Complex sentence: Following minuscule events in 1917,1927,1931, and 1939, threatening activity resumed in the late 1950s, when, in 1957, an earthquake near Birmingham extended from northern Alabama to Georgia and Tennessee, cracking and displacing small objects.
Split into simpler sentences: Following minuscule events in 1917,1927,1931, and 1939, threatening activity resumed in the late 1950s. In 1957, an earthquake near Birmingham extended from northern Alabama to Georgia and Tennessee, cracking and displacing small objects.