The Seismic Electromagnetic Emissions During the 2010 Mw 7.8 Northern Sumatra Earthquake Revealed by DEMETER Satellite

The abnormal electromagnetic emissions recorded by DEMETER (the Detection of
Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite associated
with the April 6, 2010 Mw 7.8 northern Sumatra earthquake are examined in this study.
The variations of wave intensities recorded through revisiting orbits from August 2009 to
May 2010 indicate that some abnormal enhancements at 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 the 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
suggest strong enhancements of wave intensities during the period prior to the
earthquake. We further 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 Extremely Low
Frequency emissions obliquely propagating upward from the Earth toward outer
space direction at 10 and 6 days before the main shock. The potential energy
variation of acoustic-gravity wave suggests the possible existence of acousticgravity
wave stability with wavelengths roughly varying from 5.5 to 9.5 km in the
atmosphere at the time of the main shock. In this study, we comprehensively
investigated the link between the electromagnetic emissions and the earthquake
activity through a convincing observational analysis, and preliminarily explored the
seismic-ionospheric disturbance coupling mechanism, which is still not fully
understood at present by the scientific community.