Monday, April 27, 2015

Images from Ground Zero and a stark warning from another scientist : A letter from Prof Malay Mukul (IIT, Mumbai)

Prof Malay Mukul, of  the Dept of Earth Sciences, IIT Mumbai is from Kalimpong and has done extensive studies on the seismology of the Darjeeling-Sikkim Himalaya. 

He has contributed numerous articles to this blog, besides taking part in several seminars we had  organized. I had written to him after asking his inputs after the recent Nepal quake and I reproduce his reply in toto, in the hope that we living in this beautiful, yet fragile mountains may treat our home with more respect :-

First of all the earthquake was pretty much expected. (see here)

It was an earthquake that originated on the Main Himalayan Fault which is the basal thrust fault of the Himalaya and is also known as the Himalayan Decollement. Himalaya hosts many earthquakes; but the ones that involve the decollement are the great earthquakes whose magnitude is >8.0. These are the ones that all of us dread. The April 25, 7.9 Nepal Earthquake was a decollement earthquake and was bang in the middle of the high risk zone (Please see the two pictures given in the thread above, originally prepared by Roger Bilham, the longer the bar the higher is the seismic hazard in the region). The previous earthquake in the region was in 1934 and was a 8.1 earthquake which killed 10000 people. The expected projection for a repeat of that earthquake today was 49000. So who knows what will be the eventual death toll in this one.

What is also important and is evident from the two figures in the thread above is that there are other areas in the Himalayas that are waiting to be hit. Darjeeling-Sikkim is one of them. The 2011 earthquake was a strike slip one which is not the type we see in Nepal. We actually still await a Nepal kind of earthquake. With the concrete jungle that has mushroomed in our part of the Himalaya, Gangtok is likely to be our Kathmandu!

Aftershocks will continue for sometime. We have already had 45. There usually are a few aftershocks that are about 1 magnitude less that the main shock. We have already had a 6.7 and a 6.6 but most of the activity has been between 4-5. Aftershocks greater than 6.9 are not expected for this earthquake.

A final note: Although we can predict earthquakes in space, we are hopelessly off in earthquake prediction in time. So please do not believe any rumours that give you time predictions on earthquakes.

If you have questions, please let me know.

Best regards, Malay

Photo credits: CNN.

Praful Rao,
Dist Darjeeling

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