栃木県関谷断層の活動履歴調査

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1 No. 1p Paleoseismological study of the Sekiya fault in Tochigi Prefecture Yukari Miyashita 1, Yuichi Sugiyama 1, Takahiro Yamamoto 2, Toshikazu Yoshioka 1, Akira Sangawa 1, Masanobu Shishikura 1, Naoki Maruyama 3, Akira Oishi 3 and Takashi Hosoya 4 Abstract: The Sekiya fault is an N-S-trending thrust in the northern part of Tochigi Prefecture. We conducted precise topographic survey and trenching of the northern part of the Sekiya fault in Momura area, Kuroiso City. The precise topographic survey has made clear that the early Holocene terrace is not only displaced but also involved in flexure deformation, and its total vertical displacement including flexure part attains to 9 to 10 m. The trenching survey has revealed that the last rupture event on the northern part of the Sekiya fault occurred after the fall of the Haruna-Futatsudake-Ikaho Pumice in the 6th century. It is also made clear that a penultimate event occurred 5000 to 6000 ybp. Key words: active fault, paleoseismology, Sekiya fault, Tochigi Prefecture, trench 30 km m/ m m Active Fault Research Center 2 Research Center for Deep Geological Environments 3 NEWJEC Inc. 4 Chuo Kaihatsu Corporation

2 1020 m m 12 m m 2 a m 200 m 2 b cm 2 2 b 80 m m 200 m 910 m m m m m 1 m m m m 5 2 b

3 A1 A2 A2 A3 A4 A5 A2 Hr-FP 1500 Hr-FP 2 mm yBPBC yBPAD A3 A4 15 cm yBPBC yBPBC A5 10 cm 30 cm / yBPBC yBPBC A2 Hr-FPA3 A5 A4 A5 A yBPBC yBPAD AF1 AF cm AF1 AF2 40 A5 2 m AF1 A5 A4 AF1 AF2 A B1 B2 B3 B4 B5 B6 B7 B8 B2 Hr-FP yBPBC yBPAD B yBPBC yBPBC B yBPBC B5 140 cm 20 B4 15 cm 12 cm Nm-NK 5000 ybp yBPBC yBPBC

4 B yBPBC B7 B8 510 cm 1 cm Nk-Ku cm 7 m BF1 20 B8 B2 BF1 BF1 B7 B m 7 m BF2 BF2 B5 B4 BF2 B8 B7 B7 B6 B6 B5 B7 B C1 C2 C3 C4 C5 C6 C7 C8 C2 Hr-FP yBPAD yBPAD C3 Hr-FP yBPAD yBPAD C4 13 cm C yBPBC yBPBC C yBPBC yBPBC C7 10 cm Nk-Ku Nk-Ku 14 3Nk-Ku3 1.6 Nk-Ku 1 C8 510 cm 2 CF1 15 C7 C3 CF2 C5 C4-4 -

5 Hr-FP B2 BF1 Hr-FP C3 CF1 6 Hr-FP BF1 B yBPAD yBPAD CF1 C yBPAD yBP AD Hr-FP A2 BF1 A2 A2 A5 A2 B5 B4 BF2 C5 C4 CF2 C5 C4 C5 B5 14 B5 B4 BF2 CF2 B yBPBC yBPBC B5 Nm-NK 5000 ybp B yBPBC B yBPBC yBPBC C yBPBC C yBPAD BC / AF1 A

6 no p p P Jm-P

7 栃木県関谷断層の活動履歴調査 7

8 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 8

9 栃木県関谷断層の活動履歴調査 9

10 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 10

11 栃木県関谷断層の活動履歴調査 11

12 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 Sample Mineral composition Refractive index mode Glass Opx Hbl Haruna-Futatsudake-Ikaho tephra (Hr-FP) Hr-FP Hbl > Opx, [Cpx] ( (90%) A Hbl > Opx, [Cpx] ( ( (90%) B Hbl, Opx Numazawa-Numazawako tephra (Nm-NK) Nm-NK Hbl > Opx; Qtz ( (70%) A Hbl > Opx; Qtz ( ( (80%) C Hbl > Opx, [Cpx], Q t ( ( (50%) Nikko-Nantai-Kutsukake tephra (Nk-Ku) Nk-Ku Opx > Cpx, [Ol] ( (40%) 12

13 栃木県関谷断層の活動履歴調査 13

14 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 14

15 栃木県関谷断層の活動履歴調査 15

16 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 Table 2. Radiocarbon dating results of trench A. Sample No. Lab No. (Beta-) Location trench/wall Horizon Material Method Measured 14 age (y BP) C 13 C () Conventional Calibrated age 14 C age (y BP) (Cal AD/BC; 1) SEK A/N A5 humic soil 7020± ±90 BC SEK A/S A2' humic soil 1020± ±70 AD SEK A/S A2 humic soil ext. 2400± ±70 BC , SEK A/S A2' humic soil 960± ±70 AD SEK A/S A2 humic soil 2780± ±80 BC SEK A/E A5 humic soil AMS 7270± ±40 BC SEK A/E A4 humic soil 6430± ±70 BC SEK A/E A2' humic soil 3180± ±70 BC SEK A/S A4 charcoal AMS 8050± ±40 BC SEK A/S A4 charcoal AMS 6980± ±40 BC SEK A/S A2 humic soil 1780± ±70 AD , SEK A/S A2 humic soil 4240± ±60 BC SEK A/S A4 humic soil ext. 8310± ±110 BC , SEK A/S A4 humic soil 6370± ±80 BC SEK A/S A4 humic soil 6090± ±60 BC SEK A/S A2' humic soil ext. 2630± ±70 BC

17 栃木県関谷断層の活動履歴調査 17

18 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 18

19 栃木県関谷断層の活動履歴調査 19

20 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 Table 3. Radiocarbon dating results of trench B. Sample No. Lab No. (Beta-) Location trench/wall Horizon Material Method Measured 14 C age (y BP) 13 C () Conventional Calibrated age 14 C age (y BP) (Cal AD/BC; 1) SEK B/N B5 humic soil 8760± ±60 BC SEK B/N B5 humic soil 6310± ±80 BC SEK B/N B5 humic soil 5140± ±80 BC SEK B/N B4 humic soil 4430± ±80 BC , SEK B/N B2 humic soil 2550± ±70 BC SEK B/N B5 humic soil 5180± ±70 BC SEK B/N B3 humic soil 3580± ±70 BC , SEK B/N B6 humic soil 6360± ±80 BC SEK B/N B5 humic soil 5450± ±60 BC , SEK B/N B3 humic soil 3490± ±70 BC SEK B/N B2 humic soil 2140± ±60 BC SEK B/N B2 humic soil 2280± ±60 BC SEK B/N B2 humic soil 2410± ±60 BC , SEK B/N B2 humic soil 2650± ±60 BC SEK B/N B2 humic soil 2010± ±60 BC SEK B/N B2 humic soil 2500± ±80 BC , SEK B/N B2 humic soil 1300± ±60 AD SEK B/N B2 humic soil 470± ±60 AD

21 栃木県関谷断層の活動履歴調査 21

22 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 22

23 栃木県関谷断層の活動履歴調査 23

24 宮下由香里杉山雄一山元孝広吉岡敏和寒川旭宍倉正展丸山直樹大石朗細矢卓志 Table 4. Radiocarbon dating results of trench C. Sample No. Lab No. (Beta-) Location trench/wall Horizon Material Method Measured 14 age (y BP) C 13 C () Conventional Calibrated age 14 C age (y BP) (Cal AD/BC; 1) SEK C/S C2 humic soil 1090± ±60 AD SEK C/S C2 humic soil 990± ±60 AD SEK C/S C6 humic soil 8570± ±60 BC SEK C/S C5 humic soil 5390± ±70 BC SEK C/S C3 humic soil 1170± ±60 AD , SEK C/S C3 humic soil 1370± ±70 AD SEK C/S C3 humic soil 1380± ±60 AD SEK C/S C3 humic soil 1140± ±60 AD SEK C/S C2 humic soil 1210± ±60 AD SEK C/S C2 humic soil 960± ±60 AD SEK C/S C6 humic soil 8490± ±80 BC SEK C/S C6 humic soil 10960± ±70 BC SEK C/S C5 humic soil 8970± ±60 BC SEK C/S C3 humic soil 1090± ±60 AD SEK C/S C3 humic soil 1540± ±70 AD SEK C/S C3 humic soil 1140± ±60 AD SEK C/S C3 humic soil 1250± ±60 AD SEK C/N C5 humic soil 5510± ±80 BC SEK C/N C5 humic soil 6210± ±60 BC , SEK C/S C5 humic soil 7830± ±60 BC SEK C/S C5 humic soil 8280± ±70 BC

R927清水信彦様.indd

R927清水信彦様.indd Special Issue CFRP 455-8502 9 1 Development Status of Carbon Fiber Reinforced Plastics Nobuhiko SHIMIZU Automotive Center, Toray Industries, Inc., 9-1 Oe-cho, Minato-ku, Nagoya, Aichi 455-8502 Received