GPS MEASUREMENT OF SURFACE DEFORMATION AROUND SOUFRIERE HILLS VOLCANO, MONTSERRAT FROM OCTOBER 1995 TO JULY 1996

Global Positioning System geodesy was used to measure surface deformat ion on Soufriere Hills volcano, Montserrat from October 6, 1995 to Jul y 1, 1997 during initial dome growth and gravitational collapse. Our d ata from this period show non-axially symmetric horizontal displacemen ts, and decreasing subsidence as a function of radial distance from th e former topographic high of the volcanic edifice. Forward modeling su ggests that surface deformation is caused by a shallow vertical dike ( < 3 km), which expanded approximately 1 m, coupled with a deflating Mo gi source at about 6 km depth. These inferred source parameters are in good agreement with independent observations of regional dike widths and preeruption magma storage depth.