The earthquake on Apr 1 occurred in a region of historic seismic quiescence, the Northern Chile seismic gap. The initial location is placed near the northern end of the seismic gap. The last significant earthquakes occurred in 1877 (M 8.8). Since then the region was quiet and built up stress for the last 130 years. A recent increase in seismicity has occurred just before the Mw 8.2 event, including a Mw6.7 event and three Mw 6.2 events in March.