@article {saikia_seismic_2021,
	title = {Seismic Attenuation at the Equatorial Mid-Atlantic Ridge Constrained by Local Rayleigh Wave Analysis From the PI-LAB Experiment},
	journal = {Geochemistry, Geophysics, Geosystems},
	volume = {22},
	number = {12},
	year = {2021},
	note = {_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021GC010085},
	month = {12/2021},
	pages = {e2021GC010085},
	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{\textendash}80 My old lithosphere near the equatorial Mid-Atlantic Ridge. We determine the attenuation coefficient () for periods between 15 and 40 s and invert for 1-D average shear wave quality factor values () and shear wave velocity (Vs). We find values of 175 {\textpm} 16 at 50 km depth, decreasing to 90 {\textpm} 15 at greater than 60 km. Comparison of our and Vs measurements to previous observations from oceanic settings shows agreement in terms of higher and Vs in the lithosphere in comparison to the asthenosphere. The observations from oceanic settings are in general agreement with the laboratory predictions for -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.},
	keywords = {attenuation, Mid Atlantic Ridge, surface wave},
	issn = {1525-2027},
	doi = {10.1029/2021GC010085},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2021GC010085},
	author = {Saikia, Utpal and Rychert, Catherine A. and Harmon, Nicholas and Michael Kendall, J.}
}
@article {harmon_shear_2021,
	title = {Shear Velocity Inversion Guided by Resistivity Structure From the PI-LAB Experiment for Integrated Estimates of Partial Melt in the Mantle},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {126},
	number = {8},
	year = {2021},
	note = {_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021JB022202},
	month = {08/2021},
	pages = {e2021JB022202},
	abstract = {The lithosphere-asthenosphere system is fundamental to our understanding of mantle convection and plate tectonics. The different sensitivities of seismic and electromagnetic methods can be used together to better constrain the properties of the system. Here, we re-examine the shear velocity model from Rayleigh waves in light of the magnetotelluric based resistivity models from the Passive Imaging of the Lithosphere Asthenosphere Boundary (PI-LAB) experiment near the equatorial Mid-Atlantic Ridge, with the goal of generating a structurally consistent velocity and resistivity model for the region. Cross-plots of the models suggest a linear or near-linear trend that is also in agreement with petrophysical predictions. We generate a new shear velocity model from the resistivity models based on petrophysical relationships. The new velocity model fits the phase velocity data, and the correlation coefficient between the shear velocity and resistivity models is increased. Much of the model can be predicted by expectations for a thermal half-space cooling model, although some regions require a combination of higher temperatures, volatiles, or partial melt. We use the petrophysical predictions to estimate the melt fraction, melt volatile content, and temperature structure of the asthenospheric anomalies. We find up to 4\% melt, with the lowest resistivities and shear velocities explained by up to 20\% water or 20\% CO2 in the melt or \~{}1\% nearly pure sulfide melt, depending on the set of assumptions used. Melt is required in punctuated anomalies over broad depth ranges, and also in channels at the base of the lithosphere. Melt in the asthenosphere is dynamic, yet persistent on geologic timescales.},
	keywords = {lithosphere asthenosphere, magnetotellurics, melt, Mid-Atlantic Ridge, Rayleigh wave tomography, small-scale convection},
	issn = {2169-9356},
	doi = {10.1029/2021JB022202},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2021JB022202},
	author = {Harmon, Nicholas and Wang, Shunguo and Rychert, Catherine A. and Constable, Steven and Kendall, J. Michael}
}
