Author: Emerson Lynch
Liquefaction is what happens when the ground acts like quicksand during an earthquake.
Material that is grainy and not well consolidated (like sandy soil) can hold a lot of water in pore spaces (or spaces in between the grains). When earthquake waves move through this material, it shakes, and the pressure of the water in the pore spaces pushes the grains apart and causes the material to liquefy.
Where does liquefaction happen?
Liquefaction happens where there is:
1. Loose, granular sediment that is
2. Saturated with water
3. Strong shaking
In other words, liquefaction can happen:
- Near rivers
- At beaches
- In areas built out over water
- In filled swamps or wetlands
Could liquefaction happen in Boston?
Yes! During the 1744 earthquake in Newburyport, MA, liquefaction caused multiple sand blows in southern New Hampshire and northern Mass.
(image from the Northeast States Emergency Consortium).
While the likelihood of an earthquake is not very high in New England [see Earthquakes in Boston, and Historical New England Earthquakes], the potential damage from liquefaction is high in areas that are poorly consolidated and saturated with water, like areas built on artificial fill such as Back Bay, a neighborhood near Boston University, which used to be an actual bay before it was filled with trash, mud from South Bay, and gravel from Needham, Mass.
Here in Boston, artificial fill makes up a lot of the city – over 5,000 acres! The areas filled between 1630 and 1995 are in light green in the map below:
(image adapted from National Geographic)
Any buildings built on artificial fill could be severely damaged by liquefaction, such as this apartment complex in Niigata, Japan after an earthquake in 1964:
A study conducted in 2004 looked at liquefaction hazard in the Greater Boston Area. Take a look at the map on page 52 to see if your house is at risk!
Explore liquefaction further!
Learn more about earthquakes and hazards in New England here:
Text modified from IRIS: www.iris.edu/hq/educational_resources and NatGeo: https://news.nationalgeographic.com/2017/06/Boston-landfill-maps-history/
Niigata image: https://www.geological-digressions.com/liquefaction-more-than-an-interesting-phenomenon/