We use Global Positioning System (GPS) velocity data to model eastern Asian plate kinematics. Out of 15 stations in Korea, Russia, China, and Japan studied here, three sites considered to be on the stable interior of the hypothetical Amurian Plate showed eastward velocities as fast as ∼9–10 mm/yr with respect to the Eurasian Plate. They were stationary relative to each other to within 1 mm/yr, and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity (Euler) vector of the Amurian Plate. The predicted movement between the Amurian and the North American Plates is consistent with slip vectors along the eastern margin of the Japan Sea and Sakhalin, which reduces the necessity to postulate the existence of the Okhotsk Plate. The Euler vector of the Amurian Plate predicts left‐lateral movement along its boundary with the south China block, consistent with neotectonic estimates of the displacement at the Qinling fault, possibly the southern boundary of the Amurian Plate. The Amurian Plate offers a platform for models of interseismic strain buildup in southwest Japan by the Philippine Sea Plate subduction at the Nankai Trough. Slip vectors along the Baikal rift, the boundary between the Amurian and the Eurasian Plates, are largely inconsistent with the GPS‐based Euler vector, suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies.
Abstract. To investigate the current crustal movements in and around the Sea of Okhotsk and Sea of Japan regions, we have established a continuous GPS network. By the end of 1997, the network had been expanded to include 12 new stations. Data for the period from July 1995 to November 1997 were analyzed together with data from International GPS Service for Geodynamics (IGS) global stations. To fix the estimated coordinates to the terrestrial reference frame, the Tsukuba IGS station was assumed to be moving westward relative to the stable Eurasian continent at •2cm/yr according to Heki's[1996] estimate. We find that: (1) stations in the western margin of the Sea of Japan have eastward velocity vectors, (2) the pole position of the Okhotsk plate is located near Okha, which reconfirms the Okhotsk micro plate, (3) a plate boundary of the Okhotsk and Amurian plates between southen Sakhalin and Hokkaido is suggested.
IntroductionThe tectonic plate motions in the vicinity of the Sea of Okhotsk and Sea of Japan are very complex. Because of low seismicity and having no clear geographical boundary except for Kuril-Japan trench, it has been difficult to describe the plate tectonics in this region. Seno et al. [1996]
Network and Data analysisWe established two GPS stations in Sakhalin on July 1995 at first, and further developed the station network in 1996 and 1997. By the end of 1997, 12 continuous observation stations in this region had been installed (Figure 1). We selected the station sites so that a stable power supply is available and a rigid installation of antenna can be made. The sampling rate of GPS observation in this network is every 30 seconds and the data are stored on the 100MB removable disks through a personal computer. All data collected at these stations are sent to the data center at the Hokkaido University within a half years delay at most. The data are converted to the standard receiver independent exchange (RINEX) format. We have analyzed the archived data using the Bemese GPS Software Ver-
ResultsWe show two examples of time series of horizontal and vertical coordinates with respect to TSKB in Figure 2. These can 2533
Interseismic GPS velocities in Sakhalin indicate that the island moves to the west at 3–4 mm/yr with respect to the Eurasian plate, which is about half of the relative Eurasia ‐ North America plate convergence rate. GPS measurements across the central Sakhalin fault system provide evidence of compressive and strike‐slip strain accumulation at a rate ≤3 mm/yr. Coseismic vertical displacements produced by the August 4, 2000 Mw 6.8 Uglegorsk earthquake in Sakhalin were analyzed by constrained nonlinear inversion which provided evidence for a reverse faulting mechanism on an east‐dipping fault plane.
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