The Narlı Fault: the characteristics of the surface rupture that initiated the 6 February 2023 Kahramanmaraş Earthquake Sequence (Türkiye)

Abstract

The south-southeastern Türkiye was struck by a series of earthquakes in February 2023 causing the death of more than 50,000 people and billions of USD of economical loss. The largest of these events, the February 6th Mw 7.8 Pazarcık and Mw 7.5 Ekinözü earthquakes occurred only 9 hours apart of each other generating surface ruptures of about 450 km and the majority of the destruction. All these events took place in a complex tectonic system where the boundary structures of the Anatolian Block, the Arabian Plate and the Adana-Cilicia-Hatay Basin merge together. The Pazarcık earthquake was initiated along a subsidiary splay, the Narlı Fault (NF), and continued with the bilateral rupturing of faults over a length of 300 km.In this study, our aim is to document the surface deformation along the NF in order to have a better understanding of the initiation mechanism of the ‘multi-segment’ Pazarcık earthquake. In addition to our field observations, we operated a sUAS to map the rupture and measure offsets. We used a tape measure to determine the magnitude of slip across the well-established offset markers in the field, while the ultra-precise rupture mapping and a vast number of displacement measurements were made by using sUAS-based digital surface models (DSM) and orthophotos with a ground pixel resolution of ~3–5 cm.We mapped two sets of continuous surface ruptures, the 14 km-long southern and the 10 km-long northern parts, separated by a ‘gap’ of 8 km. The average sinistral offset along the ~N20-30°–striking southern rupture is about 2 m, whereas the maximum value reaches up to 3.7 ± 0.7 meters. On the other hand, the horizontal slip along the N25-35°–striking northern rupture barely exceeds 1.2 m. In this section, it is highly probable that a large portion of the total horizontal deformation is shared by widely distributed surface shears within the wedge between the East Anatolian Fault and the NF, which can be an analogue to a variant of a Prandtl Cell Model. In addition, we identified semi-circular/elliptical surface cracks at more than 10 locations to the south of the NF rupture. These are interpreted as seismically induced sink-holes, given the widely distributed Eocene limestones in the region. The preliminary analysis of the time series of interferograms between 2015–2022 suggests a long-term systematic subsidence, supporting our hypothesis.