Geotechnical field measurements and structural damage in Iskenderun following the 2023 Turkey-Kahramanmaras earthquake sequence

Abstract

The 2023 Turkey-Kahramanmaras earthquake sequence caused damage to cities along the East Anatolian Fault. This study focuses on Iskenderun, a coastal city in Hatay province. Based on an 1896 historical map, we classify the study area into four land classifications: the old city center, reclaimed land along the coast, former marshland inland, and former canal channels built for drying the marshes. Ataturk Boulevard forms the boundary between the old city center and the reclaimed land. The earthquake triggered lateral spreading and inundation on the reclaimed land, while buildings in the former marshland experienced collapse or damage. A joint team from Turkey, Japan, and Bulgaria conducted field investigations on March 30th and from October 14th to 16th, 2023, performing visual inspections and in-situ tests including portable dynamic cone penetration testing (PDCPT), multi-channel analysis of surface waves (MASW), and horizontal-to-vertical spectral ratio (HVSR) of microtremor. Strong-motion records indicated a peak ground acceleration of 290 cm/\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {s}^2$$\end{document}, and the response spectrum exceeded the DD-2 design level, the second-highest earthquake motion level defined in the Turkish Building Earthquake Code. Visual inspections identified ground-related damage in the reclaimed land and along Ataturk Boulevard, and structural damage in the former marshland. PDCPT and MASW at a site on the reclaimed land showed shear wave velocities of 100–140 m/s at the surface, increasing to 185 m/s at 10 m depth, consistent with the lateral spreading observed there. HVSR measurements on the reclaimed land showed predominant frequencies below 1 Hz, while those toward the old city center showed higher predominant frequencies, suggesting spatial variation in the depth of the dominant impedance contrast. The field investigation documented land-class-dependent damage patterns and spatial variation in HVSR characteristics that is consistent with them. The PDCPT and MASW measurements characterize one site on the reclaimed land. At a site on the reclaimed land, shear wave velocities were 100–140 m/s near the surface, while HVSR measurements across the reclaimed land showed predominant frequencies below 1 Hz; the reclaimed land experienced lateral spreading and inundation. The HVSR predominant frequency increased from the northwest to the southeast, and the spatial distribution of HVSR amplitude above 1 Hz showed a low-amplitude zone that spatially overlapped with the area of ground-related damage; this association is interpreted as a working hypothesis rather than a demonstrated causal relationship.