTHOR]