[S-SS11] Strong Ground Motion and Earthquake Disaster

[SSS11-11] Determination of Site Effects in Antakya Basin, Turkey from Microtremor and Aftershocks from 6th February 2023 Earthquake

*Oguz Ozel¹, Hiroaki Yamanaka², Seiji Tsuno², Nobuo Takai³, Mehmet Safa Arslan⁵, Deniz Caka⁶, Pinar Duran¹, Masayuki Yoshimi⁴ (1.Istanbul Unlversity-Cerrahpasa, 2.Tokyo Institute of Technology., 3.Hokkaido University., 4.Japan Geological Survey., 5.Erzincan University., 6.Kocaeli University.)

Keywords:Earthquake Kahramanmaras., The Antakya Basin., Spectral ratio, Basin Amplification

Following the February 6 Kahramanmaras earthquakes, a collaborative project was initiated in March 2023 by researchers from Istanbul University-Cerrahpasa, Kocaeli University, and Middle East Technical University, in partnership with Tokyo Institute of Technology, Hokkaido University, Japan Railways Research Center, and Japan Geological Institute under the J-Rapid project. This project has now been completed. As part of the study, 21 accelerometer stations were deployed across Kahramanmaras, Adiyaman, Pazarcik, Iskenderun, Antakya, and Samandag, regions severely affected by the earthquakes. These stations continuously recorded aftershocks from March to September 2023. The primary objective was to investigate site effects, correlate seismic responses with damage distribution, determine the 1D S-wave velocity structure, and assess ground response through joint analysis of recorded earthquakes, microtremor measurements, and vertical electrical sounding. Based on the first three months of data, an article was submitted by Japanese researchers to Seismological Research Letters (SRL). To further these investigations, an additional field study is scheduled from September 2023 to February 2024. During this phase, accelerometers in Adiyaman, Pazarcik, Kahramanmaras, and Iskenderun will be relocated to Antakya’s central district. Preliminary analysis of Peak Ground Acceleration (PGA) for the M 7.7 and M 7.6 earthquakes revealed significant amplification as seismic waves propagated into the Antakya Basin, while acceleration diminished with increasing distance from the epicenter (see AFAD Earthquake Department Strong Motion records). These findings suggest that the Basin Effect played a crucial role in the extensive damage observed in Antakya. Therefore, the next phase of the study will focus on the Antakya Basin. As a continuation of the 1002-C project, research will resume with the same Japanese team on September 25, 2023, under the newly proposed 1002-B project.