Natural disaster study: 'Big One' could be overdue along Grapevine

Toni Houston
March 9, 2017

The offshore Newport-Inglewood/Rose Canyon fault zone poses a significant threat to both Los Angeles and San Diego. "Large, but less damaging earthquakes, like magnitude 7.5, may be the more typical type of occurrence along this stretch of the fault", Graves said. The researchers found that the maximum potential for a rupture of the entire fault can produce between magnitude 6.7 and magnitude 7.3 to 7.4 earthquakes.

New analysis of coastal fault systems in Southern California suggest the region is capable of a magnitude 7.3 natural disaster. The report's conclusion was that the two systems created a continuous fault that extends beneath the surface of San Diego Bay up to Seal Beach in Orange County, then running through the Los Angeles basin.

For the study, U.S. Geological Survey postdoctoral fellow Valerie Sahakian, and colleagues used sonar imaging to map the fault lines of the system that run from Los Angeles to San Diego.

The findings raise concerns since a powerful natural disaster can have a major impact on the affected regions, which include the most densely populated parts of California.

When conducting research, the team processed seismic surveys from the past and added in high-resolution bathymetric data, gathered offshore by Scripps researchers between 2006 and 2009, in addition to seismic surveys conducted aboard former Scripps research vessels.

This allowed them to generate a "nested survey" of the region, accounting for different resolution scales and depth penetration.

The study, "Seismic constraints on the architecture of the Newport-Inglewood/Rose Canyon fault: Implications for the length and magnitude of future quake ruptures", appears in the American Geophysical Union's Journal of Geophysical Research.

"The record shows that large earthquakes occurred near Tejon Pass on average every 100 years".

You've heard this before: "The Big One" can strike any day in Southern California.

A repeat of the 1857 natural disaster could damage aqueducts that deliver water into Southern California from the north, disrupt electric transmission lines and tear up Interstate 5, whose Grapevine section runs on top of the San Andreas Fault at Tejon Pass.

The last time a major rupture of the fault took place was in Long Beach in 1933, where 115 people died in the resulting magnitude-6.4 quake.

In the last 11,000 years, there have been three to five ruptures at the north end of the fault system. We're talking about a really big natural disaster along the southern end of the San Andreas Fault that measures magnitude 7.5 or greater.

'Further study is warranted to improve the current understanding of hazard and potential ground shaking posed to urban coastal areas from Tijuana to Los Angeles from the NIRC fault'.

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