A natural helium leak in Southern California reveals that the Newport-Inglewood fault is deeper than once thought — with a direct line from the Earth's surface to the planet's hot, dense mantle.

 

       Scientists have found high levels of helium-3 in oil wells up to 3 kilometers (1.8 miles) deep in Orange County, along a 30-mile (48 kilometers) stretch from Los Angeles' Westside to Newport Beach. Helium-3 comes only from the Earth's mantle, the semisolid rock layer beneath the crust.

 

    "The fault, which I don't think people had anticipated, was deeply connected," said Jim Boles, a professor emeritus of earth sciences at the University of California, Santa Barbara.

 

  Discovering helium-3 at the Newport-Inglewood fault is undeniably odd. About 30 million years ago, the fault was the site of a subduction zone, a region in which one continental plate is pushing under another, driving a layer of crust down toward the mantle like a conveyer belt.

 

    "The only thing you can say is that this fault looks like it's a more significant fault than people thought in terms of how deep it goes and what it communicates with," Boles said.