The Phanerozoic tectonic evolution of the Circum-North Pacific is recorded mainly in the erogenic collages of the Circum-North Pacific mountain belts that separate the North Pacific from the eastern North Asian and western North American Cratons. The collages consist of tectonostratigraphic terranes, composed of fragments of igneous arcs, accretionary-wedge and subduction-zone complexes, passive continental margins, and cratons, that are overlapped by continental margin arc and sedimentary basin assemblages. The geologic history of terranes and overlap assemblages is highly complicated because of post-accretion dismemberment and translation during strike-slip faulting that occurred subparallel to continental margins. The complex tectonics of this region is analyzed by the following steps. (1) Tectonic environments for the erogenic collage are assigned from regional compilation and synthesis of stratigraphic and faunal data. The tectonic environments include cratonal, passive continental margin, metamorphosed continental margin, continental-margin arc, island arc; oceanic crust, seamount, and ophiolite, accretionary wedge and subduction zone, turbidite basin, and metamorphic. (2) Correlations are made between terranes. (3) Coeval terranes are grouped into a single tectonic origin, i.e., a single island arc or subduction zone. (4) Igneous arc and subduction zone terranes, that are interpreted as being tectonically linked, are grouped into coeval, curvilinear arc-subduction zone complexes. (5) By use of geologic, faunal, and paleomagnetic data, the original positions of terranes are interpreted. And (6) the paths of tectonic migration are constructed. Six processes overlapping in time were responsible for most of the complexities of the collage of terranes and overlap assemblages around the Circum-North Pacific. First, in the Late Proterozoic, and the Late Devonian and Early Carboniferous, major periods of rifting occurred along the margins of Northeast Asia and northwestern part of the North American Cordillera. The rifting resulted in fragmentation and formation of cratonal and passive continental margin terranes from each continent that eventually migrated and accreted to other sites along the evolving margins of the original or adjacent continents. Second, from about the Late Triassic through the mid-Cretaceous, a succession of island arcs and tectonically paired subduction zones formed near continental margins. Third, from about mainly the mid-Cretaceous through the Present, a succession of igneous arcs and tectonically paired subduction zones formed along the continental margins. Fourth, from about the Jurassic to the Present, oblique convergence and rotations caused orogen-parallel sinistral and then dextral displacements within the upper plate margins of Northeast Asia and the North American Cordillera. The oblique convergences and rotations resulted in the fragmentation, displacement, and duplication of formerly more-continuous arcs, subduction zones, and passive continental margins. These fragments were su...

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Data from Japanese local seismograph networks suggest that the stresses in double seismic zones are in-plate compression for the upper zone and in-plate tension for the lower zone; the stresses do not necessarily appear to be down-dip. It may therefore be possible to identify other double seismic zones on the basis of data which indicate that events with differing orientations of in-plate stresses occur in a given segment of slab.A global survey of published focal mechanisms for intermediate depth earthquakes suggests that the stress in the slab is controlled, at least in part, by the age of the slab and the rate of convergence. Old and slow slabs are under in-plate tensile stresses and the amount of in-plate compression in the slab increases with increasing convergence rate or decreasing slab age. Young and fast slabs are an exception to this trend; all such slabs are down-dip tensile. Since these slabs all subduct under continents, they may be bent by continental loading. Double seismic zones are not a feature common to all subduction zones and are only observed in slabs which are not dominated by tensile or compressive stresses.

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