DOI: 10.1016/j.epsl.2018.04.060
Scopus记录号: 2-s2.0-85047062952
论文题名: Crustal anisotropy and state of stress at Uturuncu Volcano, Bolivia, from shear-wave splitting measurements and magnitude–frequency distributions in seismicity
作者: Maher S. ; Kendall J.-M.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 495 起始页码: 38
结束页码: 49
语种: 英语
英文关键词: Altiplano-Puna Magma Body
; anisotropy
; shear-wave splitting
; stress state
; Uturuncu Volcano
Scopus关键词: Anisotropy
; Compressive stress
; Earthquakes
; Maximum likelihood
; Sea level
; Shear flow
; Volcanoes
; Effusive volcanisms
; Frequency distributions
; Geophysical surveys
; Hydrothermal system
; Magma bodies
; Maximum likelihood methods
; Shear wave splitting
; Stress state
; Shear waves
; crustal structure
; frequency-magnitude distribution
; S-wave
; seismic anisotropy
; seismicity
; stress
; upper crust
; wave splitting
; Andes
; Bolivia
; Bolivia
; Potosi [Bolivia]
; Uturuncu
英文摘要: The physical signatures of unrest in large silicic magma systems are commonly observed in geophysical surveys, yet the interactions between magmatic processes and crustal stresses are often left unconstrained. Stresses in the mid and upper crust exert a strong control on the propagation and stalling of magma, and magma ascent can in turn change the magnitude and orientation of these stresses, including those associated with hydrothermal systems. This study assesses the state of stress at the restless Uturuncu Volcano in the Bolivian Andes with space, depth and time using observations of seismic anisotropy and the magnitude–frequency distributions of local earthquakes. Shear-wave splitting measurements are made for 677 events in the upper crust (1–25 km below sea level) between June 1, 2009 and March 10, 2012, and b-values are calculated using the Aki maximum likelihood method for a range of catalog subsets in the entire crust (−5 to 65 km below sea level). The b-value of the crustal events is unusually low (b=0.66±0.09), indicating that the seismogenic region features strong material with high stresses that are released with limited influence from hydrothermal fluids. The 410 good quality shear-wave splitting results have an average delay time of 0.06 ± 0.002 s and an average percent anisotropy ranging from 0.25 ± 0.04% to 6.2 ± 0.94% with a mean of 1.70 ± 0.32%. Fast shear-wave polarization directions are highly variable and appear to reflect a combination of tectonic and magmatic stresses that overprint the regional E–W compressive stress associated with the convergence of the Nazca and South American Plates. The shear-wave splitting results and b-values suggest that the upper crust beneath Uturuncu (∼0–7 km below the summit) is characterized by a weak and localized hydrothermal system in a poorly developed fracture network. We conclude that stresses imposed by crustal flexure due to magmatic unrest above the Altiplano-Puna Magma Body activate crack opening on a pre-existing fault beneath the volcano, generating seismicity and a spatially variable 1–10% anisotropy above the brittle–ductile transition zone. These results suggest that strong stresses in relatively unfractured upper crustal rocks may locally inhibit fluid migration in large silicic magma systems, leading to pluton emplacement and effusive volcanism rather than explosive eruptions. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109835
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
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作者单位: School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, United Kingdom; Department of Earth Science, Webb Hall 1006, University of California, Santa Barbara, CA 93106-9630, United States
Recommended Citation:
Maher S.,Kendall J.-M.. Crustal anisotropy and state of stress at Uturuncu Volcano, Bolivia, from shear-wave splitting measurements and magnitude–frequency distributions in seismicity[J]. Earth and Planetary Science Letters,2018-01-01,495