Subsurface pulse, crater and ejecta asymmetry from oblique impacts into granular media

We carry out experiments of 104 m/s velocity oblique impacts into a granular medium (sand). Impact craters have nearly round rims even at a grazing angle of about 10 degrees, however, the strength of seismic pulses excited by the impact is dependent upon impact angle, and the ratio between uprange and downrange velocity peaks can be as large as 5, particularly at shallow depths. Crater slope, an offset between crater center and impact site, crater volume, azimuthal variation in ejection angle, seismic pulse shapes and subsurface flow direction are also sensitive to impact angle, but to a much lower degree than subsurface pulse strength. Uprange and downrange pulse peak amplitudes can be estimated from the horizontal and vertical components of the momentum imparted to the medium from the projectile.

Automated summary

In this study, oblique impacts into a granular medium (sand) at a velocity of 104 m/s were conducted. The impact craters showed nearly round rims even at a grazing angle of about 10 degrees. However, the strength of seismic pulses excited by the impact was found to be dependent on the impact angle, with the ratio between uprange and downrange velocity peaks reaching as high as 5.