ABSTRACT

There are several elements to this research project. First, there is the research directed to define the past history of great earthquakes and thus strain release along the Himalayan Frontal Thrust (HFT) of India. Here geological principals are used to determine the past size, frequency of occurrence, and location of great earthquake displacements along the greatest continental thrust fault in the world. The location of the study is chosen because India affords the unique situation where the entirety of the crustal deformation associated with recurring earthquakes is situated on land. The ultimate purpose of the study is to compare and understand the relationship of the size and extent of earthquake displacements observed in the geology to ongoing measures of strain accumulation measured by geodesy. Understanding this relationship holds the potential for ongoing measures of geodetic strain to be used to predict the size and location of future great earthquakes along major active fault zones not just in India but also elsewhere along other major fault zones such as the San Andreas which runs through the United States. Second, there is a synergistic element of international cooperation with Indian Investigators that will leverage funding from NSF to collect many more observations than would likely be possible with funding from NSF alone. The third element is education, including the training of several Ph.D. students, the involvement of undergraduates in an exciting international project addressing a fundamental problem in fault mechanics, and the use of the proposed research as a platform to conduct a short course in Himalayan geophysics and tectonics to students and scientists from India and surrounding developing nations with the logistical and financial assistance of the International Centre for Theoretical Physics of Trieste, Italy. Thus, the proposed project will additionally produce unique liaisons for future international collaboration between emerging young scientists. It will directly impact assessment of seismic hazard and raise awareness of seismic risk along this most densely populated megathrust fault in the world, particularly for those in agencies aimed at mitigating and responding to natural disasters.

The methodology employed in this research will entail the mapping and dating of Quaternary deposits and surfaces that have been offset by earthquakes along the Himalayan Frontal Thrust of India (HFT). The age of Quaternary surfaces mapped to be offset by the HFT will be determined with radiocarbon analysis of charcoal samples taken from the deposits. Dividing the amount of the offset by the age of the deposits will define the rate of Himalayan Frontal Thrust (HFT) offset averaged over thousands of years at each site studied. The mapping will also serve to define sites that are most amenable to placing trenches across the HFT. Structural, sedimentological, and stratigraphic relationships exposed in the trenches will be the basis to determine the number, size and timing of earthquakes that have displaced the deposits. It is the goal of this project to implement the methodology at up to 9 sites along the ~2500 km length of the HFT. The resulting observations will, when combined with the results of prior studies, provide the basis to assess the rupture length and amount of coseismic slip of prior great earthquakes along the length of the HFT. It is ultimately through the collection of this type of data and its comparison to geophysical measures of strain accumulation that the seismological community will advance understanding of the physical factors that control the size of future earthquakes.

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