Appearance of seepage structures on the NE Sakhalin slope: differences and similarities in gas discharge.

Abstract

Data considered were obtained in several cruises during side-scan sonar surveys carried on NE Sakhalin slope in the framework of Korean-Japanese-Russian projects CHAOS (Hydro Carbone Hydrate Accumulation in the Okhotsk Sea, 2003-2005) (Matveeva et al., 2005) and SSGH (Sakhalin Slope Gas Hydrate, 2004-2009) (Jin et al., 2007, 2008

Shoji et al., 2008). The towed hydroacoustic system "SONIC-3M" designed in VNIIOkeangeologia (Saint-Petersburg) was used for side-scan sonar mapping (Gladysh et al., 2008). Gas discharge places appear on the side-scan sonar images as a spots of high backscatter intensity, which are considered as seepage structures (S-structures). Total square of the area mapped by side-scan sonar on the slope amounts to 2600 km2. 739 S-structures were observed in depth interval 350-1200 m. Data obtained show that S-structures are spread everywhere on the north-eastern Sakhalin slope, but their appearances strongly vary from one place to another one that are connected to changes of slope structure. The main change was observed at crossing of Lavrentiev Fault that separates slope on northern and southern segments (Fig. 1). Differences in relief morphology and sedimentary cover structure suggest that slope failure occurred in the northern segment, whereas the southern segment remained stabile.