[Paper Review] Dynamics of episodic supershear in the 2023 M7.8 Kahramanmaraş/Pazarcik earthquake, revealed by near-field records and computational modeling

Mohamed Abdelmeguid, Chunhui Zhao+4 more|arXiv (Cornell University)|May 2, 2023

Earthquake Detection and Analysis57 references8 citations

TL;DR

The paper combines near-field seismic records with a physics-based dynamic rupture model to show spatially non-uniform rupture speeds, including episodic supershear propagation along the Narli splay fault and the East Anatolian Fault, and to explain how geometric complexity and friction drive these dynamics.

ABSTRACT

The 2023 M7.8 Kahramanmaraş/Pazarcik earthquake was larger and more destructive than what had been expected. Here we analyzed near-field seismic records and developed a dynamic rupture model that reconciles different currently conflicting inversion results and reveals spatially non-uniform propagation speeds in this earthquake, with predominantly supershear speeds observed along the Narli fault and at the southwest (SW) end of the East Anatolian Fault (EAF). The model highlights the critical role of geometric complexity and heterogeneous frictional conditions in facilitating continued propagation and influencing rupture speed. We also constrained the conditions that allowed for the rupture to jump from the Narli fault to EAF and to generate the delayed backpropagating rupture towards the SW. Our findings have important implications for understanding earthquake hazard and guiding future response efforts and demonstrates the value of physics-based dynamic modeling fused with near-field data in enhancing our understanding of earthquake mechanisms and improving risk assessment.

Motivation & Objective

• Motivate understanding of the 2023 Mw7.8 Kahramanmaraş/Pazarcik earthquake beyond kinematic inversions.
• Constrain rupture velocity histories and frictional properties using near-field records and mechanistic modeling.
• Explain how geometric complexity and fault junctions influence rupture propagation and hazard implications.

Proposed method

• Analyze near-field ground motion records to identify Mach Cone signatures of supershear propagation.
• Develop a 2D dynamic rupture model of a non-planar branching fault network constrained by station data and USGS fault geometry.
• Implement a linear slip-weakening friction law with specified μs, μd, and Dc to simulate rupture on Narli splay and East Anatolian Fault segments.
• Perform a junction-phase parametric study using the dimensionless eG = Bc/Ac to assess propagation likelihood across fault junctions.
• Calibrate model parameters (S, eG, Dc, μs, μd) to reproduce observed bilateral propagation and speed transitions.
• Validate model by comparing synthetic arrival times and velocity jumps with near-field records.

Experimental results

Research questions

• RQ1 What frictional and geometric conditions enable the Narli-to-EAF transition and subsequent bilateral rupture propagation?
• RQ2 How do variations in frictional strength, fracture energy, and stress state control shifts between sub-Rayleigh and supershear speeds along multiple fault segments?
• RQ3 Can a physics-based dynamic rupture model reconcile conflicting kinematic inversions for rupture speeds on the EAF during the event?
• RQ4 How does fault junction geometry influence delayed backpropagation and branching rupture behavior?

Key findings

• Near-field records show zones with supershear rupture signatures along the Narli fault and at the SW end of the East Anatolian Fault.
• A 2D dynamic rupture model reproduces a nucleation on the Narli fault, transition to supershear at ~19.5 km, and bilateral EAF propagation with mixed speeds.
• Suppression or enhancement of propagation across the Narli–EAF junction depends on the strength parameter S and the energy ratio eG, with sustained supershear requiring certain parameter regimes.
• The model predicts delayed backpropagation to the southwest and complex bursts of supershear along branches, consistent with station data near Hatay.
• Supershear propagation provides a mechanism for strong near-field ground motion and unusual wave-field patterns captured by detectors.
• The results highlight the role of geometric complexity and heterogeneous friction in governing rupture speed, branching, and hazard.