Slab shape in subduction zones beneath the Kurile–Kamchatka and Aleutian arcs based on regional tomography results

Abstract

A 3-D model of the seismic heterogeneities of P- and S-velocities has been constructed down to 1100 km beneath the Kurile–Kamchatka and Aleutian subduction zones on the basis of the regional tomographic inversion of data from global seismic catalogs. Particular attention is paid to verifying the data by different tests. A clear image of a classic subducting oceanic slab is observed along the entire Kurile–Kamchatka arc, which coincides in the P- and S-models and with the distribution of deep seismicity. These data served as a basis for a parametric model of the upper and lower slab boundaries beneath the Kurile–Kamchatka arc. According to this model, the slab has various thicknesses and maximum penetration depths in different arc segments. In the southern part of the arc, between depths of 600 and 700 km, the slab moves horizontally and does not penetrate the lower mantle. Beneath the North Kuriles and southern Kamchatka, it subducts down to 900 km. These data suggest that the subducting slab becomes a viscous and nonelastic body and the changes in its shape may be due to phase transitions with increasing temperature and pressure. We attribute its gentler dipping and thickening beneath the South Kuriles to the oceanic “pushing” mechanism. The lithospheric thinning, steeper subsidence, and penetration into the lower mantle beneath the North Kuriles are due to the predominant “gravity sinking,” or “slab pull,” mechanism. Unlike some other researchers, we have obtained a high-velocity anomaly beneath the western Aleutian arc (not as clear as beneath the Kurile–Kamchatka arc, yet quite reliable). It suggests the presence of a slab subducting down to 200–250 km. In the eastern Aleutian arc, we clearly observe the Pacific slab subducting down to 500–600 km (somewhat deeper than in the previous studies).