A mechanical model of the large-deformation 2005 Sierra Negra volcanic eruption derived from InSAR measurements.

摘要

During the past decade, Space-borne Interferometric Synthetic Aperture Radar (InSAR) has been successfully used to measure millimeter- to meter-level deformation on the ground surface due to magmatic processes at depth. We merge two Digital Elevation Models (DEMs) of Sierra Negra volcano in Isabela Island, Galapagos, to produce a new DEM that is superior to both of the original DEMs. This DEM is used to derive deformation of the 2005 eruption at Sierra.; The magma chamber at Sierra Negra is believed to be a sill. In order to solve for the detailed geometry of the sill, we develop a new modeling technique, using a uniformly pressurized crack as a forward function in a stochastic inversion scheme of simulated annealing. This modeling approach provides physically more plausible and internally more consistent model than kinematic models. This method is used to estimate the detailed geometry of the magma chamber at Sierra Negra during the 2005 eruption.; The 2005 eruption at Sierra Negra caused about 5.4 m subsidence. Three hours prior to the onset of the eruption, an earthquake of Mw 5.4 occurred. In order to form an intra-caldera interferogram of the large and complex deformation, we develop a new interferogram formation algorithm. The resulting interferogram is used for modeling the 2005 eruption at Sierra Negra.; The 2005 eruption at Sierra Negra model consists of three main parts: trapdoor faulting, dike intrusion, and opening-closing of a sill. The estimated depth is 1.86 km +/- 0.13 km. In the trapdoor faulting model, the estimated maximum slip at the surface of the western end of the fault system is about 1.5 m, which matches the field observation very well. The equivalent moment magnitude of the total slip was estimated to be Mw 5.7 with a shear modulus of 30 GPa. The estimated average opening of the dike is 1.7 m. The sill model is the sum of two components: interaction with the trapdoor faulting event and uniformly depressurized closing during the eruption. The estimated volume decrease at the sill was 0.124 km3, and the estimated extruded volume (dense rock equivalent) was about 0.120 km3.