The occurrence of a moderately strong local earthquake in Santa Monica Bay, California, on August 30, 1930, is discussed and its epicenter and origin-time determined as follows: ϕ = 33° 57′ N., λ = 118° 38′ W., O = 4:40:36.0 p.m., P.S.T. (0h 40m 36s0, G.C.T., August 31, 1930).

The maximum intensity observed was VIII of the Modified Mercalli Intensity Scale of 1931, and the shock was perceptible at distances up to about 160 kilometers (100 miles) from the epicenter. The distribution of apparent intensity exhibits numerous irregularities which are discussed in the text.

The depth of origin cannot be determined accurately, but the data are consistent with a depth of 10 to 15 kilometers (6 to 9 miles). A significantly greater depth is not consistent with the data.

The surface and subsurface geology of the region is discussed briefly.

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