Ionospheric Quasi-static Electric Field Anomalies During Seismic Activity - Earth Science: New Methods and Studies - page 140

strong earthquakes in interval of about 10 days occurred in the region. The first event
EQ 19 (M 6.0) on August 23, 1981 took place in the area of the Kuril Islands that are
located from the westernmost point of the Japanese Island of Hokkaido to the southern
tip of the Kamchatka Peninsula.
Figure 6a. Satellite orbits 240, 283 and positions of the earthquake epicenters for period of seismic
activity in August 23 to September 5, 1981.
The Kuril Trench was formed by the subduction of the Pacifi c plate under the
North American plate and extends from the central area of Kamchatka to Hokkaido.
The Kuril Trench is one of the most active seismogenic regions due to the subduction
of the Pacifi c Ocean Plate beneath Hokkaido. Figure 6b (orbit 283) shows an increase
in the E z component of about 10 mV/m 92 hr after the EQ 19 event. The ionospheric
disturbance zone shows concentration around the earthquake epicenter. Probably, it is
not impossible that there is also infl uence of EQ 24 (the satellite passed 72 hr after the
earthquake EQ 24 ). A strong earthquake EQ 56 (M 6.6) occurs in the region of Aleutian
Islands, about 10 days later, on September 3, 1981. Another earthquake EQ 56 occurs
near Shikotan Island, in the South Kuril Island Group of Russian Far East. On the
background of the trend in the quasi-static electric fi eld, we establish an increase in the
E z component of about 15 mV/m (Figure 6b), 157 hr before this event. The ionospheric
disturbance zone is shifted to the south of the earthquake epicenter. The information
is taken in a medium quiet day K p = 5. Any disturbances from aftershocks EQ 57 , EQ 58 ,