Planning June 2014

Quake Control

A status report on seismic codes.

By William Atkinson

While everyone knows about the earthquake risks in California, fewer people may be aware of similar risks elsewhere, including the Midwest. The New Madrid Seismic Zone stretches over 5,000 square miles across seven states — Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and Tennessee — with a total population of almost 10 million. Three of the most powerful earthquakes ever to occur in the Western Hemisphere happened here — in late 1811 and early 1812.

Less powerful earthquakes have occurred throughout the region since then, some of which have caused structural damage. And, according to seismologists, more earthquakes of varying magnitude are guaranteed to occur in the region in the future.

"We know for sure that large earthquakes of magnitude 7 and above have occurred in the New Madrid Seismic Zone several times over the past 1,500 years," says Gary Patterson, the executive director of the West Tennessee Seismic Safety Commission and director of education and outreach for the Center for Earthquake Research and Information at the University of Memphis.

More specifically, seismological research suggests that powerful earthquakes occur in the region roughly every 500 years. Researchers have found deposits that indicate strong earthquakes (magnitude 7 or greater) occurred in the NMSZ around AD 900 and AD 1450. And there are historical records for the 1811-1812 earthquakes.

"Each of these three sequences had at least three large earthquakes," says Patterson.

Chances are good

Given what is already known, there is a 10 percent probability of a series of magnitude 7 or greater earthquakes within 50 years. "For magnitude 6 and greater, the probability is even greater — 25 percent to 40 percent in a 50-year time window, says Patterson.

With the wide time spans between earthquakes in the NMSZ compared with those in California, for example, why should anyone worry about earthquake risk in the NMSZ? "The difference between earthquakes in the New Madrid Seismic Zone and California relates to crustal attenuation," Patterson says. In other words, an earthquake of a certain magnitude in the NMSZ will be felt over a much larger area than an earthquake of the same magnitude in California — in fact, 10 to 20 times larger.

"Earthquakes in California might be felt in a few counties," he says, whereas earthquakes of similar magnitude in the NMSZ will be felt over several states, and even as far away as Canada. "When a large earthquake occurs again in the NMSZ, there will be up to seven states and 18 major metropolitan areas in competition for resources," Patterson says. "As a result, although earthquakes in this region don't occur often, advance planning is important in order to reduce long-term physical, economic, and social consequences."

Communities anticipating these consequences are adopting seismic building codes in the NMSZ. According to a 2010 report published by the Federal Emergency Management Agency, "Building Codes in the New Madrid Seismic Zone," because such codes generally require reference to technical documents, it makes sense for states and local jurisdictions to adopt national model codes. These include the International Building Code and the International Residential Code, both of which are created by the International Code Council, and both of which have consensus-based minimum design requirements to resist seismic and other natural disasters.

According to the FEMA report, four of seven states in the NMSZ (Arkansas, Indiana, Kentucky, and Tennessee) have adopted statewide building codes as minimum requirements. The remaining three states (Illinois, Mississippi, and Missouri) expect local jurisdictions to adopt codes on their own, but under state guidance.

Here, we look at building codes in three locations in the NMSZ and the role that local planners play in relation to these codes.

Shelby County, Tennessee

"In terms of building codes, each sequence of three earthquakes is considered to be a single event, and we look at 50-year time windows, because this is the average life of a building," says Patterson.

Currently, the state of Tennessee uses the 2009 IBC. According to Patterson, as the state adopted newer versions of these codes in earlier years, Shelby County would follow suit, but the county would make modifications and allow waivers to the codes in order to help keep construction costs down — except for critical structures, such as schools and hospitals, which have always been built to the highest standards. (The city of Memphis, which is in Shelby County, coordinates with the county on building codes.)

"As a result, Shelby County has always given commercial developers the opportunity to design to the latest codes," Patterson says. However, if the developers chose not to, they could design to the ICC's 1999 Standard Building Code. The problem with this, according to Patterson, is that the 1999 code is based on seismic standards from the 1980s and 1990s. Those were based on research going all the way back to the 1950s, and therefore don't reflect the most current science.

"What has happened gradually in recent years, though, is that pretty much everyone in Shelby County understands the seismic risk and agrees that buildings need to be built with this in mind," Patterson adds. "This includes architects, commercial developers, and other contractors and builders."

As a result, in October 2012, Shelby County adopted the 2012 IBC without modifications or waivers. "This is the first time that Shelby County's building codes have been stricter than the state's building codes," Patterson says. (Adoption of the 2012 IRC is pending.) "It is very refreshing to us that administrators and planners are adopting these new codes without modifications or waivers, as has happened in the past, and which rendered the codes less effective."

However, Patterson understands the importance of codes flexible enough to avoid discouraging existing businesses from expanding or new businesses from setting up shop in the region. "We need to make sure we have a middle ground that addresses seismic risk needs without burying businesses in a bunch of paperwork and extra costs," he says.

As for planners, he adds, it is very important for them to stay abreast of the latest building codes, as well as the latest seismic research. Earthquakes can generate different frequencies of shaking, such as high frequency and rapid shaking, as well as low frequency and slower shaking. Each frequency affects different structures in different ways. High frequency shaking tends to do more damage to short structures than to tall ones.

"Scientists with the U.S. Geological Survey and academic institutions have learned that, in this region, with its large earthquakes, the higher frequency energy will be absorbed and filtered, which decreases damage to shorter buildings, as long as they are built reasonably well," he says. "What remains are the lower frequencies, which do the most damage to tall structures."

All of this research is being incorporated into the latest codes. As such, planners need to be aware of the added seismic risk to tall buildings in the NMSZ. "One benefit we have in Shelby County is that, since there is still a lot of inexpensive land, there is no need to build many tall structures," Patterson notes.

Carbondale, Illinois

Illinois lacks a statewide building code, says John Lenzini, building inspector for the city of Carbondale. "About the only code that is adopted statewide is the NFPA Life Safety Code, but this is more of a fire prevention code than a building code," he says. "As a result, it is up to each municipality to adopt its own building code."

Carbondale currently uses the 2003 version of the IBC. "We were going to adopt the 2012 version, but that included a single-family sprinkler system requirement on all new single-family homes, and we didn't feel comfortable with that requirement," he notes.

"We rely on the IBC for our seismic building codes," says development services director Chris Wallace, AICP, who oversees the city's planning and building departments. None of these codes are handled through local ordinances, he notes, although local zoning ordinances typically include setbacks — keeping buildings certain distances from property lines for fire prevention, but also providing some value in preventing earthquake damage.

Carbondale is particularly concerned with seismic protection downtown, where a number of historic buildings predate any seismic standards. "We don't require any retrofitting of these older buildings to bring them up to seismic standards," says Wallace. "However, any new buildings being built downtown, of course, need to meet the existing code."

Lenzini adds this: "For our historic downtown area, we have a Certificate of Appropriateness, which states that we want new buildings in this area to be aesthetically pleasing and fit into the overall ‘look' of the downtown area. The most desirable new buildings for this would be brick, which are nice-looking and very good for fire prevention."

However, brick is not effective for seismic resistance because it is unreinforced masonry. Today, the goal for architects is to find ways to make the brick exterior look like an older building while the structure offers more safety in terms of seismic resistance. To address this, some architects design new buildings with wood frames and shear walls, which provide seismic flexibility and strength, with brick or cultured stone veneers added for aesthetic purposes. Other options are steel construction or reinforced concrete construction, also with brick veneer.

Such requirements haven't hampered economic growth, according to Lenzini. "Architects really don't have much of a problem with these requirements, because, once you include fire resistance requirements and energy conservation codes, these types of structures are really quite effective all around," he says.

In addition, most of what gets built in Carbondale is a maximum of two or three stories. Beyond that, seismic requirements can become very complex and expensive. "Furthermore, most of the developers in this region are used to building to seismic codes, so there really isn't a lot of pushback."

Finally, according to Lenzini, these types of structures are more likely to attract new businesses and encourage existing businesses to expand, because all of the buildings in the downtown area will end up being attractive and appealing to shoppers.

Cape Girardeau, Missouri

The city of Cape Girardeau, Missouri, currently uses the 2009 IBC and is planning to adopt the 2015 version within a year. "Since we are in a seismic zone, everything that qualifies citywide must be structurally designed to be seismically resistant," says Ryan Shrimplin, AICP, city planner in the planning services division of the city's development services department, which is responsible for engineering, planning, and inspections for the city.

"Of course, anything that increases construction costs for a business tends to be frowned upon," Shrimplin adds. "For projects that are ‘on the bubble' cost-wise, such as remodeling a building in the historic district, the extra seismic construction costs may be the deciding factor."

However, since seismic requirements are regional in the NMSZ, and not limited to the city itself, Shrimplin has found that most architects, engineers, designers, and developers understand the seismic requirements, unless they are not from the region.

"Our role in the planning department is to inform the developers, property owners, or whoever is contemplating a project, to make sure they understand the considerations they are going to need to make in planning their projects, and seismic requirements are part of these," he says. "So we will explain these requirements to developers, especially those who are from out of town."

Large national companies (retailers, restaurants, and so on) generally hire designated design and construction professionals in different parts of the country, which, while they are regional, may not be based in the same states in which all of the projects occur.

"Part of the responsibility of these companies is to conduct due diligence, including finding out what the codes and other requirements are," says Shrimplin. "One thing our department explains to them, especially if they aren't located in our area, is that they will need to prepare a budget that includes designing a seismically resistant building. However, since these firms are regional, the ones in the Midwest tend to be familiar with seismic requirements in this region and often budget for it in advance."


The experts say that while planning departments may not always be responsible for enforcing local building codes, it is important for them to be aware of these codes, to provide input into them, to understand the implications of these codes for planning and building activities, and to help developers and others understand what the codes require.

Bill Atkinson is a freelance business writer who specializes in utilities, infrastructure, sustainability, and risk management.