Permalink : http://hdl.handle.net/2115/36710

It has been considered that the Kurile Arc "collided" with the Northeastern Japan Arc or Central Hokkaido. (Kaizuka, 1972, 1976; Fujii and Sogabe, 1978). Fujii and Sogabe (1978) recognized a N-S trending suture fault zone in eastern Hokkaido. The author revealed the detailed movement picture of the fault zone on the basis of structural analysis of the fault and adjacent deformation, and called the fault zone the Abashiri Tectonic Line. The Abashiri Tectonic Line is estimated to be connected with the Kitami-Yamato Thrust in the Okhotsk Sea and the Kushiro submarine canyon in the Pacific, and traverses the trench-arc system at the southwestern margin of the Kurile Arc. The Abashiri Tectonic Line is divided into two segments; the N-S trending northern segment and the NE-SW to N-S trending southern segment. The northern segment is truncated by the southern segment in the Hombetsuzawa area, where the latter segment bends its direction from NE-SW to N-S toward south. The Abashiri Tectonic Line was formed through the tectonic process of the following two stages. First stage: A notable left-lateral strike-slip movement along the tectonic line occurred in Late Miocene time. This movement picture was revealed by analysis of echelon folding along the northern segment of the tectonic line. This movement, however, has been inactive since Pliocene time, inferred from the evidence that the Pliocene strata overlie the segment. Second stage: A right reverse displacement along the NE-SW trending southern segment and a reverse displacement along the N-S trending southern segment occurred in Pliocene time. The sense of these displacements was studied by the analysis of the deformation along the fault. The formation of the Abashiri Tectonic Line is considered to be ascribed to the initial northward shift of the Kurile Arc in Late Miocene time and the subsequent westward shift of the Outer Kurile Arc in Pliocene time.