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Open-File Report 2011–1260

In collaboration with the Evansville Area Earthquake Hazards Mapping Project (EAEHMP)

Earthquake Scenario Ground Motions for the Urban Area of Evansville, Indiana

By Jennifer S. Haase, Robert L. Nowack, Chris H. Cramer, Oliver S. Boyd, and Robert A. Bauer

Thumbnail of and link to report PDF (4.69 MB)Abstract

The Wabash Valley seismic zone and the New Madrid seismic zone are the closest large earthquake source zones to Evansville, Indiana. The New Madrid earthquakes of 1811–1812, over 180 kilometers (km) from Evansville, produced ground motions with a Modified Mercalli Intensity of VII near Evansville, the highest intensity observed in Indiana. Liquefaction evidence has been documented less than 40 km away from Evansville resulting from two large earthquakes in the past 12,000 years in the Wabash Valley. Two earthquake scenarios are described in this paper that demonstrate the expected ground motions for a 33×42-km region around Evansville based on a repeat earthquake from each of these source regions. We perform a one-dimensional analysis for a grid of sites that takes into account the amplification or deamplification of ground motion in the unconsolidated soil layer using a new three-dimensional model of seismic velocity and bedrock depth. There are significant differences in the calculated amplification from that expected for National Earthquake Hazard Reduction Program site class D conditions, with deamplification at many locations within the ancient bedrock valley underlying Evansville. Ground motions relative to the acceleration of gravity (g) in the Evansville area from a simulation of a magnitude (M) 7.7 New Madrid earthquake range from 0.15 to 0.25 g for peak ground acceleration, 0.14 to 0.7 g for 0.2-second (s) spectral acceleration, and 0.05 to 0.25 g for 1.0-s spectral acceleration. Ground motions from a M6.8 Wabash Valley earthquake centered 40 km northwest of the city produce ground motions that decrease with distance from 1.5 to 0.3 g for 0.2-s spectral acceleration when they reach the main part of Evansville, but then increase in amplitude from 0.3 to 0.6 g south of the city and the Ohio River. The densest urbanization in Evansville and Henderson, Ky., is within the area of preferential amplification at 1.0-s period for both scenarios, but the area experiences relatively less amplification than surrounding areas at 0.2 s, consistent with expected resonance periods based on the soil profiles.

First posted October 3, 2011

For additional information contact:
Center Director, Geologic Hazards Science Center
U.S. Geological Survey
Box 25046, Mail Stop 966
Denver, CO 80225
http://geohazards.cr.usgs.gov/

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Suggested citation:

Haase, J.S., Nowack, R.L., Cramer, C.H., Boyd, O.S., and Bauer, R.A., 2011, Earthquake scenario ground motions for the urban area of Evansville, Indiana: U.S. Geological Survey Open-File Report 2011–1260, 17 p.



Contents

Abstract

Introduction

Scenario Definition

Method

Geologic Input Model

Soil Amplification

Scenario Seismic Hazard Results

Conclusions

Acknowledgments

References


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