Moment tensor inversion of waveforms: a two‐step time‐frequency approach

SUMMARY We present a moment tensor inversion of waveforms, which is more robust and yields more stable and more accurate results than standard approaches. The inversion is performed in two steps and combines inversions in time and frequency domains. First, the inversion for the source‐time function is performed in the frequency domain using complex spectra. Second, the time‐domain inversion for the moment tensor is performed using the source‐time function calculated in the first step. In this way, we can consider a realistic, complex source‐time function and still keep the final moment tensor inversion linear. Using numerical modelling, we compare the efficiency and accuracy of the proposed approach with standard waveform inversions. We study the sensitivity of the retrieved double‐couple and non‐double‐couple components of the moment tensors to noise in the data, to inaccuracies of the location and of the velocity model, and to the type of the focal mechanism. Finally, the proposed moment tensor inversion is tested on real data observed in a complex 3‐D inhomogeneous geological environment: a production blast and a rockburst in the Pyhäsalmi ore mine, Finland.