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

TL;DR

This study investigates how oblique impacts into granular media affect crater shape, seismic pulse asymmetry, and ejecta distribution, revealing impact angle influences seismic signals and subsurface flow more than crater morphology.

Contribution

It provides experimental insights into the effects of impact angle on seismic and ejecta asymmetries in granular impacts, highlighting the importance of impact angle on subsurface pulse strength.

Findings

Seismic pulse strength varies significantly with impact angle.

Crater shape remains nearly round even at shallow impact angles.

Seismic asymmetry correlates with momentum transfer components.

Abstract

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 $10^\circ$, 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