Enigmatic deep and shallow low-frequency crustal earthquakes

Abstract

Crustal low-frequency earthquakes (LFEQs) are anomalous one with extremely low-frequency oscillation than those expected from earthquake size. Since LFEQs occur at deep depths where no ordinary earthquakes occur, the potential contribution of crustal fluids has been suggested; however, the contribution has not yet been quantitatively explained. Waveform simulation shows that an essential part of long-lived oscillation after the S-wave is a constructive superposition of resonant waves generated in a low-velocity body. However, a detailed examination is needed to explain the variable waveform characteristics of LFEQs. Detection and study of shallow LFEQs are important recent topics because their generation mechanism is closely related to the mechanism of ordinary earthquakes.