The correct answer to this open question is the following.
What sometimes causes earthquakes in the Pacific coastal plains is the San Andrea fault.
If you live in the coastal zone of the Pacific West, you are well aware of the San Andrea fault. This fault is the one that causes many earthquakes in the region. The fault extends 750 miles through the state of California. Scientists say that this fault in the frontier between the North America Plate and the Pacific Plate. The name of San Andrea was coined by Professor Andrew Lawson from the University of California at Berkley, in 1895.