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An Z.-H.,Lanzhou Base of Institute of Earthquake Sciecne | An Z.-H.,State Geophysics Observatory in Lanzhou | An Z.-H.,Lanzhou Institute of Seismology | Du X.-B.,Lanzhou Base of Institute of Earthquake Sciecne | And 20 more authors.
Earthquake | Year: 2015

In this paper, Hilbert-Huang Transformation method is introduced to deal with geo-electric field data observed by the stations around the epicenter of 2013 Lushan Ms7.0 earthquake. These stations include the stations of Gansu Pingliang, Sichuan Chengdu and Yunnan Yuanmou. We compare the results of the three geo-electric field stations between the normal time with the eve of the Lushan Ms7.0 earthquake, the results of Chengdu geo-electric field station about the Lushan Ms7.0 and Wenchuan Ms8.0 earthquakes are also analyzed. We conclude that: (1) HHT method is effective for the data analysis observed by the geo-electric field station, the time-frequency spectrum may be simple and intuitive; (2) About 1~2 months before the Lushan Ms7.0 earthquake, the energy of geo-electric field enhanced, with period range of approximately 90~1400 hours, the minimum amplitude of energy variation is about 3 orders of magnitude, the largest ranges up to about 6 orders; (3) The credibility of results obtained are greatly enhanced through comparison obtained from the three geo-electric field stations, and analogy obtained from the Chengdu geo-electric field station. In the discussion section of results, we discussed the situation of seismic electromagnetic signals based on the experimental and numerical simulation method in the domestic and abroad in recent years, these results obtained by them can provide theoretical support to our results in this paper. ©, Science Press. All right reserved.

Cui T.-F.,State Geophysics Observatory in Lanzhou | Du X.-B.,State Geophysics Observatory in Lanzhou | Du X.-B.,China Earthquake Administration | Ye Q.,China Earthquake Networks Center | And 10 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2013

This paper has studied the time and frequency characteristics of the geo-electric field diurnal variation along the two longitude chains and the two latitude chains, using the data of the geo-electric field observed at the 37 stations along the chains. Accordingly, the following significant results are obtained: the variation appears mainly as semi-diurnal waves twice a day at most of the stations, approximately before and after the noon; according to the big to small order of the FFT amplitude spectrums, the main periods of the diurnal variation are 12.4 h/12 h, 8 h, 24 h, etc, which are in accordance with the periods of the tidal harmonic components; the latitude effect on diurnal variation is manifested by the amplitude changing with latitude along a longitude chain, and the longitude effect is shown as phase difference consistent with the local-time difference between the stations at the same latitude. Furthermore, the amplitude of the diurnal variation is related with the Loyd season, which reduces orderly in J-, E- and D-seasons. The possible reasons for the main periodic components of the diurnal variation have been discussed, as a result, it is believed that the variation of the ground eddy current intensity caused by lunisolar tidal forces and the space electromagnetic activity aroused by the solar wind jointly produce the semi-diurnal period components of the geo-electric diurnal variation.

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