On 6 February 2023, an earthquake with magnitude Mwc. 7.0 on the Narlı Fault, a fault sub-parallel to the East Anatolian Fault Zone (EAFZ), initiated a chain of large earthquakes on the EAFZ. The earthquakes occurred in a seismic gap with low geodetic strain rates and low background seismicity, where deformation is distributed across a wide fault zone and a long recurrence time of historical earthquakes. The c. 50 km long rupture of the Narlı Fault towards Pazarcık led to an Mw 7.8 left-lateral strike-slip earthquake breaking a c. 300 km section of the c. 600 km long EAFZ bilaterally with a total duration of more than 80 s. Toward the SW, the rupture propagated on the c. 100 km long Amanos segment with a peak surface offset of 5 m, before diminishing toward the Hatay graben. In the NE direction, the rupture reached a peak surface offset of 7 m before sharply declining at the termination of the 2020 Mw 6.8 Sivrice earthquake rupture. A second large earthquake with Mw 7.6 occurred 9 h later on the Çardak Fault, located at the western margin of (and sub-parallel to) the EAFZ and breaking the surface with almost 9 m of left-lateral slip (average of c. 4 m). Following these large earthquakes, the increase in the regional stress led to a rapid seismic activation in a broad region from central to eastern Anatolia, loading the faults at various scales and increasing seismic hazard. Two weeks after the initiation of the seismic crisis, a third earthquake with Mw 6.4 occurred at the southern boundary of the Hatay graben, near the southwestern termination of the Amanos rupture. The earthquakes caused significant loss of human life, devastating 12 cities. We evaluate the observations prior to the ruptures, and present preliminary seismological results with surface displacements from sub-pixel correlation of optical satellite images and the stress perturbations computed on the nearby faults based on preliminary slip models. The re-evaluation of the seismic potential in light of the recent and historical earthquakes provides some new insight on seismic hazard assessment. The recent series of events on the EAFZ is an important reminder that large faults can generate very large earthquakes on multiple segments. The seismic potential of large earthquakes on these fault zones can be estimated only by considering multiple seismic cycles and moment deficits from very large earthquakes.

Supplementary material: Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6567094

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