A comprehensive dynamic source model of shallow very low-frequency earthquakes

Abstract

Very low-frequency earthquakes, which exhibit longer source durations and smaller stress drops than regular earthquakes of similar magnitude, possess abundant low-frequency energy but are depleted in high-frequency energy. The source processes that govern the occurrence of very low-frequency earthquakes remain unclear. Here, we implement a unified dynamic source model to illustrate the source characteristics of very low-frequency earthquakes. By comparing the source parameters of observed shallow very low-frequency earthquakes with those of numerically simulated ruptures, we conclude that very low-frequency earthquakes are slow self-arresting earthquakes that self-terminate within the nucleation patch. In addition, a composite slow self-arresting model is adopted to reproduce the source processes of VLF and LFE in Nankai area. Comparison of synthetic seismograms obtained from the composite model with the Nankai VLFs shows that slow self-arresting ruptures have the potential to explain different types of slow earthquakes. Our results indicate that very low-frequency earthquakes, low-frequency earthquakes and regular earthquakes can be explained uniformly in the same dynamic rupture phase diagram.