Mixed Subshear and Supershear Rupture Kinematics of the 2023 Kahramanmaraş, Türkiye Earthquake Doublet Modulated by Complex Fault Geometry

ABSTRACT

How does a source rupture propagate in a geometrically complex multifault system? Reconstructing the spatiotemporal evolution process of such complex geometric ruptures is a crucial way to advance understanding of earthquake source physics, but sufficient observations of such events are difficult to obtain due to their rare occurrence. On 6 February 2023, two destructive earthquakes successively struck Kahramanmaraş, Türkiye, within 9 hr, forming the largest continental earthquake doublet ever recorded by modern seismological instruments. Here, we integrate the teleseismic backprojection imaging and the joint finite-fault inversion to investigate the rupture kinematics of the two earthquakes. We find that the two earthquakes exhibit distinct rupture propagation patterns, with transient and persistent supershear ruptures occurring in the first Mw 7.8 event and the subsequent Mw 7.7 one, respectively. The Mw 7.8 earthquake originates on a splay fault branching from the east Anatolian fault (EAF), and propagates to the main strand of the EAF at a subshear velocity. After passing through fault bends, the rupture generates three transient transitions from subshear to supershear, with two located in the Amanos segment and one in the Erkenek segment. In contrast, the rupture of the Mw 7.7 earthquake initiates in the middle section of the northern strand of the EAF, and propagates bilaterally at a persistent supershear velocity. Based on the analysis of a series of potential causes contributing to the supershear rupture, we argue that the difference in the geometric complexity of the seismogenic faults directly controls the variation in rupture patterns between the two earthquakes. This highlights that the geometric complexity is a key factor capable of modulating the kinematic characteristics of large-scale source ruptures.