Study on coseismic surface deformation of the 2023 Turkey MW7.8 and MW7.5 double strong earthquakes using optical image correlation method

Objective On February 6, 2023, double strong earthquakes of MW7.8 and MW7.5 occurred consecutively within 10 hours in the Kahramanmaraş province in central-southern Turkey. After these double-strong earthquakes, domestic and foreign seismologists studied coseismic surface deformation using field measurements, GNSS, and differential InSAR methods. However, owing to the limitations in the techniques employed, the current coseismic surface deformation results suffer from low spatial resolution and missing data near fault surface ruptures. This study aims to address these limitations and comprehensively present the coseismic surface deformation of the double earthquakes in Turkey. Methods Using Sentinel-2 optical image data, the east-west and north-south surface coseismic deformation fields of Turkey' s double-strong earthquakes were obtained using the image correlation method, and these surface deformations were converted into sinistral strike-slip displacement along the fault direction. Results The deformation field results showed that the surface rupture lengths of the double earthquakes are approximately 280 and 130 km, respectively. The average strike-slip displacement of the first MW7.8 earthquake is 4.2±1.66 m; the maximum strike-slip displacement is 6.9±0.81 m. The average strike-slip displacement of the subsequent MW7.5 earthquake is 4.9±2.45 m, and the maximum strike-slip displacement is 9.6±1.16 m. Conclusion Comparison of the horizontal displacement results obtained using the COSI-Corr method and field measurements revealed that the maximum horizontal displacements obtained using the two methods are consistent. In contrast, the average displacement results obtained using the COSI-Corr method are slightly larger than the horizontal displacement results obtained using field measurements, attributed to the inclusion of "off-fault" deformations. Significance This study not only provides deformation data and constraints for the fault-slip inversion model but also deepens the understanding of factors controlling the rupture behavior of strike-slip faults.