Revolutionary or ridiculous: the link between solar activity and earthquakes

Matthew Morris discusses the link between solar activity and earthquakes.

Earthquakes are destructive natural events, causing an average of 60,000 deaths each year. They are especially devastating as they cannot be accurately predicted, unlike many volcanic eruptions. This lack of forecasting prevents the ability to prepare for these disasters, which can lead to catastrophic consequences.

However, a recent paper published in Nature (Marchitelli et al., 2020) could provide an insight into predicting tremors, due to a correlation between proton density (from the solar wind) and the occurrence of large earthquakes around the world. This may seem like ground-breaking work, however the link between solar activity and earthquake occurrence can be traced as far back as 1853, by the astronomer Rudolf Wolf. Since the correlation was first theorised, there have been studies which have both supported and disproved the link; a paper published as recently as 2013 (Love and Thomas) concluded there is no correlation at all between solar activity and earthquake occurrence. Nonetheless, Marchitelli et al. are so confident of their findings that they state their chances of being wrong are less than 1 in 100,000!

So, how does this recent paper argue that earthquakes can be triggered by the sun? Firstly, it is known that earthquakes follow a non-Poisson distribution, which means that their occurrence is not random and follows a certain pattern. This therefore means that there must be some factor which influences earthquake occurrence, either inside the Earth or external. The paper claims one factor which controls earthquake occurrence is the proton density in the magnetosphere. The magnetosphere is the area of outer space around the Earth, where particles are influenced by Earth’s magnetic field. It is formed by the interactions between the solar wind and the magnetic field of the Earth. The solar wind contains a mixture of particles, including protons. The density of these particles is controlled by solar activity, with the solar wind having periods of high proton density and lower proton density. The study analysed 20 years of proton density and velocity data, as well as the worldwide earthquake distribution over the same period. The correlation between the proton density and the occurrence of large earthquakes with a magnitude over 5.6 was “clear”, with a time-shift of only one day. Conversely, the model outlined to describe this observation was less definitive. The model presents a “reverse piezoelectric effect induced by the applied electric field related to the proton density”. In simpler terms, a high proton density in the magnetosphere could lead to the release of an electrical current through large faults deep underground, destabilising them and potentially leading to movement of the fault, which would release energy as an earthquake.

Although this paper claims the correlation is almost certain, other geophysicists are highly sceptical of the paper’s findings. Greg Beroza, the director of the Southern California Earthquake Center and professor of geophysics at Stanford University, said “the claim seems extraordinary and the physical mechanism is obscure” and labelled the research as “statistical seismology” with “many potential pitfalls” associated with this type of work. John Emilio Vidale, a seismologist at the University of Southern California, was even more scathing of the paper, saying he was “surprised it made it through review”.

Despite the scepticism from the wider geophysical community, if the claims by Marchitelli et al. are correct, this could be a major breakthrough for earthquake studies, particularly in the field of earthquake forecasting. If earthquakes could be forecasted with any degree of accuracy, this would be revolutionary and have the potential to save thousands of lives every year.

From Issue 21