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Delaware Geological Survey picks up first seismic wave from recent earthquake

The earthquake that shook Dover, Delaware, on Nov. 30 began five miles below the earth’s surface and registered 4.1 on the Richter scale, a numerical scale that quantifies the intensity or magnitude of the event. Delaware State Geologist David Wunsch said Thursday’s earthquake was the first to be felt in Delaware since August 2011, when a magnitude 5.8 earthquake struck central Virginia and subsequently reverberated through the First State.

Wunch directs the Delaware Geological Survey (DGS), a state agency housed in University of Delaware’s College of Earth, Ocean, and Environment. He said any earthquake in Delaware is surprising, but not concerning since the state is not classified as a highly active seismic zone. He shares why in the Q&A below.

Q: Why did the earthquake occur? Were there any warning signals?

Wunsch: Buried under Delaware are the same kinds of hard rocks that are visible in northern New Castle County, called Piedmont rocks. These Piedmont rocks extend underneath Delaware, buried under thousands of feet of sediment, and contain naturally occurring faults and fractures in them. As the Earth’s plates move around, it can create stresses, and occasionally these global stresses accumulate pressure that is released in the form of an earthquake. A colleague in Maryland reported small tremors measuring in Maryland last week, but we don’t know if there is any connection to the earthquake that occurred in Delaware Thursday.