Local seismicity around the Chain Transform Fault at the Mid-Atlantic Ridge from OBS observations
Local seismicity around the Chain Transform Fault at the Mid-Atlantic Ridge from OBS observations
Seismicity along transform faults provides important constraints for our understanding of the factors that control earthquake ruptures. Oceanic transform faults are particularly informative due to their relatively simple structure in comparison to their continental counterparts. The seismicity of several fast-moving transform faults has been investigated by local networks, but as of today there been few studies of transform faults in slow spreading ridges. Here, we present the first local seismicity catalogue based on event data recorded by a temporary broad-band network of 39 ocean–bottom seismometers located around the slow-moving Chain Transform Fault (CTF) along the Mid-Atlantic Ridge (MAR) from 2016 to 2017 March. We locate 972 events in the area by simultaneously inverting for a 1-D velocity model informed by the event P- and S-arrival times. We refine the depths and focal mechanisms of the larger events using deviatoric moment tensor inversion. Most of the earthquakes are located along the CTF (700) and Romanche transform fault (94) and the MAR (155); a smaller number (23) can be observed on the continuing fracture zones or in intraplate locations. The ridge events are characterized by normal faulting and most of the transform events are characterized by strike-slip faulting, but with several reverse mechanisms that are likely related to transpressional stresses in the region. CTF events range in magnitude from 1.1 to 5.6 with a magnitude of completeness around 2.3. Along the CTF we calculate a b-value of 0.81 ± 0.09. The event depths are mostly shallower than 15 km below sea level (523), but a small number of high-quality earthquakes (16) are located deeper, with some (8) located deeper than the brittle-ductile transition as predicted by the 600 °C-isotherm from a simple thermal model. The deeper events could be explained by the control of sea water infiltration on the brittle failure limit.
Atlantic Ocean, Mid-ocean ridge processes, Oceanic transform and fracture zone processes, Seismicity and tectonics
1111-1124
Schlaphorst, David
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Rychert, Catherine A.
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Harmon, Nicholas
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Hicks, Stephen P.
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Bogiatzis, Petros
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Kendall, J-Michael
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Abercrombie, Rachel E.
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24 March 2023
Schlaphorst, David
ce763c91-8236-4eac-b256-b35a8613d62b
Rychert, Catherine A.
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
Hicks, Stephen P.
f7c5bbf5-2200-4849-ac31-a650385c6e8b
Bogiatzis, Petros
8fc5767f-51a2-4d3f-aab9-1ee9cfa9272d
Kendall, J-Michael
746f7fc0-ee9e-4436-89d6-a6f26cdec6aa
Abercrombie, Rachel E.
969f3007-9648-4437-8693-21b20eaa6412
Schlaphorst, David, Rychert, Catherine A., Harmon, Nicholas, Hicks, Stephen P., Bogiatzis, Petros, Kendall, J-Michael and Abercrombie, Rachel E.
(2023)
Local seismicity around the Chain Transform Fault at the Mid-Atlantic Ridge from OBS observations.
Geophysical Journal International, 234 (2), .
(doi:10.1093/gji/ggad124).
Abstract
Seismicity along transform faults provides important constraints for our understanding of the factors that control earthquake ruptures. Oceanic transform faults are particularly informative due to their relatively simple structure in comparison to their continental counterparts. The seismicity of several fast-moving transform faults has been investigated by local networks, but as of today there been few studies of transform faults in slow spreading ridges. Here, we present the first local seismicity catalogue based on event data recorded by a temporary broad-band network of 39 ocean–bottom seismometers located around the slow-moving Chain Transform Fault (CTF) along the Mid-Atlantic Ridge (MAR) from 2016 to 2017 March. We locate 972 events in the area by simultaneously inverting for a 1-D velocity model informed by the event P- and S-arrival times. We refine the depths and focal mechanisms of the larger events using deviatoric moment tensor inversion. Most of the earthquakes are located along the CTF (700) and Romanche transform fault (94) and the MAR (155); a smaller number (23) can be observed on the continuing fracture zones or in intraplate locations. The ridge events are characterized by normal faulting and most of the transform events are characterized by strike-slip faulting, but with several reverse mechanisms that are likely related to transpressional stresses in the region. CTF events range in magnitude from 1.1 to 5.6 with a magnitude of completeness around 2.3. Along the CTF we calculate a b-value of 0.81 ± 0.09. The event depths are mostly shallower than 15 km below sea level (523), but a small number of high-quality earthquakes (16) are located deeper, with some (8) located deeper than the brittle-ductile transition as predicted by the 600 °C-isotherm from a simple thermal model. The deeper events could be explained by the control of sea water infiltration on the brittle failure limit.
Text
PILAB_locating_revision2_final_wotc
- Accepted Manuscript
More information
Accepted/In Press date: 15 March 2023
e-pub ahead of print date: 24 March 2023
Published date: 24 March 2023
Additional Information:
DS would like to acknowledge the financial support FCT through project UIDB/50019/2020–IDL. CAR and NH acknowledge funding from from the Natural Environment Research Council (NE/M003507/1), and the European Research Council (GA 638665). CAR acknowledges funding from from the National Science Foundation (NSF-EAR-2147918). J-MK was funded by the Natural Environment Research Council (NE/M004643/1).
Keywords:
Atlantic Ocean, Mid-ocean ridge processes, Oceanic transform and fracture zone processes, Seismicity and tectonics
Identifiers
Local EPrints ID: 476779
URI: http://eprints.soton.ac.uk/id/eprint/476779
ISSN: 0956-540X
PURE UUID: 9d654eaf-e827-478e-ae3c-2013a28e1340
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Date deposited: 15 May 2023 17:10
Last modified: 17 Mar 2024 03:18
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Author:
David Schlaphorst
Author:
Stephen P. Hicks
Author:
Petros Bogiatzis
Author:
J-Michael Kendall
Author:
Rachel E. Abercrombie
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