Zusammenfassung
We have developed a Web-based program for quickly estimating the regional
environmental consequences of a comet or asteroid impact on Earth
(www.lpl.arizona.edu/ impacteffects). This paper details the observations,
assumptions and equations upon which the program Is based. It describes
our approach to quantifying the principal impact processes that might
affect the people, buildings, and landscape in the vicinity of an
impact event and discusses the uncertainty in our predictions. The
program requires six inputs: impactor diameter, impactor density,
impact velocity before atmospheric entry, impact angle, the distance
from the impact at which the environmental effects are to be calculated,
and the target type (sedimentary rock, crystalline rock, or a water
layer above rock). The program includes novel algorithms for estimating
the fate of the impactor during atmospheric traverse, the thermal
radiation emitted by the impact-generated vapor plume (fireball),
and the intensity of seismic shaking. The program also approximates
various dimensions of the impact crater and ejecta deposit, as well
as estimating the severity of the air blast in both crater-forming
and airburst impacts. We illustrate the utility of our program by
examining the predicted environmental consequences across the United
States of hypothetical impact scenarios occurring in Los Angeles.
We find that the most wide-reaching environmental consequence is
seismic shaking: both ejecta deposit thickness and air-blast pressure
decay much more rapidly with distance than with seismic ground motion.
Close to the impact site the most devastating effect is from thermal
radiation; however, the curvature of the Earth implies that distant
localities are shielded from direct thermal radiation because the
fireball is below the horizon.
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