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USGS Open-File Report 2013–1170 and CGS Special Report 229, Chapter B

Alaska Earthquake Source for the SAFRR Tsunami Scenario

By Stephen Kirby, David Scholl, Roland von Huene, and Ray Wells

Thumbnail of and link to report PDF (26 MB)Abstract

Tsunami modeling has shown that tsunami sources located along the Alaska Peninsula segment of the Aleutian-Alaska subduction zone have the greatest impacts on southern California shorelines by raising the highest tsunami waves for a given source seismic moment. The most probable sector for a Mw ~ 9 source within this subduction segment is between Kodiak Island and the Shumagin Islands in what we call the Semidi subduction sector; these bounds represent the southwestern limit of the 1964 Mw 9.2 Alaska earthquake rupture and the northeastern edge of the Shumagin sector that recent Global Positioning System (GPS) observations indicate is currently creeping. Geological and geophysical features in the Semidi sector that are thought to be relevant to the potential for large magnitude, long-rupture-runout interplate thrust earthquakes are remarkably similar to those in northeastern Japan, where the destructive Mw 9.1 tsunamigenic earthquake of 11 March 2011 occurred.

In this report we propose and justify the selection of a tsunami source seaward of the Alaska Peninsula for use in the Tsunami Scenario that is part of the U.S. Geological Survey (USGS) Science Application for Risk Reduction (SAFRR) Project. This tsunami source should have the potential to raise damaging tsunami waves on the California coast, especially at the ports of Los Angeles and Long Beach. Accordingly, we have summarized and abstracted slip distribution from the source literature on the 2011 event, the best characterized for any subduction earthquake, and applied this synoptic slip distribution to the similar megathrust geometry of the Semidi sector. The resulting slip model has an average slip of 18.6 m and a moment magnitude of Mw = 9.1. The 2011 Tohoku earthquake was not anticipated, despite Japan having the best seismic and geodetic networks in the world and the best historical record in the world over the past 1,500 years. What was lacking was adequate paleogeologic data on prehistoric earthquakes and tsunamis, a data gap that also presently applies to the Alaska Peninsula and the Aleutian Islands. Quantitative appraisal of potential tsunami sources in Alaska requires such investigations.

First posted September 3, 2013

For more information contact:

U.S. Geological Survey
Science Application for Risk Reduction (SAFRR)
http://www.usgs.gov/natural_hazards/safrr/

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Suggested citation:

Kirby, S., Scholl, D., von Huene, R., and Wells, R., 2013, Alaska earthquake source for the SAFRR tsunami scenario, chap. B in Ross, S.L., and Jones, L.M., eds., The SAFRR (Science Application for Risk Reduction) Tsunami Scenario: U.S. Geological Survey Open-File Report 2013–1170, 40 p., http://pubs.usgs.gov/of/2013/1170/b/.



Contents

Abstract

Introduction

Tectonic Setting and the Instrumental, Historical, and Prehistoric Seismic and Tsunamic Record of the Semidi Sector

Comparisons Between the Semidi and Tohoku Subduction Sectors

Characterizing the Scalar Seismic Moment of the 11 March 2011 Tohoku Earthquake, Slip Models, and Development of a Synoptic Slip Distribution Model and Target Range of Model Parameters

Creating a Subfault Grid and Applying a Tohoku-Type Slip Distribution to the Semidi Sector

Scaling of Average Slip During Seismogenic Rupture for Giant Earthquakes with Moment Magnitude: How Useful a Guide is it?

Summary

References Cited

Appendix. Supplementary Information


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