Scattering of Extremely Low Frequency Electromagnetic Waves by a Localized Seismogenic Ionospheric Perturbation: Observation and Interpretation

A significant anomaly in the extremely low frequency (ELF) spectra of Schumann resonance (SR) was discovered for the 1999 Chi‐Chi earthquake (EQ) in Taiwan as observed in Japan. Similar phenomena were confirmed for other EQs remote from the observer by a few megameters. An additional effect was dete...

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Bibliographic Details
Published in:Radio science 2020-12, Vol.55 (12), p.n/a
Main Authors: Hayakawa, M., Nickolaenko, A. P., Galuk, Yu P., Kudintseva, I. G.
Format: Article
Language:English
Subjects:
Schumann resonance (SR)
seismogenic nonuniformity
spectral modifications and EQ magnitude
spectral modifications versus distance to a nearby EQ
threshold in EQ magnitude
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Summary:A significant anomaly in the extremely low frequency (ELF) spectra of Schumann resonance (SR) was discovered for the 1999 Chi‐Chi earthquake (EQ) in Taiwan as observed in Japan. Similar phenomena were confirmed for other EQs remote from the observer by a few megameters. An additional effect was detected for nearby EQs. The anomalies were explained by ELF radio wave scattering from a seismogenic disturbance. The global thunderstorms serve as the source positioned at the equator, and the localized seismogenic perturbation was placed above the EQ epicenter. We evaluate a seismic impact on SR power spectra using the realistic conductivity profile of atmosphere. The nonuniformity above EQ epicenter is axially symmetric varying along the radius according to Gaussian law whose scale depends on the magnitude. We use the complex characteristic heights relevant to the regular and disturbed cavities. These are substituted into the two‐dimensional telegraph equation (2DTE) for electric and magnetic fields. Deviations from the regular spectra are the seismogenic modifications that depend on the EQ magnitude. Computations indicate that a distant localized seismogenic nonuniformity provides a noticeable impact when the EQ magnitude exceeds the M = 7 threshold. The effect is also modeled of the nearby (up to 500 km) moderate (magnitude 5.5) EQs. The resonance spectra of disturbed fields become elevated as a whole. The distance dependence of field disturbance repeats seismogenic modifications in the characteristic heights above the observer. Model computations are compared with available observations. Key Points Seismic process generates a nonuniformity in mesosphere conductivity which leads to modifications in Schumann resonance spectra We discuss the link between spectral modifications and EQ magnitude, with indicating a threshold in EQ magnitude We also model a connection between modifications in Schumann resonance spectra and the distance to a nearby moderate EQ
ISSN:0048-6604
1944-799X
DOI:10.1029/2020RS007130