Abstract
The abnormal electromagnetic emissions recorded by the DEMETER satellite associated with the April 6, 2010 Mw 7.8 northern Sumatra earthquake are examined in this study. The variations of wave intensities recorded by revisiting orbits from August 2009 to May 2010 indicate that some abnormal enhancements at ELF (Extremely Low Frequency) range of 300 - 800 Hz occurred from 10 to 3 days before the main shock, while they remained a relatively smooth trend during quiet seismic activity times. The perturbation amplitudes relative to the background map which were built by using the same-time seasonal window (February 1 to April 30) data from 2008 to 2010 further suggested strong enhancements of wave intensities during the period prior to the earthquake. We computed the wave propagation parameters for the electromagnetic field waveform data by using the Singular Value Decomposition method, and results show that there are certain portions of the ELF emissions obliquely propagating upward from the Earth towards outer space direction at 10 and 6 days before the main shock. The potential energy variation of acoustic-gravity wave (AGW) suggests the possible existence of AGW stability with wavelengths roughly varying from 5.45 to 9.49 km in atmosphere at the time of the main shock. In this study, we comprehensively investigate the link between the electromagnetic emissions and the earthquake activity through a convincing observational analysis, and preliminarily explore the seismic-ionospheric disturbance coupling mechanism, which is still not fully understood at present by the scientific community.
Highlights
The abnormal electromagnetic emissions associated with earthquake (EQ) activities, during either its preparation phase or its occurrence, have been widely documented since the last century
Both ground-based observations and lab experiments on rock-rupture-processing confirm that the electromagnetic emissions induced by EQ activities can appear over a broad frequency range from Direct Current (DC) to Ultra Low Frequency (ULF), Extremely Low Frequency (ELF), Very Low Frequency (VLF), and even up to High Frequency range (e.g., Gokhberg et al, 1982; Huang and Ikeya, 1998; Sorokin et al, 2001; Pulinets et al, 2018)
These ideas were not universally accepted: for example, Henderson et al (1993) stated no clear ELF/VLF signatures related to earthquakes based on a statistical analysis on DE 2 satellite; Rodger et al (1996) reported no significant precursory, co-seismic or post-seismic effects associated with ELF/VLF electromagnetic activities recorded by ISIS (International Satellites for Ionospheric Studies) 2 satellite
Summary
The abnormal electromagnetic emissions associated with earthquake (EQ) activities, during either its preparation phase or its occurrence, have been widely documented since the last century. We examined the wave intensity values of the variant magnetic field at different frequency ranges (200 Hz–20 kHz) from March 20 to April 10, 2010 over the Mw 7.8 northern Sumatra epicentral area by using PSD values provided by surveymode observations of DEMETER These results reveal that those orbits passing over the epicentral area show certain enhancement of wave intensity at ELF frequency (300–800 Hz) (Figure 1). It can be seen that the 2010 Mw 7.8 northern Sumatra EQ occurred during the recovery phase of a moderate geomagnetic storm (Dst index reached a minimum of - 80 nT on April 6, 2010) For this reason, those orbits recorded during the main phase and recovery phase (mostly from April 3–8) are FIGURE 1 | The variation of extremely low frequency magnetic field wave intensity during the 2010 April 6, Mw 7.8 Sumatra earthquake from March 20 to April 8, 2010, represented by power spectral density (PSD) values at frequency range (300–800 Hz).
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