Earthquake in Washington DC area

By Maureen Aylward

With cracks in the Washington Monument and spires and statues toppled from the National Cathedral, the US East Coast earthquake was a wake up call. We asked our Zintro experts about issues that might come up as a result of the US East Coast earthquake.

Carolyn Hunter, an architect, says that there are many known but inactive earthquake fault lines in the US that are on GIS maps; however, the local building codes and construction practices for smaller buildings and single family homes do not change until these fault lines become active. “It is important to remember that while a building’s shape, weight, material choice, and detailing can make it more earthquake resistant, there is no such thing as an earthquake-proof building,” she says. “When planning a new building or new community, the best thing to do is to choose a building site with bedrock close to the ground surface, sit the building’s foundations directly on it, and even tie into it with steel reinforcing bars.”

Hunter recalls when Valdez, Alaska was relocated after the 1965 earthquake/tsunami event: “Community leaders deliberately chose the new town site to be on a large area of bedrock. As a result, even moderate earthquakes (3 to 4 on the Richter Scale) are not very noticeable and cause no damage,” she says.

Additionally, Hunter says to avoid building on sites with large amounts of imported soils (landfills), because these amplify earthquake forces (like shaking a bowl of jello). “GIS and geology maps, available from most local planning departments, indicate fault lines (both active and inactive) and soil types, which may need interpretation with respect to behavior during a seismic event. Everyone from architects to builders to real estate agents will need to supplement their education with this topic to better advise clients on this issue, which is new to the East Coast, but familiar to the West Coast.”

Paul Selman, a mechanical engineer, says that the seismic-related building codes provide a uniform method of determining the seismic induced forces for any location. “The forces must be determined with enough accuracy to ensure a safe and economical design. All of the United States have adopted standard codes and modified applicable portions of model codes to fit their particular needs,” says Selman.

The International Building Code (IBC) was originally prepared in 1997 by five drafting subcommittees appointed by the International Code Council (ICC) and consisting of representatives of Building Officials and Code Administrators International, Inc. (BOCA), International Conference of Building Officials (ICBO), and Southern Building Code Congress International (SBCCI). The intent was to draft a comprehensive set of regulations for building systems consistent with and inclusive of the scope of the existing model codes. “The IBC is available for adoption and use by jurisdictions in the United States and internationally. The 50 states and the District of Columbia have adopted the IBC as their governing building code. Because the IBC is the dominant code for seismic and wind load design issues, a detailed review of IBC design force determination is required in order to prevent widespread seismic-related damage,” says Selman.

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