Determination of microseismic event azimuth from S-wave splitting analysis

Abstract

P-wave hodogram analysis has been the only reliable method to obtain microseismic event azimuths for one-well monitoring. However, microseismic data usually have weak or even no P-waves due to near double-couple focal mechanisms and limited ray path coverage, which causes large uncertainties in determined azimuths and event locations. To solve this problem, we take advantage of S-waves, which are often much stronger than P waves in microseismic data, and determine event azimuths by analyzing S-wave splitting data. This approach utilizes the positive correlation between the accuracy of event azimuth and the effectiveness of measuring S-wave splitting parameters and finds the optimal azimuth through a grid search. We have demonstrated that event azimuths can be well constrained from S-wave splitting analysis using both synthetic and field microseismic data. This method is less sensitive to noise than the routine P-wave hodogram method and provides a new way of determining microseismic event azimuths.