One of the 13 original States, Delaware entered the Union in 1787. But its residents had noted effects from two earthquakes before that time, a strong New York shock a half-century earlier and another in 1755 off the Massachusetts coast. Neither caused damage in Delaware, but the first knocked chimneys over in the New York City area; the second downed walls and chimneys in the Boston vicinity, broke gable ends and vanes on buildings, and opened small ground cracks, an undually severe shock for that area.
The only earthquake to center in Delaware and cause severe property damage occurred on October 9, 1871. At Wilmington, Delaware's largest city, chimneys toppled, windows broke, and residents were quite bewildered by the unusual event. Lighter damage was sustained in northern Delaware at Newport, New Castle, and Oxford. Earth noises, variously described as "rumbling" and "explosive," accompanied the shock in several areas.
A tremor in March 1879 on the Delaware River, not far from Dover, was felt "strongly" in that area according to old seismic records. The records, however, do not describe the "strong" effects.
The last shock to center in Delaware and cause minor effects occurred on May 8, 1906, just three weeks after the noted San Francisco earthquake in California. Records state this shock was strong at Seaford, in southwest Delaware, but list no details concerning the event.
Two tremors in recent years, both below intensity V, occurred in Delaware, one on the Lower Delaware in December 1937, and one near Wilmington in January 1944.
Nine earthquakes centered outside Delaware have been felt within the state. These include the two previously described in New York and Massachusetts, four minor New Jersey, and three major earthquakes - two in Canada and one in South Carolina. The South Carolina quake, the strongest in Eastern U.S. history, destroyed much of Charleston in August 1886, and shook up a region from Boston and Milwaukee in the north to Bermuda and Cuba in the south.
The most recent earthquake to be "felt" in Delaware occurred in southern New Jersey in December 1968. Wilmington residents noted slight effects of the Richter magnitude 2.5 tremor, which caused no damage as it rumbled through New Jersey, Pennsylvania, and Delaware.
Abridged from Earthquake Information Bulletin, May - June 1971, Volume 3, Number 3.
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