New satellite view of Tibet’s tectonic clash

The study, published in Science, includes several high-resolution maps based on data from Copernicus Sentinel-1 satellites. It shows how the region is being stretched and squeezed by Earth’s geological movements.

Authors of the paper say the study is “one of the most extensive geodetic datasets ever assembled”. Their findings show that the solid masses of rock in Earth’s crust and its uppermost, rigid mantle – the material that makes up our planet’s tectonic plates – are not rigid blocks as previously thought, but can shift in a flowing movement.

The ground displacement map shows how the eastern part of the Tibetan Plateau is moving eastwards by as much as 25 mm per year (shown on the map below in dark brown). This area contrasts, however, with zones of the plateau that are moving at a slower rate of up to 10 mm per year (light brown). Areas in green are moving in an opposing direction, showing the ‘stretch’ of the tectonic plates, in this case as they move away from each other. Vectors are shown in the image on the right.

The Tibetan Plateau, often called the ‘roof of the world’, was formed by the ongoing collision of the Indian and Eurasian tectonic plates – see map below. This region, north of the Himalayas and south of the Kunlun mountains in China, covers about 2.5 million sq km and has an average elevation above 4500 m. The plateau spans numerous countries including the Tibet Autonomous Region, several Chinese provinces, as well as parts of India, Pakistan, Nepal, Bhutan, Tajikistan and Kyrgyzstan.

The plateau is of interest to geophysicists studying our planet’s tectonic movements because it is the largest and highest continental ‘collision zone’ on Earth. According to the paper’s authors, studying this region provides crucial insights into how continents change their shape, position or structure when they are compressed or stretched on a geological scale. This process is not fully explained by standard plate tectonic theory and this paper recalibrates some of the long-standing ideas about how continents change.

Whereas previous models often considered the Tibetan Plateau as a mosaic of strong, rigid blocks separated by major faults that slip horizontally past each other, these findings show that the blocks are not rigid and that fault lines are weaker than previously thought.

The horizontal deformation is clearly shown in the map below, where the ‘strain rate’ along the Altyn Tagh, the Kunlun and the Xianshuihe fault lines is visible in dark red. These are points where Earth’s crust is being stretched, shortened or sheared and the strain rate tells us how quickly this is happening over a specific time period.

The study could provide the basis for similarly detailed maps in other areas of deformation, where seismic activity is likely. The new tools and maps produced by the research team are already being used to improve seismic hazard models used to help countries and communities prepare for earthquakes.

A new view of tectonic movement

The research, led by Tim Wright, is a collaboration between the UK Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET) and the universities of Leeds, Edinburgh, Exeter, and Oxford, and the University of Geosciences (Beijing, China), Monash University (Australia), GNS Science (New Zealand), Columbia University (New York, USA) and South China Agricultural University (Guangzhou, China).

“This is the clearest picture yet of how a continent deforms under extraordinary forces,” said lead author Tim Wright, of the University of Leeds/COMET. “By mapping land surface motion across the whole region in incredible detail, we can finally see how the Tibetan Plateau is actually moving, and the story it tells is very different from what the old models predicted. It is the highest resolution view to date of how the collision between India and Eurasia – one of the most powerful tectonic events on the planet – is reshaping Asia.”

Co-author of the study, Greg Houseman, of China University of Geosciences Beijing and University of Leeds, said, “The data show that continents don’t behave like a mosaic of stiff plates. They flow, but their flow is enabled by major faults which act as weak zones. This helps explain why the extension in the southern and central Tibetan plateau is so widespread.”

One of the study’s most striking findings, according to the authors, is the clear explanation for Tibet’s widespread east–west extension, particularly in the plateau’s interior. The new models used in the study show that the Kunlun Fault must be extremely weak, allowing the northern edge of central Tibet to slide freely relative to the region north of it. This weak boundary enables the plateau interior to collapse and stretch east–west, releasing gravitational potential energy accumulated by the immense thickness of the crust.

“The weakness of the Kunlun Fault is the key that unlocks what’s happening in central Tibet,” said co author Jin Fang, of the University of Leeds/COMET. “It allows the interior of the plateau to essentially flow eastwards, helping to explain the region’s widespread extension, something that has puzzled geologists for decades.”

The study also shows vertical ground movement, as seen on the map below, where the green areas have sunk by up to 5 mm over a year, while the brown areas have risen by up to 5 mm.

Satellite imaging for ground movement

The study is based on data from more than 44 000 Copernicus Sentinel 1 radar images. With its synthetic aperture radar (SAR) instrument, Sentinel-1 can capture interferometric measurements that detect minute changes in land surface, including ground level displacement – more than 340 000 interferograms were used in the study.

More than 14 000 Global Navigation Satellite System (GNSS) measurements were also analysed. These are derived from ground-based measurements that use GPS, Galileo and other satellite positioning systems.

This wealth of satellite data enabled the research team to produce an unprecedented, millimetre scale velocity map of the entire plateau.

ESA’s Sentinel-1 Mission Manager, Nuno Miranda, said, “This work is a remarkable achievement in geoscience. The team has leveraged a decade of Sentinel-1 observations to produce the highest-resolution deformation maps of the Tibetan Plateau to date, revealing the pivotal role of major fault systems in continental tectonics. This study not only advances our fundamental understanding of continental deformation but also sets a new benchmark for seismic hazard assessment. Truly exceptional science.”

Sentinel-1 is the first of the series of Copernicus Sentinel satellites, developed by ESA. It provides data for the Copernicus information services, helping to manage the environment, monitor and react to climate change, and safeguard lives. Copernicus is the Earth observation component of the European Union’s Space Programme.