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Kashmir earthquake: history repeats itself

R.N. Iyengar

Seismic microzonation of cities provides a way to compute future risk so that building owners, legislators, and other stakeholders can draw up prudent action plans.

BETWEEN THE Independence Day earthquake of 1950 in Assam and the Republic Day shock of 2001 in Kutch, India experienced 12 earthquakes. The Kashmir earthquake of October 8 therefore came as no surprise. Nevertheless, one may wonder whether the subcontinent is passing through a peak in its seismic activity. It is pertinent to note here that the last decade of the 20th century was marked by the United Nations as the international decade for natural disaster reduction, based on a perception that natural calamities might peak during this period.

Data show that peninsular India was relatively quiet during 1870-1920; prior to and after this period it was seismically more active. Earthquakes are unpredictable, but recur in the same region. Hence history plays a significant role in delineating seismic hazard. Kashmir has suffered earthquakes from the remote past. A severe earthquake occurred in October 1555, during the reign of king Shamsha Shah. Shuka, continuing the chronicle tradition of Rajatarangini, describes this in detail. It is said that River Vitasta changed its course and gaping holes formed in the ground, into which houses fell. The earthquake continued for several days, occurring several times daily. People lived in rows of tents (pata-mantapa-pankti in Sanskrit). Nizamuddin Ahmad, an officer in Akbar's court records this in his Tabaqat-e-Akbari, an important source of history.

According to him "in the year 962 (Hijri) there was a devastating earthquake in Kashmir and many villages and towns were destroyed. The villages of Jalu [Nilu?] and Dampur with their buildings and trees were removed from one bank of River Bihat to the opposite bank. In the town of Mardar situated at the foot of a hill, owing to a landslip about sixty-thousand people perished." Five other writers of later dates describe this event. Tarik-e-Ferishta puts the number of dead at 600, which may be nearer reality. It would appear the present earthquake has shaken the same region devastatingly after 450 years.

Surprisingly, 16th century India seems to have passed through a spate of major earthquakes. Srinagar and the rest of Kashmir experienced earthquakes in 1501, 1555, 1560, and during 1569-77. Five Persian sources mention an earthquake that destroyed Agra on July 6, 1505. Even though only Agra is mentioned by name, the quake is said to have disturbed all of India. Two years later, in 1507, an earthquake occurred near Bangalore, important enough for a blacksmith to have inscribed the event in a village called Billanakote. Two earthquakes occurred in the Northeast in 1548 and 1596 near Ghargaon.

In the17th century, only two events were reported from Kashmir. But, the Sadiya, Arunachal Pradesh, earthquake of 1696-97 should have been very severe, reaching Mercalli intensity of at least X, near its epicentre. Another report of a violent earthquake at a place called Mandran on June 4, 1669, is available in the book Mirat-e-Alam by Bhaktwar Khan. Mughal records locate this in Bengal consisting of present day Burdwan, Vishnupur, Bankura, and West-Hugli. Garh-mandaran was the centre of this region with a fort. This earthquake was very violent causing deep and wide fissures in the ground, which joined later to change the topography of the region all of a sudden.

For the 18th century we have information from all over India, but the event that should be of current concern is the rude jolt experienced by Delhi on July 17, 1720. Kafi Khan, Chief of the Mughal army, records "... there was extensive damage and innumerable people perished at Shahjahanabad and Delhi ... the market road from Kabuliwala gate in the north up to Lal Darwaza in the south had broken down at several places and buildings razed to ground ... one month and ten days the earth trembled four or five times daily. People got so scared they no longer slept under their roofs. Earth and buildings vibrated occasionally for the next four or five months ... the shocks gradually ceased."

Seen in perspective, all of India is susceptible to earthquakes, but ground vibration is felt more often in the northern parts than in the south. This makes us wonder what may be in store for our present cities and towns. About one-third of the population of more than 100 crore is concentrated in 30-40 urban areas. Besides active migration from rural areas, cities also capture nearby villages into their territory. Thus about 25 per cent of the urban population lives in slum-like localities. On top of this is the perennial shortage of urban housing, which was estimated at 66.4 lakh units in 2001. The percentage of informal, semi-formal, and formal building types in our cities is roughly in the proportion 10:15:75. For rural areas, this figure is almost uniform at 35:35:30.

We have a situation where quality of life and vulnerability of constructions show greater spatial variability in a city than in a village. The greed of land mafia and local governments to convert every piece of land into real estate is only too well known. Dried up tank beds, hill slopes, landfills, riverbanks, and coastlines with heavy construction are ready recipes for disastrous ground failure in case of strong earthquakes. Engineers can design against earthquakes provided the likely ground motion due to future events within a region of about 300 km around the city is known; and, equally importantly, the ground below the city does not fail. When buildings collapsed in Ahmedabad, there was a hue and cry leading to the arrest of a few persons. While no one condones poor quality construction, a question should have been why buildings built to the same standard at other places remained stable. It took some time for the authorities to realise that there should be something special in the local geology and ground conditions for the peculiar failure pattern.

This brings up the question, what has been learnt from previous earthquakes and whether we have realised the hazard looming over our cities. Being ignorant of how subsurface conditions modify ground vibration, we may be unwittingly increasing the seismic risk to our urban habitat with no worthwhile land use planning in place. Earthquakes being rare, the less informed among the technocrats deny the importance of risk mapping as a pro-active step towards disaster mitigation. They would maintain status quo or at best meddle with the number of seismic zones in the national building code, which has been changed from three to seven to five to four.

Seismic map needs revision

The present official seismic map showing four zones needs revision. Varaha-mihira in the 5th century classified earthquakes into four types in the decreasing order of intensity and also listed regions where each type is to be expected, thus indirectly dividing the country into four seismic zones. In the intervening 1500 years, no further knowledge has been accumulated by the Bureau of Indian Standards; there are still only four zones for this vast country! The issue is not how many zones the country should have, but how the hazard should be represented for use by practising engineers. The tendency the world over, as represented by the international building code, is to have contours of seismic accelerations mapped for the country, at several levels of probability or confidence. One can also map this at regional and city scales for use by local municipalities.

After the Khillari earthquake in 1993, the Maharashtra Government commissioned a study by Columbia University. The resulting report Probabilistic Assessment of Seismic Hazard for Maharashtra has been shelved conveniently. The computed ground acceleration value for Mumbai and its environs is 0.33g with a confidence of 98 per cent, in a foreseen period of 50 years. This is more than that recommended by the official design code, which is presently used by engineers. A logical step would have been to improve the above report to arrive at a city-specific seismic hazard map for Mumbai. After every earthquake, the importance of community participation and administrative preparedness is highlighted. But what is the road map for achieving preparedness?

Seismic microzonation of cities provides a way to compute future risk so that building owners, legislators, and other stakeholders can chalk out prudent action plans. This would indicate where to build, how to design, and also how to protect existing weak buildings and monuments. Risk mapping is a before-the-earthquake exercise so that the city is technologically prepared not just with building byelaws, but also with streamlined relief protocols and insurance for foreseen losses. It is estimated that in Delhi, if things stand as they are, an earthquake could cause damage worth $9-16 billion (Munich Re Group, 2002). For Delhi we have information about ground motion at rock level but not yet at the surface level. Delhi consists of large areas of deep soil deposits that may settle or liquefy under vibration. To have an understanding of this issue, an accurate picture of the variation of shear wave velocity in the top 100-200 meters of the soil is required. After every earthquake the country spends large amounts on instrumentation, leading to acquisition of teleseismic data, which has little impact on safety of either the urban or the rural habitat. It is high time existing fault-lines between civil engineering and earth sciences in the higher echelons of science and technology management were eliminated. Engineering research focussed on our cities, leading to mapping of surface level hazard, vulnerability, economic loss, and informed administrative intervention could cut down foreseen losses by half. Let us not forget: forewarned is forearmed.

(The writer is Raja Ramanna Fellow, Indian Institute of Science, Bangalore)

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