The Great Himalayan Earthquakes
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. Tragic as it was, earthquakes are common in the Himalaya. This calls for better understanding of Himalayan earthquakes, better preparedness against earthquakes, and regional cooperation of governments, scientific institutions, and communities to mitigate the disastrous effects of these natural events in the Himalaya.
The Himalayan mountains are the tallest and the youngest on Earth. Earthquakes in the Himalaya are related to the formation and uplift of these mountains. As the Indian tectonic plate is moving and converging with the Asian tectonic plate at a rate of five-six centimetres a year, the Himalaya is uplifting along active faults. This process of continent-to-continent collision, Himalayan uplift, faults and earthquakes has been going on for the past 55 million years, predating the appearance of humans on Earth. (Upright walking humans emerged only about two million years ago.) We enjoy the beauties of the Himalayan landscape because of geologic processes that have shaped these mountains and valleys. Earthquakes are also parts of the same geological processes. Therefore, instead of blaming nature, God or each other's religion, Himalayan communities should be better informed, prepared, and equipped to cope with nature.
Historical Earthquakes in the Himalaya
Although earthquakes have struck the Himalaya for millions of years, historical documents of these earthquakes go back to only the 13 th century and were compiled in the 19th century. A British scholar, R. Baird-Smith, prepared 'Memoir on Indian Earthquakes' and published it in three parts (1843, 1844, and 1845) in the Journal of Asiatic Society of Bengal. In 1883, Thomas Oldham, the first director of the
Geological Survey of India in Kolkata, published 'A Catalogue of Indian Earthquakes from the Earliest Times to 1869' in the Memoirs of the Geological Survey of India. A more recent catalogue of historical earthquakes in the Himalaya has been published in the Indian journal Current Science ('Seismology in India', 25 January 1992).
Since the early decades of the twentieth century we have a better database of earthquakes (even very small tremors) in the Himalaya - thanks to the network of seismic stations monitoring earthquakes all over the world and development of communication systems. The Indian Meteorological Department, for instance, maintains a National Seismological Database Centre in New Delhi and runs 54 seismological observatories including more than a dozen in the Himalayan region. (For more information visit the Website: www.imd.ernet.in
The earliest Himalayan earthquake on record dates back to 1255 in Kathmandu in which (according to a historical document) 'one third of the Kingdom of Nepal perished.' In June 1505 an earthquake wrecked several monasteries in southern Tibet, and a month later, another earthquake hit Kabul in Afghanistan. The earliest historical record of Kashmir earthquakes is one that hit Srinagar in 1555 and killed hundreds of people. Since then, large earthquakes have been documented from the Himalayan region. In the following paragraphs, I describe some of the major earthquakes that have occurred over the past two centuries with information recently obtained about them.
The 1833 Nepal Earthquake
On 26 August, 1833 an earthquake hit an area close to Kathmandu, followed by several large aftershocks. Archibald Campbell, an assistant surgeon to the British Residency in Nepal, reported on this earthquake in the Journal of Asiatic Society of Bengal in 1833. A reassessment of this earthquake in 1995 by Roger Bilham, a geologist at the University of Colorado, indicates that the earthquake measured 7.7 on the Richter scale and that it killed 414, injured 172 people, and destroyed 4040 buildings in Kathmandu.
The 1897 Assam Earthquake
On 12 June, 1897, the Shillong plateau in the Assam region of northeast India was hit by an earthquake with a magnitude larger than 8, killing over 1500 people.
Richard Oldham, son of Thomas Oldham and then Director of the Geological Survey of India, studied the areas affected by this earthquake and analysed the graphs of seismic (earthquake) waves. His mapping shows that an east-west trending area of 200-300 kilometres long was ruptured. Oldham's studies of the Assam earthquake and the comparison of this earthquake with some other large earthquakes have been published, notably in his 379-page 'Report on the great earthquake of 12 June 1897' in Memoirs of the Geological Survey of India, 1899, and his subsequent article, 'The constitution of the earth as revealed by earthquakes' in the Quarterly Journal of the Geological Society of London in 1906.
Oldham's studies made significant contributions to seismology (the science of earthquakes). Oldham showed that if we record earthquake waves arriving in three different stations around the world, we can determine the earthquake location by simple geometric calculations. Similarly, if we know the travel times of seismic waves and the distance between the epicentre (earthquake point on the surface of the Earth) and a receiving seismic station, we can calculate the depth (focal point) of the earthquake. By studying the character of the seismic waves, Oldham distinguished two types: P waves (primary or pressure waves) which travel faster and are first recorded by the seismograph, and S waves (secondary or shear waves) which travel only through solid material. From travel paths of the P and S waves through the Earth, Oldham and some other seismologists discovered that the Earth's core consists of an inner solid core surrounded by an outer fluid core. What a major scientific discovery from the study of the Assam earthquake!
The 1905 Kangra Earthquake
On 4 April 1905, a large earthquake struck the Kangra valley in northwest India. Charles Middlemiss, a British geologist at the Geological Survey of India, visited the areas affected by this earthquake and prepared a 409-page report ('The Kangra earthquake of 4th April, 1905', published in Memoir of Geological Survey of India, 1910) which is still probably the longest report written by a single geologist on a single earthquake! Middlemiss mentions that about 20,000 people were killed in this catastrophe. Charles Richter, an American seismologist who designed the Richter Scale for the magnitude of earthquakes, estimated the magnitude of the 1905 Kangra earthquake to have been 8.6; however, more recent assessments suggest that the magnitude was lower, probably 7.8.
The 1934 Bihar-Nepal Earthquake
On 15 January 1934 an earthquake with a magnitude of over 8 shook a large area in Nepal and Bihar, killing 10,500 people. Seismologists M. R. Panday (from Nepal) and Peter Molnar (from the US) have estimated that this earthquake ruptured an area of 100-300 km long and displaced rocks by six meters on average.
The 1950 Assam Earthquake
On 15 August 1950 an earthquake with a magnitude of 8.7 struck Assam in northeast India. This was the largest recorded earthquake in the Himalaya but it hit a low-population region, causing relatively fewer casualties. Peter Molnar has suggested that a fault of some 200 kilometres long was ruptured in this earthquake and displaced rocks by nine meters.
The 1991 Uttarkashi Earthquake
On 20 October 1991 an earthquake measuring 6.6 on the Richter scale hit the Uttarkashi-Tehri area in north India, killing 769 people, wrecking 28,000 houses and severely damaging another 21,000. The focal depth of the earthquake was 12 kilometres.
This earthquake was particularly significant because it was close to the Tehri dam that the Indian government was building despite protests from environmentalists who were concerned about flooding and submergence of habitable and cultivable land that is already limited in the Himalayan tight valleys. Although the Tehri dam was not damaged by the 1991 earthquake, the renowned Indian geologist, K. S. Valdiya, argued against construction of large damns in the vicinity of active faults in the Himalaya because not only earthquakes would play havoc with such dams but also water accumulation behind the dams would possibly lubricate the underground faults and induce artificial earthquakes (this has been demonstrated for several other dams around the world). Construction of large dams on the Himalayan rivers is still an on-going issue in India, Nepal, and Pakistan, but it is imperative that comprehensive environmental and geological assessments should be conducted before planning such risky and costly ventures.
The Chamoli Earthquake of 1999
The Chamoli district of the Uttar Pradesh state witnessed an earthquake of magnitude 6.8 on 29 March 1999, killing 103 people and causing extensive damage to property. The focal depth of the earthquake was 21 kilometres.
The Great Kashmir Earthquake of 2005
This earthquake, with a magnitude of 7.6, took place at 8:50 a.m. on 8 October 2005. The epicentre of the earthquake was 34.493° North and 73.629° East, some 10 kilometres (6.2 miles) northeast of Muzaffarabad (capital of the Pakistan-administered Kashmir), and very close to the boundary of the Indian and Asian tectonic plates. The focal depth at of the earthquake was about 26 kilometre (16.2 miles). Most of the casualties were in the Muzaffarabad area and the Balakot area, although the tremors were felt as far north as Kabul and as far south in Delhi. In the days that followed, more than a dozen aftershocks, including a magnitude 6.2 tremor two hours after the main shock, continued to shake Kashmir. Earthquake-triggered landslides destroyed many houses on hillsides and blocked roads. In terms of death toll, this was the most fatal earthquake in the recorded history of the Himalaya.
A Big One is Overdue in the Central Himalaya
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.
Do small earthquakes release this tectonic stress and prevent a Big One? Bilham argues that the number of smaller earthquakes in the region has not been sufficient to release the accumulated stress for a Big One. Is it possible that slow movement of rocks along the fault without earthquake rupture (a process that geologists call 'aseismic creep') takes some stress off the area? This is possible. However, studies of topographic changes by levelling surveys and in recent years by Global Positioning Systems (GPS) measurements indicate that creep without earthquake can only absorb less than one-third of the plate movement of India beneath the Himalaya.
For all these considerations, Bilham and some other seismologists believe that the likelihood of an earthquake with magnitude over 8 hitting the 'central Himalayan seismic gap' anytime in the near future is quite serious. 'We know the inevitable outcome,' Bilham told Scientific American in 2001, 'The lock holding the spring will break, propelling the Himalaya southward in a giant earthquake.' And when this happens, the impact on human life and property and the national economies of India and Nepal will be catastrophic because the central parts of the Himalaya face the cultivated plains of the Ganges and populous cities of north India.
Himalayan Earthquakes and Regional Cooperation
Earthquakes in the Himalaya, in general, and in Kashmir, in particular, pose serious challenges. The Himalaya is lofty, remote, and less accessible for transportation. National and religious differences also contribute to strife and conflict in the region. However, the geological reality is that the Himalayan lands and peoples are inter-linked via natural processes transcending beliefs, political follies or personal wishes. Earthquakes are one of these natural processes. Historical records of the past centuries show that several big earthquakes have destroyed parts of the Himalayan settlements (and many earthquakes have possibly gone unrecorded). The earthquake record of the past decades shows that the Kashmir region has been hit at least by one earthquake of magnitude 5 or larger every year or two. This earthquake pattern can be extended back in time, for
which we do not have a complete record, as well as far into the future. Earthquakes are a norm rather than an exception in the Himalaya.
Geologic studies of the Himalaya and efforts to mitigate the adverse impact of earthquakes on life and property should provide a catalyst for mutual understanding and cooperation among the Himalayan countries. These efforts include (1) expanding and modernizing educational and research institutions in the region, (2) engineering strong houses and buildings, and (3) setting up a network of disaster relief and rescue teams jointly operated by the Himalayan countries. These efforts promote a spirit of peace and cooperation in place of hatred and conflict, and the international community can significantly help with these ventures via diplomatic, economic, cultural, educational, research, tourism, and humanitarian avenues of action.
Studies of past earthquakes both in the historical and in the geological record are important to understand the location, repeat time, and magnitude of Himalayan earthquakes. Ancient earthquakes can be inferred from studying geologic features such as (1) faults displacing very young sediments, and (2) locations of soil that has undergone liquefaction (in which water-saturated soil turns from a solid to a liquid material due to high pressure) during large earthquakes. Finding and investigating localities of soil liquefaction in the Indus and Ganges plains can be very instructive.
Although scientists are not able to predict the exact location and time of a large earthquake, several activities can help us to move in that direction. These include (1) putting in place an array of seismometers in the Himalaya to study the pattern and size of seismic tremors, (2) setting up a network of seismic stations communicating critical information and signals to nearby towns, and (3) increasing our knowledge of tectonic deformation and landscape changes by GPS measurements, geophysical surveys, and field geologic studies. All these activities require budget to which the international community should also help because the knowledge derived from such studies improves science itself (recall Oldham's investigations of the 1897 Assam earthquake).
While much attention has been given to human-made conflicts and divides in the Himalaya, the mountainous landscape and geological setting of the Himalaya actually offer unique opportunities for economic development and cooperation in the region. Earthquakes simply demonstrate the necessity of creating a peaceful atmosphere and cooperation among the Himalayan communities. The Great Kashmir Earthquake of2005 once again proved that death toll as a result of shortage of shelter, food, water, medicine and health care may exceed the direct casualties of an earthquake. This is not what the Himalaya wishes.
Bilham, Roger,(1994) 'The next great earthquake.'Himal (Nepal), May-June 1994. Bilham, Roger, Vinod K. Gaur, and Peter Molnar (2001), 'Himalayan seismic hazard.' Science (USA), 24 August 2001. Gupta, G. D. (editor) (1992) Himalayan Seismicity. Geological Society of India (Bangalore) Memoir 23. Gupta, H.K. (editor) (1992) Special Issue: Seismology in India. Current Science (India), 25 January 1992. Gaur, V.K. (editor) (1993) Earthquakes and Large Dams in the Himalaya.lntach, New Delhi (India). Molnar, Peter (1990) 'A review of the seismicity and the rates of active underthrusting and deformation at the Himalaya.' Journal of Himalayan Geology (India), volume 1, pages 131-154. Sorkhabi, Rasoul (2005) 'The geology of the "Roof of the Earth" quake.' World & I (US), December 2005. Valdiya, K.S. (1992) 'Must we have high dams in the geodynamically active Himalayan domain?' Current Science (India), 25 September 1992.
Himalayan lover and geologist Rasoul Sorkhabi uses the 2005 Kashmir earthquake disaster as a pretext to review the great earthquakes in the Himalaya and what lessons we can learn from them.