[S-CG50] 島弧の構造・進化・変形とプレート沈み込み作用

[SCG50-P01] 庄内平野(遊佐・中野俣・余目地域)における高分解能反射法地震探査

*加藤 直子¹、石山 達也²、佐藤 比呂志²、越谷 信³、小池 太郎⁴、野田 克也⁴ (1.日本大学文理学部、2.東京大学地震研究所、3.岩手大学理工学部、4.株式会社ジオシス)

Understanding the relationship between active fault and seismic source fault with more detailed structural data on source faults is crucial to estimate seismic hazards. For this purpose, we carried out seismic reflection profiling to illuminate geometry of blind thrusts in the Shonai plain, Northeast Japan. Three seismic lines (Yuza, Nakanomata and Amarume) are located across the central to eastern margin of the Shonai plain to image underlying blind thrust structures. The length of seismic line is 6-12 km. In seismic data collection, we used vibrator trucks as a seismic source and deployed 10 Hz geophones at 10 m interval covering whole seismic line. Seismic shots with sweep frequencies of 5-100Hz were provided at all midpoints of receivers and corresponding seismic signals were recorded by fixed 600-1000 channels of seismic recorders. The obtained seismic data were processed using conventional common midpoint (CMP) reflection methods. All seismic sections successfully illuminate subsurface images down to 2 seconds in two-way travel time, and depth converted seismic sections show detailed structures of fault-related folds above blind thrust faults and east-dipping reflectors in 1.5km depth in the Amarume and Nakanomata seismic line. These experiments show validity of high-resolution seismic imaging techniques to identify otherwise inaccesible active blind structures beneath Quaternary sedimentary basins.