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Ground-motion site effects from multimethod shear-wave velocity characterization at 16 seismograph stations deployed for aftershocks of the August 2011 Mineral, Virginia, earthquake

By
William J. Stephenson
William J. Stephenson
U.S. Geological Survey, Box 25046, MS 966, Denver, Colorado 80225, USA
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Jack K. Odum
Jack K. Odum
U.S. Geological Survey, Box 25046, MS 966, Denver, Colorado 80225, USA
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Daniel E. McNamara
Daniel E. McNamara
U.S. Geological Survey, Box 25046, MS 966, Denver, Colorado 80225, USA
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Robert A. Williams
Robert A. Williams
U.S. Geological Survey, Box 25046, MS 966, Denver, Colorado 80225, USA
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Stephen J. Angster
Stephen J. Angster
U.S. Geological Survey, Box 25046, MS 966, Denver, Colorado 80225, USA
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Published:
January 01, 2015

We characterize shear-wave velocity versus depth (Vs profile) at 16 portable seismograph sites through the epicentral region of the 2011 Mw 5.8 Mineral (Virginia, USA) earthquake to investigate ground-motion site effects in the area. We used a multimethod acquisition and analysis approach, where active-source horizontal shear (SH) wave reflection and refraction as well as active-source multichannel analysis of surface waves (MASW) and passive-source refraction microtremor (ReMi) Rayleigh wave dispersion were interpreted separately. The time-averaged shear-wave velocity to a depth of 30 m (Vs30), interpreted bedrock depth, and site resonant frequency were estimated from the best-fit Vs profile of each method at each location for analysis. Using the median Vs30 value (270–715 m/s) as representative of a given site, we estimate that all 16 sites are National Earthquake Hazards Reduction Program (NEHRP) site class C or D. Based on a comparison of simplified mapped surface geology to median Vs30 at our sites, we do not see clear evidence for using surface geologic units as a proxy for Vs30 in the epicentral region, although this may primarily be because the units are similar in age (Paleozoic) and may have similar bulk seismic properties. We compare resonant frequencies calculated from ambient noise horizontal:vertical spectral ratios (HVSR) at available sites to predicted site frequencies (generally between 1.9 and 7.6 Hz) derived from the median bedrock depth and average Vs to bedrock. Robust linear regression of HVSR to both site frequency and Vs30 demonstrate moderate correlation to each, and thus both appear to be generally representative of site response in this region. Based on Kendall tau rank correlation testing, we find that Vs30 and the site frequency calculated from average Vs to median interpreted bedrock depth can both be considered reliable predictors of weak-motion site effects in the epicentral region.

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GSA Special Papers

The 2011 Mineral, Virginia, Earthquake, and Its Significance for Seismic Hazards in Eastern North America

J. Wright Horton, Jr.
J. Wright Horton, Jr.
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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Martin C. Chapman
Martin C. Chapman
Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, Virginia 24061, USA
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Russell A. Green
Russell A. Green
Department of Civil and Environmental Engineering (MC 0105), 120B Patton Hall, Virginia Polytechnic Institute and State University, 750 Drillfield Drive, Blacksburg, Virginia 24061, USA
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The Geological Society of America
Volume
509
ISBN print:
9780813725093
Publication date:
January 01, 2015

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