Application of Microtremor HVSR Method for Assessing Site Effect in Residual Soil Slope

— This paper investigates the local site effect of the earthquake induced slope instabilities using microtremor horizontal- to-vertical ratio (HVSR) method. It is accepted that soil effects (soil thickness and variation of surface soil parameter) and topographic effects namely local site effects, is considered having a significant effect on the seismic amplifications. However the understanding of seismic slope response is still limited. The research was carried out in a residual soil slope near Batu town, Malang District–Indonesia. The microtremor investigation had been conducted on 54 free-field measurements having 20 x 20 m dense grid. The HVSR analysis has been carried out using Geopsy Software. The predominant frequency (f0) ranges between 1 and 5.5 Hz and amplification factor (Am) varies from 2.5 to 10 though most of the areas having 4 to 5 Am value. The topographic patterns are identified by the fo value as related to bedrock depth. Variations of both parameters are indicated as a result of variations in surface soil parameters. Surface soil parameters are considered having more significant effect comparing to those of topographic effects. The vulnerability index (Kg) is indicated the soil damage level due to ground motions. The weak zone, failed during earthquake on the Southern slopes was identified by the highest Kg value. Index Terms—Site effects, the predominant frequency, amplification factor, vulnerability index, microtremor HVSR, residual soil slope, Malang.