Near instantaneously triggered Mw 5.9 aftershock during the 2025 Mw 7.1 Dingri earthquake revealed by radar interferometry

On 7th January 2025, a Mw 7.1 normal-faulting earthquake struck the southern segment of the Xainza-Dinggye rift (XDR) in southern Tibet. Multi-track InSAR observations from radar interferometry reveal a ∼30 cm circular deformation anomaly located west of the main rupture, which cannot be explained by any cataloged aftershocks. Although several nearby aftershocks are detected in strong-motion records, their magnitudes and locations do not match the observed deformation. The spatial extent and amplitude of the anomaly suggest a normal-faulting event of approximately Mw 5.9, whose seismic signals were likely buried within the mainshock waveform. This Mw 5.9 event is located approximately 20 km from the main fault F1 and 10 km from its conjugate fault F2. Static Coulomb stress modeling indicates significant stress unloading near the anomaly, and 3D dynamic rupture simulations demonstrate that dynamic stress perturbations during the fault slip of mainshock could have unclamped the fault within ∼15.0 s. These findings, together with its shallow afterslip and downdip aftershocks, indicate that the deformation anomaly being a near-instantaneously triggered rupture-branching rather than a slow-slip event. This study highlights the value of combining high-resolution InSAR observations with dynamic rupture simulations to characterize near-field dynamic triggering and to detect concurrent seismic events that remain obscured in conventional seismic catalogues.