A persistent localized microseismic source near the Kyushu Island, Japan

Abstract

Very strong signals with apparent velocity higher than Rayleigh wave velocity are observed on noise correlation functions (NCFs) between seismic stations in East Asia. These signals are present on one‐month NCFs in ten years period with stable arrival times, indicating their persistent and localized nature. The signals are strong in the frequency band of 0.07–0.12Hz, and their amplitudes show inter‐annual but not seasonal variation. Location obtained from two algorithms with GSN and FNET data indicates that the source is situated in Kyushu Island, Japan. After an earthquake is used to account for heterogeneity effects, the location is closer to the Ariake bay but still in the island. The non‐seasonal amplitude variation and the peak frequency of 0.1Hz suggest the signals are probably not generated by oceanic sources. This persistent localized microseismic source needs to be taken into consideration in ambient noise tomography studies in East Asia.