Liquefaction hazard mapping at the town of Edessa, Northern Greece

Abstract

The town of Edessa is located on Northern Greece at a region that is characterized as low seismicity zone due to the fact that few moderate events of M \ 6 occurred during the last century. According to the Greek Seismic Code, the expected acceleration having a 10% probability of being exceeded in 50 years is equal to 0.16g. However, an amplification of ground motion is likely to occur due the local geology that is consisted of Holocene fluvio-torrential deposits. The basic aim of this paper is to evaluate the site amplification due to geological conditions and to assess the liquefaction hazard. In order to achieve this, 1-D site response analyses were performed. The data that were employed for the construction of the numerical models have been collected from borings with standard penetrations tests (SPT) that were drilled for construction purposes. Afterward, the liquefaction potential of the subsoil layers was evaluated taking into consideration two seismic scenarios. The first scenario was based on the seismic parameters, earthquake magnitude and PGA, assigned by the Greek Seismic Code. On the second seismic model, we employed the values of acceleration, resulted from the 1-D analyses and the earthquake magnitude as it was defined by the Greek Seismic Code. In order to compile the liquefaction hazard maps, we initially estimated the liquefaction potential index (LPI) of the soil columns using the parameters provided by SPT, for both seismic loadings, and afterward we correlated these values with the proposed classification of the severity of liquefactioninduced deformations. In addition, having computed the value of probability based on the LPI, liquefaction manifestations probability maps were compiled for both scenarios. The result of this study was that liquefaction-induced ground disruptions are likely to occur at the center of the city, among the branches of Voda River, only when the amplified values of acceleration are taken into account to the computation of liquefaction potential.

Probabilistic Evaluation of Liquefaction-Induced Ground Failures Triggered by Seismic Loading in Urban Environment; Case Studies From Greece

“…Thus, we concluded that the proposed value of PGA, 0.16g, by the EAK (2000) is not representative for a "microzonation" study and we decided to perform 1-D site response analysis using data provided by seven borings with SPT. In order to achieve this, several real acceleration time histories were selected with respect to the type of causative fault, the magnitude of the earthquake and the geological conditions at the recorded station, and were downloaded by the web site of European Strong motion Database (ESD) www.isesd.cv.ic.ac.uk/ESD (Papathanassiou and Valkaniotis, 2009). …”