An evaluation of the possibility of tectonic triggering of the Sinabung eruption

Abstract

The aim of this work is to determine if tectonic seismicity may have had a role in triggering volcanic activity at Sinabung volcano and to evaluate the relative importance of different seismic parameters that could contribute to triggering an eruption. We focus on the potential role of static strain, including the timing and magnitude of changes in volumetric strain and the direction of principal strain to investigate the relation between tectonic strain changes and variations in volcanic activity at Sinabung volcano. Sinabung erupted first in August and September 2010, and then following three years of quiescence, a seismic swarm at the volcano began on 4 July 2013, two days after the Bireun earthquake (Mw 6.1), which was located 252 km from the volcano. Subsequent to these events a new series of eruptions started on 15 September 2013 and continues through today. Ground deformation, as measured with GPS, showed significant changes at Sinabung during the 4 months following the Bireun earthquake and before the September 15 eruption, reaching 8–11 mm of horizontal displacement. To evaluate the possibility of seismic triggering of activity at Sinabung, we used Global CMT solutions of large tectonic earthquakes within 1000 km of the volcano to estimate strain changes and compared these changes to the timing of volcanic activity and seismicity and to ground deformation. We find no unequivocal relationship between changes in the volumetric strain from the regional tectonic earthquakes and timing of volcanic activity at Sinabung. However, we find that the orientation of the extensional component of the strain produced by the Bireun earthquake is perpendicular to the strike of a mapped fault the crosses the volcano. We suggest that because the Sinabung magmatic system was already pressurized, this small change in extensional strain across this fault zone could have initiated the magma ascent and the consequent seismic swarm that led to the 2013 eruption.