What do the destructive Ecuador, Japan, Burma, and Italy quakes—and the Louisiana flood—all have in common?

Ross Stein, Temblor

Answer: They are the ‘one percent.’

That is, they have a 1% chance per year of occurring, equivalent to 1 chance in 10 in a decade. When events of this rarity strike land or coastlines, they do tremendous damage, and so make headlines.


Neither common nor extremely rare

The recent 16 April M=7.0 Japan and M=7.8 Ecuador quakes, and the 24 August M=6.8 Burma and M=6.2 Italy quakes, all fall into the 1% per year occurrence rate, as does the 12-18 August 2016 Louisiana flood. So, these are neither once-in-a-millennium events like the 2011 M=9 Tohoku-Oki quake, nor are they garden-variety shocks like Parkfield earthquake, which has ruptured roughly the same section of the San Andreas fault in central California every 20-40 years since 1857.

All four of the magnitudes are close to the 1% chance per year forecast in the GEAR model.


Look how closely this portion of the Louisiana flood matches FEMA’s 1% chance per year (1 chance in 10 in a decade).


As the distinguished UCLA professor emeritus, David D. Jackson, said about the recent events, “Most earthquakes know where to go—they follow the crowd.” What Dave means is that the rate and distribution of past earthquakes, as well as the straining of the Earth’s surface caused by deep fault slip, are the best indicators of future earthquake behavior. That is why Temblor’s ‘Earthquake Forecast’ layer displays the Global Earthquake Activity Rate (GEAR) model of Peter Bird, David Jackson, Yan Kagan, Corné Kreemer and myself, published in 2015 and now undergoing independent testing by the Collaboratory for the Study of Earthquake Predictability (CSEP).


Cognitive Dissonance

But consider this: If you have a mortgage, and your home lies within FEMA’s 1% chance per year of flood inundation, you are required to carry flood insurance. But earthquakes? Most of us ignore them.

Here is Temblor’s earthquake forecast for California, based on GEAR (Bird et al., 2015), which gives almost exactly the same rate of M≥7 events in California as the 2014 USGS model.


Take a look at the GEAR map for California, above: A M~7 shock has a 1% chance per year of occurring in much of the Southland (greater Los Angeles) and the San Francisco Bay area. But although the lion’s share of buildings are much younger—and therefore stronger—in California than Italian Apennine towns, a M=7 is twenty times more powerful (by released energy) than Italy’s recent M=6.2. In a M=7, we will be shaken about three times harder, and ten times longer.

Earthquakes that strike once in a lifetime are easily forgotten, and catch us unawares. So, the spate of recent destructive global events should remind all Californians that we need to be ready to withstand a M=7 quake. Because if earthquakes do indeed follow the crowd, they’ll be with us again.


Earthquakes from the USGS and EMS seismic catalogs


Bird, P., D.D. Jackson, Y.Y. Kagan, C. Kreemer, and R.S. Stein (2015), GEAR1: A Global Earthquake Activity Rate Model Constructed from Geodetic Strain Rates and Smoothed Seismicity, Bull. Seismol. Soc. Amer., 105, 2538–2554, doi: 10.1785/0120150058, Link

  • Robin Luethe

    I live in a six story concrete/steel less than 10 year old condo very near the Seattle fault, and the discussion regarding buying earthquake insurance was interesting. You might be interested in this summary as I understood the debate.
    If you have a lot of money, or your income is going up a whole lot in the future it may not make sense to buy insurance. You can afford to self insure. It is expensive.
    If you are among the lower income of people in the building, and have a mortgage you likely will decide that you can’t afford the insurance, and that you can walk from your mortgage. If you can walk after the earthquake LOL
    If you are in the middle income group and have a mortgage you likely should get insurance. But oddly if you are older, and the home owners association decides/is required to rebuild you may not live long enough to ever move in the rebuilt building. Highways, hospitals, and other infrastructure will have first dibs on materials and labor. I think it could take 10 years to rebuild.
    I voted for the building being insured which is the vote that prevailed , but decided not to get the interior insurance which is not covered by the condo building insurance.

    • Ross Stein

      Because insurance on a 10-story building will be expensive, I suggest that the cost of an inspection and analysis by a licensed structural engineer would be well worth it, so you can first find out if the building is as strong as it should be, and needs no retrofitting. If it does need an upgrade, make this your top priority.

      If the building is sound, then cost compare insurance offers. If you don’t get Personal Property coverage, the cost will decrease. Loss of Use is probably something, however, that you should get, but check how much lower the policy would be without it.

      I would say that if the lowest cost quake insurance is not more than twice your homeowner’s policy, you should buy it. This is simply the cost of living in a place as beautiful–and seismically active–as Seattle. And very few of us are actually so wealthy as to be able to walk away from a mortgage or home financially unscathed.

      • Robin Luethe

        The innumerable main columns of the building likely go down to bed rock (which emerges from place to place if you know where to look in our neighborhood), and the building with its three underground parking levels is probably as ready as any building in the region for either of the really big faults that threaten us.
        The building insurance is adequate to cover most of our loss. I am not sure we would live long enough ever to move back into the unit were the building not recoverable. If the building remains usable, the unit’s electrical, plumbing, and other mechanicals likely remain undamaged.
        The real threat will be the enormous infrastructure damage in the wider region. I don’t think anyone really has a handle on it.