Introduction

The possible existence of independently rotating Okhotsk and Amurian microplates has been examined by many in an attempt to explain both seismological and geologic data in Northeast Asia (Cook et al., 1986; Seno et al., 1996). Geodetic measurements can be used to fully characterize the motion of tectonic plates; however, because most GPS sites in this region are in such close proximity to plate boundaries, previous attempts to firmly confirm or refute an independent Okhotsk plate have been inconclusive (Heki et al., 1999; Steblov et al., 2003). Independent Amurian plate motion is notably more difficult to constrain because of the uncertainty of the southwestern plate boundary and the sparsely spaced geodetic data.

Horizontal surface velocities of 122 GPS sites (82 from within the proposed Okhotsk and Amurian plate boundaries) constrain the plate kinematics of northeast Asia and allow for a rigorous test of the possibility of independent Okhotsk and Amurian plate motion. We use a block modeling approach to incorporate both rigid block rotation and near-boundary elastic strain accumulation effects in a formal inversion of the GPS velocities. Considered models include scenarios with and without independent microplates and a number of different plate boundary locations and locking depths.

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