Frequently Asked Questions

Natural Hazards

The USGS monitors and conducts research on a wide range of natural hazards to help decision-makers prepare for and respond to hazard events that threaten life and property.

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New Madrid Seismic Zone
Faults vs. Fault Lines on a Map In order to answer this question, we first need to explain some basics about faults. Faults are different from fault lines. A fault is a three-dimensional surface within the planet that might extend up to the surface or might be completely buried. In contrast, a fault line is where the fault cuts the Earth's surface...
map with gray dots
Sometimes. Earthquakes, particularly large ones, can trigger other earthquakes in more distant locations though a process known as dynamic stress transfer/triggering. This means that the energy from the seismic wave passing through can cause a new earthquake, usually in vulnerable locations prone to frequent earthquakes (e.g., volcanic regions)....
Hotspots...
Most volcanic eruptions occur near the boundaries of tectonic plates, but there are some exceptions. In the interior of some tectonic plates, magma has been erupting from a relatively fixed spot below the plate for millions of years. As the plate continuously moves across that spot, a trail of progressively older volcanic deposits is left at the...
Oil production and wastewater disposal
Most induced earthquakes are not directly caused by hydraulic fracturing (fracking). The recent increase in earthquakes in the central United States is primarily caused by disposal of waste fluids that are a byproduct of oil production. Wastewater disposal wells typically operate for longer durations and inject much more fluid than is injected...
Danville CA earthquake map
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...
mud around house and car upside down
Several kinds of maps are used to depict danger from landslides. These maps might be as simple as a map that uses the locations of old landslides to indicate potential instability, or as complex as a map incorporating probabilities based on variables such as rainfall, slope angle, soil type, and levels of earthquake shaking. The following types of...
geocoded Did You Feel It? responses for a sonic boom off the coast of New Jersey on January 28, 2016
Steps to identification of a sonic boom: The USGS sees either nothing on our seismic records or a fairly short high-frequency signal  that doesn't look like an earthquake. On rare occasions, we see the event on multiple stations, and the time difference between stations matches the speed of sound in air, which is slower than the speed of...
world map showing time zones
UTC stands for Coordinated Universal Time, and for this purpose is the same as GMT (Greenwich Mean Time). Since the USGS and other seismic network agencies record earthquakes around the globe in all the various time zones, using a single standard time reference is best for record-keeping and exchange of data. Also, we tried converting Coordinated...
Large umbrella shaped cloud of volcanic ash viewed from a distance
Deadliest Volcanic Eruptions Since 1500 A.D. Eruption Year Casualties Major Cause Nevado del Ruiz, Colombia 1985 25,0001,3 Mudflows3 Mont Pelée, Martinique 1902 30,0001 (29,025)2 Pyroclastic flows2 Krakatau, Indonesia 1883 36,0001 (36,417)2 Tsunami2 Tambora, Indonesia 1815 92,0001,2 Starvation2 Unzendake, Japan 1792 15,0001 (14,030)2 Volcano...
Chaitén Volcano in Chile
Sometimes, yes. A few large regional earthquakes (greater than magnitude 6) are considered to be related to a subsequent eruption or to some type of unrest at a nearby volcano. However, volcanoes can only be triggered into eruption by nearby tectonic earthquakes if they are already poised to erupt. This requires two conditions to be met: Enough "...
Earthquake damage from the 1959 Hebgen Lake event in the Yellowston...
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. Those stresses could trigger earthquakes as...
snow-covered Mt. Hood volcano on the horizon overlooking tall building in city of Portland
Felt earthquakes on Mount Hood (Oregon) occur every two years on average. Seismic monitoring, in effect since 1977, indicates a generalized concentration of earthquakes just south of the summit area and 2-7 kilometers below sea level. A seismic swarm in July 1980, during which nearly 60 earthquakes (mostly 5-6 kilometers deep with a maximum...