v. sajama, bolivia kevin m. ward, george zandt, susan l. beck, … · 2015-06-03 · kevin m. ward,...
TRANSCRIPT
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Kevin M. Ward, George Zandt, Susan L. Beck, Ryan C. Porter, Lara S. Wagner, Estela Minaya, Hernando Tavera
V. Sajama, Bolivia
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Central Andean Plateau (CAP) • Average elevation ~4 km
• Max width ~300 km
• Total length ~2,000 km
• Abundant arc magmatism
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Central Andean Plateau (CAP) • Average elevation ~4 km
• Max width ~300 km
• Total length ~2,000 km
• Abundant arc magmatism • Data from 315 broadband
seismic stations
• Deployed piecemeal from May 1994 through August 2012
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Ambient Noise Tomography Method
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Ambient Noise Tomography Method
Ambient Noise Source • Lower periods ~ ocean waves
against the shore • Higher periods ~ atmospheric
disturbances • Not limited by event distribution
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Ambient Noise Tomography Method
Ambient Noise Source • Lower periods ~ ocean waves
against the shore • Higher periods ~ atmospheric
disturbances • Not limited by event distribution
Raw Waveform Processing • Visually inspect waveforms • 5 to 150 sec band-pass filter • Spectral whitening and running
absolute mean normalization
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Ambient Noise Tomography Method
Ambient Noise Source • Lower periods ~ ocean waves
against the shore • Higher periods ~ atmospheric
disturbances • Not limited by event distribution
Raw Waveform Processing • Visually inspect waveforms • 5 to 150 sec band-pass filter • Spectral whitening and running
absolute mean normalization
Cross Correlations • CC each station pair for each day • 3,519,011 CCs • Stack each CC station pairs to
approximate the EGF
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Ambient Noise Tomography Method
Ambient Noise Source • Lower periods ~ ocean waves
against the shore • Higher periods ~ atmospheric
disturbances • Not limited by event distribution
Raw Waveform Processing • Visually inspect waveforms • 5 to 150 sec band-pass filter • Spectral whitening and running
absolute mean normalization
Cross Correlations • CC each station pair for each day • 3,519,011 CCs • Stack each CC station pairs to
approximate the EGF
Empirical Green’s Function • Approximates the seismic
response of a Rayleigh wave traveling between stations
• Frequency-time analysis to extract dispersion curves
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Rayleigh Wave Dispersion Curves
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Rayleigh Wave Dispersion Curves
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Phase Velocity Inversion Results
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Phase Velocity Inversion Results
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Phase Velocity Inversion Results
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Shear Wave Inversion Results
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Shear Wave Inversion Results
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Shear Wave Inversion Results • Low velocity zone is
too shallow to represent a zone of crustal !ow
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Shear Wave Inversion Results • Low velocity zone is
too shallow to represent a zone of crustal !ow
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Shear Wave Inversion Results • Low velocity zone is
too shallow to represent a zone of crustal !ow
• Resistivity studies indicate the low velocity zone is not a body of interconnected aqueous !uids
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Shear Wave Inversion Results • Low velocity zone is
too shallow to represent a zone of crustal !ow
• Resistivity studies indicate the low velocity zone is not a body of interconnected aqueous !uids
• Previous work in the Altiplano-Puna Volcanic Complex (APVC) and Cretaceous Sierra Nevada Batholith (CSNB) might provide answer
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Model of Batholith Formation
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Shear Wave Inversion Results
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Shear Wave Inversion Results
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Looking for the Batholith • "e 3.25 km/s velocity contour
outlines the extent of the APVC
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Looking for the Batholith • "e 3.25 km/s velocity contour
outlines the extent of the APVC
• "e 3.25 km/s velocity contour correlates well with known Neogene ignimbrite eruption centers
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Looking for the Batholith • "e 3.25 km/s velocity contour
outlines the extent of the APVC
• "e 3.25 km/s velocity contour correlates well with known Neogene ignimbrite eruption centers
• "e 3.25 km/s velocity contour agrees with low isostatic gravity anomalies
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3D view of the Neogene “Batholith”
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Concluding Remarks
• "e 3.25 km/s velocity contour correlates well with known Neogene ignimbrite eruption centers and low isostatic gravity anomalies
• Our interpretation of a large Neogene batholith associated with active volcanism revisits the idea of magmatic addition as a contributing mechanism to the growth of the western portion of the CAP
• How much of a contributing mechanism?
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Supplementary Material ~ PV Inversion
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Supplementary Material ~ Vsv Inversion
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Supplementary Material ~ Vsv Mis#t