Plate-scale crustal strain patterns (2009-2023) preceding the 2023 Turkey-Syria earthquake pair (Mw 7.8, 7.7) coupled with the Anatolian extrusion regime (Anatolian diagonal, Turkey): Inferences from geodetic and earthquake data

Investigating the composite relationships between geodetic and seismic deformations is one of the most important and long-lasting problems along the North and East Anatolian Fault Zones (NAFZ and EAFZ) across the Anatolian diagonal region (Turkey). Here, we report the first evidence for geodetic strain-displacement behavior and interplay between geodetic and seismic deformations along the EAFZ through the Anatolian diagonal. The latest seismic phenomenon, on the 6th February 2023 in the Maras Triple Junction (MTJ) area of the Anatolian diagonal, catastrophic earthquake doublets (Mw 7.8, 7.7), raises a series of outstanding questions. Firstly, whether these doublets are progressively preceded by geodetic precursory anomalies and/or preparatory phases linked with the 2010 and 2020 earthquakes along the EAFZ. Secondly, whether both events are geodetically expanded and dissipated through subsequent aftershocks into a large volume at regional scale and finally, how the 2023 seismic activation evolved from multiple faulting along the EAFZ and MTJ to a plate-scale seismic and geodetic phenomenon. To answer these questions requires a plate-scale understanding of this phenomenon. Moreover, it will be necessary to consider and analyse the fifteen years-long (2009–2023) earthquake transients and the GPS velocity field-derived strain-displacement propagation patterns using Continuously Operating Reference Stations-Turkey (CORS-TR, TUSAGA-Aktif), Global Navigation Satellite Systems (GNSS) observations over a large spatial extent in the Anatolian diagonal, to obtain a reliable explanation of a long-term strain-displacement accumulation prior to the 2023 events. The analysis is closely complemented by well-constrained fault focal solutions resolved from regional Centroid Moment Tensor (CMT) inversion for 41 located aftershock events (Mw 3.7–5.3) recorded by Kandilli Observatory and Earthquake Research Institute (KOERI) during the subsequent seven months after the 2023 mainshocks. The key results conclude that geodetic patchy structure and precursory field variation of asymmetric strain-displacement accumulation patterns, accompanied by the 2010 and 2020 seismic sequences, drive the preparatory process of the 2023 events as well as the 2010 and 2020 events, adjust the strain budget of the EAFZ and unravel the evolutionary process of the Anatolian extrusion to the W. The conclusion is complemented by off-fault aftershock CMT solutions that characterize interactively repeated and widely distributed strike-/oblique-slip faulting patterns (~ 15 km centroid depth) in a large volume at the regional scale, which led to ongoing plate-scale reorganization to accommodate the westward Anatolian extrusion. Geodetic pattern structure and CMT solutions reveal a large-scale, strain-expanding and -accommodating area through a wide diffuse deformation zone embedded within the Anatolian diagonal. The 2023 seismic sequence shifted plate motions, disrupted previously existing strain patterns, redistributed crustal stress-strain, and portrayed plate-scale, diffuse aftershock deformation across the Anatolian diagonal.