Bulletin of the Seismological Society of America
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Bulletin of the Seismological Society of America; April 1986; v. 76; no. 2; p. 463-481
© 1986 Seismological Society of America
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by BOYD, T. M.
Right arrow Articles by JACOB, K.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation

Seismicity of the Unalaska region, Alaska

THOMAS M. BOYD* and KLAUS JACOB

LAMONT-DOHERTY GEOLOGICAL OBSERVATORY OF COLUMBIA UNIVERSITY, PALISADES, NEW YORK 10964

Abstract

The Wadati-Benioff zone beneath Unalaska Island, in the eastern Aleutian arc, is shown to dip at approximately 48° between the depths of 50 and 150 km. Above this depth, the seismic zone appears to dip at a more shallow angle (~12°). The depth of the Wadati-Benioff zone beneath Makushin Volcano on Unalaska Island is about 100 km. Events located within the upper plate near the Wadati-Benioff zone indicate that the maximum depth of seismic coupling between the subducting and overriding plates is about 30 km. This suggests that the maximum width of seismic coupling between the downgoing and overriding plates is about 75 km. Earthquake locations based on the local network data and 20 yr of teleseismic data (PDE), define similar seismically active and quiescent regions. A major seismicity gap exists for events of magnitudes greater than at least 4.6 in the forearc region near Unalaska Island. This seismicity gap correlates well with the eastern edge of the tsunami source area of the great (Mw = 8.6) 1957 earthquake, and a large forearc basin 75 km south of Unalaska Island suggesting a similar process may be controlling the location of all three phenomena. Only one intermediate-sized (mb = 6.1) earthquake has occurred within the seismicity gap during the past 20 yr. This event is shown to be a high stress drop (690 bars) intraplate event within the subducting slab at a depth of 35 km that may be related to lateral compressive stress induced by a change in slab curvature with depth. A review of the historic record from about 1770 reveals that the Unalaska region may have ruptured in a great earthquake in 1878 and a large earthquake in 1902. If this region is currently locked, an earthquake of magnitude 8.2 could rupture this section of the Alaska-Aleutian arc. Estimates of the recurrence interval for events of this size vary from between 40 and 70 yr.

Footnotes

* Also at the Department of Geological Sciences, Columbia University, New York.




This article has been cited by other articles:


Home page
 Bulletin of the Seismological Society of AmericaHome page
T. M. BOYD and J. L NABeLEK
Rupture process of the Andreanof Islands earthquake of May 7, 1986
Bulletin of the Seismological Society of America, October 1, 1988; 78(5): 1653 - 1673.
[Abstract] [PDF]

Home page
 Bulletin of the Seismological Society of AmericaHome page
T. M. BOYD and A. L. LERNER-LAM
Spatial distribution of turn-of-the-century seismicity along the Alaska-Aleutian Arc
Bulletin of the Seismological Society of America, April 1, 1988; 78(2): 636 - 650.
[Abstract] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 1986 by the Seismological Society of America.