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Anomalous crust of the Bolivian Altiplano, central Andes: Constraints from broadband regional seismic waveforms
Author(s) -
Zandt G.,
Beck S. L.,
Ruppert S. R.,
Ammon C. J.,
Rock D.,
Minaya E.,
Wallace T. C.,
Silver P. G.
Publication year - 1996
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/96gl00967
Subject(s) - felsic , geology , seismometer , crust , seismology , broadband , mantle (geology) , poisson's ratio , poisson distribution , geophysics , volcano , statistics , mathematics , political science , law
A one‐year deployment of broadband seismographs in the Bolivian Altiplano recorded numerous intermediate‐depth earthquakes at near‐regional distances. We modeled the associated broadband waveforms of two earthquakes to estimate an average crustal structure for the Altiplano. The resulting model is characterized by an anomalously low mean P velocity of 6.0 km/s, a low Poisson's ratio of 0.25, and a crustal thickness of 65 km. The combination of the low mean velocity and low Poisson's ratio can be explained only by a predominantly quartz‐rich, felsic bulk composition. This constraint precludes significant volumes of magmatic addition from the mantle contributing to the great thickness of the Altiplano crust, but is consistent with thickening by compressive shortening concentrated in a weak felsic layer.