Search for deep slab segments under Alaska

The evolution of the northeastern Pacific Basin is very complicated, featured by many ancient plates, microplates, ridge subduction and a series of slab windows. In this work, we collected 15,804 teleseismic arrival times from original seismograms of 889 distant earthquakes to determine a three-dimensional P-wave velocity structure down to 700km depth beneath Alaska using a local and teleseismic joint inversion method. Our results show that the Pacific slab imaged as high-velocity (high-V) anomalies is subducting down to 300-400 km depth and it becomes deeper westwards under south-central and western Alaska. While in eastern Alaska, the Pacific slab is visible down to only about 90 km depth. Beneath western Alaska, high-V anomalies at 400-600 km depths are revealed, which represent the extinct Kula plate, and a gap between the subducted Pacific slab and the Kula slab is considered to represent the ancient Kula-Pacific spreading center. In southeastern Alaska, a large low-velocity (low-V) anomaly is found, which may reflect the upwelling mantle in the Pacific-Juan de Fuca slab window near the subducted edge of the Pacific plate. Our results support the existence of the Pacific-Juan de Fuca slab window suggested by the previous studies. (c) 2007 Elsevier B.V. All rights reserved.