Emergency planners and structural engineers say Tuesday's earthquake centered in Virginia served as a reminder that aging buildings carry a special public safety hazard during times of seismic activity because of the threat of falling bricks and other debris.
The 18th- and 19th-century buildings that add so much charm to towns and cities scattered along the East Coast are rarely tested by the forces that accompanied the 5.8-magnitude temblor _ much different forces than those created by the more common high winds or deep snows.
The elements that connect brick or stone facades to buildings can deteriorate over time with moisture penetration, and a good shaking can then send the material raining down on anyone unlucky enough to be standing below, said Leo Argiris, a principal in the New York consulting engineering firm Arup.
"The worst thing that happened was when everybody emptied the buildings and sat down in the street," Arup said. "You want to stay in the building."
Widespread damage from the February earthquake in Christchurch, New Zealand, showed how much damage, including building collapses, can occur when older structures are subjected to even relatively moderate seismic activity, said Dave Applegate, associate director for natural hazards for the U.S. Geological Survey.
"Shaking can shake loose parapets, brick chimneys," Applegate said. "You can get also get a lot of nonstructural damage _ what's inside the structure can cause damage, can cause injury."
Jerry Gorski, who heads a design-build contracting firm for commercial and industrial construction in Collegeville, Pa., said modern foundation systems are designed to handle seismic loads, but those forces are generally less powerful than the much more common high winds, particularly for taller structures.
"When you figure out all this stuff, the wind is going to be one of our great loads in the northeast, exceeding the seismic loads," he said.
Pennsylvania's standards for wall bracing for houses and townhouses are based on wind speed and not seismic forces, said Bob Buddenbohn, executive officer of the Pennsylvania Association for Building Code Officials, Inc.
"You see stories all the time of brick facades falling off of buildings all over New York City just from wind conditions or weather conditions having nothing to do with earthquakes," Buddenbohn said. "It has more to do with building deterioration than anything else."
These days people who design newer buildings tend to be "hyper aware" of seismic events and catastrophes such as the 9/11 events, said New York architect Frederic Schwartz, a fellow of the American Institute of Architects.
"The buildings that are at greatest risk are the old buildings that are, let's say, two to five stories that are freestanding brick buildings," Schwartz said. "Because, if you're in a row house where there's buildings next to each other in a city, those buildings help _ side-by-side _ work together to reinforce each other."
In Philadelphia, home to many of Pennsylvania's tallest buildings, including the 975-foot Comcast Center, inspectors fielded only seven calls regarding damage from Tuesday's quake, according to the city's Department of Licenses and Inspections. They all pertained to private homes, covering such minor damage as facade cracks and falling bricks. Inspectors were dispatched to those sites on Wednesday.
East Coast residents have much more to worry about from hurricanes, floods and other more common natural disasters, said Ricardo Taborda, a post-doctoral researcher in computational seismology and earthquake engineering at Carnegie Mellon University in Pittsburgh.
"Make sure you don't have loose bricks, which is something that may happen quite often," Taborda said. "Try to make sure that facade accessories are well-tied to the walls. Those are things that usually come off in earthquakes."
Retrofitting a building may be an overreaction in a part of the country that rarely sees powerful quakes, he said.
"That doesn't mean to say that if there's an inspection that shows that some particular structure needs to be taken care of, not to do it," Taborda said.
Argiris said building owners should maintain a good skin on the building, repoint the masonry and do what they can to anchor the facade. They also should be looking inside, tying down any mechanical equipment and large pipes, hanging pictures properly, connecting large bookshelves to walls and looking for whatever else might topple over during an earthquake.
Associated Press reporter Patrick Walters in Philadelphia contributed to this report.