HR: 1330h
AN: P52A-0476    [PDF]
TI: The Seismic Effect of Impacts on Asteroids: Early Modeling Results
AU: * Richardson, J E
EM: jrich@lpl.arizona.edu
AF: Dept. of Planetary Sciences, University of Arizona, P.O. Box 210092, Tucson, AZ 85721-0092 United States
AU: Melosh, H J
EM: jmelosh@lpl.arizona.edu
AF: Dept. of Planetary Sciences, University of Arizona, P.O. Box 210092, Tucson, AZ 85721-0092 United States
AU: Greenberg, R J
EM: greenberg@lpl.arizona.edu
AF: Dept. of Planetary Sciences, University of Arizona, P.O. Box 210092, Tucson, AZ 85721-0092 United States
AB: Crater counts made from the NEAR spacecraft images of the asteroid 433 Eros have revealed a paucity of small craters on this small body. Seismic shaking from impacts has been cited as a potential means of small crater erasure, and we present early results from mathematical, hydrocode, and seismic waveform modeling used to investigate this hypothesis. The seismic effects of an impact on a small body can be divided into two categories: (1) surface shaking due to the passage of discrete seismic pulses shortly after impact, and (2) surface shaking due to reverberations following the dispersion of seismic energy throughout the body. Seismic pulse effects are magnified due to the very low surface gravity of these bodies, with relatively small impacts having global seismic effects. An impact producing a 1 km diameter crater on a 20 km diameter asteroid will generate surface accelerations of over 10 g (where g is the asteroid's surface gravitational acceleration) out to an angular radius of 50 deg from the impact site, more than 2 g accelerations over the remaining surface of the asteroid, with a secondary peak of 2-10 g accelerations near the antipode of the impact. In addition, due to their small size and potentially high seismic quality factors (Q $> 3000$, based upon the lunar seismic data), asteroids can experience seismic reverberations lasting for several minutes following an impact. These reverberations will cause additional surface shaking, primarily at the peak frequencies injected by the impact (1-200 Hz). Impacts which produce craters in the 0.1-1 km diameter range on a 20 km diameter asteroid are able to generate reverberations of better than 1 g vertical acceleration over the entire surface. This secondary shaking may thus contribute strongly to modification of the surface topography.
DE: 6022 Impact phenomena
DE: 6040 Origin and evolution
DE: 6055 Surfaces and interiors
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting