A brittle failure model for long-period seismic events recorded at Turrialba volcano, Costa Rica

Thomas S. Eyre (1, 2) , Christopher J. Bean (2) , Louis De Barros (3, 2) , Francesca Martini (2, 4) , Ivan Lokmer (5) , Mauricio M. Mora (6) , Javier F. Pacheco (7) , Gerardo J. Soto (8)

1 Department of Physics [Edmonton]
2 School of Geological Sciences [Dublin]
3 GEOAZUR 6526 - Géoazur
4 Tullow oil Ltd, Dublin, Ireland
5 Seismology and Computational Rock Physics Laboratory, School of Geological Sciences
6 Escuela Centroamericana de Geología
7 Ovsicori-UNA
8 ICE - Área de Amenazas y Auscultación Sísmica y Volcánica

A temporary seismic network, consisting of 23 broadband and six short-period stations, was installed in a dense network at Turrialba Volcano, Costa Rica, between 8 March and 4 May 2011. During this time 513 long-period (LP) events were observed. Due to their pulse-like waveforms, the hypothesis that the events are generated by a slow-failure mechanism, based on a recent new model by Bean et al. (2014), is tested. A significant number (107) of the LPs are jointly inverted for their source locations and mechanisms, using full-waveform moment tensor inversion. The locations are mostly shallow, with depths < 800 m below the active Southwest Crater. The results of the decompositions of the obtained moment tensor solutions show complex source mechanisms, composed of high proportions of isotropic and low, but seemingly significant, proportions of compensated linear vector dipole and double-couple components. It is demonstrated that this can be explained as mode I tensile fracturing with a strong shear component. The source mechanism is further investigated by exploring scaling laws within the data. The LPs recorded follow relationships very similar to those of conventional earthquakes, exhibiting frequency-magnitude and corner frequency versus magnitude relationships that can be explained by brittle failure. All of these observations indicate that a slow-failure source model can successfully describe the generation of short-duration LP events at Turrialba Volcano.

Domaines: Géophysique [physics.geo-ph]

Thomas S. Eyre, Christopher J. Bean, Louis De Barros, Francesca Martini, Ivan Lokmer, et al.. A brittle failure model for long-period seismic events recorded at Turrialba volcano, Costa Rica. Journal of Geophysical Research, 2015, pp.10.1002/2014JB011108. ⟨10.1002/2014JB011108⟩. ⟨hal-01142480⟩