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 700 km 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.