The tenth anniversary of the most widespread US earthquake – Homeland Security today

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Ten years ago, in the early afternoon of August 23, 2011, millions of people across the eastern United States felt the shaking from a 5.8-magnitude earthquake near Mineral, Virginia. No lives were lost, which experts called “lucky” given the extent of the shaking, but property damage was estimated at $200-300 million.

Although it is not the most powerful earthquake that has ever occurred in the eastern United States, let alone the western United States, it is likely that more people have felt the Virginia earthquake than any other earthquake in North American history. This is due to the large distances at which people felt the shaking of the earth and due to the density of the population in the eastern United States

“The 2011 earthquake in Virginia was important in raising awareness of East Coast earthquake hazards and the importance of research to understand when and where earthquakes can occur,” said David Applegate, associate director of the USGS Natural Hazards. from the outlet. “Destructive earthquakes do not strike the eastern United States very often, but the potential consequences of not understanding and planning for such events with their widely spread vibrations may be severe. The next major earthquake may not occur on the eastern United States fault for hundreds of years, but there is little possibility happen at any time.”

Scientific studies by the USGS and its partners played an important role in helping to prepare for and respond to this earthquake. The USGS is the federal government’s lead agency for assessing seismic risk before, during, and after earthquakes, and provides critical information used to reduce risks to life and property nationwide. Over the past decade, scholars have continued to build on their knowledge of earthquakes in the eastern United States, with a particular focus on what can be learned from the Virginia earthquake.

“One of the remarkable things we’ve discovered is the intense shaking of the ground in Washington, D.C., which has caused damage to buildings in the city at normally unexpected distances,” said Thomas Pratt, a USGS geophysical researcher and expert on eastern seismicity. .

Science since the earthquake

Severe shaking in Washington, DC

The initially amplified vibration from the mineral earthquake was documented by USGS’ detailed analyzes of “Have you felt it?” reports. Each of these reports from a member of the audience describes their earthquake experience. Analyzes showed that people in Washington noticed stronger shaking than scientists had expected.

“Later research determined that it was the underlying sediment that amplified the vibration,” Pratt said. “We were aware of this phenomenon on the West Coast of the United States and internationally, but the mineral earthquake demonstrated the importance of this effect in the eastern United States. Areas on the sediments received much stronger shaking than nearby sites on more solid rock.”

The USGS and its partners installed temporary seismometers in the city after the earthquake to better understand the variation in the strength of the shaking and its relationship to the sediments under the city. Sediments are weaker than the underlying bedrock and therefore move more, while also trapping more energy.

Amplification by sediment was seen in earthquakes in other regions, for example in the damage focus in the Marina District of San Francisco during the 1989 Loma Prieta earthquake, but the strength of this effect was not well known for sediments along the East Coast. It is now recognized that this amplification can be severe in the eastern United States

vibration direction

USGS scientists found that the ground shaking force from the mineral quake was much greater in the northeast than in other directions. This trend is roughly parallel to that of the Appalachian Mountains and the eastern edge of the continent, which indicates the influence of large-scale features such as mountain ranges on the Earth’s vibration. A similar pattern was observed in the magnitude 5.1 earthquake in Sparta, North Carolina in 2020, which also showed stronger shaking along the direction of the Appalachian Mountains.

inform decisions

Knowing the amplification caused by these sediments and the direction of shaking will help emergency managers identify communities that may be more vulnerable to shaking. This knowledge will help the USGS improve its seismic hazard maps, which estimate the strength of ground shaking that can be expected during earthquakes in each region of the country.

These ideas can also be used by emergency managers when planning and responding to disasters; state and local governments as they revise building codes; and architects and engineers as they design and renovate buildings to mitigate the effects of future earthquakes. In addition, science helps in the planning of major infrastructure investments such as dams and reservoirs.

Read more at USGS

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