Integrating Reservoir Dynamics, Crustal Stress, and Geophysical Observations of the Laguna del Maule Magmatic System by FEM Models and Data Assimilation

• Published in: Journal of geophysical research. Solid earth 2019-12, Vol.124 (12), p.13547-13562
• Main Authors: Zhan, Y., Gregg, P. M., Le Mével, H., Miller, C. A., Cardona, C.
• Format: Article
• Language: English
• Subjects: Crustal stress; Data assimilation; Data collection; Dilatancy; Earthquakes; Eruptions; failure; fault zone; geophysical observation; Geophysics; Gravity; Hydraulic fracturing; Inflating; Interferometric synthetic aperture radar; Laguna del Maule; Lake dynamics; large silicic magmatic system; Lava; Magma; Microfracture; Microgravity; numerical modeling; Pore pressure; Pore water pressure; Pressure; Radar data; Reservoirs; SAR (radar); Seismic activity; Seismic tomography; Seismicity; Stress propagation; Synthetic aperture radar; Tomography; Trajectory analysis; Uplift; Volcanic eruptions; Volcanic fields
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2019JB018681

The Laguna del Maule volcanic field is a large rhyolitic magmatic system in the Chilean Andes, which has exhibited frequent eruptions during the past 20 ka. Rapid surface uplift (>20 cm/year) has been observed since 2007 accompanied by localized earthquake swarms and microgravity changes, indicating the inflating magma reservoir may interact with a preexisting weak zone (i.e., Troncoso fault). In this investigation, we model the magma reservoir by data assimilation with Interferometric Synthetic Aperture Radar data. The reservoir geometry is comparable to the magma body inferred by seismic tomography, magnetotelluric, and gravity studies. The models also suggest that a weak zone, which has little effect on surface displacement, is important as a fluid transport channel to promote earthquakes and microgravity changes. In particular, concentrated dilatancy within the weak zone facilitates the microfracture formation during reservoir inflation. High‐pressure fluid can inject into the weak zone from the magma reservoir to trigger earthquakes and further migrate upward to create positive gravity changes by occupying unsaturated storages. The pore pressure will then decrease, halting the seismicity swarm until the next cycle. This “hydrofracturing” process may release some accumulated stress along the magma reservoir delaying an eventual eruption in turn. Besides, the resultant models are propagated forward in time to evaluate potential stress trajectories for future unrest. Key Points The presence of a weak, Troncoso fault zone significantly impacts the stress field of the host rock surrounding the LdM magma system Fault zone permeability can increase due to deformation of an adjacent, inflating magma reservoir Pore fluid injecting from a magma system into a dilatant fault zone can trigger earthquakes and microgravity changes