Earthquakes at Yellowstone
From 1,500 to 2,500 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 earthquakes of magnitude 3 to 4 are felt by people inside and ouside the park.
Although rising magma and hot-ground-water movement cause some earthquakes, many occur as the result of Basin and Range extension of the western U.S. This tectonic environment has created a series of regional faults that are responsible for large and devastating earthquakes in the Yellowstone region along the Teton and Hebgen Lake Faults. Most recently, a devastating Mw 7.3 (Ms 7.5) earthquake in 1959 killed 28 people and caused $11 million in damage (1959 dollars). The majority of the damage occurred as a result of a large 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.
Earthquakes cannot be predicted yet, but modern surveillance conducted with seismographs (instruments that measure earthquake locations and magnitudes) and Global Positioning System (GPS) instruments that measure slow ground movements help scientists understand the state of stress in the Earth's crust that could trigger earthquakes as well as magma movement.