Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB Experiment
Abstract The ocean lithosphere represents a simple realisation of the tectonic plate, offering a unique opportunity to better understand its physical and chemical properties in relationship to those of the underlying asthenosphere. While seismic velocity is frequently used to image the plate, seismi...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Wiley
2021-12-01
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| Series: | Geochemistry, Geophysics, Geosystems |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2021GC010085 |
| _version_ | 1827771622665224192 |
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| author | Utpal Saikia Catherine A. Rychert Nicholas Harmon J. Michael Kendall |
| author_facet | Utpal Saikia Catherine A. Rychert Nicholas Harmon J. Michael Kendall |
| author_sort | Utpal Saikia |
| collection | DOAJ |
| description | Abstract The ocean lithosphere represents a simple realisation of the tectonic plate, offering a unique opportunity to better understand its physical and chemical properties in relationship to those of the underlying asthenosphere. While seismic velocity is frequently used to image the plate, seismic attenuation (Qμ−1) offers an important complimentary observation. We use fundamental mode Rayleigh waves from 17 local, M > 4.2 earthquakes recorded at stations located on 0–80 My old lithosphere near the equatorial Mid‐Atlantic Ridge. We determine the attenuation coefficient (γ) for periods between 15 and 40 s and invert for 1‐D average shear wave quality factor values (Qμ) and shear wave velocity (Vs). We find Qμ values of 175 ± 16 at 50 km depth, decreasing to 90 ± 15 at greater than 60 km. Comparison of our Qμ and Vs measurements to previous observations from oceanic settings shows agreement in terms of higher Qμ and Vs in the lithosphere in comparison to the asthenosphere. The observations from oceanic settings are in general agreement with the laboratory predictions for Qμ‐Vs relationships for thermal models. However, a small amount of partial melt (1%) is required to explain several previous observations. Our result also compares favorably to previous observations of lithospheric and asthenospheric attenuation with respect to frequency. Melt is not required for the 1‐D average of our study area, consistent with previous electromagnetic and seismic imaging that suggested melt in punctuated and/or thin channel anomalies rather than over broad regions of the mantle. |
| first_indexed | 2024-03-11T12:56:51Z |
| format | Article |
| id | doaj.art-c63e2668376f4d50bda37342b7e11f74 |
| institution | Directory Open Access Journal |
| issn | 1525-2027 |
| language | English |
| last_indexed | 2024-03-11T12:56:51Z |
| publishDate | 2021-12-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj.art-c63e2668376f4d50bda37342b7e11f742023-11-03T17:00:43ZengWileyGeochemistry, Geophysics, Geosystems1525-20272021-12-012212n/an/a10.1029/2021GC010085Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB ExperimentUtpal Saikia0Catherine A. Rychert1Nicholas Harmon2J. Michael Kendall3Ocean and Earth Science, University of Southampton Southampton UKOcean and Earth Science, University of Southampton Southampton UKOcean and Earth Science, University of Southampton Southampton UKDeparment of Earth Sciences University of Oxford Oxford UKAbstract The ocean lithosphere represents a simple realisation of the tectonic plate, offering a unique opportunity to better understand its physical and chemical properties in relationship to those of the underlying asthenosphere. While seismic velocity is frequently used to image the plate, seismic attenuation (Qμ−1) offers an important complimentary observation. We use fundamental mode Rayleigh waves from 17 local, M > 4.2 earthquakes recorded at stations located on 0–80 My old lithosphere near the equatorial Mid‐Atlantic Ridge. We determine the attenuation coefficient (γ) for periods between 15 and 40 s and invert for 1‐D average shear wave quality factor values (Qμ) and shear wave velocity (Vs). We find Qμ values of 175 ± 16 at 50 km depth, decreasing to 90 ± 15 at greater than 60 km. Comparison of our Qμ and Vs measurements to previous observations from oceanic settings shows agreement in terms of higher Qμ and Vs in the lithosphere in comparison to the asthenosphere. The observations from oceanic settings are in general agreement with the laboratory predictions for Qμ‐Vs relationships for thermal models. However, a small amount of partial melt (1%) is required to explain several previous observations. Our result also compares favorably to previous observations of lithospheric and asthenospheric attenuation with respect to frequency. Melt is not required for the 1‐D average of our study area, consistent with previous electromagnetic and seismic imaging that suggested melt in punctuated and/or thin channel anomalies rather than over broad regions of the mantle.https://doi.org/10.1029/2021GC010085attenuationsurface waveMid Atlantic Ridge |
| spellingShingle | Utpal Saikia Catherine A. Rychert Nicholas Harmon J. Michael Kendall Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB Experiment Geochemistry, Geophysics, Geosystems attenuation surface wave Mid Atlantic Ridge |
| title | Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB Experiment |
| title_full | Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB Experiment |
| title_fullStr | Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB Experiment |
| title_full_unstemmed | Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB Experiment |
| title_short | Seismic Attenuation at the Equatorial Mid‐Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI‐LAB Experiment |
| title_sort | seismic attenuation at the equatorial mid atlantic ridge constrained by local rayleigh wave analysis from the pi lab experiment |
| topic | attenuation surface wave Mid Atlantic Ridge |
| url | https://doi.org/10.1029/2021GC010085 |
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