Seismic Cycles on Oceanic Transform Faults

Seismic Cycles on Oceanic Transform Faults Figure 1. Updated after McGuire [2008]. Earthquakes in the Global CMT catalogs for the Gofar and Discovery transform faults for the time period from 1990–2010. Pairs of MW ≥ 5.5 mainshocks that have been determined to have overlapping rupture areas are shown with matching colors and are not at exactly the same longitude due to errors in the CMT location estimates. Major and minor spreading centers are shown by thick and thin gray lines, respectively.
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The long-standing hypothesis that the timing of the largest earthquakes is primarily controlled by quasi-periodic seismic cycles, where stress builds up for an extended period of time and then is released suddenly in a large earthquake, has been difficult to verify due to the long repeat times (50-1000 years) of the largest earthquakes on most faults. By contrast, repeat times of the largest oceanic transform fault earthquakes are remarkably short and regular. Thermal processes appear to have a strong control on oceanic transform seismicity including the magnitude of the largest earthquake on a particular fault [Boettcher and Jordan, 2004]. Using datasets from the Global Seismic Network that span 20+ years of recording at the same sites, we determined that the largest earthquakes on warm EPR transform faults repeat every ~5 years on a relatively regular cycle [McGuire, 2008]. Moreover, the duration of the seismic cycle increases for colder faults according to a simple scaling relation [Boettcher and McGuire, 2009]. The quasi-periodic nature of oceanic transforms seismic cycles allowed us to successfully position an array of ocean bottom seismometers on the Gofar Transform Fault to capture a Mw 6.0 earthquake in 2008. Our successful experiment on the Gofar Fault has further demonstrated that oceanic transform faults have predictable seismic characteristics including relatively regular seismic cycles.
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References
</p><p>Boettcher, M. S., and T. H. Jordan (2004), Earthquake Scaling Relations for Mid-Ocean Ridge Transform Faults, J. Geophys. Res., B12302, doi:1029/2004JB003110.
</p><p>Boettcher, M. S., and J. J. McGuire (2009), Scaling relations for seismic cycles on mid-ocean ridge transform faults, Geophys. Res. Lett., 36, L21301, doi:21310.21029/22009GL040115.
</p><p>McGuire, J. J. (2008), Seismic Cycles and Earthquake Predictability on East Pacific Rise Transform Faults, Bull. Seismol. Soc. Amer., 98, 1067- 1084, doi: 1010.1785/0120070154.
</p><p>Acknowledgements: We thank the Global Seismic Network program for collecting the datasets over the last 20+ years that were necessary for us to conduct this research.</p>

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