Near-field evidence for early supershear rupture of the Mw 7.8 Kahramanmaraş earthquake in Turkey

Abstract

The M_w 7.8 Kahramanmaraş/Pazarcik earthquake was larger and more destructive than was expected based on historical seismicity in southeastern Turkey in the past few centuries, raising questions about the nature of rupture initiation and propagation. Here we analyse near-field ground velocity records from seismometers to constrain the rupture propagation speed along the Narli splay fault, which hosted the initial rupture that eventually reached the main East Anatolian Fault. The measured particle velocities provide evidence for an early transition of the rupture from sub-Rayleigh to supershear behaviour, whereby the rupture speed exceeds that of the seismic shear waves. The near-in-situ field observational evidence is consistent with mechanistic understanding of supershear rupture. We estimate the instantaneous supershear rupture propagation speed to have been 1.55 times that of the shear wave speed and the sub-Rayleigh-to-supershear transition length to have been around 19.45 km. This work reveals the value of near-field instrumentation in characterizing the initiation of earthquakes along major faults.