The noise on the 02:00 line of this seismogram from the Borgarfjordur seismic station in Iceland represents a magnitude 5.2 earthquake and small aftershocks that hit Iceland starting at 2:01 AM, local time, on 7 March 2021. The epicenter was located in Iceland's Reykjanes Peninsula (= Southern Peninsula), southwest of the town of Reykjavik. This is ongoing activity that started in late February 2021 - numerous small and moderate-sized earthquakes have occurred in the Reykjanes Peninsula area. Temporal and geographic clusters of earthquakes are called "swarms". Over 20,000 events have been recorded since late February.

Iceland is a volcanic island in the North Atlantic Ocean between Britain and Greenland. It is situated on the Mid-Atlantic Ridge, along which the North American Plate and the Eurasian Plate separate and new oceanic crust forms. Seismicity in the area is due to subsurface magma movement from hotspot (mantle plume) activity, as well as seafloor spreading (= tectonic divergence).

Available information indicates that an igneous dike is being intruded in southwestern Iceland, and magma is within 1-2 kilometers of the surface.

See info. at: <a href="https://earthquake.usgs.gov/earthquakes/eventpage/us7000dgpz/executive" rel="noreferrer nofollow">earthquake.usgs.gov/earthquakes/eventpage/us7000dgpz/exec...</a> and <a href="https://en.wikipedia.org/wiki/Iceland_hotspot" rel="noreferrer nofollow">en.wikipedia.org/wiki/Iceland_hotspot</a> and <a href="https://icelandgeology.net/wp-content/uploads/2021/03/earthquake-zones-Fagradalsfjall-volcano.jpg" rel="noreferrer nofollow">icelandgeology.net/wp-content/uploads/2021/03/earthquake-...</a> and <a href="https://icelandgeology.net/?p=9043" rel="noreferrer nofollow">icelandgeology.net/?p=9043</a>

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.