SIN-Polarity: A Novel Algorithm for Automatic Identification of P -Wave First-Motion Polarity Based on a Sine-Wave Template

Abstract

Focal mechanism is crucial for understanding seismogenic tectonic characteristics and assessing earthquake hazards. First-motion polarity is one of the key constraint parameters for solving the focal mechanism problem, but how to accurately and efficiently pick the first-motion polarity remains a challenging issue in seismology. To address this, we developed a novel algorithm, named SIN-Polarity, for automatic picking of P-wave first-motion polarity. The distinctive feature of this algorithm is the use of an adaptive period-length sine-wave template, which allows SIN-Polarity to flexibly adapt to P-wave morphological changes caused by different focal mechanisms, rupture directions, and local velocity structures. We applied SIN-Polarity to the 2014 Mb 4.5 Oklahoma earthquake and the 2025 Mw 7.7 Myanmar earthquake. The results show that SIN-Polarity can correctly identify the P-wave first-motion polarity of local and teleseismic earthquakes. We also conducted tests on the robustness of SIN-Polarity using an Italian earthquake sequence from the INSTANCE dataset and an earthquake sequence from Southern California. The results demonstrate that SIN-Polarity has good practicality and robustness.