Debating “The Big One”: ‘99% Likelihood’ Forecast for Catastrophic Southern California Earthquake

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A recent scientific forecast has predicted probability risks of up to an 8.0 magnitude LA area earthquake striking within the next three years (99 percent chance large earthquake strikes Los Angeles in next 3 years, study says).  The study found a 99.9 percent probability that a magnitude-5.0 or larger earthquake would strike the greater Los Angeles area between April 1, 2015, and April 1, 2018.

A summary of the study and the debate surrounding is reported in an article in the
“Results of the study, titled “Potential for a large earthquake near Los Angeles inferred from the 2014 La Habra earthquake,” published on October 1 in the American Geophysical Union’s Earth and Space Science journal by a team of NASA geophysicists led by Dr. Andrea Donnellan, has sparked a controversy among seismologists.”

The study finds that there is “a 99.9 percent chance of a magnitude-5 or greater earthquake striking within three years” in the greater Los Angeles area. The study, based on GPS (Global Positioning System) data and airborne radar measurements of the magnitude-5.1 LA area quake on March 28, 2014.

The study found that a magnitude-5.0 quake was “extremely likely” to occur by April 1, 2018, and one of magnitude-6.0 or higher was likely at a probability of 35 percent. The largest anticipated earthquake at this location, based on this analysis, is predicted as a magnitude-6.3. The 1994 Northridge earthquake (magnitude-6.7) caused $25 billion in destruction, disrupted business operations, transportation, utility infrastructure, schools and public service providers.

The U.S. Geological Survey (USGS) criticized the new study by questioning its method of analysis and limited justification for the for 99.9 percent probability conclusion (scientific consensus has previously set the probability at 85 percent) (Federal agency slams study’s claim of 99.9 percent chance of large LA earthquake). The previous Uniform California Earthquake Rupture Forecast (March 2015) found the Southern California region has a 100 percent chance of 1 or more at least magnitude-5 (or larger) earthquakes and a 93 percent chance of a magnitude-6.7 earthquake during the next 30 years.

The USGS said the 99.9 percent probably number calculated in the new study is suspect. The probability percentage used by the USGS for such an earthquake in that area over the next three years is (only) 85 percent. Despite the dispute over the precise probability percentage, the USGS agrees that the probability favors a major earthquake in the southern California area to occur within the next three years.

One aspect of the study on which differing scientists agree is that the study accurately concludes that deeper layers of the Earth and fault zones did not move during the studied La Habra earthquake in the same way that the shallower areas did move. This supports the analysis that the deeper layers retain pent-up seismic strain, and an earthquake must eventually release that strain in the same zone, which affects the same area of greater Los Angeles in the coming years. (NASA: Los Angeles Area Has 99.9 Percent Chance Of Magnitude 5.0 Earthquake Or Greater In Next Three Years ).

According to the article:

“Donnellan explained that the recent La Habra earthquake that occurred in the spring of 2014 only relieved some of the stress in the faults. There remains enough pent-up seismic energy waiting to be released, and it could trigger a stronger quake within a 60-mile radius of the epicenter of the last earthquake. ‘When the La Habra earthquake happened, it was relieving some of that stress, and it actually shook some of the upper sediments in the LA basin and moved those a little bit more,’ Donnellan told CBS Los Angeles. ‘There’s enough energy stored to produce about a magnitude 6.1 to 6.3 earthquake,’ she added. Evidence that the earthquake relieved only part of the overall stress in the crust came partly from the fact that the deformation caused by the quake was larger than expected for a 5.1 magnitude event. The researchers said in their study that, ‘The shallow ground movements observed from this [La Habra] earthquake likely reflect strain accumulated on deeper faults, which remain locked and may be capable of producing future earthquakes.’”

One vital take-away from this discussion is that whether it is 99.9% or 85% probably – the predictive odds favor a coming major earthquake in the southern California basin and it is likely to occur sooner rather than later. Are you prepared?

It may well be that these new findings remind us of the earthquake risks based on our location and preparedness plans, especially those who are in southern California. This new report is a good “prompt” to revisit earthquake readiness for all of us no matter where we are located for our businesses, homes, schools and not-for-profit organizations. Recent news headlines chronicle the geographical diversity of earthquake risks across the USA including locations such as Oklahoma and the central plains; the western US; Southeast; Illinois and the Midwest; and New England. No matter where you live and work, the essential question is: are you prepared? You can learn more about earthquake readiness on the FEMA website. This may be a great wake-up call reminder for us to consider seriously our own revised exposure to earthquake risks.

There are specific steps that businesses can take to reduce the chances that earthquakes will injure employees, customers, or other workplace visitors, damage workplaces, or jeopardize the survival of the business operations. Such steps include: assess your seismic risks and how to develop and implement a plan to cost-effectively mitigate those risks; educate your people with earthquake-related information resources, ranging from reports, handbooks, guides, and manuals to posters, software, web-based tools, and instructional materials; and implement training and readiness preparation focused on earthquake risk reduction, and managing an earthquake disaster. These efforts can supplement or be integrated with other training and preparation efforts to addresses mitigation, preparedness, and response subjects that are applicable to earthquakes and as well as other hazards.

Links – Suggestions for Further Reading

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