abstract

Strong motion parameters from the Project gnome operation were measured in the region extending 60 to 480 meters from the center of detonation or working point along both vertical and horizontal radii.

Travel time data from the horizontal radius reveals three distinct arrivals. First arrivals are propagated through a polyhalite layer with a velocity of 4.839 km/sec. This is followed by the direct elastic wave arrival in the salt horizon (4.318 km/sec) and the plastic wave which decreases in velocity as the stress level diminishes.

Vertically, the velocity varies from 5.1 km/sec at about 60 meters above the shot to 0.785 km/sec a few meters below the surface.

Peak accelerations in the salt are best fitted by the relations A = 890 R−5.3 from 60 to 122 meters and A = 560 R−2.7 from 122 to 480 meters. (R in hundreds of meters and A in units of gravity.) Peak particle velocity in the salt is given by U = 13 R−3.56 from 60 to 100 meters and U = 13 R−1.36 from 100 to 480 meters.

Motion of the ground above the shot reveals that spalling occurred at several horizons. The deepest spall separation was below 92 meters. These effects were most pronounced at the surface where the initial acceleration, velocity and displacement peak values were A = 25 g, U = 5.6 m/s, and D = 168 centimeters. Residual upward displacement at surface zero at +5 minutes was 79 centimeters.

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