DELAWARE'S LARGEST MEASURED EARTHQUAKE 2017

A magnitude 4.1 earthquake occurred November 30,, 2017 at 4:47 pm EST

with it's epicenter located 6 miles northeast of Dover in Bombay Hook National

Wildlife Refuge, reported by U.S. Geological Survey.

Analysis of the Dover earthquake indicates that that the source was nearly

five (5 ) miles or 23,000 feet, beneath land surface in deep crystalline basement rock,

in a sideways movement along a deep preexisting fault zone related to past tectonic

episodes.

The Dover earthquake was felt in Delaware and along the eastern seaboard from

central Virginia to Massachusetts. Reports by USGS indicate ' Modified Mercalli

Intensity ' of four felt close to epicenter and three around the rest of the region.

An intensity of four generally is a light shaking felt indoors but not outdoors., like

dishes and windows rattling, Intensity of three felt indoors, upstairs, vibrations like a heavy

laden truck passing by.

Why was the quake felt in such a large region? Mid Atlantic geology favors the

travel of earthquake energy for great distances when they are deep.

Why did this quake happen? The geology of the earthquake epicenter area is

characterized by soft sediments and sedimentary rocks near the earth's surface and

hard basement rocks below 4000 feet, similar to land surface in the Appalachian

Piedmont region north of Delaware. The basement rocks contain old faults formed by

tectonic movements of earths crustal plates..

The Appalachians were formed by continental collisions 440 and 380 million

years ago, followed by 230 and 190 million years ago, a 'rifting' that opened the

Atlantic Ocean. Since then the east coast has been tectonically quiet

Since 1871 Delaware has documented 58 earthquakes but it is only every decade

or so that one people would feel, 3.8 magnitude or more, occur. A perspective: 3 million

earthquakes world wide happen a year, 98% are less than 3 magnitude.

The 2017 quake matched the 1871 at 4.1 magnitude. A 1973 Delaware quake had a 3.8 magnitude. 

Abstract: May 27, 2018 by Harrison H. for www.iinni.blogspot.com & facebook

Delaware Geological Survrey.