The towering peaks of the Himalayas continue to grow taller each year as the Indian tectonic plate collides with the Eurasian plate. This colossal collision is responsible for building the world’s highest mountains, but new research suggests it may also be splitting one region apart at the seams.
Analyses of seismic activity under the Tibetan Plateau indicate that the eastern part of the plateau is detaching from the rest of the Eurasian plate along a zone of intense shearing and faulting. If the process continues, eastern Tibet may eventually break free as a smaller microplate caught between India and Asia. The findings provide insight into how plate tectonics shape some of Earth’s most iconic topographic features.
The India-Asia Collision Zone
The India-Asia collision zone is an area of intense tectonic activity that has puzzled researchers for decades. Around 50-55 million years ago, the Indian tectonic plate broke free from an ancient southern supercontinent called Gondwanaland. It began drifting northward toward the much larger Eurasian plate at speeds averaging around 6.5 centimeters per year – about the rate fingernails grow.
When the leading edge of India made contact with southern Asia 20-30 million years ago, the advance of the subcontinent gradually slowed. But the momentum of the India plate continues to drive into the Eurasian plate today, squeezing, wrinkling, and thickening Earth’s crust in between. This builds the Himalayas ever higher year after year through a combination of thrust faulting and folding of the crust.
|India breaks off Gondwanaland
|50-55 million years ago
|India collides with Asia
|20-30 million years ago
|Uplift of Himalayas
|Continuing to present day
The collision zone extends over 2,400 kilometers across southern Asia. It encompasses the entire Himalayan mountain belt from Pakistan in the west to Myanmar in the east. This makes it the largest and fastest growing collisional mountain range on Earth.
Seismic Signs of Straddling Two Plates
In most continental collision zones, intense compression forces the two plates to fuse together across the impact area. But new evidence indicates the eastern half of the Tibetan Plateau sits atop both the Indian and Eurasian plates along a tenuous boundary running just north of the Himalayas.
Yong Ren from the Chinese Academy of Sciences and colleagues analyzed seismic activity recorded by over 1,200 stations across Tibet and the Himalayas since 1967. They found a pattern of earthquake clusters and changes in wave velocities consistent with movement between the Indian plate below southern Tibet and areas farther north.
“Eastern Tibet sits above a torn Indian plate that is broken in two beneath the Tibetan Plateau, with the lower part attached to India and breaking from the upper part attached to the Eurasian plate” said Ren.
The researchers say the most likely explanation is the Indian plate is splitting as it descends under Eurasia. They estimate shear stress in the rupture area is building at nearly 50 times the rate it can be relieved by earthquakes, indicating a huge amount of accumulated energy that could power future quakes.
If the process continues long enough, eastern Tibet may evolve into a smaller tectonic block riding atop a remnant piece of India broken off from the rest of the subcontinent’s oceanic lithosphere. Something similar occurred when the Arabian and Somali plates separated from Africa along the East African Rift.
Impacts on Landscape Changes
The tectonic tearing and eastward extrusion occurring under Tibet is consistent with surface changes observed within the plateau. Groups of parallel faults and grabens – down-dropped blocks of crust – seen at the surface suggest shear and stretching processes in the subsurface.
There are also significant contrasts in topography, crustal thickness, gravity, and deformation rates across central Tibet that may reflect underlying tectonic fragmentation. The region east of the discontinuity has experienced more continuous shortening and compressional crustal thickening in the past 15 million years than areas farther west.
“Surface deformation and crustal flow seem to work differently east and west of the tectonic boundary, which map and quantify the crustal response to mantle processes” says Fabrizio Bizzarini from the German Research Centre for Geosciences.
Ongoing GPS measurements indicate central Tibet expands outward at 3 millimeters per year as softer lower crustal rocks flow laterally in response to the squeezing from the collision. Below this ductile zone, the uppermost mantle rocks exhibit relatively rigid east-west flow. The opposing horizontal movements are likely related to shear tractions across the inferred plate boundary.
|Contrasting Tibetan Plateau Features
|Higher average elevation with isolated mountain ranges
|Lower rolling plains incised by rivers
|Thicker crust (up to 75 km)
|Thinner crust (60-65 km)
|Shortening and crustal thickening dominate
|Periods of crustal thinning and east-west extension
|Rigid eastward flow
|Ductile crustal flow outward
“The signal of deformation caused by the India-Eurasia collision becomes significantly more distributed west of the tectonic boundary” says Bizzarini. Researchers think the crust and possibly mantle there have decoupled to some degree from the relatively rigid driver of the Indian plate.
Looming Megaquake Threat
The study authors say the newly discovered torn structure beneath Tibet poses a major seismic hazard. Historical records of just a few big earthquakes in the region indicate strain continues to accumulate with time across the discontinuity.
Ren and colleagues estimate enough elastic energy for a possible magnitude 9 megaquake has already built up from deformation occurring since the 1950s. Such an event could produce severe and widespread impacts, especially if the rupture broke through to Earth’s surface.
For comparison, the magnitude 9 Tohoku earthquake that struck Japan in 2011 unleashed an extreme tsunami after a fault ruptured along the seafloor. The disaster killed over 15,000 people and caused the Fukushima nuclear accident. Megaquakes of similar scale also occurred offshore of Chile in 1960 and Alaska in 1964.
“Future study and monitoring of the eastern Tibetan region can improve understanding of the signals preceding this looming hazard” notes Ren. Establishing more seismic stations and GPS networks in the area to track subsurface changes could help forecast when a major rupture may occur. That would give communities across Nepal, Bhutan, India, and China advance warning to implement disaster readiness measures.
The tectonic collision process slowly elevating the Himalayas and Tibetan Plateau likely generates extreme stresses below the surface as well. Seismic imaging reveals evidence of the Indian plate rupturing and its lower portion splitting off from the rest beneath eastern Tibet. The area sits atop the ragged boundary between the detached Indian slab fragment and overriding Eurasian plate.
Surface expressions like faulting and changes in crustal thickness and flow patterns across central Tibet also reflect the underlying plate fragmentation. The shearing and potential eastward extrusion of the region will probably persist for millions of years – dictating future landscape changes.
Most concerning is the tremendous earthquake risk posed by strain accumulation along the tectonic boundary. Much more elastic energy has accumulated across the faults than historical quakes have relieved. Monitoring for precursors of a looming megaquake is crucial for disaster mitigation efforts in future.
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