Peeled-apart Indian Plate could be affecting earthquake hazards

The towering peaks of the Himalayas are a geologic battleground—a slowmotion collision of the Indian and Eurasian tectonic plates. The crunch began some 60 million years ago as India, then an island, plowed into Eurasia, buckling the surface and forming the highest mountains on Earth. But the peaks are just the noise and smoke of the battle; tectonic maneuvers tens of kilometers below them drive the clash—and hold mysteries.

Continental tectonic plates, unlike their dense oceanic cousins, are thick and buoyant, so they don’t easily sink, or subduct, into the mantle during collisions. Some scientists believe the Indian Plate resists plunging into the mantle and continues to slide horizontally under Tibet. Others suggest the most buoyant part of the Indian Plate rumples like a rug along the front edge of the collision, making it easier for the lower half of the plate to sink into the depths.

Now, a new analysis of earthquake waves traveling beneath Tibet and telltale gases rising to the surface points to yet another possibility, one that in effect splits the difference between the two scenarios. Part of the Indian Plate appears to be “delaminating” as it slides under the Eurasian Plate, with the dense bottom part peeling away from the top. The study also finds evidence for a vertical fracture, or tear, at the boundary between the peeled-apart section of the slab and its intact neighbor.