Unraveling the Preparatory Processes of the 2023 Kahramanmaraş MW7.8-7.6 Earthquake Doublet

Within a span of 9 hours on February 6, 2023, two significant earthquakes, with magnitudes of M_w7.8 and M_w7.6, struck the southeastern part of Türkiye and the northern region of Syria, resulting in significant casualties and widespread economic losses. The occurrence of such intense earthquakes in rapid succession on adjacent faults, especially within a highly complex intraplate region with a multi-fault network, poses a rare phenomenon, presenting new challenges for seismic hazard analysis in such areas. In order to investigate whether the preparatory processes for the M_w7.8-7.6 earthquake doublet could be identified on a large spatial scale prior to the seismic events, we employed a data-driven approach for b-value calculation. The difference in b values from the background values (Δb) in a reference period were used as inputs, and the Cumulative Migration Pattern (CMP) method, quantitatively describing the migration of seismic activity, was utilized to calculate the corresponding probability distributions. The results indicate a widespread phenomenon of decreasing b-values in the study area over a decade before the occurrence of the earthquake doublet, revealing a significant enhancement of differential crustal stress over a large region. Additionally, despite not being the region with the most pronounced decrease in b-values, there is a distinct high probability distribution of CMP near the nucleation points of the earthquake doublet, indicating a spatial and temporal "focus" of increased crustal differential stress in the study area, unveiling the preparatory process of the earthquake doublet. This study reveals quantifiable migration patterns over a long-time scale and a large spatial extent, providing new insights into the evolution and occurrence processes of the 2023 Kahramanmaraş M_w7.8-7.6 earthquake doublet. Moreover, it offers potential clues for seismic hazard analysis in such intraplate regions with multiple fault systems.