Low-Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite

Emmanuel C. David; Nicolas Brantut; Lars N. Hansen; Ian Jackson

doi:10.1029/2018GL081271

Low-Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite

Emmanuel C. David, Nicolas Brantut, Lars N. Hansen, Ian Jackson

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Abstract

Laboratory measurements of seismic moduli and attenuation in antigorite serpentinite at a confining pressure of 200 MPa and temperatures up to 550 °C provide new results relevant to the interpretation of geophysical data in subduction zones. A polycrystalline antigorite specimen was tested via forced oscillations at small strain amplitudes and seismic frequencies (millihertz to hertz). The shear modulus has a temperature sensitivity, ∂G/∂T, averaging −0.017 GPa/K. Increasing temperature above 500 °C results in more intensive shear attenuation (Q ⁻¹ _G ) and associated modulus dispersion, with Q ⁻¹ _G increasing monotonically with increasing oscillation period and temperature. This “background” relaxation is adequately captured by a Burgers model for viscoelasticity and possibly results from intergranular mechanisms. Attenuation is higher in antigorite (log ₁₀ Q ⁻¹ _G ≈ -1.5 at 550 °C and 0.01 Hz) than in olivine (log ₁₀ Q ⁻¹ _G « −2.0 below 800◦C), but such contrast does not appear to be strong enough to allow robust identification of antigorite from seismic models of attenuation only.

Original language	English (US)
Pages (from-to)	1993-2002
Number of pages	10
Journal	Geophysical Research Letters
Volume	46
Issue number	4
DOIs	https://doi.org/10.1029/2018GL081271
State	Published - Feb 28 2019
Externally published	Yes

Bibliographical note

Funding Information:
The UK Natural Environment Research Council supported this work through grants NE/K009656/1 to N. B. and NE/M016471/1 to N. B. This work has been enriched by discussions and help from Thomas Mitchell (UCL) and discussions with Greg Hirth (Brown University). Hayden Miller and Harri Kokkonen (ANU) provided technical support. The help of Christopher Cline (ANU) during experimental work and of Jackie Kendrick (University of Liverpool) during specimen preparation has been greatly appreciated. Ana Ferreira (UCL) provided useful comments on the manuscript. Comments from Christine McCarthy and an anonymous reviewer are greatly appreciated. Experimental data are available from the UK National Geoscience Data Centre (http://www.bgs.ac.uk/services/ngdc/) or upon request to the corresponding author.

Funding Information:
The UK Natural Environment Research Council supported this work through grants NE/K009656/1 to N.?B. and NE/M016471/1 to N.?B. This work has been enriched by discussions and help from Thomas Mitchell (UCL) and discussions with Greg Hirth (Brown University). Hayden Miller and Harri Kokkonen (ANU) provided technical support. The help of Christopher Cline (ANU) during experimental work and of Jackie Kendrick (University of Liverpool) during specimen preparation has been greatly appreciated. Ana Ferreira (UCL) provided useful comments on the manuscript. Comments from Christine McCarthy and an anonymous reviewer are greatly appreciated. Experimental data are available from the UK National Geoscience Data Centre (http://www.bgs.ac.uk/services/ngdc/) or upon request to the corresponding author.

Publisher Copyright:
©2019. The Authors.

Keywords

antigorite serpentinite
seismic attenuation
seismic velocity
subduction zones
viscoelastic relaxation

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10.1029/2018GL081271

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title = "Low-Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite",

abstract = " Laboratory measurements of seismic moduli and attenuation in antigorite serpentinite at a confining pressure of 200 MPa and temperatures up to 550 °C provide new results relevant to the interpretation of geophysical data in subduction zones. A polycrystalline antigorite specimen was tested via forced oscillations at small strain amplitudes and seismic frequencies (millihertz to hertz). The shear modulus has a temperature sensitivity, ∂G/∂T, averaging −0.017 GPa/K. Increasing temperature above 500 °C results in more intensive shear attenuation (Q −1 G ) and associated modulus dispersion, with Q −1 G increasing monotonically with increasing oscillation period and temperature. This “background” relaxation is adequately captured by a Burgers model for viscoelasticity and possibly results from intergranular mechanisms. Attenuation is higher in antigorite (log 10 Q −1 G ≈ -1.5 at 550 °C and 0.01 Hz) than in olivine (log 10 Q −1 G « −2.0 below 800◦C), but such contrast does not appear to be strong enough to allow robust identification of antigorite from seismic models of attenuation only.",

keywords = "antigorite serpentinite, seismic attenuation, seismic velocity, subduction zones, viscoelastic relaxation",

author = "David, {Emmanuel C.} and Nicolas Brantut and Hansen, {Lars N.} and Ian Jackson",

note = "Funding Information: The UK Natural Environment Research Council supported this work through grants NE/K009656/1 to N. B. and NE/M016471/1 to N. B. This work has been enriched by discussions and help from Thomas Mitchell (UCL) and discussions with Greg Hirth (Brown University). Hayden Miller and Harri Kokkonen (ANU) provided technical support. The help of Christopher Cline (ANU) during experimental work and of Jackie Kendrick (University of Liverpool) during specimen preparation has been greatly appreciated. Ana Ferreira (UCL) provided useful comments on the manuscript. Comments from Christine McCarthy and an anonymous reviewer are greatly appreciated. Experimental data are available from the UK National Geoscience Data Centre (http://www.bgs.ac.uk/services/ngdc/) or upon request to the corresponding author. Funding Information: The UK Natural Environment Research Council supported this work through grants NE/K009656/1 to N.?B. and NE/M016471/1 to N.?B. This work has been enriched by discussions and help from Thomas Mitchell (UCL) and discussions with Greg Hirth (Brown University). Hayden Miller and Harri Kokkonen (ANU) provided technical support. The help of Christopher Cline (ANU) during experimental work and of Jackie Kendrick (University of Liverpool) during specimen preparation has been greatly appreciated. Ana Ferreira (UCL) provided useful comments on the manuscript. Comments from Christine McCarthy and an anonymous reviewer are greatly appreciated. Experimental data are available from the UK National Geoscience Data Centre (http://www.bgs.ac.uk/services/ngdc/) or upon request to the corresponding author. Publisher Copyright: {\textcopyright}2019. The Authors.",

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AU - David, Emmanuel C.

AU - Brantut, Nicolas

AU - Hansen, Lars N.

AU - Jackson, Ian

N1 - Funding Information: The UK Natural Environment Research Council supported this work through grants NE/K009656/1 to N. B. and NE/M016471/1 to N. B. This work has been enriched by discussions and help from Thomas Mitchell (UCL) and discussions with Greg Hirth (Brown University). Hayden Miller and Harri Kokkonen (ANU) provided technical support. The help of Christopher Cline (ANU) during experimental work and of Jackie Kendrick (University of Liverpool) during specimen preparation has been greatly appreciated. Ana Ferreira (UCL) provided useful comments on the manuscript. Comments from Christine McCarthy and an anonymous reviewer are greatly appreciated. Experimental data are available from the UK National Geoscience Data Centre (http://www.bgs.ac.uk/services/ngdc/) or upon request to the corresponding author. Funding Information: The UK Natural Environment Research Council supported this work through grants NE/K009656/1 to N.?B. and NE/M016471/1 to N.?B. This work has been enriched by discussions and help from Thomas Mitchell (UCL) and discussions with Greg Hirth (Brown University). Hayden Miller and Harri Kokkonen (ANU) provided technical support. The help of Christopher Cline (ANU) during experimental work and of Jackie Kendrick (University of Liverpool) during specimen preparation has been greatly appreciated. Ana Ferreira (UCL) provided useful comments on the manuscript. Comments from Christine McCarthy and an anonymous reviewer are greatly appreciated. Experimental data are available from the UK National Geoscience Data Centre (http://www.bgs.ac.uk/services/ngdc/) or upon request to the corresponding author. Publisher Copyright: ©2019. The Authors.

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N2 - Laboratory measurements of seismic moduli and attenuation in antigorite serpentinite at a confining pressure of 200 MPa and temperatures up to 550 °C provide new results relevant to the interpretation of geophysical data in subduction zones. A polycrystalline antigorite specimen was tested via forced oscillations at small strain amplitudes and seismic frequencies (millihertz to hertz). The shear modulus has a temperature sensitivity, ∂G/∂T, averaging −0.017 GPa/K. Increasing temperature above 500 °C results in more intensive shear attenuation (Q −1 G ) and associated modulus dispersion, with Q −1 G increasing monotonically with increasing oscillation period and temperature. This “background” relaxation is adequately captured by a Burgers model for viscoelasticity and possibly results from intergranular mechanisms. Attenuation is higher in antigorite (log 10 Q −1 G ≈ -1.5 at 550 °C and 0.01 Hz) than in olivine (log 10 Q −1 G « −2.0 below 800◦C), but such contrast does not appear to be strong enough to allow robust identification of antigorite from seismic models of attenuation only.

AB - Laboratory measurements of seismic moduli and attenuation in antigorite serpentinite at a confining pressure of 200 MPa and temperatures up to 550 °C provide new results relevant to the interpretation of geophysical data in subduction zones. A polycrystalline antigorite specimen was tested via forced oscillations at small strain amplitudes and seismic frequencies (millihertz to hertz). The shear modulus has a temperature sensitivity, ∂G/∂T, averaging −0.017 GPa/K. Increasing temperature above 500 °C results in more intensive shear attenuation (Q −1 G ) and associated modulus dispersion, with Q −1 G increasing monotonically with increasing oscillation period and temperature. This “background” relaxation is adequately captured by a Burgers model for viscoelasticity and possibly results from intergranular mechanisms. Attenuation is higher in antigorite (log 10 Q −1 G ≈ -1.5 at 550 °C and 0.01 Hz) than in olivine (log 10 Q −1 G « −2.0 below 800◦C), but such contrast does not appear to be strong enough to allow robust identification of antigorite from seismic models of attenuation only.

KW - antigorite serpentinite

KW - seismic attenuation

KW - seismic velocity

KW - subduction zones

KW - viscoelastic relaxation

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JO - Geophysical Research Letters

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ER -

Low-Frequency Measurements of Seismic Moduli and Attenuation in Antigorite Serpentinite

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