We investigate the crustal structure of the Hengill triple junction in southwestern Iceland, applying tomographic methods to local earthquake data recorded in two field experiments with different network geometries and instrumentation. Data from the two experiments enable us to derive three-dimensional models of the compressional-wave speed vp and the wavespeed ratio vp/vs. Well resolved high-vp bodies correlate with sites of gabbroic intrusions. A small reduction in vp/vs associated with the high-temperature part of the geothermal area is probably due to mineral alteration or supercritical fluids. The RMS difference between the two vp models, about 0.26 km s-1, indicates the approximate repeatability that may be expected of good tomographic inversions. ¿ American Geophysical Union 1995