The Importance of Seismic Microzonation under the Threat of an Earthquake of the North Anatolian Fault in Nilüfer, Bursa, Turkey

Abstract

The district of Nilüfer experienced the most recent urbanization among the central districts of Bursa in South Marmara with completion of rapid construction. Since 358 BC, there were many destructive earthquakes on the branches of the North Anatolian Fault reported which caused great damage in the city of Bursa and cost many lives. Besides some studies conducted to define the soil behaviour in the vicinity of Bursa, the seismic hazard of Nilüfer and the surrounding region remains a problem. In this study, an earthquake hazard analysis was first conducted and the peak ground acceleration (PGA) values were determined with respect to an expected earthquake. In the next step, MASW (Multi-Channel Analysis of Surfave Wave) measurements were conducted at 54 points in 28 neighborhoods of Nilüfer district. Soil mechanical parameters were determined at 11 boroholes, which were calculated as the probability of liquefaction. It was found that almost half of the study area suffers from low damage considering only the vulnerability index (Kg) index, which depends on the site effect. Therefore, in addition to the Kg values, we created a microzonation map using the results by soil liquefaction, settlement, changes of ground water level and the average values of spectral acceleration. The results showed four different areas with low to high damage. Altınşehir, Hippodrome, Ürünlü and Alaaddinbey, Ertuğrul, 29 Ekim, 23 Nisan, Ahmetyesevi and Minareliçavuş districts also have high risk of damage levels that could not be quantified by Kg index alone. The results of this study clearly show that considering the Kg index, which depends only on the local site effect, may lead to inadequate damage values.