A moderately strong earthquake initially registered by the USGS as M5.1 and later revised to M4.1 hit near Dover, Delaware at 21:47 UTC on November 30, 2017. The agency is reporting a depth of 8.1 km (5 miles). EMSC is reporting M4.4 at a depth of 6 km (3.7 miles). This is the first registered earthquake in this region ever.
The epicenter was located 1.2 km (0.8 miles) SE of Donas Landing (population 0), 10.3 km (6.3 miles) ENE of Dover (population 36 047), 19 km (11.8 miles) SE of Smyrna (population 10 023), Delaware, and 29.5 km (18.4 miles) SSW of Bridgeton (population 25 349), New Jersey.
The epicenter is also about 10 km (6.2 miles) ENE of Dover Air Force Base. Sgt. Rene Carberry, a spokeswoman at Dover AFB, told the Associated Press that people on the military installation felt it. "Some went outside to see if something had fallen down," Carberry said.
The USGS received more than 14 900 felt reports from users as far away as Massachusetts to the north and South Carolina to the south.
Some 153 000 people are estimated to have felt moderate shaking and 972 000 weak.
There are no reports of injuries or damages to infrastructure or buildings.
Geophysicist Dale Grant of the USGS said an earthquake in Delaware is 'exceptionally rare.' There is no known fault associated with this earthquake and the hazard maps produced by the USGS do not show Delaware having a significant seismic hazard, he said.
Paul Caruso, another geophysicist with the USGS described as unusual. "I was talking with the other seismologists and we said, ‘Wow, we don’t ever remember a quake in Delaware," he said.
It was the first significant earthquake felt in that region since the 2011 M5.8 Virginia earthquake.
Estimated population exposure to earthquake shaking
The USGS issued a green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.
Overall, the population in this region resides in structures that are resistant to earthquake shaking, though vulnerable structures exist. The predominant vulnerable building types are unreinforced brick masonry and reinforced masonry construction.
Selected cities exposed
Featured image credit: USGS