Earthquakes can occur just about anywhere there is a fault. In fact, the worst earthquake ever recorded in the Lower 48 States was nowhere near the tectonic plates of California. It happened in Missouri! It is referred to as the New Madrid Earthquake and it was so strong, in fact, that the Mississippi River (biggest river in the USA) ran backwards!
I live in West Texas and I have experienced 3 earthquakes in my lifetime: 1 in San Jose, California, and 2 in Texas. One of the ones in Texas was so strong, I fell out of bed because I was sleeping on the edge. After that, I got curious about earthquakes nowhere near California and I learned that the region around the New Mexico/Texas border used to be an active location for earthquakes, with the epicenters for over 20 earthquakes dating back to 1900 located within a 45 mile radius of my house.