Kondo, H., et al. (2024). Re-excavation of the 2014 Kartal trench displaced by the 2023 Kahramanmaraş earthquake on the East Anatolian fault system, Turkey, Conference: American Geophysical Union (AGU) 2024 Fall MeetingAt: Washington, D.C., USA

Kondo, H. and Ozalp, S. (2025), Paleoseismological Researches Before and After the 2023 Destructive Earthquakes on the East Anatolian Fault System, Hokudan International Symposium on Active Faulting

Geological Survey of Japan

Mineral Research and Exploration General Directorate (MTA) - Turkey

• from Kondo et al. (2024)

The East Anatolian fault system (EAFS) is a plate boundary transform fault system between the Anatolia micro-plate and the Arabia plate. The 2023 M_W 7.8 Kahramanmaraş earthquake ruptured through the southern section of the EAFS longer than 310 km ,and it caused severe damages and casualties in the surrounding area. In 2014, we had excavated paleoseismic trenches at the Kartal site along the EAFS. The site is located ~25 km east of Kahramanmaraş. The surface rupture during the 2023 earthquake cuts just across the refilled trenches with left-lateral displacement. In October 2023, we re-visited the Kartal site and reexcavated the displaced trenches. Here, we report the preliminary results of the re-excavation survey, fault structure, event chronology, and a cumulative left lateral offset. We re-excavated two fault-crossing trenches and newly excavated two additional fault-parallel trenches to reconstruct the cumulative offset based on buried channel deposits across the faults. We could precisely re-expose the original trench walls based on the previously- used nails and strings in 2014. The left-lateral displacement of the 2014 trench walls was measured at 1-2 meters with vertical displacement of several tens cm. The exactly the same faults mapped in 2014 trench re-activated and ruptured through the ground surface during the 2023 event, but no obvious faults were newly created during the 2023 event. The preliminary C dating results indicate that the last event before the 2023 earthquake occurred at least after 1054 AD. The average recurrence interval for 5 events including the 2023 event is 650-690 years, slightly longer but comparable with the most recent two historical earthquakes, previously reported in 1513 AD and 1114 AD. Assuming the recurrence interval of ~400 years and the elapsed time of ~500 years since the 1513 earthquake, the occurrence probability within the next 30 years in the BPT model could have been evaluated as ~35 % just before the 2023 earthquake. Such paleoseismological evidence shows the high possibility of the occurrence of the 2023 event, though the evaluation of the total rupture length, rupture process, and the final size of the multi-segment earthquake may have been room for consideration due to the limited dataset especially in space.

• from Kondo and Ozalp (2025)

The M_W 7.8 and M_W 7.5 earthquakes produced by the East Anatolian fault system (EAFS) caused severe damages and casualties in and around the southeastern Turkey and Syria. Geological Survey of Japan and MTA have collaboratively worked on the EAFS since 2014 in order to map active faults, obtain paleoseismological data for long-term forecast, and understand the recurrence of past multi-segment earthquakes. We here briefly introduce some results of our joint research project before and after the 2023 earthquakes.

In 2014, we have started paleoseismological research on the southern section of the EAFS. The first paleoseismic trench site was selected at the Kartal site, which is about 25 km east of Kahramanmaraş. We opened two test trenches across the EAFS at the Kartal site, and identified 5-6 events but very few carbon dating samples were collected. Once the project suspended, and the joint project re-started in October 2022. We then decided to re-excavate the Kartal site for better constraint of individual paleoearthquakes and offset reconstruction based on additional 3D trenches.

On 6th February 2023, the first M_W 7.8 earthquake occurred on the southernmost section of the EAFS. About nine hours later, some of the branch faults along the EAFS, Çardak fault and Doğanşehir fault caused the M_W 7.5 earthquake. Immediately after the occurrence of the earthquakes, we collaboratively worked on collecting source fault information as emergency response. After publication of post-earthquake airphotos and satellite photos on the web site by HGM, General Directorate of Mapping in Turkey, we started mapping of surface ruptures and measurement of displacement based on photogrammetric interpretation. The first report on the source faults of two respective earthquakes appeared on GSJ web site on 22th February, and the sixth report as final version appeared on 20th March. MTA also independently carried out the surface rupture mapping in the field We thus quickly reported on the spatial distribution of primary surface ruptures and slip distribution along the faults.

In October 2023, we re-visited the Kartal site for re-excavation of the refilled 2014 trenches and additional excavation of 3D trench for offset reconstruction (Kondo et al., 2024, AGU abstract). We re-opened two fault-crossing trenches and newly excavated two additional fault-parallel trenches to reconstruct the cumulative offset based on buried channel deposits across the faults. We could precisely re-expose the original trench walls based on the same nails and strings used in 2014. The left-lateral displacement of the 2014 trench walls was measured at 1-2 meters with vertical displacement of a few tens cm. The exactly same faults mapped in 2014 trench re-activated and ruptured through the ground surface during the 2023 M_W 7.8 event, but no obvious faults were newly created during the 2023 event. The preliminary ¹⁴C dating results indicate that the last event before the 2023 earthquake occurred at least after 1054 AD. The average recurrence interval for the last 5 events including the 2023 event is 650-690 years. This interval is slightly longer but comparable with the most recent two historical earthquakes, previously reported as in 1513 AD and 1114 AD. Assuming the recurrence interval of 400 years and the elapsed time of 500 years since the 1513 earthquake, the occurrence probability in BPT model within the next 30 years could have been evaluated as ~35 % just before the 2023 earthquake. These paleoseismological evidences exhibit that high occurrence possibility before the 2023 event, though the evaluation of the total rupture length, rupture process and the fina size of the multi-segment earthquake may have been room for consideration due to shortage of the dataset especially in space.

Acknowledgment: We deeply express our condolences to the victims due to the 2023 earthquakes. We thank to all collaborators in the joint research project ‘Paleoseismological Study on the East Anatolian Fault System, Turkey’ between Geological Survey of Japan/AIST and MTA. The re-excavation of the Kartal site was partly supported by JST J-RAPID program ‘Verification study on long-term forecast of the 2023 Kahramanmaraş earthquake along the East Anatolian fault system’.