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Subducting plate geology in three great earthquake ruptures of the western Alaska margin, Kodiak to Unimak

Geosphere

By:
, , and
DOI: 10.1130/GES00715.1

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Abstract

Three destructive earthquakes along the Alaska subduction zone sourced transoceanic tsunamis during the past 70 years. Since it is reasoned that past rupture areas might again source tsunamis in the future, we studied potential asperities and barriers in the subduction zone by examining Quaternary Gulf of Alaska plate history, geophysical data, and morphology. We relate the aftershock areas to subducting lower plate relief and dissimilar materials in the seismogenic zone in the 1964 Kodiak and adjacent 1938 Semidi Islands earthquake segments. In the 1946 Unimak earthquake segment, the exposed lower plate seafloor lacks major relief that might organize great earthquake rupture. However, the upper plate contains a deep transverse-trending basin and basement ridges associated with the Eocene continental Alaska convergent margin transition to the Aleutian island arc. These upper plate features are sufficiently large to have affected rupture propagation. In addition, massive slope failure in the Unimak area may explain the local 42-m-high 1946 tsunami runup. Although Quaternary geologic and tectonic processes included accretion to form a frontal prism, the study of seismic images, samples, and continental slope physiography shows a previous history of tectonic erosion. Implied asperities and barriers in the seismogenic zone could organize future great earthquake rupture.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Subducting plate geology in three great earthquake ruptures of the western Alaska margin, Kodiak to Unimak
Series title:
Geosphere
DOI:
10.1130/GES00715.1
Volume
8
Issue:
3
Year Published:
2012
Language:
English
Publisher:
Geological Society of America
Publisher location:
Boulder, CO
Contributing office(s):
Central Energy Resources Science Center
Description:
17 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geosphere
First page:
628
Last page:
644
Number of Pages:
19
Country:
United States
State:
Alaska