A wide chamber from East to West of America’s northern tier, sometimes in Canada’s southern tier.
What use would become available if the structure existed?
It’s like finding water. Either you know where the water is under the ground, or you don’t.
In this case it’s down beyond the Earth’s crust. And there may be ways to exploit that structural phenomenon.
Like the continents the Discoverer seeks to profit from the occurrence.
The structure would be awesome. Practically, things could happen. Transportation may be super quick with bullet trains, for example, going east to west and west to east.
It may be home if civilization makes Earth too hot, as another example.