Local Site Effects Evaluation Using Microtremor Measurements at North Side of Pandan Mountain

Abstract

Disaster mitigation has been undertaken to reduce the impact of loss or damage caused by the earthquake. For disaster mitigation purpose, it is necessary to conduct a local geological assessment. The horizontal to vertical spectral ratio (HVSR) of microtremor analysis is very popular in the context of seismic micro-zonation. Microtremor method is cheap, data acquisition is easy, and does not cause noise, so suitable for use in residential areas. This research aims to determine the distribution of the natural frequency value, the amplification factor value, and the soil vulnerability index value. This study was conducted geographically between 7°26'17.45" – 7°26'53.16" S and 111°47'14.76" – 111°48'7.06" E. Data processing using HVSR analysis method on Easy HVSR software. The results showed that the natural frequency (<em>f_o</em>) values range 0,95 Hz to 8,3 Hz and the amplification factor values range 2,05 to 8,67. From the result data of the natural frequency and the amplification factor, the soil vulnerability index can be calculated. The vulnerability index (Kg) value ranges from 1,09 to 68,33. The northeast side of the study area is indicated as a weak zone where have high potential to damage when the earthquake occurred.