This is a seismogram from the Lake Erie Bluffs seismic station in Ohio, USA. The blip on the 13:00 line (click on the image once or twice to zoom in) was caused by a magnitude 3.0 earthquake that hit Lake Erie, 2 to 3 kilometers northwest of (offshore from) the town of Timberlake, northeastern Ohio. The quake occurred at 8:20 AM, local time, on 4 January 2022. The hypocenter was about 2 to 2.5 kilometers deep.
The United States Geological Survey assigned a magnitude value of 2.8 and a hypocenter depth of 5 kilometers to this quake. The Ohio Geological Survey assigned a magnitude value of 3.0 and a hypocenter depth of 2 or 2.3 kilometers.
Update: another earthquake of magnitude 1.9 occurred nearby the following day.
Ohio earthquakes are rare and usually small in magnitude. Two areas in Ohio have more frequent quakes than elsewhere: 1) western Ohio and 2) northeastern Ohio.
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From Dart & Hansen (2008) - Earthquakes in Ohio and vicinity, 1776-2007. United States Geological Survey Open-File Report 2008-1221:
The Northeast Ohio seismic zone has had moderately frequent earthquakes at least since the first one was reported in 1836. The largest earthquake in this zone (magnitude 5.0) occurred in 1986. This event produced Modified Mercalli intensities of VI in the epicentral region. A damaging earthquake (magnitude 5.2) occurred in 1998 near Pymatuning in northwestern Pennsylvania, just east of the Ohio border. An earthquake in the Ashtabula, Ohio area (magnitude 4.3) in 2001 caused minor damage. Historically, this zone has recorded only a few earthquakes per decade, but felt earthquakes have been reported more frequently in recent decades. This is probably a result of increased population, greater public awareness, improved communications, and perhaps episodic seismicity.
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See info. at:
earthquake.usgs.gov/earthquakes/eventpage/us7000g8x2/exec...
and
earthquake.usgs.gov/earthquakes/eventpage/us7000g8x2/regi...
[scroll down from there]
and
ohiohistorycentral.org/w/Earthquakes
and
c2.staticflickr.com/4/3768/32761626386_11098c17da_o.gif
and
www.flickr.com/photos/jsjgeology/51317417047
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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.
