A review of tidal triggering of global earthquakes

Earthquake prediction remains a challenging and difficult task for scientists all over the world.The tidal triggering of earthquakes is being proven by an increasing number of investigations,most of which have shown that earthquakes are positively correlated with tides,and thus,tides provide a potential tool for earthquake prediction,especially for imminent earthquakes.In this study,publications concerning the tidal triggering of earthquakes were compiled and analyzed with regard to global earthquakes,which were classified into three main types:tectonic,volcanic,and slow earthquakes.The results reveal a high correlation between tectonic earthquakes and tides(mainly for semidiurnal and diurnal tides;14-day tides) before and after the occurrence of significant earthquakes.For volcanic earthquakes,observations of volcanoes on the seafloor and land indicate that volcanic earthquakes in near-shore volcanic areas and mid-ocean ridges have a strong correlation with tidal forces,mostly those with semidiurnal and diurnal periods.For slow earthquakes,the periodicity of the tremor duration is highly correlated with semidiurnal and diurnal tides.In conclusion,the tidal triggering of these three types of earthquakes makes a positive contribution to earthquake preparation and understanding the triggering mechanism,and thus,the prediction of these types of earthquakes should be investigated.However,there are still several inadequacies on this topic that need to be resolved to gain a definitiveanswer regarding the tidal triggering of all earthquakes.The main inadequacies are discussed in this paper from our point of view.

Tidal triggering of seismicity in the region of Palu, Central Sulawesi, Indonesia

This paper investigates the correlation between tidal stress and earthquakes for periods ranging from hours to months in the limited zone of the Palu region(Central Sulawesi,Indonesia).Through Schuster and binomial tests,we examined the relation between the seismicity(time density of seismic events)and tidal potential arising from the Moon and Sun,using all tidal components simultaneously and focusing on the estimation of specific terms.The results show significant correlations between the seismicity and tidal potential for S2(0.5 d)and O1(1.075 d)tidal components in the case of solely isolated earthquake events,particularly for shallow earthquakes.Meanwhile,there is a strong relationship between aftershocks and tidal components larger than the Mf period(13.661 d).Finally,the analysis of the temporal variation of the earthquake-tide relation reveals an optimal correlation for about six years before the 2018 great Palu earthquake.The correlation becomes insignificant afterwards.

Evidence of earthquakes triggered by the tidal force of the sun and the moon——On the temporal characteristics of the earthquakes in Xingtai,Hejian and Tangshan

Studies by many scientists show that Hebei, China is an area with strong correlation between the tidal force and the occurrences of major earthquakes, the Xingtai earthquake of 1966, the Hejian earthquake of 1967 and the Tangshan earthquake of 1976 were triggered by the tidal force, in this paper the study on the common characteristics of their occurrence times confirms these facts. The computed times of maximum horizontal of the semi diurnal solid tide tidal force show that the occurrence times of the above mentioned earthquakes were close to the times of maximum horizontal tidal force of the semi diurnal solid tide at new moon or full moon. The Longyao earthquake of M =6.8, the Ningjin earthquake of M =7.2 and the Hejian earthquake of M =6.3 occurred tens of minutes after the maximum horizontal tidal force of the semi diurnal solid tides, and the Tangshan earthquake of M =7.8 occurred 16 minutes before the maximum horizontal tidal force. The tidal forces were directed to the west. This is their temporal characteristic. It is generally accepted that the 1969 Bohai earthquake of M =7.4 and the 1975 Haicheng earthquake were not triggered by the tidal force. These events did not show such characteristics. The temporal characteristics of the earthquakes indicate that the occurrences of these events were not random, but were controlled by the tidal force from the sun and the moon, and triggered by the tidal force. These facts agree with the triggering mechanism of the tidal force, are evidences of earthquakes triggered by tidal force.