In July and August 1980, an array of five ocean bottom seismographs was deployed within 3 km of the 350 ¿C hydrothermal vents at the Rivera submersible experiment (RISE) site at 21¿N, on the East Pacific Rise. Two of these instruments were placed within 600 m of the vents, using a transponder navigation network. The array detected four basic types of events. The first type consisted of local, very small microearthquakes. Locations obtained for 11 of these events place three within 1 km of the vents, with the others elsewhere along the rise crest. They appear to originate either from movement on the faults in the area or from the hydrothermal system beneath this area. A study of the S-P times of this type indicates a maximum hypocentral depth of 2-3 km, implying a similar limit to the depth of hydrothermal circulation and brittle fracturing in the vicinity of the vents. The second type of event found consisted of emergent earthquakes that have many of the characteristics of volcanic harmonic tremor. The frequency of these events falls in the 1-5 Hz range and are similar in appearance to those seen at Mount St. Helens prior to and during its May 1980 eruption. They may be either hydrothermal or volcanic in origin. The third type of event produced a very monochromatic, high-frequency seismogram, with the energy concentrated at 20 Hz. These events also appear to have a local origin. The particle motion of these earthquakes shows almost pure Stonely wave propagation, and they appear to originate from a regularly oscillating dilatational source. The nature of the source of event types two and three is clearly not the usual sort of motion on a fault and is still not understood. The fourth type of earthquake recordings were regional events, apparently from the nearby Rivera and Tamayo fracture zones. The low-frequency acoustic noise in the water was 16--64 times higher within 300 m of the vents than it was 2 km away. This implies that the black smoker vents may be generating a large acoustical disturbance as the 350 ¿C water pours into the ocean. The observations are among the first of seismicity on moderate to fast spreading ridges, and many of the events appear to be related to the hydrothermal activity found there.