Earthquake 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.

[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.

Noto earthquake swarm (2020–2024)
Chronology of the 2003–2004 Ubaye earthquake swarm
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Each red bar shows the number of earthquakes daily detected (left-handside scale). More than 16,000 earthquakes were detected within 2 years. White circles show the magnitude of ~1,400 earthquakes which could be located (right-handside magnitude scale). Sismalp (the local monitoring network) was not able to locate all events below magnitude 1, which explains why very-small-magnitude events are seemingly lacking. (According to the Gutenberg–Richter law , M 0 events are approximately 10 times more numerous than M 1 events.) [ 1 ]
Ubaye earthquake swarms
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White: 2003–2004 swarm; pink: 2012–2015 swarm up to 2014-04-06; red: earthquakes as of 2014-04-07; pink and red lined up in white: epicentres of 2012-02-26 earthquake ( M =4.3) and 2014-04-07 earthquake ( M =4.8); brown: latest 20 earthquakes in July 2015, just before the map was drawn. Symbol size directly proportional to magnitude. Blue triangles show the 3 nearest seismic stations. [ 6 ]
Guy-Greenbrier earthquake swarm: map of epicentres for the period 2010-08-06 to 2011-03-01. [ 29 ]