Fault Tectonics and Deep Structure of Seismic Zones in the Eastern Priamurye Region

This paper is concerned with spatial relationships between seismic zones in the eastern Priamurye region (M >= 5) on the one hand and, on the other, regional faults and zones of hidden faults as indicated by axes of gravity and magnetic anomalies. The seismoactive zones where M >= 5 earthquakes occurred are mostly confined to regional faults, while there are two cases where no such relationship has been detected. Seismic zones are observed both at intersections of regional faults and at intersections of regional faults with hidden faults of different rank. The seismic zones comprise inclined and subvertical deep-seated faults as identified by deep seismic sounding (DSS), the earthquake converted wave method (ECWM), and magnetotelluric sounding (MTS) surveys. The seismoactive zones were studied by geophysical techniques to identify indication of fluid saturation, as follows: the seismoactive faults frequently control low velocity and low resistivity inhomogeneities in the Earth's crust and upper mantle; some seismoactive faults have displaced the Moho interface; there are dome-shaped flexures of crustal interfaces and of the Moho interface; and the crust is found to contain numerous conversion interfaces. The deep occurrence of seismoactive faults and the indications of fluid saturation suggest that the seismoactive faults in the eastern Priamurye region provide supply of fluids from the mantle to the crust.