Sediment structure at the equatorial mid-atlantic ridge constrained by seafloor admittance using data from the PI-LAB experiment

Abstract

Well-constrained marine sediment characteristics (sediment thickness and shear wave velocity) are important not only for the study of climate over geologic times scales but also for correcting and accounting for its presence in seismic data used to investigate deeper structures. We use data from the PI-LAB (Passive Imaging of the Lithosphere Asthenosphere Boundary) experiment, which consisted of 39 broadband ocean bottom seismometers deployed at the Equatorial Mid-Atlantic Ridge near the Chain fracture zone covering 0-80 Myr old seafloor. We compute admittance between the pressure to the vertical displacement at the seafloor at frequencies between 0.1 and 0.2 Hz for microseism-generated Rayleigh waves for 18 stations where data quality is good to determine the sediment thickness and shear wave velocity. We find a general trend of increasing sediment thickness with the seafloor ages, as expected with sediment thicknesses that range from 10-450 m and, shear wave velocities that range from 0.05-0.34 km/s. We find sediment thickness varies almost uniformly across both sides of the ridge, and it indicates that both sides experienced a similar sedimentation process. Our results are in good agreement with the global sediment model that is based on drilling cores and active source experiments, but thinner by up to 50 m at several stations on seafloor older than 25 My. Overlap of the 95% confidence regions between admittance and Ps estimates for thickness and shear velocity is found at 15 stations where we have both Ps and admittance estimates. It suggests that both methods yield accurate estimates for sediment thickness. In addition, our admittance result extends the lateral resolution of sediment characteristics to stations that were not previously resolved by Ps.

Upper Mantle Anisotropic Shear Velocity Structure at the Equatorial Mid‐Atlantic Ridge Constrained by Rayleigh Wave Group Velocity Analysis From the PI‐LAB Experiment

“…Here, we present results from the Passive Imaging of the Lithosphere Asthenosphere Boundary (PI-LAB) experiment and the Experiment to Unearth the Rheological Oceanic Lithosphere-Asthenosphere Boundary (EURO-LAB) at the equatorial mid-Atlantic (Agius et al, 2018;Harmon et al, 2018Harmon et al, , 2020Saikia et al, 2020), which was designed to image the base of the tectonic plate (2018a, 2018bRychert & Shearer, 2009). In this paper, we present a new shear wave velocity and azimuthal anisotropy model for the upper mantle using a combination of local earthquake events and ambient noise data.…”

Shear Velocity Inversion Guided by Resistivity Structure From the PI‐LAB Experiment for Integrated Estimates of Partial Melt in the Mantle

“…The Imaging the Lithosphere-Asthenosphere Boundary (I-LAB) experiments including: (a) Passive Imaging of the Lithosphere Asthenosphere Boundary (PI-LAB) experiment, (b) Experiment to Unearth the Rheological Lithosphere-Asthenosphere Boundary (EURO-LAB), and (c) the Central Atlantic Lithosphere-Asthenosphere Boundary (CA-LAB) experiment presented a unique opportunity for interpretation of MT and seismic data in order to understand the oceanic lithosphere-asthenosphere system at the equatorial Mid-Atlantic Ridge. We deployed 39 ocean bottom seismometers (OBS) and 39 ocean bottom magnetotelluric (OBMT) instruments on 0-80 Myr seafloor across the long offset Chain and Romanche as (Agius et al, 2018(Agius et al, , 2021Harmon et al, 2018Harmon et al, , 2020Hicks et al, 2020;Rychert et al, 2021;Saikia et al, 2020Saikia et al, , 2021Wang et al, 2019Wang et al, , 2020, allowing us to sample a wide seafloor age range in one experiment. The OBS and OBMT were co-located (within 1-2 km), in three lines perpendicular to the ridge (Figure 1).…”

Shear‐Wave Velocity Structure of Sediments on Cascadia's Continental Margin From Probabilistic Inversion of Seafloor Compliance Data

“…Whereas prior compliance inversion schemes have used traditional linearized or fully non-linear inverse techniques (e.g., Crawford et al, 1991;Doran & Laske, 2019;Saikia et al, 2020;Zha & Webb, 2016), Mosher et al (2021) implemented a non-linear inversion scheme making use of MDNs. MDNs were first devised by Bishop (1994) and have been adapted and used to study a diverse range of inverse problems in seismology, from inverting surface wave dispersion data for S V , to inverting degree-zero spheroidal mode splitting MOSHER ET AL.…”

“…Alternatively, passive methods that exploit compliance signals recorded by ocean‐bottom seismometers (OBSs) have been successfully used to study and sediment thickness of shallow oceanic structures (e.g. Bell et al., 2015; Crawford et al., 1991, 1998; Doran & Laske, 2019; Mosher et al., 2021; Ruan et al., 2014; Saikia et al., 2020; Yamamoto & Torii, 1986; Zha & Webb, 2016). However, such an approach has not been extensively applied to OBSs deployed on the Cascadia continental shelf.…”