The soil characterization of the region between the Maltepe-Beykoz Fault and the Marmara Sea in İstanbul (Türkiye) with the integrated HVSR (Nakamura technique) and MASW method

Abstract

Completing the earthquake recurrence period of the Marmara segment, one of the two seismic gaps of the northern Anatolian fault zone, necessitates earthquake hazard studies for Istanbul, considering the population density. This study focuses on determining the soil properties of the study area in the Maltepe district of Istanbul. The Maltepe, with its large population density, stands very close to this fault zone and is vulnerable to earthquake damage. The soil properties such as Vs30, dominant period (T0), and amplification ratio (A0) were determined with the MASW from surface wave analysis methods at 48 points and the HVSR approach of microtremor analysis methods at 26 points. These point-based properties were mapped in the GIS environment, and spatial distribution maps were prepared. In addition, seismic vulnerability (Kg) and effective shear strain (γe) calculations for different acceleration values were carried out to detect deformation-failure on the surface. It was understood from the maps and the 2D cross-sections produced to examine the lateral and vertical changes that the soil conditions in the study area developed under the control of the Maltepe Beykoz fault (MBF). Accordingly, the two sides of the MBF lineament were determined with different geophysical outputs by their different geological origins. Namely, the alluvial part in the coastal part was defined by low Vs30, high period, and Kg values; on the contrary, the more rigid parts located at high elevations were described by relatively high Vs30, low period, and Kg values. In addition, it was understood that the deltaic sediments spread loosely and undulated in the alluvium at the SE part of the MBF lineament. These results obtained in the study are significant for predicting disaster damages and taking precautions before disasters. In addition, the scientific data potential of the outcomes of this study will make future studies, which are carried out to determine other parameters to be used during the taking of the precautions, more accessible.