Analysis of landslide in Bungkah, Sepakung, Banyubiru using ground shear strain method and shear wave profile from HVSR method

Abstract

In Bungkah, Sepakung, Banyubiru there was a landslide several times Monday to Thursday, 17 to 20 October 2017 which occurred due to the high intensity of rain in the region within 2 consecutive days. The landslide material was able to close the road that became access to local residents’ settlements. Besides that, in Bungkah, there is a resident’s house made of permanent walls that are curved on the wall due to ground movement while the house next to it does not occur. To analyze these phenomena, a single station microtremor method is used, namely the HVSR analysis with amplification values and dominant ground frequency of the curves obtained can be used to determine the peak ground acceleration and seismic vulnerability index which can then be used to analyze ground shear strain value or the ability of the soil layer to stretch and shift when receiving elastic wave propagation. Based on the ground shear strain value, Bungkah has values ranging from 10−3 to 10−1, the phenomenon that will occur is landslides with the dynamic nature of the soil included in the category of soil or rock collapse. Based on the results of frequency and amplitude inversion, the profile of Vs is obtained to the depth that can accurately image the shape of the slip surface from landslide that occurred in October 2017. The sensitivity of Vs to the presence of fluid imaged an accumulation of water below the landslide limit. The mechanism of land movement in the Bungkah hamlet is a rotational slide avalanche type. The movement of the soil which causes the curvature of the walls of one of the permanent houses in Bungkah due to the existence of a vertical soil layer with very low Vs which is directly bordered by massive Vs. The boundary of this layer may be cavity or cavity. The existence of a massive layer in the east of the area makes no continuity of soil movement to the east.