Nonuniform seismic unzipping of East Anatolian Fault reveals supercycle behavior

Devastating earthquakes continue to surprise scientists, especially when they exhibit unexpected characteristics, such as the 2023 doublet of Mw>7.5 earthquakes in a day along the same fault system in eastern Türkiye. These earthquakes struck the East Anatolian Fault, a major >600 km long tectonic boundary, separating the Anatolian, Arabian, and Eurasian plates, resulting in approximately 60,000 fatalities in Türkiye and Syria and causing more slip than expected. Occurrences of temporally and spatially close earthquakes are hence rare and unmissable opportunities to advance our understanding of active fault mechanics and regional hazard. Such superevents could be part of a supercycle, wherein the likelihood of a large earthquake is determined by accumulated strain rather than time since past earthquakes. To advance our understanding of multiple earthquakes along fault systems and hence of seismic supercycles, we compare tectonic and seismological features of the two 2023 earthquake sequences near Pazarcik and Elbistan with those of the two previous Mw≥6.1 sequences, which occurred in 2010 and 2020, respectively, near Elâzığ along the northeastern East Anatolian Fault. We examined the four strong sequences along the East Anatolian Fault within a multimillennial context of historical seismicity and discovered progressively younger and nonuniform earthquakes moving southwestward. This pattern corresponds to a general progression and dispersion of seismic ruptures southwestward and we use it as a proxy to understand the mechanism of at least two major supercycles identified over the last two millennia. The supercycles evolved from the northeast spreading southwestward with an increasing number of earthquakes. Earthquakes to the northeast are spatially and kinematically well channelized along the main fault, efficiently translating slip toward the southwest, where dispersed and kinematically nonuniform earthquakes are triggered by the push from the northeast, until a new supercycle restarts from the northeast. Insights from recent events offer a crucial framework for interpreting past supercycles and enhancing seismic hazard assessment, providing essential guidance for future mitigation strategies.