气候变化领域集成服务门户(CCPortal): Shear attenuation and anelastic mechanisms in the central Pacific upper mantle

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DOI	10.1016/j.epsl.2020.116148
	Shear attenuation and anelastic mechanisms in the central Pacific upper mantle
	Ma Z.; Dalton C.A.; Russell J.B.; Gaherty J.B.; Hirth G.; Forsyth D.W.
发表日期	2020
ISSN	0012821X
卷号	536
英文摘要	We determine the mantle attenuation (1/Qμ) structure beneath 70 Myr seafloors in the central Pacific. We use long-period (33-100 sec) Rayleigh waves recorded by the NoMelt array of broadband ocean-bottom seismometers. After the removal of tilt and compliance noise, we are able to measure Rayleigh wave phase and amplitude for 125 earthquakes. The compliance correction for ocean wave pressure on the seafloor is particularly important for improving signal-to-noise at periods longer than 55 sec. Attenuation and azimuthally anisotropic phase velocity in the study area are determined by approximating the wavefield as the interference of two plane waves. We find that the amplitude decay of Rayleigh waves across the NoMelt array can be adequately explained using a two-layer model: Qμ=1400 in the shallow layer, Qμ=110 in the deeper layer, and a transition depth at 70 km, although the sharpness of the transition is not well resolved by the Rayleigh wave data. Notably, Qμ observed in the NoMelt lithosphere is significantly higher than values in this area from global attenuation models. When compared with lithospheric Qμ measured at higher frequency (∼3 Hz), the frequency dependence of attenuation is very slight, revising previous interpretations. The effect of anelasticity on shear velocity (VS) is estimated from the ratio of observed velocity to the predicted anharmonic value. We use laboratory-based parameters to predict attenuation and velocity-dispersion spectra that result from the superposition of a weakly frequency dependent high-temperature background and an absorption peak. We test a large range of frequencies for the position of the absorption peak (fe) and determine, at each depth, which values of fe predict Qμ and VS that can fit the NoMelt Qμ and VS values simultaneously. We show that between depths of 60 and 80 km the seismic models require an increase in fe by at least 3-4 orders of magnitude. Under the assumption that the absorption peak is caused by elastically accommodated grain-boundary sliding, this increase in fe reflects a decrease in grain-boundary viscosity of 3-4 orders of magnitude. A likely explanation is an increase in the water content of the mantle, with the base of the dehydrated lid located at ∼70-km depth. © 2020 Elsevier B.V.
关键词	anelastic mechanism oceanic lithosphere Pacific Ocean shear attenuation
英文关键词	Grain boundary sliding; Oceanography; Rayleigh waves; Seismology; Signal to noise ratio; Velocity; Water waves; Broadband ocean-bottom seismometers; Frequency dependence; Frequency dependent; Grain-boundary viscosity; High-temperature backgrounds; Oceanic lithosphere; Pacific ocean; Shear attenuation; Shear flow; anelasticity; ocean bottom seismometer; oceanic lithosphere; Rayleigh wave; seafloor; seismic attenuation; upper mantle; Pacific Ocean; Pacific Ocean (Central)
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/202767
作者单位	State Key Laboratory of Marine Geology, Tongji University, Shanghai, China; Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, United States; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, United States
推荐引用方式 GB/T 7714	Ma Z.,Dalton C.A.,Russell J.B.,et al. Shear attenuation and anelastic mechanisms in the central Pacific upper mantle[J],2020,536.
APA	Ma Z.,Dalton C.A.,Russell J.B.,Gaherty J.B.,Hirth G.,&Forsyth D.W..(2020).Shear attenuation and anelastic mechanisms in the central Pacific upper mantle.Earth and Planetary Science Letters,536.
MLA	Ma Z.,et al."Shear attenuation and anelastic mechanisms in the central Pacific upper mantle".Earth and Planetary Science Letters 536(2020).