Turkiye Earthquake Sequence on February 6, 2023: Preliminary Earthquake Reconnaissance Report

On February 6th, 2023, a Mw 7.8 earthquake hit southern Turkey at 4:17 am (local time), followed by a Mw 7.5 earthquake in the same region about 9 hours later, at 1:24 pm (local time). The epicentral coordinates reported by both the U.S. Geological Survey (USGS, 2023) and the AFAD Seismological Center (Disaster and Emergency Management Presidency, 2023) were 37.288oN, 37.043oE for Mw 7.8 event. The USGS reported a hypocenter depth of 10.0 km for both events, whereas the AFAD Seismological Center reported a depth of 8.6 km for the mainshock. There have been several earthquakes of magnitude 6.0 and larger in the sequence (USGS, 2023). Earthquake sequences with consequent large magnitude events separated by short time intervals have been occurring at different parts of the world in the past years (e.g., 2019 Ridgecrest earthquakes (Mosalam et al., 2019); 2022 Iran earthquake sequence (Mosalam et al., 2022), 2022 Taiwan earthquake sequence (Mosalam et al., 2022)). From a structural engineering and design perspective, this is a reminder that strong pre-shocks and aftershocks (even with the same magnitude) can occur before and after the mainshock and their cumulative effects should be characterized and considered in the design codes of buildings and other infrastructure systems.
As a result of this unprecedented series of back-to-back earthquakes, in populated regions, damage was observed for residential buildings, industrial structures, bridges, transportation systems, earth structures, harbors and lifelines, with direct infrastructure loss exceeding $34 billion according to initial estimates (World Bank, 2023). In addition to strong ground sharing in the near-field, one of the root causes that exacerbated this natural hazard into a catastrophic disaster was the large ground deformations such as landslides, fault rupture, and ground subsidence which severely affected critical infrastructure including lifelines and roads. The cities affected most by these sequential earthquakes are Kahramanmaras, Adiyaman, Hatay, Osmaniye, Gaziantep, Malatya, Adana, Diyarbakir, Elazig and Kilis with residents of over 15 million (which constitute about 17% of Turkey’s population). According to official records, the number of fatalities was about 50,000 and more than 100,000 people were injured. A total of 19,284 buildings in ten different cities collapsed and 373,038 buildings were reported as damaged to different levels (Ministry of Environment, Urbanization and Climate Change, 2023).