Renewed unrest at Laguna del Maule, Chile, 2016–2020.

Abstract:

The Laguna del Maule (LdM) volcanic field in Chile has been exhibiting unrest since 2005. New GPS and InSAR data reveal accelerating uplift beginning in late 2016 and continuing through at least June 2020, with a maximum uplift rate of 291 mm/yr measured between February 2019 and February 2020. The 2019-2020 GPS velocities are best modeled using a 7.1 by 1.9 by 1.3 km pressurized ellipsoidal reservoir at 4.8 km depth in a heterogeneous viscoelastic crust. To describe the temporal pattern of deformation we apply a 3D numerical configuration of the magma-injection model proposed by Le Mével et al. (2016) in which magma flows through a conduit into a fluid-filled reservoir surrounded by a crust with a heterogeneous, viscoelastic rheology. A Monte Carlo procedure optimizes the inlet pressure history driving the flow. We find that the two measured episodes of accelerated uplift (2005–2010 and 2016–2020) are similarly modeled with an inlet pressure increasing at a rate of ~9 MPa/yr. In total, 0.37 cubic kilometers of magma has been added to the system between 2005 and 2020, of which 0.10 cubic kilometers has been injected since late 2016. The number of seismic events recorded at LdM has also recently increased. The changes in deformation rates (inflection points) do not coincide with the occurrence of a particular earthquake swarm. However, the temporal evolution of the cumulative number of earthquakes seems to follow the long-term trend of deformation rates as illustrated by the larger number of seismic swarms recorded during the recent period of accelerated deformation. In addition, a high CO₂ degassing anomaly has been identified to the SW of the lake basin near the Troncoso fault. We will present geodetic data and modeling results updated through 2020 and interpret them together with seismic and gas data to investigate the dynamic processes in the magmatic system that govern the current unrest.