Precise mapping of active faults along the Itoigawa-Shizuoka Tectonic Line in the southern part of Matsumoto Basin

概要

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Precise air-photo interpretation of tectonic landforms in the south of Matsumoto basin was made in order to clarify the overall nature of active faulting along the Itoigawa-Shizuoka Tectonic Line. The fault zone consists of both thrust and strike-slip faults. At the eastern boundary of the basin is an east-dipping thrust fault, which has become inactive progressively from the south to the north in late Quaternary time. Three to four kilometers west of the boundary fault is another west-dipping thrust fault, which, however, is still active in Holocene time. Thus, the thrust front is likely to have migrated basin-ward in late Quaternary time. A purely strike-slip fault (Gofukuji fault) exists on the upthrown side of, and parallel to, the boundary fault; the Gofukuji fault has a slip rate as high as 8.6±1.0 mm/yr and is still active. Our observations indicate that the overall movement on the Itoigawa-Shizuoka Tectonic Line at depth is transpressional and is transferred at shallow depths into both thrust and left-slip movements. We therefore interpret that significant slip partitioning is taking place on the up-dip extension of an east-dipping fault, which was originated from a normal fault bordering the west margin of the Northern Fossa Magna rift of early and middle Miocene age, and has rejuvenated as oblique slip fault since Pliocene time.
Japanese Society for Active Fault Studiesの論文