The Earthquake Threat--How Great Is Your Risk?
- Published on Monday, 29 October 2007 00:32
Over a year has passed since the Loma Prieta earthquake struck, and repercussions can still be felt and observed in northern California. In the Midwest, Iben Browning, who predicted a quake of 7.0 or greater on the Richter scale to strike along the New Madrid fault in December, is practically a household name. The reports of death and destruction resulting from the Armenia and Philippine earthquakes were overwhelming. Finally, management is becoming persuaded that the “it will never happen to us” mentality could be the equivalent of corporate suicide. Although Browning’s credentials are questionable (he also claimed that the weather conditions caused the downfall of communism in Eastern Europe), his prediction at least proved to be the overdue catalyst for several businesses to take the earthquake threat seriously and, if they hadn’t already, initiate a plan.
With the threat of an earthquake becoming more of a tangible prospect, companies must research the probable risks for their particular regional location, and then learn to manage those risks. In the investigative process, it is necessary to both assess existing structures and retrofit them accordingly, and also to design all new structures to be able to survive the maximum potential earthquake for the location.
DETERMINE YOUR RISK
Obviously, geographical location is a large determinant of your earthquake risk. While the extreme west and Midwest are the most hazardous zones in the U.S. with the ever-present threats of the San Andreas and New Madrid faults, the rest of the country is not immune from danger; quakes causing major damage have occurred throughout the western third of the country, and smaller quakes have affected, to some degree, virtually every state in the continental U.S.
Another crucial risk factor is the vulnerability of the land at your particular location. Your hazard assessment can hardly be considered complete before you review the geography of the land on which your business is located and conduct a site survey. The geological makeup of the ground will result in different levels of potential damage during a quake. Take two phenomena that are standard in any earthquake:
This essentially defines an earthquake, and the Richter scale is used as a measurement of magnitude. So a 6.0 earthquake in California is the same as a 6.0 earthquake in Missouri, right? Not quite--that same magnitude could shake up to 10 times a greater area in the Midwest due to a different composition of the ground.
Groundmotion is a function of exposure time. The longer the duration of the quake, the better your chances for soil failure and greater structural damage. Liquefaction, an earthquake phenomenon that tends to densify soils, can cause the ground to take on qualities of quicksand if the shaking is strong enough and of sufficient duration. Prime conditions for liquefaction are flood plain soils, sandy or silty soils, shallow groundwater surfaces, and loose density of soil.
Remember, the magnitude of the earthquake alone is only one factor in the overall outcome. If the weatherman tells you it’s 35 degrees with a gusty arctic wind chill of two above, do you only account for the outside temperature before you step outside?
A final risk factor to consider is the frequency of past events at your location. In general, the trend is that events of a higher magnitude are less frequent over time.
After you have determined the earthquake risk to the best of your ability, the next step is to review design drawings of your facility (or facilities) and estimate the probable maximum loss to buildings, equipment and inventory.
When surveying your buildings and/or considering new construction, keep in mind that steel construction has proven to be the best performer in other quakes. The worst is unreinforced masonry--in this design, the walls are not well attached to the interior, causing the exterior to peel away when shaken. This invariably leads to cracking and failure of the walls and the eventual collapse of the entire building. Older non-ductile structures and concrete frame structures also tend to perform badly during earthquakes.
Your final step in the risk assessment procedure is to estimate your insurance requirements. All that this process really entails is a comparison of retrofitting/rebuilding costs to insurance costs. Depending on the outcome of your research, you may choose to go wholly with one or the other, or else try some combination of the two.
Now that you know your risks, you have to decide what to do about them. The consequences of the once-solid ground suddenly metamorphosing into quicksand can be quite dire. Expected outcomes can include landslides or lateral movements, settlement, reduction or loss of bearing capacity, increased pressure on retaining structures, and uplift of buried structures. Unfortunately, being a risk bestowed by nature, liquefaction-prone areas are not easily stabilized. However, means have been developed to increase soil density and/or strength, lower groundwater levels, and reduce buildup of pore pressure.
Mitigation techniques can be performed more easily on the actual structures that are vital to your organization. In addition to retrofitting facilities, it is also crucial to anchor equipment and brace suspended utilities.
Your underground pipe system, though unseen, is another critical component of your entire facility. During an earthquake, pipes can rupture, become misaligned, or become elevated due to ground and/or soil failure. Not only would any of these events inevitably result in grave long-term economic repercussions for your organization, but you would also find yourself without the water system needed immediately to combat fires, for sanitation, for drinking, etc.
To increase the probability of survival during a quake, design all new pipes with flexible joints and avoid sites with bad soil conditions. When retrofitting old pipe systems, you can take any or all of the following steps:
- construct protective walls around portals
- construct engineered sea walls
- check pipes for and protect from corrosion, especially at joints
- strengthen or replace the most vulnerable portions
If you will be undertaking the design of a new pipe system for your organization, take note that in the Loma Prieta quake, ductile iron pipes and asbestos cement pipes with rubber gasket joints brought in the best performance.
INDIRECT LOSSES--TRANSPORTATION SYSTEMS
Be wary of the losses that don’t immediately affect your business, for it may well transpire that destruction occurring miles from your facility may result in a devastating outcome for your organization. Highways, bridges, and airports are all susceptible to liquefaction, landslides, rupture and cracking; with bridges is the added possibility of connection failure (which occurred on the San Francisco Bay Bridge) and other structural damage; airports have the additional potential for collapse and damage of unsecured equipment as well as a loss of power and communications. As a consequence of these damages, you may find that emergency supplies are inaccessible by road or air, and you may also have no means to transport employees to and from work.
It is time that businesses come to realize that earthquakes are an omnipresent threat. The extent of your recovery from one will depend on how prepared you are, and your preparedness can only be as adequate as the time you invest in researching the geographical location of the facility as well as the ground on which it is located. If you do conduct a thorough risk assessment and retrofit program, you will find that this relatively simple process very well may be the saving grace for your business when an earthquake strikes.
Margo Young is a staff writer for the Disaster Recovery Journal.
This article adapted from Vol. 4, No. 1, p. 12.