How does the USGS tell the difference between an earthquake and a sonic boom?

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 seismic waves in rock.

  • Felt reports come from a wide area, which is typical of a fairly large earthquake, but no such event is on our records. 

  • Reports of a bang are a clue that it's a sonic boom, but not an ironclad indicator since shallow earthquakes often sound like booms or bangs.

  • All of the above indicates an atmospheric source such as a sonic boom, artillery fire, or a meteorite or bolide explosion. Bolides are often accompanied by bright light, sound, and ground motion.

  • The final step is getting the military to admit responsibility. In most cases, the best we get is a confirmation that there were planes in the area that "might have gone supersonic."

 

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What are earthquake lights?

Phenomena such as sheet lightning, balls of light, streamers, and steady glows, reported in association with earthquakes are called earthquake lights (EQL).  Geophysicists differ on the extent to which they think that individual reports of unusual lighting near the time and epicenter of an earthquake actually represent EQL

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Can you feel an earthquake if you're in a cave? Is it safer to be in a cave during an earthquake?

There is nothing different about a cave that would make it immune to the shaking from an earthquake.  Just as there are safer and less safer places to be on the surface of the earth during an earthquake, there are also various characteristics inside caves that make some cave locations safer or less safe than others.  First

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What is liquefaction?

Liquefaction takes place when loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking. Liquefaction occurring beneath buildings and other structures can cause major damage during

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Why do earthquakes in other countries seem to cause more damage and casualties than earthquakes in the U.S.?

There is more damage and more deaths from earthquakes in other parts of the world primarily because of buildings which are poorly designed and constructed for earthquake regions, and population density.

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How can an earthquake affect groundwater or changes in wells?

Groundwater levels in wells may oscillate up and down while seismic waves pass, and in some cases, the water level may remain higher or lower for a period of time after the seismic wavetrain has ended.

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What are those booms I sometimes hear before or during an earthquake?

"Booms" have been reported for a long time, and they tend to occur more in the Northeastern US and along the East Coast. Of course, most "booms" that people hear or experience are actually some type of cultural noise, such as some type of explosion, a large vehicle going by, or sometimes a sonic boom, but there have been

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At what magnitude does damage begin to occur in an earthquake?

It isn't that simple. There is not one magnitude above which damage will occur. It also depends on other variables, such as the the distance from the earthquake, what type of soil you are on, etc. That being said, damage does not usually occur until the

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What does an earthquake feel like?

The way an earthquake feels depends on where you are, where the earthquake is, and how big the earthquake is:

  • A large earthquake nearby will feel like a sudden large jolt followed quickly by more strong shaking that may last a few seconds or up to a couple of minutes if it's a rare great event. The shaking

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Date published: June 10, 2015

6 Facts about Human-Caused Earthquakes

The central United States has undergone a dramatic increase in seismicity over the past 6 years. From 1973-2008, there was an average of 24 earthquakes of magnitude 3 and larger per year. 

Date published: January 8, 2014

New Sensor Network to Detail Virginia Earthquakes

Scientists from the U.S. Geological Survey and Virginia Tech will install a 20-station seismic network in the central Virginia area beginning Jan. 8. The new sensors – each about the size of a soda can – will provide information to help the researchers study the background seismicity in the area and any continuing aftershocks of the Aug. 23, 2011 earthquake near Louisa and Mineral, Va.

Date published: March 1, 2013

"Living in Earthquake Country: Los Angeles and the Big One" - Dr. Lucy Jones presentation at LA Natural History Museum

"Living in Earthquake Country: Los Angeles and the Big One" - Dr. Lucy Jones presentation at LA Natural History Museum

Date published: August 15, 2003

Eavesdropping on the Earth: USGS Conducts Seismic Study in San Jose Area

Scientists from the U.S. Geological Survey (USGS) will be "eavesdropping" on the echoes of the earth in the West San Jose area from Aug. 19-30 to help researchers better estimate how and when the ground will shake in regional earthquakes.

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Image: USGS Scientist Installing Seismograph
March 17, 2015

USGS scientist John Hamilton installing a seismograph in the offices of the major-league soccer team San Jose Earthquakes’ new stadium.

Map showing locations of ANSS stations
November 30, 2000

Map of ANSS free-field seismic stations across the U.S. in 2016 (not shown are additional seismic instruments in buildings and other structures).  Map colors show seismic hazard across the United States derived from the National Seismic Hazard Model.  Background colors indicate the levels of shaking that have a 2% chance of being exceed in a 50-year period.  Shaking is expressed in a percentage of g, which is the acceleration of a falling object due to gravity, with red colors indicating highest shaking and thus higher hazard.  Notice the greater density of stations in regions with either higher hazard, higher risk (e.g., southern California), or both.

Image: Seismographs at the U.S. Geological Survey
October 17, 1989

Seismographs at the U.S. Geological Survey record (1) north-south horizontal, (2) east-west horizontal, and (3) vertical components of the earthquake.