A huge fault in the Earth’s crust near Los Angeles is leaking helium, researchers have discovered. They say the unexpected find sheds new light on the Newport-Inglewood Fault Zone in the Los Angeles Basin. It reveals that the fault is far deeper than previously thought, and that a quake would be far more devastating. This comes on the heels of a report from the U.S. Geological Survey warning that the risk of ‘the big one’ hitting California has increased dramatically.
UC Santa Barbara geologist Jim Boles found evidence of helium leakage from the Earth’s mantle along a 30-mile stretch of the Newport-Inglewood Fault Zone in the Los Angeles Basin. (The Newport–Inglewood Fault extends for 47 miles from Culver City southeast to Newport Beach at which point the fault trends east-southeast into the Pacific Ocean.) He claims the results show that the Newport-Inglewood fault is deeper than scientists previously thought. Using samples of casing gas from two dozen oil wells ranging from LA’s Westside to Newport Beach in Orange County, Boles discovered that more than one-third of the sites show evidence of high levels of helium-3 (3He). “The results are unexpected for the area, because the LA Basin is different from where most mantle helium anomalies occur,” said Boles, professor emeritus in UCSB’s Department of Earth Science. “The Newport-Inglewood fault appears to sit on a 30-million-year-old subduction zone, so it is surprising that it maintains a significant pathway through the crust.” Considered primordial, 3He is a vestige of the Big Bang, and its only terrestrial source is the mantle.
When Boles and his co-authors analyzed the 24 gas samples, they found that high levels of 3He inversely correlate with carbon dioxide (CO2), which Boles noted acts as a carrier gas for 3He. An analysis showed that the CO2 was also from the mantle, confirming leakage from deep inside the Earth. Blueschist found at the bottom of nearby deep wells indicates that the Newport-Inglewood fault is an ancient subduction zone – where two tectonic plates collide – even though its location is more than 40 miles west of the current plate boundary of the San Andreas Fault System.
Found 20 miles down, blueschist is a metamorphic rock only revealed when regurgitated to the surface via geologic upheaval.
“About 30 million years ago, the Pacific plate was colliding with the North American plate, which created a subduction zone at the Newport-Inglewood fault,” Boles explained. “Then somehow that intersection jumped clear over to the present San Andreas Fault, although how this occurred is really not known. This paper shows that the mantle is leaking more at the Newport-Inglewood fault zone than at the San Andreas Fault, which is a new discovery.”
The San Andreas system in Northern California consists of five major branches with an overall length of about 1,25O miles. Experts say there is a 99 percent chance of a magnitude-6.7 earthquake or larger in the next 30 years in California because of the number of fault lines in the region. The San Andreas Fault that forms the tectonic boundary between the Pacific Plate and the North American Plate is the biggest.
“We are fortunate that seismic activity in California has been relatively low over the past century,” said Tom Jordan, Director of the Southern California Earthquake Center and a co-author of the study. But he ominously continued, “But we know that tectonic forces are continually tightening the springs of the San Andreas fault system, making big quakes inevitable.”
According to The Third Uniform California Earthquake Rupture Forecast, or UCERF3, the estimate for the likelihood that California will experience a magnitude 8 or larger earthquake in the next 30 years has increased from about 4.7% for UCERF2 to about 7.0%.
“The new likelihoods are due to the inclusion of possible multi-fault ruptures, where earthquakes are no longer confined to separate, individual faults, but can occasionally rupture multiple faults simultaneously,” said lead author and USGS scientist Ned Field. “This is a significant advancement in terms of representing a broader range of earthquakes throughout California’s complex fault system.”
The UCERF3 model is of the first kind, and is the latest earthquake-rupture forecast for California. It was developed and reviewed by dozens of leading scientific experts from the fields of seismology, geology, geodesy, paleoseismology, earthquake physics and earthquake engineering.