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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Image: Closeup of the San Andreas Fault
Seismologists evaluate the hypocenter location and the focal mechanism of an earthquake to decide if the earthquake occurs on a named fault. Research shows that many earthquakes occur on small, un-named faults located near well-known faults. For example, most of the aftershocks of the 1989 M6.9 Loma Prieta earthquake occurred on small, subsidiary...
Earthquake Catalog Map Results Example
The USGS and networks contributing to the Advance National Seismic System (ANSS) take great effort to provide accurate and timely earthquake information. Occasionally our systems produce erroneous information that is released to the public via our web pages or Earthquake Notification System. These mistakes are generally promptly identified by...
Latest Earthquakes Interface
The maps and lists show events which have been located by the USGS and contributing agencies within the last 30 days. They should not be considered to be complete lists of all events in the US and adjacent areas and especially should not be considered to be complete lists of all events M4.5+ in the world. In most cases, we locate and report on...
“Did You Feel It?” community intensity map indicating the severity of shaking felt by people in central California during the So
Report an earthquake experience or related observation through the Did You Feel It? citizen science webpage. The best way to do this is to click on the earthquake that you think you felt on one of the lists on the Earthquakes webpage, and then select the "Tell Us!" link. If you don't see the earthquake you think you felt, use the green "Report an...
Latest Earthquakes Interface
The Earthquake Hazards Program Latest Earthquakes Map displays earthquakes in near-realtime and up to the past 30 days of earthquakes. The interface includes three panels: a list of earthquakes, a map, and a settings/options panel. You can pan and zoom the map to view specific areas. Click on an event on the list or map for additional information...
aerial photograph of steaming & smoking lava lake. Orange lava is visible through cracks & spatter in the lake's black crust.
Ninety-nine percent of the gas molecules emitted during a volcanic eruption are water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2). The remaining one percent is comprised of small amounts of hydrogen sulfide, carbon monoxide, hydrogen chloride, hydrogen fluoride, and other minor gas species. Learn more: Volcanic Gas
scientist with camera and spectrometer at the edge of smoking volcanic crater.
The U.S. Geological Survey's Hawaiian Volcano Observatory (HVO) determines the amount and composition of gases emitted by Kīlauea Volcano. Changes in gas emissions can reveal important clues about the inner workings of a volcano, so they are measured on a regular basis. HVO scientists use both remote and direct sampling techniques to measure...
Ferns outside of Thurston Lava Tube, Hawaii Volcano National Park
The sulfuric acid droplets in vog have the corrosive properties of dilute battery acid. When vog mixes directly with moisture on the leaves of plants it can cause severe chemical burns, which can damage or kill the plants. Sulfur dioxide (SO2) gas can also diffuse through leaves and dissolve to form acidic conditions within plant tissue. Farmers...
USGS
On September 10, 1996, the United Nations General Assembly voted 158-3 to approve a treaty prohibiting all nuclear tests. The Comprehensive Test Ban Treaty has been signed by 130 nations - including the United States. President Clinton signed the agreement on September 24, 1996. Seismology is one of several fields which plays a role in monitoring...
Seismic refraction source explosion
No. Even huge amounts of explosive almost never cause even small earthquakes, and it would take hundreds and thousands of small earthquakes to equal a large one, even if it could be done. In addition, we wouldn't have any control over the size of the earthquake being created if it worked, since small and large earthquakes all start out in exactly...
Screen shot of earthquake mapper.
Explosions and earthquakes both release a large amount of energy very quickly, and both can be recorded by seismic instruments. However, because the forces involved in each are very different, the waveforms that each creates look different.  Nuclear tests are very near the surface of the earth; all of the energy is released from a small volume...
Image: Ground Photo of Fault
A nuclear explosion can cause an earthquake and even an aftershock sequence. However, earthquakes induced by explosions have been much smaller than the explosion, and the aftershock sequence produces fewer and smaller aftershocks than a similar size earthquake. Not all explosions have caused earthquakes. The range of a possible earthquake...