2011 Virginia earthquake
On August 23, 2011, a magnitude 5.8 earthquake hit the Piedmont region of the U.S. state of Virginia at 1:51:04 p.m. EDT. The epicenter, in Louisa County, was 38 mi (61 km) northwest of Richmond and 5 mi (8 km) south-southwest of the town of Mineral. It was an intraplate earthquake with a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale.[2] Several aftershocks, ranging up to 4.5 Mw in magnitude, occurred after the main tremor.
The quake was felt across more than a dozen U.S. states and in several Canadian provinces, and was felt by more people than any other quake in U.S. history.[5] No deaths and only minor injuries were reported. Minor and moderate damage to buildings was widespread and was estimated by one risk-modeling company at $200 million to $300 million, of which about $100 million was insured.[6][7]
The earthquake prompted research that revealed that the farthest landslide from the epicenter was 150 miles (240 km), by far the greatest landslide distance recorded from any other earthquake of similar magnitude. Previous studies of worldwide earthquakes indicated that landslides occurred no farther than 36 miles (58 km) from the epicenter of a magnitude 5.8 earthquake. The Virginia earthquake study suggested that the added information about East Coast earthquakes may prompt a revision of equations that predict ground shaking.
Aftershocks[edit]
Numerous aftershocks occurred after the main tremor. The first four (of magnitude 2.8, 2.2, 4.2 and 3.4) occurred within 12 hours of the main shock. A 2.5-magnitude shock occurred just after midnight on August 25, followed at 05:07 UTC by the strongest, a magnitude 4.5 aftershock that woke many residents in Northern Virginia and Washington, D.C., and was felt as far away as New England, Georgia, and Illinois.[15][16][17][18]
Internet activity and social media[edit]
The USGS "Did you feel it?" citizen-based earthquake intensity website received about 60,000 reports in the first two hours after the quake, and over 100,000 responses within four hours.[122] As of March 7, 2018, the earthquake has 144,178 felt reports.
According to Facebook, the word "earthquake" appeared in the status updates of 3 million users within four minutes of the quake. Twitter said users were sending as many as 5,500 messages ("tweets") per second, which exceeds the maximum rate immediately after the death of Osama bin Laden and was "on par with" the rate after the Tōhoku earthquake and tsunami.[123]
Due to the significantly slower propagation of seismic waves compared to the near-speed-of-light transmission of Internet traffic, some Twitter users read about the earthquake seconds before feeling the tremors. For example, Twitter users in such cities as New York City and Boston reported reading tweets about the earthquake from users in Washington, D.C., or Richmond, Virginia, 15 to 30 seconds before feeling the quake itself.[124]
The European-Mediterranean Seismological Centre (EMSC) website, one of the top global earthquake information website experienced a massive and immediate traffic surge caused by the convergence of eyewitnesses looking for information about the shaking. Their hit times proved to mimic the seismic wave propagation generated by the earthquake. On average eyewitnesses hit the website 90 seconds after the ground start shaking. The epicenter was determined within 30 km by retropropagating 2 minutes of EMSC website traffic without using any seismic data. The authors argue that eyewitnesses can be considered as a real-time sensor, their website visit being triggered by the ground shaking.[125]
The English version of Wikipedia had an encyclopedia article dedicated to the earthquake by 2:03 PM, 12 minutes after the event, and it was mentioned in two other Wikipedia articles even earlier.[126]
Zoo animal reactions[edit]
Staff at the National Zoo in Washington, D.C., reported that some of the animals in the park appeared to show behavior suggesting that they anticipated the earthquake from seconds to minutes before it was felt in the area. The earthquake was felt at the great ape exhibits during afternoon feeding time. About three to ten seconds before the quake, many of the apes abandoned their food and climbed to the top of a tree-like structure in the exhibit. The red ruffed lemurs sounded an alarm call about 15 minutes before the quake, and the flock of 64 flamingos rushed around and grouped themselves together just before the quake. During the quake, some animals vocalized, some ran or dived for cover, and some stood up and stared at the walls of their enclosures. Some of the animals remained agitated for the rest of the day, while others calmed quickly. The Zoo's giant pandas did not appear to respond to the quake.[127]