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Project Details

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Project Information Sheet

An evaluation of high-resolution seismic-reflection data (HRSRD) in a portion of the Bluegrass Creek drainage basin for seismic risk studies in the greater Evansville area, Indiana

Funding Source:	Central United States Earthquake Consortium State Geologists (CUSEC-SG)
Status:	active — Definition of status type
Project Director:	John R. Hill and Marni D. Karaffa

Issue

After nearly 15 years of periodic study, seismic hazard investigations in the greater Evansville area of southwestern Indiana still lack scientifically robust predictive models needed to map shaking and liquefaction potentials of various lithologic materials in three dimensions. Such mapping is important because, in the event of an earthquake, water-saturated sands are prone to liquefaction, and thicker soft clays amplify ground shaking. Yet, there is not a clear depositional model that can be used to predict the three-dimensional distribution of sediment types in the greater Evansville area.

Objective

To use high-resolution seismic-reflection data (HRSRD) to better evaluate and map the distribution of unconsolidated gravels, sands, silts, clays, and muds in the greater Evansville area to more precisely assess shaking and liquefaction potential and better predict earthquake damage.

Approach

We propose two short seismic lines in the Bluegrass Creek basin, linking areas where vertical two-dimensional sedimentary packages have been defined by extant downhole geophysical log profiles. These HRSRD lines were also selected to intersect recently acquired U.S. Geological Survey Cone Penetrometer Test (CPT) soundings in order to compare to the CPT output. A single new continuously cored test will be drilled (approx. depth of 100 ft) to provide seismic shear-wave calibration and to provide the critical cornerstone sample and log-profile data necessary for future seismic risk studies in this area. This will provide a geologic and procedural background for necessary future studies into urban Evansville and Kentucky.

Products

(1) Small-scale maps of the study area showing bedrock surface, and thickness and layering of unconsolidated sediments. (2) A report that discusses the details of this mapping effort and correlates this data to liquefaction susceptibility and ground-shaking potential (done in collaboration with Illinois State Geological Survey and USGS personnel) as well as a public outreach article published on the IGS Web site.

Benefits

We believe that the acquisition of HRSRD will allow us to generate the information essential to adequately define the three-dimensional distribution and thickness of seismically sensitive sediments such as wet sands and thick, soft clays. Such information is essential to evaluate tributary fill models, and to provide the data needed to map lithologies and associated liquefaction and shaking susceptibilities here and in similar tributary basins associated with the Ohio, Wabash, and Mississippi Rivers.

Locations Affected:

Vanderburgh

Warrick

Indiana House Districts Affected:

75

78

Indiana Senate Districts Affected:

50

Indiana Congressional Districts Affected:

Information Updated January 25, 2007

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