Abstract

The Himalaya is an exceptional example of an active mountain range where the processes which have shaped the range over tens of millions of years can be observed at work. In this presentation, I will give an overview of what we have learned from using a variety of different techniques to investigate its structure and current activity. I’ll describe how the various observations and data (seismicity, geodesy, morphotectonics) can be reconciled from a simple model which involves recurring large earthquakes, aseismic deformation and some coupling between crustal deformation and erosion. A most intriguing observation is that strain and seismic activity in the Himalaya vary seasonally: as the Himalaya rises in response to the huge forces generated by Earth internal dynamics, it also shows a surprising sensitivity to very small climate-driven stress changes. I will discuss what can be learned from these observations about earthquake processes and how our understanding of earthquake physics, combined with improved numerical simulation, can help evaluate the probability and characteristics of future large earthquakes. I’ll single out some outstanding questions that I am planning to address in the future to make progress on this issue: why is it that some faults ‘stick’ and accumulate elastic strain to be released in future earthquakes whilst some others creep quietly? How is seismicity hazard modified when fluids are injected in the crust (relevant to CO2 storage, geothermal energy, fracking)?