Geophysical Surveys

Geophysical surveys are used when information on what is below ground is needed. Geophysics has many uses such as looking at the depth and extent of landfills, determining the depth and strength of bedrock, looking for old buried infrastructure, finding buried stream channels and faults, imaging landslides, measuring shear wave velocities and shear strength, and monitoring ground vibrations during construction.

Seismic Refraction
The main use for seismic refraction is determining the depth to bedrock and rock rippability for grading projects. It is also used for finding groundwater depth and locating fault offsets.

MASW Shear Wave Surveys
Multichannel Analysis of Surface Waves (MASW) is a method for determining shear wave velocities and geologic structures. We use it for Vs30 shear strength studies, general geology profiling, and to locate faults.

Magnetic Investigations
Magnetic investigations are our main tool for finding buried objects such as old fuel tanks, old foundations, and old trash pits that can hinder construction at redevelopment sites.

Ground Penetrating Radar
Ground penetrating radar (GPR) provides images of near-surface buried objects. In sandy and coarse grained soils it can image buried pipes, fuel tanks, and detect voids beneath pavement. It also maps rebar in concrete walls and pads.

Resistivity Profiling
Resistivity maps changes in soil and rock types with depth. It distinguishes conductive materials like clays and trash, from nonconductive materials like sandy soils and bedrock. It maps permeable zones for groundwater and environmental studies and maps landfill depths.

Vibration Monitoring
Vibration monitoring confirms that ground vibrations during pile driving or vibratory compaction are at safe levels and not damaging to nearby buildings. Vibration levels are permanently recorded to address possible complaints.

Recent Surveys

Below are four examples of recent geophysical investigations

Salton Sea Geophysical Study

We performed seismic refraction surveys to determine groundwater depth and performed dipole resistivity surveys to determine near surface soil types in four regions around the Salton Sea. The geophysics supported a dust storm mitigation study.

Fort Funston Bedrock Mapping

Multichannel Analysis of Surface Waves (MASW) was used to determine the depth to bedrock for a proposed sewer outfall at Fort Funston.

$Salton Sea Refraction Profiles$

Refraction Profiles

Resistivity Profiles

MASW Line Locations

Shear Wave Profile

Landfill Investigation

To characterize an old landfill, a combination of magnetics, resistivity, and seismic refraction was used. Magnetics defined the fill's lateral boundaries. Seismic refraction and resistivity found the fill's depth.

Rippability Study

We performed a seismic refraction survey to determine rock rippability for a new sewer line along a road in Napa.

Magnetic Map Showing Fill Boundaries

Refraction and Resistivity Profiles

Portable Seismic Equipment

$Refraction Profile$

Refraction Profile

J R Associates

Geophysical Surveys

Seismic Refraction

MASW Shear Wave Surveys

Magnetic Investigations

Ground Penetrating Radar

Resistivity Profiling

Vibration Monitoring