Hydro-TISAR – A New High Resolution Seismic Imagery Method for Hydrogeological Investigations
Several complementary geophysical tools have been used to characterize the physical properties of the overburden and/or rock for relatively shallow hydrogeological investigations of less than 50 meters. They include classic geophysical methods such as Electromagnetics (EM), Very Low Frequency EM (VLF), Time Domain EM (TDEM), Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT). Seismic methods have been underutilized despite the fact that refraction and Multi-channel Analysis of Surface Waves (MASW) provide hard numbers for depth as well as soil and rock strength. Great efforts have been made to improve the resolution of P or S wave reflection, but little to nothing could be achieved in the critical upper 30 meters where over 95% of groundwater problems and engineering interest resides. Thus, an alternative method is proposed using frequency domain analysis, Hydro-TISAR. Thin groups of a few millimeter joints in rock can be detected as well as narrow gravel lens within sedimentary materials. Consequently, water bearing geological structures can be resolved. The seismic method is very field flexible in terms of survey design and simple seismic sources and a typical engineering seismograph. The presentation is in the form of a 2D sections, but also pseudo-3D and real 3D seismic imagery can also be produced. Moreover, the same seismic records can be re-processed as MASW records over targets of interest (in the case of overburden), to improve the identity of the geologic features. Conversely, 2D MASW data set can be process as Hydro-TISAR. Separate Hydro-TISAR case histories related to overburden and rock as they relate to groundwater exploration and contaminant flow path detection are presented.