On December 22, 1983 an earthquake with a magnitude of 6.3 struck northern Guinea, killing around 300 people, and injuring 1,500. Around 200 people went missing. An earthquake of this magnitude was unusual for this region of West Africa, which was previously believed by most seismologists to be aseismic. The earthquake destroyed 5,000 houses. It had an intensity of IX (Violent) on the Mercalli intensity scale, although USGS reported it as VIII (Severe) The earthquake caused cracks in the ground, and an entire cavern to collapse.