A New Automatic Full‐Waveform Regional Moment Tensor Inversion Algorithm and Its Applications in the Taiwan Area

Abstract

A new algorithm is developed in this study to automatically determine regional moment tensor (MT) and its centroid depth with real-time waveforms in 2–4 min after the Central Weather Bureau (CWB) issues an earthquake notice. The program selects 3–7 BATS (Broadband Array for Taiwan Seismology) stations under three criteria: best azimuthal distribution, highest signal-to-noise ratio, and shortest distances. It then inverts MT solutions in parallel with various settings including Moho depth of velocity models, frequency bands, and isotropic constraints. The optimal solution is determined by searching for the best waveform-fit with an acceptable non-double-couple component from the results of combinations of these inversion settings. Our new rapid MT report system greatly reduces computational resources and avoids human judgments. By applying this full-scanning approach on BATS (named AutoBATS), we re-determine the MTs for over 3000 regional earthquakes from 1996 to 2016 to provide the most up-to-date MT catalog for the Taiwan area. The AutoBATS MTs are overall consistent with the Global Centroid Moment Tensors with a mean difference in Kagan angle of 22.0 ± 16.6° and MW of − 0.08 ± 0.10. Those focal mechanisms better illuminate the tectonic structures owing to the much improved resolving ability for shallow ( 140 km) earthquakes. With the new regional MT catalog, we refine the relationship between moment and local magnitudes: MW = 0.87 ML + 0.23 for the Taiwan region.