Distinguishing the Earthquake Type and Predicting the Next Strong Aftershock for Today’s M7 Earthquake at Cape Mendocino, California, 2024-12-05, 13:44:21 UTC-5)

Wang Zhi, a researcher at the Key Laboratory of Marginal Sea and Ocean Geology of the Chinese Academy of Sciences, and his collaborators, with funding from the National Natural Science Foundation of China and the Chinese Academy of Sciences, have made important progress in studying the different rupture processes of the 2023 Turkish double earthquake. Relevant results were recently published in Science China Earth Sciences. Although geodetic and seismological observations have revealed the preliminary processes and propagation patterns of dual earthquake ruptures in Turkey, the role of deep structural changes in the East Anatolia Fault Zone during earthquake rupture remains unclear. In order to understand this in depth, the researchers analyzed a large number of high-quality P-wave and S-wave travel time data, and used seismic double-difference relocation and nonlinear multi-parameter joint inversion methods to obtain high-resolution longitudinal and transverse waves in the dual seismic rupture zone. Velocity and Poisson's ratio structures. The study found that the two earthquakes had different induction mechanisms, which were closely related to significant seismic structural property changes in the fault zone and plate tectonic processes. The first earthquake of magnitude 7.8 occurred at the northern end of the Dead Sea Fault Zone, where the rock strength gradually changes from strong to weak, forming a rigid transition zone. The second earthquake of magnitude 7.6 started in the plastic zone of the seismogenic layer, which is characterized by low seismic wave speeds and high fluid saturation and extends along the ?ardak fault. The study believes that the significant seismic structure difference in the rupture zone of the magnitude 7.8 earthquake is mainly due to the strong oblique collision between the weakened part of the East Anatolian Plate and the brittle part of the Arabian Plate. The rupture zone of the magnitude 7.6 earthquake was caused by fluid intrusion caused by the northward subduction and subsequent delamination of the Cyprus plate, which increased the fluid pressure in the earthquake source area and led to plastic deformation. Wang Zhi, the first author and corresponding author of the paper, said that the occurrence of the first earthquake helped reduce the shear stress on the fault of the second earthquake, which may delay the rupture of the second earthquake. However, due to the existence of double left-lateral strike-slip structures in the triangular area formed by the intersection of two large strike-slip faults, the first earthquake significantly reduced the normal stress effect of the East Anatolian Plate on the second earthquake fault, which not only reduced It reduces the effective friction on the fault plane and increases the porosity of the rocks within the fault. It also leads to a decrease in strain stress and a redistribution of Coulomb stress, which contributes to the occurrence of the second earthquake. "This finding provides a good explanation for why the second earthquake occurred approximately 9 hours after the first earthquake, i.e. fluids penetrating into the source area from deep and surrounding areas needed sufficient time to accumulate the stresses required to induce fault imbalances. "Wang Zhi pointed out that the dual earthquake rupture model proposed by the research is different from the model that controls a single earthquake rupture, and it provides important information for mitigating potential earthquake disasters in Turkey or Europe. At the same time, the lessons learned from this earthquake event will also help to re-evaluate the risk of catastrophic earthquakes in China's northern and southern seismic zones or other areas with similar geological structures around the world.