The Texas earthquake of August 16, 1931*

Abstract

The travel-time curve of P for the Texas earthquake of August 16, 1931, shows that there is a definite break in the travel-time curve near Δ = 16°. This is interpreted as indicating a first-order discontinuity at a depth of about 300 kilometers. Another break in the travel-time curve at Δ = 25° is strongly suggested. Beyond Δ = 75° the curve has two branches, the lower following most existing curves, the upper following the Montana curve which latter seems to be a usual one for American earthquakes. This part of the curve is interpreted as indicating that the discontinuity at depth about 2,400 kilometers is a first-order one at which the speed of P waves drops discontinuously. From the direction of first motion on the records it is concluded that a sufficient source would have been motion on a fault of strike about N 35° W, the movement being up on the easterly side and down on the westerly side. The travel times of all waves read on the records are plotted on graphs. The scattering of all waves after P is marked.