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<p>The Marmara region, situated along the seismically active North Anatolian Fault Zone (NAFZ) and including the densely populated Istanbul metropolitan area, is considered one of the most critical regions in Türkiye for a future large earthquake. This study investigates coseismic magnetic field perturbations recorded during the Mw 6.2 (KOERI) earthquake of 23 April 2025 in the Sea of Marmara, using geomagnetic data from the Iznik (IZN) observatory together with seismic records from nearby strong-motion stations. The primary aim is to evaluate whether the observed magnetic perturbations reflect physical crustal electromagnetic processes or are more plausibly associated with strong-motion-induced instrumental effects under single-station observational conditions. Transient magnetic disturbances were observed during the mainshock and two subsequent Mw 5.2 aftershocks. These signals appear simultaneously in all three geomagnetic components (H, D, and Z), emerge within the P and S wave arrivals, and exhibit impulsive, short-duration waveforms closely matching the corresponding seismic waveform records. The consistent timing, waveform similarity, and repeatability across multiple events indicate strong coupling between ground motion and the recorded magnetic variations. Rather than indicating a primary crustal electromagnetic source, the observed characteristics are more consistent with strong-motion–induced mechanical instrumental effects, likely caused by mechanical coupling between seismic vibrations and the geomagnetic sensor system or its installation environment. These findings highlight the sensitivity of high-resolution geomagnetic measurements to intense ground motion and demonstrate how synchronous seismic observations can help identify likely motion-induced magnetic artifacts, even under limited observational conditions such as single-station geomagnetic measurements and low sampling rate data. The combined analysis of geomagnetic and seismic data provides a framework for identifying such disturbances and underscores the importance of rigorous instrumental assessment in tectonically active regions such as the NAFZ.</p>

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Coseismic magnetic field perturbations recorded during the 23 April 2025 Mw 6.2 Sea of Marmara earthquake, Türkiye

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Elif Çiftçi,
  • Özlem Hacıoğlu

摘要

The Marmara region, situated along the seismically active North Anatolian Fault Zone (NAFZ) and including the densely populated Istanbul metropolitan area, is considered one of the most critical regions in Türkiye for a future large earthquake. This study investigates coseismic magnetic field perturbations recorded during the Mw 6.2 (KOERI) earthquake of 23 April 2025 in the Sea of Marmara, using geomagnetic data from the Iznik (IZN) observatory together with seismic records from nearby strong-motion stations. The primary aim is to evaluate whether the observed magnetic perturbations reflect physical crustal electromagnetic processes or are more plausibly associated with strong-motion-induced instrumental effects under single-station observational conditions. Transient magnetic disturbances were observed during the mainshock and two subsequent Mw 5.2 aftershocks. These signals appear simultaneously in all three geomagnetic components (H, D, and Z), emerge within the P and S wave arrivals, and exhibit impulsive, short-duration waveforms closely matching the corresponding seismic waveform records. The consistent timing, waveform similarity, and repeatability across multiple events indicate strong coupling between ground motion and the recorded magnetic variations. Rather than indicating a primary crustal electromagnetic source, the observed characteristics are more consistent with strong-motion–induced mechanical instrumental effects, likely caused by mechanical coupling between seismic vibrations and the geomagnetic sensor system or its installation environment. These findings highlight the sensitivity of high-resolution geomagnetic measurements to intense ground motion and demonstrate how synchronous seismic observations can help identify likely motion-induced magnetic artifacts, even under limited observational conditions such as single-station geomagnetic measurements and low sampling rate data. The combined analysis of geomagnetic and seismic data provides a framework for identifying such disturbances and underscores the importance of rigorous instrumental assessment in tectonically active regions such as the NAFZ.