"Los Angeles is subject to earthquakes due to its location in the Pacific Ring of Fire. The geologic instability produces numerous fault lines both above and below ground, which altogether cause approximately 10,000 earthquakes every year. One of the major fault lines is the San Andreas Fault. Located at the boundary between the Pacific Plate and the North American Plate, it is predicted to be the source of Southern California's next big earthquake"
from wikipedia. The pacific and N.A plates will eventually slip by each other and the other half of cali will fall into the sea.