A network of five high-gain portable seismographs was operated around Mt. Rainier, Washington, from July 13 to August 11 1968, to study microearthquakes associated with this volcano. Approximately 345 microearthquakes were detected during the 30-day recording interval. Of these, hypocenters and magnitudes were determined for 65 selected events. The microearthquakes were concentrated in two general regions: (1) about 80 per cent were in a roughly concentric pattern around the western side of the volcano at depths ranging from 0.5 to 15 km, and (2) about 8 per cent were beneath the summit crater at depths ranging from 0.2 to 20 km. About 75 per cent of the microearthquakes were at depths less than 5 km. These two groups of microearthquakes can be further defined genetically, as the first may be teatonic earthquakes not related directly to volcanic processes and the second appear to be earthquakes possibly of volcanic origin. The cumulative frequency versus magnitude relation for the tectionic microearthquakes is

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