Japan Geoscience Union Meeting 2014

Presentation information

Print

Oral

Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG64_30PM2] Slow earthquakes

Wed. Apr 30, 2014 4:15 PM - 6:00 PM 501 (5F)

Convener:*Hitoshi Hirose(Research Center for Urban Safety and Security, Kobe University), Kazushige Obara(Earthquake Research Institute, The University of Tokyo), Ryoko Nakata(Japan Agency for Marine-Earth Science and Technology), Chair:Ryoko Nakata(Japan Agency for Marine-Earth Science and Technology), Naoki Suda(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University)

4:30 PM - 4:45 PM

★ [SCG64-16] Spatiotemporal Distribution of Shallow Very Low Frequency Earthquakes along the Nankai Trough and the Ryukyu Trench

*Youichi ASANO1, Takanori MATSUZAWA1, Kazushige OBARA2 (1.National Research Institute for Earth Science and Disaster Prevention, 2.Earthquake Research Institute, The University of Tokyo)

Keywords:Very Low Frequency Earthquakes, Nankai Trough, Ryukyu Trench

We have investigated spatiotemporal distribution of shallow very low frequency earthquakes (sVLFEs) along the Nankai trough and the Ryukyu trench. Three component seismograms recorded at 40 broadband stations of the NIED F-net were analyzed by using waveform-correlation and back-projection techniques after processing a band-pass filter (0.02 to 0.05 Hz). Here we used known 6 sVLFEs and 17 regular interplate earthquakes near the trench axis as template events. Time series of cross-correlation function (CC) at each station was calculated from continuous waveform data and triggered seismograms of template events. Assuming surface wave propagation, CCs are back-propagated onto possible origin times and horizontal locations. We obtained sVLFE epicenters by performing a grid search in time and space domains to maximize the averaged CCs from all stations under the condition of high signal to noise ratios that was defined as amplitude ratios between two time windows before and after the surface wave arrivals from the epicenters. As the result of this analysis for the last decade, we detected infrequent activity of sVLFE episodes at a few clusters adjacent to the locked zone related to the megathrust earthquakes along Nankai trough: in 2004 and 2009 of Kii peninsula, in 2003 and 2009 off cape Muroto, and in 2003 and 2010 off cape Ashizuri. On the other hand, sVLFE episodes in Hyuga-nada and areas along the Ryukyu trench are frequent. Such a variation of seismicity of sVLFEs revealed from this study based on the same detection capability may suggest the difference of the plate coupling in the seismogenic zone.