Characterization of Glacial Materials Using Seismic Refraction and Multichannel Analysis of Surface Waves Glenn Larsen Ohio Department of Natural Resources Division of Geological Survey Glenn Larsen Ohio Department of Natural Resources Division of Geological Survey

P-Wave Refraction In the Beginning the OGS used P-wave refraction as a cost effective tool to determine the thicknesses of the glacial materials and the depths to bedrock. Can not differentiate between the different types of glacial materials. The water table can become a barrier preventing any detection of P-wave arrivals from deeper refractive layers. Water Problems:

To over come these problems the OGS adopted combining S-wave refraction data with P-wave data. S-waves travel slower than P-waves and the velocity contrast between geologic layers tend to be greater. S-wave are not affected by water. S-Wave Refraction

Multichannel Analysis of Surface Waves (MASW) Estimates material Strength, shear modulus Estimates S-velocity from surface waves Data quality is high because surface wave is generally the dominant wave Most noise-tolerant seismic method MASW

Geometrics Geode Seismometer Geophones Laptop Computer Seismic Equipment

Thumper!

Acquire P- and S- wave velocity data to characterize the glacial materials in terms of their engineering and seismic properties. Build a database of P- and S- wave velocity data from glacial materials already identified by surficial mapping. Relate shear wave velocities to SPT-N values. Integrate this data to the stack maps to assess engineering and seismic hazards state wide. Survey’s Focus Since 2006

Acquiring P- and S-wave data is important for determining the engineering properties of the bedrock and glacial materials. The material properties derived from P- and S-waves: Bulk ModulusBulk Density Shear ModulusPoisson’s Ratio Young’s ModulusVelocity Ratio NEHRP Site Classification Engineering Properties

S-wave velocities of the upper 100 feet are important predictors of site amplification factors for earthquake shaking. Characterizing the glacial materials for prediction of earthquake shaking provides added value to the surficial mapping. Site amplification factors describe how the surficial strata amplify (or attenuate) ground motion during an earthquake. Seismic Properties

Seismic Investigations

Bainbridge Project

HCWC Well Field No. 1 Water Fall Well Field Depth to bedrock 78+ ft. Seismic Survey

P-Wave Velocity Model

S-Wave Velocity Model

HCWC Well Field No. 1 Water Fall Well Field Depth to bedrock 78+ ft. Seismic Survey

Well Field Quarry HCWC Well Field No. 2 Depth to bedrock 94+ ft. Seismic Survey

P-Wave Velocity Model

S-Wave Velocity Model

Passive Remote MASW

Well Field Quarry HCWC Well Field No. 2 Depth to bedrock 94+ ft. Seismic Survey

HCWC New Well Field

Engineering Borehole Database

Geotechnical Soil Borings

Vsa is the average shear wave velocity Na is the average field SPT blow count Sua is the average undrained shear strength 1997 NEHRP Soil Classification for Ground Motion Amplification Dorset Quadrangle Example

Earthquake Risk Potential