In the Coastal Plain of Delaware, the non-marine Cretaceous sands and clays are separated from the Tertiary formations by a series of marine formations of Upper Cretaceous age. The sedimentary and hydrologic characteristics of these formations deserve detailed study because some of them are water-bearing beds. whereas others act as confining beds. A clear understanding of their relative age. and the presence or absence of unconformities is needed for proper correlation with formations found in wells throughout the State. as well as in Maryland and New Jersey.
When the earthquake hit a little before 10 a.m., everyone who heard the crack and felt the ground rumble thought something had exploded or crashed. Chimneys fell over, windows shattered, people panicked -- on Oct. 9, 1871. The magnitude 4.1 earthquake that shook Wilmington that morning -- the most intense temblor ever recorded in Delaware -- easily outshook the magnitude 2.8 quake that hit the state Wednesday morning.
Earthquakes occur in northern Delaware and adjacent areas of Pennsylvania, Maryland, and New Jersey. Over 550 earthquakes have been documented within 150 miles of Delaware since 1677, and 69 earthquakes have been documented or suspected in Delaware since 1871.