One fault near Diablo Canyon links to another

November 30, 2015

Diablo Canyon Nuclear Power PlantAn earthquake fault that neighbors Diablo Canyon nuclear power plant links to a second, larger fault, scientists have discovered. [SF Chronicle]

The Hosgri fault was discovered three miles offshore of Diablo Canyon during construction of the power plant in 1971. After the discovery, the plant’s design was retrofitted to withstand a magnitude 7.5 earthquake.

Seafloor mapping has now revealed the Hosgri connects to the San Gregorio fault, which is located to the north. When combined, the two faults total 250 miles in length, or more than double the length of the Hosgri.

Generally, the longer a fault is, the more potential there is for powerful shaking. Ground shaking from a quake linking multiple faults could be 20 percent larger than movement on the Hosgri alone.

It remains unclear whether there are breaks in the Hosgri-San Gregorio structure, which could limit a full rupture during an earthquake, said Sam Johnson, a research geologist with the U.S. Geological Survey. The San Andreas fault, for instance, is believed to have distinct north and south sections that would not shake simultaneously, Johnson said.

PG&E spokesman Blair Jones said experts have evaluated a possible rupture linking the Hosgri and other faults, including the San Gregorio and northern San Andreas faults. Scientists found the prospect of that occurring very unlikely, but the plant could still shut down properly, Jones said.

In 2008, the USGS discover another fault in the area, which was dubbed the Shoreline fault. The Shoreline is smaller than the Hosgri fault, but it was discovered less than one mile from the power plant.

Earlier this year, the Nuclear Regulatory Commission directed Diablo Canyon to conduct in-dept analysis of earthquake risks by June 2017. Diablo Canyon is among the nuclear power plants in the United States that is most vulnerable to ground shaking, the NRC found.



  1. Robert1 says:

    Can you hear that large sucking sound???
    That’s the jobs and tax revenue going with Diablo if it closes.
    PGE has been a excellent corporate citizen of SLO county.

    Economic Benefits of Diablo Canyon Power Plant – An Economic Impact Study.

    DCPP produced an estimated 18,566 megawatt hours of electricty in 2011, with a wholesale
    value of $675.6 million. In conjunction with the utilization of the industry-standard IMPLAN®
    software version 3.0 to analyze the impact of local expenditures for goods and services
    exceeding $22 million, a local payroll of $202.5 million, and 714 local retired PG&E employee pensions totaling over $19 million, this created a total 2011 economic impact on San Luis Obispo and Northern Santa Barbara counties of $919.8 million (Figure 1).

    (1) 9 Total Votes - 5 up - 4 down
    • Kaiser Bill says:

      The plant will close at some point, local governments need to prepare for that eventuality. Even if Diablo is re licensed, it will only be for 20 years. The tax revenues from the plant will depreciate as the plant ages. This has already happened to some extent. For example, arounf 2000, the San Luis Coastal district had to close schools due to declining revenue from Diablo Canyon.

      As for PG&E being an excellent corporate citizen, ask the folks in San Bruno how they feel about PG&E. PG&E only cares about lining its own pockets.

      (0) 6 Total Votes - 3 up - 3 down
  2. Kaiser Bill says:

    Since the plant is already old (built in the 70s, years of construction fubars and delays, opened in the early 80s), it might be time to retire the Plant. Re licensing from the Nuclear Regulatory Commission would only add another 20 years to the plants life, after which in all likelihood Diablo Canyon will close. San Onofre in northern San Diego County, the only other nuclear plant in California, closed a few years back,

    (0) 18 Total Votes - 9 up - 9 down
  3. hijinks says:

    This is not surprising. PG&E would like us to believe Hosgri is isolated. However, geologists know that all these faults running more or less parallel, including the Hosgri and San Andreas, are a single fault system. They also know now that quakes can “jump” from one to another of these previously-assumed-to-be-independent faults. Diablo is doomed, some day, due to this. Let’s hope not till it gets shut down, whenever that may be. Some day maybe we’ll learn that San Andreas and Cascadia are linked — what a mess that could be!

    (-2) 22 Total Votes - 10 up - 12 down
    • hijinks says:

      Why are you guys thumbs-downing a factual scientific summary? Must be a bunch of science-deniers out there.

      (0) 12 Total Votes - 6 up - 6 down

Leave a Comment