Why has tidal triggering effect been controversial?
Speaker: Hong-Jia Chen
Abstract
Even though the effects of the tidal triggering on the occurrence of earthquakes has been investigated since 1930s, whether the tidal triggering is one of the triggering mechanisms is still debatable. Knopoff [1964] used two types of correlations to analyze earthquake catalog of Southern California with tidal acceleration, but did not find any correlation between the occurrence times of earthquakes and the tidal potential. On the basis of the congruence of the actual distribution and the theoretical random distributions of 22561 global earthquakes, Simpson [1967] concluded that earthquakes are not triggered by specific amplitudes of earth tide component forces. Hartzel and Heaton [1989] searched earthquake catalogs for one periodicity by plotting occurrence times of earthquakes on rose diagrams, but no statistically significant periodicity is seen in either the Southern California network catalog or the world-wide catalog at the fortnightly tidal period or at periods of 1 day or 365 days. Wilcock [2001] investigated 1899 microearthquakes on Endeavour segment of the Juan de Fuca Ridge for tidal triggering, and he found earthquakes occur more frequently near low tides when the extensional stresses are a maximum. Tolstoy et al. [2002] analyzed 402 microseismic events on the summit caldera of Axial volcano on the Juan de Fuca Ridge, and the microearthquakes show a strong correlation with tidal lows. Some of the reports claim to find positive correlations of earthquake events with solar or lunar periodicities and others do not. The inconsistency between those studies may result from statistically small samples, earthquake magnitudes used in research, and region effects, etc.
Reference
Knopoff, L., Earth tides as a triggering mechanism for earthquakes, Bull. Seismol. Soc. Am., 54, 1865-1870, 1964.
Wilcock, W. S. D., Tidal triggering of microearthquakes on the Juan de Fuca Ridge, Geophys. Res. Lett., 28, 3999-4002, 2001.