The residents of Los Angeles, Calif., may be rocking-and-rolling a lot harder than expected when the next major earthquake hits, scientists say.

Scientists at Stanford University in Palo Alto -- using weak vibrations generated by the planet's oceans to construct models of "virtual earthquakes" -- are predicting the Los Angeles region will be hit by shaking much more powerful than generally anticipated if a big quake occurs south of the city, the university reported Friday.

"We used our virtual earthquake approach to reconstruct large earthquakes on the southern San Andreas Fault and studied the responses of the urban environment of Los Angeles to such earthquakes," said study lead author Marine Denolle, who received her doctorate in geophysics from Stanford and is now stationed at the Scripps Institution of Oceanography in San Diego.

Said Stanford geophysics professor and study leader Greg Beroza: "If you put a seismometer in the ground and there's no earthquake, what do you record? It turns out that you record something."

Specifically, when an earthquake isn't happening, there's nonetheless the ongoing ambient seismic field, which is caused by ocean waves interacting with solid earth.

The researchers said they found a way to use the ambient seismic waves to make calculations about the seismic waves generated by actual earthquakes, therefore allowing them to predict the behavior of the much stronger waves generated from more powerful temblors.

That approach revealed the possibility of more varied ground motion if a large earthquake of a magnitude 7.0 or greater strikes along the southern San Andreas Fault, south of Los Angeles near the Salton Sea, approximately 152 miles southeast from the city's downtown.

"The seismic waves are essentially guided into the sedimentary basin" that underlies the city, Beroza said. "Once there, the waves reverberate and are amplified, causing stronger shaking than would otherwise occur."

The Stanford study announcement comes after the devastating 6.7 magnitude Northridge earthquake, which shook L.A. at 4:31 a.m. on Jan. 17, 1994, killing 57 and injuring upwards of 5,000. Causing more than $20 billion in damage, the quake, which lasted between 10-20 seconds, proved one of the costliest natural disasters in United States history.