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Tidal Triggering of Microseismicity at the Equatorial Mid-Atlantic Ridge, Inferred from OBS Network
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  • Konstantinos Leptokaropoulos,
  • Nicholas Harmon,
  • Stephen P. Hicks,
  • Catherine A. Rychert,
  • David Schlaphorst,
  • John-Michael Kendall
Konstantinos Leptokaropoulos
University of Southampton

Corresponding Author:k.leptokaropoulos@soton.ac.uk

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Nicholas Harmon
University of Southampton
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Stephen P. Hicks
Imperial College London
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Catherine A. Rychert
University of Southampton
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David Schlaphorst
Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa
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John-Michael Kendall
University of Oxford
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The gravitational pulls from the moon and the sun result in tidal forces which influence both Earth’s solid and water mass. These stresses are periodically added to the tectonic ones and may become sufficient for initiating rupture in fault systems critically close to failure. Previous research indicates correlations between increased seismicity rates and low tides for mid-ocean, fast-spreading ridges in Pacific ocean. Here, we present a microseismicity dataset (4719 events) from an Ocean Bottom Seismometer (OBS) network at the equatorial Mid-Atlantic Ridge, suggesting a significant correlation between seismic potential and tidal forces. We show that low as well as decreasing ocean water level results in elevated seismicity rates and lower b-values, translated into considerably increased probabilities of stronger event occurrence at or towards low tides. In addition, seismic bursts (enhanced activity rate clusters), occurring at rates fairly above the reference seismicity, are exclusively present during either high extensional stresses or high extensional stress rates. Our results exhibit remarkable statistical significance, supporting the previous findings for tidal triggering at low tides within normal-faulting regimes and extending the range of observations to slow-spreading ridges. Observed triggering of slip on low angle faults at low tides is predicted by Coulomb stress modelling. The triggering of slip on high angle faults observed here, is not easily explained without another factor. It may be related to fatigue and/or the presence of a shallow magma body beneath the ridge, as suggested by previous seismic imaging in the region.