Distinct triggering mechanisms of the 2023 Türkiye earthquake doublet

Despite advancements in understanding the rupture processes and surface deformations of the 2023 Türkiye earthquake doublet, their seismogenic mechanisms remain elusive. Here, we employed a joint tomographic method utilizing 215,906 P- and S-wave arrival time pairs to determine the fine-scale seismic and porosity structures in the rupture zones. We find that the first Mw 7.8 earthquake occurred in a brittle or near-brittle structure zone with low porosity and fluid saturation, offering a potential condition for brittle failure with supershear rupture. By contrast, the second Mw 7.6 quake initiated in a ductile belt characterized by high porosity and fluid saturation, explaining the observed sub-shear rupture behaviors. The former induces large decreasing normal stress, thus opening the Çardak fault, accelerating the migration of saturated fluids towards the fault zone through intra-crustal faults and extended cracks, increasing pore pressure, and delaying triggering a second earthquake. Our findings reveal the diverse seismogenic mechanisms of the Türkiye earthquake doublet, suggesting that fluid intrusion may have played a crucial role in triggering the second Mw 7.6 quake. Seismic tomography investigations suggest the initial rupture occurred in brittle and weak rock units, highly susceptible to seismicity, while the second rupture was triggered by the first and occurred in a ductile belt with high porosity and fluid saturation