BEDROCK DEPTH AND SEISMIC VELOCITY ESTIMATES AT SRBA TRAINING SITES IN COMAL, HAMILTON, PECOS, TAYLOR, AND TRAVIS COUNTIES, TEXAS

During training exercises for TxDOT staff, seismic refraction data were acquired at seven sites in six TxDOT districts using the prototype Seismic Refraction Bedrock Analyzer (SRBA). These data were acquired in a variety of settings that included bedrock depths ranging from a few tens of centimeters to more than 6 meters and bedrock types of sandstone, limestone, and mudstone. Analysis of the data consisted of analyzing first seismic arrivals, attributing the arrivals to a direct wave traveling in the fill below the pavement and a more rapidly propagating wave that is critically refracted along the underlying bedrock surface, and creating seismic velocity models that match the observed first arrivals and allow seismic velocities and bedrock depths to be estimated. SRBA data were acquired on U.S. 281 in the San Antonio district, I-10 in the Midland district, U.S. 84 in the Abilene district, U.S. 290 in the Austin district, U.S. 190 in the Brownwood district, and S.H. 36 in the Waco district. Compressional wave velocities measured in layer 1 and interpreted to represent compacted fill between pavement and bedrock ranged from 551 m/s to 1117 m/s. Compressional wave velocities measured in layer 2 and interpreted to represent bedrock ranged from 1079 m/s in sandstone to 2964 m/s in limestone. Estimated depths to layer 2, interpreted to approximate bedrock depth, ranged from 0.33 m to 6.46 m. Depths to bedrock deeper than 6 m cannot be reliably estimated using the SRBA in its current configuration. The SRBA prototype was easy to deploy, acquired data sufficient for shallow refraction analysis in a few minutes, and was used to produce reasonably accurate estimates of bedrock depth and seismic velocity in bedrock and overlying layers. Further near-term development should include integration of first arrival picking and refraction analysis. Longer-term development might include full integration of data acquisition, first break picking, and refraction analysis in a custom software environment. These improvements would shorten the time required to estimate bedrock depth from an hour or more to near real-time.

• Record URL:
  http://www.utexas.edu/research/ctr/pdf_reports/5_2990_01_1.pdf
• 
• Corporate Authors:

  University of Texas, Austin

  Center for Transportation Research, 3208 Red River Street
  Austin, TX  United States  78705

  Texas Department of Transportation

  Research and Technology Implementation Office, P.O. Box 5080
  Austin, TX  United States  78763-5080

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Paine, J G
• Publication Date: 2002-8

Language

• English

Media Info

• Features: Figures; References; Tables;
• Pagination: 34 p.

Subject/Index Terms

• TRT Terms: Bedrock; Depth; Earthquakes; Elastic waves; Refraction; Seismicity; Velocity
• Uncontrolled Terms: Seismic refraction bedrock analyzer
• Geographic Terms: Comal County (Texas); Hamilton County (Texas); Pecos County (Texas); Taylor County (Texas); Travis County (Texas)
• Subject Areas: Geotechnology; Highways; I43: Rock Mechanics;

Filing Info

• Accession Number: 00988117
• Record Type: Publication
• Report/Paper Numbers: FHWA/TX-03/5-2990-01-1, Implementation Report, 5-2990-01-1
• Files: TRIS, USDOT, STATEDOT
• Created Date: Mar 28 2005 12:00AM