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 1989 Loma Prieta, California earthquake, liquefaction of the soils and debris used to fill in a lagoon caused major subsidence, fracturing, and horizontal sliding of the ground surface in the Marina district in San Francisco.

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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...

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.

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"...

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: May 19, 2016


Just as loose lips sink ships, loose soils can create this week’s EarthWord...

Date published: January 27, 2009

New Maps Identify Liquefaction Hazard in Santa Clara Valley

New hazard maps that describe the probability of earthquake-induced liquefaction in Northern Santa Clara Valley are now available from the U.S Geological Survey (USGS.)

Date published: February 24, 2006

New Maps Identify Bay Area Liquefaction Risk

Two new maps give first responders, land use planners, decision makers and Bay Area residents a new and more detailed look at the risk of "liquefaction" in the soils underlaying buildings and other important components of the Bay Area infrastructure, such as roads and pipelines.

Date published: December 16, 1996

USGS Researcher Introduces New Method To Assess Potential Losses From Liquefaction During Earthquakes

A new method of assessing the danger of ground failure due to soil liquefaction during an earthquake made its debut in San Francisco, Tuesday afternoon, December 17.

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Image shows sediments in California after the Loma Prieta earthquake
May 19, 2016

Loma Prieta Liquefaction

Liqufaction from the 1989 Loma Prieta Earthquake in California. Credit: J. Tinsley, from U.S. Geological Survey.

February 25, 2016

The Gold Rush and the 1906 Earthquake

The Gold Rush and the 1906 Earthquake: How they combined to create the breakthrough discovery of modern seismic science

  • Accidents of Gold Rush merchant marine navigation transformed a seismic disaster into a seminal discovery and led to San Francisco's extreme liquefaction vulnerability today.
  • Just about everything that we love about the Bay area is
Image: Liquefaction in Subsurface Layer of Sand
October 17, 1989

Liquefaction in Subsurface Layer of Sand

Ground shaking triggered liquefaction in a subsurface layer of sand, producing differential lateral and vertical movement in a overlying carapace of unliquified sand and silt, which moved from right to left toward the Pajaro River. This mode of ground failure, termed "lateral spreading," is a principal cause of liquefaction-related earthquake damage.

Image: "Sand Boil" on Bay Bridge
October 17, 1989

"Sand Boil" on Bay Bridge

"Sand boil" or sand volcano measuring 2 m (6.6 ft) in length erupted in median of Interstate Highway 80 west of the Bay Bridge toll plaza when ground shaking transformed loose water-saturated deposit of subsurface sand into a sand-water slurry (liquefaction). Vented sand contains-marine shell fragments.

Image: Liquefaction in Deposits of River
October 17, 1989

Liquefaction in Deposits of River

Liquefaction in recent deposits of the Pajaro River formed sand volcanoes along a fissure 6-7 m (19.7-23 ft) long. Variation in grain size and partial erosion of the conical deposits of sand show that venting of the slurry of sand and water was a complex series of depositional and erosional events triggered by the main shock and renewed in some instances by principal

Image: Liquefaction in Deposits of River
October 17, 1989

Liquefaction in Deposits of River

Liquefaction in recent deposits of the Pajaro River formed these sand volcanoes along extensional fissures in a field prepared for autumn planting near Pajaro, across the Pajaro River from Watsonville. Furrows are spaced about 1.2 m (4 ft) apart.

Image: Liquefaction in Deposits of River
October 17, 1989

Liquefaction in Deposits of River

Liquefaction in recent deposits of San Lorenzo River caused cracking and differential settling of river levee southeast of Riverside Avenue Bridge. Bridge piers and the north abutment area were also damaged by liquefaction.