Far-field postseismic deformation of the 2023 Kahramanmaraş earthquake doublet

On 6 February 2023, a major earthquake doublet (Mw 7.8 and Mw 7.6) ruptured the Anatolian plate boundary system. The first event occurred on the East Anatolian Fault (EAF), the principal plate-boundary zone between the Arabian and Eurasian plates, and the second ruptured the Çardak fault north of the western termination of the EAF. Continuous GNSS observations acquired in the months following the sequence indicate that deformation is not confined to the near-fault region: GNSS time series reveal substantial changes relative to pre-event interseismic velocities over distances of several hundred kilometers. These deviations extend northward across the North Anatolian Fault toward the Black Sea coast and westward across the Central Anatolian Plateau. Furthermore, seismicity rates appear to have been perturbed at locations far from the rupture area, and early postseismic investigations have suggested a measurable far-field signal, particularly to the west of the main rupture zones. Given the magnitude of the sequence and the dense regional geodetic coverage, this earthquake doublet provides an exceptional opportunity to investigate earthquake-cycle processes and to constrain spatial variations in rheological properties of fault zones and the surrounding lithosphere within an actively deforming tectonic setting.

We characterize the postseismic deformation of the far-field domain spanning from eastern Anatolia to the western Hellenic trench using regional GNSS networks. For each station, we isolate the transient component by removing the secular (interseismic) contribution using interseismic velocity fields estimated from long-duration pre-earthquake time series. We then extract coherent postseismic signals from the GNSS residuals using Independent Component Analysis (ICA) implemented in a variational Bayesian framework. To interpret the recovered far-field transients, we perform forward viscoelastic modeling to evaluate contrasts in crustal and lithospheric structure and rheology, and we test sensitivity to alternative coseismic rupture models derived primarily from space-geodetic constraints employing different strategies. We further examine the role of major far-field tectonic structures, particularly the Hellenic trench to the southwest and the Cyprus arc to the southeast, on the observed deformation patterns. Finally, we assess the relationship between postseismic deformation and seismicity by comparing far-field seismic activity with postseismic strain-rate fields inferred from the GNSS displacements, using the VDoHS (Vertical Derivatives of Horizontal Stress rates) approach.