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Holocene slip rate for the western segment of the Castle Mountain fault, Alaska

Bulletin of the Seismological Society of America

By:
, , , and
DOI:10.1785/0120060109

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Abstract

The western segment of the Castle Mountain fault poses a significant seismic hazard to the most populated region of south-central Alaska. We identify a previously unrecognized margin of a postglacial outwash channel that is offset right laterally 36 ± 4 m across the western segment of the Castle Mountain fault. This offset occurred after glaciers withdrew from the lowland 11,300–15,380 cal yr b.p. and after outwash channel margins were cut and stabilized 11,210–13,470 cal yr b.p. Using these ages and the measured separation, we obtain a maximum slip rate of 3.0 ± 0.6 mm yr−1 and a minimum slip rate of 2.8 ± 0.7 mm yr−1. These are the first lateral slip rates for the Castle Mountain fault established by a field measurement. Based on timing of the most recent earthquake, 670 ± 60 yr b.p., the Castle Mountain fault could have accumulated an average single-event slip of about 1.9 m (extremes range from 1.3 to 2.6 m). The fault consists of two segments; a surface-rupturing earthquake likely will be limited to the 62-km-long western segment. Area-magnitude regression calculations suggest that such an earthquake on the western Castle Mountain fault would have a moment magnitude of 6.9 to 7.3.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Holocene slip rate for the western segment of the Castle Mountain fault, Alaska
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1785/0120060109
Volume:
97
Issue:
3
Year Published:
2007
Language:
English
Publisher:
Seismological Society of America
Contributing office(s):
Alaska Science Center
Description:
6 p.
First page:
1019
Last page:
1024
Online Only (Y/N):
N
Additional Online Files (Y/N):
N