@article {russell_rayleigh_2022,
	title = {Rayleigh Wave Attenuation and Amplification Measured at Ocean-Bottom Seismometer Arrays using Helmholtz Tomography},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {n/a},
	number = {n/a},
	year = {2022},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2022JB025174},
	month = {10/2022},
	pages = {e2022JB025174},
	abstract = {Shear attenuation provides insights into the physical and chemical state of the upper mantle. Yet, observations of attenuation are infrequent in the oceans, despite recent proliferation of arrays of ocean-bottom seismometers (OBS). Studies of attenuation in marine environments must overcome unique challenges associated with strong oceanographic noise at the seafloor and data loss during OBS recovery in addition to untangling the competing influences of elastic focusing, local site amplification, and anelastic attenuation on surface-wave amplitudes. We apply Helmholtz tomography to OBS data to simultaneously resolve array-averaged Rayleigh wave attenuation and maps of site amplification at periods of 20{\textendash}150 s. The approach explicitly accounts for elastic focusing and defocusing due to lateral velocity heterogeneity using wavefield curvature. We validate the approach using realistic wavefield simulations at the NoMelt Experiment and Juan de Fuca (JdF) plate, which represent endmember open-ocean and coastline-adjacent environments, respectively. Focusing corrections are successfully recovered at both OBS arrays, including at periods < 35 s at JdF where coastline effects result in strong multipathing. When applied to real data, our observations of Rayleigh wave attenuation at NoMelt and JdF revise previous estimates. At NoMelt, we observe a low attenuation lithospheric layer (Qμ>1500) overlying a highly attenuating asthenospheric layer (Qμ\~{}50{\textendash}70). At JdF, we find a broad peak in attenuation (Qμ\~{}50{\textendash}60) centered at a depth of 100{\textendash}130 km. We also report strong local site amplification at the JdF Ridge (>10\% at 31 s period), which can be used to refine models of crust and shallow mantle structure.},
	keywords = {amplification, attenuation, Helmholtz, ocean-bottom seismology, surface waves, tomography},
	issn = {2169-9356},
	doi = {10.1029/2022JB025174},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2022JB025174},
	author = {Russell, Joshua B. and Dalton, Colleen A.}
}
@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 {booth_upper_2014,
	title = {Upper mantle Q structure beneath old seafloor in the western Pacific},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {119},
	number = {4},
	year = {2014},
	note = {_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/2013JB010589},
	pages = {3448{\textendash}3461},
	abstract = {The Pacific Lithosphere Anisotropy and Thickness Experiment ocean bottom seismometer array south of the Shatsky Rise allows imaging the attenuation structure of the upper mantle in the oldest parts of the Pacific Ocean. The array consisted of eight seismometers with a lateral extent of 200 km by 600 km. Intermediate- and deep-focus earthquake sources in the Mariana and Izu-Bonin subduction zones provide paths that probe different depths beneath the seafloor. Acceleration spectra from the vertical component of P waves are inverted for the attenuation operator and corner frequency. Pn propagation indicates very high Qp values in the lithosphere, of order 1000, while path-average Qp values in the upper mantle are on the order of 400. The variety of source epicentral distances and depths enables us to deduce the vertical Qp-1 structure of the upper mantle. Using the amplitude spectra directly in a weighted least squares problem that accounts for the effects of triplications in the traveltime curves, we invert for Qp-1 as a function of depth. We demonstrate that Qp is frequency dependent and adopt a power law dependence with coefficient α = 0.27. We resolve three distinct layers using a reference frequency of 1 Hz with Qp on the order of 145 at depths 100{\textendash}250 km, Qp on the order of 350 at depths 250{\textendash}410 km, and very high Qp with attenuation indistinguishable from zero for depths below 410 km. The P waves have a component of scattering, and thus, Qp-1 represents the maximum intrinsic attenuation beneath normal undisturbed oceanic lithosphere.},
	keywords = {attenuation, Pacific, upper mantle},
	issn = {2169-9356},
	doi = {10.1002/2013JB010589},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/2013JB010589},
	author = {Booth, Catherine M. and Forsyth, Donald W. and Weeraratne, Dayanthie S.}
}
