State and local inspectors examined sections of California's extensive levee system on Wednesday, a day after a moderate earthquake rattled a wide area of northern and central California.
Experts said the magnitude-5.6 earthquake, centered about 9 miles northeast of San Jose, was too far from the delta to threaten the state's water supply.
"Last night's jolt was not large enough to cause extensive damage, but it's a reminder of what will come," said Les Harder, deputy director of the state Department of Water Resources.
The quake's epicenter was at least 30 miles from the southern point of the Sacramento-San Joaquin Delta, but tremors were felt within an 80-mile radius, as far away as Santa Rosa, Sacramento and Monterey.
It marked the largest earthquake in Northern California since Loma Prieta in 1989 and the first since Hurricane Katrina underscored the vulnerability of the nation's levees.
Studies in the last few years have shown large parts of the delta's 1,600-mile levee system could crumble during an earthquake of magnitude 6.5 or greater.
The energy of a major earthquake along the Hayward and Calaveras
faults threatens to liquefy the peat soils that were used to build the now-fragile levees built by landowners during the 19th century.
A massive levee failure in the delta would cripple California's water supply system, which relies on the inland river delta to feed freshwater from the state's northern rivers to 750,000 acres of farmland and 25 million people in Southern California and the San Francisco Bay area.
In an effort to prepare, California voters last November passed nearly $5 billion in bond money to strengthen the delta's levees and improve flood control throughout the state.
Gov. Arnold Schwarzenegger also convened a task force to devise
strategies for managing the delta.
As a precaution, the Department of Water Resources dispatched inspectors Wednesday to the delta and instructed several dozen water districts to visually inspect the levees for cracks or water seepage, Harder said.
"It's probably the prudent thing to do, and it's good practice," he said.
He said more high-tech inspections would not be needed because of the earthquake's low impact on the delta.
The agency also planned Wednesday to inspect its pumping plants, reservoirs and canals in the region.
Preliminary surveys immediately following Tuesday's earthquake showed only superficial damage at Dos Amigos Pumping Plant, about
85 miles southeast of San Jose, where some plaster fell off the wall, said Department of Water Resources spokesman Ted Thomas.