A terrestrial survey, depth soundings and side scan sonar surveys were carried out to establish baseline topographic data.
A borehole survey (depth 150 m) was conducted in the central part of Motoyama, and it provides the only result that has been published (Ossaka et al. 1985).
In the borehole survey (depth 150 m) carried out near the northeast 900 m of the seismic array, alternating layers consisting of lava flows and pyroclastic rocks were found (Ossaka et al. 1985).
The method increases the survey depth of penetration because it galvanically injects electric current into the ground using a large-moment source and a long transmitter receiver distance (Abd Allah et al. 2013a).
The method, called grounded-electrical-source airborne transient electromagnetics, or GREATEM (Mogi et al., 1998), should enhance survey depth in coastal areas, since this method galvanically injects electric current into the ground.
The basic principles of NDT methods are described with particular reference to the five major factors that influence the success of a survey: depth of penetration, vertical and lateral resolution, contrast in physical properties, signal to noise ratio and existing information about the structure.
