Seismic activity of the Nevados de Chillán volcanic complex after the 2010 Mw8.8 Maule, Chile, earthquake

Abstract

Couplings between large magnitude subduction zone earthquakes and the subsequent response of their respective volcanic arcs are generally accepted, but the mechanisms driving this coupling are not known. The 2010 Maule earthquake (Mw8.8) ruptured approximately 500km along strike in the south-central part of Chile, and provides an opportunity to investigate earthquake–volcano interactions. In an exploratory campaign, we deployed four broadband seismometers atop and surrounding the Nevados de Chillán volcanic complex because it is located directly behind one of the two primary slip patches of the Maule Earthquake. The data recorded (from December 2011 to April 2012) shows significant seismic activity, characterized by numerous volcano tectonic events and tremor episodes occurring within the volcanic complex. We recorded two strong aftershocks of the Maule earthquake (Mw 6.1 in January 2012, and Mw 7.1 in April 2012) and investigated the response of the volcano to the incoming seismic energy. We find that volcanic tremor increased significantly upon arrival of the seismic waves from the Mw 6.1 event, which was then followed a few hours later by a significant increase in volcano-tectonic events when tremors subsided. This delay between tremor and volcano-tectonic events suggests that fluid and/or magma migration (manifested as tremor) readjusted the local stress state that then induced the volcano-tectonic events. The increased activity persisted during the subsequent two weeks. In contrast, the Mw 7.1 event, which occurred at a similar epicentral distance from the volcano, did not produce any significant seismic response of the volcanic complex. Analysis of the particle velocity records of the two events shows that the volcanic system was perturbed in different ways because of the incidence angle of the incoming energy, inducing a back-elliptical vertical and fault parallel motion for the Mw 6.1 and no clear directional dependence for the Mw 7.1. This suggests dilatation-induced fluid migration within the complex, and a kinematic mechanism of the perturbation rather than the perturbation amplitude. Our results demonstrate the importance for continued monitoring of the arc behind Maule, with an increased seismometer and GPS array density to determine the style of deformation currently occurring in the arc.