Understanding where shallow low velocity zones function is important in assessing their relationship to eruption history. In Sierra Negra, a basaltic shield volcano in the Galapagos Islands[Delaney, 2006] that has experienced extraordinary uplift, the results of a combination of InSAR and CGPS data suggest the existence of a sill at roughly 2 km depth. I believe this sill is, in part, responsible for the areas uplift [Chadwick, 2006] by allowing release of strain through faulting. To find both the thickness and velocity of the sill, as well as, shed light on its relationship to uplift, I created a model of the sill with varying thickness and velocity. I found the best fit of the model to the data to be a 6km thick sill with a velocity of 4.29km/sec.