High-resolution seismic reflection survey across the Western Boundary Fault Zone of the Nagano Basin, Central Japan: Data acquisition and processing

Abstract

The Western Boundary Fault Zone of the Nagano Basin borders the eastern margin of Northern Fossa Magna, which has undergone strong horizontal shortening since Pliocene. The Western Boundary Fault Zone of the Nagano Basin is considered to be a back thrust that developed on the hanging wall side of the Itoigawa-Shizuoka Tectonic Line. To reveal the subsurface structure of the Western Boundary Fault Zone of the Nagano Basin, we carried out a high-resolution seismic reflection survey along the Saigawa River, southern Nagano City. The source used in this survey was a mini-vibrator (T-15000). Source and receiver spacing was 10 m. 180 channels of geophone arrays were used to record each shot. The seismic section obtained after careful data processing shows fairly flat Quaternary basin fillings in the eastern part of the seismic line. The Quaternary basin fillings are interpreted to be in west-dipping fault contact with west-dipping Neogene strata underlying the Saigawa Hills