%0 Journal Article %T Review of unprecedented ULF electromagnetic anomalous emissionspossibly related to theWenchuan MS = 8.0 earthquake,on 12 May 2008 %+ Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E) %+ China University of Geosciences [Beijing] %+ China Earthquake Networks Center %+ Gaobeidian Observation Station %A Li, M. %A Lu, J. %A Parrot, Michel %A Tan, H. %A Chang, Y. %A Zhang, X. %A Wang, Y. %Z NSFC(National Natural Science Foundation of China) under grantagreement no. 41204057 and 12th Five-Year Plan of NationalScience and Technology Support (2012BAK19B02-03). This workwas also supported by China Earthquake Administration %< avec comité de lecture %@ 1561-8633 %J Natural Hazards and Earth System Sciences %I Copernicus Publ. / European Geosciences Union %V 13 %P 279-286 %8 2013 %D 2013 %R 10.5194/nhess-13-279-2013 %Z Sciences of the Universe [physics]Journal articles %X This work presents ground based ultra low frequency(ULF) electromagnetic field measurements in thefrequency range 0.1–10 Hz from January 2007 to December2008. In this time period a strong earthquake serieshits the Wenchuan region with a main shock of magnitudeMS =8.0 on 12 May 2008. The Hebei ULF electromagneticobservation network includes eight observation stations innorth China and the observation system named E-EM is employedto record the electric potential difference between twoelectrodes with an analog automatic real-time continuous penrecorder. First, weak electric signals appeared on 11 October2007 at Ningjin station, most of which are with relativelong periods 0.4–3 s and unequal amplitudes 0.5–20 mm.Then, similar signals appeared at Gaobeidian station at theend of October. Abnormal behavior with various time intervalsappeared randomly and not every day. At the beginningof April 2008, one and a half months before the WenchuanMS =8.0 earthquake, the anomalies were gradually subjectto an intensive increase mainly in Gaobeidian SN directionand Ningjin EW direction. The abnormal behavior appearedalmost every day and the amplitudes of electric signals, withshort periods of 0.1–0.3 s, enhanced to 3–30 mm. Qingxianstation started to record marginally high frequency signalsin SN and EW components in the middle of April. On9 May, 3 days before the main shock, the amplitude of highfrequency information increased sharply at the same timein two components at Gaobeidian station and the maximumamplitude was up to 70 mm, i.e. 1.3mVm−1 for the electricfield. This situation did not stop until 17 May, 5 days after themain event. However, this kind of climax phenomena did nothappen at Ningjin station and Qingxian station. Then weakanomalous information lasted about four months again, andstrong signals appeared again for a short time before severalpowerful aftershocks. It is the first time that an abnormitywith so large an amplitude and so long a duration time inthe observation history of this network though several strongearthquakes were recorded. Furthermore, no obvious interferenceshave been found during this period. So this event ispossibly related to this shock although all these three stationsare more than 1300 km away from the Wenchuan earthquakeepicenter. %G English %2 https://insu.hal.science/insu-01178902/document %2 https://insu.hal.science/insu-01178902/file/nhess-13-279-2013.pdf %L insu-01178902 %U https://insu.hal.science/insu-01178902 %~ OBSPM %~ CEA %~ INSU %~ CNRS %~ UNIV-ORLEANS %~ CNES %~ OSUC %~ LPC2E %~ PSL %~ OBSPM-PSL