Computer and Geode set up for real-time data quality control in southeast Alaska

Computer and Geode set up for real-time data quality control in southeast Alaska

Seismic Methods

Near-surface seismic surveys estimate subsurface properties (for example, stiffness and depth to bedrock) from propagating acoustic energy: reflected, refracted, and/or surface waves.  Often we can simply use a sledgehammer for the energy source, making acquisition in remote locations possible without the expense associated with explosives or heavy equipment. When explosive are used, we partner with a certified explosive handler to operate safely.

 

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Seismic Tools

Logic Geophysics uses cutting-edge seismic survey systems from Geometrics and corresponding industry-leading interpretation software.  A new development, a tool called the Atom, enables us to collect seismic data passively, thereby decreasing survey time and exposure for personnel. This system eliminates the need for traditional seismic cables, greatly reducing weight and therefore cost for deployments to remote locations. Combined with our extensive expertise in data processing and interpretation, these tools allow us to provide cost-effective surveys in minimal time to maximize your results!

Using a sledgehammer for the seismic source

Using a sledgehammer for the seismic source

Applications - Seismic refraction and shear wave velocity profiles

These tools are useful for a variety of applications, including estimating depth to bedrock, locating faults, and estimating material properties such as rippability and stiffness. Multi-Spectral Analysis of Surface Waves (MASW) can provide subsurface velocity profiles (and inferred corresponding soil properties) needed for earthquake and loading analysis, while refraction tools are commonly used for depth-to-bedrock profiling.The method chosen depends on a number of factors including dimensions of the area of investigation, depth of investigation, desired resolution of overburden/bedrock interface, type of bedrock (i.e. sedimentary vs. igneous) and expected contrast with overburden, expected induration of bedrock, depth to groundwater, cultural features, and sources of noise or interference in the area. 

 

An array of geophones along a roadway

An array of geophones along a roadway

About the Method

Seismic methods are a surface-based, non-invasive, non-destructive methods that use the properties of acoustic waves to interpret the estimated velocity of the waves throughout the subsurface and the thickness of subsurface layers. Commonly accepted methods then allow us to translate these velocities into material properties often of interest to engineering and environmental applications. Because seismic velocity is usually diagnostic for different types of material, and generally increases with degree of induration or hardness, the seismic  method not only can often measure depth to a hard layer such as bedrock but maybe used to non-invasively classify the type of material (e.g. soft sedimentary vs. igneous) and rippability of the layer encountered.