Not sure what you mean by "a new gouge under that water," Glen. I think you are suggesting that the existence of a tsunami implies that the quake ruptured to the surface. Remember, the tsunami, so far as is yet known (by me, anyway), was apparently quite localized. So it could be simply due to a sub-sea landslide, without any sea floor displacement at all.

And, even if the tsunami was due to sea-floor displacement, I don't think it can be concluded that the rupture necessarily extended to the surface. And, of course, the fault preceded the quake, so the "gouge" would have been there all along. Though perhaps covered by a thin layer of sediment. So, if it did rupture to the surface, there would be a fresh-looking scarp of some sort. I hope that John V. will add his learned comments to the welcome ones provided by Chris.

Also, Chris, who were those seismologists that you disagreed with about aftershocks representing rupture zones? I'm just an amateur, but, like you, was under the impression that, for very large quakes rupturing many tens or hundreds of kilometers, the aftershock pattern gave a fairly good approximation of the rupture dimensions (throw out the outlying ones). Is this not the general thinking among professionals?

Michael F. Williams
Arroyo Grande, CA USA