HR: 14:55h
AN: T13F-06    [Abstracts]
TI: Slow earthquakes with duration of about 100 s suggested by the scaling law
AU: * Ide, S
EM: ide@eps.s.u-tokyo.ac.jp
AF: Dept. EPS, Univ. Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo, 113-0033, Japan
AU: Imanishi, K
EM: imani@ni.aist.go.jp
AF: AIST, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8567, Japan
AU: Yoshida, Y
EM: yyoshida@mri-jma.go.jp
AF: Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki, 305-0052, Japan
AB: Slow earthquakes in western Japan are considered as a group of interplate slip events that obey the scaling law proposed by Ide et al. (2007), in which the seismic moment is proportional to the event duration. However, the population of events in this group is not continuous. In the Nankai slow earthquake zone, we have found deep low-frequency earthquakes (LFE) below 1 s, very low-frequency earthquakes (VLF, Ito et al., 2006) between 20-50 s, and slow slip events (SSE) above a few days. Are there any slow events other than these? If a slow earthquake that satisfies the scaling relation with duration of about 100 s occurs within the Nankai slow earthquake zone, it is observable at low-noise stations with a vertical broadband sensor only if they are located near the maximum direction of the near-field signal. One station that satisfies these conditions is F-net KIS with STS-1 seismometers, maintained by National Research Institute for Earth Science and Disaster Prevention, Japan. This station records tremor activities a few times per year since 1996. During most of the activities, we can detect many large low-frequency signals. Longer events include VLFs and we can show that some previously reported VLFs are actually a part of a longer event. We installed a temporary observation station at 15 km from KIS station and recorded a sequence of low frequency tremor for July 17-20, 2007. Although the low frequency signals are visible at two stations, the amplitudes are quite different, which suggests that we can determine the location and orientation of the source using a small dense array of broadband seismometers. As expected, the moment magnitudes of 100 s events are around 4, which satisfy the scaling relation of slow earthquake. Existence of much larger and longer events is implied from the records of KIS, although large low- frequency noise less than 3 mHz impedes reliable judgments. The existence of such events suggests that any size of slow earthquakes may occur like regular earthquakes.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting