Preliminary Result : Classification of Soil Using Fundamental Frequency and Vs30m

Abstract

Geologically, Ngamprah – Padalarang is located above Lembang Fault which stretched from east to west of Bandung, with a length of 29 Km. therefore, to understand disaster risk around the area, a seismic microzonation study is needed. Microtremor measurement has been done in 21 locations around Ngamprah, West Bandung. Microtremor measurement is a passive seismic method that utilizes natural vibration so it can provide a fundamental frequency of microtremor data and can be applied to understand the lithology of the local site area. Furthermore, the fundamental frequency can be used to obtain Vs30m and correlate it to Eurocode 8 for classification of soil type. The result has shown, the fundamental frequency at Ngamprah around 3 – 4 Hz, meanwhile, we found an anomaly of high frequency around 9 – 11 Hz at Cimeta River. Low frequencies correlated to deep sedimentation meanwhile high frequencies may correlated to Lembang Fault Segment Cimeta which cut through Cimeta River and also indicated as slow sedimentation. In addition to that, VS30m obtained from fundamental frequency show around Cimeta river has high velocity (550 m/s) meanwhile at Ngamprah area is low velocity < 400 m/s . High velocity is indicated as very dense sand or very stiff clay meanwhile low velocity indicates deep deposits of gravel or stiff clay with thickness several tens to hundreds of meters.