Geophysics and Tectonics Seminar spring-2019

Assessing the magnitude and return period of large earthquakes along the Himalayan arc is both a major societal concern and scientific challenge. Therefore, efforts to establish a better understanding of the physics governing fault and earthquake dynamics are of utmost importance. In this talk, I will discuss recent progress we have made towards that goal. In the first part, I present physics-based numerical models, which are used to constrain the geometry of the Main Himalayan Thrust (MHT) and to explore the conditions that could explain the bimodal seismicity (Mw ≤ 7.8 vs. Mw 8+) of the large Himalayan earthquakes. These models establish the dependence of earthquake rupture patterns on fault frictional properties and non-planar geometry of the MHT due to variations in strength excess. In the second part, I propose the first probabilistic estimates of interseismic coupling along the MHT based on a recent compilation of geodetic data. Using a fully Bayesian approach, I evaluate the population of plausible coupling models given geodetic data and forward problem uncertainties. I will show how the spatial variability in coupling and complexity in earthquake history suggest lateral segmentation in the collisional structure, which are related to inherited tectonic structures from the India-Eurasia collision. The Himalayan megathrust appears to be paved with low- and high-coupling patches and the resulting pattern seems to have a profound influence on its long-term seismic behaviour, as well as on individual earthquakes.