Identification of Source Faults of Large Earthquakes in the Turkey-Syria Border Region Between AD 1000 and the Present, and their Relevance for the 2023 Mw 7.8 Pazarcık Earthquake

The February 6^th, 2023, M_w 7.8 Pazarcık earthquake in the Turkey-Syria border region raises the question of whether such a large earthquake could have been foreseen, as well as what is the maximum possible magnitude (M_max) of earthquakes on the East Anatolian fault system and on continental transform faults in general. To answer such questions, knowledge of past earthquakes and of their causative faults is necessary. Here, we integrate data from historical seismology, paleoseismology, archeoseismology, and remote sensing to identify the likely source faults of fourteen M_w ≥ 7 earthquakes between AD 1000 and the present in the region. We conclude that, based on the historical seismic records of the region, the 2023 M_w 7.8 Pazarcık earthquake was foreseeable in space and time, but not in size. M_max for the EAF is likely ~ 8.2, with the limit rupture length being the distance between the Karliova and Amik triple junctions. The 2023 earthquake may not have reached M_max simply by a fortuitous combination of factors: if the 2020 Elȃziǧ earthquake had not happened where and when it did, would the 2023 rupture have continued propagating towards the northeast? This is a question that could be answered by combining Coulomb stress models and dynamic rupture models. If nothing else, what we have learned from the 2023 M_w 7.8 Pazarcık earthquake is that segmentation of continental transform faults is not relevant for calculating M_max, because some earthquakes can jump across segment boundaries. Such earthquakes are so infrequent, however, that they are difficult to study, and therefore hard to foresee.