Nearly 1500 recent northern California and western Nevada earthquakes of magnitude 2 and above have been used to study aspects of the seismicity of the region. In an area covering 512 degrees of latitude by 8 degrees of longitude, each square degree was subdivided into 16 approximately equal quadrilateral blocks. The seismic energy and associated strain release in each block were computed for time intervals up to five years. The computed representations of strain release for each year are contoured to define the distribution of seismic zones in the area and to give a dynamic measure of thier variation.

The observed surface creep along the San Andreas fault at the Vineyard seismographic station is compared with the intensity of the seismic activity in the immediate neighborhood of the fault zone. The frequency distribution of earthquakes of different magnitude is discussed.

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