Improved Techniques to Map Continental Mantle Earthquakes to Study the Extent of Indian Lithosphere beneath the Tibet Plateau

About This Grant

Continental drift and plate tectonics lead to continental collisions. The collision process forms the Himalaya, Earth’s highest mountain range, and many mineral deposits including those in new copper mines under development in southern Tibet. Consequently, study of Earth’s only large active continental collision, between India and Asia, offers societally important outcomes. Understanding the geologic processes of continental collision allows better targeting of the mineral deposits needed to maintain U.S. economic leadership, whether copper for a more secure grid or rare-earth elements for stronger magnets. Understanding a modern continental collision yields transferable knowledge to understand the ancient continental collisions preserved in the geology of the United States. This project will develop and apply new techniques to understand the way India collides with Asia, mapping earthquakes that locate where India lies at depth directly beneath Tibet and hence where direct interaction between the two continents can create mineral deposits. The locations of earthquakes will help distinguish between two possibilities for the location of former Indian continent beneath Asia. United States economic success also requires a trained workforce, and this NSF grant will enable outreach to expand middle-school student participation in STEM subjects. The project will also provide research opportunities and training for high school, undergraduate, and graduate students. A key to understanding Earth's rheology is mapping the occurrence of earthquakes at different temperatures, depths, and tectonic settings, as well as between the crust and mantle. Establishing whether earthquakes occur above or below the Moho has historically been challenging. New methods using Sn and Lg amplitudes can reliably recognize earthquakes that occur in the mantle, including those too small for their depths to be determined teleseismically. Until now, the new Sn/Lg method has been applied to single earthquakes recorded on many seismometers and to many earthquakes recorded on a single seismometer. This project will develop the Sn/Lg technique to study many earthquakes recorded on many stations. The method will be tested using continuous and event data recorded at permanent stations within Tibet and applied to map mantle earthquakes beneath the archetypal active continental collision, the Himalaya and Tibet. The presence of upper-mantle earthquakes requires cold upper mantle that represents Indian cratonic lithosphere underthrust directly beneath Tibet, whereas regions lacking upper-mantle earthquakes must lack lithospheric mantle. Hence, mapping the extent of mantle earthquakes in this project will test conflicting interpretations of the India-Asia collision zone, notably the northern limit of Indian craton beneath Tibet. 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.