We already know that Himalayas are one of the world's most seismically active zones from the studies undertaken over half a century. How has our understanding about seismicity in the Himalayas evolved?
With the advancement of geodetic and GPS measurement technologies, scientists can now measure the convergence rate between India and Eurasia at high precision. The measured convergence gives an overall estimate of the amount of energy and the equivalent frequency of earthquakes for the region.
A good paper on the subject is given by Ader et al., Journal of Geophysical Research, 2012, v. 117 B04403.
Scientists have stated that the devastating earthquake in Nepal is perhaps not what they were expecting and that the big temblor is yet to arrive. How far do you agree with this theory?
Geophysical observations show that some of the faults, for example, the Main Central Thrust, are seismically less active than others. These faults that have been inactive for long period of time could pose a greater hazard since they are probably locked, allowing energy to build up in the process. Seismologists have identified various segments of the Himalayas' thrust system they are somewhat locked . The estimated energy that has built up is probably greater than that released in the Nepal earthquake. But it is commonly known that earthquakes may not dissipate all the accumulated energy in a single go. The question whether we should prepare for a bigger earthquake is not a sensible one. People residing in seismically active areas should always be prepared for large earthquakes. There is no evidence that energy is being dissipated through aseismic means (not by earthquakes) for the concerned region and for that earthquakes will eventually recur.
What advancements have we made in predicting these earthquakes? What are the new challenges, if any? Is there any mechanism to overcome these challenges?
Sorry to say that there have been very limited advancements in earthquake predictions, in spite of seismologists' diligence and efforts. Over the years, seismologists have studied various phenomena that may be used as precursors to predict earthquakes. A fundamental issue is that in order to study these precursors, we better know in advance where an earthquake is going to occur to allow scientists to deploy observational instruments. Trying to capture an earthquake is a great challenge. Also, in many places, earthquakes occur at intervals measured in terms of decades. It is difficult for scientists to commit very long-term projects to study the earthquakes of a particular fault zone.
South India, since the Bhuj Earthquake of 2001 has been experiencing increased seismicity with scientists discovering new faults. Can you point out if there are any new areas which are becoming seismically vulnerable for human habitation in India and its neighbourhood?
Indeed, in many places, new faults were found. Sometimes, earthquakes occurred on previously unknown faults blind faults. I could not say which areas in India are particularly vulnerable. Doing so requires detailed mapping and geological studies by local geologists. I am not knowledgeable of the local geological structures.