Do you think you're ready for an earthquake?

Unlike some other natural disasters, an earthquake can strike completely without warning. As such, even though Delaware is not as quake-prone as states along the western seaboard, it’s a good idea to know what to do when a tremblor strikes.

That’s one reason the Delaware Emergency Management Agency is encouraging Delawareans to take part in its first earthquake preparation event Oct. 18. It’s part of a nationwide scenario, sponsored in part by the Federal Emergency Management Agency.

By registering online for the Great ShakeOut Earthquake Drill, families can learn how to survive a quake. The event is subdivided by area, with Delaware being part of the southeast region. Almost 4,200 groups have signed up to participate in the Thursday drill, which will take place at 10:18 a.m.

Nationwide, more than 1.4 million participants have registered at https://www.shakeout.org/.

Thirty-nine Delaware quakes since 1973

In the First State, the Delaware Geological Survey at the University of Delaware is charged, among other tasks, with monitoring seismic activity under the state.

Just because Delaware isn’t in a prime zone for earthquakes, that doesn’t mean they can’t happen here, noted state geologist and DGS Director David R. Wunsch.

“Earthquakes can occur almost anywhere,” Wunsch said, adding the largest ones typically happen along Pacific coasts of the Americas and Asia. It’s a region known as the “Ring of Fire” because of its volcanic and tectonic activity.

Earthquakes are caused when layers of rock, under pressure deep in the earth, move sideways, upward or downward against each other.

“You can picture these plates of rock as a flat surface, but the Earth is round and so you have these hard ridges being bent around a curved surface,” Wunsch said. “They’re readjusting all the time and that readjusting sometimes sets off earthquakes.”

And although tremblors are rare in Delaware, there have been at least 39 measurable quakes centered under the First State since January 1973. Records of events from earlier quakes are sparse but there have been at least 69 documented or suspected events in Delaware since 1871.

And since earthquakes don’t respect political boundaries, Delaware can be counted among the many states rattled by earthquakes whose epicenters -- the area underground where the quakes take place -- are in other states or under the Atlantic seabed. More than 550 earthquakes have been noted within 150 miles of the First State since 1677.

A ‘seething cauldron’

The study of quakes has undertaken tremendous advances in recent years, but they were not always well understood in the past.

Newspapers of the time reported an Oct. 9, 1871, quake that shook New Castle, Salem, N.J. and Wilmington. The shock in Delaware’s largest city, “was no doubt that of an earthquake, and if so, the heaviest ever experienced here,” according to a contemporary report.

“Great excitement was caused among the people, but no great alarm, because all thought it was a powder explosion,” the paper reported.

A local minister later preached the quake foretold the world’s destruction, saying it was proof of “a mighty, boiling, seething cauldron in the centre of the earth, that may at any moment burst forth in a general conflagration.”

Many New Castle residents reported only a slight shock during a March 1879 quake, with many thinking it was a thunderstorm.

24/7 monitoring

Additional studies and improvements in technology have changed the picture somewhat since those early reports.

An Aug. 23, 2011, earthquake that occurred in central Virginia was felt widely across the First State, with reports of swinging lamp fixtures and people recounting a slight rolling feeling as the earth shook. There were no reports of serious damage.

The largest quake to hit Delaware itself was recorded Nov. 30, 2017, with an epicenter under the Bombay Hook National Wildlife Refuge, north of Dover. That quake lasted around 15 seconds and affected areas as far away as Lancaster, Pa.

Unlike earthquake zones in California where faults often can be seen on the surface and are easier to study, they’re harder to spot in Delaware, Wunsch said.

“In Delaware, the solid rocks are buried by soft sediments, so it’s difficult to see them. They’re coated over like coats of paint,” he said.

The DGS keeps track of seismic activity under the First State through the use of two monitoring stations, one in Greenville and the other in southern Kent County.

Both are large, stainless steel containers packed with instruments, attached to concrete pads and buried six feet underground.

Information gathered by the 24-7 monitors is sent to the USGS and compiled with similar data from other stations across the country.

All of this data should eventually lead to a greater understanding of how earthquakes can occur and possibly give seismologists a means to predict when a tremblor will take place.

In the meantime, Wunsch said Delaware residents should be prepared, just in case.

“Although we’re not prone to large earthquakes, it’s a good idea to do these kinds of drills and for the public to be educated,” he said.