Temporal and spatial variation of the stress state of Popocatépetl Volcano, Mexico

The fault plane solutions (FPS) of volcano-tectonic events (VTs), can help in the determination of the stress state of a volcano, before, during and after an eruptive period. Hence, for Popocatépetl, we have calculated the FPS from 1996 to 2003, and we have compared the results with its volcanic activity. For Popocatépetl, there are two main areas of VTs, one below the crater and another in the southeastern zone. For the below crater we have 398 solutions and for the southeastern zone 64. The FPS below the crater have pressure axes (P) with a preferential orientation of S70°W–N70°E, which is consistent with the regional stress state. For the tension axes (T) a radial tension is observed, although a great amount of axes exists with a direction of NW–SE. Most of the FPS are normal solutions and these are present at depths mainly between 0 and 3 km asl, although we have periods where an increase is observed in the number of reverse events, approximately between −3 and 0 km asl. The variability of the solutions with depth is probably associated with the intrusion of magma inside the volcano. The group of events located in the southeastern part of the volcano have pressure axes (P) with directions of S–N and W–E, and the same orientations are observed for the tension axes (T). Most of the mechanisms in this area are strike–slip solutions, which follow two possible faults, which were activated during the early magma intrusions inside of the volcano.