Full Idea
Physical evil (e.g. earthquakes) may be attributable to a fallen angel (Satan), who is the enemy of God, and this is enough to retain the idea that God is omnipotent and benevolent, and yet evil exists.
Gist of Idea
It is logically possible that natural evil like earthquakes is caused by Satan
Source
report of Alvin Plantinga (Free Will Defence [1965], III) by PG - Db (ideas)
Book Reference
'The Philosophy of Religion', ed/tr. Mitchell,Basil [OUP 1971], p.118