If you do not know what a liquefaction zone is, then you probably are not concerned if your home is in a liquefaction zone. However, if you own a home or want to purchase a home in the San Francisco area, it may be prudent to learn about liquefaction and the dangers of living in a liquefaction zone.
What is Liquefaction?
Liquefaction occurs when loosely packed, waterlogged soil loses its strength because of strong ground shaking, such as in the event of an earthquake. The soil acts more like a fluid than a solid, which can result in substantial damage to buildings and other structures. It would be like placing a large brick in a bucket full of cake batter. In other words, if a building or home is situated in a liquefaction zone, the chance of the home “sinking” during a major earthquake increases.
Why Does San Francisco Have Liquefaction Zones?
Some of the highest hazard areas for liquefaction are areas in which fill dirt was used to create a human-made landfill in areas that were once submerged bay floors. Therefore, many of the areas along the Bay margins in San Francisco and other areas around San Francisco Bay may be at high risk for liquefaction in a major earthquake (5.5 or greater on the Richter scale). Because earthquakes in the Bay area of 5.5 or greater are common, homes that are not built on solid bedrock could be at a higher risk of damage or destruction.
Is My San Francisco Home in a Liquefaction Zone?
If you are concerned that your San Francisco home might be in a liquefaction zone, you can check the updated Seismic Hazard Zone Map maintained by the California Geological Survey.
By entering your home address, you can check to see if your home is within one of the CGS’s mapped earthquake hazard zones or if your home lies within an area that has not been evaluated yet by the CGS. The map indicates if a property lies within a zone that could be at risk for fault rupture, liquefaction, and/or earthquake-induced landslides.
According to the map, areas that may be at risk of liquefaction caused by an earthquake include:
- South Beach
- Treasure Island
- Most of SoMa
- The Marina area
- Ocean Beach
- The Financial District
- Hunters Point
- India Basin
- Candlestick Point
- The East Cut
- A large section from San Francisco International Airport through most of San Jose and Santa Clara along the Peninsula and South Bay
- Also, some portions of the Mission, Ingleside Terraces, the Castro, the Haight, San Francisco State University, and Miraloma
Can I Protect My San Francisco Home from Liquefaction?
There are steps that a homeowner can take to retrofit a house to withstand the effects of liquefaction. However, for many homeowners, the retrofitting expense is too costly. While the retrofitting methods used vary depending on the home and the soil beneath the home, retrofitting for liquefaction typically involves soil excavation, compacting, and home foundation improvements. The law firm of Panish Shea & Boyle recommend that if you are going to take on retrofitting your house, you need to make sure that the parties working on it are insurance so you are not liable.
Homeowners may want to consider purchasing earthquake insurance that covers damage caused by liquefaction. You can read information about earthquake insurance online from the California Department of Insurance.