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Aftershocks are a sequence of earthquakes that happen after a larger mainshock on a fault. Aftershocks occur near the fault zone where the mainshock rupture occurred and are part of the "readjustment process” after the main slip on the fault. Aftershocks become less frequent with time, although they can continue for days, weeks, months, or even years for a very large mainshock.
A swarm, on the other hand, is a sequence of mostly small earthquakes with no identifiable mainshock. Swarms are usually short-lived, but they can continue for days, weeks, or sometimes even months. They often recur at the same locations. Most swarms are associated with geothermal activity.
Learn more: Aftershocks? Swarm? What is the difference, and what do they mean?
An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel. In California there are two plates - the Pacific Plate and the North...
"Foreshock" and "aftershock" are relative terms. Foreshocks are earthquakes that precede larger earthquakes in the same location. An earthquake cannot be identified as a foreshock until after a larger earthquake in the same area occurs. Aftershocks are smaller earthquakes that occur in the same general area during the days to years following a larger event or "mainshock." They occur within 1-2...
Earthquakes are equally as likely to occur in the morning or the evening. Many studies in the past have shown no significant correlations between the rate of earthquake occurrence and the semi-diurnal tides when using large earthquake catalogs. Several recent studies, however, have found a correlation between earth tides (caused by the position of the moon relative to the earth) and some types of...
Surface rupture occurs when movement on a fault deep within the earth breaks through to the surface. NOT ALL earthquakes result in surface rupture.
Earthquakes occur in the crust or upper mantle, which ranges from the earth's surface to about 800 kilometers deep (about 500 miles). The strength of shaking from an earthquake diminishes with increasing distance from the earthquake's source, so the strength of shaking at the surface from an earthquake that occurs at 500 km deep is considerably less than if the same earthquake had occurred at 20...
The Geysers Geothermal Field is located in a tectonically active region of Northern California. The major seismic hazards in the region are from large earthquakes occurring along regional faults that are located miles away from the geothermal field, such as the San Andreas and Healdsburg-Rodgers Creek faults. However, activities associated with the withdrawal of steam for producing electric power...
Earthquakes do occur in Antarctica, but not very often. There have been some big earthquakes--including one magnitude 8.1--in the Balleny Islands (between Antarctica and New Zealand). The boundary between the Scotia Plate and the Antarctic Plate just grazes the north tip of the Antarctic Peninsula (look "northwest" from the Pole toward South America). There is also a hint of a line of seismicity...
Start with our Earthquake Hazards Education site. That includes: Earthquakes for Kids Cool Earthquake Facts Earthquake Science for Everyone Other good starting points include: State Geological Surveys for states in earthquake-prone regions The Great ShakeOut Earthquake Drills website SAGE (Seismological Facility for the Advancement of Geoscience), which is a non-profit consortium
Earthquakes induced by human activity have been documented at many locations in the United States and in many other countries around the world. Earthquakes can be induced by a wide range of causes including impoundment of reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground formations. While most induced earthquakes...
Map showing aftershock zones of great Aleutian Islands, Alaska, earthquakes in the 20th century. Red solid line with pink fill indicates aftershock zone of the 1957 Aleutian Islands earthquake from Sykes et al.
Map showing aftershock zones of great Aleutian Islands, Alaska, earthquakes in the 20th century. Red solid line with pink fill indicates aftershock zone of the 1957 Aleutian Islands earthquake from Sykes et al.
A technician installs strong motion and high frequency sensors April 11 at a station selected to record aftershock data from the April 5, 2024 Whitehouse Station, N.J. earthquake.
A technician installs strong motion and high frequency sensors April 11 at a station selected to record aftershock data from the April 5, 2024 Whitehouse Station, N.J. earthquake.
U.S. Geological Survey electronics technician Greg Tanner installs an "aftershock kit" in New Jersey April 10 following the April 5, 2024 Whitehouse Station earthquake.
U.S. Geological Survey electronics technician Greg Tanner installs an "aftershock kit" in New Jersey April 10 following the April 5, 2024 Whitehouse Station earthquake.
May 2020 earthquake swarm at Lōʻihi seamount
The inferred rupture area (white dashed line) of the May 4, 2018, magnitude-6.9 earthquake, with its foreshocks and first 10 days of aftershocks, spans an area of about 800 sq km (300 sq mi). Circle size indicates earthquake magnitude; color indicates earthquake depth. Magnitudes for some of the larger events are labeled.
The inferred rupture area (white dashed line) of the May 4, 2018, magnitude-6.9 earthquake, with its foreshocks and first 10 days of aftershocks, spans an area of about 800 sq km (300 sq mi). Circle size indicates earthquake magnitude; color indicates earthquake depth. Magnitudes for some of the larger events are labeled.
December 13 - 14, 2016 Long Valley Caldera earthquake swarm recorded on instrument MDH1 webicorder. Swarm begins at 23:28 PST.
December 13 - 14, 2016 Long Valley Caldera earthquake swarm recorded on instrument MDH1 webicorder. Swarm begins at 23:28 PST.
Aftershocks are earthquakes that follow the largest shock of an earthquake sequence. They are smaller than the mainshock and within 1-2 fault lengths distance from the mainshock fault. Aftershocks can continue over a period of weeks, months, or years.
Aftershocks are earthquakes that follow the largest shock of an earthquake sequence. They are smaller than the mainshock and within 1-2 fault lengths distance from the mainshock fault. Aftershocks can continue over a period of weeks, months, or years.
An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel. In California there are two plates - the Pacific Plate and the North...
"Foreshock" and "aftershock" are relative terms. Foreshocks are earthquakes that precede larger earthquakes in the same location. An earthquake cannot be identified as a foreshock until after a larger earthquake in the same area occurs. Aftershocks are smaller earthquakes that occur in the same general area during the days to years following a larger event or "mainshock." They occur within 1-2...
Earthquakes are equally as likely to occur in the morning or the evening. Many studies in the past have shown no significant correlations between the rate of earthquake occurrence and the semi-diurnal tides when using large earthquake catalogs. Several recent studies, however, have found a correlation between earth tides (caused by the position of the moon relative to the earth) and some types of...
Surface rupture occurs when movement on a fault deep within the earth breaks through to the surface. NOT ALL earthquakes result in surface rupture.
Earthquakes occur in the crust or upper mantle, which ranges from the earth's surface to about 800 kilometers deep (about 500 miles). The strength of shaking from an earthquake diminishes with increasing distance from the earthquake's source, so the strength of shaking at the surface from an earthquake that occurs at 500 km deep is considerably less than if the same earthquake had occurred at 20...
The Geysers Geothermal Field is located in a tectonically active region of Northern California. The major seismic hazards in the region are from large earthquakes occurring along regional faults that are located miles away from the geothermal field, such as the San Andreas and Healdsburg-Rodgers Creek faults. However, activities associated with the withdrawal of steam for producing electric power...
Earthquakes do occur in Antarctica, but not very often. There have been some big earthquakes--including one magnitude 8.1--in the Balleny Islands (between Antarctica and New Zealand). The boundary between the Scotia Plate and the Antarctic Plate just grazes the north tip of the Antarctic Peninsula (look "northwest" from the Pole toward South America). There is also a hint of a line of seismicity...
Start with our Earthquake Hazards Education site. That includes: Earthquakes for Kids Cool Earthquake Facts Earthquake Science for Everyone Other good starting points include: State Geological Surveys for states in earthquake-prone regions The Great ShakeOut Earthquake Drills website SAGE (Seismological Facility for the Advancement of Geoscience), which is a non-profit consortium
Earthquakes induced by human activity have been documented at many locations in the United States and in many other countries around the world. Earthquakes can be induced by a wide range of causes including impoundment of reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground formations. While most induced earthquakes...
Map showing aftershock zones of great Aleutian Islands, Alaska, earthquakes in the 20th century. Red solid line with pink fill indicates aftershock zone of the 1957 Aleutian Islands earthquake from Sykes et al.
Map showing aftershock zones of great Aleutian Islands, Alaska, earthquakes in the 20th century. Red solid line with pink fill indicates aftershock zone of the 1957 Aleutian Islands earthquake from Sykes et al.
A technician installs strong motion and high frequency sensors April 11 at a station selected to record aftershock data from the April 5, 2024 Whitehouse Station, N.J. earthquake.
A technician installs strong motion and high frequency sensors April 11 at a station selected to record aftershock data from the April 5, 2024 Whitehouse Station, N.J. earthquake.
U.S. Geological Survey electronics technician Greg Tanner installs an "aftershock kit" in New Jersey April 10 following the April 5, 2024 Whitehouse Station earthquake.
U.S. Geological Survey electronics technician Greg Tanner installs an "aftershock kit" in New Jersey April 10 following the April 5, 2024 Whitehouse Station earthquake.
May 2020 earthquake swarm at Lōʻihi seamount
The inferred rupture area (white dashed line) of the May 4, 2018, magnitude-6.9 earthquake, with its foreshocks and first 10 days of aftershocks, spans an area of about 800 sq km (300 sq mi). Circle size indicates earthquake magnitude; color indicates earthquake depth. Magnitudes for some of the larger events are labeled.
The inferred rupture area (white dashed line) of the May 4, 2018, magnitude-6.9 earthquake, with its foreshocks and first 10 days of aftershocks, spans an area of about 800 sq km (300 sq mi). Circle size indicates earthquake magnitude; color indicates earthquake depth. Magnitudes for some of the larger events are labeled.
December 13 - 14, 2016 Long Valley Caldera earthquake swarm recorded on instrument MDH1 webicorder. Swarm begins at 23:28 PST.
December 13 - 14, 2016 Long Valley Caldera earthquake swarm recorded on instrument MDH1 webicorder. Swarm begins at 23:28 PST.
Aftershocks are earthquakes that follow the largest shock of an earthquake sequence. They are smaller than the mainshock and within 1-2 fault lengths distance from the mainshock fault. Aftershocks can continue over a period of weeks, months, or years.
Aftershocks are earthquakes that follow the largest shock of an earthquake sequence. They are smaller than the mainshock and within 1-2 fault lengths distance from the mainshock fault. Aftershocks can continue over a period of weeks, months, or years.