Valuation of Building strength against earthquake Vibrations using Microtremor Analysis (case study: the city of Surabaya)

The potential damage due to earthquakes is not only identified by the magnitude and the epicenter distance to a particular region, but also by the topography and it's near surface geological condition. In the inhabited area, such as the urban locations, it is necessary to assess buildings against the earthquake vibration. For this purpose the microtremor vibration analysis was conducted in the city of Surabaya, in order to determine the earthquake-prone buildings and their vulnerability against the vibrations induced by earthquake. The possibility of resonance structure-soil in this specific area was also studied. The microtremor on grounds was analyzed using the Horizontal to Vertical Spectral Ratio (HVSR) and the microtremor inside the buildings was analyzed using the spectrum analysis method, the Floor Spectral Ratio (FSR) and the Random Decrement Method (RDM). This study was performed on ten-borne buildings throughout the region, which represent the one-story buildings, governmental buildings, historic buildings and public buildings. We found that from these buildings, seven of them have low-level, two have low- to medium-level of resonance, and one has a high-level of resonance. The minimum building vulnerability index in the horizontal direction EW (East- West) is 4.55 and in the NS direction (North-South) is 4.14. The maximum vulnerability index was found in the horizontal direction EW (East-West) and the NS directions, which amounts to 143.47 and 171.233.