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 knows for sure, but scientists speculate that these "booms" are probably small shallow earthquakes that are too small to be recorded, but large enough to be felt by people nearby.

Large sonic booms can be recorded on the seismic instruments and have lead to some interesting observations.

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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...

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...

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 of all, whether or not you...

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,...

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)

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 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.

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 earthquake magnitude reaches somewhere above 4 or 5.

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...
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Date published: August 21, 2015

South Napa Earthquake – One Year Later

One year ago, the largest earthquake in over 25 years hit the San Francisco Bay Area, causing significant damage in California’s famous Napa Valley. The magnitude 6.0 earthquake occurred early in the morning on August 24, 2014, on the West Napa Fault.

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: November 8, 2002

Shaking it Up in Alaska: ShakeMap Released for 7.9 Earthquake

A ShakeMap portraying the variations in shaking intensity from the Nov. 3, 2002, 7.9-magnitude earthquake was released today by the U.S. Geological Survey and the University of Alaska, Fairbanks.

Date published: January 16, 2001

Earthquake Shaking— Find the ’Hotspots’

In conjunction with the seventh anniversary of the 1994, 6.7 Northridge earthquake, the U.S. Geological Survey, in cooperation with the Southern California Earthquake Center (SCEC) and the National Science Foundation (NSF), has produced a two-page fact sheet that explains how geologic conditions in the Los Angeles basin affect the amount of shaking experienced by various areas of the basin.

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Damage from South Napa Earthquake
February 13, 2017

Damage from South Napa Earthquake

Damaged unreinforced masonry building on Main Street in downtown Napa, California. Photograph credit: Erol Kalkan, USGS

Image: USGS Scientist Installing Seismograph
March 17, 2015

USGS Scientist Installing Seismograph

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

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

Seismographs at the U.S. Geological Survey

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