The Controllable Seismic Source (CSS) solves the problem by generating impulsive
shear waves whose frequency content can be controlled.
The unit is self-contained and designed to be used from a vehicle with minimum effort for the operator. The CSS can
be used with any commercially available seismograph system with a standard trigger input.
The CSS makes use of a linear magnetic servo motor to impulse a variable load inside a shock cavity. By adjusting the speed, acceleration and mass of the load, a variety of frequencies can be
obtained. A computer controlled interface provides the means for adjusting these
parameters plus repetition rate. The unit is attached to a standard 2” trailer hitch
receiver in the back of a vehicle and powered by the vehicle 12V electrical system.
A pneumatic system is used to quickly deploy or retrieve the unit and to produce a
solid coupling to ground. A remote control handheld unit is used to manually trigger
the unit, either from inside or outside of the vehicle, minimizing operator’s exposure
and physical fatigue. These unique features make the CSS a powerful tool
compared to sledge hammers or conventional ground shakers.
The system is operated by attaching the shock unit to a standard 2” receiver on a vehicle. Using the computer
interface, the operator adjusts the speed and acceleration of the load to change the frequency of the shock wave,
depending on the depth and size of the intended target. A low frequency is used to obtain wide data of the area
whereas a higher frequency is used to obtain greater resolution. A wider range of frequencies can be obtained by
changing the weight of the internal striker. Data is then collected by geophones or other sensors and then transmitted
to the seismograph for processing and storage.
This tool provides three levels of improvement over the limitations of conventional seismic sources. First, the energy,
repetition rate and frequency of the shock waves are controllable by using a magnetic linear motor. The impact mass
is coupled to the motor by a set of rails and springs that allow the mass to freely impact the shock cavity, improving
the frequency characteristics of the wave. Second, the unit is adaptable for mobile deployment using a vehicle with a
conventional trailer hitch. Since the unit is electrically operated, all controls
and data acquisition systems can be inside the vehicle, making it safer
than manually carried units. Third, the configuration of the shock cavity
and the coupling with the magnetic linear motor provides higher frequency
content with better repeatability than those obtained using sledge
hammers, elastic or explosive sources.
Other advantages of this tool include the capability of generating inward or
outward shear waves as well as vibrational waves. Wave profiles can be
saved in the computer and recalled for later use. Ergonomic advantages
include low external acoustic noise eliminating the need of ear protection
and reduced operator’s fatigue because hammering is not required.
- Geophysical Surveys
- Subsurface Structures and Void Detection
- Oil and Gas Exploration
- Road Defect Analysis