Note>

Although those areas related are mostly associated/over a continental shelf... there are expansion features which are somewhat in the middle between continental expansion featureas and oceanic expansion rifts... while you go farther from the coasts and into the Pacific basin/ocean... those features develop into oceanic expansion rifts. Some of the oldest ocean floor is found adjacent to those areas, with more than 280 million years since its formation.

As those areas are among the first that started to expand through volcanotectonic major failures and rift formation, then it must be understood that their geology should be (and actually is) quite complex... as some vertical adjustments, relatively minor horizontal adjustments, erosion, isostatic equilibration and differential volcanism had played their role through pretty much million years.