DEPTH OF CRACKING BENEATH IMPACT CRATERS: NEW CONSTRAINT FOR IMPACT VELOCITY

Both small-scale impact craters in the laboratory and less than 5 km in diameter bowl-shaped craters on the Earth are strength (of rock) controlled. In the strength regime, crater volumes are nearly proportional to impactor kinetic energy. The depth of the cracked rock zone depth beneath such craters depends on both impactor energy and velocity. Thus determination of the maximum zone of cracking constrains impact velocity. We show this dependency for small scale laboratory craters where the cracked zone is delineated via ultrasonic methods. The 1 km deep cracked zone beneath Meteor Crater is found to be consistent with the crater scaling of Schmidt et al. (1980) and previous shock attenuation calculations.