From the risk mavens at RMS:
You may have noticed recent headlines
making some scary apocalyptic 2018 earthquake predictions. Scientific
thinking generally evolves slowly and thoughtfully. A headline that
proclaims a revolutionary or shocking change in our understanding of
earthquakes is likely overstating the certainty of a hypothesis, or may
be a misinterpretation that is sensationalized by the media. In such
cases, it is always best to go back to the original source of
information.
These headlines are based on an article published back in August in Geophysical Research Letters entitled Do Weak Global Stresses Synchronize Earthquakes?
This article and its authors have indicated:
- Worldwide there is a temporal pattern to large earthquake (M7+) occurrence.
- The shift in earthquake occurrence seems to correlate with variations of a few milliseconds in the length of the day on Earth.
- The theory proposes that shifts in mass are changing the speed of
the Earth’s rotation (like an ice skater unfolding her arms) and are
related to the build-up in stress that precedes earthquakes.
- The most recent change in rotation began in 2011, so the authors of
the paper propose we are now at the start of a new higher period of M7+
earthquake activity.
- The increase in seismicity will be in the equatorial regions where there are large populations at risk.
Let’s examine these new assertions and see whether we should be concerned.
Starting in about 1900, the worldwide coverage of seismic monitoring
instrumentation has been sufficient that all earthquakes in the M7+
range should have been observed, wherever they were located.
For some time, it has been recognized that there have been “temporal
groupings” of these large M7+ earthquakes with four peaks in 1910, 1943,
1970, and 2011, implying a cycle with an average length of 32 years —
ranging from 27 to 41 years. These temporal groupings of earthquakes,
however, are not generally spatial clusters, so any linkages between the
events have been hard to identify. The August 2017 article is proposing
that these temporal variations are due to very small changes in the
rotation speed of the Earth. This correlation is a hypothesis and only
time (i.e., decades) will tell if the evidence supports there being a
physical connection. The observed correlation does not necessarily
indicate causation.
Given the most recent peak in seismicity was in 2011, you might think we
should now be on a downward trend. However, the Earth’s rotation has
continued to increase its rate of slowing over the past few years, so if
there is a correlation between slowing and seismicity then, according
to the hypothesis, we may instead be heading into another period of
higher M7+ earthquake activity. This is what has spawned the sensational
headlines. One of the authors of the paper, Dr. Roger Bilham, was quoted in the Observer newspaper as saying
“We could easily have 20 a year starting in 2018.” However, the fact
that the most recent 2011 peak in seismicity does not correspond to the
peak in slowing may undermine this argument....MUCH MORE
