神奈川県西部山北南高感度地震観測井の掘削および孔内検層，Borehole Drilling and Physical Properties of the Yamakita-minami Seismic Observatory in Western Ka

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2 *1 *2 *3 *4 *5 *5 *6 *6 *2 *7 *5 *4 *5 *5 *6 *6 Borehole Drilling and Physical Properties of the Yamakita-minami Seismic Observatory in Western Kanagawa Prefecture, Central Honshu, Japan Hiroki HAYASHI *1, Tanio ITO *2, Yo UESUGI *3, Hiroko OYAMADA *4, Keiji KASAHARA *5, Shoji SEKIGUCHI *5, Masaki TAKAHASHI *6, Yuichiro TANAKA *6, Masashi TSUKUI *2, Tomoyuki MATSUI *7, Takumi MATSUMOTO *5, Masaru YAMAZAKI *4, Ryuji YAMADA *5, Fumio YAMAMIZU *5, Yukio YANAGISAWA *6, and Mahito WATANABE *6 * 1 Shimane University, Japan * 2 Chiba University, Japan, * 3 Tsuru University, Japan, * 4 University of Tokyo, Japan * 5 National Research Institute for Earth Science and Disaster Prevention, Japan * 6 Geological Survey of Japan /AIST, Japan * 7 Earthquake Research Institute, University of Tokyo, Japan Abstract The Yamakita-Minami deep observation well was drilled to 2,035.4 m deep near an active fault in the arc-arc collision zone, in western Kanagawa Prefecture, Japan. Whole-core samples were recovered from 0 to 1,076.6 m deep and four spotcore 1 to 2 m long samples at 1,492, 1,799, 2,025, and 2,033 m deep. Geophysical logging and vertical seismic profiling were conducted to measure in-situ physical properties of rocks such as P-wave velocity and density. The geological profile of the borehole was presented based on geophysical logging data and microscopic examination of core and slime samples. Key words : Borehole geology, Kanagawa Prefecture, Logging, Yamakita Town A C * 1 *2 *3 *4 * 5 *6 * 7 1

3 Kobayashi and Koketsu, ,000m 1,076.6m VSP P S Hi-net m 870m 243.5m P 3.5km Hi-net N.MTDH 1 Table 1 Drilled cores of the Yamakita-minami observatory. 2 Table 2 Geographical loggings carried out for the Yamakita-minami observatory km/s 7.5km Hi-net N.YM2H P 4.0km/s 2,000m P 4km/s 2,035.4m m, m, 752.9m, 761.4m, 864.7m, 974.5m, 1,116.4m 3 1,405.0m 1,530 1,600m 50m 3 5m 500ml 0 1,076.6m VSP P S 2

4 3 Table 3 Heat conductivities of the cores from the Yamakita-minami observatory. VSP VSP 3. VSP A-H 8, 2006;, m 2g/cm g/cm 2 VSP 800m P 700-2,500m/s S 370-1,500m/s P 3,500-4,500m/s S 2,120m/s P KiK-net KNGH19 SZOH38, SZOH39, SZOH40, SZOH41, SZOH42 P 3,000-3,500m/s S 1,500m/s 2,030.6m m 1.86 K/100m W/mK 1,500m 20mW/m ,030.0m H RR2002 I 1 Kobayashi, R., and Koketsu, K Source process of the 1923 Kanto earthquake inferred from histrical gedetic, teleseismic and strong motion data. Earth, Planets and Space, 57, p ,

5 ,035.4m Hi-net 1,076.6m 4 VSP P 4

6 1 1:25,000 HNF: HRF: MKF: Fig. 1 Map of drilling site for the Yamakita-minami seismic observatory well. Topographic map: Yamakita 1:25,000 scale published by Geographical Institute of Japan. HNF: Hinata Fault. HRF: Hirayama Fault. MKF: Matsudakita Fault. 5

7 2 Fig. 2 Well structure of the Yamakita-minami observatory. 6

8 7 3 4 Fig. 3 Geologic and logging section of the Yamakita-minami observatory. The lithologic legend is indicated in Fig. 4.

9 8 4 N Fig. 4 Borehole televiewer profile at the Yamakita-minami observatory, with geologic and caliper profiles. Distribution of fracture dip direction is indicated by rose-diagram at each depth interval.

10 9 Depth, km YAMAKITA MINAMI 0 A B C 0.5 D E 1.0 F G 1.5 H km/sec km/sec 8 km/sec km/sec km/sec gr/cc Geology P Velocity S Velocity Sonic Density 5 VSP P S Fig. 5 Comparison of well geology, P and S wave velocity structure obtained by the VSP measurement, and sonic and density logs of the Yamakita well.

11 Appendix Photographs of core samples from the Yamakita-minami observatory. 10

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5 6 7 Seismic observation station Agency Seismic intensity South- North (NS) Maximum acceleration (Gal ) East-West (EW) Vertical (UD) Combining threecomponent Epicentral distance (km) Kawaguchi* JMA 7