If you live or work in the Marina, SOMA, FiDi, the Mission, Mission Bay, Dogpatch, or Hunter's Point, you likely do.
San Francisco's coastline looks different now than it did 150 years ago. As SF developed and grew, the city expanded our scraggly bay coastline into a smooth, straight line. We reclaimed land from the Bay, building docks and piets, offices and apartments. Take back the land! Eminent Domain! The Pioneer Spirit!
All good things, but parts of modern San Francisco are now built on what is essentially landfill. Parts of the Marina, for example, were created when a lagoon was filled with dune sand and building rubble from the Great San Francisco Earthquake of 1906 to create space for the Panama-Pacific International Exposition. Mission Bay was previously an actual bay, until the city filled it in to expand the city. The area previously known as the Barbary Coast in the Financial District is located a half-mile from today's coastline. Those filled-in parts of the city are built on soil that isn't as densely packed, so they are much more susceptible to damage. When this soft soil starts moving during an earthquake, it becomes like quicksand (liquefaction) and can shift the the structural integrity of buildings, and lead to water and gas pipes bursting.
If you live in one of these areas, it is even more important that you are prepared to act quickly, and potentially evacuate your building quickly. I have the Earthquake Bag underneath my bed because it has everything I need to get out of my building in under a minute. I want to know I'll have food and water, an emergency radio, first aid kit, tools for evacuating, helping others evacuate, and surviving the first few days after the next major earthquake. Take a look at the map and find where you live and work...
What is liquefaction? It's when the strength and stiffness of a soil is reduced by earthquake-shaking or other rapid loading. It occurs when the space between individual particles of soil is filled with water, exerting a pressure on the soil that influences how tightly the particles are pressed together. Prior to an earthquake, the water pressure is relatively low. However, the shaking can cause the water pressure to increase to the point where the soil particles move easily with respect to each other (imagine shaking a bowl of oatmeal).
Liquefaction has been responsible for tremendous amounts of damage during earthquakes around the world, and in the Bay Area. The 1989 quake devastated the Marina in particular because of it's composition, and led to 1990 Seismic Hazards Mapping Act, requiring the California Geological Survey to map and publish liquefaction risk areas. Knowing is half the battle, and it's allowed us to fortify the buildings that are in the most compromising locations.
That's why my favorite thing about the Earthquake Bag is the survival guide that comes with it. It has emergency contact sheets, instructions of how to turn of gas lines, and a cheat sheet for how to approach any emergency situation.
Whether you live in a liquefaction risk area or not, make sure that you have the tools you need, food and water, and a plan by the door or under the bed. We know San Francisco will experience major earthquakes again, and we are smart enough to be prepared for whatever happens.
-the Earthquake Bag team