The monster quake that rocked Baja California on Sunday probably increased the chance that the Big One will roll through Riverside and San Diego counties, but only slightly, scientists said Monday.

"It is well known that, when a large earthquake happens, it kind of rearranges the forces in the rocks in the nearby region," said David Oglesby, a geologist at UC Riverside. "It relieves stress on some faults and increases stress on other faults."

But, Oglesby said in a telephone interview, "the changes in the stresses on the faults are small either way."

Given that the magnitude-7.2 shaker struck near Mexicali, well to the east of Tijuana, the rearrangement likely was concentrated on inland faults and did little to upset the balance of tectonic power along the coast.

"You can't say for sure," said Tom Rockwell, a San Diego State University geologist. "But clearly, this has increased the state of stress on the southern Elsinore and the southern San Jacinto. The Rose Canyon likely would not have been affected by this."

The Elsinore fault lies beneath Lake Elsinore, Temecula, Palomar Mountain and Julian.

The San Jacinto fault lies to the east of there, parallel to the Elsinore fault, extending from Hemet in Riverside County to Anza-Borrego Desert State Park in San Diego County.

Both are capable of triggering the same size quake that shook much of Southern California over the weekend.

Rose Canyon is the fault that represents the biggest threat to coastal San Diego County. It runs just offshore of Oceanside, Carlsbad, Encinitas, Solana Beach and Del Mar, but it runs onshore at La Jolla and directly under downtown San Diego.

The biggest concern for Southern California as a whole is the San Andreas fault.

The San Andreas fault runs 800 miles across the state, extending from San Francisco to the Salton Sea.

In Southern California, it runs east-west at the base of the San Gabriel and San Bernardino mountains, then southeast across the Palm Springs area.

The San Andreas fault is capable of generating a much larger quake than Sunday's shaker, which was the largest to strike the region since the 7.3-magnitude Landers temblor of 1992.

When scientists talk of the widely anticipated Big One, they usually are envisioning a quake of near-magnitude 8 on the southern San Andreas.

That section of the fracture that divides the North American and Pacific plates is believed to be overdue for a powerful slip.

Measurements are based on a logarithmic scale. An earthquake measured at 1 point higher on the scale is actually 10 times larger ---- and releases 31 times as much energy, according to the U.S. Geological Survey.

On average, one quake of magnitude 8 or larger occurs once a year somewhere around the world.

"We are always worried about a large earthquake on the southern San Andreas," Rockwell said. "(The Baja quake) probably had a minor effect on the San Andreas. But that effect is decreasing with each passing hour."

Oglesby emphasized that, if anything, the Baja shaker ---- were it to trigger a massive quake locally ---- would only be speeding up, slightly, one that already was set to go off because of other, built-up stresses.

"It's not going to produce an earthquake that never would have happened otherwise," Oglesby said. "It's more of a reminder that we always need to be prepared for the inevitable earthquake of that size in our area."

Call staff writer Dave Downey at 951-676-4315, ext. 2623.