Volcano Statistics Casebook: Tentative evidence from two real-time analyses for an Earth tide influence on volcano-seismic events

Abstract

Based on rapid analyses done in near real-time and in support of scientific advice, I present two cases of prima facie evidence for an Earth tide triggering effect on earthquake activity during two volcanic eruption episodes: the first in relation to large magnitude earthquakes during August 2014 in the 2014-15 Bárðarbunga-Holuhruan, Iceland, eruption; and the second concerning the timing of VT strings at the Soufrière Hills Volcano, Montserrat. In both cases, statistical testing of the hypothesis that the timings of the seismic events of interest and vertical Earth tide phase were not correlated produced probabilities at or below a 5% significance level, suggesting rejection of the hypothesis can be argued. This note outlines the method used for computing Earth tide amplitudes at the two volcanoes and the basis and results of the Schuster test for relative phase timings; some comments on the volcanological contexts are added. These findings suggest further, more formal analysis may be warranted.