156 earthquakes in the South Sandwich Trench area (12-19 August 2021)

This simplified map shows 156 significant earthquakes that occurred from 12 to 19 August 2021 in the South Sandwich Trench area of the far-southern Atlantic Ocean. The earliest and most powerful events were a magnitude 7.5 quake that hit at 4:32 PM, local time, and a magnitude 8.1 quake that hit about 3 minutes later. Aftershocks have occurred throughout the trench area. So far, large aftershocks have included five quakes in the 6s, 114 quakes in the 5s, and the rest in the upper 4s. The small light-colored spots are the South Sandwich Islands. The red lines are tectonic plate boundaries.

The South Sandwich Trench is a deep seafloor trough formed by subduction - oceanic lithosphere of the South American Plate is diving westward beneath oceanic lithosphere of the Sandwich Plate. Earthquake activity and volcanic islands occur next to the trench.

See info. at:
earthquake.usgs.gov/earthquakes/eventpage/us6000f4ly/exec...
and
earthquake.usgs.gov/earthquakes/eventpage/us6000f53e/exec...
and
en.wikipedia.org/wiki/South_Sandwich_Trench
and
en.wikipedia.org/wiki/South_Sandwich_Plate
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An earthquake is a natural shaking or vibrating of the Earth caused by sudden fault movement and a rapid release of energy. Earthquake activity is called "seismicity". The study of earthquakes is called "seismology". The actual underground location of an earthquake is the hypocenter, or focus. The site at the Earth's surface, directly above the hypocenter, is the epicenter. Minor earthquakes may occur before a major event - such small quakes are called foreshocks. Minor to major quakes after a major event are aftershocks.

Most earthquakes occur at or near tectonic plate boundaries, such as subduction zones, mid-ocean ridges, collision zones, and transform plate boundaries. They also occur at hotspots - large subsurface mantle plumes (Examples: Hawaii, Yellowstone, Iceland, Afar).

Earthquakes generate four types of shock waves: P-waves, S-waves, Love waves, and Rayleigh waves. P-waves and S-waves are body waves - they travel through solid rocks. Love waves and Rayleigh waves travel only at the surface - they are surface waves. P-waves are push-pull waves that travel quickly and cause little damage. S-waves are up-and-down waves (like flicking a rope) that travel slowly and cause significant damage. Love waves are side-to-side surface waves, like a slithering snake. Rayleigh waves are rotational surface waves, somewhat like ripples from tossing a pebble into a pond.

Earthquakes are associated with many specific hazards, such as ground shaking, ground rupturing, subsidence (sinking), uplift (rising), tsunamis, landslides, fires, and liquefaction.

Some famous major earthquakes in history include: Shensi, China in 1556; Lisbon, Portugal in 1755; New Madrid, Missouri in 1811-1812; San Francisco, California in 1906; Anchorage, Alaska in 1964; and Loma Prieta, California in 1989.

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Taken on: August 19, 2021

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Sets appears in: • 2021 Earthquakes • Aftershocks more » • Scotia Plate-Sandwich Plate area Earthquakes • Magnitude 8+ Earthquakes • Earthquakes « less

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