Himalayan earthquakes did break the surface in 1255 and 1934

The Indian Tectonic Plate split from Godwana some 140 million years ago and started colliding into the Eurasian Plate some 40 – 50 million years ago. The Indian 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 region is geologically active and earthquakes are not uncommon as the Himalayas continue to grow. It was thought that Himalayan earthquakes rarely, if ever, broke the surface and were “blind quakes”. But a new paper describes field work with novel imaging and dating techniques which show that at least the earthquakes of 1255 and 1934 have left discernible ruptures.

S. N. Sapkota, L. Bollinger, Y. Klinger, P. Tapponnier, Y. Gaudemer, D. Tiwari. Primary surface ruptures of the great Himalayan earthquakes in 1934 and 1255Nature Geoscience, 2012; DOI: 10.1038/ngeo1669

Wikipedia: The Indo-Australian plate is still moving at 67 mm per year, and over the next 10 million years it will travel about 1,500 km into Asia. About 20 mm per year of the India-Asia convergence is absorbed by thrusting along the Himalaya southern front. This leads to the Himalayas rising by about 5 mm per year, making them geologically active. The movement of the Indian plate into the Asian plate also makes this region seismically active, leading to earthquakes from time to time.

Even blind quakes can be devastating as with the Kashmir quake of 2005:

Himalayan Club: The earthquake that devastated the Kashmir region in Pakistan and India in October 2005 will go down in history as the ‘Great Kashmir Earthquake of 2005′ that killed over 87,000 people (about 86,000 people in the Pakistan side and 1,350 in the Indian side of Kashmir), injured at least 100,000 people, ruined tens of thousands of houses and buildings, and made some three million people homeless.

The 6,000 km plus journey of the India landmass (Indian Plate) before its collision with Asia (Eurasian Plate) – Wikipedia

Science Daily: Massive earthquakes are not unknown in the Himalayas, as quakes in 1897, 1905, 1934 and 1950 all had magnitudes between 7.8 and 8.9, each causing tremendous damage. But they were previously thought not to have broken the earth’s surface — classified as blind quakes — which are much more difficult to track.

However, Prof Tapponnier said that by combining new high resolution imagery and state of the art dating techniques, they could show that the 1934 earthquake did indeed rupture the surface, breaking the ground over a length of more than 150 kilometres, essentially south of the part of the range that harbours Mt Everest. 

… Prof Tapponnier warns that the long interval between the two recently discovered earthquake ruptures does not mean people should be complacent, thinking that there is still time before the next major earthquake happens in the region.

“This does not imply that the next mega-earthquake in the Himalayas will occur many centuries from now because we still do not know enough about adjacent segments of the MFT Mega-thrust,” Prof Tapponier explains.

“But it does suggest that areas west or east of the 1934 Nepal ground rupture are now at greater risk of a major earthquake, since there are little or no records of when last earth shattering temblor happened in those two areas.”

As the Himalayan Club points out the region between Kathmandu in Nepal and Dehradun in India has been relatively quiet for over 200 years and has a fault which is ominous:

Large earthquakes are thought to follow a ‘seismic cycle’ as it takes time to accumulate tectonic stress in an area and then release it during a large earthquake. When an earthquake of magnitude over 7 (on the Richter scale) hits some area in the Himalaya, it takes decades for a similar earthquake to hit the same area. Conversely, if no large earthquake has occurred in an area for a long time, the possibility of a Big One should be taken seriously. The Indian seismologist K. Khattri and Roger Bilham of the University of Colorado have identified one such ‘seismic gap’ in the central parts of the Himalaya (between Kathmandu in Nepal and Dehra Dun in India) which has not experienced a large earthquake over the past two hundred years.

Bilham’s studies show that the Indian tectonic plate is moving along a major fault beneath the Himalaya at about 1.8 centimetres a year. (This is about one-third of the total plate movement of India toward Asia – 5.4 centimetres a year. The remaining rate of plate motion is responsible for tectonic deformation and uplift in Tibet and other parts of central Asia). This plate motion is sufficient to generate huge fault movements and catastrophic earthquakes; however, the absence of a Big One in the central parts of the Himalaya in historical times indicates that huge amount of tectonic stress accumulated in this area is waiting to be released.

A major M8 quake in this region will directly impact the densely populated regions of Northern India. In 1934 Bihar was devastated:

Himal Mag: Two million square miles of northern India and western Nepal shook violently for 5 minutes starting at 2:13 in the afternoon of 15 January 1934. The occasion was the Great Bihar Earthquake. It took a further 15 minutes for hanging lamps to stop swinging in Calcutta. It took many days for the dust to settle from landslides in the mountains of Nepal. It took many weeks for sand ejected from the ground to be removed from fields and villages in Bihar, and the roads and railways of Bihar to be brought into service. ….

The difference between a moderate earthquake such as the Uttar Kashi earthquake of 20 October 1991,and a great earthquake like the Bihar event, is that great earthquakes alone permit the Earth´s tectonic plates to slip past each other. …. 

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.

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