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 ( QG−1) and associated modulus dispersion, with QG−1 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 ( log10QG−1≈−1.5 at 550 °C and 0.01 Hz) than in olivine ( log10QG−1≪−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.

Measurements of Wave‐Induced Attenuation in Saturated Metapelite and the Band‐Limitation of Low‐Frequency Earthquakes

“…Next, we scale our laboratory results to geologic conditions by considering the influence of temperature and pore fluid pressure on the measured frequency‐dependent attenuation. We assume that the attenuation of the mineral framework is unaffected by temperature differences between laboratory and geologic conditions because previous laboratory experiments report a relatively small decrease in elastic moduli of up to 12% under dry conditions between room temperature and 450°C (Christensen, 1979; David et al., 2019) resulting in a small attenuation (1/ Qs ∼ 0.006) at 450°C (David et al., 2019). However, it is apparent from the models of patchy saturation (Equation ) and squirt flow (Equation ) that wave‐induced fluid flow causes attenuation that is inversely dependent on fluid viscosity.…”

Insight into the microphysics of antigorite deformation from spherical nanoindentation

“…This serpentinite is primarily composed of antigorite (> 95%) with minor amounts of magnetite and magnesite. We worked specifically on a 1 cm×1 cm×0.3 cm section cut from a larger core sample that was originally investigated by (David et al, 2018(David et al, , 2019. The section was cut normal to the antigorite foliation.…”

Enhanced Visibility of Subduction Slabs by the Formation of Dense Hydrous Phase A

“…Recently, elastic bulk and shear properties for antigorite at pressure and temperature conditions of subduction zones have also become available by static compression and acoustic studies (e.g., David et al., 2019; Hilairet et al., 2006; D. Wang et al., 2019). We thus also calculated the velocity perturbations above 200 km by assuming antigorite as the main hydrous phase (e.g., Mookherjee & Capitani, 2011; Mookherjee & Mainprice, 2014; Schmidt & Poli, 1998) and a homogeneous hydration throughout the entire subducted lithospheric mantle.…”

“…Recently, elastic bulk and shear properties for antigorite at pressure and temperature conditions of subduction zones have also become available by static compression and acoustic studies (e.g., David et al, 2019;Hilairet et al, 2006;D. Wang et al, 2019).…”

“…The data presented in this study are available on Dryad (https://doi.org/10.5061/dryad.59zw3r26v). The phase A and other mantle minerals' data on which Table 1 is based are available in: Sanchez-Valle et al (2008), Phan (2008), Crichton and Ross (2002), Kudoh et al (2002), Kuribayashi et al (2003), Holl et al (2006), Yang et al (2021), Abramson et al (1997), Liu et al (2005), Zha et al (1998), Cammarano et al (2003, Kung et al (2004), Shinmei et al (1999), Isaak et al (2006), Kung et al (2006), Kung et al (2005), Zhao et al (1998), Gwanmesia et al (2006), Sinogeikin and Bass (2002), David et al (2019), Hilairet et al (2006), andD. Wang et al (2019).…”