Seismic vulnerability indices for ground in Derince-Kocaeli (NW Turkey).

The study area, Derince town, is one of the most densely industrialized (oil refineries, ports, etc.) and, therefore, populated urban areas located on the North Anatolian Fault Zone in Turkey. The study area is one of the areas that was most affected by the August 17, 1999 Kocaeli Earthquake (Mw = 7.4). A total of 10,984 buildings were heavily damaged, 6131 buildings were moderately damaged, 6803 buildings were slightly damaged and 5239 people were killed during the earthquake. The study area is located on thick sediments and therefore new settlements and industrial facilities have high earthquake hazard. The consequences of any possible earthquake will be very significant for the study area. Therefore, it is important to determine soil properties in earthquake hazard mitigation studies. The seismic vulnerability index (Kg), which depends on resonant frequency, amplification and V_s30 velocity, is a simple but powerful parameter that reflects local soil conditions which affect damage caused by an earthquake. The Kg value shows weak areas of the ground and therefore Kg can be considered to be a vulnerability index for the soil. To obtain Kg characteristics of the study area, the microtremor horizontal-to-vertical spectral ratio (HVSR) method was applied to single site measurements at 43 stations over an area of 40 km². Calculated seismic vulnerability indices were compared with structural damage occurring during the August 17, 1999 Kocaeli Earthquake (Mw = 7.4). The results indicate that the Kg values are in good agreement with damage distribution. Large Kg values indicate weak points in the study area and most of the damage occurred in areas with large Kg values. The areas with Kg values greater than 10 seem to be the most vulnerable locations in the study. Ground conditions should be taken into account during the planning and design of urban areas. The results obtained by considering ground conditions can be used as a quick method to identify risky areas for urban planning. [ABSTRACT FROM AUTHOR]