Comment on 'Seismic coupling along the Chilean subduction zone' by B. W. Tichelaar and L. R. Ruff

The Chilean subduction zone was studied by Tichelaar and Ruff (1991) as part of a worldwide project to map the depth extent and the width of the seismogenic interplate contact in subduction regimes. They conclude that there is a change in the maximum depth of seismogenic coupling in the Chilean subduction zone at 20 deg S. They argue that to the south of this latitude the seismically coupled zone in Chile extends to depths of 48 to 53 km. Their critics discuss locally recorded data using permanent and temporary networks in Chile which suggest that the depth of the coupled zone does not vary along the Chilean subduction zone. Different results from earthquakes with magnitudes greater than 6.0 vs data from microseismicity studies are presented. Tichelaar and Ruff reply that, if the new Taltal earthquake in Suarez and Comte (1993) and the bootstrap error estimates of earthquake depths in Tichelaar and Ruff are taken into account, and if the Chilean subduction zone is divided into six or fewer segments, they agree with the 'modified' conclusion of Suarez and Comte that the maximum depth extent of the seismogenic plate interface extends down to between 40 and 50 km along Chile.