Originally posted by Josephus
"Not possible."
Oh I disagree, unless you are unwilling to try. 
"Could you tell us why the rifts formed where they did?"
Well, let's see. The Gulf of Mexico, the site of the world's largest meteor impact, and compatible for Flood Theory, is no where near a fracture point. In fact, it's almost dead center from the nearest fractures. I wonder... if we can make a hypthetical experiment. A water balloon. Believing the surface to be uniformly strong in all areas, no matter how hard you smack your hand down on this balloon, even in mid-air (with enough force to make it explode) the breaks of the balloon would be almost equatorily split from the center of impact to the opposite impact axis. But if the water balloon were non-uniform, meaning there were peaks of strength, and areas of weakness, then the areas of greatest weakness from a distance of equatorial strength would be the locations of a split.
For example, take a mountain on this figurative water ballon, resting right on the equidistant locale of impact and pole of that impact... the energy would be transferred to the lowest point of resistance from that mountain.. to say, the nearby valley. I don't know, but thoughtfully it seems sound. Anyone got a way to prove this?
The analogy of course is if the earth's crust was pressured to "rest" above a vast, mostly uniform underground layer of water, if that crust were ever to recieve the energy of the impact (say a large asteroid), the water layer would act as a shock absorber, but in the place of greatest pressure (the equitorial distance from the point of impact) would erupt outwards if unable to contain the energy. Of course, the asteroid would leave a very large crater.
The asteroid (or comet) that struck Siberia in the early 1900's didn't cause any rifts in the earth's crust. Not saying it couldn't happen, just that it didn't in the one time people were around to observe it. The BIG IFs of your theory seem to be that there was a substantial layer of water underground, and that there were one or more asteroid impacts that were energetic enough to crack a previously solid rock crust. Now if there were something to explain, i.e. evidence that a global flood had occurred, then those big if's would be a good question. Having a fact (the global flood) to explain, we would need to look at the geology of the earth to see if it was consistent with your explanation (a subterranean sea, a whole and intact crust, and asteroid impact(s) that ruptured the crust in several places allowing that water to escape). We would have to determine whether the earth's crust could have remained intact before the impact under the intense pressure of superheated water underneath (ever cook anything in a pressure cooker? After all, the earth's crust can still break just under the pressure of hot magma in some places - how did it contain all of the superheated steam prior to the asteroid impacts?
Unless we have something to explain, like evidence for a flood, it makes more sense to interpret all of these geological features in terms of well-understood gradualistic events known to create them.
But do we have anything to explain? Conventional uniformitarian geology explains every feature that you have mentioned at least as well as the hypotheses you have offered.
The big question is - is there evidence for the global flood? In other words, is there evidence that there was a recent extinction of all life on earth except for a boat-load of people and animals, and ((maybe)) a very hardy fish or two. Humans themselves have too much genetic variability to have descended from just one family circa 4000 years ago, and we have relatively little genetic variability. Chimpanzees could not have had a common ancestor for at least four or five million years. Same for Orangatans. Same for most species.
Is there geological evidence for the global flood? Oil and coal deposits won't do... All of the biological mass on the planet could barely account for one oil field in terms of oil production. If the flood accounts for coal and oil, why is there not one continuous deposit everywhere on earth that life existed 4000 years ago? Why just here and there: the Middle East, Venezuela, Alaska, Texas, Siberia (for oil)? Why just here and there: England, West Virginia, etc. (for coal)? How do you account for diamonds? They were formed form intense pressure on coal deposits, right? So, was there a second great flood after the first one to turn all of this coal into diamonds?
Where is the evidence of worldwide uniform deposits of sediments? Where is the one thick stratum with tools and remains of all of those people and animals who were living at that time?
Why do we find none of these features on a global scale, correlated in time with the impact crater(s) of one or more asteroids?
Are you beginning to see why scientists don't accept the global flood model?
