Well that is hard to determine but California is definitely up there on the charts because California sits on the San Andreas fault which is a massive fault. Also California is in the Ring of Fire which is where a large number of earthquakes and volcano eruptions happen. 90% of earthquakes are in the Ring of Fire and 80% of the worlds largest earthquakes are there too which means California is very vulnerable for a large earthquake. Therefore leaves California at the top for the next major earthquake.
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Southern California