Nepal earthquake and possible impact on Sri Lanka

6 May 2015 03:12 am

Plate tectonics and continental drift
The earth is divided into seven tectonic plates with subduction (sinking) or divergent (spreading) margins, according to the theory of continental drift and both Sri Lanka and India are included in the Indian Plate that started to move northwards after the continent of Gondwanaland, which consisted of India, Australia, Africa and South America started to split from the mega continent Pangaea (which consisted all the landmass of the present day world) about 170 million years ago. India’s   flight together with Australia (Indo-Australian Plate) continued northwards. India moved 2000 kilometres north at a rate of 5 cms per year sliding beneath the Eurasian Plate. With this movement the crust became thicker (78 kilometres) and the lighter crust rode on top of the denser mantle and after collision with the Eurasian Plate about 40 MY BP gave rise to the Himalayas and this movement is still continuing  triggering  earthquakes. 



Tectonic summary of Nepal earthquake
According to the records of the United States Geological Survey (USGS) National Earthquake Information Centre, at the location of the Nepal earthquake, approximately 80 kilometres from Kathmandu, the India Plate is converging with Eurasia at a rate of 45 mm/yr towards the north–northeast, contributing to further uplift of the Himalayas. The location, intensity and generation of this earthquake are similar to others at the   occurrence of the main subduction interface (one plate going under the other as explained above) between India and Eurasia plates.
It has also been reported according to the past records, maintained by the USGS, that although the Himalayan range is in a major tectonic trust with a past history of large to great size earthquakes, large are rare. The USGS reports that only four events of M 6 or larger have occurred within 250 kilometres of the April 25 earthquake over the past century. A M 6.9 earthquake in August 1988, 250 kilometres southeast of the April 25 event caused close to 1500 deaths. The largest the M 8 event, known as the 1934 Nepal–Bihar earthquake in a similar location to the 1988 event, caused severe damage to Kathmandu and around 10000 deaths.



USGS aftershock forecast for M 7.8 earthquake in Nepal
The USGS expects three to 14 events of M>_ 5 aftershocks after the above earthquake. Further, the USGS has also estimated that there is a 54 percent chance of a M>_ 6 aftershock and a 7 percent chance of a M>_7 aftershock during the first week.  During the following month and the following year, the USGS predicts several >_5 aftershocks with a significant chance of a M>_ 6 aftershock. The potential of an aftershock larger than the main shock remains but is small (1-2 percent in each time period).
The USGS also predicts “felt earthquakes” (those less than M>_ 3 or 4) may be common over the next weeks to months. The expected location of the aftershocks will be in the zone of current activity and its edges. At present aftershocks are reported to occur in a zone extending about 200 kilometres away from the main shock epicentre.



Seismotecnotics of Himalaya and its surroundings
Extensive research has been carried out by geologists and geophysicists in the past to unravel the complex geology, tectonics and seismicity of the Himalayan range of mountains generally classified into the greater and lesser Himalayas.
The USGS has compiled a map of the tectonic summary of the region based on data collected and is a useful tool to understand the recent seismic events and also speculate in future events such as earthquakes but there are no definite tools to predict earthquakes.
Seismicity in the Himalayas results from the continental collision of India and Eurasia plates as explained earlier converging at a  relative rate of 40-50 mm/yr. Northward movement of India (under thrusting) beneath Eurasia generates  a number of earthquakes and as a consequence, makes this area one of the most seismically hazardous regions on earth.  According to the USGS, the surface features of this plate boundary is marked by north south trending Sulaiman Range in the  west, the indo–Burmese Arc in the East and the east–west Himalaya Front in the north of India.
The India–Eurasia plate boundary is a diffuse boundary (zone of deformation 100 to 1000 kilometres wide with slipping sideways both on land and in the ocean) near the Indus-Tsangpo suture to the north and the Main Frontal Thrust to the south (suture is a joining together of main fault zones of separate terrains after larger horizontal movements due to continent-continent collision and also by closing of ocean basin as evident by the Himalaya with younger rocks containing marine fossils).
The narrow Himalaya Front (<200 kilometres) includes numerous east–west trending parallel structures. According to the USGS, the region has the highest rates of seismicity, causing   the largest earthquakes in the Himalayan region mainly due to movement of thrust faults (a low angle reverse fault where older rocks are thrust over younger rocks). Examples given by the USGS include the 1934 M 8.0 Bihar, the 1905 M 7.5 Kangra and the 2005 M 7.6 Kashmir earthquakes. The last two together   reported   the   highest deaths for Himalayan earthquakes up to present day, together killing over 100,000 people and leaving millions homeless. The largest earthquake recorded was the Assam earthquake, eastern India with a magnitude of M 8.6 and was widely felt over a large area of central Asia causing extensive damage but strangely no deaths were recorded.
The other seismo tectonic active regions in Himalayas and its surroundings to the north and east as well as the west include the Tibetan Plateau stretching about 1000 kilometres north–south and 2500 kilometres east–west and are geologically and tectonically complex with several sutures (joining together of different fault zones) which are 100s of kilometres long. Collectively, these faults give rise to crustal shortening associated with the ongoing collision of the India and Eurasia plates, with thrust faults giving rise to north–south compression and strike slip giving east–west extension.



Impact of Nepal earthquake on Sri Lanka
The connection between the Nepal earthquake and Sri Lanka tectonically is that both Nepal  and Sri Lanka located in the Indian Plate drifted northwards as explained earlier until its collision with the Eurasian Plate about 40 MYBP, which gave rise to the complex Himalayan range. Although the Indian Plate is still moving and sinking below the Himalayan range on its collision with the Eurasian Plate, this movement is hardly felt in Sri Lanka as it is distanced from the subduction zone.
The writer now likes to draw the attention of the reader to a news item in The Sunday Times of May 1, 2015 titled ‘Lanka safe from major quakes but “home plate” is splitting’, where a number of   geoscientists from various government institutions and universities gave their views on this subject.
The writer would now like to state that all the issues raised in this news item were covered by the writer at length with detailed articles published in The Sunday Times Plus features section, Financial Times on Sunday and The Daily Mirror business section under Opinion columns, respectively. The writer will quote in brief the views expressed by him below:

• In an article in Financial Times on Sunday dated April 24, 2005 under the heading ‘Another tsunami unlikely in next 400 years’ the writer carried out a desk study of research by relevant scientists from the world on tsunamis with particular emphasis on the December 2004 tsunami and related events and recorded the findings. The main reason given for the Indian tsunami was that the enormous stress built up over a very period of time may be centuries caused the rupturing of the Indian Plate and over thrusting over the Burmese Plate as a major aftershock of the M 9.5 unprecedented Southern Sumatra earthquake that ran along the subduction zone and moved west from Andaman Islands. However, the stress on the subduction zone north of India would be released at later times and an example was the Kashmir earthquake of M 7.6 of 2005. It is 10 years since this event that the Nepal earthquake was triggered. It is also likely that more earthquakes will occur in the future along this complex fault zones but a major earthquake of the magnitude of over M 9.5 giving rise to a devastating tsunami will not occur for at least the next 400 years, according to the writer’s study.

 

• An article in The Sunday Times features section on August 5, 2007 titled ‘On moving plates and aftershocks’ was an insight on recent tremors felt in Sri Lanka as a consequence of the breaking up of the Indo Australian Plate along a fault zone running east west about 400 kilometres south of Sri Lanka around 10 MY BP, which the writer should bring to the attention of the present researchers. 

 

• The writer’s article titled ‘Authorities  overreact on ‘borrowed’ info’ published in The Daily Mirror Business Opinion on the scare caused on April 11, 2012 in Sri Lanka related to the undersea earthquake of M 8.7 that occurred at depth of 33 kilometres in offshore Indonesia’s Ache Province. In this article, the writer pointed out the urgent need to study earth tremors and highlighted the lack of coordination among the government agencies as well as the universities.

 

• In an article the writer wrote to Financial Times on Sunday, September 16, 2007 under the heading ‘Was tsunami alerts necessary?’ he stressed the need for designating the Meteorology Department as a focal point for tsunami alerts resulting in evacuation of people from coastal areas. The writer also highlighted the difference of three major undersea earthquakes that occurred since the tsunami of 2004. 

 

• On October 16, 2012, the writer published an article in The Daily Mirror Business Opinion column on the heading ‘Will   earth tremors engulf Asia’s miracle?’ focusing on the urgent need for adopting proper urban construction methods to withstand earth tremors and a new building code to cope with the unprecedented increase of high-rise buildings being constructed especially in Colombo. The writer also compared the tremors in Sri Lanka with south India.

 

• On June 11, 2013, the writer also published in The Daily Mirror Business Opinion an article titled ‘Weather advisories and disaster management in Sri Lanka’ suggesting that a single entity like the Environment and Earth Sciences Ministry in India be established for effective and proper coordination of disaster management in Sri Lanka.

 

• On June 18, 2013, the writer published an article titled ‘Collaborating with India to forecast it right!’ in The Daily Mirror Business Opinion highlighting close collaboration with India for forecasting and mitigation of natural disasters related to weather, tsunami, flooding, landslides, sea level rise, storm surges, etc., in Sri Lanka, which is mostly in the range of Indian forecasting systems. Accordingly, if Sri Lanka collaborates with India, it will avoid duplication of resources and efforts as the land, atmosphere and the ocean space of Sri Lanka encompass the Indian subcontinent of the northern Indian Ocean.

Conclusions and recommendations
It is unfortunate that the various earth scientists have no idea about the articles written by the author since 2005 on the tsunami, its connection to the Indian Plate boundary and the earth tremors that are being experienced in Sri Lanka since the past decade. The reasons have been elaborated in the above articles and the splitting of the Indo-Australian Plate was first highlighted by the writer. If these geoscientists are keen to further research on this diversified subject, the writer would recommend them to read the articles the writer has quoted above.
It is recommended the Government of Sri Lanka (GoSL) should initiate immediate action to closely collaborate with India on the issues highlighted above, which the writer recommended and stressed about three years back.
Further, with the writer’s experience as a senior professional geoscientist for the past 50 years locally and internationally, the writer regrets that there is no effective coordination within the geosciences community and most of them individually or occasionally in groups, either work in water tight compartments or just sit on their past achievements, without disseminating effectively their knowledge to the younger generation.

(Dulip Jayawardena, a retired Economic Affairs Officer United Nations ESCAP, can be contacted at fasttrack@eol.lk)