Quake-prone areas in Delhi
By Our Staff Reporter
NEW DELHI, JAN. 26: The quake that rocked Delhi this morning has once again brought to the fore the vulnerability of the National Capital Region to seismic activity.
Delhi has had a long seismic history, having been affected by earthquakes of local origin as well as those emanating in the Himalayas. In the past, five earthquakes registering 5.5 to 6.7 on the Richter scale are known to have occurred in and around the Capital. Two major lineaments namely Delhi-Hardwar ridge and Delhi-Moradabad faults pass through the territory, both having potential of generating earthquakes of magnitude up to 6.5 or 6.7.
According to a background paper prepared by the Centre for Spatial Database Management and Sohttions, the Delhi Action Group and the Joint Assistance Centre on Delhi’s preparedness visavis earthquakes, there has been a marked cessation of seismic activity since 1994. Stresses, which were earlier being released periodically are now getting stored in rocks.
If this trend continued, the paper observed, these stresses will be released resulting in an earthquake. The magnitude of the quake will depend on the amount of energy stored in the rocks. The Naraina Patel Road section and the Yamuna river bed section extending till Noida and Faridabad are more vulnerable to damage even by a moderate quake as they are on alluvial soil for up to 200 metre deep.
According to Geological Survey of India reports, the bedrock depth in the Patel Road area is 60 m while in Connaught Place it is 15 m. Near Rajghat, the bedrock depth is 4050m and in the Yamuna river bed, it is 150 m and beyond. Similarly, the depth is reported to be 80100 m in the Aurobindo MargHauz Khas area.
Another issue of concern accentuated by today’s earthquake is the city’s settlement pattern which has never been viewed in relation to location and geological characteristics. Pockets with high rise buildings or ill designed high risk areas exist without specific consideration of earthquake resistance. Similarly, unplanned settlements with substandard structures are also prone to heavy damage even in moderate shaking.
Connaught Place, in the heart of the Capital, numerous other district centres and high rise group housing societies are highly vulnerable. The Walled City and trans-Yamuna areas besides scattered pockets of unplanned settlements also figure as high risk zones due to their substandard structures and high densities.
In so far as housing is concerned, vulnerability analysis has never been carried out and preliminary estimate of damages is not available for strengthening of structures under normal development schemes. During the Chamoli earthquake of 1999, there were reports of cracks in a few tall buiidings in the transYamnua ar ea. Friday’s quake has, therefore highlighted the need for a vulne ability analysis on all fronts an constitution of a futuristic disaster management group, if necessary.
NEW DELHI, JAN. 26: The high intensity earthquake that shook many parts of the nation this morning was acutely felt in the Capital with people scurrying out of their homes fearing the worst.
Coming as it did exactly an hour before the Republic Day celebrations began at Rajpath, the tremor caught Delhiites unawares. The instant reaction of many was a "flight" into the open. Rattling doors and windows, rocking fans and beds only compounded the feeling of terror. Even as panic gripped the residents of various localities, none could initially flgure out what was happening. And even those who realised that It was an earthquake were prepared to meet any eventuality.
Though described as a "mild tremor" by met officials later, panic was writ large for the 4045 seconds that it lasted. People from different parts of the Capital from the West to the East and from the North to the South could feel the ground underneath them shake. Those staying in multi storeyed buildings dropped whatever they were doing and rushed out. "I could see the building next to ours rock as if it would come down any moment," said a resident of Rohini in NorthWest Delhi.
There were many who started reciting prayers to save themselves from this "deafening roar of mother earth", as one elderly lady described it. Such was the impact of the quake that men and women complained of nausea and giddiness due to a sudden rise in their blood pressure.
Though there was no loss of life or damage to property in the Capital, the quake did bring out Delhi’s vulnerability out into the open. And much to the relief of people, the tremor was mild. But then, it was the earthquake that remained the focal point of conversations all day long. Though the epicenter of the quake was Bhuj in Gujarat, its intensity and magnitude was quite big. "Small tremors keep on occurring in this region also, but this one was acutely felt by Delhiites due to the high magnitude of the earthquake," said a met department official.
The Times of India News Service DEHRA DUN: Scientists studying the Garhwal earthquake had predicted there would be stronger earthquakes along the western coast of India, that includes the highly active seismic zone of Ahmedabad, Ajmer, Delhi (Aravali range).
Their view was based on the ongoing palaeo-seismological investigations along the Himalayan region. Given the vulnerabitity of this region to large quakes, they had suggested the need for adopting an altogether new strategy. Following the detailed study of Chamoli earthquake and that of Uttarkashi in 1991, most geologists were alarmed over the high seismicity along the Main Boundary Thrust and Main Central Thrust due to the rapid rate of convergence between the Indian and Eurasian plates National and international workshops from time to time at the Wadia Institute of Himalayan Geology here have expressed concern over the neotectonic activities in the region.
Many geologists attending a workshop on the Chamoli earthquake at the institute inferred that a great detachment underlying the sedimentary and metamorphic cover of the Himalayas which raptures from time to time leads to great quakes in the region.
During the past 100 years, apart from Uttarkashi and Chamoli quakes, which hit the region within the past one decade four major quakes, measuring above 7 on the Richter Scale, shook the sub-Himalayan region causing a great loss to life and property. These big tremors hit the region in 1897,1905,1934 and 1950.
V C Thakur, former director of WIHG, says there are inherent similarities in source processes of these quakes, which point to their occurrence on the sub-horizontal plate boundary fault. The diverse data, according to another Himalayan geologist, K N Khattari, CSIR emeritus scientist, provides ample evidence that a uniform type of deformation exists in the Himalayan region for the occurrence of great quakes. He says the thrust type earthquake hypocentres define the plate boundary fault and sense of slip on it. Hence, the future greai earth quakes are expected to occur in a similar manner. The physical processes involved in the evolution of the Himalayas were well understood under the theory of plate tectonics.
According to another senior scientist at the WIHG Devendra Pal, a major fundamental fracture which divides the Himalayas in two parts, eastern and western, is very active seismically. He named it as "Delhi-Hardwar-Harsil ridge" (DHH). While the western part of this ridge comprises Himachal, Jammu and Kashmir, the eastem part comprises eastem Garhwal, Nepal and Kumoun. This underground ridge is 65 to 70 kilometres in width between Ganga and Yamuna across Dehra Dun and is expected at a depth of 2.5 kilometres.
The structures of east and west are totally different. Explaining the difference between the two structures, Pal says the DHH forms a western limit of newly created Indo-China plate. The ridge originates from Carlberg ridge in the Indian Ocean, runs as a submarine ridge via Chagos archipelago, Male, Lakshwadeep and Gulf of Cambay along the west coast of India, Ahmedabad Ajmer, Delhi (Arvalli range) and continues in north northeastem direction as an underground ridge between Dellhi and Hardwar and further below Himalayas in Harsil in Uttarkashi district of Garhwal.
Some time ago, Robert S Yeast, a scientist from Oregon State University, had said there was a consensus among the scientists that in future great quakes would strike the Himalayan front. Some of these might be of magnitude 8 in the Richter Scale.
He said because of great increases in population in the region, loss to life and property in the impending quakes were expected to be catastrophic.
Having found the region highly quakeprone, some scientists have begun to talk about an ad hoc disaster management plan and need for evolving a definite methodology for the prediction of major quakes in the the area. Such a plan, according to them, would also have to address the problem of seismic safety on top priority basis.
New Delhi, January 26: A MAJOR environmental disaster is feared in the Gulf of Kutch following reports of a "big" oil slick off the Kandla Port in Gujarat after the earthquake this morning.
Government sources said the Coast Guard hard rushed two ships (offshore patrol vessels) from Wadinar port to investigate the incident in Kandla waters. They said the oil slick was "fairly big and deep" and was reportedly spreading fast.
While initial reports indicated that the oil slick had been caused by rupture in the hull of a merchant oil tanker, it is now feared that even the storage oil tanks at the oil jetty at the Kandla port may have been ruptured due to the high intensity quake. Two Indian Navy ships, INS Tir and INS Nirdeshak, have also been moved to the Gulf of Kutch.
Sources said that a number of oil tankers are currently lined up at the oil jetty to offload the crude oil at the Kandla Port. These tankers pump out crude oil to massive underground storage tanks near the jetty, which is then taken to refineries through pipelines, trains and oil trucks.
According to them, the Coast Guard and the Kandla Port authorities are now trying to locate the source of the oil slick whether it was from a merchant vessel or underground tanks have been ruptured and oil is seeping into the sea, then we are heading for a big ecological problem," a senior official said.
The Kandla Port, which is close to the quake’s epicentre, is one of the biggest in the country and supplies crude oil to refineries at Jamnagar and Hazira.
THE MOST commonly cited measure of the intensity of the Bhuj earthquake is the Indian Meteorological Department’s figure of 6.9 on the Richter scale. Other seismological centres have given higher figures.
The United States Geological Survey and the Hong Kong Observatory rate the quake as 7.9. The USGS website says this is a "preliminary" figure. China’s Seismological Bureau registered the quake as 7.8 on the Richter Scale. The Earth Sciences Observatory in Strasbourg, France, put it at 7.6.
In India, Dr Harsh K. Gupta, director, National Geophysical Research Institute, Hyderabad, placed the quake at 7.9 on the Richter scale. Dr V. Subramanian, department of earth sciences, IIT Guwahati, said Kutch earthquakes "normally" have an intensity of "around 7.0." Many things, such as the type of soil a seismic wave travels through, can distort measurements of an earthquake. Seismologists normally analyse the different figures afterwards to come to a more accurate figure.