Analysis of Microtremor Data Using Horizontal to Vertical Spectral Ratio (HVSR) Method of Makassar, South Sulawesi

Abstract

Makassar has experienced earthquakes indicating that the city is an area vulnerable to earthquake hazards.  The regional tectonic setting supports the hazard in which several major faults develop surrounding the area. Earthquake events in the Makassar Strait of 4.5 SR in December 2015 is one of the hazard in this area. However not all the area was shaking at the same magnitude. The assumption is the different rock formation composing Makassar. Data taken from microtremor measurement supported by coring suggest a dominant frequency distribution has a significant relationship with the rock formation. Low dominant frequency arose at the area with thin sediment deposit (dominantly Camba Volcanic rock) and a high dominant frequency value came up at the area with thick sediment deposits (alluvial).  High seismic susceptibility index is found in thick sediment deposit. The area consists of interlayering between sand and clay and has shallow ground water table. On the other hand low vulnerability index is found in thin sediment deposit. It consists dominantly of tuff of Camba Volcanic Rock and has deep groundwater table