Characteristics and simulations of ground motions in Turkey Mw7.8 and Mw7.6 great earthquakes on 6 February 2023

Two great earthquakes with M(w)7.8 and M(w)7.6 successively hit southeast Turkey on 6 February 2023. The dense strong-motion observation networks captured large numbers of strong-motion recordings from both events. The recordings after manually processing were used to analyze the attenuation characteristics of ground motions by comparisons with the ground-motion prediction equations applicable for Turkey. We then investigated the spatial distribution of near-fault ground motions, the generation of pulse-like velocity waveforms, and the correlation between total residuals and station azimuths to provide some explanations on the source rupture characteristic of the M(w)7.8 event. Finally, the stochastic finite-fault method was used to simulate the three-component ground motions for mapping the instrumental seismic intensity. The meaningful conclusions were drawn as following. (1) The source effects of both Turkey events on ground motions are significantly stronger than the mean effect for shallow crustal earthquakes over Turkey. The stronger source effects on ground motions at moderate-to-long periods are observed in M(w)7.8 event than those in the M(w)7.6 event. (2) Compared with the average level in Turkey, the far-field ground motions in both events showed the stronger anelastic attenuation. (3) The strongest ground motions in the M(w)7.8 event are concentrated in a narrow region from Kahramanmaras in the north to Antakya in the south where most strong-motion recordings were characterized by the bilateral velocity pulse. The total residuals show a significant dependency on the station azimuth. Comprehensively considering these phenomena, we inferred that the M(w)7.8 event ruptured to the northeast along the northeast-trending East Anatolia fault, meanwhile ruptured to the south-southwest along the south-southwest-trending Kahramanmaras-Antakya section of East Anatolia fault. (4) The simulated ground motions roughly describe the intensity of near-fault ground motions and the attenuation trend with distance. The instrumental seismic intensities around the ruptured fault plane reach IX and VIII in the M(w)7.8 and M(w)7.6 events, respectively. The spatial distributions of intensity were mainly affected by the fault rupture and local site effects.