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From 1,000 to 3,000 earthquakes typically occur each year
within Yellowstone National Park and its immediate surroundings. Although most
are too small to be felt, these quakes reflect the active nature of the
Yellowstone region, one of the most seismically active areas in the United
States. Each year, several quakes of magnitude 3 to 4 are felt by people in the
park.
Although some quakes are caused by rising magma and
hot-ground-water movement, many emanate from regional faults related to crustal
stretching and mountain building. For example, major faults along the Teton,
Madison, and Gallatin Ranges pass through the park and likely existed long
before the beginning of volcanism there. Movements along many of these faults
are capable of producing significant earthquakes. The most notable earthquake in
Yellowstone’s recent history occurred in 1959. Centered near Hebgen Lake, just
west of the park, it had a magnitude of 7.5. This quake caused $11 million in
damage (equivalent to $70 million in 2005 dollars) and killed 28 people, most of
them in a landslide that was triggered by the quake.
Geologists conclude that large earthquakes like the
Hebgen Lake event are unlikely within the Yellowstone Caldera itself, because
subsurface temperatures there are high, weakening the bedrock and making it less
able to rupture. However, quakes within the caldera can be as large as magnitude
6.5. A quake of about this size that occurred in 1975 near Norris Geyser Basin
was felt throughout the region.
Even distant earthquakes can affect Yellowstone. In
November 2002, the magnitude 7.9 Denali Fault earthquake struck central Alaska,
1,250 miles (2,000 km) northwest of Yellowstone. Because this quake’s energy was
focused toward the active Yellowstone volcanic and hydrothermal system, it
triggered hundreds of small earthquakes there. The region’s hydrothermal system
is highly sensitive to quakes and undergoes significant changes in their wake.
Earthquakes may have the potential to cause Yellowstone’s hot-water system to
destabilize and produce explosive hydrothermal eruptions.
The above text is from the USGS website.
February 2005 Yellowstone Seismicity Summary
During the month of February 2005, 61 earthquakes were located in the
Yellowstone region. The largest of these shocks was a magnitude 2.8 on February
22, 2005 at 6:49 PM MST, located about 9.1 miles north northwest of Madison
Junction, Wyoming. No earthquakes in this period were reportedly felt.
Earthquake activity in the Yellowstone region is at relatively low background
levels.
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