Japanese survey discovers giant Godzilla Megamullion on Philippine Sea floor

Around 2001, researchers working with a Japanese government seafloor survey, led by Japan's Coast Guard hydrographic agency, mapped an unusually large structure in the Parece Vela Basin of the Philippine Sea, roughly 2,000 kilometres south of Tokyo. Sonar mapping revealed a broad, gently curved dome with parallel ridges and grooves running across its surface.

Scientists identified it as an oceanic core complex, also called a megamullion. These form where tectonic plates pull apart and a large fault drags deep crust and upper mantle rock up onto the seabed, exposing material normally buried far below. The ridged surface records the sliding of the fault.

The feature was so much larger than other known examples that it was nicknamed the Godzilla Megamullion. It is widely described as the largest known structure of its kind, spanning more than a hundred kilometres. Its discovery mattered because it offered a rare window into how new ocean crust forms and how the deeper Earth is exposed, and it later became the basis for its recognition as a notable geological site.