Long-term geomagnetic observations in the Vrancea Seismogenic Zone and their relationship with seismic energy release: The bright and dark sides of statistical correlation

The Vrancea seismic zone represents one of the most distinctive seismic regions in Europe, characterized by its capacity to generate high-magnitude intermediate-depth earthquakes with widespread impact. However, the relatively low frequency of these major events poses significant challenges for seismic prognosis and reliable hazard assessment.

Since 1996, the National Institute for Earth Physics has been continuously monitoring the geomagnetic field in the Vrancea area, identifying several significant anomalous fluctuations on the (east-west horizontal) component. Initially observed within narrow one-month windows, these precursors were later identified as components of broader seasonal anomalies extending over periods of six to eight months.

This work analyzes 19 years of geomagnetic data recorded at the Muntele Roșu (MLR) Seismic Observatory, correlated with local intermediate-depth seismicity. The methodology involved the primary identification of geomagnetic anomalies, followed by the calculation of cumulative seismic energy for all events with occurring during the anomalous periods. To quantify the magnitude of these magnetic anomalies, a statistical approach was employed, utilizing standard deviation analysis between the MLR station and a reference station. The standard deviation results were Pearson correlated with seismic energy releases to point the statistical reliability of geomagnetic anomalies as precursory indicators.

This study adopts a dual perspective by analyzing the same dataset at different temporal scales. We present a comparative statistical analysis between a restricted interval (5–6 years) and the full 19-year monitoring period. Although a 5-year data window is often considered sufficient in seismomagnetic studies, our results challenge this assumption, demonstrating how temporal scaling can significantly alter correlation outcomes.