Comment on “Coincident locations of rupture nucleation during the 2019
Le Teil earthquake, France and maximum stress change from local cement
quarrying” by De Novellis et al.
De Novellis et al. (2020, hereafter DN20) studied the effect of mass
extraction from a quarry on the occurrence of the Mw 4.9 Le Teil,
France, earthquake of November 11 2019. This topic was also the focus of
the report of the French working group mandated by CNRS INSU (“Groupe
de Travail Teil” of Institut National des Sciences de l’Univers du
Centre National de la Recherche Scientifique; Delouis et al, 2019).
Despite using similar data and methods, these two independent research
efforts reached contrasting conclusions. While both concluded the
earthquake was possibly a triggered event (i.e. its initiation was
possibly promoted by the quarry activity but its further rupture growth
was primarily enabled by natural pre-existing stresses), DN20 deemed
realistic the hypothesis that the earthquake was an induced event (i.e.
both the earthquake initiation and its further growth, up to its final
size, were caused by the quarry activity). This distinction is critical
for our understanding of future anthropogenic hazards in the region and
in similar settings elsewhere, and may have significant social,
economical and legal repercussions. Here, we show that a severe error in
the calculations carried by DN20 undermines their conclusion.