In this study, a series of microtremor measurements were carried out in a deep-seated gravitational deformation slope. Three dimensional seismometer sets were set on the deformation boundary, in and out of the deformation area, also in and out of a tunnel that pass through the slope. Data processing procedure including fast Fourier transformation, horizontal-to-vertical spectral ratio (HVSR) computation, Hilbert-Huang transformation, and the energy proportion of different frequency in the spectra. The results show that in vertical direction, the energy distribution with frequency are similar whether in or out of the deformation area; while in horizontal direction, the energy distribution varied with location. Inside the deformation area, the proportion of lower frequency is higher, although outside the deformation area, the proportion of high frequency would be higher. The results provide a solid reference to swift investigation on deformation boundary of deep-seated gravitational slope.
Aseismic microtremor signal of a location on ground surface are the response of that location to background factors. It has the potential to represent the intrinsic dynamic characteristics of a certain location. In this research, aseismic microtremor signal was monitored simultaneously on two locations with different physical conditions, ex., one is in the slope movement area, but another is out of the slope movement area. The objective is to differentiate the boundary of slope deformation according to aseismic microtremor monitoring on the ground surface.
Often referred as a sign of large scale landslide, deep-seated gravitational deformation of a slope is difficult to investigate both in deformation extent and in sliding amount (Bonzanigo, Eberhardt, and Loew, 2007; Dramis and Sorriso-Valvo, 1994). The potential boundary of deforming slope is often hard to recognize before slope deformation reaches ultimate limit. Microtremor is a low amplitude vibration of the ground induced by natural or anthropogenic disturbances. Microtremors have recently been used to investigate site effects and geological structures on the scale of kilometres (Bonnefoy-Claudet, Cotton, and Bard, 2006; Nakamura, 1989).