March 11, 2015
The last day has been chock full of big public-facing announcements regarding earthquakes, so it’s a good time to step in and sort them out, as well as a good time for (real life) earthquake scientists to capitalize on the surge of awareness.
The big real news comes from the USGS, which has finalized and released the most advanced seismic hazard model of California to date, the Uniform California Earthquake Rupture Forecast (Version 3), UCERF3.
I’ve been disappointed with the media headlines that suggest there’s been a sudden increase in the likelihood of a big quake in California. Headlines like the following offenders may get readers’ attention, but do a disservice to public perception of the science, suggesting that some natural phenomenon has increased the chances of an earthquake. Instead they should be clear that the chance of a large earthquake hasn’t risen; our estimate of the chance of a large earthquake has.
(Hint: Play “guess the source” and then use the rollover text to check your answers)
The Odds of a Massive Earthquake Hitting California Just Went Up
California’s Odds of an 8.0-magnitude Quake Rising, According to New USGS Study
Chance Risk of 8.0 earthquake in California rises, USGS says
USGS report says risk of mega-earthquake in California within next 30 years increases
…and the dreadful P-word: Predictions Claim Magnitude 8.0 Plus California Earthquake More Likely In Next 30 Years
Those contrast with this last one, however. A more responsible take, imho:
New earthquake forecast revises risks in California <–the best one of the lot… technically; perhaps not when ranked as click-bait.
The difference between this last and the previous headlines hinges on a crucial distinction: we don’t know the inherent chances of an earthquake at any given time in California; we estimate those chances, and it’s the method to calculate that solution that has changed. The calculations are based on clever synthesis of the best available knowledge about various faults–which of course is always improving–and the best contemporary understanding of how (and at what rate) they produce earthquakes. The regular changes in seismic hazard assessments generally arise from new information and new models, rather than from any fundamental change in the natural processes that produce earthquakes and shaking… except in the case of human-induced seismic hazard increases à la the central U.S, or evolving seismic hazards from aftershocks in the wake of a large quake.
The lead scientist on the UCERF project has published alongside this release an Opinion piece in Seismological Research Letters that more technically expands this issue of choosing the right model to guess earthquake chances. The piece is sort of a “Fantasia on the Box Quote,” in its application to earthquake reccurrence models.
In this case, the change in calculated chances of a magnitude 8.0 earthquake have arisen largely from the treatment of how faults may link together during earthquakes by way of ruptures jumping between them across gaps and steps, which were previously treated as boundaries. This question of how earthquake ruptures navigate these “boundaries” along fault systems is one that has underpinned my own research since my undergrad days. In this case, the details are explained in the full technical report and its stack of appendices.
The new hazard model was a timely announcement from the USGS because it coincided with the release of the second major trailer for San Andreas, the movie (although… you could argue over whether it quells or justifies the movie’s sensationalism regarding fault-linking megaquakes…)
For any of you who missed the first one, here it is in all its cliche disaster flick glory, complete with what would appear to be all the unused (and some of the used?!) footage/animation from 2012. In a casting choice that would appear to be… hastily conceived, the Rock will have a lead role. No doubt he plays either a renegade employee who knows all the answers when no one else does, or an estranged father/husband having to reassemble is family. The preview also prominently features the looming destruction of the Golden Gate Bridge, a structure that the world just loves to trash.
Mika McKinnon at i09 has already done the noble and daunting duty of confronting one of the movie’s main… liberties, and I look forward to a great deal more of that as we all go laugh our way through the flick after May 29 (don’t even think of seeing it without an[other] earthquake scientist by your side). In the meantime, with just those trailers to go by (although they probably encompass all the main action scenes in the movie, of course), I have to wonder: with so much modern footage of these phenomena, how are filmmakers using such jenky, misguided representations of what happens?! What if scientific simulations could get the budgets and animatiors of film industry graphics departments behind them, as in Interstellar… wouldn’t everyone be happier?
In summary for this week, my headline: Hollywood blockbusters and USGS scientists agree that California is doomed to suffer gigantic earthquakes. But let’s not get carried away… nothing’s changed about that.
I’ll dedicate a moment here to the anniversaries of several huge[ly important] earthquakes: Of course the 2011 Tohoku earthquake that rocked the entire Japanese archipelago, and the ensuing tsunami that stunned the world, but also the 1933 Long Beach earthquake that rocked L.A. and led to improved school construction in California, and the 1922 Parkfield earthquake, middle among a scientifically important string of quakes along the central San Andreas fault.