著者

須貝 俊彦 水野 清秀 八戸 昭一 中里 裕臣 石山 達也 杉山 雄一 細矢 卓志 松島 紘子 吉田 英嗣 山口 正秋 大上 隆史

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.116, no.3-4, pp.394-409, 2007-08-25 (Released:2009-11-12)

参考文献数

26

被引用文献数

5 9

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The northern Ayasegawa fault is a part of the Fukaya fault system, which is the longest active fault in the Kanto district. The paleoseismology of the northern Ayasegawa fault was revealed by a combination of arrayed boring and ground penetrating radar (GPR) survey. The northern Ayasegawa fault produced a fold scarp with the NW-SE direction running along the boundary between the Oomiya 2 (O2) surface and fluvial lowland. The O2 was formed in Marine Isotope Stage 5a, and was slightly deformed with a wide warping zone. Sixteen sediment cores arrayed across the warping zone contain a series of tephra layers such as Hk-TP (ca. 60-65 ka), KMP, AT (26-29 ka), As-BP group (20-25 ka), and As-YP (15-16.5 ka). These key beds except Hk-TP were deposited and deformed parallel to each other, suggesting that no faulting events occurred between KMP and As-VP fall. The timing of the last faulting event is after the As-YP fall, and is probably younger than 10 ka based on an interpretation of GPR profiles and 14C ages. KMP should be deposited horizontally because it intervened in the peaty silt layer, which accumulated conformably on lacustrine deposits overlapping the fold scarp. Thus, the KMP horizon roughly indicates the vertical offset produced by the events occurred after the As YP fall. The events were probably singular, and the last one formed a vertical offset of more than 4 m. The older event occurred at around 70 ka between Hk-TP fall and O2 formation. Vertical deformation of the O2 was at least 7 m, indicating the possibility that the vertical offset caused by the penultimate event is at least 3 m. The vertical slip per event might reach 5 m, and the average vertical slip rate is nearly 0.1 mm/yr because the warping zone detected by the arrayed boring above is within the flexure zone shown by the P-wave seismic profile. The northern Ayasegawa fault is considered to be a single behavioral segment because of its longer recurrence interval and lower slip rate of 0.1 mm/yr in comparison with those of the other part of the Fukaya fault system.

著者

須貝 俊彦 鳴橋 竜太郎 大上 隆史 松島 紘子 三枝 芳江 本多 啓太 佐々木 俊法 丹羽 雄一 石原 武志 岩崎 英二郎 木本 健太郎 守屋 則孝

出版者

東京大学

雑誌

基盤研究(C)

巻号頁・発行日

2008

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関東平野の綾瀬川断層、濃尾平野の養老断層を主な対象として、地形、表層地質調査を行い、とくに河川による土砂移動プロセスと活断層の活動との関係に着目して、伏在変動地形の識別と伏在活断層の活動性評価を目的として研究を進めた。その結果、綾瀬川断層では、最終氷期の海面低下期に形成された埋没段丘面群と沖積層基底礫層の堆積面(埋没谷底面)において、明瞭な断層上下変位が見出され、その平均上下変位速度は約0.5 mm/年と見積もられた。養老断層では地震動による土石流発生と沖積錐の成長が繰り返され、断層崖を埋積してきたことなどが明らかになった。同時に平野の地震性沈降が、コアのEC、粒度、全有機炭素/窒素、帯磁率等の分析によって検出可能であることが示され、そのタイミングが^<14C>年代測定値によって与えられた。