The international team studied two recent giant tsunamis including the Japanese tsunami in 2011 and a similar disaster in Java in 2006.
California's tsunami warning system was criticized after the northern coastline sustained damage from high waves triggered by the Japanese tsunami two years ago. Monday marks the second anniversary of that deadly tsunami.
The new report contradicts earlier theories that tsunamis will decrease in height as they move across the ocean. Scientists say offshore conditions can create bigger, more intense waves, and shorelines with earthquake zones are even more vulnerable.
"Our results show that some shorelines with huge earthquake zones just offshore face a double whammy: not only are they exposed to tsunamis, but under certain conditions, focusing amplifies these tsunamis far more than shoaling, and produces devastating results," said Utku Kanoglu, a professor at the Middle East Technical University who worked with USC on the study.
Fortunately, researchers say the geography in southern California makes it unlikely the Southland will be hit with a huge tsunami.
The study was published in the online journal "Proceedings of the Royal Meteorological Society."
CNS contributed to this report.