[U-13] February 2023 Earthquake Sequence of the East Anatolian fault zone in Turkey

[U13-01] February 2023 Earthquake Sequence of the East Anatolia fault zonw in Turkey: The Outline of the Earthquakes and their forecasts

*Koji Okumura¹, Shinji Toda² (1.Hiroshima University, 2.Tohoku University)

Keywords:Turkey, East Anatolian fault, 2023 earthquake sequence, historic earthquake, surface rupture, paleoseismology

On February 6, 2023 at 04:17 and 13:24 in local time, ,Mw 7.8 and Mw 7.5 earthquakes occurred in the East Anatolian fault zone in south central Turkey. This paper first introduces the outline of the faults, crustal movements, earthquakes, and ground motion through the review of research results before and after the earthquake sequence. Then the possibility of forecasting these earthquakes is examined through historic and geologic records of earthquakes in the source areas. According to USGS, the epicenter of the Mw 7.8 main shock is located about 35 km WNW of Gaziantep where the faults consisting the north end of the Dead Sea Rift fault zone are distributed. The rupture did not propagate on the Dead Sea Rift fault zone but ruptured the East Anatolian fault about 27 km NW and propagated to SES and ENE in total for 300 km. The right-lateral strike-slip displacement on the East Anatolian fault was 7 m at most and usually within 3 to 5 m. 9 hours after the main shock, Mw 7.5 after shock occurred about 90 km north of Mw 7.8 epicenter rupturing 150 km long Cardak and Surgu faults. Along 100 km long western portion of the fault, right-lateral strike-slip was 6 to 8 m. The ground motion by the Mw 7.8 main shock was very strong. According to USGS, PGA and PGV exceeds respective 1000 gal and 200 cm/s. These values are similar to those recorded in JMA intensity 7 zones during Kobe 1995 and Kumamoto 2016 earthquakes. It seems there was no clear warning like the North Anatolian fault in south of Istanbul on the 2023 earthquakes on the East Anatolian fault based on forecasts. 1822 (M7.4) earthquake was the only very well recorded historic earthquake, but the source fault has not been identified. Since the damages were more severe in Syria in 1822, the source might have been the Dead Sea Rift fault zone. There is an idea to locate the source on the southernmost East Anatolian fault. In any case, there seems to be no clear evidence. After 18 century CE only M 7.0 to M 7.1 rather small events occurred in these areas. Before 17 century CE, there is no clear evidence to locate large earthquake such as 1513 (M 7.4). We are going to discuss if there was a way to forecast the 2023 sequence based on historic and geologic records.