P & S Wave Seismic Refraction Services

Seismic refraction is one of the key geophysical methods for understanding lithological variations. As one of the longest understood geophysical techniques, it is common to use the collected datasets to link boreholes information within a geotechnical investigation.

The technique allows for comprehensive geophysical geological models to be constructed supporting greater accuracy in the larger design processes of infrastructure projects.

Seismic refraction methods have been continuously developed and refined to be used across a wide range of applications from shallow engineering investigations to oil exploration.

SEP Geophysical are experienced in providing P-Wave and S-Wave seismic refraction surveys. We have a range of equipment that can be used to tailor the survey to your specific needs, depending on the application.

How Seismic Refraction Works

Near-surface seismic refraction is the analysis of the first arrival times of seismic waves as they are refracted from interfaces with varying acoustic/elastic properties.

Seismic wave velocities are strongly dependent on the medium through which they travel and so the velocity of a seismic wave is related to the physical properties of the medium.

Through their examination, it is possible to determine subsurface velocity and layer structures. A geological boundary (or geological interface) can be indicated by contrasting seismic velocity layers.

Seismic refraction survey data is used to produce tomographic velocity models and interpreted cross-sections.

Applications of Seismic Refraction Surveys

The seismic refraction method is commonly used to determine:

Depth to bedrock/rockhead

By understanding the seismic velocities of the overlying materials it is possible to produce an estimate of the depth to rockhead/bedrock. This is essential information for many engineering and environmental projects.

Water Table Mapping

A seismic refraction survey can help to map the position of a water table. The water table is typically a low-velocity layer and as such will be imaged as a high reflector on the seismic sections.

Geological Interpretations

A seismic refraction survey can provide detailed information on the shallow subsurface. This information can be used to support engineering designs or for environmental site characterisation.

Landfill Delineation

A seismic refraction survey can be used to delineate the boundaries of a landfill. A seismic survey will produce a velocity model of the subsurface.

The waste materials within the landfill will generally have a lower seismic velocity than the surrounding soils. As such, the landfill will appear as a low-velocity zone on the seismic sections.

Cavity and fracture detection

The seismic refraction method can be used to detect the presence of voids and fractures within the subsurface. These features will produce reflections on the seismic sections.

The amplitude and character of the reflections can provide information on the size, orientation, and depth of the voids/fractures.

Near-surface faulting

Faults can be imaged using seismic refraction data. The position of the fault will produce a reflection on the seismic sections. The amplitude and character of the reflection can provide information on the type of faulting present.

Seismic Refraction FAQs

What is seismic velocity?

Seismic velocity is a measure of how fast seismic energy travels through a material. The velocity is calculated by dividing the distance the waves have travelled by the time it has taken them to travel that distance.

What are P-Waves and S-Waves?

P-Waves and S-Waves are two different types of seismic waves. P-Waves are compression waves that travel through the earth faster than S-Waves. S-Waves are shear waves that travel more slowly than P-Waves.

What is the difference between seismic reflection and seismic refraction?

Seismic reflection is when seismic waves reflect off of an interface between two different materials. Seismic refraction is when seismic waves are refracted as they travel through a material.

What is MASW geophysics?

MASW (Multichannel Analysis of Surface Waves) is a type of geophysical survey that uses surface waves to image the subsurface. Learn more about MASW here.