Collaborative Research: Full waveform inversion for P and S seismic structure beneath Tibet

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A fundamental event in Earth evolution is when two continents collide. The India-Asia collision is the premier example of this happening today. The collision has produced the Tibetan Plateau, the region with the highest topography in the world, as well as deformation resulting in earthquakes and volcanic activity throughout eastern Asia affecting over a billion people. Despite more than 150 years of research on the topic, the evolution of the crust and mantle (lithosphere) beneath the Tibetan Plateau remains an enigma. There is surprisingly little agreement on the configuration of where Indian lithosphere is beneath Tibet and thus little agreement on the processes driving plateau uplift and growth as well as the evolution of the mantle beneath. This proposal is to develop a comprehensive high-resolution P and S wave seismic image of the crust and mantle beneath Tibet and surrounding regions. The goal is to better understand the dynamics of crust-mantle evolution during continental collision. This work will help in understanding past continental collisions and thus provide a better understanding of the geology of continents and the occurrence of natural resources. In the past 500 years more than one million people lost their lives in earthquakes within the study area of this project. The detailed lithospheric structures to be imaged in this work will improve our understanding of seismicity in this vast tectonically active zone of continental collision. This work involves international collaborations with scientists in China and India, as well as training of graduate and undergraduate students at collaborating institutions in the US and internationally.Seismic images will be developed through the application of full waveform inversion of three component regional broadband data that sample the crust and mantle beneath Tibet. The investigators will also incorporate teleseismic travel-time measurements and receiver functions in their model development. A large regional waveform database will be created using all available stations within and around the Tibetan plateau, taking full advantage of the enormous resources that have been dedicated to studies of Tibet in the past. Based on prior experience the team expects to be able to constrain structures with dimensions on the order of 50 km, both laterally as well as vertically. Their main goal is to map the Indian continental lithosphere (ICL) from northern India to regions below the Himalayas and the Tibetan Plateau. The investigators expect to be able to make relatively precise estimates of the thickness of the mantle lithosphere beneath northern India and various parts of Tibet and the surrounding regions. This should put constraints on thickening of the Indian mantle lithosphere as well the location of a possible transition from very thick Indian cratonic lithosphere to thinner Indian continental marginal lithosphere. Further goals will be to see if any instabilities can be imaged at the base of either the Indian or Tibetan lithosphere, and if and where Indian lithosphere is descending into the deeper mantle. Descent of cratonic lithosphere into the deeper mantle has implications for the permanence of cratonic mantle. With accurate P and S images, as well as improved transition zone discontinuity depths, the team hopes to distinguish chemical and thermal anomalies in the deeper mantle beneath Tibet. Using a full 3D image of the upper mantle in this region, they should also be able to see whether the colliding Indian lithosphere is segmented at depth and exhibits variable behavior along strike of the collision. Finally, they hope to place constraints on the behavior of the Tibetan lithosphere and determine whether there is any evidence for southward subduction of Eurasian lithosphere and whether any of the original Tibetan lithosphere been delaminated.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.