Towards better understanding of the mechanisms of magma transport and storage before explosive eruptions by seismic interferometry and study of deformation.

Supervisors: Philippe Lesage, Corentin Caudron}

Thesis detailed overview
Volcanoes are now better monitored and understood than in the last century. Despite this, explosive eruptions, as opposed to effusive eruptions that passively extrude large amounts of magma at the surface, remain particularly challenging. Some explosive eruptions appear to be triggered by magma injections or volatile saturation whereas others start following dome unloading.
Deformation and seismicity are the key features to detect reawakening of a volcanic system. Seismic interferometry has been used for the last decade to measure subtle changes in the elastic properties of the subsurface, e.g., aseismic volcanic conduit formation. Results are however complicated and sometimes showing opposite velocity variation patterns2. Improved understanding of explosive eruptions requires (1) a controlled and standardised data processing using high-quality local seismic networks (<20 km) and (2) complementary observations.
Among them the most complementary parameter is the ground deformation. Volcano inflation or deflation can be accompanied by cracks opening/closing that in turn decrease/increase seismic velocities. Centimeter-scale displacements of the Earth’s surface can be derived from space using interferometric SAR (InSAR) with a temporal resolution that can reach 6 days for many volcanic areas. The comparison of InSAR with seismic interferometry holds great promise to investigate the genesis of explosive eruptions. Donaldson et al.3,4 for example recently reconciled contrasting velocity observations by considering the depth of deformation that would control the seismic velocity patterns observed at the surface.
To reach a comprehensive understanding of the dynamics of magma transport prior to explosive eruptions, we selected 15 high-quality volcano-seismic networks encompassing an explosive eruption where ground deformation measurements are available. In case a significant signal is detected, source characterization will be performed using classical inversion techniques. Uncovering the mechanisms of magma transport and storage would pave the way to improved understanding of explosive eruptions.
References
1. Lesage, P., Carrara, A., Pinel, V., & Arámbula-Mendoza, R. Absence of detectable precursory deformation and velocity variation before the large dome collapse of July 2015 at Volcán de Colima, Mexico. Frontiers in Earth Science, 6, 93 (2018)
2. Budi-Santoso, A. et al. Analysis of the Seismic Activity Associated with the 2010 Eruption of Merapi Volcano, Java. J. Volcanol. Geotherm. Res. doi:10.1016/j.jvolgeores.2013.03.024.
3. Donaldson, C., Caudron, C., Green, R. G., Thelen, W. A. & White, R. S. Relative seismic velocity variations correlate with deformation at Kīlauea volcano. Sci. Adv. 3, e1700219 (2017).
4. Donaldson, C., Winder, T., Caudron, C. & White, R. S. Crustal seismic velocity responds to a magmatic intrusion and seasonal loading in Iceland’s Northern Volcanic Zone. Sci. Adv. 5, eaax6642 (2019).
5. Biggs, J. et al. Global link between deformation and volcanic eruption quantified by satellite imagery. Nat. Commun. 5, (2014).
6. Tait, S., Jaupart, C. & Vergniolle, S. Pressure, gas content and eruption periodicity of a shallow, crystallising magma chamber. Earth Planet. Sci. Lett. 92, 107–123 (1989).