M 5.6 Piltun earthquake of June 12, 2005, and the contemporary seismicity in the area of oil-and-gas fields in the northeastern shelf of Sakhalin Island.

On June 12, 2005, at 04 h 17 min UT, the M 5.6 earthquake occurred northeast of Sakhalin Island in the vicinity of the Piltun-Astokh offshore oil-and-gas field. Oil and gas have been recovered here since 1999, and it is the strongest event in the region. All the available instrumental data have been collected to construct an objective model of the source. The contemporary seismicity of the region is analyzed on the basis of the detailed seismological observations. The obtained results are compared to the new data on the geologic-tectonic setting of the studied area. The results of the present work give ground to search for objective criteria of recognition of natural and induced seismicity in the tectonically active regions, including the region of oil-and-gas fields in the northeastern shelf of Sakhalin Island, and to reveal the physical mechanisms leading to these phenomena. [ABSTRACT FROM AUTHOR]