Electromagnetic anomaly before earthquakes measured by electromagnetic experiments

Abstract

Three experiments are carried out for earthquake monitoring using electromagnetic (EM) methods in recent years. Some earthquakes occurred in chance of the measurement time period for each experiment and the anomalies were recorded before the shocks. The observation at a site 20 km away from the epicenter of Zhangbei M S 6.2 earthquake in 1998 shows that the apparent resistivity decreases in the strike direction before and/or during the earthquake and the resistivity increases in the decline direction. This anomalous variation in apparent resistivity accounts for about 20%. The apparent resistivities at a site in the epicentral area decrease in the strike and decline directions before and/or during the earthquake and increase after shocks. The experiments using artificial electromagnetic signals with super low frequency carried out in 1999 show that the resolution and stability of electric and magnetic spectra are improved. The spectra of electric and magnetic fields and apparent resistivity at the Baodi station began to anomalously change two days before the Qian'an earthquake with 120 km distant to the station. The anomalous variation of electric and magnetic spectra is about twice as great as normal variation and the apparent resistivity changes by about 20%. The measurements in active seismic area of Yunnan province in the year 2005 indicate that the electric and magnetic spectra anomalously change by one order before the Taoyuan earthquake about 100 km away from the observatories. But the measurements at the sites in Beijing area 2 000 km away from the epicenter do not show any anomaly.

Assessing the Potential Earthquake Precursory Information in ULF Magnetic Data Recorded in Kanto, Japan during 2000–2010: Distance and Magnitude Dependences

“…The measurement of ultra-low-frequency (ULF: less than one Hertz) electromagnetic phenomena may be one of the most promising candidates, because of their deeper skin depths [ 1 , 2 , 8 , 17 ]. To date, a large number of ULF electromagnetic phenomena associated with earthquakes has been reported from different parts of the world, e.g., Greece [ 18 , 19 , 20 , 21 , 22 , 23 ], Italy [ 24 , 25 ], Russia [ 26 , 27 ]; America [ 28 , 29 , 30 ], Mexico [ 31 , 32 , 33 , 34 ], Taiwan [ 35 , 36 , 37 , 38 ], Indonesia [ 39 , 40 ], China [ 41 , 42 , 43 , 44 , 45 , 46 , 47 ] and Japan [ 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]. Furthermore, experiments and simulations have confirmed the existence of ULF seismo-electromagnetic phenomena [ 61 , 62 , 63 , 64 , ...…”

Statistical analysis of ULF seismomagnetic phenomena at Kakioka, Japan, during 2001–2010

“…Recently, ultralow frequency (ULF, less than 1 Hz) has been considered as a prospective band in search of earthquake precursory signatures because of its larger skin depth [ Fraser‐Smith et al ., ; Hattori , ; Hattori et al ., , ; Yen et al ., ; Liu et al ., ; Telesca et al ., ; Zhao et al ., ; Chen et al ., , ; Hirano and Hattori , ; Wen et al ., ; Han , ; Xu et al ., ]. Furthermore, abundant indoor and/or outdoor experiments and numerical simulations have confirmed the existence of ULF seismoelectromagnetic phenomena [ Molchanov and Hayakawa , ; Yoshida et al , ; Freund , , ; Huang , , ; Huang and Lin , ; Enomoto , ; Ren et al ., ].…”

Investigation of the characteristics of geoelectric filed earthquake precursors: a case study of the Pingliang observation station, China

“…Whether a GEF station can observe earthquake anomalies is dependent on the magnitude of the earthquake's energy and the epicentral distance (D) [Zhuang et al, 2005;Zhao et al, 2009]. In the process of selecting earthquake events, two factors, seismic energy and D, are considered, and the calculation method of determining seismic energy presented by Gutenberg and Richter [1956], Hattori et al [2006], and Han et al [2014] is adopted.…”