Review: Earthquakes and the Moon

Title: Earthquakes and the Moon: Syzygy Predictions Fail the Test

Authors: Matthew Kennedy, John E. Vidale and Michael G. Parker
Journal: Seismological Research Letters (2004) 75 (5): 607-612

Why I read it:

Recently, I wonder if the Super Moon would influence the number of earthquakes (and maybe volcanic eruptions). Which led me to just check first if the Moon had any influence at all on earthquake rates.

Summary:

The authors use statistics, mathematics, and experimental data to assess the validity of the claim (called Syzygy predictions) that new and full moon tides add enough stress to trigger more earthquakes, and that larger earthquakes can be registered during this period. The authors take two sets of data off the U.S. coast on earthquakes (with magnitude above 2) and tidal records. They make a Monte-Carlo simulation to have a random distribution of earthquakes, which have a certain probability to happen randomly during the Syzygy’s predicted time period (probability distribution function).  This simulation allows them to set the minimum correlation to at least 90%. Then, they carefully apply a tidal envelope function (to set a recurring time period corresponding to high-low tides) to their data sets, as a whole, and separated by magnitude range. For both data sets (two different geographical locations) as a whole, the distribution function (Gaussian-like) shows that no correlation can be found. It is their conclusion that the correlation advanced by some other publications could be then interpreted as statistically flawed.

My view on the article:

I really like the cautious way the authors defined their data sets. Removing aftershocks (any earthquakes occurring in less than 24 hours interval) and verifying if the tidal change depending on the geographical setting (they found none significant within a single day). I appreciate the use of simulation to assess the randomness of a set of earthquakes happening periodically (they made a simulation with 25K events). It was also quite clever to assess the occurrence of the earthquake at different magnitude range since some had claimed to find a correlation between higher frequency of stronger earthquakes and the Syzygy effect (alignment of Moon, Earth, and Sun). Though I would like to point out that the number of earthquakes above magnitude 4 is too low for any statistical significance, in my opinion.

What to make of it all:

while the idea of the high tides having a triggering effect on the release of earthquakes is an alluring one, as it could be a valuable tool to predict their occurrence, it is most likely only whimsical thinking. Mind that I only read few articles (from scientific journals and newspapers) and that this article has made an analysis on a specific type of geological formation and has a limited data set (for accuracy purposes I assume).

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