Earthquake swarm near Denio, Nevada, February to April, 1973
AuthorRichins, William D
Geological Sciences & Engineering
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An investigation of historic earthquake activity in northwest Nevada shows that earthquake swarms are typical. Evidence suggests that these swarms are associated with geothermal activity. An earthquake swarm occurred during February, March and April, 1973, 20 kilometers south of Denio on the Nevada/'Oregon border. The largest event of the sequence was a magnitude 5.3 shock on 3 March. Fault plane solutions indicate right-lateral oblique-slip motion on a plane striking N11°W and dipping 60°E. This mechanism is very similar to those of the 1954 Fairview Pc ale and other earthquakes in the western Basin and Range, and is consistent with regional extension in a WNW-ESE direction. During March and April, a small tripartite array recorded more than 1,500 events of this sequence, and 221 of these were selected for detailed analysis. Epicenters of these events fall in a north-south trending zone, 8 kilometers in length and 2 kilometers wide; focal depths range from 5 1/2 to 8 1/2 kilometers. The b-value for this sequence is 1.00 which is considerably higher than 0.81 found for northwest Nevada as a whole, high b-values have been found in laboratory experiments for heterogeneous materials and for rocks under low to moderate stress.
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