PASADENA, Calif. — Landslides coming off Catalina Island's steep slopes could send tsunamis racing toward popular Los Angeles and Orange County beaches with just a few minutes of warning, geoscientists said on April 23 here at the annual meeting of the Seismological Society of America.

Researchers discovered chaotic deposits that are characteristic of landslides while probing underwater rocks offshore Catalina Island. Seismic waves provide images of underground sediment and rock layers in a manner similar to medical CT scanners that search for cancer and broken bones. [Waves of Destruction: History's Biggest Tsunamis]

The landslides were buried underwater because Catalina Island is sinking, said lead study author Chris Castillo, a Stanford University graduate student. The remnants of old beaches have dropped beneath the waves as the island descends, creating a stair-stepped series of nine terraces.

"Catalina is rare," Castillo told Live Science. "We knew there was evidence of subsidence, but it's the only [Southern California] island that has these submerged beaches."

Catalina's nearest neighbor to the south, San Clemente Island, has ancient beaches that sit about 1,800 feet (550 meters) above sea level.

Castillo does not yet know how fast Catalina Island is sinking. The oldest terrace is about 720 feet (220 m) below current sea level. The island is also tilting as it descends, which increases the landslide threat by destabilizing the steep coastal slopes, he added.