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Constraining the maximum depth of brittle deformation at slow- and ultraslow-spreading ridges using microseismicity.

Grevemeyer, I. and Hayman, N.W. and Lange, D. and Peirce, C. and Papenberg, C. and Van Avendonk, H.J.A and Schmid, F. and Gomez de La Pena, L. and Dannowski, A. (2019) 'Constraining the maximum depth of brittle deformation at slow- and ultraslow-spreading ridges using microseismicity.', Geology., 47 (11). pp. 1069-1073.

Abstract

The depth of earthquakes along mid-ocean ridges is restricted by the relatively thin brittle lithosphere that overlies a hot, upwelling mantle. With decreasing spreading rate, earthquakes may occur deeper in the lithosphere, accommodating strain within a thicker brittle layer. New data from the ultraslow-spreading Mid-Cayman Spreading Center (MCSC) in the Caribbean Sea illustrate that earthquakes occur to 10 km depth below seafloor and, hence, occur deeper than along most other slow-spreading ridges. The MCSC spreads at 15 mm/yr full rate, while a similarly well-studied obliquely opening portion of the Southwest Indian Ridge (SWIR) spreads at an even slower rate of ∼8 mm/yr if the obliquity of spreading is considered. The SWIR has previously been proposed to have earthquakes occurring as deep as 32 km, but no shallower than 5 km. These characteristics have been attributed to the combined effect of stable deformation of serpentinized mantle and an extremely deep thermal boundary layer. In the context of our MCSC results, we reanalyze the SWIR data and find a maximum depth of seismicity of 17 km, consistent with compilations of spreading-rate dependence derived from slow- and ultraslow-spreading ridges. Together, the new MCSC data and SWIR reanalysis presented here support the hypothesis that depth-seismicity relationships at mid-ocean ridges are a function of their thermal-mechanical structure as reflected in their spreading rate.

Item Type:Article
Full text:Publisher-imposed embargo
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Full text:(VoR) Version of Record
Available under License - Creative Commons Attribution.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1130/G46577.1
Publisher statement:© 2019 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license.
Date accepted:22 August 2019
Date deposited:27 August 2019
Date of first online publication:23 September 2019
Date first made open access:22 October 2019

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