Characterization of Glacial Materials Using Seismic Refraction and

Multichannel Analysis of Surface Waves

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 RefractionP-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 RefractionS-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

MASWMASW

Geometrics Geode Seismometer

Geophones

Laptop Computer

Seismic EquipmentSeismic Equipment

Thumper!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 2006Survey’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 Modulus Bulk Density

Shear Modulus Poisson’s Ratio

Young’s Modulus Velocity Ratio

NEHRP Site Classification

Engineering PropertiesEngineering 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 PropertiesSeismic Properties

Seismic InvestigationsSeismic Investigations

Bainbridge ProjectBainbridge Project

HCWC Well Field No. 1HCWC Well Field No. 1

Water Fall

Well Field

Depth to bedrock 78+ ft.

Seismic Survey

P-Wave Velocity Model P-Wave Velocity Model

S-Wave Velocity ModelS-Wave Velocity Model

HCWC Well Field No. 1HCWC Well Field No. 1

Water Fall

Well Field

Depth to bedrock 78+ ft.

Seismic Survey

Well Field

Quarry

HCWC Well Field No. 2HCWC Well Field No. 2

Depth to bedrock 94+ ft.

Seismic Survey

P-Wave Velocity ModelP-Wave Velocity Model

S-Wave Velocity ModelS-Wave Velocity Model

Passive Remote MASWPassive Remote MASW

Well Field

Quarry

HCWC Well Field No. 2HCWC Well Field No. 2

Depth to bedrock 94+ ft.

Seismic Survey

HCWC New Well FieldHCWC New Well Field

Engineering Borehole DatabaseEngineering Borehole Database

Geotechnical Soil BoringsGeotechnical 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 ExampleDorset Quadrangle Example

Earthquake Risk PotentialEarthquake Risk Potential