Preparing Your Home for an Earthquake (Full story)
9 Tips for Preparing for the Big One
Roughly 50 miles west of Washington State, under thousands of feet of chilly green Pacific Ocean water, lies the Cascadia subduction zone where the dense Pacific plate dives underneath the lighter North American plate. Running a distance of over 1000 kilometers from northern Vancouver Island, BC to northern California, this massive fault is storing energy as the plates rub and chafe against each other. A sudden release of this stored energy has the potential to unleash a “megathrust” earthquake along the North American west coast, an alarming event for which we are distinctly unprepared.
The Cascadia subduction zone, along with several other notable large faults in the region, puts Seattle in the D2 earthquake zone for building design criteria. This is helpful if you are buying or building a new home. Unfortunately, many of our older buildings and infrastructure were not designed for such an event.
This article will discuss basics about seismic codes and help you to see potential weaknesses in your own home as they relate to seismic preparedness. It will also provide a few practical tips on how to prepare yourself and your house for The Big One.
Was Your Home Built to Seismic Codes?
If your home was built in the last 40 years or so, it should be built to some version of a seismic code and should be better prepared to resist catastrophic failure than an older building. However, as you will learn, even owners of modern homes can make their homes safer.
If you have an older home, I would consider performing some amount of seismic retrofitting work. Generally, the older the home, the less it was designed to resist the forces of a seismic event.
Seismic Codes and Retrofitting
It is important to understand that seismic codes are designed to protect people inside of buildings; they do not result in earthquake proof houses. Structures built to modern seismic codes should be able to resist small and moderate earthquakes with little to no damage and should resist catastrophic failure in even the largest earthquakes. Seattle’s D2 seismic design criteria is one notch below the most stringent standard of E. If you live outside of Seattle and are wondering what category your area falls into, check out this map from the National Earthquake Hazards Reduction Program (NEHRP).
In addition to prescribing design criteria for structures to resist failure in a seismic event, seismic codes also recommend the installation of advanced safety features that can prevent mundane house systems from becoming lethal or destructive in an earthquake. In Seattle, this includes strapping the hot water heater to the wall with listed seismic restraints, but interestingly, it does not include installing seismic protection for your gas meter or propane tank; presumably these precautions will become code after the earthquake.
9 Things to Check on Your House
Below is a short list of seismic design features you can check for on your house. Remember that comprehensive seismic designs are complex; you can quickly find yourself in a gray area regarding how far to go in seismically retrofitting your house. This article is just a brief overview. If you are interested in more detailed information, I recommend consulting with a local contractor who specializes in seismic retrofitting. The Homebuilder’s Guide to Earthquake-Resistant Design and Construction is also a great resource and is available for free on-line.
- Water heater. Secure your water heater with strapping (here’s a Youtube video explaining how to check). If your water heater is knocked down it can create water damage and a serious safety hazard with scalding water and disconnected electric or gas lines. This is required for all homes located in a D2 seismic design category.
- Gas meter. Install an earthquake gas shut off valve (like this one). These are currently not required in Washington State but help to protect against gas leaks when pipelines rupture.
- Propane tank. If you have one be sure it has some type of restraint or anchoring system. This is also not required in Washington State but will protect your tank from falling over and causing an explosion or a propane leak.
- House Foundations. Install positive connectors at the joints where posts meet beams and beams meet footings. This is often very inexpensive (the low-hanging fruit of retrofitting) and can greatly strengthen the house. Homes built in the last 25 years will have this, as it is part of modern code. The Eichler Network offers more information on seismic retrofitting.
- Foundation to Frame. Connect the wood frame of your house to the foundation so the house will not be thrown off the foundation. This is typically done with lag bolts and washers but there are also some neat metal plates that can be used for retrofitting. (This is part of the modern code in D2 areas).
- Pony walls. Where you have exposed pony walls (the short wood framed walls between your foundation and the floor joists on your first floor), use plywood as a sheer wall to strengthen this wall. (Modern code in D2).
- Foundations. If you have a post and pier, masonry block, stone or brick foundation, consult with a qualified contractor about options for strengthening the foundation. One great option is installing a redundant post and beam system adjacent to a humble foundation, creating a wooden backup support structure in case the old foundation fails.
- Generators. Lots of people ask me about generators: If you want a reliable generator system to help you after a severe earthquake, consider propane as a fuel source with your own tank. Here are three reasons:
- It is easier to store propane than gas because gasoline goes bad quickly.
- It is physically hard and dangerous to have too many gasoline cans around your house.
- The natural gas lines will likely be disrupted.
- Secure Large Objects Inside Your House. Large TV sets, bookshelves and heavy framed artwork can become lethal in a substantial earthquake. Use restraints to secure these large heavy items to walls or floors or ceilings to protect the people inside your house.
What to have on hand to be prepared for an earthquake
- Flashlights and fresh batteries for every member of the family.
- A battery operated radio.
- Talk about “safe places” in the house if there is a warning time.
- At least two weeks food and water. According to the World Health Organization, short-term survival requires a minimum of ½ gallon of water per day, per person. For a family of four, this would be 28 gallons…. Yes, that’s almost six, five-gallon buckets!
- Be sure you have some backup means of preparing your food. Assume that electricity and gas will both be off. Camping gear such as tents, sleeping bags, and stoves make great backup survival equipment.
What to Plan
- Have an out-of-state contact that every member of your family can contact as a mutual check-in point. Local phone systems could be down for a long time.
- A first aid kit and basic tool kit in a convenient location.
- Know where the breaker box and gas and water shut off valves are (and how to turn them off).
- If you live or work in a low-lying area, have a plan for getting to high ground as soon as possible, in case there is a tsunami that follows the earthquake.
I hope this brief article helps you better prepare for the big one and I hope we are not around to find out if all your preparation was helpful!