IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

3W_2A-P13

Date/Time: July 23 Poster

Explosion quakes and Long Period events with similar waveforms at Tungurahua
volcano (Ecuador)
Jean Battaglia1 , Mario Ruiz2
1

Laboratoire Magmas et Volcans, CNRS UMR 6524, Univ. B. Pascal, IRD, Clermont-Ferrand, France,
2Instituto Geofisico Escuela Politecnica Nacional, Ladron de Guevara E11-253 y Andalucia, Quito,Ecuador
E-mail: battag@opgc.univ-bpclermont.fr

Tungurahua is one of the most active volcanoes in Ecuador. It is a large andesitic stratovolcano which has been
erupting since 1999. Its activity during recent years is characterized by the occurrence of well-defined eruptive
phases lasting from several weeks to months, separated by quiescence periods with a comparable duration range.
Eruptive phases include the emission of ash and gases with periods of enhanced activity and the occurrence ofStrombolian to Vulcanian explosions that can cause pyroclastic flows. The volcano is monitored by the Instituto
Geofisico, whose monitoring networks include 5 broadband stations coupled with acoustic sensors.

Theseinstruments record a wide range of seismic signals generated by the volcano. During quiescence periods, mostly
LP events and few volcano-tectonic events are observed. During eruptive phases, the seismicity is dominated by
the occurrence of tremors, LP events and explosion quakes characterized by the presence of acoustic phases.

We examined the seismicity recorded from August 2009 to December 2010 with the aim to determine thecharacteristic events among the transients recorded by the seismic monitoring network. For this purpose, anLTA/STA algorithm has been applied to data from a reference station located 4.5 km from the summit in order toidentify the transients. The detected signal windows have been classified using cross-correlation to identify familiesof events with similar waveforms. For each family, a synthetic master event has been generated by stacking thesimilar waveforms. To recompose precisely the temporal evolution of each family, the different stacks have beenused to scan the continuous data using matched filtering.

The procedure indicates a rather reduced number of families as only 6 are identified with more than 5 events.
Most of these are families of explosion quakes or LP events active during the eruptive phases which occurred
during our study period. The largest include 182 explosion quakes recorded during the May 2010 eruptive phase.
Most interestingly, the second largest family with 121 events is active during the entire year 2010, during eruptive
phases as well as during quiescence periods. It groups explosion quakes with clear acoustic phases, occurring
during enhanced periods of activity, as well as smaller events identified as LP events, occurring during repose
periods associated with no surface activity. This result has two possible outcomes. (1) Some of the explosion
quakes and LP events at Tungurahua may share a common location and source process such as the resonanceof the same fluid column or crack but caused by diverse triggering mechanisms. (2) Alternately, our result may
indicate the existence of small undetected explosions at depth during quiescence period leading to no significant
surface emissions. In both cases, our result may have important implications in terms of signal interpretation andmonitoring.

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