Receiver Function Analyses of Uturuncu Volcano, Bolivia and Lastarria/Cordon Del Azufre Volcanoes, Chile

Abstract:

Uturuncu Volcano and a zone between Lastarria and Cordon del Azufre Volcanoes (also called
Lazufre), have seen much attention lately because of significant and rapid inflation of one to two
centimeters per year over large areas. Uturuncu is located near the Bolivian-Chilean border, and
Lazufre is located near the Chilean-Argentine border. The PLUTONS Project deployed 28
broadband seismic stations around Uturuncu Volcano, from April 2009 to Octobor 2012, and also
deployed 9 stations around Lastarria and Cordon del Azufre volcanoes, from November, 2011 to
April 2013. Teleseismic receiver functions were generated using the time-domain iterative
deconvolution algorithm of Ligorria and Ammon (1999) for each volcanic area. These receiver
functions were used to better constrain the depths of magma bodies under Uturuncu and Lazufre,
as well as the ultra low velocity layer within the Altiplano-Puna Magma Body (APMB). The
low velocity zone under Uturuncu is shown to have a top around 10 km depth b.s.l and is
generally around 20 km thick with regional variations. Tomographic inversion shows a well resolved,
near vertical, high Vp/Vs anomaly directly beneath Uturuncu that correlates well with a
disruption in the receiver function results; which is inferred to be a magmatic intrusion causing a
local thickening of the APMB. Preliminary results at Lazufre show the top of a low velocity
zone around 5-10 km b.s.l with a thickness of 15-30 km.