A shallow-dipping dike fed the 1995 flank eruption at Fernandina Volcano, Galapagos, observed by satellite radar interferometry

Satellite radar interferometry data reveal strong localized uplift in a semi-circular pattern on the southwest flank of Fernandina volcano, Galapagos where an eruption took place in January to April, 1995. The observations show a maximum decrease in radar range of 0.75 m, and they are consistent with a model of a shallow-dipping dike intrusion feeding this fissure eruption. We solve for the best-fit single rectangular dislocation dike source using non-linear inversion techniques where simulated annealing searching algorithm is used to avoid local minima. The best-fit dike is 3.8 km long, 2.3 km high, 0.86 m thick and with a 34 degrees dip. The total dike volume (7.5 x 10(-3) km(3)) is similar to 40% of the volume of extrusive materials estimated to have been produced during the eruption. The data do not permit a sub-vertical dike, implying that the least principal stress direction is not horizontal as is usually assumed.