New Evidence for Segmentation of the Alaska Subduction Zone

Abstract

The purpose of this article is to provide additional evidence for segmentation of the subducted plate in Alaska and to introduce a catalog of the relocated earthquakes for future studies. We used the Joint Hypocenter Determination method to relocate 14,099 subduction-zone earthquakes that occurred from July 1988 to July 1998 and were located between 58° N and 65° N latitude. The earthquake data were taken from the Alaska Earthquake Information Center catalog. The selected earthquakes were divided into 16 blocks on the basis of their hypocentral locations, and each block was relocated separately. Average epicenter shift was 3.8 km and average upward and downward depth shifts were 4.1 and 4.4 km, respectively (roughly the same number of earthquakes shifted upward [47%] and downward [53%]). The overall change with respect to the initial locations is that the seismicity became more compact, revealing details about the fine structure of the Wadati-Benioff zone. In particular, we were able to identify more precisely the boundary between the Kenai and McKinley blocks of the subducting plate. In addition, there is evidence for plate segmentation within the McKinley block. Manuscript received 15 November 2000.