  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.
