My sleep was jolted at 11:45am IST when I felt a jolt and felt my bed shaking for over a minute. I realised it was an earthquake as I had already experienced tremors twice before. The magnitude in Kolkata, nearly 1000 km from the origin was a 4 on a scale of 12, thus not affecting human lives.
The earthquake originated 34km ESE of Lamjung, Nepal i.e. 77km NW of Kathmandu.The epicenter is marked by a star in the map given below.
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| Epicenter marked with a star ; NW of Katmandu |
The April 25, 2015 M 7.8 Nepal earthquake occurred as the result of thrust faulting on or near the main frontal thrust between the subducting India plate and the overriding Eurasia plate to the north. At the location of this earthquake, approximately 80 km to the northwest of the Nepalese capital of Kathmandu, the India plate is converging with Eurasia at a rate of 45 mm/yr towards the north-northeast, driving the uplift of the Himalayan mountain range. The preliminary location, size and focal mechanism of the April 25 earthquake are consistent with its occurrence on the main subduction thrust interface between the India and Eurasia plates.
The earthquake was a shallow focussed crustal earthquake having a depth of around 11km. Shallow focussed earthquakes generally cause the most damage to human lives and property as the waves propagate with greater magnitude on the surface.
The question is often asked, "How many aftershocks will there be? "
Generally, an earthquake large enough to cause damage will produce several felt aftershocks within the first hour as with 25th April earthquake there were 14 aftershocks of magnitude 6-6.5 as per the Richter Scale.
The rate of aftershocks dies off quickly with time so even the second day will have many less aftershocks than the first.
The question is often asked, "How many aftershocks will there be? "
Generally, an earthquake large enough to cause damage will produce several felt aftershocks within the first hour as with 25th April earthquake there were 14 aftershocks of magnitude 6-6.5 as per the Richter Scale.
The rate of aftershocks dies off quickly with time so even the second day will have many less aftershocks than the first.
Although a major plate boundary with a history of large-to-great sized earthquakes, large earthquakes on the Himalayan thrust are rare in the documented historical era. Just four events of M6 or larger have occurred within 250 km of the April 25, 2015 earthquake over the past century. One, a M 6.9 earthquake in August 1988, 240 km to the southeast of the April 25 event, caused close to 1500 fatalities. The numbers on the rise.
The largest, an M 8.0 event known as the 1934 Nepal-Bihar earthquake, occurred in a similar location to the 1988 event. It severely damaged Kathmandu, and is thought to have caused around 10,600 fatalities.
It takes an earthquake to remind us that we walk on the crust of an unfinished earth.
It takes an earthquake to remind us that we walk on the crust of an unfinished earth.
Sincere prayers go out to the victims of this calamity.
