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

TL;DR

This study analyzes how surface seismic waves from earthquakes induce vertical midscale ionospheric disturbances using Irkutsk ionosonde data from 2011-2016, introducing a new index to quantify seismic impact on the ionosphere.

Contribution

It presents a new index $K_{W}$ to estimate seismic wave impact on the ionosphere and statistically analyzes earthquake-related ionospheric irregularities over a five-year period.

Findings

Nine earthquakes showed associated multicusp ionospheric irregularities.

Multicusp occurrence is mostly during daytime for $K_{W} extgreater 4.7$.

Deep-focus earthquakes can produce strong multicusp far from epicenter.

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 $K_{W}$. 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 is observed mostly at daytime [07:00-17:00]LST for $K_{W}\ge4.7$. The observations of intrinsic gravity waves by GPS technique in the epicenter vicinity do not show such a daytime dependence. Based on 24/05/2013 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. Three cases of sporadic E bifurcation in far epicentral zone were also detected and discussed.