Vertical midscale ionospheric disturbances caused by surface seismic waves based on Irkutsk chirp ionosonde data in 2011–2016

Abstract

Based on the Irkutsk fast monostatic chirp ionosonde data, we made a statistical analysis of ionospheric effects for 28 earthquakes which appeared in 2011–2016 years. These effects are related with surface (Rayleigh) seismic waves far from epicenter. The analysis has shown that nine of these earthquakes were accompanied by vertical midscale ionospheric irregularities (multicusp). To estimate the ionospheric efficiency of the seismic waves, we proposed new index KW. The index estimates the maximal amplitude of the acoustic shock wave generated by given spatial distribution of seismic vibrations and related with maximal spectral power of seismic oscillations. Based on the analysis of experimental data, we have shown that earthquake-related multicusp (5–25 s irregularities) is observed mostly at daytime [07:00–17:00] LST for KW≥4.7. The observations of acoustic waves by GPS technique in the epicenter vicinity (120–600 s irregularities) do not show such a daytime dependence. Based on 24 May 2013 Okhotsk Sea earthquake example, we demonstrated that deep-focus earthquakes can produce strong multicusp far from the epicenter, although do not produce significant GPS ionospheric response in the epicenter vicinity.