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The results of a study of the relative excitation of long‐period and short‐period seismic waves by earthquakes and explosions in the California‐Nevada region are presented. The Richter magnitude M, which is based on the amplitudes of short‐period waves recorded at sites less than 600 km from the epicenter is used as a measure of short‐period waves. A new parameter AR—the sum of the areas of the envelopes of the surface waves on certain three‐component long‐period instruments—is defined and used as a measure of the long‐period waves. The surface wave parameter was determined from long‐period seismograph records from Pasadena and Berkeley, California, Ruth and Reno, Nevada, and Palisades, New York. The four West Coast stations provide good azimuthal sampling of most of the events studied. Surface waves recorded at Palisades from the Fallon‐Stillwater and Fairview Peak‐Dixie Valley aftershock sequences were also studied. There is a wide range in the excitation of surface waves for a given Richter magnitude, both for explosions and, especially, for earthquakes. For any given earthquake there may also be a wide range in the excitation of surface waves as a function of azimuth, an indication of an asymmetrical radiation pattern. Generally speaking, the relative excitation of surface waves by explosions is much smaller than by earthquakes of the same Richter magnitude. Most of the earthquakes studied generated surface waves 5 to 10 times greater than the maximum observed for explosions of the same Richter magnitude. A comparison of the relative excitation of surface waves in different regions indicates a very large regional variation. Shocks off the coast of northern California generate relatively large surface waves, whereas shocks near Laguna Salada in Baja California often generate very small surface waves. An empirical curve is derived for the variation of the surface wave parameter AR as a function of distance. A formula for estimating the surface wave magnitude MS is derived from the parameter AR.

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