| Some ten years ago the Authors presented the Underwater Surface-Wave Survey Method (Fujimura et al, 2007) and in 2014 the Authors also introduced the Hybrid Surface-Wave Survey Method which is a combination of MASW (Multichannel Analysis of Surface-Waves) and LAMS (Linear Array Microtremor Survey) (Kita et al., 2014). Based on these two methods, we have now conducted test surveys in a river to develop a new marine survey method in the evaluation of the bearing capacities of sea and river bed sub-surface layers. At the test survey, we deployed Ocean Bottom Cables (OBC) and Ocean Bottom Recorders (OBR) as receivers. As the source of the surface-wave signals, a kind of weight drop method was utilized. Ambient vibration noise on the riverbed was also recorded for the passive measurement.As results of the test survey, dispersion curves of surface-wave on riverbed were successfully obtained by both the active source survey (MASW) and the passive source survey (LAMS). And then, the dispersion curves were combined to create dispersion curves which demonstrate wide frequency ranges of from 2 to 20Hz. Using the combined dispersion curves, a shear-wave velocity section of riverbed sub-strata up to 60m in depth were successfully displayed. Accordingly, we have concluded that the Hybrid Surface-Wave Survey Method is applicable for marine geotechnical exploration. We call this new technique the Underwater Hybrid Surface-Wave Survey Method (UWHSW). |
