Landslides in tuff of the Kobe Group Yokoyama, S., Murai, M., Katoh, Y., Tani, Y. and Fujita, T.

Landslides in tuff of the Kobe Group Yokoyama, S., Murai, M., Katoh, Y., Tani, Y. and Fujita, T.

Landslides in tuff of the Kobe Group * Shunji Yokoyama*, Masanori Murai, Yasuo Katoh, Yasutaka Tani and Takashi Fujita 931m 100 300m 1 2 Department of Natural Environmental Science, Kochi University, Kochi 780-8520, Japan Graduate School of Kuroshio Science, Kochi University, Kochi 780-8520, Japan Kawasaki Geological Engineering Co., Gion-cho 1-40, Hakata-ku, Fukuoka 812-0038, Japan Faculty of Engineering, Osaka Institute of Technology, Omiya 5-16-1, Asahi-ku, Osaka 535-8585, Japan Fault Research Data Center, Tachiuribori 4-3-2, Nishi-ku, Osaka 550-0012, Japan 1980 1969 34 60 1987 kyu-tf 2 kyu-tf 2 1/ 50,0001988 113

135 E 135 15 E Sanda C. 34 50 N Ono C.? SandaBasin Miki C. Kakogawa C. RokkoMountains 34 40 N SetoInland Sea Awaji Island Akashi C. Akashi Straits OsakaBay 0 10km KobeCity 1:upper PleistoceneHolocene, 2:Pliocenemiddle Pleistocene, 36:Kobe Group(3:Hosokawa Formation, 4:Yokawa Formation, 5:Sanda Formation, 6:Iwaya Formation), 7:pre-Tertiary, 8:fault 1 2 3 4 5 6 7 8 1 1996 1988 19381976 19831987 K Ar 1,000 1988 199419962 19911991 1999319992 3 114

42 30Ma 1973 1986Imaoka et al.1988 1994 1994 19993 2 0 1993 5 100m 20km 0 8 2 3 (1961) 19711971 19831988 4 3 1971, 1983 Huzita et al. (1971) 1988 1971 115

Miocne Mitsuda F. 60m+ Ougo F. 110m± Yokawa F. 160m+ Arino F. 175m Lower Upper Lower Upper Lower Upper Lower Upper Ougo F. 190m Yokawa F. 180m± Arino F. 175m Upper Lower Lower Upper Lower Upper Kurumi T. Horinji T. Ishigamiyama T. Yokawa T. Myotomatsu T. Late Eocene - Early Oligocene? Ishigamiyama T. Rengeji T. Okutani T. Kitahata T. Ichihiara T. Toyooka T. Nakaoozo T. Taki T. Toda T. Ishigamiyama T. Kitahata T. Kamikume T. Tojo-ko T. Hosokawa F. 60m Harasaka Ms. M. 25m Kichiyasu Ss., Ms. and Cgl. M. 170-270m Nagao Ss. & Ms. M. 30-m Shimoisawa Ms. M. 10-50m Nitta Cgl. M. 40-m Toishigawa Ms. & Ss. M. -50m Yokawa F. 400m Sanda F. 100-300m Ikebe (eds.)(1961) Huzita and Kasama(19711983) Huzita et al.(1971) Kinki Regional Agricultural Administration Office(4) Ozaki and Matsuura(1988) 3 (4)(0) 1 3 1998 2km 3 1988 1998 116

0 4 1988 0 14ab EPMA Mg/(Fe+Mn+Mg) mg 1 1 4 mg mg mg = 0.56 0.580.58 mg = 0.480.510.49 mg = 0.540.55 mg = 0.69 mg = 0.55 117

4 Mg/Fe+Mn+Mg 0 118

5 3 5 1993 gull CaCaNa K Ca Yasuoka et al., 19950 10 20m 78.35m 80 130 1 Ca 10 3 10 4 4 6 4 3 119

Columnar section Lithofacies Conglomerate Fine-grained tuff Coarse-grained tuff Unit4 Fine-grained tuff Unit3 Lapilli tuff Unit2 Fine-grained tuff Unit1 Coarse-grained tuff thickness m 2030 23 2 45 35 24 1 Ss/Ms Alt. 20+ softness high low Sliding surface Sliding surface Sliding surface 4 10 3 10 4 m 3 10 10 m 3 6 3 103 167MPa 2 3 4 1 1 " 30 100MPa C L C M 10 6 m 3 10 15 2km 82 7 STOP1 0 500m 7STOP11/25,000 120

Slope moving area F1 F2 South Unit North Unit Moving body inner fault Bedding structure 5 N25E Subsidence part of moving body moving body Non subsidence part of Slope moving area? 190? 210 >4m >7m 6m 5m Nishihata R. 4m 3m Cross section 2m Lower graben 2m <2m Upper graben 190 Separating scarp 0 190 >7m 4m 5m6m 3m >7m 180 180 Main-moving domain >7m >7m? Nishihata R. 50 100 m Slope moving direction Scarp Collapse Open crack Fault Graben >7m Isopach of tuffaceous mudstone bed 190 170 170 180 8 0 4 1999 15 20m 8 19990 F2 7m 121

190 : bore hole Lower graben Upper graben Separating scarp 190 180 180 170 tfmd3 170 160 tfmd3 160 0 10 20 30 m Mudstone Sandstone mudstone Tuffaceous Tuffaceous sandstone Tuff Landslide debris 9 4 1m 9 10cm 10cm m cm cm 60 120 22 36 122

STOP2 0 500m 10 STOP2 1/25,000 17 1km 10 4,110ppm 42 43 C 30m 4m 1923 12 123

STOP3 STOP4 0 500m 11 STOP3 STOP4 1/ 25,000 17 2km ( 506 ) 2km 11 3 3 3 BOB&MOM 500 1,000 10 12 m 30m 124

250 Yokawa R. 250 140 LEGEND landslide body contour of ground surface contour of bottom of tuff beds bore hole moving direction pond 10 5 3 2 1 dip 160 170 180 0 500m 190 12 250 1 3 4 13 14 1 1 1m 50 80cm 1 5cm 1 1 1 1 3 1 1 2 3 ( 17 125

Yokawa R. 250 250 LEGEND contour of terrace deposit ground surface conglomerate landslide body tuff moving direction alternation of sandstone and mudstone pond 0 500m 250 13 A 250(m) 100 B 250(m) B A 5-1 5-1 5-2 C 7-11 C 7-11 5-3 D 7-10 D 7-10 5-5 E 5-6 F 5-7 7-12 G A 250(m) 100 H:V=2:1 E 8-2 F G 7-14 8-3 B 250(m) A - LEGEND terrace deposits conglomerate tuff alternation of sandstone and mudstone bore hole sliding surface A geological cross section 100 C 250(m) C 250(m) H:V=2:1 100 T7-3 T7-6 7-9 B 7-11 A 8-6 Yokawa R. B A C D 250 100 H:V=2:1 100 D 250(m) T53-3 T7-4 B 7-10 A 5-8 5-9 D 250(m) C 0 500m D A B 250 100 H:V=2:1 100 14 126

STOP5 0 500m 15 STOP5 1/25,000 (m) 2 0 fine-grained tuff coarse-grained tuff sandstone conglomerate 16 127

P.10 P.9 P.8 P.7 P.6 P.5 P.0 P.1 P.2 0 10m P.3 P.4 LEGEND fine-grained tuff coarse-grained tuff sandstone conglomerate 10(m) 5 0 10(m) 5 0 Line 0 Line Line Line Line Line Line Line Line Line 10(m) 5 0 10(m) 5 0 17, 0, 39, 375 378, 1987,,, no. 6, 119 130, 1976,,, 293p, 1983,,, 206p, 1971, 5 1, 58p, 1983, (5 1 ),, 115p Huzita, K., Kasama, T., Hirano, M., Shinoda, T. and Yamashita, M., 1971, Geology and geomorphology of the Rokko area, Kinki district, Japan with special reference to Quaternary tectonics Jour. Geosci. Osaka City Univ., 14, 71 124, 1961, 17 1, 171p, 1986,, no. 26, 1 109, 0, 39, 373 374 128

uniaxial compressive strength (MPa) cm 0.41.3 rainfall LEGEND fine-grained tuff coarse-grained tuff sandstone conglomerate concretion rill spring 2.412.5 6.26.8 100 5.839.1 340 10 5.910.7 120+ columnar section cross section frontal sketch 18, 3, Sr, 109, 106 115 Imaoka, T., Murakami, N., Matsumoto, T. and Yamasaki, H., 1988, Paleogene cauldrons in the western San-in district, Southwest JapanJour. Fac. Liberal Arts, Yamaguchi Univ., 22, 41 75, 1999,, no. 53, 393 401, 1994,, no. 20, 3 57, 0, 39, 395 398, 4, 43, 497 500, 1999, lateral spreads 38, 431 434, 1993, 32, 79 82, 3,, no. 4, 69 75, 2,, 56, 289 294, 4, 15 5, 0, 39, 383 386, 1987, 16, 138p, 2, 20 1,, 1991,, 129

, 97, 671 674, 3, 15, 81 86, 3, 15, 303 306, 1973,, no. 9, 93 105, 0, 39, 379 382, 4a, 43, 487 490, 4b, 43, 303 306, 1999, FT, 53, 391 396, 1991,, 97, 251 254, 1988, (5 1 ),, 89p, 1996,, 102, 73 83, 1994,,, 100, 692 708, 1998,, 9, 9 18, 1938,, 45, 621 640, 3,, 112, 35 49, 1, 2, 55, 157 171, 1,,, 145p Yasuoka, T., Kitagawa, R., Takeno, S. and Yokoyama, S., 1995, Mineralogical characteristics of smectite from the landslide area in the Neogene Kobe group, southwest JapanJour. Sci. Hiroshima Univ., Ser. C, 10, 487 505, 3, 16, 37 56, 0, 39, 371 372, 1994,, no. 7, 38 39 130

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