In seismology, an earthquake swarm is a sequence of seismic events occurring in a local area within a relatively short period. The time span used to define a swarm varies, but may be days, months, or years. Such an energy release is different from the situation when a major earthquake is followed by a series of aftershocks: in earthquake swarms, no single earthquake in the sequence is obviously the main shock. In particular, a cluster of aftershocks occurring after a mainshock is not a swarm.
The 1983 Borah Peak earthquake occurred on October 28, at in the western United States, in the Lost River Range at Borah Peak in central Idaho.
The 2009 Swan Islands earthquake occurred on May 28 at with a moment magnitude of 7.3 and a maximum Mercalli intensity of VII. The epicenter was located in the Caribbean Sea, 64 kilometres (40 mi) northeast of the island of Roatán, 19 miles northeast of Port Royal, Isla de Bahias, 15 miles northwest of Isla Barbaretta, and 130 kilometres (81 mi) north-northeast of La Ceiba. Three aftershocks followed the earthquake within magnitude 4 range.
The 2010 Haiti earthquake was a catastrophic magnitude 7.0 Mw earthquake that struck Haiti at 16:53 local time on Tuesday, 12 January 2010. The epicenter was near the town of Léogâne, Ouest department, approximately 25 kilometres (16 mi) west of Port-au-Prince, Haiti's capital.
The 2010 Baja California earthquake occurred on April 4 with a moment magnitude of 7.2 and a maximum Mercalli intensity of VII. The shock originated at south of Guadalupe Victoria, Baja California, Mexico.
The 2010 Canterbury earthquake struck the South Island of New Zealand with a moment magnitude of 7.1 at on 4 September, and had a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale. Some damaging aftershocks followed the main event, the strongest of which was a magnitude 6.3 shock known as the Christchurch earthquake that occurred nearly six months later on 22 February 2011. Because this aftershock was centred very close to Christchurch, it was much more destructive and resulted in the deaths of 185 people.
The June 2011 Christchurch earthquake was a shallow magnitude 6.0 earthquake that occurred on 13 June 2011 at 14:20 NZST. It was centred at a depth of 7 km (4.3 mi), about 5 km (3 mi) south-east of Christchurch, which had previously been devastated by a magnitude 6.2 MW earthquake in February 2011. The June quake was preceded by a magnitude 5.9 ML tremor that struck the region at a slightly deeper 8.9 km (5.5 mi). The United States Geological Survey reported a magnitude of 6.0 Mw and a depth of 9 km (5.6 mi).
On August 23, 2011, a magnitude 5.8 earthquake hit the Piedmont region of the U.S. state of Virginia at 1:51:04 p.m. EDT. The epicenter, in Louisa County, was 38 mi (61 km) northwest of Richmond and 5 mi (8 km) south-southwest of the town of Mineral. It was an intraplate earthquake with a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale. Several aftershocks, ranging up to 4.5 in magnitude, occurred after the main tremor.
The 2014 Orkney earthquake occurred at 12:22:33 SAST on 5 August, with the epicentre near Orkney, a gold mining town in the Klerksdorp district in the North West province of South Africa. The shock was assigned a magnitude of 5.5 on the Richter scale by the Council for Geoscience (CGS) in South Africa, making it the biggest earthquake in South Africa since the 1969 Tulbagh earthquake, which had a magnitude of 6.3 on the Richter scale. The United States Geological Survey (USGS) estimated a focal depth of 5.0 km (3.1 mi). The CGS reported 84 aftershocks on 5 August and 31 aftershocks on 6 August, with a magnitude of 1.0 to 3.8 on the Richter scale. According to the CGS, the earthquake is the biggest mining-related earthquake in South African history.
On May 4, 2018, an earthquake with a magnitude of 6.9 struck Hawaii island in the Hawaii archipelago at around 12:33 p.m. local time. The earthquake's epicenter was near the south flank of Kīlauea, which has been the site of seismic and volcanic activity since late April of that year. According to the United States Geological Survey the quake was related to the new lava outbreaks at the volcano, and it resulted in the Hilina Slump moving about two feet. It was the largest earthquake to affect Hawaii since the 1975 earthquake, which affected the same region, killing two people and injuring another 28.
On 18 June 2018, around 7:58:35 a.m. Japan Standard Time, an earthquake measuring 5.6 Mw on the moment magnitude scale struck in northern Osaka Prefecture, Japan. The earthquake's epicenter was near Takatsuki and occurred at a depth of approximately 13 kilometres (8.1 mi). The Japan Meteorological Agency reported a magnitude of 6.1 Mj and an intensity of 6 lower on the shindo scale.
On August 21, 2018, a magnitude 7.3 earthquake struck just off the northern coast of Venezuela, near Cariaco, Sucre. The earthquake is thought to be the largest in the country since the 1900 San Narciso earthquake. It prompted evacuations in Caracas, and caused shaking in Colombia, Guyana, Brazil, Grenada, Dominica, Barbados, St. Vincent and the Grenadines, St. Lucia, and Trinidad and Tobago, the last of which also suffered damage and brief phone and power outages from about 100 miles away. A tsunami was not expected, though the Pacific Tsunami Warning Center warned of wave potential, and an alert had been broadcast for tsunami waves along coastlines. In terms of damage, concrete fell from the unfinished Tower of David skyscraper, blocking the sidewalk and closing traffic.
A strong earthquake measuring magnitude Mw 6.8 occurred in the Ionian Sea near the coasts of Greece during the night between 25 and 26 October 2018 at 22:54:51 UTC. Sea level changes were predicted, and a tsunami advisory was issued. Reports of sea level change of up to 20 centimeters were reported in Greece and Italy.
At 7:09 AM MDT on March 18, 2020, a 5.7 magnitude earthquake hit Salt Lake City, Utah, United States, with an epicenter 6 km (3.7 mi) north-northeast of Magna, Utah, beneath the site of the planned Utah Inland Port. It was the first major earthquake to occur within the Salt Lake Valley since the city was founded, the state's strongest earthquake since the 1992 St. George earthquake, and the first earthquake of comparable magnitude to occur near Salt Lake City since 1962, when a magnitude 5.0 earthquake struck a similar location in Magna.
The 2013 Craig, Alaska earthquake struck on January 5, at 12:58 am (UTC–7) near the city of Craig and Hydaburg, on Prince of Wales Island. The Mw 7.5 earthquake came nearly three months after an Mw 7.8 quake struck Haida Gwaii on October 28, in 2012. The quake prompted a regional tsunami warning to British Columbia and Alaska, but it was later cancelled. Due to the remote location of the quake, there were no reports of casualties or damage.
At 08:29:09 EDT on 14 August 2021, a magnitude 7.2 earthquake struck the Tiburon Peninsula of southern Haiti. It had a 10-kilometre-deep (6.2 mi) hypocenter near Petit-Trou-de-Nippes, approximately 150 kilometres (93 mi) west of the capital, Port-au-Prince. Tsunami warnings were briefly issued for the Haitian coast. At least 2,248 people were confirmed killed as of 1 September 2021 and more than 12,200 injured, mostly in the Sud Department. An estimated 650,000 people were in need of assistance. At least 137,500 buildings were damaged or destroyed.
An earthquake struck approximately 53 kilometres SSE of the town of Mansfield, in the Victorian Alps of Australia on 22 September 2021, at 09:15 local time. The earthquake measured 5.9 on the moment magnitude scale. The earthquake caused minor structural damage in parts of Melbourne and left one person injured. The earthquake was also felt in New South Wales, Australian Capital Territory, South Australia and Tasmania. The earthquake was substantially stronger than the 1989 Newcastle earthquake that measured 5.6 and killed 13 people.
The 1992 Joshua Tree earthquake occurred at 9:50:25 p.m. PDT on April 22 in Southern California. The magnitude 6.2 earthquake struck under the Little San Bernardino Mountains, near the town of Joshua Tree, California. Though no deaths were reported, the earthquake caused 32 injuries. A maximum Mercalli intensity of VII was observed in Joshua Tree and caused light to moderate damage. The event preceded the Landers and Big Bear earthquakes by two months but is now recognized as the beginning of a series of major earthquakes that culminated in two events on June 28, 1992.
