The effect of P- and S-phase arrivals on the accuracy of microseismic source location

In this paper, the conventional microseismic monitoring is classified into two types: body and line monitoring cases. And the phase arrival conditions are classified into three types: 1) Only including P-arrivals and P-picks being in error; 2) Both including P- and S-arrivals and P-picks being in error; 3) Both including P- and S-arrivals and S-picks being in error. Then the effect of P- and S-phase arrivals on the accuracy of source location is studied under six conditions. In body monitoring case, the location accuracy will be improved dramatically when S-picks are added. In line monitoring case, the convergence rate of location function is dramatically improved when S-picks are added. This kind of phenomena is called P-picks effect. Then a pair of mutually exclusive hypothesizes are put forward based on P-picks effect. And another set of numerical tests are designed to verify which one is true. The tests results show that the location accuracy and the iterative convergence rate of the objective function can be dramatically improved when S-picks are added. What's more, this effect cannot be offset by increasing P-picks. To understand this effect deeply, the location model is simplified further. The properties of location functions with or without S-picks are studied and compared. And the S-picks effect is analyzed mathematically based on the simplified location model and the properties of objective function. Two field data tests, 81,307# workface microseismic monitoring of Baode Coal Mine and 4# branch tunnel microseismic monitoring of Hanjiang-to-Weihe River Valley Water Diversion Project, are analyzed to verify the conclusion that the participation of S-picks can improve converge rate and location accuracy. In both cases, the location results with P- and S-picks are consistent with the rock mechanics theoretical results. Both of them confirm that S-picks are indispensable in source location. •The effect of P- and S-phase arrivals on the accuracy of microseismic source location is researched based on the numerical source location models.•The mathematical analysis show that the participation of S-picks can improve converge ratio and location accuracy greatly.•Two monitoring cases are illustrated to verify the conclusion again.