Ionospheric Quasi-static Electric Field Anomalies During Seismic Activity - Earth Science: New Methods and Studies - page 137

Caribbean Region, Central America, West Coast of South America, and
South-West Pacific Ocean
The pre- and post-seismic effects of the region bounded between latitudes 20 ° N-50 ° S

and longitudes 60 W are shown in Figure 5a. Four events EQ 36 , 38,59,71 with

magnitudes M > 4.8 occurred in the region (Table 1) during the time period August
19-September 19, 1981.

° W and 120 °

Figure 5a. Satellite orbits 196, 244, 250, 251, 405, 505, 546, 547, 602, and positions of the
earthquake epicenters for period of seismic activity in August 5-September 29, 1981.

Their epicenters lie on the Caribbean plate (a region with relatively quiet seismic-
ity). Any disturbances around 55-101 hr before to and 9-58 hr after these earthquakes
are not marked (see Table 1). Now we do not explain these phenomena. We show
also Figure 5b (orbit 250) when the satellite passes at ∆λ = 12°E-13°E, about 11 hr
before earthquake EQ 29 . The earthquake EQ 29 occurred in the Andes Mountains region
of Peru on August 25, 1981 (latitude 6.93 W, 16:54:38 UTC and

depth 33 km) with M 5.2. Apart from the main shock, a number of earthquakes with
comparatively smaller magnitudes happened in the same region like EQ 30,34,39 as well
(see Table 1). Two disturbances in the E z component of the quasi-static electric fi eld
are noted in this situation. The fi rst one situated to the south of the earthquake epi-
centers (projection over the equipotential magnetic fi eld lines in the low ionosphere
at satellite altitude) and the second one--in the magnetic conjugate region of about 5
mV/m (for the main event) are shown in Figure 5b.

° N, longitude 76.59 °