Magnetic field anomalies associated with geodynamic phenomena

Abstract

Abstract. Significant variations of the Earth's magnetic field seem to be associated with geodynamie phenomena, particularly volcanic eruptions and earthquakes. The variations have small amplitudes, generally only a few nT. These small signals are embedded into larger transient variations due to other natural or artificial causes. An original method of recovering interesting signals having amplitudes down to 1 nT, is to describe the whole variation analytically so that each component may be isolated. Several studies have shown that significant signals exist for tectonically active regions: 10-30 nT for large-scale arrays over periods of years; 5-15 nT for volcanic phenomena; 1-5 nT for earthquakes.Only a few test sites for volcanoes (New Zealand, Hawaii, Antilles) and earthquakes (essentially the San Andreas fault system) have been monitored so far.The cause of the type of magnetic variations studied here, which are associated with volcanism and rock failures, has most often been attributed to piezomagnetism. Some authors have suggested that electrokinetic effects associated with porosity-changes may also play a role.The isolated signals may, in the future, be used for hazard forecasting when the time-constants associated with the effects are known more precisely.

Artificial magnetic disturbance from the mass rapid transit system in Taiwan

“…Observation of the geomagnetic field is considered to be a promising method for monitoring volcanoes (Okubo, Kanda, & Ishihara, ; Sasai et al., ; Takla, Yoshikawa, Kawano, Uozumi, & Abe, ; Uyeda et al., ; Yukutake et al., ) and has been used to study the generation of geomagnetic signals during volcanic activity (Johnston & Stacey, ; Stacey, Barr, & Robson, ; Tanaka, ; Uyeda et al., ). Volcano‐related geomagnetic signals generally range from 5 nT to 15 nT (Rossignol, ) and are mainly distributed within the Pc3 range (0.1 Hz–0.022 Hz) in the frequency domain. Thus, geomagnetic stations are carefully situated to be far away from highly developed urban areas to avoid disturbances from electric power, iron materials and artificial noise, and to make it possible to use them effectively to monitor relatively small signals.…”

“…Volcano-related geomagnetic signals generally range from 5 nT to 15 nT (Rossignol, 1982) and are mainly distributed within the Pc3 range (0.1 Hz-0.022 Hz) in the frequency domain. Thus, geomagnetic stations are carefully situated to be far away from highly developed urban areas to avoid disturbances from electric power, iron materials and artificial noise, and to make it possible to use them effectively to monitor relatively small signals.…”

Anomalous geomagnetic variations associated with the volcanic activity of the Mayon volcano, Philippines during 2009–2010

“…The origin of anomalous geomagnetic signal associated with the dynamic activities (earthquakes and volcanoes) has been theoretically investigated by several scientists (Rossignol, 1982;Del Negro and Ferrucci, 1994;Sasai et al, 2002, among many others). Generally, these anomalous geomagnetic signals are mainly related to the Piezomagnetic, Electrokinetic and Thermal effects.…”

“…Noteworthy observed geomagnetic field variations had been considered as anomalous signals associated with some volcanic eruptions. These variations have small amplitudes, generally a few nTs; 5-15 nT (Rossignol, 1982). In addition, these previous studies are aimed to understand the generation mechanisms of the observed anomalous geomagnetic signals (Stacey et al, 1965;Johnston and Stacey, 1969;Tanaka, 1993;Uyeda et al, 2002).…”

On the geographical distribution of induced time‐varying crustal magnetic fields

“…In the same way, the concept of secular variation (SV) anomalies has been introduced to describe possible unmodelled field variations that would occur over years. However, this concept is broad because SV anomalies may be caused by any long term geodynamic phenomena occurring in the Earth's core or crust [e.g., Rossignol , 1982], if not the upper mantle, the ionosphere, or the magnetosphere.…”