High-resolution Study of the Correlation of Earthquakes and Earth Tides: Constraints on Earthquake Nucleation

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The lunar tide has been suspected of causing earthquakes for more than a century. It is important to understand the influence of tides on the occurrence of earthquakes to improve understanding of the stress and the strain patterns just as an earthquake begins. A better understanding of earthquake nucleation could aid attempts to predict earthquakes.Most previous studies of whether earthquakes are sensitive to tides have been inconclusive. A recently completed project by the investigators showed that earthquake rates are no more than a few percent higher when tides favor stresses than when tides act to discourage earthquakes. This work used tens of thousands of earthquakes on simple parts of the San Andreas fault in northern and central California and computes the tides with a sophisticated model including the moon, the observed tides in the world's oceans, and the detailed coast line in California.This project examines an expanded dataset with greater resolution and resolves the level of tidal influence on earthquakes. The work will also check to be sure that several possible confounding effects, including the temporal clustering of earthquakes into swarms and aftershock sequences and the presence of artifacts in earthquake catalogs do not affect the results. A refined estimate of the effect of lunar tides on the rate of earthquake occurrence will be produced. Results of this study will be useful in the search for new ways to further improve understanding of earthquake nucleation.