How does the USGS tell the difference between an earthquake and a sonic boom?
Steps to identification of a sonic boom:
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The USGS sees either nothing on our seismic records or a fairly short high-frequency signal that doesn't look like an earthquake.
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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.
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Felt reports come from a wide area, which is typical of a fairly large earthquake, but no such event is on our records.
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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.
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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.
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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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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 depends on other variables, such as the distance from the earthquake, what type of soil you are on, building construction, etc. That being said, damage does not usually occur until the earthquake magnitude reaches somewhere above 4 or 5. Learn more: Glossary of earthquake terms Earthquake Magnitude, Energy Release...
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 will feel violent and it will be difficult to stand up. The contents of your house will be a...
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 many reports of "booms" that cannot be explained by man-made sources. No one...
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.
How does an earthquake affect groundwater levels and water quality in wells?
Groundwater levels in wells can oscillate up and down when seismic waves pass. The water level might remain higher or lower for a period of time after the seismic waves end, but sometimes a long-term offset of groundwater levels follows an earthquake. The largest recorded earthquake-induced offset in a well is a one meter rise. Water quality can also be affected by earthquakes, typically in...
Where can I find photographs of earthquake damage?
Two sources for photographs that show earthquake damage are: Earthquake Hazards Program - Earthquake Photo Collections U.S. Geological Survey Photographic Library (see 'earthquakes' in the categories left column)
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 earthquakes. For example, the 1964 Niigata earthquake caused widespread liquefaction in Niigata, Japan which destroyed many buildings. Also, during the...
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 safe 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 of all, whether or not you feel an earthquake in a cave depends chiefly upon...
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: some doubt that any of the reports constitute solid evidence for EQL...
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- FAQ
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 depends on other variables, such as the distance from the earthquake, what type of soil you are on, building construction, etc. That being said, damage does not usually occur until the earthquake magnitude reaches somewhere above 4 or 5. Learn more: Glossary of earthquake terms Earthquake Magnitude, Energy Release...
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 will feel violent and it will be difficult to stand up. The contents of your house will be a...
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 many reports of "booms" that cannot be explained by man-made sources. No one...
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.
How does an earthquake affect groundwater levels and water quality in wells?
Groundwater levels in wells can oscillate up and down when seismic waves pass. The water level might remain higher or lower for a period of time after the seismic waves end, but sometimes a long-term offset of groundwater levels follows an earthquake. The largest recorded earthquake-induced offset in a well is a one meter rise. Water quality can also be affected by earthquakes, typically in...
Where can I find photographs of earthquake damage?
Two sources for photographs that show earthquake damage are: Earthquake Hazards Program - Earthquake Photo Collections U.S. Geological Survey Photographic Library (see 'earthquakes' in the categories left column)
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 earthquakes. For example, the 1964 Niigata earthquake caused widespread liquefaction in Niigata, Japan which destroyed many buildings. Also, during the...
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 safe 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 of all, whether or not you feel an earthquake in a cave depends chiefly upon...
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: some doubt that any of the reports constitute solid evidence for EQL...
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