Iranian Journal of Geophysics

Iranian Journal of Geophysics

Investigation of the pre-indicator of VLF signals received at the receiver of the Institute of Geophysics, University of Tehran

Articles in Press

Document Type : Research Article

Authors
Saba Nazari 1
Mehdi Rezapour 2
Somayeh Sabri 3
1 M.Sc., Institute of Geophysics, University of Tehran, Tehran, Iran
2 Professor, Institute of Geophysics, University of Tehran, Tehran, Iran
3 Assistant Professor, Institute of Geophysics, University of Tehran, Tehran, Ira
10.30499/ijg.2025.522865.1696
Abstract
Short-term earthquake prediction is vital for mitigating the destructive impacts of seismic events by providing timely information on the expected time, magnitude, and location, thus enabling preparedness days or months in advance. This is especially critical in seismically active regions such as Iran, where monitoring earthquake precursors is a major research focus. Among various precursors, anomalies in Very Low Frequency/Low Frequency (VLF/LF) radio signals propagating through the lower ionosphere have been repeatedly observed prior to significant earthquakes. In this study, we analyzed VLF signals recorded by the Geophysics Institute of the University of Tehran in relation to the M=5.9 earthquake that occurred in Khoy on January 28, 2023. A few days before the event, distinct anomalies were detected along the TBB-TEH signal path passing above the earthquake epicenter. To verify these anomalies as precursors, we compared the 26.7 kHz VLF signal data from this path on the earthquake day and the anomaly occurrence day (January 4, 2023) with baseline data from January 2021, which exhibited stable signal propagation. The analysis revealed clear amplitude variations, with elevated nighttime and reduced daytime amplitudes preceding the earthquake, while investigations excluded other seismic or environmental factors as causes. These findings affirm that the observed VLF signal anomalies are linked to the Khoy earthquake, highlighting the potential of VLF monitoring as an effective tool for short-term earthquake prediction in tectonically active regions.
 
Keywords
Earthquake
Khoy
precursor
VLF signals

Subjects

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Iranian Journal of Geophysics

Articles in Press, Accepted Manuscript
Available Online from 16 December 2025