Co-evolution of seismic b-values and pre-earthquake ionospheric magnetic anomalies across the Iranian Plateau

Large earthquakes are preceded by complex interactions across the lithosphere, atmosphere and ionosphere, yet reproducible multi-parameter indicators of stress accumulation remain elusive. We analyze Swarm magnetic field observations together with regional seismicity for six Mw ≥ 6 earthquakes across the Iranian Plateau (2014–2025) to test whether independent observables co-evolve in the months preceding rupture. We find that decreases in the Gutenberg–Richter b-value and rising entropy —both interpreted as proxies for increasing differential stress—are systematically accompanied by enhanced pre-earthquake ionospheric magnetic anomalies as observed by satellites. These coupled patterns persist across multiple events within the studied tectonic framework, and remain robust even for incompletely recorded border-zone earthquakes when using the b⁺ estimator. The results suggest a physically consistent pre-earthquake behavior that links crustal stress evolution to ionospheric electromagnetic variability, supporting the lithosphere–atmosphere–ionosphere coupling (LAIC). This multi-sensor framework offers new insight into the physics of earthquake preparation and provides a basis for developing physically grounded precursory indicators.