By Ann Robinson and Annie Vernon
Northern Utahns know California is not the only earthquake country in the western United States. Even though we are not confronted with catastrophic earthquakes every day here in the Wasatch Front, we know the risk is there.
According to the Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings, “Utah experiences about 700 earthquakes every year, with about 13 measuring 3.0 or above on the Richter scale. A moderate, potentially damaging earthquake has a magnitude ranging from 5.5 to 6.5, and one occurs in Utah about every seven years. A large earthquake (magnitude 6.5 to 7.5) occurs about once every 300 to 400 years. The probability of a large earthquake occurring along the Wasatch Fault during the next 50 years is about 1 in 5 or a 20 percent chance this will happen.”
The front of this California home collapsed in the Coalinga earthquake of May 2, 1983. Older houses surrounding the downtown area were badly damaged.
Most of us are at least minimally prepared for this probable disaster. But what happens after the 72-hour kit is empty if we have nowhere to live? Is there anything we could do to prepare our homes to survive an earthquake?
Sorry to say, there is no simple answer. Ultimately, it depends on the severity of the earthquake. There are ways to fortify our homes against a 5- or 6-magnitude quake, but anything larger may be untenable. It is important to understand that the purpose of a seismic upgrade is not to “earthquake proof” a home, but to focus on safety. The primary goal is to keep the building from collapsing and injuring or killing someone, while minimizing damage to the home is secondary.
Even with the benefits of a seismic upgrade, the outlay may be hard to justify when there is no assurance that we will need it during our lifetimes. Like any form of insurance, it is a gamble. Obviously, it makes sense to address seismic issues when adding on or remodeling your home and, in fact, the International Residential Code and municipal officials will require you to do this. It minimizes the labor costs for a seismic upgrade if you do it when you add on or reconfigure parts of your home.
The Uniform Building Code added seismic regulations in 1970, so a home built before that may or may not include structural considerations for earthquakes. Some home types are more resilient than others. A home’s shape, height, materials, and construction techniques are important risk factors when considering the potential for earthquake damage.
In the next few weeks, we will discuss how to evaluate your home in terms of structural risk as well as what steps to take to diminish the risk. Since knowledge is power, let’s try to equip ourselves to make educated judgments on this difficult subject. As always, we welcome your home architect design questions at firstname.lastname@example.org.