Northeast Asia, where the Pacific, North American, and Eurasian plates come together, is one of the last frontiers of plate tectonics. The location of the North America - Eurasia plate boundary is not well established. The problem is further complicated by a number of smaller microplates in the region, including the Okhotsk, Arctic, Bering, and Amurian plates, whose existence, rates of motion, and boundaries are still uncertain. This project relies on space geodesy to study the broad zone of deformation encompassing the boundary of the Eurasian and North American plates, intervening microplates, and their interaction with the Pacific plate. This investigation is motivated by the recent initiation of high-precision GPS measurements in eastern Siberia, Korea, and Japan, which provide the opportunity for a significant advance in understanding of this enigmatic region. New GPS measurements provide constraints for tectonic models, which take into account plate tectonic angular velocities and deformation associated with strain accumulation and release at the plate boundaries.
The geodetic analysis helps constrain the kinematics of deformation from central Asia to western North America through careful integration of regional and global GPS data. New measurements focus on three areas not well constrained by current data: Sakhalin, the Cherskiy Range in eastern Siberia, and the Kamchatka cusp. Expected results will include an improved location (in northern Siberia) of the pole of rotation between Eurasia and North America; more precise delineation of plate boundaries in northeast Asia; and constraints on the existence, location and present-day motion of the Okhotsk microplate and other regional blocks.
The major problem preventing a straightforward inversion of GPS velocities for rigid plate motions is that displacements of many GPS stations are affected by inter-seismic strain accumulation along plate boundary faults, especially along the Pacific subduction margin. Where large earthquakes (such as the 1995 Mw = 7.0 and 2000 Mw = 6.8 Sakhalin, and the 1997 Mw = 7.7 Kamchatka events) occurred within our study region, the deformation field is further disturbed by co-seismic and post-seismic motions. Thus, the investigation addresses the inextricably linked regional plate kinematics and subduction zone dynamics. Elastic and visco-elastic models are used to evaluate the inter-seismic strain accumulation process and to estimate the amount of seismic coupling on major plate boundary faults. The modeling allows for separation of the contributions of plate boundary strain and plate tectonic angular velocities to the measured GPS velocity field.
