| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | January 20, 2015 |
| Latest Amendment Date: | January 20, 2015 |
| Award Number: | 1447100 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Eva Zanzerkia
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 1, 2015 |
| End Date: | July 31, 2018 (Estimated) |
| Total Intended Award Amount: | $190,000.00 |
| Total Awarded Amount to Date: | $190,000.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
2550 NORTHWESTERN AVE # 1100 WEST LAFAYETTE IN US 47906-1332 (765)494-1055 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
550 Stadium Mall Drive West Lafayette IN US 47907-2051 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
Tectonics, Geophysics |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The theory of plate tectonics was revolutionary in the field of geophysics and explained the motion of plates and locations of earthquakes and volcanoes. However, this theory breaks down at continental boundaries where earthquakes extend 1000?s of km and significant topography is created. The ongoing collision of the Indian and Eurasian plate provides a natural laboratory for studying such regions and the factors controlling deformation patterns in continental collisional zones. In the absence of direct sampling of the lithosphere with depth, numerical modeling can provide bounds on physically allowable lithospheric properties. Understanding the variation in strength within the continental lithosphere is fundamental to assessing the forces that generate earthquakes and build mountains. Results obtained within this proposal will have important implications relating to forces generating deformation of the Tibetan Plateau, stress transfer within the lithosphere, the depth to which surface observations sample lithospheric properties, partitioning of strength between upper crust, lower crust and lithospheric mantle, influence of the lower Indian plate beneath southern Tibetan, and flow the base of the lithosphere resulting from convection of the interior of the Earth.
This project will perform 3-D geodynamic modeling solving Stokes flow to investigate the lateral and vertical strength variations within the Eurasian lithosphere. Geophysical observations will be used to construct a physically accurate model volume of the India-Eurasian collision zone, and numeric simulations will be performed to determine the effects of variations in lithospheric strength (both vertically and laterally) on predicted surface deformation. Comparisons between predicted surface velocities and the observed surface deformation field, constrained by GPS and quaternary fault slip data, will differentiate between physically viable models. This work will seek to: (1) Map out the allowable vertical strength contrasts within the Eurasian deforming lithosphere; (2) Isolate the depth sensitivity of surface observations within Eurasia; (3) Investigate the influence of variable lithospheric thickness and mantle flow on the observed surface deformation field.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The objective of this research was to understand how strength is partitioned throughout the Tibetan lithosphere and how possible horizontal layers of strong or weak crust and vertical weak fault zones influenced the surface motions and deformation at the surface recorded by GPS observations. This was done through 3-D numerical simulations of different assumed strength partitioning. The output at the surface of the model was then compared to surface measurements of GPS and earthquake observations to determine the bounds of allowable strength of the lower crust in Tibet and the relative contrast between the Tibetan upper crust and lithospheric mantle. In addition, we investigated possible configurations of the underthrust Indian Plate and how it changed the predicated motions at the model surface.
We found that a weak lower crust, with a value of 10^20 Pa•s, is important for numerically replicating observed horizontal and vertical surface motions as measured with GPS and geologic data. Interestingly, horizontal velocities were insensitive to the strength of the weak lower crust but vertical velocities were highly sensitive. Flow of the weak lower crust generates two east-west trending bands of surface subsidence and dilatation consistent with observed normal faulting and estimates of vertical velocity. These results suggest that viscous buckling of the upper crust, induced by lower crustal flow from gravitational pressure gradients due to the thickened crust and high topography, is responsible for the observed extension in Tibet. Results showed a west-to-east decrease in crustal strength, with a stronger upper crust required in the west with the Indian plate extending deep into the Tibetan lithosphere transitioning to the upper crust and mantle being of equivalent strength to the east with no Indian plate beneath the lithosphere. Finally, we found localization of strain accommodation along large-scale strike-slip faults in tandem with a weak lower crust in Tibet is required to numerically replicate observed surface rotation about the Eastern Himalayan Syntaxis.
The results presented in this report provide a new mechanism for explaining the origins of normal faulting in Tibet. They also provide tight bounds on allowable viscosities of the lower crust. Finally, they demonstrate how much lower crustal material is transmitted out of the plateau. These results have been incorporated into teaching modules for geophysics majors class and large surface course to teach about convergent processes and mountain building. This project supported the PhD of a female student and an undergraduate student exploring research.
Last Modified: 02/09/2020
Modified by: Lucy Flesch
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