Drivers and modulators of collisional tectonics and their impact on geohazards

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Understanding distribution of tectonic plate forces is key to predicting future earthquake activity around the globe. Although earthquakes mostly occur at tectonic plate edges due to the forces generated by relative movements of the plates, they can also be caused by remote forces, interior plate movements, and climatic effects that are poorly studied. Conventional plate tectonics assumes that mountain belts form by compression and thickening of Earth's crust along convergent plate margins. Yet theoretical and observational studies show that deformation also occurs in plate interiors. Collisional forces at mountainous boundaries oppose forces driving plate movement. This antagonism transmits stress into plate interiors, causing intraplate deformation and potentially leading to the disintegration of a plate. Conversely, breakup of a tectonic plate will reduce the amount of force transmitted to a collisional margin, influencing the amount of deformation and earthquake activity there. Although documented, these connections and feedback mechanisms remain unclear. *** The project's scientific contributions and long-term objectives will: 1) Develop a theory explaining how tectonic deformation is partitioned between plate margins and interiors; 2) Determine how plate-scale stress propagates from incipient breakup areas to collision zones; and 3) Ascertain whether distant forces influence stress along colliding plate boundaries. For this thematic research program, combining observational and theoretical framework, we chose to study the Himalayan region because (a) upper crustal deformation can be directly observed; (b) parameters controlling deformation and morphology of the fold-and-thrust belt are well established; (c) unidirectional moisture sources allow simpler investigation of climatic parameters; and (d) the Indian plate is currently deforming at suspected breakup zones within the Indian Ocean. *** The program proposes multiple hypotheses to be tested by multidisciplinary projects led by graduate students. Projects include compilation, synthesis and interpretation of seismic data; calculation of plate margin and plate interior forces; numerical simulations of orogenic wedge evolution; and detailed field studies. The distribution and magnitude of stresses in the Himalayan region is not merely an academic issue. A deeper understanding of stress propagation and deformation across the Himalaya will improve monitoring and prediction of seismic hazards. In broader terms, this program addresses potential dynamic links between subduction mega-earthquakes and stress loading within plates and along subduction margins around the world, including similar settings like the Cascadia of western Canada.**