Downhole shear-wave velocity studies in the unconsolidated sediments in Evansville, Indiana
- Ball State Univ., Muncie, IN (United States). Geology Dept.
- Indiana Geological Survey, Bloomington, IN (United States)
Extensive downhole shear-wave velocity studies of mid-western Quaternary unconsolidated sediments have been undertaken to evaluate seismic hazards in southwestern Indiana. As part of the study, 21 bore holes in Evansville were drilled to obtain data using a 12 channel signal enhanced seismic recorder with a three component downhole geophone. All holes drilled have cuttings and natural gamma ray logs; some holes have split spoon samples and standard penetration test data. Generally, the data indicates two different depositional environments within the Evansville area. The southern half of the city is underlain by predominantly sand and gravel fluvial deposits that range in thickness from 21 m to 41 m. These sites have an average shear-wave velocity of 244 m/s. The northern and western section of Evansville are underlain by lacustrine deposits with thicknesses of 7 m to 22 m and an average shear-wave velocity of 202 m/s. An east-west trending, mile wide transition zone between these two environments is predominantly sand and gravel with interbedded overbank or lacustrine deposits. This zone ranges from 22 m to 38 m in thickness and has an average shear-wave velocity of 244 m/s. Shear-wave velocity measurements were made downhole on a 2-5 m interval from surface to hole bottom. Shear-wave velocities are generally slowest in the near surface 2--3 m depth at each site averaging 142 m/s. Not including this shallow zone, the individual sand and gravel downhole measurement intervals have shear-wave velocities averaging 297 m/s and generally increases with depth. The silt and clay overbank and lacustrine intervals have an average shear-wave velocity of 236 m/s.
- OSTI ID:
- 5807461
- Report Number(s):
- CONF-921058--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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580000* -- Geosciences
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