SUMMARY
Conventionally, the routine workflow of stress field estimation from seismic data consists of two steps: focal mechanism inversion and stress inversion. This two-step workflow suffers from the cumulative uncertainties of both the focal mechanism inversion process and the stress inversion process. To mitigate the cumulative errors, a few previous studies have put efforts to directly estimate the stress field using P-wave polarities. In this study, we develop a new approach to directly estimate tectonic stress fields with better accuracy through waveform matching. This new approach combines the two steps into a one-step workflow to mitigate the cumulative uncertainties through the physical relationship between a stress field and the recorded waveforms. This method assumes a homogeneous stress field in space in the local source region and that the fault slip occurs in the direction of the resolved shear stress acting on the fault plane. Under these assumptions, the stress pattern that generates the theoretical waveforms that best fit the waveforms observed is directly retrieved as the true stress field. The merits of the new approach include that this approach can mitigate the cumulative uncertainties suffered from the conventional two-step workflow and does not require determination of the focal mechanisms of each event; thus, this method is applicable to data sets with few stations. Synthetic tests with and without noise are conducted to demonstrate the performance and merits of this method. Then, the new approach is applied to a real data set from central Oklahoma between March 2013 and March 2016. The resulting stress pattern is consistent with that estimated from previous studies examining the same region. These applications show the benefits and validity of the new approach.
