Geophysical processes and biosphere: article

Аnnotation: One of the strongest earthquakes on August 12, 2021, MW = 8.3, near the South Sandwich Islands, where the South Sandwich Microplate is distinguished, often considered in conjunction with the Scotia Microplate, is considered. It has been established that the territory of the South Sandwich Microplate is characterized by extremely high seismic activity, the maximum values being A4.5 ≈ 3.5–3.7. The highest A4.5 ≥ 1.0 are in the South Sandwich Islands, the eastern part of the North Scotia Range, along which the Sandwich Microplate borders the South American Plate, and, to a lesser extent, the eastern part of the South Scotia Range, along which the Sandwich Microplate borders the Antarctic Plate. The western boundary of the microplate with the Scotia Plate does not manifest itself in any way in terms of the noticeable A4.5 values recorded here. The aftershock field of the 1st day indicates that the earthquake source is elongated sub longitude, and its length is estimated as approximately 370–380 km. The nature of the aftershock process partially obeys the universal laws of Omori and Båth. The regular stage period of 12 days and the decay rate of the number of aftershocks p = 1.2 are comparable with similar parameters obtained earlier for a series of strong earthquakes with MW = 8.0–8.3 in the areas of Sumbawa Island of August 19, 1977, Macquarie Islands of May 23, 1989, and Balleny Islands of March 25, 1998. The strongest aftershock of the earthquake of August 12, 2021, MW = 8.3 was the aftershock occurred on August 22, 2021 at 21:03, MW = 7.1; thus, the magnitude difference is ΔM = 1.2.