We propose to use space-time behavior of seismicity to obtain an improved model of Mt. St. Augustine's plumbing sytem and to infer the magma migration processes associated with its 1986 eruption. The ability to accurately determine hypocentral parameters would be achieved by using a) a realistic two- dimensional model of the volcano's seismic velocity structure and b) both travel time and amplitude data of seismic waves recorded at seismic stations on the volcano. Preliminary results using data from an eruption in 1976 indicate that amplitude data from forward modeling based on the Gaussian beam method might provide a powerful means of constraining focal depth. The potential of that method for volcano seismology requires detailed exploration, which we propose to conduct in this investigation. Magma movement up the conduit of a central stratovolcano always produces microearthquake activity due to fracture propagation, dike emplacement, brecciation of host rocks and eventually vent excavation. Precise location (especially of depth) of precursor earthquakes prior to eruptions can give important clues about the evolution of the physical/chemical instability in the magma reservoir that eventually erupts. If we succeed in developing an earthquake location scheme that is highly sensitive to depth of focus it could have an important application for eruption prediction.
