DOI: 10.1016/j.epsl.2020.116148
论文题名: Shear attenuation and anelastic mechanisms in the central Pacific upper mantle
作者: Ma Z. ; Dalton C.A. ; Russell J.B. ; Gaherty J.B. ; Hirth G. ; Forsyth D.W.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 536 语种: 英语
中文关键词: 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)
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. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165145
Appears in Collections: 气候变化与战略
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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
Recommended Citation:
Ma Z.,Dalton C.A.,Russell J.B.,et al. Shear attenuation and anelastic mechanisms in the central Pacific upper mantle[J]. Earth and Planetary Science Letters,2020-01-01,536