Villarrica and Llaima Volcanoes in Southern Chile: an infrasound factor / S. Barrientos, F. Riquelme, Nicolas Brachet, Alfred Kramer and Paola Campus.

Villarrica and Llaima Volcanoes in Southern Chile: an infrasound factor / S. Barrientos, F. Riquelme, Nicolas Brachet, Alfred Kramer and Paola Campus.

Vienna, Austria: CTBTO Preparatory Commission , 2009.

English

On March 19-21, 2009, a PTS portable infrasound array was installed near the town of Los Laureles in south central Chile, approximately 55 km away from Villarrica and Llaima volcanoes. This collaborative effort between PTS and Universidad de Chile is a pioneering project for both institutions from an engineering and data processing perspectives. The array is scheduled to operate at the same site until July 2009. The preliminary observations during the first few weeks are encouraging as described below. The array is composed of four elements arranged in a triangular geometry with a central element; the sides of this equilateral triangle are 450-500 m apart. Each element had a sensor MB-2005 with a Reftek 130, 24-bit DAS acquiring data from a multiple that concentrated pressure changes through six pipes, 15-m long each. The array was deployed in a forest of eucalyptus trees 8-10 m tall which provide excellent shelter against the wind. During the first days of operation, the array detected episodic signals originated at the same azimuth of Villarrica volcano. This volcano has an almost perfect conic shape lying on top of a previ$~$us caldera, located along the Liquifie-Ofqui Fault Zone. The volcanic edifice covers an area of approximately 250 km", with a diameter at its I base of about 28 km. It rests on Miocene plutonic and stratified volcanic layers. The crater, located at 2800 above sea level, is about 200 m in diameter and exhibits intense fumarolic activity. The bottom of the crater, about 50 -100 m deep, is Icovered by a lava lake which exhibits frequent, but weak, eruptive activity (Sernageomin). Llaima volcano began an eruptive cycle from 3 April at 21 :00 to 6 April at around midnight (both local times). The infrasound array detected significant activity during this period, consistent with a source at the same azimuth. Llaima volcano is one of the largest of the Southern Volcanic Zone with an elevation of 3125 m above sea level. Its crater is about 3150 m wide with significant fumarolic activity. To the south another crater, 2920 m above sea level, also exhibit$~$ weak fumarolic activity. The base of the volcanic edifice, located above Tertiary granitic structures, is about 130 km in a north-south direction and about 25 km in an east-west orientation (Sernageomin). Additionally, on March 22, at 03:29:22.4 a 3.9 magnitude (Ml) earthquake took place about 70 km away from the infrasound array, at a depth of 47 km. Both P and S waves clearly stand out in the infrasound records.

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Infrasound: INFRA-16/G (2009)

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