Multi-Faceted Investigations of Crustal Deformation and Ionospheric Perturbations Associated With the 6 February 2023 Kahramanmaraş Earthquake Doublet in South-Eastern Türkiye

The 6 February 2023 Kahramanmaraş Earthquake Doublet (Mw 7.8 and Mw 7.7) involved complex rupture patterns across multiple strands of the East Anatolian Fault (EAF) and Sürgü-Çardak Fault (SCF) in SE Türkiye. The Mw 7.8 earthquake, triggered on a secondary fault, caused the rupture to propagate along the EAF for a distance of ∼300 km mainly towards north-east direction. The subsequent Mw 7.7 earthquake ruptured an ∼150 km segment of the SCF with a prominent bilateral propagation from the hypocenter. Joint inversion of co-seismic deformation fields derived from GPS and SAR observations reveals consistent left-lateral strike-slip motions for both the Mw 7.8 and Mw 7.7 events with peak slip amplitudes of ∼9.5 m and ∼11 m, respectively. GPS-TEC estimates show co-seismic ionospheric perturbations (CIP) with substantially larger amplitudes (∼1 TECU vs. 0.17 TECU) during the Mw 7.7 event, despite its lower magnitude. The compact high-slip rupture and greater surface displacements (up to 4.41 m horizontal, 0.47 m subsidence) of the Mw 7.7 event represent the decisive source-side factors elevating CIP amplitudes, with secondary amplification from favorable geomagnetic coupling southward of the epicenter and higher background ionospheric ionization.