Utilities crews say two recent earthquakes have not caused any detectible damage to the Calaveras Dam, a 75-year-old structure holding back a reservoir that straddles Santa Clara and Alameda counties.

A 4.1-magnitude earthquake Thursday and a 3.7-magnitude quake Friday were both centered along the Calaveras Fault near the Calaveras Reservoir, according to the U.S. Geological Survey.

The San Francisco Public Utilities Commission dispatched workers and found no signs of damage to the reservoir infrastructure, including Calaveras Dam, an earth-filled structure built in 1925.

Water in the reservoir is currently lowered by 60 percent of full capacity due to concerns about the seismic stability of the dam.

“The timing of this tremor highlights the importance of our ongoing Water System Improvement Program to repair, upgrade and seismically reinforce these facilities,” SFPUC General Manager Ed Harrington said in a statement.

“This work includes replacing Calaveras Dam, upgrades to the nearby treatment plant and strengthening the pipelines that cross this vault in the valley,” Harrington said.

The project to replace Calaveras Dam is in environmental review, according to the SFPUC.

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