Changes in the ultra-low frequency wave field during the precursor phase to the Sichuan earthquake: DEMETER observations

Walker, S. N.; Kadirkamanathan, Visakan; Pokhotelov, O. A.

doi:10.5194/angeo-31-1597-2013

Cited by 37 publications

(27 citation statements)

References 19 publications

(14 reference statements)

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“…Many researchers have also performed investigations on seismo-ionospheric effects since the occurrence of the Wenchuan M S 8.0 EQ. These studies include at least ionospheric changes of ground-based ionosonde data [57][58][59][60][61][62][63][64], DEMETER satellite data [17,[65][66][67][68][69][70][71][72][73][74][75][76][77][78], ground-based GPS satellite data [17,28,57,58,74,77,[79][80][81][82][83][84], radio occultation data from six microsatellites of FORMOSAT3/COSMIC (F3/C) data [81,84,85], and CHAMP (challenging minisatellite payload) satellite data [77].…”

Section: Spatial Ionospheric Anomaliesmentioning

confidence: 99%

Indications of Ground-based Electromagnetic Observations to A Possible Lithosphere–Atmosphere–Ionosphere Electromagnetic Coupling before the 12 May 2008 Wenchuan MS 8.0 Earthquake

Lü

Zhang

et al. 2019

Atmosphere

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A large number of various precursors have been reported since the Wenchuan M S 8.0 earthquake (EQ) took place on 12 May 2008 in China. In this work, previous investigations of both ground-based electromagnetic (EM) parameters and spatial ionospheric parameters were first examined. The statistical results showed that various anomalies presented different time-scale variations but tended to be characterized by a common feature -reaching their climax on 9 May, three days before the Wenchuan event, which indicates a lithosphere-atmosphere-ionosphere (LAI) electromagnetic coupling. Second, the fluctuations on 9 May based on the observational ground-based ultra low frequency (ULF) electrical field at the Gaobeidian (GBD) station and the direct current/ultra low frequency (DC-ULF) geomagnetic vertical Z field at the Chengdu (CD) station were comparably analyzed with those of ionospheric disturbances reported previously. The results showed that distinct electromagnetic changes, geomagnetic "double low-point" phenomena, and ionospheric disturbances above both sides of the Earth started in turn, respectively, but reached their climax simultaneously within dozens of hours on 9 May. This evolutionary process increases the probability that electromagnetic energy propagates from the epicentral area, via the atmosphere and ionosphere, to the equatorial plane, and through this plane finally to its magnetically conjugated area in the opposite hemisphere, causing electromagnetic disturbances on the Earth's surface, in the atmosphere, and in the ionosphere and its conjugate point, in that order.

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Section: Spatial Ionospheric Anomaliesmentioning

confidence: 99%

Indications of Ground-based Electromagnetic Observations to A Possible Lithosphere–Atmosphere–Ionosphere Electromagnetic Coupling before the 12 May 2008 Wenchuan MS 8.0 Earthquake

Lü

Zhang

et al. 2019

Atmosphere

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“…Since the Wenchuan large earthquake in May 2008, a number of papers have been published that describe the precursory increase of the total electron content (TEC) related to the earthquake [ Zhao et al , ; Pulinets et al , ; Klimenko et al , ]. Walker et al [] reported that an increase in ULF wave activity was found in the vicinity of the epicenter of the Wenchuan earthquake. Therefore, the ionospheric disturbances related to the Wenchuan earthquake of May 2008 have been revisited through investigating the N e and O + densities, the electric field data of DEMETER [ Parrot , ], and the N e of CHAMP [ Lühr et al , ], in addition to the global VTEC data provided by the International GNSS (Global Navigation Satellite Systems) Service (IGS) [ Hernández‐Pajares et al , ].…”

Section: Introductionmentioning

confidence: 99%

Suspected seismo‐ionospheric coupling observed by satellite measurements and GPS TEC related to the M7.9 Wenchuan earthquake of 12 May 2008

et al. 2014

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Anomalous changes in the ionospheric conditions related to the Wenchuan earthquake of 12 May 2008 are investigated using electron density (Ne) from Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and CHAMP satellites, electric field from DEMETER, and GPS‐total electron content (TEC) maps. The normalized Ne from the DEMETER satellite reveal that the previously reported TEC increments before the earthquake can be considered as fragments of the gradual equatorial ionization anomaly (EIA) enhancements near the epicenter longitude that began approximately 1 month before the earthquake and reached its maximum with an exceptionally large strength index 8 days prior to the main shock. This feature is indirectly confirmed through the CHAMP Ne and GPS TEC data. Following the EIA intensity peak, disturbances in the Ne and O+ density were observed in the nightside. Based on the concurrent electric field and Ne changes, it is suggested that EIA intensification could be triggered by the E field disturbances over the epicenter.

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“…However, we have succeeded in identifying the depression of ULF horizontal magnetic field as the signature of lower ionospheric perturbation, which occurs a few days before the EQ. Though there have been published several papers on the ionospheric plasma and wave characteristics before the Sichuan EQ on the basis of DEMETER satellite data [15]- [17] [36], the ground-based observation is definite to provide us with the detailed temporal evolution of different seismogenic phenomena when the number of stations is sufficient to form a network. We will compare our results on the lower ionosphere with those in the upper (F region) ionosphere based on the ground-based ionospheric measurements.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

On the Anomalies in ULF Magnetic Field Variations Prior to the 2008 Sichuan Earthquake

Li¹,

Schekotov²,

Asano³

et al. 2015

OJER

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There have been reported several papers on the ionospheric F region perturbations prior to the 2008 Sichuan earthquake (EQ) (magnitude 8.0), but it seems that very few reports have been published on the characteristics of ground-based ULF (ultra low frequency) magnetic field variations for this EQ. This paper deals with two different aspects of ground-based ULF magnetic field variations: 1) ULF radiation from the lithosphere, and 2) depression of ULF horizontal magnetic field as a signature of lower ionospheric perturbations. ULF data from two Chinese stations [Chengdu (epicentral distance, 80 km) and Xichang (about 300 km away from the EQ epicenter)] are analyzed, with paying attention to the local nighttime period (LT = 22 h to 02 h, UTC = 14 h to 18 h) in order to avoid man-made noise. We have analyzed powers of the horizontal component (H 2 ), vertical component (Z 2 ), polarization as their ratio (Z 2 /H 2 ), depression of the horizontal component (as an inverse of horizontal magnetic field component power, 1/H 2 ) and δDep as a variation of depression at a particular frequency of 0.01 -0.02 Hz (10 -20 mHz). It is then found that there seems no clear signature of lithospheric ULF radiation. Whilst, the most evident fact is the finding of depression of ULF horizontal magnetic field at Chengdu a few days before the Sichuan EQ, which suggests that the lower ionosphere was perturbed before the EQ. The characteristics of the lower ionospheric perturbations are compared with those of upper ionospheric perturbations reported before.

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Changes in the ultra-low frequency wave field during the precursor phase to the Sichuan earthquake: DEMETER observations

Cited by 37 publications

References 19 publications

Indications of Ground-based Electromagnetic Observations to A Possible Lithosphere–Atmosphere–Ionosphere Electromagnetic Coupling before the 12 May 2008 Wenchuan MS 8.0 Earthquake

Indications of Ground-based Electromagnetic Observations to A Possible Lithosphere–Atmosphere–Ionosphere Electromagnetic Coupling before the 12 May 2008 Wenchuan MS 8.0 Earthquake

Suspected seismo‐ionospheric coupling observed by satellite measurements and GPS TEC related to the M7.9 Wenchuan earthquake of 12 May 2008

On the Anomalies in ULF Magnetic Field Variations Prior to the 2008 Sichuan Earthquake

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