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Open-File Report 2011–1231

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

Probabilistic Seismic Hazard Assessment Including Site Effects for Evansville, Indiana, and the Surrounding Region

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

Thumbnail of and link to report PDF (16.1 MB)Abstract

We provide a probabilistic seismic hazard assessment for the Evansville, Indiana region incorporating information from new surficial geologic mapping efforts on the part of the U.S. Geological Survey (USGS) and the Kentucky and Indiana State Geological Surveys, as well as information on the thickness and properties of near surface soils and their associated uncertainties. The subsurface information has been compiled to determine bedrock elevation and reference depth-dependent shear-wave velocity models for the different soil types. The probabilistic seismic hazard calculation applied here follows the method used for the 2008 U.S. Geological Survey National Seismic Hazard Maps, with modifications to incorporate estimates of local site conditions and their uncertainties, in a completely probabilistic manner. The resulting analysis shows strong local variations of acceleration with 2 percent probability of exceedance in 50 years, particularly for 0.2-second (s) period spectral acceleration (SA), that are clearly correlated with variations in the thickness of unconsolidated soils above bedrock. These values are much greater than the USGS national seismic hazard map values, which assume B/C site conditions. When compared to the national maps with an assumed uniform site D class amplification factor applied, the high-resolution seismic hazard maps have higher amplitudes for peak ground acceleration and 0.2-s SA for most of the map region. However, deamplification relative to the D class national seismic hazard maps appears to play an important role within the limits of the ancient bedrock valley underlying Evansville where soils are thickest. For 1.0-s SA, the new high-resolution seismic hazard maps show levels consistent with D class site response within the limits of this ancient bedrock valley, but levels consistent with B/C site conditions outside.

First posted October 18, 2011

For additional information contact:
Center Director, USGS Geologic Hazards Science Center
Box 25046, MS-966
Denver, CO 80225-0046

http://geohazards.cr.usgs.gov/

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Suggested citation:

Haase, J.S., Bowling, Tim, Nowack, R.L., Choi, Y.S., Cramer, C.H., Boyd, O.S., and Bauer, R.A., 2011, Probabilistic seismic hazard assessment including site effects for Evansville, Indiana, and the surrounding region: U.S. Geological Survey Open-File Report 2011–1231, 29 p.

 



Contents

Abstract

Introduction

Data

Analysis of Local Geology and S-CPT Soil Profile Data

Bedrock Elevation

Soil Response Sensitivity Tests

Site Amplification Calculation

Probabilistic Seismic Hazard Calculation and Results

Conclusions

Acknowledgments

References


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