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The time of the first arrival of seismic waves generated by explosions at the Nevada Test Site and recorded along a 300‐km line southeastward through Kingman, Arizona, is expressed as T0 = Δ/5.2, T1 = 0.34 + Δ/6.15, and T2 = 5.82 + Δ/7.81, where time is in seconds and the shot‐detector distance (Δ) is in kilometers. Assuming constant velocities for the layers, the thicknesses are H0 = 1.7 km, H1 = 26.7 km, and H0 + H1 ≐ 28 km (below a 1‐km datum). The average Bouguer anomaly is about −120 milligals, and the average elevation is about 1.1 km. Seismograms were examined for P waves indicating the presence of other discontinuities within and below the H2 layer, but the separation between seismic stations was too great to establish the presence of such discontinuities. A questionable alignment of weak arrivals following the T2 refraction time by less than 1 second may indicate the presence of a discontinuity below 28 km. Fair alignments of strong second arrivals in the range 200 to 400 km might be interpreted as direct P waves or channel waves in the H1 layer.

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Seven thousand seismograms of small earthquakes in the Mammoth Lakes‐Bishop area were used to measure values of Q from the decay of the earthquake coda. These measurements were compared between events that occurred before and after the Round Valley earthquake (M=5.7). We found that in regions near the main shock epicenter, measurements of coda Q−1 for earthquakes that occurred after the main shock were higher than for those earthquakes that occurred prior to the main shock. The opposite behavior was found for regions farther away from the main shock, namely, lower coda Q−1 after the main shock than before. Measurements of coda Q−1 in the Long Valley caldera, outside of the immediate source region of the earthquake, were higher than in surrounding areas before the main shock, but the difference disappeared after the occurrence of the main shock. This indicates that the temporal variation in coda Q−1 is comparable to its spatial variation. The doughnut model (seismicity quiescence surrounded by a zone of activity) which was invoked for explaining the precursory seismicity pattern appears to be similar with the observed coda Q−1 variation associated with the Round Valley earthquake. The observed spatial variations in coda Q−1 also help to reconcile conflicting results published in previous studies of the coda Q−1 precursor.

Seismic‐refraction measurements were made at 117 spreads along a line trending north from a shot point near Lamar, Colorado, to near Sidney, Nebraska, between April and August 1961. Crustal thickness from computation based on first and prominent secondary arrivals is about 48 km. The speed of compressional waves in the upper layers of the crust ranges from 2.9 (near surface) to 6.1 km/sec. Evidence was found for a crustal layer of compressional‐wave velocity 6.7 km/sec at a depth of about 28 km. The velocity of compressional waves in the upper‐mantle rocks is about 8.0 km/sec.