Nepal earthquake toll near 1500 with casualties also in India and Tibet

The Indian Tectonic Plate is being subducted under the Eurasian Plate. The collision is still going on with the Indian Plate moving North East at about 6 -7 cm per year while the Eurasian Plate is moving Northwards at about 2 cm per year. The subduction occurs in fits and starts and relies on earthquakes to release the slip pressure. The likelihood of a single Himalayan earthquake of magnitude 8 or a series of magnitude 7 quakes was discussed a few years ago

If a great earthquake has not occurred on a specific segment in the Himalaya for 200 years, that segment will slip 4m because the convergence rate between India and Tibet is roughly 2cm each year. If it has not occurred for 500 years the segment would slip 10m, enough for an event that would measure 8, or Magnitude Eight on the Richter Scale. The time interval between great earthquakes thus determines the amount of slip that will occur in the next one.

…. A large segment of the Himalaya between Kathmandu and Dehradun has a record of several earthquakes but only two large ones: an event in 1803 and another in 1833. If these were great earthquakes then there is now roughly 3m of slip ready to go. However, if they were magnitude 7 earthquakes, then there may be more than 20m of slips availabIe for a future great earthquake.

Nepal earthquake map

graphic: BBC

It would seem that this earthquake near Kathmandu was a large one (7.8 magnitude) and may have released around 5 – 8 m of slip but as has been pointed out there may be a total of around 20m of slip waiting to occur. The current quake has so far seen some 16 aftershocks of magnitude 4.5 or greater. Deaths in India are over 40 and the Indian government is mounting a large rescue effort in support of the Nepali government, “Fifty doctors have arrived from India to provide emergency services. India dispatched as many as four aircraft including a C-130 plane carrying three tonnes of relief supplies and a 40-member rescue team to Nepal.” Three more planes are to follow carrying a mobile hospital and medical supplies.

FirstPost: The quake measuring 7.9 on Richter scale, which was followed by 16 aftershocks of magnitude 4.5 or greater, striking heavy casualties in Kathmandu and injuring thousand others. Hundreds were feared missing across the country. “Army estimates death toll as much as 1457 so far,” Nepal’s Finance Minister Ram Sharan Mahat tweeted. …….

The earthquake around 11:56 am with epicentre at Lamjung, around 80 kilometers northwest of Kathmandu, had its impact in several cities in Bihar, West Bengal and Uttar Pradesh and tremors were felt across vast stretches of east and North East India. It was also felt in Southern and Western parts of India, China, Bhutan and as far as Pakistan and Bangladesh.

The US Geological Survey reports:

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.

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 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.

Was this the big earthquake that was predicted in the Himalayas?

In an interview to The Hindu in May 2013, Vinod Kumar Gaur, seismologist with the Centre for Mathematical Modelling and Computer Simulation, had said: “Calculations show that there is sufficient accumulated energy [in the MFT], now to produce an 8 magnitude earthquake. I cannot say when. It may not happen tomorrow, but it could possibly happen sometime this century, or wait longer to produce a much larger one.”

In a study published in the journal Nature Geoscience in December 2012, a research team led by Nanyang Technological University (NTU) discovered that massive earthquakes in the range of 8 to 8.5 magnitudes on the Richter scale had left clear ground scars in the central Himalayas

High resolution imagery and dating techniques showed that in 1255 and 1934, two great earthquakes ruptured the surface of the Earth in the Himalayas. The 1934 earthquake broke the surface over a length of more than 150 km.

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