‘We know where earthquakes can strike, but never when’

What is the biggest gap in our understanding about earthquakes in Himalayas?

We know where earthquakes are likely to go off, but the biggest problem is we can never know precisely when. Earthquakes generally occur when faults rupture, releasing the built-up stress in the Earth's crust. The Nepal earthquake went off on the main interface between the down-going Indian plate and the rising Himalaya above. This is a large-scale compressional thrust fault called the Main Himalayan thrust.

What kind of research is being carried out to find the answers to these questions?

Seismologists can locate earthquakes with increasing precision locations of epicentres, the seismic moment tensor (whether it is a compressional extensional or strike-slip earthquake or a combination of these) and the ground surface movements before, during and after large earthquakes. They use satellite data on the movement of ground surface to millimetre accuracy.