Anomalous total electron content (TEC) and atmospheric refractivity prior to the very strong China earthquake of May 2008

Adaptive techniques for extraction of pre-seismic parameters of Total Electron Content (TEC) at anomaly crest station

“…In this context, we refer here to the work of Liu et al (2010), who reported a significant decrease in TEC, five days prior to the very strong equatorial earthquake of M ¼ 9. Xia et al (2011), on the other hand, observed an enhancement in daytime TEC 2-3 days before the severe China earthquakes of 12 May 2008, a finding similar to that reported by Devi et al (2010a). Thus, the above reports highlight the facts that earthquake induced modification in TEC around the low latitude zone is complex.…”

“…However, the limitation of DTW is such that it cannot resolve finer temporal and spatial information because of the enormous increase in size of the necessary matrix. The next attempt will be to make the algorithm capable of preparing large matrices and to adopt the same for identification of finer details of an earthquake event, through use of multiple features of TEC as discussed by Devi et al (2010a).…”

“…So, identification of earthquake signatures from TEC will be a complex process. It is seen that in many cases TEC peak itself may work as a reasonably good cursor (Devi et al 2001(Devi et al , 2004(Devi et al , 2010a, although there are events when its use leads to certain ambiguity. It is therefore preferable to have more than one approach to such an exercise, as will be discussed in subsequent sections.…”

Modification in Atmospheric Refractivity and GPS Based TEC as Earthquake Precursors

“…They found that the transmission anomalies were significantly enhanced within five days prior to M ≥ 4.8 earthquakes. Increase in propagation horizon of VHF has been reported and the role of seismic effect on the refractive index has been examined to explain the observed TEC features for some earthquakes recently [8] [13].…”

Precursory signals using satellite and ground data associated with the Wenchuan Earthquake of 12 May 2008

“…Zhao et al (2008) found persistent enhancement of total electron content in the surrounding region three days prior to the main event; this abnormal enhancement could be a seismoionospheric signature of the Wenchuan Earthquake. Some of the papers included in this special issue show strong changes in ionospheric parameters , Devi et al 2010, Kakinami et al 2010, Zhang et al 2010a, 2010b, Zhao et al 2010) and electromagnetic signals in extremely low frequency (ELF) range detected by the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite (Błeçki et al 2010). These anomalies are also found to be dependent on the coupling between land, ocean, atmosphere and ionosphere, apart from the enhancement of the stress prior to earthquakes in seismically active regions.…”