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.
Debris flows are fast-moving landslides that are particularly dangerous to life and property because they move quickly, destroy objects in their paths, and often strike without warning. They occur in a wide variety of environments throughout the world, including all 50 states and U.S. Territories. Debris flows generally occur during periods of...
The USGS issues ShakeAlert® Messages but alert delivery will come by other public and private means (internet, radio, television, cellular), including Wireless Emergency Alerts (WEA) -- think of an AMBER Alert -- delivered by FEMA’s Integrated Public Alert and Warning System (IPAWS). Alert delivery via the WEA system is available in California,...
In addition to naturally occurring earthquakes, human activities such as mining and construction blasts can sometimes produce seismic waves large enough to be detected on the USGS national seismic network. These artificially-generated events have a different seismic ‘fingerprint’ from tectonic earthquakes, so they can be discerned by a...
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...
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)....
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...
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...
For the automated naming of earthquakes we use a GeoNames dataset to reference populated places that are in close proximity to a seismic event. GeoNames has compiled a list of cities in the United States where the population is 1,000 or greater (cities1000.txt). This is the primary list that we use when selecting nearby places. In order to provide...
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...
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...
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...
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. The individual event pages with...