The biggest exposed fault on Earth

Geologists conducting research off the coast of eastern Indonesia have identified what they claim to be the biggest exposed fault on Earth — a find that will help researchers assess dangers of future tsunamis in the area.

The milestone occurred when a research team, comprising geologists from The Australian National University (ANU) and Royal Holloway, University of London, were analysing high-resolution maps of the Banda Sea floor off eastern Indonesia. Writing in the journal Geology, the team explained that this area is home to the 7.2 km Weber Deep forearc basin — the deepest point of the Earth’s oceans not within a trench.

“Several models have been proposed to explain the tectonic evolution of the Banda arc in the context of the ongoing (ca. 23 Ma–present) Australia–Southeast Asia collision, but no model explicitly accounts for how the Weber Deep achieved its anomalous depth,” the study authors wrote.

Map of Eastern Indonesia, showing the 7 km deep basin of the Weber Deep (in red, pointed to by white arrow).

The maps showed that the rocks flooring the seas were cut by hundreds of straight parallel scars. The wounds themselves show that a piece of crust bigger than Tasmania must have been ripped apart by 120 km of extension along a low-angle crack, or detachment fault, to form the present-day ocean-floor depression.

Lead researcher Dr Jonathan Pownall, from ANU, said this previously unidentified fault — dubbed the ‘Banda detachment’ by the team — represents a rip in the ocean floor exposed over 60,000 km². He said the abyss was thus “formed by extension along what might be Earth’s largest-identified exposed fault plane”.

Scars on the ocean floor, which were created by the Banda detachment ripping open and extending the Banda Sea.

Dr Pownall added that the discovery of the Banda detachment fault will help assesses dangers of future tsunamis and earthquakes, which is especially important given that it is located in the infamous Ring of Fire.

“In a region of extreme tsunami risk, knowledge of major faults such as the Banda detachment, which could make big earthquakes when they slip, is fundamental to being able to properly assess tectonic hazards,” he said.

Top image: A view from a boat, sailing along the south coast of the island of Seram. The planar slope, dipping gently to the right (south), is the surface of the Banda detachment fault.