3.4 quake prompts inspection at future dam’s site

San Francisco water officials were inspecting for earthquake damage Monday at a dam under construction in the South Bay after a small temblor shook the area the night before.

The U.S. Geological Survey reported a 3.4-magnitude quake just after 7 p.m. Sunday about 4 miles beneath the Calaveras Reservoir, which sits east of Milpitas on the rural Santa Clara-Alameda county line. It’s part of San Francisco’s sprawling water supply system.

Officials with the San Francisco Public Utilities Commission said the earthen dam, which is being built to replace an older dam at the reservoir, probably wasn’t affected by the earthquake. But they sent inspectors to check on the structural integ-

rity of the dam as well as a concrete spillway, intake tower and boat ramp as a precaution.

“The team did not see any issues,” said Chris Colwick, spokesman for the utility. “Everything looked good.”

The inspectors were expected to continue their review Tuesday.

Small earthquakes are a fact of life in the Bay Area, with dozens occurring each month, most well below magnitude 3. On Saturday, though, a 3.4-magnitude quake struck near Crockett.

The area around the Calaveras Reservoir is particularly earthquake prone. Scientists say the nearby Calaveras Fault is capable of producing a 7.25-magnitude jolt.

A major reason the dam is being rebuilt is so it can withstand more powerful seismic activity. The new $810 million dam, which will eventually rise 220 feet, is expected to be finished next year.

Reservoir levels have been kept far below the facility’s 96,850 acrefoot capacity during the dam’s construction, which began in 2011.