Scientists from the Innovation Academy for Precision Measurement Science and Technology of the Chinese Academy of Sciences have studied the 2023 Kahramanmaras earthquake doublet, revealing the crucial role of fault geometry in earthquake propagation.
On February 6, 2023, two devastating earthquakes, known as the 2023 Kahramanmaras earthquake doublet, caused more than 50,000 deaths and displaced 5 million people in Turkey and Syria. The earthquakes, with magnitudes of Mw 7.8 and Mw 7.6 occurring approximately nine hours apart, ruptured the southern East Anatolian Fault Zone (EAFZ) and its northern strand.
The Kahramanmaras earthquake doublet has attracted considerable attention from the scientific community due to its catastrophic damage and unique cascading rupture of multiple fault segments with varying rupture velocities. The elongated rupture provides a rare opportunity to understand the role of fault geometry in the irregular multi-scale rupture behavior of earthquakes.
Fault geometry plays a key role in the propagation of an earthquake. Variations in fault geometry can lead to segmentation of the rupture along the fault and heterogeneous rupture velocities. Therefore, understanding the relationship between fault geometric complexity and rupture kinematics is essential for assessing the seismic risk associated with a specific fault and for exploring the underlying rupture mechanics.
By integrating InSAR and pixel offset tracking techniques, the scientists mapped the fault traces and performed a finite fault inversion to decipher the refined slip distribution of the Kahramanmaras doublet. They also performed a back-projection (BP) of high-frequency (HF) teleseismic array waveforms to trace the HF wave sources and estimate the rupture velocity during the doublet.
They found that the slip asperities of this earthquake doublet were significantly separated by fault bends. Large slips occurred along continuous and linear parts of fault segments, while fault bends are characterized by sparse slip. Correspondingly, a slowing of rupture propagation and a rapid decrease in slip amplitude were observed near bends, which may act as geometric barriers.
The intense higher-frequency (HF) (~1 Hz) sources of the Mw 7.8 event inferred from BP episodes show a pronounced concentration near fault branching junctions where ruptures with shorter heterogeneity wavelengths might have occurred, potentially leading to stronger HF energy radiation. During the Mw 7.6 event, intense BP signals from the CN array initially emerged near the epicenter and then propagated westward toward the branching junction between the Goksun and Cardak faults.
Spatial relationship between geometric features of faults and seismic kinematics. (Image by APM)
