Supplementary Information for Fault segmentation controls seismotectonic variability before major earthquakes on the East Anatolian Fault

Understanding seismotectonic activity preceding major earthquakes is key to clarifying fault mechanics and improving hazard assessment. We investigate interseismic geodetic data and premainshock seismicity of the 2023 Kahramanmaraş Mw ≥7.6 earthquake doublet on the East Anatolian Fault (EAF), comparing them with two earlier Mw ≥6.1 events along the same fault. The results reveal contrasting behaviors between fault segments. In the northeast, where the EAF is relatively linear, slip rates reach ~7 mm a^-1 and significant creep occurs. Here, seismic slip is channeled along the fault, and mainshocks are typically preceded by concentrated seismic moment near the epicenter months in advance. In contrast, the southwestern EAF is structurally complex, with multiple strands, slower slip rates (~0.4 mm a^-1), partitioned slip, and unchanneled or off-fault seismicity. Premainshock activity is diffusely distributed, showing weak or absent correlation with mainshock epicenters. These findings advance understanding of spatiotemporal earthquake initiation along the EAF and comparable tectonic settings.