We present the first seismic model of the crust beneath Sakhalin based on P and S‐wave arrival time data from local earthquakes. Based on the results of numerous synthetic tests, we conclude that this model has fair horizontal and vertical resolution to 20–25 km depth. At shallow depths, seismic anomalies are clearly associated with known geological structures, such as the high‐velocity Paleozoic Susunai block and the low‐velocity Cenozoic fold belts along the West Sakhalin Mountains. In vertical sections, we observe westward underthrusting of the Susunai block to a distance of at least 70 km, which may represent the regional compression and considerable crustal shortening in this area. Based on the tomography results, we hypothesize about the origin of the mud volcanism in southern Sakhalin. We propose that because of the general westward underthrusting regime in Sakhalin, hydrocarbon‐rich shelf sediments may be entrained to considerable depths under the rigid Susunai block, which serves as a nonpermeable cover. The released gases find the weakest zones around the Susunai block and along the Tym‐Poronay Fault and escape to the surface to form the South Sakhalin and Lesnovsky mud volcano fields.

No abstract

No abstract

Based on the new regional catalog of focal mechanisms for 396 strong (M ≥ 6.0) earthquakes in the Kuril Okhotsk region and Japanese one in part for the period of 1964-2009 and with the data of seismic continuous profiling and multichannel common depth point sounding by reflection method used, the pecu liarities of the structure and seismotectonics of the Kuril arc trench system have been analyzed. Additionally, the features of the Benioff and Tarakanov opposite seismofocal zones, associated with the Kuril arc trench system, are studied. It is shown that the Benioff zone is a deep thrust through which the Kuril Arc (or Eurasian tectonic forefront) has thrust on the Pacific Plate by up to 50-70 km for the last 0.5-1.0 Ma (Pasadenian glo bal phase of folding and orogeny). The thrusting process formed the middle and lower parts of the Pacific Ocean slope, the tectonic couple of Pegasus regional nappe and accretionary prism, the ramp structure of the Kuril Trench, and probably the opposite seismofocal zones.