Lucifer's hammer.

Lucifer's Hammer is a post-apocalyptic science fiction novel by Larry Niven and Jerry Pournelle, first published in 1977. It was nominated for the Hugo Award for Best Novel in 1978. The story details a cometary impact on Earth, an end to civilization, and the battle for the future. It encompasses the discovery of the comet, the LA social scene, and a cast of diverse characters whom fate seems to smile upon and allow to survive the massive cataclysm and the resulting tsunamis, plagues, famines and battles amongst scavengers and cannibals.