Several changes have occurred in seismicity associated with Mount St. Helens since it last erupted in October 1986. Perhaps the most significant is the recurrence of earthquakes deeper than 3 km, previously observed only in the months following the cataclysmic eruption of May 18, 1980, and briefly in March 1982. Events located below 6.5 km define a circular aseismic zone, similar in location to one observed after May 18, 1980. Focal mechanisms are computed for two depth ranges, 4--6.5 km (Intermediate) and 6.5--10 km (Deep), using both polarity and amplitude ratio data. Mechanisms for Intermediate events are mostly strike-slip, and many P and T axes point in directions ~80¿ offset from the regional stress field, indicating that earthquakes in this zone are caused by magmatic as well as tectonic forces. Mechanisms for Deep events are also mostly strike-slip, and P and T axes from a pattern suggestive of a pressure increase within the aseismic zone. The observed Deep patterns are compared with theoretical stress fields generated by a numerical model of a pressurized hole in an elastic plate. Results from modeling support the pressure increase hypothesis for 1987--1992 seismicity, in contrast to a pressure drop for post-May 18, 1980, earthquakes. This apparent repressurization is proposed to be a result of the sealing of the shallow conduit system.