Tidal triggering of microseismicity at the equatorial mid-atlantic ridge, inferred from the PI-LAB experiment
Tidal triggering of microseismicity at the equatorial mid-atlantic ridge, inferred from the PI-LAB experiment
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 fast- and intermediate-spreading mid-ocean ridges in the Pacific Ocean. Here, we present a microseismicity data set (4,719 events) recorded by an ocean bottom seismometer deployment at the equatorial Mid-Atlantic Ridge. We show that low, as well as decreasing ocean water level, result in relatively elevated seismicity rates at higher magnitudes (lower b-values), translated into increased probabilities of stronger event occurrence at or towards low tides. Moreover, seismic bursts (enhanced activity rate clusters), occurring at rates well above the reference seismicity, are exclusively present during values of either high tidally induced extensional stresses or high extensional stress rates. Although the b-value differences are not significant enough to be conclusive, the seismicity rate variations exhibit 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 modeling. The triggering of slip on high angle faults observed here, is not easily explained without another factor. It may be related to the presence of a shallow magma body beneath the ridge, as supported by previous seismic imaging in the region.
Coulomb stress, Mid-Atlantic Ridge, b-values, magnitude distribution, seismicity, tidal triggering
e2021JB022251
Leptokaropoulos, K.
6176f4d8-7af0-4575-bf2c-5aaba3d182ce
Harmon, N.
10d11a16-b8b0-4132-9354-652e72d8e830
Hicks, S. P.
036d1b3b-bb7a-4a22-b2ce-71618a1723a3
Rychert, C. A.
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Schlaphorst, D.
ce763c91-8236-4eac-b256-b35a8613d62b
Kendall, J. M.
b756ae31-0e86-465c-92c4-083eaab3f6d5
September 2021
Leptokaropoulos, K.
6176f4d8-7af0-4575-bf2c-5aaba3d182ce
Harmon, N.
10d11a16-b8b0-4132-9354-652e72d8e830
Hicks, S. P.
036d1b3b-bb7a-4a22-b2ce-71618a1723a3
Rychert, C. A.
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Schlaphorst, D.
ce763c91-8236-4eac-b256-b35a8613d62b
Kendall, J. M.
b756ae31-0e86-465c-92c4-083eaab3f6d5
Leptokaropoulos, K., Harmon, N., Hicks, S. P., Rychert, C. A., Schlaphorst, D. and Kendall, J. M.
(2021)
Tidal triggering of microseismicity at the equatorial mid-atlantic ridge, inferred from the PI-LAB experiment.
Journal of Geophysical Research: Solid Earth, 126 (9), , [e2021JB022251].
(doi:10.1029/2021JB022251).
Abstract
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 fast- and intermediate-spreading mid-ocean ridges in the Pacific Ocean. Here, we present a microseismicity data set (4,719 events) recorded by an ocean bottom seismometer deployment at the equatorial Mid-Atlantic Ridge. We show that low, as well as decreasing ocean water level, result in relatively elevated seismicity rates at higher magnitudes (lower b-values), translated into increased probabilities of stronger event occurrence at or towards low tides. Moreover, seismic bursts (enhanced activity rate clusters), occurring at rates well above the reference seismicity, are exclusively present during values of either high tidally induced extensional stresses or high extensional stress rates. Although the b-value differences are not significant enough to be conclusive, the seismicity rate variations exhibit 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 modeling. The triggering of slip on high angle faults observed here, is not easily explained without another factor. It may be related to the presence of a shallow magma body beneath the ridge, as supported by previous seismic imaging in the region.
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Published date: September 2021
Additional Information:
Funding Information:
C.A. Rychert, N. Harmon and K. Leptokaropoulos acknowledge funding from the Natural Environment Research Council (NE/M003507/1) and the European Research Council (GA 638665). J.‐M. Kendall was funded by the Natural Environment Research Council (NE/M004643/1). D. Schlaphorst was supported by the Portuguese Science and Technology Foundation (FCT/Fundação para a Ciência e Tecnologia), under project PTDC/CTA‐GEF/30264/2017 and UIDB/50019/2020 – IDL. We thank the captain and crew of the R/V and the RRS , and also the scientific technicians. We thank William Wilcock and an anonymous reviewer, the Associate Editor and Editor, Rachel Abercrombie, for their insightful suggestions and comments. Marcus G. Langseth Discovery
Funding Information:
C.A. Rychert, N. Harmon and K. Leptokaropoulos acknowledge funding from the Natural Environment Research Council (NE/M003507/1) and the European Research Council (GA 638665). J.-M. Kendall was funded by the Natural Environment Research Council (NE/M004643/1). D. Schlaphorst was supported by the Portuguese Science and Technology Foundation (FCT/Funda??o para a Ci?ncia e Tecnologia), under project PTDC/CTA-GEF/30264/2017 and UIDB/50019/2020 ? IDL. We thank the captain and crew of the R/V Marcus G. Langseth and the RRS Discovery, and also the scientific technicians. We thank William Wilcock and an anonymous reviewer, the Associate Editor and Editor, Rachel Abercrombie, for their insightful suggestions and comments.
Publisher Copyright:
© 2021. The Authors.
Keywords:
Coulomb stress, Mid-Atlantic Ridge, b-values, magnitude distribution, seismicity, tidal triggering
Identifiers
Local EPrints ID: 451316
URI: http://eprints.soton.ac.uk/id/eprint/451316
ISSN: 2169-9313
PURE UUID: c8f9eb5a-f0d5-4589-8357-0977d0f2f521
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Date deposited: 20 Sep 2021 16:32
Last modified: 17 Mar 2024 04:05
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Contributors
Author:
S. P. Hicks
Author:
D. Schlaphorst
Author:
J. M. Kendall
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