1. SEISMICITY AND CRUSTALL STRUCTURE ALONG THE SOUTHERN JAPANESE ALPS SEGMENT OF THE ITOIGAWA-SHIZUOKA TECTONIC LINE (ISTL) Speaker: Yannis Panayotopoulos Yannis PANAYOTOPOULOS [1], Naoshi HIRATA [1], Hiroshi SATO [1], Aitaro KATO [1], Kazutoshi IMANISHI [2], Ikuo CHO [2], Yasuto KUWAHARA [2] [1] ERI, Univ. Tokyo; [2] GSJ, AIST;

2. The geological setting along the Itoigawa- Shizuoka tectonic line (ISTL). Northern J-Alps ISTL: western boundary of the Northern Fossa Magna rift basin 、 east dipping faults. Southern J-Alps ISTL ： boundary between the Izu-Bonin Arc crust and the Honshu Island crust (Chichibu-Shimanto belts). I.S.T.L Paleozoic-Mesozoic rocks Miocene rocks  Yatsugatake volcano  Yatsugatake volcano Mt. Fuji  Crataceous-Tertiary rocks Crataceous-Tertiary rocks Izu-Bonin rocks Izu-Bonin rocks M.T.L ・ Geology

3. Investigate the relation between the micro earthquake activity,crustall velocity structure and geological structure in the vicinity of the ISTL and correlate it with its present time activity. For this purpose: We monitor the seismicity in the southern part of the ISTL. Estimate the 3D seismic wave velocity structure and compare it with the geological structure in the area. Investigate the relation between the regional seismicity and the active parts of the ISTL fault system. ・ Objectives

4. 1.From 2003/8/25 to 2003/10/16 1 linear station array of 58 offline recorders 2.From 2005/9/16 to 2005/12/22 2 lines of 26 and 30 offline stations 14 more stations in collaboration with the Japanese Geological Survey Institute 3.Near by 100 online Japanese national network stations ・ Stations

5. 89 events from 2003/08/25 to 2003/10/16, recorder by the 2003 probe 348 M > 0.5 events from 2005/09/01 to 2005/12/31, recorded by the 2005 probe 13 explosion scheduled for the same period Manually repicked 83,053 P and S faze arrivals ・ Selected events From 2003/08/25~10/16 and 2005/09/01~12/31

6. x y ・ Data processing Method ： Double-difference tomography (Zhang and Thurber 2003) Grid point distribution ： x-axis ： 5km spacing for the central 60km 、１５ｋ ｍ or ２０ｋｍ spacing for the rest y-axis ： 8km spacing for the central 5 lines, 16 and 24 for the outer lines at depth ： 0 、 3, 6, 9, 12,16, 20, 30, 35, 100, 200 km

7. DD relocated events The difference between the hypocenter depth published by the Japanese National Meteorological agency and the one relocated by this study progressively grows with depth. ・ Results （１） 2005/09/01~12/31

8.         Mechanism solutions Imanishi et al 、 2006 ・ Results （２） MTL Wakamiya Aoyagi Hakushu Hoouzan Onajika-toge Ichinose Shimotsuburai East-west Vp cross sections near each fault segment Mechanism solutions Imanishi et al 、 2006 Mechanism solutions Imanishi et al 、 2006

9. ・ Discussion （１） MTL Hakushu Cross section near Hakushu fault MTL 発震機構解 今西・他、 2006 Hakushu(ISTL)

10. ・ Discussion （２） Onajika-toge Ichinose Onajika-toge Ichinose （ ISTL) Koma block (Tanzawa) Koma block (Tanzawa) Kofu Basin Chichibu-Shimanto belts Cross section and geology near Ichinose and Onajika-toge faults Koma bloc ｋ (Tanzawa) Misaka block (pIc) (Tanzawa) Chichibu-Shimanto belts Kofu Basin Yamanashi Pref. (2004)

11. The deeper extension of the ISTL in the southern Japanese Alps region becomes the boundary between a low and a high Vp region. We identify the low Vp region as the Chichibu-Shimanto accretionary prism belts of the Honshu island crust and the high Vp region as part of the Izu-Bonin arc paleo-crust. The ISTL deeper extension, forms an approximately 50 0 west dipping thrust fault. The seismic activity near the Hakushu fault segment occurs on the ISTL. The crustall structure near the Ichinose fault also has the characteristics of a west dipping thrust. ・ Conclusions