Frequency structure of deep low-frequency tremors occurring in western Shikoku region, Japan

Since the discovery of deep low-frequency tremors in southwestern Japan, various types of low-frequency oscillation phenomena have been reported and analysed. Among these phenomena, non-volcanic, deep, low-frequency tremors in southwestern Japan are outstanding low-frequency oscillation phenomena occurring over a wide region along the Philippine Sea Plate. However, the weakness of these signals makes it difficult to apply usual analyses to derive source characteristics. In this paper, we apply a new algorithm to obtain a frequency structure from highly noisy data and reveal the characteristic frequency structure of deep low-frequency tremors with peaks lined up from 1 to 5 Hz at intervals of 0.5 Hz. In addition, we present one piece of evidence that the deep low-frequency tremors and low-frequency earthquakes have a common source mechanism.