"Wild" earthquake in Delaware highlights lesser-known seismic risks | Global Resilience Institute

On Thursday, November 30, the U.S. Geological Survey (USGS) confirmed that an earthquake struck Delaware, with its epicenter just northeast of the state’s capital. Reports show that it was felt as far north as Newark and as far west as Washington, though at a very mild intensity. While the quake didn’t seem to cause substantial damage or loss of life, it stood out as being an uncommon event for the region.

Initial computer-generated reports of its magnitude ranged from 4.4 to 5.1, but experts later determined that it was actually a 4.1 on the Richter scale. This 4.1 measure is 10 times less intense than the earthquake’s highest magnitude estimation of 5.1.

USGS geophysicist Dale Grant said the event “exceptionally rare,” while his colleague Cheng Shengzao, also a geophysicist, called it “wild.”

Map of Delaware Earthquake
U.S. Geological Survey map of the earthquake’s epicenter (USGS Public Domain)

Current USGS data does not categorize Delaware as being particularly prone to earthquakes. Paul Caruso, a geophysicist affiliated with the National Earthquake Information Center, explained that while all earthquakes happen at fault lines, he wasn’t certain that the fault associated with this event even had a name.

He continued, “I was talking with the other seismologists and we said, ‘Wow, we don’t ever remember a quake in Delaware.”

Some argue that seismic hazard maps in their current state don’t capture risk well, failing to outline all regions at risk and inaccurately predicting quake intensity. This can lead area residents to underestimate their vulnerability to earthquakes–a phenomenon already evident in anecdotes from Delaware, which describe confusion and lack of preparedness among witnesses. Many had trouble identifying that an earthquake was happening, taking the tremors for everything from trees falling in the backyard to a bomb exploding.

“When we felt it, we looked at each other like, ‘Are we losing it?'” University of Maryland graduate student Husam Albarmawi said after he and his wife fled their apartment complex. “It was actually pretty scary and pretty surprising.”

Delaware isn’t the only place that has recently been surprised by an earthquake. On September 7 of this year, the Mexican states of Oaxaca and Chiapas were rocked by a magnitude 8.2 quake. While Mexico is known as being a hotbed of seismic activity, this event was unique in both its extraordinary strength and location. It rattled the Tehuantepec gap, an area previously thought to be “aseismic,” or largely inactive. This region had never seen a major quake. But despite its improbability, the earthquake still hit, virtually leveling the city of Juchitán, killing nearly 100 people, and making the population even more vulnerable to another devastating earthquake that would strike less than two weeks later.


Sources and further reading:

Earthquake hits Delaware, rattling windows as far as D.C. – Washington Post

Here’s why early magnitude estimates for the Delaware earthquake were shaky – Baltimore Sun

This is wild,’ USGS says of Dover 4.1 earthquake – Delaware Online

Rare quake shudders through Northeast; centered in Delaware – ABC News

Why seismologists didn’t see Mexico’s deadly earthquake coming – The Conversation

Strength and resilience in Mexico City – Global Resilience Institute