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Seismicity and accretion processes along the Mid-Atlantic Ridge south of the Azores using data from the MARCHE autonomous hydrophone array

Seismicity and accretion processes along the Mid-Atlantic Ridge south of the Azores using data from the MARCHE autonomous hydrophone array
Seismicity and accretion processes along the Mid-Atlantic Ridge south of the Azores using data from the MARCHE autonomous hydrophone array
The seismicity of the South Atlantic Ocean has been recorded by the MARCHE network of 4 autonomous underwater hydrophones (AUH) moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). The instruments were deployed south of the Azores Plateau between 32° and 39°N from July 2005 to August 2008. The low attenuation properties of the SOFAR channel for earthquake T-wave propagation result in a detection threshold reduction from a magnitude completeness level (Mc) of ~4.3 for MAR events recorded by the land-based seismic networks to Mc=2.1 using this hydrophone array. A spatio-temporal analysis has been performed among the 5600 events recorded inside the MARCHE array. Most events are distributed along the ridge between lat. 39°N on the Azores Platform and the Rainbow (36°N) segment. In the hydrophone catalogue, acoustic magnitude (Source Level, SL) is used as a measure of earthquake size. The source level above which the data set is complete is SLc=205 dB. We look for seismic swarms using the cluster software of the SEISAN package. The criterion used are a minimum SL of 210 to detect a possible mainshock, and a radius of 30 km and a time window of 40 days after this mainshock (Cevatoglu, 2010, Goslin et al., 2012). 7 swarms with more than 15 events are identified using this approach between 32°et 39°N of latitude. The maximum number of earthquake in a swarm is 57 events. This result differs from the study of Simao et al. (2010) as we processed a further year of data and selected sequences with fewer events. Looking at the distribution of the SL as a function of time after the mainshock, we discuss the possible mechanism of these earthquakes : tectonic events with a "mainshock-aftershock" distribution fitting a modified Omori law or volcanic events showing more constant SL values. We also present the geophysical setting of these 7 swarms, using gravity, bathymetry, and available local geological data. This study illustrates the potential of hydrophone data to monitor segment-scale ridges processes in the vicinity of the Lucky Strike seafloor observatory (lat. 37°20'N), the Azores node of the EMSO (European Multidiciplinary Subsea Observatory) system.
Perrot, Julie
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Cevatoglu, Melis
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Cannat, Mathilde
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Escartin, Javier
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Maia, Marcia
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Tisseau, Chantal
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Dziak, Robert
de0b46c8-6be9-4344-9123-3a89e562705d
Goslin, Jean
15652f62-2da5-409f-90aa-ebe7235a98eb
Perrot, Julie
c4967046-80c4-4d08-9354-a9c79a4832bc
Cevatoglu, Melis
bcd1a613-f62c-4ae2-bd6e-d59038b6940a
Cannat, Mathilde
11857dcd-89f7-470a-8714-250a0b43f239
Escartin, Javier
43307177-8a31-43f6-a803-32ead6382526
Maia, Marcia
f279b156-f836-4cfb-bfcd-1ee521a4f97c
Tisseau, Chantal
2bd0b942-2984-4982-a2ff-9f2eb92df25f
Dziak, Robert
de0b46c8-6be9-4344-9123-3a89e562705d
Goslin, Jean
15652f62-2da5-409f-90aa-ebe7235a98eb

Perrot, Julie, Cevatoglu, Melis, Cannat, Mathilde, Escartin, Javier, Maia, Marcia, Tisseau, Chantal, Dziak, Robert and Goslin, Jean (2013) Seismicity and accretion processes along the Mid-Atlantic Ridge south of the Azores using data from the MARCHE autonomous hydrophone array. EGU General Assembly 2013, Vienna, Austria. 07 Apr 2013 - 12 Apr 2017 .

Record type: Conference or Workshop Item (Other)

Abstract

The seismicity of the South Atlantic Ocean has been recorded by the MARCHE network of 4 autonomous underwater hydrophones (AUH) moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). The instruments were deployed south of the Azores Plateau between 32° and 39°N from July 2005 to August 2008. The low attenuation properties of the SOFAR channel for earthquake T-wave propagation result in a detection threshold reduction from a magnitude completeness level (Mc) of ~4.3 for MAR events recorded by the land-based seismic networks to Mc=2.1 using this hydrophone array. A spatio-temporal analysis has been performed among the 5600 events recorded inside the MARCHE array. Most events are distributed along the ridge between lat. 39°N on the Azores Platform and the Rainbow (36°N) segment. In the hydrophone catalogue, acoustic magnitude (Source Level, SL) is used as a measure of earthquake size. The source level above which the data set is complete is SLc=205 dB. We look for seismic swarms using the cluster software of the SEISAN package. The criterion used are a minimum SL of 210 to detect a possible mainshock, and a radius of 30 km and a time window of 40 days after this mainshock (Cevatoglu, 2010, Goslin et al., 2012). 7 swarms with more than 15 events are identified using this approach between 32°et 39°N of latitude. The maximum number of earthquake in a swarm is 57 events. This result differs from the study of Simao et al. (2010) as we processed a further year of data and selected sequences with fewer events. Looking at the distribution of the SL as a function of time after the mainshock, we discuss the possible mechanism of these earthquakes : tectonic events with a "mainshock-aftershock" distribution fitting a modified Omori law or volcanic events showing more constant SL values. We also present the geophysical setting of these 7 swarms, using gravity, bathymetry, and available local geological data. This study illustrates the potential of hydrophone data to monitor segment-scale ridges processes in the vicinity of the Lucky Strike seafloor observatory (lat. 37°20'N), the Azores node of the EMSO (European Multidiciplinary Subsea Observatory) system.

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More information

Published date: April 2013
Venue - Dates: EGU General Assembly 2013, Vienna, Austria, 2013-04-07 - 2017-04-12
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 382723
URI: http://eprints.soton.ac.uk/id/eprint/382723
PURE UUID: db77758c-f09c-47e6-b8f7-0d7cff42f7cb

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Date deposited: 16 Oct 2015 12:22
Last modified: 01 Aug 2023 17:02

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Contributors

Author: Julie Perrot
Author: Melis Cevatoglu
Author: Mathilde Cannat
Author: Javier Escartin
Author: Marcia Maia
Author: Chantal Tisseau
Author: Robert Dziak
Author: Jean Goslin

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