Complex sentence: From December 16,1811 to February 4,1812, the area was struck by a series of more than 2,000 earthquakes, known as the New Madrid Earthquake, a series of shock waves believed by some to have been the greatest in North American history.
Split into simpler sentences: From December 16,1811 to February 4,1812, the area was struck by the 1811--12 New Madrid earthquakes (a series of more than 2,000 events). They are believed by some to have been the greatest in North American history.