Shallow S-wave seismic reflection profiling across the northern section of the East Matsumoto Basin fault in the Itoigawa–Shizuoka tectonic line active fault system, central Japan

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  • 糸魚川―静岡構造線断層帯松本盆地東縁断層北部におけるS波浅層反射法地震探査
  • イトイガワ-シズオカ コウゾウセン ダンソウタイ マツモト ボンチ トウエン ダンソウ ホクブ ニ オケル Sハセンソウ ハンシャホウ ジシン タンサ

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Abstract

<p>　 We conducted S-wave shallow seismic reflection profiling to reveal subsurface structure and strata deformed by the faulting on the northern section of the East Matsumoto Basin fault (N-EMBF) along the Itoigawa–Shizuoka tectonic line active fault system. The Itoigawa–Shizuoka tectonic line divides into the NE and SW Japan arcs, and it is one of the most major tectonic lines in Japan. The N-S trending and east dipping N-EMBF extends along the eastern margin of the Matsumoto Basin, and it is one of the reverse faults that compose the northern segment of the ISTL active fault system. The seismic profiling consisted of E-W trending survey lines EW-1, 2, and 3 and N-S trending lines NS-1, 2, and 3 whose lengths range 130-500 m. A S-wave portable vibrator (OYO-CAG) was used as seismic source. Both the standard shot intervals and receiver intervals were 2 m. After careful processing for the acquired common mid-point seismic reflection data, we obtained depth converted seismic sections showing subsurface structures above the maximum depth of about 50 m. The sections EW-1 and 3 revealed the east dipping fault with 20 degrees. The section EW-2 exhibits a flexure zone which is located along an active fault trace reported by the past tectonic geomorphic surveys. Considering the vertical component of coseismic displacement and the ages of seismic events estimated by the previous paleoseismic investigation and subsurface structure of the active reverse fault detected in this study, we have calculated that the coseismic displacement and the Holocene slip rate at the survey site are about 5.3 m and 1.5-2.1 mm/yr respectively.</p>

Journal

  • Active Fault Research

    Active Fault Research 2021 (54), 23-38, 2021

    Japanese Society for Active Fault Studies

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