Abstract
We developed a newly portable time-domain electromagnetic exploration (PTDView) equipment to explore three-dimensional (3D) resistivity structure for depth around 10-100m that was effective for investigations of groundwater or disaster prevention (i.e., landslides). The 3D exploration requires high-density multi-point measurements, a costly and time-intensive requirement. The proposed PTD View equipment offers improvements in both these areas owing to its ability to quickly measure the resistivity structure developed by the recent electromagnetic exploration.
The equipment requires precision in two factors for time domain electromagnetic equipment to explore the objective depths. It must have a precision factor higher than 1 μs to allow time synchronization between transmitter and receiver. The signal resolution needs less than 10－4 for the normalized amplitude. The PTDView is able to realize the high resolution by both GPS synchronization and the 24-bit analog-to-digital converter.
At first we performed the experiment in two districts (Miura Peninsula in Kanagawa Prefecture and Southern Osaka Prefecture) which 1D inversion analysis was able to apply to the horizontal layer structure. Furthermore we compared the results of the electrical logging and electrical survey with the resistivity structure which obtained by the PTDView. Both resistivity characters are corresponding and the exploration using PTDView is effective.
Next we conducted the field experiment at the Nojima Separated Fault in northern Awaji Island. As a result, the location of the subsurface fault was traced by a resistivity structure obtained from the PTDview.
These two results demonstrated that PTDView was sufficiently practical in terms of cost and the time spent for the 3D exploration. The resistivity structure obtained from PTD View defined the detail location of the Nojima Separated Fault.
