9:45 AM - 10:00 AM
[SSS04-04] Slow earthquakes in microseism frequency band (0.1-2 Hz) off Kii peninsula
Keywords:slow earthquake, microseism, hypocenter determination, tremor, VLF
The data are broadband seismograms recorded at 20 stations of DONET, from April 1st to April 17th. We detected hypocenters by calculating arrival time differences between stations using an envelope correlation method of Ide (2010). Unlike ordinary applications, we repeated analyses for seismograms bandpass-filtered in four separated frequency bands, 0.1-1, 1-2, 2-4, and 4-8 Hz. For each band, we successfully detected events and determined their hypocenter locations. The number of detected events were 32, 44, 177, and 643 in 0.1-1, 1-2, 2-4, and 4-8 Hz, respectively. During the study period, tremors determined in the three high-frequency bands, 1-2, 2-4, and 4-8 Hz, migrated from a small spot near the source of Mw 6.5 event to a broader region in the south-east direction. In the 0.1-1 Hz microseism band, the hypocenters were determined mainly on April 10th, when microseism noises are exceptionally small. On this day, the numbers of evets in the highest frequency band, 4-8 Hz, decreased, while that in lower frequency bands increased.
Many VLF events have been detected in this region in the frequency band of 0.03-0.05 Hz, with location and focal mechanism using a method of Nakano et al. (2008). These VLF events and tremors detected in this study appear to have occurred at the almost same time and locations.