Tomographic imaging of the Alaska subduction zone

The Alaska subduction zone is characterized by the Pacific plate descending beneath the North American plate, causing abundant seismic activity in the crust and along the Wadati-Benioff zone down to a depth of approximately 200 km. 142 908 P wave arrival times from 12 237 shallow- and intermediate-depth earthquakes have been used to investigate the three-dimensional (3-D) P wave velocity structure beneath central and southern Alaska. Detailed P wave tomographic images are obtained for the crust and upper mantle down to a depth of 200 km with spatial resolutions of 30-60 km. The tomographic image of the upper crust correlated well with the major surface geological features, such as slow sedimentary basins and fast ultramafic bodies. The results suggest that the subducting Pacific plate has a thickness of 45-55 km and a P wave velocity 3-6% higher than that of the surrounding mantle. -from Authors