Three‐dimensional υp and υp/υs structure of the Hengill Triple Junction and Geothermal Area, Iceland, and the repeatability of tomographic inversion

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 υ p and the wave‐speed ratio υ p /υ s . Well resolved high‐υ p bodies correlate with sites of gabbroic intrusions. A small reduction in υ p /υ s 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 υ p models, about 0.26 km s −1 , indicates the approximate repeatability that may be expected of good tomographic inversions.