The origin and mechanism of active folding in Japan

Abstract

Active fold belts in Japan are likely to be underlain by detachment faults with flat-ramp geometry. These fold belts fall into two categories: (1) the tectonic inversion type and (2) the foreland fold-and-thrust belt type. The former includes the Uetsu and the Northern Fossa Magna fold belts, which are located in Miocene rift basins. The normal faults that formed the rift basins have rejuvenated as thrust faults due to regional compression since the Pliocene, resulting in folding in a thick pile of rift sediments. The latter category includes the Teshio-Ishikari and the Southern Fossa Magna fold belts. They are located in foreland basins that have been formed since Neogene time up to the present in association with arc-arc collision. The master faults underlying these fold-and-thrust belts are likely to extend down-dip to the plate boundary faults.