Master´s thesis defense by Jeanette Aabye – Niels Bohr Institute - University of Copenhagen

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Master´s thesis defense by Jeanette Aabye

Tidal Triggering of Earthquakes on the Reykjanes Peninsula
he possibility of earthquake triggering induced by tidal forces from the Sun and the Moon has been discussed for more than a century without any final conclusion.
The possibility of triggering is investigated on small, shallow independent earthquakes on the Reykjanes Peninsula for the years 1995-2011. Shuster's test is used to find a correlation between the occurrence times of these events and the solid earth tide stresses effective in both the normal and shear direction at the surface. Further investigation of tide gauge data depicting the ocean tide is performed to indirectly test the triggering effect of ocean tidal loading. Based on findings it is suggested that Shuster's test should be applied to subsets containing 800 independent events or more in order to ensure reliable results.

The solid earth tide is found to be a triggering factor in the occurrence times of earthquakes, however no indication of triggering due to ocean loading are found. Tidal triggering is found for the whole Reykjanes Peninsula at times of increasing tensile solid earth tide stresses. The triggering effect is most prominent in the eastern part of the peninsula dominated by an oblique stress state whereas no tidal triggering is observed in the western part where normal stresses are most effective on the fault planes. The increase in earthquakes observed during maximum triggering are around 1\% mostly consisting of microearthquakes.

Tidal Triggering occur during time of increasing tensile solid earth tide stresses and at time periods of crustal instability implying that tidal triggering of earthquakes could be used as a precursor of impending moderate to large earthquakes. It is further implied that aftershocks surrounding these larger events are tidal triggered, however further investigations are needed.