David Jacobson reports that a new study by researchers at the Scripps Institution of Oceanography, the Nevada Seismological Laboratory, and USGS has revealed that the Newport-Inglewood/Rose Canyon fault zone, which extends offshore from San Diego to Los Angeles, is capable of rupturing in M=7.3+ earthquakes. Such a quake could cause significant damage to some of the most densely populated areas in California.
The Newport...Inglewood...Rose Canyon fault zone is a strike-slip system in Southern California, and is part of the Pacific-North American plate boundary. Prior to this study, the Newport-Inglewood and Rose Canyon faults were believed to be separate systems. However, using a combination of seismic surveys, and high-resolution bathymetric data, the researchers determined that they are actually a continuous fault system, posing an even greater hazard to millions of people.
By using these two types of data, which differ in their resolution and depth of penetration, the team was able to define the fault structure in great detail, which could then be used to calculate earthquake magnitudes.
The Newport...Inglewood...Rose Canyon fault zone exhibits a mainly continuous fault trace over four distinct segments. These segments are separated by what geologists term as stepovers, which are where a fault is horizontally offset. Most scientists believe that stepovers at least 3 km wide are likely to prevent through-going ruptures. However, along the Newport...Inglewood...Rose Canyon fault zone, none of the three stepovers exceed 2 km in width, leading the team to believe that an earthquake could rupture the entire length of the fault zone in M=7.3+ events. This was based historical ruptures worldwide which have been shown to rupture through stepovers of this width.
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