(2008 11 2009 4 ) Short-term slow slip event with non-volcanic tremors in southwest Japan (November, 2008 April, 2009) National Research Institute for Earth Science and Disaster Prevention (SSE) 1, 2) 2008 11 2009 4 3) SSE Hi-net SSE (1) 2008 11 (2) 2009 2 (3) 2009 4 (1) 2008 11 2008 11 10 1 3) 10 12 (VLFE) 4) 11 10 14 SSE ( 1 ) 5 SSE 2 SSE 2008 6 5) 5 Mw6.2 2008 3 6) 6 5) (2) 2009 2 2009 2 5 14 3) 2 10 11 3) 2 6 9 SSE ( 3 ) 4 SSE 4 (VLFE) 4) 0.04 rad 2008 8 9 SSE 5) 2008 5 5) - 392 -
(3) 2009 4 2009 4 2 17 3) 3) 4 7 14 SSE ( 5 ) 12 12 ( (a) (b)) SSE 6 (b) (VLFE) (b) (a) (b) (a) Bootstrap ( 2) ) 2008 9 10 5) ( ) Hisanori Kimura, Shutaro Sekine, Hitoshi Hirose, and Kazushige Obara 1) Obara, K., H. Hirose, F. Yamamizu, and K. Kasahara, Episodic slow slip events accompanied by non-volcanic tremors in southwest Japan subduction zone, Geophys. Res. Lett., 31 (23), doi:10.1029/2004gl020848, 2004. 2) Hirose, H. and K. Obara, Repeating short- and long-term slow slip events with deep tremor activity around the Bungo channel region, southwest Japan, Earth Planets Space, 57 (10), 961-972, 2005. 3), (2008 11-2009 4 ),. 4) Ito, Y., K. Obara, K. Shiomi, S. Sekine, and H. Hirose, Slow Earthquakes Coincident with Episodic Tremors and Slow Slip Events, Science, 315, 503-506, 2007. 5), (2008 5-2008 10 ),, 81, 539-548, 2008. 6), (2007 11-2008 3 ),, 80, 426-433, 2008. 7) Tamura, Y., T. Sato, M. Ooe, M. Ishiguro, A procedure for tidal analysis with a Bayesian information criterion, Geophys. J. Int., 104, 507-516, 1991. - 393 -
1 2008 11 1 17 2. BAYTAP-G 7) Fig.1 Time series of tiltmeter records, daily tremor counts of this episode, atmospheric pressure and precipitation from Nov. 1 to 17, 2008. N and E followed by a station code with four characters denote the northward and eastward ground down components, respectively. The atmospheric pressure and precipitation were observed at Tsu meteorological observatory. These station locations are shown in Fig.2. The records are plotted after removing their linear trend, and tidal and atmospheric pressure components estimated by BAYTAP-G 7). - 394-2 11 10 14 Fig.2 Tilt change vectors (green arrows; ground downward direction), the estimated short-term slow slip model( red rectangle area and arrow) from these tilt change data, and the calculated tilt changes due to this short-term slow slip event model (purple arrows) for the western Shikoku region. Brown Stars are epicenter of the VLF earthquakes. Epicenters distribution of deep low-frequency tremor activity is also plotted during the same time period.
4 2009 2 SSE. 2. 2 6 9. Fig. 4 Same as Fig. 2 but for the February 2009 Aichi prefecture short-term SSE. 3 2009 1 27 2 19. 1. 4.. Fig. 3 Same as Fig. 1 but for the records observed around the Aichi and Shizuoka prefectures from Jan 27 to Feb 19, 2009. The atmospheric pressure and the precipitation were observed at the JMA Nagoya meteorological observatory. The station locations and the tilt changes during the time window indicated by broken lines are shown in Fig. 4. - 395 -
5 2009 3 29 4 19. 1. 6.. Fig. 5 Same as Fig. 1 but for the records observed around the western Shikoku Aichi from March 29 to April 19, 2009. The atmospheric pressure and the precipitation were observed at the JMA Uwajima meteorological observatory. The station locations and the tilt changes during the time window indicated by broken lines are shown in Fig. 6. - 396 -
6 2009 4 SSE. 2. 4 7 11 ( (a)) 12 14 ( (b)). Fig. 6 Same as Fig. 2 but for the April 2009 western Shikoku short-term SSE. Fault models estimated from tilt records from April 7 to 11 (period (a)) and 12 to 14 (period (b)) are shown. - 397 -