Plate Resolution

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Science  17 Oct 2003:
Vol. 302, Issue 5644, pp. 361
DOI: 10.1126/science.302.5644.361a

Unlike political boundaries, plate tectonic boundaries are determined by geologic, geodetic, and seismic data. These data can be difficult to interpret because the motion of one plate must be considered relative to the motions of other plates. One of the commonly used plate models is NUVEL-1, in which 11 or 14 moving plates are fitted like puzzle pieces around a fixed Pacific plate to create a protective skin over the convecting mantle. Surprisingly, some of the major plate boundaries are not unambiguous, and microplates sometimes are used to resolve discrepancies.

Steblov et al. combined geodetic data from eastern Siberia, the western Pacific, and the global network, collected between 1995 to 2002, to determine the boundary between the Eurasian and North American plates. Eastern Siberia, east of the Cherskiy Range, belongs to the North American plate, settling a 30-year debate. The geodetic pole of relative rotation for Eurasia-North America is shifted slightly north of the pole from the NUVEL-1A model; this difference may reflect plate motions recorded by the geodetic data from the past 7 years versus the longer-term motions (past 3 million years) estimated by the geologic data used in NUVEL-1A. Still to be determined is whether two proposed microplates, Okhotsk and Amurian, exist to the south of the Cherskiy Range in eastern Asia.

The 8.3 magnitude Hokkaido earthquake on 25 September 2003, which occurred offshore of the north island of Japan, is attributed to thrust faulting near the North American-Eurasian-Pacific plate triple junction, but if the microplates do indeed exist, then the earthquake occurred near the Okhotsk-Amurian-Pacific plate triple junction instead. — LR

Geophys. Res. Lett. 10.1029/2003GL017805 (2003).

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