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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 (main shock) 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. [2]
The Ore Mountains (Erzgebirge), which form the border between the Czech Republic and Germany, western Bohemia and the Vogtland region, have been known since the 16th century as being prone to frequent earthquake swarms, which typically last a few weeks to a few months. In 1899, Austrian geologist Josef Knett, while studying a swarm of about a hundred events felt in western Bohemia/Vogtland between January and February 1824, coined the noun Schwarmbeben, i.e. "swarm [earth]quake". [3] The term "swarm" comes from the fact that hypocentres give the impression of agglutinating like a bee swarm when plotted onto a map, a cross-section or a 3D model.[ citation needed ]
One of the best-documented swarms occurred near Matsushiro, a suburb of Nagano, to the north-west of Tokyo. The Matsushiro swarm lasted from 1965 to 1967 and generated about 1 million earthquakes. This swarm had the peculiarity of being sited just under a seismological observatory installed in 1947 in a decommissioned military tunnel. It began in August 1965 with three earthquakes too weak to be felt, but three months later, a hundred earthquakes could be felt daily. On 17 April 1966, the observatory counted 6,780 earthquakes, with 585 of them having a magnitude great enough to be felt, which means that an earthquake could be felt, on average, every two and a half minutes. [4] The phenomenon was clearly identified as linked to a magma uplift, perhaps initiated by the 1964 Niigata earthquake, which occurred the previous year. [5]
Earthquake swarms are common in volcanic regions such as Japan, Central Italy, the Afar depression or Iceland, where they occur before and during eruptions, but they are also observed in zones of Quaternary volcanism or of hydrothermal circulation, such as Vogtland/western Bohemia and the Vosges massif, and less frequently far from tectonic plate boundaries in locations such as Nevada, Oklahoma or Scotland. In all cases, high-pressure fluid migration in the Earth's crust seems to be the trigger mechanism and the driving process that govern the evolution of the swarm in space and time. [6] [7] The Hochstaufen earthquake swarm in Bavaria, with 2-km-deep foci, is one of the rare examples where an indisputable relationship between seismic activity and precipitation could be established. [8]
Earthquake swarms raise public-safety issues: first, because the end of seismic activity cannot be predicted; second, because it is uncertain whether another earthquake with a magnitude larger than those of previous shocks in the sequence will occur (the 2009 L'Aquila earthquake in Italy illustrates this, with an MW 6.3 shock following a swarm activity with magnitudes between 1 and 3). Even though swarms usually generate moderate shocks, the persistence of felt earthquakes can be disruptive and cause distress to the population.
The following examples were chosen for peculiarities of certain swarms (for instance: large number of events, complex interaction with larger shocks, long period of time, ultra-shallow focal depth), or because of their geographical region, some swarms occurring in otherwise aseismic regions. It is not intended to be a list of all the swarms happening worldwide.
An earthquake – also called a quake, tremor, or temblor – is the shaking of the surface of Earth resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those that are so weak that they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume. The word tremor is also used for non-earthquake seismic rumbling.
The Yellowstone Caldera, sometimes referred to as the Yellowstone Supervolcano, is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States. The caldera and most of the park are located in the northwest corner of Wyoming. The caldera measures 43 by 28 miles, and postcaldera lavas spill out a significant distance beyond the caldera proper.
The New Madrid Seismic Zone, sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the Southern and Midwestern United States, stretching to the southwest from New Madrid, Missouri.
A volcano tectonic earthquake or volcano earthquake is caused by the movement of magma beneath the surface of the Earth. The movement results in pressure changes where the rock around the magma has experienced stress. At some point, this stress can cause the rock to break or move. This seismic activity is used by scientists to monitor volcanoes. The earthquakes may also be related to dike intrusion or occur as earthquake swarms.
The 2006 Gulf of Mexico earthquake occurred in the eastern Gulf of Mexico on September 10 at 10:56 AM Eastern Daylight Time. The intraplate earthquake measured 5.9 on the moment magnitude scale and its epicenter was located about 250 miles (400 km) west-southwest of Anna Maria, Florida. The event was felt throughout much of the Gulf Coast of the United States and was the second earthquake of magnitude 5 or greater in the Gulf during 2006. Felt intensities, as measured on the Mercalli intensity scale, were as high as IV (Light) in Florida, with parts of Georgia at III (Weak).
The 1976 Moro Gulf earthquake and tsunami occurred on August 17, 1976, at 00:11 local time near the islands of Mindanao and Sulu, in the Philippines. It measured 8.0 on the moment magnitude scale occurring at a depth of 20 km (12 mi). The earthquake was accompanied by a destructive tsunami that resulted in a majority of the estimated 5,000 to 8,000 fatalities. It was the deadliest and strongest earthquake in the Philippines in 58 years since the 1918 Celebes Sea earthquake.
Earthquakes have occurred in Western Australia (WA) on a regular basis throughout its geological history.
A series of small volcanic earthquakes measuring less than 4.0 on the Richter magnitude scale took place in the sparsely populated Nazko area of the Central Interior of British Columbia, Canada, from October 9, 2007, to June 12, 2008. They occurred just west of Nazko Cone, a small tree-covered cinder cone that last erupted about 7,200 years ago.
This is a list of different types of earthquake.
The 1993 Klamath Falls earthquakes took place in Klamath Falls, Oregon, beginning on Monday, 20 September at 8:28 p.m. The doublet earthquake registered respective magnitudes of 6.0 and 5.9 on the moment magnitude scale. The earthquakes were located at a depth of 5.6 miles (9 km) and tremors continued to be felt more than three months after the initial shocks.
The geological deformation of Iceland is the way that the rocks of the island of Iceland are changing due to tectonic forces. The geological deformation explains the location of earthquakes, volcanoes, fissures, and the shape of the island. Iceland is the largest landmass (102,775 km²) situated on an oceanic ridge. It is an elevated plateau of the sea floor, situated at the crossing of the Mid-Atlantic Ridge and the Greenland-Iceland-Faeroe Ridge. It lies along the oceanic divergent plate boundary of North American Plate and Eurasian Plate. The western part of Iceland sits on the North American Plate and the eastern part sits on the Eurasian Plate. The Reykjanes Ridge of the Mid-Atlantic ridge system in this region crosses the island from southwest and connects to the Kolbeinsey Ridge in the northeast.
On May 4, 2018, an earthquake with a magnitude of Mw 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.
As part of the Comoro Islands chain in the Mozambique Channel, the geology of Mayotte is virtually the same as the geology of the Comoros, the rest of the island chain which is independent of France. The island resulted from the rifting of Madagascar away from Africa as well as "hotspot" mantle plume activity, and is also impacted by seismicity and deformation associated with the East African Rift. However, because Mayotte is a part of France its geology is significantly more researched than that of other islands in the chain.
The 11 November 2018 Mayotte seismic event is a seismic event of unknown origin that occurred about 24 kilometres (15 mi) off the coast of Mayotte, an overseas department and region of France in the Indian Ocean. It was recorded by seismograms globally, including in Kenya, Chile, New Zealand, Canada, and Hawaii, almost 18,000 kilometres (11,000 mi) away. Despite this, no one felt it. The seismic waves lasted for over 20 minutes. Most earthquakes have P waves and S waves, which are later followed by long-period surface waves. The Mayotte event lacked P waves and S waves, but did cause a long-period surface wave travelling at 14,000 km/h (9,000 mph) around the globe. Additionally, the signal released by the earthquake resembled a clean sine wave, while most earthquake waves have multiple frequencies.
The 2019 Ridgecrest earthquakes of July 4 and 5 occurred north and northeast of the town of Ridgecrest, California located in Kern County and west of Searles Valley. They included three initial main shocks of Mw magnitudes 6.4, 5.4, and 7.1, and many perceptible aftershocks, mainly within the area of the Naval Air Weapons Station China Lake. Eleven months later, a Mw 5.5 aftershock took place to the east of Ridgecrest. The first main shock occurred on Thursday, July 4 at 10:33 a.m. PDT, approximately 18 km (11.2 mi) ENE of Ridgecrest, and 13 km (8.1 mi) WSW of Trona, on a previously unnoticed NE-SW trending fault where it intersects the NW-SE trending Little Lake Fault Zone. This quake was preceded by several smaller earthquakes, and was followed by more than 1,400 detected aftershocks. The M 5.4 and M 7.1 quakes struck on Friday, July 5 at 4:08 a.m. and 8:19 p.m. PDT approximately 10 km (6 miles) to the northwest. The latter, now considered the mainshock, was the most powerful earthquake to occur in the state in 20 years. Subsequent aftershocks extended approximately 50 km (~30 miles) along the Little Lake Fault Zone.
The 2019 Cotabato earthquakes were an earthquake swarm which struck the province of Cotabato on the island of Mindanao in the Philippines in October 2019. Three of these earthquakes were above 6.0 on the moment magnitude scale with a Mercalli intensity of VIII. More than 40 people have been reported dead or missing and nearly 800 were injured as a result of these events.
An earthquake struck near the Hawaiian island of Lanai on February 19, at 10:11 pm HST with an estimated magnitude of 7.5 on the moment magnitude scale (Mw ). It remains one of the largest seismic event to hit the Hawaiian Islands since the 1868 Ka‘ū earthquake, with its effects being felt throughout the entire archipelago. It caused severe damage on the islands of Lanai, Molokai and Maui. A tsunami may have been generated however there are speculations if it had actually happened. Despite the size of the quake and the extent of damage, there were no deaths.
An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time. The large megathrust earthquake had a moment magnitude of 8.2 according to the United States Geological Survey (USGS). A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled. The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively.
On 9 July 2019, at 8:36 PM (PST), an earthquake measuring Mw 5.6 jolted the province of North Cotabato, Davao del Sur, and other nearby provinces. The National Disaster Risk Reduction and Management Council reported one dead and three injured in Makilala after the earthquake, and a total of 164 families affected in Cotabato Province. Near the epicenter of the earthquake, the severity of strong ground motion was assigned VI (Strong) on the Modified Mercalli intensity scale. A total of 106 schools, 119 houses, and 14 other infrastructures were damaged by the earthquake.