Lancaster County, Pennsylvania 1984 April 23 01:36:00 UTC (local
April 22) This earthquake was centered near Marticville. It
caused minor damage at Conestoga, where a garage shifted 1.3 cm
off its foundation; plaster fell from a ceiling; and cracks
formed in windows, concrete basement walls, and a cistern.
Similar kinds of damage occurred at Lampeter, Mount Nebo, and
New Providence. Also felt in Connecticut, Delaware, District of
Columbia, Maryland, New Jersey, New York, Virginia, and West
Virginia. One foreshock occurred 5 days earlier and many slight
aftershocks occurred. Aftershock data suggested a north-
northeast fault dipping steeply east, with reverse, right-
lateral slip consistent with a horizontal east-northeast axis of
maximum compression. The geometry of the 1984 rupture conforms
to the strike of Jurassic dikes and associated faults in the
epicentral area. Abridged from Seismicity of the United States,
1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman,
U.S. Geological Survey Professional P