Tidal triggering evidence of shallow and intermediate depth earthquakes
Speaker: Shao Yilien
Abstract
There has been a lot of use of statistical methods to explore the correlation between tides and earthquakes. The gravitational force is the main external force which could affect the dynamic process of the inner earth. As for the Earth's interior, its tidal stresses increase with decreasing depth due to the deeper the greater the confining pressure, and tidal forces are the total stress about the earth tide and the oceanic loading imposed a point on the ocean. Therefore, we calculate the Earth's interior phase angle relationship between the tidal wave and the tidal stress, and use different statistical methods to view the tidal forces whether triggering earthquakes or not. Using the statistical methods : 1. Statistical tests has been widely used in tidal triggering studies. 2. Permutation tests allow for calculating the probability (Pp ) of the significance level to reject the null hypothesis in which the distribution is random. It could extend statistical where Schuster's test is not adequate. Validation of the conclusions becomes more robust if both test show similarity. 3. Binomial test: it is an exact test of the statistical significance of deviations from a theoretically expected distribution of observations into two categories. These method can be use to determine the relationship between the earthquake and the tide. It is not only to test the tidal-earthquake time relation, but also test different values of friction coefficient Łg (0.2, 0.4, or 0.6). From the result, data set systematic temporal patterns related to the decrease of the P values seem to precede the occurrence of larger earthquakes. And study shows a statistically significant increase in triggering of globally distributed large tectonic events ( M >5.5) with increasing tidal stress amplitudes.
Reference
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N. Cadicheanu, M. van Ruymbeke, and P. Zhu (2007) Tidal triggering evidence of intermediate depth earthquakes in the Vrancea zone (Romania). Nat. Hazards Earth Syst. Sci., 7, 733-74.