Geodynamics and Regularities of Seismicity in the Eastern Segment of the Amurian Plate

Abstract

Geodynamic and seismic activation in the southeastern part of Far Eastern Russia is associated with nucleation of strain waves in the buffer zone of the Amurian Plate when it moves northeastward. The highest crustal seismicity is typical of Lower Priamurye, where a zone of М ≥ 4.5 earthquakes originated in its central part that was related to reactivation of the Bureya Orogen. The maximum of the regional compression is confined to the meridional dome, under which the depth of the Moho discontinuity increases from 36 to 40 km. The area of lower rock density in the central part of the Bureya Orogen is exhibited by an intense negative gravity anomaly. A contemporary uplift of the orogen initiated the centrifugal migration of seismicity during 1983–2009, when epicenters of М ≥ 5.0 earthquakes migrated from the center of the dome to its periphery. Strong earthquakes (М ≥ 5.0) are also concentrated south of the Bureya Orogen in the transregional Tan-Lu Fault zone, where the earthquake foci migrate in the northeastern direction. Geodynamic activation is controlled here by the tangential rotation (pressure) of the Amurian Plate, forcing the Central Sikhote-Alin tectonic block to move in the southern direction. North of the block, a 500 × 950 km crustal plate is formed due to extension, which is inclined along the Tan-Lu Fault. In the compression area, a mountain uplift of the same name is formed at the opposite boundary of the Central Sikhote-Alin block. Being rotated clockwise, the block interacts with the subduction zone of the Pacific Plate at a depth of 400–600 km, where deep-focus earthquakes with М ≥ 6.0 are generated due to bilateral pressure.