Earth Quakes

Study shows fault near key California water supply among 4 at risk of major quake

  • FILE - In this Aug. 24, 2014, file photo, pedestrians examine a crumbling facade following an earthquake at the Vintner's Collective tasting room in Napa, Calif. Four long fault segments running beneath northern California and its roughly 15 million people all have become locked far underground, and loaded with enough tension to produce earthquakes of magnitude 6.8 or greater, a geological study published Monday, Oct. 13, 2014 says. (AP Photo/Noah Berger, File)

    FILE - In this Aug. 24, 2014, file photo, pedestrians examine a crumbling facade following an earthquake at the Vintner's Collective tasting room in Napa, Calif. Four long fault segments running beneath northern California and its roughly 15 million people all have become locked far underground, and loaded with enough tension to produce earthquakes of magnitude 6.8 or greater, a geological study published Monday, Oct. 13, 2014 says. (AP Photo/Noah Berger, File)  (The Associated Press)

  • FILE - This file photo from Aug. 24, 2014, shows a cracked section of roadway following an earthquake in Napa, Calif. Four long fault segments running beneath northern California and its roughly 15 million people all have become locked far underground, and loaded with enough tension to produce earthquakes of magnitude 6.8 or greater, a geological study published Monday, Oct. 13, 2014 says. (AP Photo/Eric Risberg, File)

    FILE - This file photo from Aug. 24, 2014, shows a cracked section of roadway following an earthquake in Napa, Calif. Four long fault segments running beneath northern California and its roughly 15 million people all have become locked far underground, and loaded with enough tension to produce earthquakes of magnitude 6.8 or greater, a geological study published Monday, Oct. 13, 2014 says. (AP Photo/Eric Risberg, File)  (The Associated Press)

  • FILE - In this file photo from Aug. 24, 2014, an upper corner of the Napa County Courthouse displays structural damage after an earthquake in Napa, Calif. Four long fault segments running beneath northern California and its roughly 15 million people all have become locked far underground, and loaded with enough tension to produce earthquakes of magnitude 6.8 or greater, a geological study published Monday, Oct. 13, 2014 says. (AP Photo/Ben Margot, File)

    FILE - In this file photo from Aug. 24, 2014, an upper corner of the Napa County Courthouse displays structural damage after an earthquake in Napa, Calif. Four long fault segments running beneath northern California and its roughly 15 million people all have become locked far underground, and loaded with enough tension to produce earthquakes of magnitude 6.8 or greater, a geological study published Monday, Oct. 13, 2014 says. (AP Photo/Ben Margot, File)  (The Associated Press)

A new study says four stretches of fault running under northern California are primed for quakes of magnitude 6.8 or more.

The study by scientists with the U.S. Geological Survey and San Francisco State University looked at 35 years of measurements along northern California's San Andreas fault system. Geologists looked for fault creep, meaning tiny surface movements along fault lines that help ease tension.

The study, released Monday, found that close to one-third of the 1,250 miles of fault lines in the San Andreas fault system appear locked. That means there is no fault creep on those stretches, and pressure is building for an earthquake.

Geologist James Lienkaemper of the U.S. Geological Survey says the study found the Green Valley fault in Napa and Solano counties appears ready for a major quake. That fault is near the dams and aqueducts that supply much of California's water.