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

The February 6th, 2023, Mw 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 (Mmax) 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 Mw ≥ 7 earthquakes between AD 1000 and the present in the region. We find that the 2023 Pazarcık earthquake could have been foreseen in terms of location (the East Anatolian Fault) and timing (an earthquake along this fault was if anything overdue), but not magnitude. We hypothesize that the maximum earthquake magnitude for the East Anatolian Fault is in fact 8.2, i.e. a single end-to-end rupture of the entire fault, and that the 2023 Pazarcık earthquake did not reach Mmax by chance only. In fact, we suggest that such unusually large events are hard to model in terms of recurrence intervals, because they need a very specific set of circumstances to line up before they can happen. We also conclude that seismic hazard assessment along continental transforms cannot be done on individual fault systems, but must include neighboring systems as well, because they are not kinematically independent at any time scale.