15:45 〜 16:00
[SSS11-12] Displaced pre-existing trenches by the 2023 Mw7.8 earthquake on the East Anatolian fault system, Turkey
キーワード：活断層、古地震、東アナトリア断層系、歴史地震
The East Anatolian fault system (EAFS) extends with the strike of north-east to south-west, and it forms plate boundary transform faults between the Anatolia micro-plate and teh Arabia plate. The 2023 Mw 7.8 Kahramanmaras earthquake was produced by the southern section of the EAFS and it caused severe damages and casuallities. We, GSJ and MTA, have conducted international collaborative studies since 1980’s. In 2014, we excavated paleoseismic trenches at the Kartal site along the EAFS, that is located ~25 km east of Kahramanmaras on the EAFS. Surface rupture during the 2023 Kahramanmaras earthquake cut through just on the refilled trenches in 2014 and caused remarkable left-lateral displacement. In October 2023, we have revisited the Kartal site and re-excavated the displaced trenches. Here, we report the preliminary results of the re-excavation research, fault structure, event chronology and a cumulative left-lateral offset.
The trench excavation in 2023 was planned for pleo-offset re-construction. We re-excavated displaced two trenches, that were originally excavated in 2014. In addition, we addtionally opened two fault-parallel trenches in order to reconstruct the cumulative offset based on buried channel deposit across the fault. The re-construction of re-filled and displaced trenches were not easy due to difficulties to distinguish original trench wall in 2014 and re-filled debris. But, nails and strings used in 2014 were well-preserved on the 2014 walls, therefore we could precisely exposed and re-construct the original trench walls. The right-lateral displacement of the 2014 trench walls were measured at 1-2 meters with vertical displacement. The faults during the 2023 event were newly developed and cut through the ground surface. However, some faults recognized in 2014 were not re-activated during the 2023 earthquake, suggesting the upward termination of the faults to be recognized as paleoearthquake event horizon. The preliminary 14C dating results show that the last event before the 2023 earthquake is estimated at least after 1054 AD, and 5-6 events including the 2023 event occurred after 3060±30 y.B.P. More dating results will help to identify more precise timing of the paleoearthquakes and recurrence intervals, in order to consolidate the long-term forecast of the occurrence of the 2023 event.
This work is supported by the J-RAPID program of JST and a part of GSJ-MTA Joint research project ‘Paleoseismological Study on the East Anatolian Fault System, Turkey’.
The trench excavation in 2023 was planned for pleo-offset re-construction. We re-excavated displaced two trenches, that were originally excavated in 2014. In addition, we addtionally opened two fault-parallel trenches in order to reconstruct the cumulative offset based on buried channel deposit across the fault. The re-construction of re-filled and displaced trenches were not easy due to difficulties to distinguish original trench wall in 2014 and re-filled debris. But, nails and strings used in 2014 were well-preserved on the 2014 walls, therefore we could precisely exposed and re-construct the original trench walls. The right-lateral displacement of the 2014 trench walls were measured at 1-2 meters with vertical displacement. The faults during the 2023 event were newly developed and cut through the ground surface. However, some faults recognized in 2014 were not re-activated during the 2023 earthquake, suggesting the upward termination of the faults to be recognized as paleoearthquake event horizon. The preliminary 14C dating results show that the last event before the 2023 earthquake is estimated at least after 1054 AD, and 5-6 events including the 2023 event occurred after 3060±30 y.B.P. More dating results will help to identify more precise timing of the paleoearthquakes and recurrence intervals, in order to consolidate the long-term forecast of the occurrence of the 2023 event.
This work is supported by the J-RAPID program of JST and a part of GSJ-MTA Joint research project ‘Paleoseismological Study on the East Anatolian Fault System, Turkey’.