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U.S. Geological Survey Crustal Studies Technical Letter Number 26

In cooperation with the Defense Advanced Research Projects Agency

Seismic-Refraction Measurements of Crustal Structure Between Nevada Test Site and Ludlow, California

By J.F. Gibbs and J.C. Roller


Thumbnail of and link to report PDF (21.1 MB)Abstract

Seismic-refraction measurements from nuclear and chemical explosions were made along a line from the Nevada Test Site (NTS) to Ludlow, California, and additional recordings from nuclear explosions were made southward toward Calexico, California. The time of first arrivals from the Ludlow shotpoint is expressed as T0 = 0.00 + Δ/2.50 (assumed), T1 = 1.00 + Δ6.10, T2 = 2.81 + Δ/6.80, and T3 = 5.48 + ~7.76, where T is in seconds and distance Δ is in km. First arrival times from NTS fit the lines T1 = 0.74 + Δ/6.10, T2 = 2.81 + Δ/6.80 (assumed), T3 = 6.70 + Δ/8.04 to a distance of 265 km, beyond 265 km T3 = 5.83 + Δ/7.75. The difference in the apparent velocities of the Pn (T3) arrival is caused by variations in the dip of the Mohorovicic discontinuity. The thickness of the successive layers at NTS are H0 s 1.0 km (V0 ~ 2.5 km/sec), H1 = 13 km (v1 = 6.1 km/sec), and H2 = 20 km (v2 = 6.8 km/ sec); the total crustal thickness is 34 km. The successive crustal layers at Ludlow have a thickness of H0 = 1.4 km, H1 = 13 km, and H2 = 13 km; the total crustal thickness is 27 km.

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Menlo Park, California 94025

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Suggested citation:

Gibbs, J.F., and Roller, J.C., 1964, Seismic-refraction measurements of crustal structure between Nevada Test Site and Ludlow, California: U.S. Geological Survey Crustal Studies Technical Letter Number 26, 30 p. (Available at




Geology and Physiography

Characteristics of Seismograms

Time of First Arrivals

Depth Calculations




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