Wednesday, October 21, 2015

Regarding that 99.9% Probability Of A > M5.0 L.A. Earthquake Study


 Credit USGS – Probability of the `Big One’ over 30 years



# 10,646


Earthquake predictions are a dime a dozen on the Internet, and if you add in killer asteroids, the approach of planet Nibiru, and extraterrestrial invasions, even a little cheaper on Youtube.  Once a week someone posts a video about the imminent eruption of Yellowstone, a catastrophic pole shift, or a  mega-tsunami coming to your neighborhood soon. 

And on a cosmic timescale, all of these are possible (except the nonsense about Nibiru, which doesn’t exist).

Despite this inane chatter, there are serious scientists out there who are looking for NEOs (Near Earth Objects), who study fluctuations in the earth’s magnetic field, and who are attempting to pick up geological signals that can `predict’ earthquakes.  


It isn’t all rubbish.


So when a study, prepared by scientists at California’s JPL, appearing in a respected journal like Earth and Space Science, predicting a 99.9% probability of a M5.0 magnitude (or greater) quake in Los Angeles over the next three years, the media – and other scientists – take notice.


The full study may be read at:


Potential for a large earthquake near Los Angeles inferred from the 2014 La Habra earthquake

Andrea Donnellan1,2, Lisa Grant Ludwig3, Jay W. Parker1, John B. Rundle4, Jun Wang5, Marlon Pierce5,
Geoffrey Blewitt6, and Scott Hensley1


Tectonic motion across the Los Angeles region is distributed across an intricate network of strike-slip and thrust faults that will be released in destructive earthquakes similar to or larger than the 1933 M6.4 Long Beach and 1994 M6.7 Northridge events. Here we show that Los Angeles regional thrust, strike-slip, and oblique faults are connected and move concurrently with measurable surface deformation, even in moderate magnitude earthquakes, as part of a fault system that accommodates north-south shortening and westerly tectonic escape of northern Los Angeles. The 28 March 2014 M5.1 La Habra earthquake occurred on a northeast striking, northwest dipping left-lateral oblique thrust fault northeast of Los Angeles. We present crustal deformation observation spanning the earthquake showing that concurrent deformation occurred on several structures in the shallow crust. The seismic moment of the earthquake is 82% of the total geodetic moment released. Slip within the unconsolidated upper sedimentary layer may reflect shallow release of accumulated strain on still-locked deeper structures. A future M6.1–6.3 earthquake would account for the accumulated strain. Such an event could occur on any one or several of these faults, which may not have been identified by geologic surface mapping.


Although you have to read through a heavy dose of science and math, the money quote can be found near the end, where the authors write:


The calculated probability for a M ≥ 6 earthquake within a circle of radius 100 km, and over the 3 years following 1 April 2015, is 35%. For a M ≥ 5 earthquake within a circle of radius 100 km, and over the 3 years following 1 April 2015, the probability is 99.9%.


Before anyone gets too shook up (sorry, couldn’t resist), over the past 81 years Los Angeles has seen 32 - M5.0 quakes, and the USGS already had set the three-year risk of that size quake at a respectable 85%. This report ups the ante, but either way, the risks of seeing a M5.0 quake in L.A. during that time frame are pretty high.


A 99.9% certainty is a pretty bold prediction, however, and the USGS has posted a statement on their Facebook page urging caution in interpreting these results.


U.S. Geological Survey (USGS)

11 hrs ·

USGS Statement on JPL La Habra Study in the news:

This paper claims a 99.9% probability of an earthquake of magnitude 5 or greater occurring in the next 3 years within a large area of Southern California without providing a clear description of how these numbers were derived. The area—a 100 km radius circle centered on the city of La Habra—is a known seismically active area. For this same area, the community developed and accepted model of earthquake occurrence, "UCERF3", which is the basis of the USGS National Seismic Hazard Maps, gives a 3-year probability of 85%. In other words, the accepted random chance of a M5 or greater in this area in 3 years is 85%, independent of the analysis in this paper.

While the earthquake forecast presented in this paper has been published in the online journal Earth and Space Sciences, it has not yet been examined by the long-established committees that evaluate earthquake forecasts and predictions made by scientists. These committees, the California Earthquake Prediction Evaluation Council, which advises the California Office of Emergency Services, and the National Earthquake Prediction Evaluation Council, which advises the U.S. Geological Survey, were established to provide expert, independent assessment of earthquake predictions.

The earthquake rate implied by the 99.9% probability is significantly higher than observed at any time previously in Southern California, and the lack of details on the method of analysis makes a critical assessment of this approach very difficult. Therefore, the USGS does not consider the analysis presented in this paper a reason to change our assessment of the hazard.



None of this falls in my wheelhouse, so I can offer no opinion other than to say - while the consequences aren’t as dire - the difference between these two estimates is essentially the difference between playing Russian Roulette with 6 rounds in the chamber (JPL), or only 5 (USGS).  Either way, you’re going to wish you had your insurance premiums paid up.


In this case, `insurance’ is preparedness.  


And while this JPL prediction centers on Los Angeles, a recent  USGS study published in the journal Earthquake Spectra, nearly doubles – to 143 million - the number of Americans who live or work in areas susceptible to potentially damaging ground shaking  (see USGS: Nearly Half Of U.S. Population Exposed to Potentially Damaging Earthquakes).


Every home should have no less than a 72-hour supply of emergency food and water, for all of its occupants (including pets!). 


Basic kit : NWS radio, First Aid Kit, Lanterns, Water & Food & cash


This is a bare minimum, here in the United States many agencies and organizations recommend that households work towards having a 10-day supply of food, water, and emergency supplies on hand.

In When 72 Hours Isn’t Enough, I highlighted  a colorful, easy-to-follow, 100 page `survival guide’ released by Los Angeles County, that covers everything from earthquake and tsunami preparedness, to getting ready for a pandemic.


While admittedly California-threat specific, this useful guide may be downloaded here (6.5 Mbyte PDF).


For more on earthquake risks, and preparedness, you may wish to revisit:

Dr. Lucy Jones: `Imagine America Without Los Angeles’

California Quakes : Concrete Concerns

Estimating The Economic Impact Of A San Andreas Quake

USGS/OGS Joint Statement On Increased Earthquake Threat To Oklahoma

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