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