Complex sentence: The last major earthquake in the region occurred on 20 March 2012 which was 7.4 on the Richter scale, centered near Ometepec and the strongest since the 1985 quake.
Split into simpler sentences: The last major earthquake in the region occurred on 20 March 2012, and was 7.4 on the Richter scale. It was centered near Ometepec and was the strongest since the 1985 quake.