Complex sentence: The source of the earthquake was the Nootka transform fault which separates the Juan de Fuca and Explorer plates and has been the origin of at least five additional moderate to large events since 1918.
Split into simpler sentences: The source of the earthquake was the Nootka transform fault. The fault separates the Juan de Fuca and Explorer plates and has been the origin of at least five additional moderate to large events since 1918.