Many observations and researches show that abundant and intense ultra low frequency (ULF) electromagneticanomalies appears before local earthquakes. In order to understand this phenomenon systematically, the trans-mis...Many observations and researches show that abundant and intense ultra low frequency (ULF) electromagneticanomalies appears before local earthquakes. In order to understand this phenomenon systematically, the trans-mission property and the formation of the seismic-electric dipole are discussed in this paper. The results showthat the vertical component Of the ULF electric anomaly before earthquake has the properties of better penetration, less disturbance and high signal-to-noise ratio. The signal can be easily extracted and received. The anomaly should be an important way to seek for reliable short-term and imminent earthquake precursors. After thespectrum analysis of the (ULF) electric field anomalies, we found that the periods of the anomaly related to localearthquakes are from a few minutes to a dozens minutes. There is a relation between the spectrum of the anomaly and the epicentral distance. The ULF electric field anomalies strongly rely on the orientation of the seismo-genie zone. The percolation electric field anomaly and its spectrum amplitude do not have obvious relation withthe size of local earthquakes.展开更多
The seismic activities on the Earth can produce a disturbance of the electromagnetic field and particles in the ionosphere. The search coil magnetometer(SCM) mounted on China Seismo-Electromagnetic satellite(CSES) is ...The seismic activities on the Earth can produce a disturbance of the electromagnetic field and particles in the ionosphere. The search coil magnetometer(SCM) mounted on China Seismo-Electromagnetic satellite(CSES) is designed to measure the magnetic field fluctuation of low frequency electromagnetic waves in the frequency range of 10 Hz–20 k Hz. The SCM comprises a three-axis search coil sensor mounted on a 4.5 m boom and an electronic box inside satellite module. The sampling rate of the SCM is 51.2 k Hz and the time resolution of the power spectrum density(PSD) is 2 s. The frequency resolution is 12.5 Hz.There are three operation modes: survey, detailed survey and calibration. In the survey mode, the SCM can provide a PSD in the whole frequency range of 10 Hz–20 k Hz and wave forms in the low frequency range below 2 k Hz while in the detailed survey mode the SCM can provide both PSD and wave forms in the whole frequency range of 10 Hz–20 k Hz. The sensitivity of the SCM instrument is 5.0×10^(-4) n T Hz^(-1/2) at 10 Hz, 5.0×10^(–5) n T Hz^(-1/2) at 200 Hz, 3.4×10^(-5) n T Hz^(-1/2) at 2 k Hz and 1.1×10^(-4) n T Hz^(-1/2) at 20 k Hz. The telemetry rate is ~0.85 Mbps in the survey mode and ~3.0 Mbps in the detailed survey mode. The phase difference between three axes can be made generally with a precision of less than 1.0°. The dynamic range of the SCM instrument is over 100 d B. The orthogonality of three mechanical axes of search coil senor is better than 0.13°. The performance of SCM can satisfy the requirement of scientific objectives of CSES mission.展开更多
文摘Many observations and researches show that abundant and intense ultra low frequency (ULF) electromagneticanomalies appears before local earthquakes. In order to understand this phenomenon systematically, the trans-mission property and the formation of the seismic-electric dipole are discussed in this paper. The results showthat the vertical component Of the ULF electric anomaly before earthquake has the properties of better penetration, less disturbance and high signal-to-noise ratio. The signal can be easily extracted and received. The anomaly should be an important way to seek for reliable short-term and imminent earthquake precursors. After thespectrum analysis of the (ULF) electric field anomalies, we found that the periods of the anomaly related to localearthquakes are from a few minutes to a dozens minutes. There is a relation between the spectrum of the anomaly and the epicentral distance. The ULF electric field anomalies strongly rely on the orientation of the seismo-genie zone. The percolation electric field anomaly and its spectrum amplitude do not have obvious relation withthe size of local earthquakes.
基金supported by the National Natural Science Foundation of China(Grant No.41431071)
文摘The seismic activities on the Earth can produce a disturbance of the electromagnetic field and particles in the ionosphere. The search coil magnetometer(SCM) mounted on China Seismo-Electromagnetic satellite(CSES) is designed to measure the magnetic field fluctuation of low frequency electromagnetic waves in the frequency range of 10 Hz–20 k Hz. The SCM comprises a three-axis search coil sensor mounted on a 4.5 m boom and an electronic box inside satellite module. The sampling rate of the SCM is 51.2 k Hz and the time resolution of the power spectrum density(PSD) is 2 s. The frequency resolution is 12.5 Hz.There are three operation modes: survey, detailed survey and calibration. In the survey mode, the SCM can provide a PSD in the whole frequency range of 10 Hz–20 k Hz and wave forms in the low frequency range below 2 k Hz while in the detailed survey mode the SCM can provide both PSD and wave forms in the whole frequency range of 10 Hz–20 k Hz. The sensitivity of the SCM instrument is 5.0×10^(-4) n T Hz^(-1/2) at 10 Hz, 5.0×10^(–5) n T Hz^(-1/2) at 200 Hz, 3.4×10^(-5) n T Hz^(-1/2) at 2 k Hz and 1.1×10^(-4) n T Hz^(-1/2) at 20 k Hz. The telemetry rate is ~0.85 Mbps in the survey mode and ~3.0 Mbps in the detailed survey mode. The phase difference between three axes can be made generally with a precision of less than 1.0°. The dynamic range of the SCM instrument is over 100 d B. The orthogonality of three mechanical axes of search coil senor is better than 0.13°. The performance of SCM can satisfy the requirement of scientific objectives of CSES mission.
