What is the difference between aftershocks and swarms?

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.

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Do earthquakes occur in Antarctica?

Earthquakes do occur in Antarctica, but not very often. There have been some big earthquakes--including one magnitude 8 --in the Balleny Islands. 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...

Where can I find earthquake educational materials?

The USGS has earthquake education resources on several websites: Earthquakes for Kids Topics for Earthquake Education USGS Resources for Teachers Other good starting points include: State Geological Surveys for states in earthquake-prone regions The Great ShakeOut Earthquake Drills website IRIS (Incorporated Research Institutions for Seismology),...

Can we cause earthquakes? Is there any way to prevent earthquakes?

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...

What is surface faulting or surface rupture in an earthquake?

Surface rupture occurs when movement on a fault deep within the earth breaks through to the surface. NOT ALL earthquakes result in surface rupture.

At what depth do earthquakes occur? What is the significance of the depth?

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 500km deep is considerably...

Why are there so many earthquakes in the Geysers area in Northern California?

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...

What is an earthquake and what causes them to happen?

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...

Foreshocks, aftershocks - what's the difference?

"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...

Can the position of the moon or the planets affect seismicity? Are there more earthquakes in the morning/in the evening/at a certain time of the month?

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...
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Date published: December 10, 2018

A closer look at the 2017 Maple Creek earthquake swarm

In June of 2017, an earthquake swarm began beneath the western edge of Yellowstone National Park, just east of Hebgen Lake. This swarm proved to be one of the more persistent swarms observed in Yellowstone, with the main episode lasting more than 3 months and producing thousands of recorded earthquakes.

Date published: May 12, 2015

Magnitude 7.8 Earthquake in Nepal Aftershocks

A magnitude 7.8 earthquake struck Nepal on April 25, 2015 at 06:11:26 UTC. Visit the USGS event page to learn more about this earthquake.

Date published: February 10, 2015

Virginia Earthquake Aftershocks Identify Previously Unknown Fault Zone

RESTON, Va.-- Aftershocks from the 2011 Virginia earthquake have helped scientists identify the previously unknown fault zone on which the earthquake occurred.

Date published: September 26, 2012

Rare Great Earthquake in April Triggers Large Aftershocks All Over the Globe

MENLO PARK, Calif. — Large earthquakes can alter seismicity patterns across the globe in very different ways, according to two new studies by U.S. Geological Survey seismologists. Both studies shed light on more than a decade of debate on the origin and prevalence of remotely triggered earthquakes.

Date published: October 1, 2011

A Gassy Link to Past Earthquake Swarm

Over the past three years we've witnessed two large earthquake swarms at Yellowstone (2010 and 2009). Recent history tells us that these earthquake swarms are common, but we would like to know how frequently they have occurred in the more distant past. USGS researcher Bill Evans may have found an answer.

Date published: May 3, 2004

2004 Yellowstone Earthquake Swarm

In April 2004 there was an increase in earthquake activity at Yellowstone National Park that drew interest from scientists and the public.

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Danville CA earthquake map
February 28, 2018

Map of earthquake swarms in the San Ramon valley since 1970

Map of earthquake swarms in the San Ramon valley since 1970. The current 2018 sequence is shown by the red dots. The dot sizes scale with earthquake magnitude.

Attribution: Earthquake Hazards
Foreshocks, mainshocks, and aftershocks - oh, my!...
February 26, 2017

Foreshocks, mainshocks, and aftershocks - oh, my!

The graph shows the daily number of aftershocks (as of November 12) for the October 15, 2006 M6.7 Kiholo Bay earthquake. Note the exponential decay in activity.

Nevada Earthquake Swarm December 28, 2016...
December 28, 2016

Nevada Earthquake Swarm Dec. 28, 2017

Satellite image of the Aurora-Bodie Volcanic Field with December 28, 2016 Nevada earthquake swarm locations.

Map showing aftershocks of 7.8 earthquake in Oaxaca, Mexico

Oaxaca, Mexico earthquake aftershock sequence

Aftershock sequence from the M7.8 Oaxaca, Mexico earthquake on February 16, 2018. The blue circle is the mainshock and the gray and white smaller circles are the aftershocks through April 3, 2018.

Attribution: Earthquake Hazards