Electromagnetic anomalies preceding earthquake occurrence

Published reports describe electric, magnetic, geomagnetic, radio-propagation, and ionospheric anomalies during periods preceding some earthquakes. Proposed explanations include stress-related electrical processes in rock and coupling between the lithosphere, atmosphere, and ionosphere. However, reported signals vary across events, instruments, locations, frequencies, and analytical methods, and similar anomalies may arise from solar and geomagnetic activity, lightning, weather, human technology, data processing, or instrument effects. The available evidence therefore supports investigation of a reported temporal association but does not establish a diagnostically specific precursor, reliable forecasting method, or causal relationship.