A Moment Tensor Inversion Scheme for Local Earthquakes: Application to Haida Gwaii

The relative abundance of small earthquakes renders them potentially useful tools in improved understanding of regional seismotectonics; however, determination of moment tensors for such events recorded on regional networks is exacerbated by low signal-to-noise ratios, sparse station sampling and complex wave propagation at short periods. We build upon previous work in designing a multiple-event, simultaneous moment tensor inversion scheme for small earthquakes that employs constraints from P-wave polarities, relative amplitudes of P and S-waves recorded at common stations, S/P amplitude ratios determined for common events, and reference estimates of radiated amplitudes. The scheme exploits principal component decomposition of clustered-event waveforms to derive high-fidelity measures of the aforementioned quantities. We demonstrate our approach on seismicity in the Haida Gwaii region, the site of abundant seismicity associated with the Queen Charlotte Plate boundary in a complex transpressive regime.