An Integrated Application Ground Penetrating Radar and Seismic Refraction for Non-Intrusive Investigation of Geophysical and Geotechnical Targets

Introduction

The seismic refraction method is one among a suit of methods available to a geophysicist to investigate the Earth’s interior. It makes use of seismic waves that are recorded at the surface after travelling through the Earth along boundaries between layers with different acoustic properties. Seismic refraction investigations can be carried out at three distinct scales: global, crustal and near-surface investigations. The source of waves at global scale is mostly earthquakes and at the other two scales the source can either be explosives and or low energy sources like impact weights. Generally, the waves recorded at the surface represent energy of different wave types that arrive sequentially at the detectors. Together with the direct waves, refracted waves are the first to arrive at the detectors. After recording, refracted waves are processed to determine the velocity of the geologic layers present under the subsurface. For near-surface investigations the seismic velocities obtained can be inverted for geotechnical parameters such as rock strength, rippability, and potential fluid content.

For near-surface work, surveying is done along profile lines which are typically between five to ten times the required depths of investigation (Kearey et al, 2002). Initial interpretation of seismic refraction data assumes planar boundaries between layers. However, refinements can be made later during processing to account for irregularities. The refraction method can be used as a complementary tool to other geophysical methods such as reflection, gravity and magnetic, electrical, and electromagnetic. Its major application is in the oil industry and in regional geological studies (Reynolds, 2011). It can also be used in geotechnical and environmental investigations.