Wilcock
Tidal Triggering of Earthquakes on the Endeavour Segment of the Juan de Fuca Ridge
W. Wilcock¹, R. Weekly¹, E. Hooft², & D. Toomey²
Corresponding author: wilcock@u.washington.edu
¹School of Oceanography, University of Washington, Seattle, WA
²Department of Geological Sciences, University of Oregon, Eugene, OR 97403
Abstract:
A number of studies on mid‐ocean ridges have documented a clear tidal triggering signal for volcanic/hydrothermal microearthquakes with earthquake rates increasing during intervals when the tidal stresses are least compressive. Tidal triggering has been demonstrated for the Endeavour segment in 19951, Axial Seamount2 and the East Pacific Rise near 9°50’N3,4. The results from the EPR are particularly exciting because they show a very strong tidal triggering signal indicating that the crust was critically stressed prior to the 2005‐6 volcanic eruption and they show spatial variations in the earthquake phase that can be reproduced by poroelastic models the predict the permeability5. A preliminary analysis for tidal triggering in the first year of the Keck microearthquake data set at the Endeavour ISS (2003‐4) reveals a clear tidal triggering signal (see attached figure) that is much stronger than observed in 1995 although not quite as strong as seen at the EPR. The preliminary catalog for the full 3‐year Keck data set (2003‐6) shows a strong decrease in the levels of seismicity following a regional earthquake swarm in February, 2005. This is interpreted in terms of a change in the regional stress state at the end of a 6‐year noneruptive spreading event6. We speculate that this change in stress state may lead to a decrease in the strength of the tidal triggering signal for the portion of the catalog after February 2007 and plan to analyze the catalog once it is finalized to test this idea.
Contributions to Integration and Synthesis:
This work is part of a more extensive study to complete the analysis of the Keck microearthquake data set and integrate it with other observations at the Endeavour. The 3‐year catalog will be released to the Ridge community by the end of this colander year. Timothy Crone is funded by NSF to model spatial variations in tidal triggering at the EPR and will extend his studies to the Endeavour using our data. We will compare the tidal triggering signals between the EPR and Endeavour.
References
- Wilcock, W. S. D., Tidal triggering of microearthquakes on the Juan de Fuca Ridge. Geophys. Res. Lett 28, 3999‐4002 (2001).
- Tolstoy, M., Vernon, F. L., Orcutt, J. A., and Wyatt, F. K., Breathing of the seafloor: Tidal correlations of seismicity at Axial Volcano. Geology 30, 503‐506 (2002).
- Stroup, D. F. et al., Pulse of the seafloor: Tidal triggering of microearthquakes at 9°50'N East Pacific Rise. Geophys. Res. Lett. 34, L15301, doi:15310.11029/12007GL030088 (2007).
- Stroup, D. F. et al., Tidal triggering of microearthquakes constrains permeability at 9º50'N East Pacific Rise. Eos Trans. AGU 89 (53), Fall Meet. Suppl., Abstract B21A‐0324 (2008).
- Crone, T. J., Tolstoy, M., and Stroup, D. F., Two‐dimensional models of poroelastically controlled earthquake triggering at the East Pacific Rise. Eos Trans. AGU 89 (53), Fall Meet. Suppl., Abstract B23F‐06 (2008).
- Weekly, R. T. et al., An automatically generated earthquake catalog for the Endeavour Segment of the Juan de Fuca Ridge: Linkages between segment and vent‐field scale seismicity. Eos Trans. AGU 89 (53), Fall Meet. Suppl., Abstract V54B‐02 (2008).
Figures
Figure 1. Histogram showing tidal triggering on the Endeavour for 2003‐2004. The number of earthquakes is plotted against the phase of ocean tides with a phase of 180° indicating low tides. The incidence of earthquakes at low tide is over two times higher than at high tide. Wilcock_fig1.jpg
