Observations Of Electromagnetic Emissions Research Articles

Rockburst hazard assessment based on electromagnetic emission in Xingfu Mine

In order to research the danger caused by the rockburst, the electromagnetic emission (EME) in the coal rock was monitored and analyzed. The higher the stress in the coal is, the stronger the deformation and the failure are, and also the signal of the EME will be. The EME is increased by a relatively large margin before the slight shock and rockburst break out at spot. Therefore, some methods to monitor and forecast the danger of rockburst were proposed, including the critical point and deviation values, which was by non-contract method. In the end, the observation of EME in Xingfu was used to analyze and forecast the danger level by the rockburst. Then, the measures were proposed to prevent and cure the rockburst.

Ground observation of electromagnetic emissions related to clusters of earthquakes

Ultra-low frequency (ULF) and very low frequency (VLF) data obtained from three ground-based experiments at Agra station (latitude 27.2° N, longitude 78.0° E) in India, namely measurement of ULF magnetic field emissions using a three-component search coil magnetometer, the vertical component of VLF electric field emissions with a borehole antenna, and the phase and amplitude of fixed frequency VLF transmitter signals using an Absolute Phase and Amplitude Logger (AbsPAL) receiver, were analysed in search of possible precursors of two major seismic activities that occurred in Sumatra (Indonesia) during the post-tsunami period between January and April 2005. These two major seismic events occurred as clusters of earthquakes during 27–29 January and 28–30 March 2005. The results show that, apart from the borehole antenna, all the experiments showed precursors due to these clusters of earthquakes. Such precursors were not seen in the case of isolated large-magnitude earthquakes. Furthermore, the precursory duration was influenced by a magnetic storm that occurred about a week before the clusters. The mechanism of ULF propagation to long distances between Sumatra and Agra and perturbations in the ionosphere before the clusters are discussed.

Observation results of low frequency electromagnetic emissions as precursors of volcanic eruption at Mt. Mihara in november, 1986.

At the time of the major volcanic eruptions on November 15 and 21, 1986 at Mt. Mihara, Izu-Ohshima Island, Tokyo territory, Japan, a detector from a multipoint direction-finding network to detect electromagnetic emissions was operating. Since October 20, 1986 impulsive noises at 82kHz were recorded, and these anomalous burst-like noise observations increased after November 3. At 10-16 JST (Japanese Standard Time, UT+9 hours) on November 14, several strong noise bursts were observed, and the first major eruption occurred at the main summit crater of this volcano at 16 JST on November 15. At 10-12 JST on November 21, noise bursts were observed and four hours later, 19 new craters erupted suddenly on the side slope of the mountain, both in and outside the caldera, simultaneously with the intrusion of dykes in the mountain body. These records are the first observations of electromagnetic emissions as precursors to volcanic eruptions ever recorded. The authors present this paper in the form of a short note for data presentation, because analysis of these data and comparison with other observations is still continuing.

Observation of low-frequency electromagnetic emissions as precursors to the volcanic eruption at Mt. Mihara during November, 1986

Abstract At the time of the major volcanic eruptions on November 15 and 21, 1986, at Mt. Mihara, Izu-Ohshima Island, in the Tokyo territory of Japan, one detector of a multi-point (multi-static) direction finding network for detection of electromagnetic emissions was operating. Since October 20, impulsive noise bursts at 82 kHz were recorded, and the occurrence of these anomalous burst-like noise observations increased after November 3. At 10–16 JST (Japanese Standard Time, UT + 9 hr) on November 14, several strong noise bursts were observed, and the first major eruption occurred at the main summit crater of this volcano at 16 JST on November 15. At 10–12 JST on November 21, noise bursts were observed, and 4 hr later, 19 new craters erupted suddenly on the side of the mountain, both inside and outside the caldera. These data are the first observations of electromagnetic emissions as precursors to volcanic eruptions correlated in time with the intrusion of dykes in the mountain body.

Tromsø Heating Experiments: Stimulated emission at HF pump harmonic and subharmonic frequencies

Observations of electromagnetic emissions on the HF heater subharmonic and several harmonic frequencies are presented. Often the second harmonic emissions show characteristic amplitude variation, frequency shift, and spectral broadening that clearly have their origin in ionospheric plasma processes. The strongest candidate is a combined parametric decay and Raman up‐conversion process. The subharmonic emission is believed to be evidence of absolute stimulated Raman scattering and/or two plasmon decay processes which have not been observed before in ionospheric heating experiments.