Detecting landslide vulnerability using anisotropic microtremors and vulnerability index

The vulnerability of the Nan-Shi-Keng landslide area in Taiwan is investigated via single-station horizontal-to-vertical spectral ratio analysis. The measurement stations in the area are arranged as follows: (1) a transverse arrangement through the landslide site along Highway No. 175 (Case 1) and (2) two longitudinal arrangements down the slope (Case 2). In Case 1, the distribution of the vulnerability index along the highway indicates that the risk of surface deformation is high on sections of the highway located outside the potential sliding zone. The low vulnerability index of highway sections within areas where the protection measures have been taken indicates that they successfully stabilize the highway and the upper slope area. In Case 2, the deformation-prone directions (i.e., the directions with the maximum vulnerability index) evaluated at various stations using anisotropic microtremor measurements of the landslide site correlate strongly with the local sliding directions obtained using conventional inclinometer measurements and telemetry monitoring. The value of the vulnerability index is related to the highway damage and soil movement behavior. Therefore, the vulnerability index serves as a useful warning parameter to locate sites with a high probability of slope failure.