Space Geodetic Insights to the Dramatic Stress Rotation Induced by the February 2023 Turkey‐Syria Earthquake Doublet

The February 2023 Turkey‐Syria Earthquake doublet ruptured multiple segments of the East Anatolian Fault (EAF) Zone. Dominating seismicity focal mechanism shifted dramatically from strike‐slip to normal‐faulting after the doublet. To better understand this shift, here we derived a comprehensive 3D co‐seismic displacement field and performed the stress analysis. Abundant space geodetic data were used to generate high‐resolution 3D surface displacement, which provide tight constraints on fault geometry, slip distribution and stress field. Together with stress inversion from aftershock focal mechanisms, we show that the principal stress direction rotation in the region with the most normal‐faulting aftershocks is the staggering 29°. The induced heterogenous stress may explain the shift of the dominant focal mechanism toward normal faulting. We suggest that the extensional horsetail splay faults, likely formed through geologic time scale related to the releasing bend on the EAF, are the hosts of most of the normal faulting aftershocks. Plain Language Summary Sudden dislocation of two sides of a fault, or the rupture of rocks, produces an earthquake. The dislocation direction relative to the fault traces reflects the direction of stress that are responsible for the earthquake. When dislocation direction is parallel to the fault strike, the earthquake is termed as strike‐slip type, and termed as normal‐faulting type when they are perpendicular. A remarkable feature for the 2023 Turkey‐Syria Mw7.8 & 7.7 earthquake doublet is that, background seismicity shifted dramatically from strike‐slip to normal type of faulting after the doublet. To unravel the physical process resulted in this feature, we use space geodetic measurements to derive the surface displacements and stress field associated with the doublet. The derived stress field shows a staggering 29° rotation occurred in a horsetail splay fault structure where many normal‐faulting earthquakes happened. The large stress rotation indicates the doublet released considerable stress and may result in a heterogeneous stress field due to the stress change. The combination of the identified horsetail structure and stress rotation can help better explain the occurrence of pervasive normal‐faulting earthquakes. Key Points We map the 3D displacements, slip distribution, and stress fields related to the 2023 Turkey‐Syria Earthquake doublet Dramatic stress rotation occurred after the Earthquake doublet, up to 29° Stress ro