3-D modeling of ground deformation by conduit pressurization at Soufrière Hills volcano, Montserrat (B.W.I.)

Dome growth at the Soufrière Hills volcano between 1996 and 1998 was frequently accompanied by repetitive cycles of earthquakes, ground deformation, degassing, and explosive eruptions. In particular, high-resolution tiltmeters recorded in real-time 6-14 h inflation cycles up to 20 microrad at two stations near the dome. These tilt data were used in eruption forecasting since peak rockfall and pyroclastic flow activity occurred with deflations. The cyclic ground deformation was ascribed to pressurization of the conduit magma beneath the degassing plug. The pressure source has been previously modeled as a point source or finite line source in an elastic medium without considering the topography of the volcano. Using the finite difference code FLAC3D, we modeled the edifice as an elastic medium in three dimensions by integrating surface topography from Montserrat DEMs. We use the available tilt and geodetic data to constrain the geometry and the pressure distribution of the source and the properties of the edifice model. We analyse the effect of the edifice shape as compared to flat free surface models as well as the influence of varied pressure source geometries, pressure distributions, depths and conduit location. Results are compared with previous studies based on analytical models of point or line source and numerical models of conduit pressurization.