Structure of the Kuril Trench from seismic reflection records

Abstract

Three multichannel seismic reflection records across the Kuril convergent margin provide the first deep data in this area. The records are located across the southern tip of Kamchatka, the central Kuril arc, and the northern extension of Hokkaido Island platform which show three distinct tectonic regimes. The lower slope contains a wedge‐shaped buttress surrounded by low velocity sediments. Underplating sediment uplifts the buttress, as indicated by faults that displace its upper surface. The middle slope is a block of acoustic basement, which has a rough surface with significant arcward dipping faults. The middle slope is separated from the upper slope along a steep arcward dipping reflection, the “middle‐slope boundary.” The upper slope structure off Kamchatka is different from that off Hokkaido. Off Kamchatka a regular stratified sediment section has been uplifted, tilted, and dips seaward. Off Hokkaido, stronger uplift has tilted regional blocks seaward and arcward. Along the southern line north of Hokkaido, well‐studied nonthrust earthquakes with lateral motions occur beneath the middle slope boundary and on the boundary of the subducting plate. Thrust earthquakes occur under the middle and upper slope, whereas tsunami earthquakes occur under the lower slope. High‐amplitude reflections along the lower boundary of the wedge‐shaped buttress and along the active decollement, indicate high fluid concentrations which reduce the friction along the tectonic units so that through the weak coupling, slow rupture may extend up to the seafloor from a tsunami earthquake.

Tectonic regime of the southern Kurile Trench as revealed by multichannel seismic lines

“…Five of them are consistent with thrust motion along fault planes that strike nearly orthogonal to the nearby trench (Suzuki et al, 1983;Seno, 1985). Furthermore, three earthquakes, labelled by De Mets: 6, 25 and 26, are located closer to the trench axis and may indicate that the shear induced by oblique subduction is distributed along two or more subparallel strikeslip faults in the forearc (De Mets, 1992;Klaeschen et al, 1994). Earthquake 26 is located just at the northern edge of line P-856 and supports the hypothesis of a trench-parallel, strikeslip fault cutting the section at the edge of the continental terrace (km 72).…”

Physiographical and sedimentological characteristics of submarine canyons developed upon an active forearc slope: The Kushiro Submarine Canyon, northern Japan

“…2 and 5). The upper terrace is underlain by wellstratifi ed refl ectors (Schnürle et al, 1995;TuZino et al, 2006) and possibly formed via a combination of subsidence and regional tilting (Klaeschen et al, 1994). TuZino et al (2006) reported the formation of half-grabens along the upper terrace Table DR2).…”

“…Clift et al, 1998;Dickinson and Seely, 1979;Gulick et al, 2002;McNeill et al, 2000). The high can be correlated with the middle-slope boundary of a steep landward-dipping refl ection described by Klaeschen et al (1994). Two terraces are recognized on the slope: the upper terrace (3200 m water depth) is located on the upper slope immediately behind the outer high, and the lower is located on the trenchward side of the outer high (5000-5500 m water depth) (Figs.…”

“…The slope between the upper and lower terraces exceeds 5° and is covered by a 600-mthick series of low-amplitude refl ections oriented parallel to the slope and underlain by weakly folded Neogene sediments (Schnürle et al, 1995). Uplift of this slope might have resulted from the underplating of sediment within the subduction zone (Klaeschen et al, 1994). The origin of the lower terrace has been explained in terms of the upheaval of the ridges located immediately trenchward of the terrace (Ogawa et al, 1993).…”

Paleoseismicity along the southern Kuril Trench deduced from submarine-fan turbidites

“…The lower slope is bounded by the outer high that consists of non-layered acoustic basements ( Fig. 5B and C) (Honza et al, 1978;Klaeschen et al, 1994;Schnürle et al, 1995). The sediments of the lower slope represent the formation of a half-graben, suggesting Fig.…”