Last month’s earthquake exceeded the design standards of the North Anna nuclear plant, the Associated Press reports. That came out after a Nuclear Regulatory Commission inspection of the plant, using USGS data. That’s based not on the magnitude of the quake, but based on the peak ground acceleration (PGA)—the measurement of how hard and fast the ground was shaking at the plant. You can see that on the USGS’ “shakemap” of the earthquake. PGA varies enormously, based on distance from the quake, soil makeup, and other factors. It’s measured in G-force, a term that you’ll have heard in the descriptions of the forces on fighter pilots when pulling sharp turns, or on astronauts upon launch. Lake Anna was constructed to withstand 0.12–0.18g, but the 5.8 earthquake caused peak ground movement of 0.26g, substantially more than the designed limits of the reactor.
The plant remains closed, as it has been since the August 23 earthquake. The NRC says that it suffered “minor” damage, but no specifics have been provided.