- Indicates Newport-Inglewood fault more important than previously thought
- Risk in the next 30 years of ‘big one’ increased from about 4.7% to 7.0%
- However, study says risk of smaller quakes has actually gone down
A huge fault in the Earth’s crust near Los Angeles is leaking helium, researchers have found.
They say the unexpected find sheds new light on the Newport-Inglewood Fault Zone in the Los Angeles Basin.
It reveals the fault is far deeper than previously thought, and a quake would be far more devastating.
It follows a report from the U.S. Geological Survey has warned 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.
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.
Boles’s findings appear in Geochemistry, Geophysics, Geosystems (G-Cubed), an electronic journal of the American Geophysical Union and the Geochemical Society.
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.
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% to about 7.0%, they say.
‘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 we know that tectonic forces are continually tightening the springs of the San Andreas fault system, making big quakes inevitable.
‘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.
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.