New Evidence for Segmentation of the Alaska Subduction Zone

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.

[1]  Robert A. Page,et al.  Seismicity of the Wrangell and Aleutian Wadati‐Benioff Zones and the North American Plate along the Trans‐Alaska Crustal Transect, Chugach Mountains and Copper River Basin, southern Alaska , 1989 .

[2]  Jose Pujol,et al.  Comments on the joint determination of hypocenters and station corrections , 1988 .

[3]  J. Davies,et al.  Additional evidence for down-dip tension in the Pacific plate beneath central Alaska , 1986 .

[4]  Jose Pujol,et al.  Relocation of earthquakes in the Cook Inlet area, south central Alaska, using the joint hypocenter determination method , 1997, Bulletin of the Seismological Society of America.

[5]  J. Chatelain,et al.  Lateral velocity variations in the Andean foreland in Argentina determined with the JHD method , 1991 .

[6]  C. Frohlich,et al.  Intermediate and Deep Seismicity and Lateral Structure of Subducted Lithosphere in the Circum-Pacific Region (Paper 6R0298) , 1986 .

[7]  A. Johnston,et al.  On the relocation of earthquake clusters. A case history: The Arkansas earthquake swarm , 1989 .

[8]  A. DOUGLAS,et al.  Joint Epicentre Determination , 1967, Nature.

[9]  Jose Pujol,et al.  Joint hypocentral location in media with lateral velocity variations and interpretation of the station corrections , 1992 .

[10]  E. Engdahl,et al.  Earthquake location in island arcs , 1982 .

[11]  C. Frohlich,et al.  Geometry of the subducted plate near Kodiak Island and Lower Cook Inlet, Alaska, determined from relocated earthquake hypocenters , 1985 .

[12]  C. Frohlich.  Triangle diagrams: ternary graphs to display similarity and diversity of earthquake focal mechanisms , 1992 .

[13]  J. Lahr.  HYPOELLIPSE; a computer program for determining local earthquake hypocentral parameters, magnitude, and first-motion pattern , 1979 .

[14]  L. House,et al.  Aleutian subduction zone seismicity, volcano‐trench separation, and their relation to great thrust‐type earthquakes , 1979 .

[15]  F. Waldhauser,et al.  A Double-Difference Earthquake Location Algorithm: Method and Application to the Northern Hayward Fault, California , 2000 .

[16]  J. Davies,et al.  Seismicity and plate tectonics in south Central Alaska , 1974, Bulletin of the Seismological Society of America.

[17]  Zhong Lu,et al.  Details of stress directions in the Alaska subduction zone from fault plane solutions , 1997 .