A 5.8-magnitude earthquake struck Virginia on Tuesday, with shaking felt in Washington, D.C., New York City, and all the way to New England. The East Coast doesn’t get many serious earthquakes. Are building standards more lax in Washington, D.C., than they are in San Francisco or Los Angeles?
Yes. The International Building Code’s seismic provisions apply across the United States, but the specific requirements vary based on seismic hazard maps. Using extremely detailed data on the location of fault lines, seismic history, and the composition of the earth in a particular area, the code sets a maximum acceleration that buildings in that zone must be able to withstand. The standards are meant to account for a quake so strong that it should only occur once in a 500-year period.
For the Los Angeles area, the code sets a maximum acceleration of 2.49 Gs, or 2.49 times the acceleration of gravity. The relationship between earthquake intensity and building acceleration depends on several factors, including the height of the building and the distance from the epicenter, but that kind of acceleration would likely require an earthquake of around 8.0 in magnitude. * The maximum acceleration for New York State is just 0.59 Gs. You can find the data on your location using ZIP code or longitude and latitude coordinates at the United States Geological Survey website.
What does this mean for an architect or civil engineer? Buildings must contain seismic resistance areas that can absorb the force of the maximum foreseeable earthquake. If you’re putting up a relatively short structure in New York, you might be able to satisfy that requirement by building the external walls of hollow cinderblocks stuck together with mortar. In Los Angeles, an unreinforced masonry building would never be allowed. At the very least, you’d need to run steel rails through the gaps in the cinderblocks, fill the rest of the space with mortar, and add a few horizontal steel bars across the floors of the building. In especially seismically active areas, more sophisticated design is required.
If you work in the Empire State Building or the Chrysler building and today’s earthquake has you worried, breathe easy. Skyscrapers are built to withstand high winds, which in most cases apply stronger lateral forces than any quake that’s likely to strike Gotham.
Got a question about today’s news? Ask the Explainer.
Explainer thanks Andre Filiatrault of the Multidisciplinary Center for Earthquake Engineering Research at SUNY Buffalo and Matthew Tobolski of Tobolski Watkins Engineering.
Correction, Aug. 24, 2011: The article originally referred to the Richter scale. Seismologists now prefer the moment magnitude scale, which is not equivalent to the Richter scale for large earthquakes. (Return to the corrected sentence.)