Or, remember that seismic/tectonic activity maybe also be gradually affecting plates in that area.. Things go up. And things go down, sometimes over wide geographical areas.. That applies to seabeds as well, considering the globe is mostly covered by water to start with
Wull Norm... I got my proof offa PBS with their recent "Nature" show on some of Australia's pelicans that all of a sudden head to the middle of their continent, deep into the "outback" into an area known as Ayer's sea. Just about the time they are circling to land, here comes that monsoonal moisture in humunguous cloud-bursts and the floods all rush to the middle of the country filling a huge natural sump-hole like an inland sea!!!
It's probably still showing on www.PBS.org.