Supershear triggering and cascading fault ruptures of the 2023 Kahramanmaraş, Türkiye Earthquake doublet
Jan 19, 2024
Peking University, January 19, 2024: Earthquakes are the most devastating natural disaster that cause the greatest loss of lives. Their rupture processes are complex, involving fault sliding, stress release, and seismic wave propagation. The rupture evolution of an earthquake, from the epicenter to a catastrophic event, is influenced by many factors. In a complex fault system, even the rupture of a minor branch can trigger adjacent faults, resulting in cascaded rupture across the entire fault system. Therefore, it is important and challenging to understand the rupture process of a big earthquake and the triggering mechanisms that lead to the catastrophic ruptures of the entire fault system.
On Feb. 6, 2023, at 04:17:34 AM Turkish local time, a magnitude 7.8 earthquake struck the Türkiye – Syria neighboring regions. About nine hours later, a magnitude 7.6 earthquake occurred approximately 100 kilometers to the north-northwest. This earthquake doublet is the largest continental earthquake doublet sequence ever recorded with contemporary seismological observations, resulting in tragic loss of approximately 50,000 lives, injuries to 100,000 people, and an economic loss of over $100 billion. The 2023 earthquake doublet attracted worldwide attention. Researchers from the School of Earth and Space Sciences at Peking University, together with seven other global institutions, conducted a joint analysis of multiple datasets combining seismic ground motion, Global Positioning System (GPS), and Synthetic Aperture Radar (SAR) observations. The study reconstructed the spatiotemporal evolution of the earthquake sequence, including a 3D fault rupture model, rupture kinematics of each segment, the dynamic stress state, and the triggering process of the major earthquakes.
Their results suggest that the initial rupture during the first event occurred at a branch located on the southern side of the main fault. By analyzing continuous waveforms from near-fault seismometers, a supershear velocity was determined to be about 4.2 km/s, exceeding the shear wave velocity of the medium of ~3.6 km/s. Contrary to a common assumption in dynamic modeling, the rupture on the main fault is not triggered at the junction with the branch fault. Instead, the Mach wave generated by the supershear rupture reaches the main fault first and dynamically triggers the rupture about 10 km west of the junction. Subsequently, the rupture propagated bilaterally along the main fault at subshear velocities. To the northeast, it transitioned to supershear rupture (approximately 4.0 km/s) after passing the junction. To the southwest, it propagated at a subshear velocity (averaging to be between 2.0 and 3.2 km/s). The rupture of the second earthquake was also non-uniform, beginning in the center of the fault, propagating westward and eastward with supershear and subshear ruptures, respectively. Mach waves generated by supershear ruptures do not exhibit spatial geometric spreading compared to subshear ruptures, thus transporting energy over further distances and resulting in greater destruction (Figure 2). Simulations suggest that in comparison with the subshear scenario, the supershear rupture increased the intensity range of six or higher by 20%. The study analyzed the dynamic triggering process on the main fault and found that the original stress level on the supershear rupture segment was almost twice that of the subshear segment, which is closer to the failing criterion. This phenomenon is consistent with the observed supershear rupture. The study's reported rupture processes and triggering relationships offer valuable insights into earthquake mechanisms and the cascading rupture processes that lead to major earthquakes.
Figure 1. The observations and rupture model of the 2023 Türkiye doublet. (Left) Coseismic observations were utilized in this study. The red zebra crossing marks the main rupture range of the two earthquakes. The green triangles stand for the strong motion stations. The yellow squares denote the GPS stations. And the blue-to-red fringes are interference patterns from synthetic aperture radar (SAR). (Right) The coseismic slip model and simulated ground shaking. The amount of the fault slip (color) and the kinematics (rupture velocities) are plotted on the fault planes. The initial point of the main fault (Pnt I) and the junction (Pnt J) of the first event are marked respectively. The color of the ground surface is the simulated peak ground acceleration. The inset box in the lower right corner shows the rupture kinematic characteristics near the junction of the initial branch and the main fault.
The result has been published in Science on Jan. 19, 2024, titled "Supershear Triggering and Cascading Fault Ruptures of the 2023 Kahramanmaraş, Türkiye Earthquake Doublet". This is a teamwork (Figure 1) led by the Department of Geophysics of the School of Earth Sciences at Peking University, in collaboration with the Department of Geophysical Engineering in Istanbul Technical University, the Department of Earth and Space Sciences in Southern University of Science and Technology, the SinoProbe Laboratory of the School of Earth and Space Sciences at Peking University, the Department of Earth, Planetary, and Spaces Sciences in University of California Los Angeles, GNSS Research Center in Wuhan University, Department of Geophysical Engineering in Kocaeli University, and Department of Earth and Planetary Sciences in University of California, Riverside. Ph.D. students Ren Chunmei and Wang Zexin are the co-first authors, and Associate Professor Yue Han and Professor Song Xiaodong are the corresponding authors. This research was funded by the National Key R&D Program of China and several NSFC projects.
Figure 2. Group picture. The authors are as follows from left to right. First Row: Shen Zhengkang, Yue Han (corresponding author), Xu Haoyu, Luo Heng, Wang Zexin (co-first author), Ren Chunmei (co-first author), Hu Nan, Zhao Zeyan, Song Xiaodong (corresponding author), Tuncay Taymaz. Second Row: T. Serkan Irmak, Geng Jianghui, Li Zhen, Cao Bonan, Xu Hang, Ding Hongyang, Zhou Yijian, Ge Zengxi, Wang Teng, Zhang Wei, Ceyhun Erman.
The School of Earth and Space Sciences, Peking University, has five undergraduate majors (geology, geochemistry, solid geophysics, space science and technology, and geographic information systems). The Peking University’s geophysical program is the earliest one in China.
Reference:
Ren, C.M., Z.X. Wang, T. Taymaz, N. Hu, H. Luo, Z.Y. Zhao, H. Yue, X.D. Song, Z.K. Shen, H.Y. Xu, J.H. Geng, W. Zhang, T. Wang, Z.X. Ge, T. S. Irmak, C. Erman, Y.J. Zhou, Z. Li, H. Xu, B.N. Cao, and H.Y. Ding. Super-shear triggering and cascading fault ruptures of the 2023 Kahramanmaraş, Türkiye earthquake doublet. Science, January 19, 2024.
Source:
School of Earth and Space Sciences, Peking University
