Based on first stage of surveys using ocean bottom seismometers(1974-1987) P-wave velocities in the upper mantle’s oceanic block for thenorth-western Pacific area adjacent to the Kurile-Kamchatka and the Japanese trenches were rectified. Critical analysis of observational data obtained by scientists of different countries in seismological experiments using ocean bottom seismometers is made. Ocean bottom seismometers observational data obtained in the Japanese Longshot-2 experiments (oriented along the structures)are considered to be the most reliable [Duennebier, Lienezt, 1987; McDermott,Labhart, Marshall; Revenaugh, Jordan T, 1989]. P-wave velocity section constructed based on these data is characterized by anomalously high velocities within the 10-250 km depth interval. Wave channel with P-wave velocity drop of 0,2 km/sec was identified in the 60-120 km depth interval. Anomalously high velocities in the oceanic block can apparently be explained by eclogitization of the matter at these depths or phase transitions [Городницкий, 1985].Anisotropy of the velocities can also be a factor contributing to velocities’anomaly [Revenaugh J., Jordan T, 1989].

The second stage of ocean bottom seismometers’ surveys (2012) showedthat aftershocks of the 2011 catastrophic earthquake with slips predominating might suggest further subduction of the Philippine plate under the Japanese islands. Experiments in the Boussole Strait in 2000 delineated the focus of the strong earthquake of November 15, 2006.