Magnetic measurement discrepancies in the Ionosphere prior to the 2025 Kamchatka Mw 8.8 earthquake

Abstract Magnetic field data from Swarm’s magnetometers were investigated during the 2025 M w 8.8 Kamchatka earthquake. The examination focuses on the spatiotemporal distribution of magnetic data with Flag 8, which indicates discrepancies between the scalar and vector magnetometers. Flag 8 was observed along Swarm satellite orbits near the epicenter prior to the earthquake, initially appearing approximately 16 days before the mainshock and persisting until 9 days after. The results indicate that the spatial distribution of Flag 8 exhibits high density and extensive coverage around the epicentral region, showing a close relationship with the earthquake. Further examination suggests that neither polar geomagnetic activity nor the South Atlantic Anomaly can adequately explain the observed pattern. This implies that the observed Flag 8 is more likely associated with the seismic activity in the Kamchatka Peninsula. This study highlights Flag 8 as a complementary tool for detecting pre-earthquake magnetic anomalous phenomenon and advancing earthquake precursor research.