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Vol. XXV
No. 06
February 11, 2001 |
People’s Democracy
Earthquake
Raghu
THE devastating earthquake in Gujarat
centred in the Kutch region reminds us once more of the devastation that can be unleashed
by natural events. The loss of tens of thousands of lives, the injuries caused to many
times that many people and the enormous destruction to property also again focuses
attention on the unforgivable failures of governance in India as regards preventive
measures against the damage to life and property caused by earthquakes or other natural or
man-made calamities and regarding rescue, relief and rehabilitation measures in the face
of such cataclysmic happenings. The latter will come under increasing scrutiny over the
next few weeks and months, numerous comments would doubtless be forthcoming from various
quarters, including in this journal, and even these columns may have occasion to
contribute to the debates as they unfold. At this juncture, and given the focus of this
column, this article sets out to outline the salient scientific facts about earthquakes,
their causes and impact, possible measures to reduce their impact on society and some
other overall aspects, all of course with reference to the Gujarat quake, so that PD
readers are better informed about various issues and are enabled to better follow and
respond to the discussions which are sure to follow in the coming days.
WHAT AND WHY OF EARTHQUAKES
Earthquakes are among the most
devastating natural events on earth, and a severe quake such as the one that rocked
Gujarat can release 10,000 times or more energy than the atomic bomb which destroyed
Hiroshima. Worldwide powerful quakes occur about every alternative year but at least 40
moderate quakes cause damage each year somewhere or the other. About 40,000-50,000 mild
quakes occur every year, large enough to be felt but not cause damage. Some quakes cannot
be felt as tremors by human beings but can only be noticed on seismometers, instruments
which monitor and measure earthquakes, or by sensitive burrowing animals. The city of
Delhi routinely experiences a quake or two, usually mild, every year and Tokyo registers
at least one mild earthquake every day.
All these remind us that the earth is
still a dynamic, changing body. Most of the solid mass of the earth, as compared to its
stormy oceans and skies, appears to be passive. However, the outermost layer of the earth
known as the crust, which goes down to about 80 km in depth, is quite active and liable to
movements. Indeed, movements also occur far deeper down inside the next layer called the
mantle (especially in its upper portion) which consists of hot rock and metals going down
to about 3000 km below the surface. These movements, as they affect the rocky crust by
subjecting it to severe stresses, cause earthquakes.
Most earthquakes occur along major belts
in the most active areas of the crust mostly in the middle of ocean basins but also at
ocean-rims such as around the Pacific (which also has most of the worlds active
volcanoes which also cause earthquakes in the so-called “ring of fire”) and
across continental land mases as along the Alpine-Himalayan belt. The most
earthquake-prone regions are thought to be California in the USA, Italy, Turkey and Japan
including its off- shore areas. These several well-defined dynamic zones have been
identified based on observations and history but also following from the theory of plate
tectonics according to which the outer layers of the earth are made up of large, rigid
plates. Most plates are very large, covering millions of square kilometres but are only
75-150 km thick. Movements of these plates produce the earths major structural
features such as mountains, mid-ocean ridges or trenches and large faults where different
plates meet. As may be imagined, the active areas are on the edges of tyhese plates while
the passive areas lie in the middle.
The point of origin of an earthquake
lies well below the surface and is known as the focus or hypocentre, while the point on
the surface vertically above the focus is known as the epicentre. The focus of most
earthquakes lie less than 70 km below the surface but have been known to be as deep as 700
km. Since seismic waves i.e. the shock waves emanated by earthquakes become less intense
between 100-400 km depth, geologists conclude that the outermost layer of the earth
“floats” on a less rigid layer which, because it is plastic or more pliable,
allows the plates to move.
These plates move apart, collide or
slide past each other quite slowly in absolute terms (such as the north-easterly movement
of the Indian-Australian plate at the rate of 5 centimetres per year) but generate
enormous force in so doing. Plate separation occurs along mid-ocean ridges produced by
material from further below welling up to form a new crust. Sometimes plates collide, as
when the Eurasian continental mass collided with India some 50 million years ago resulting
in the Himalayas which is relatively recent and therefore unstable. Sliding or transform
faulting neither makes nor destroys the crust and the famous San Andreas fault in
California is the best example. Most earthquakes occur along a fault, that is cracks in
the crust caused by the movements of these plates and the huge stresses generated, where
rocky surfaces slide past or against each other.
India is known to lie in a seismically
active zone due to the frequent interactions and collisions between the Arabian plate to
the west, the Eurasian plate to the north and the Indian-Australian plate which includes
the sub-continent and most of the Indian ocean floor to the south. Within India,
certain regions are known to be more seismically active than others, these regions being
divided into 5 zones, Zone-V being the most earthquake-prone and Zone-1 the least. Almost
all of Kutch lies in Zone-V as does most of the North-East and pockets of the Himalayan
region notably in J&K and in the Garhwal Himalayas. Most of the Himalayan and
sub-Himalayan region, Delhi with its surrounding areas and pockets of Gujarat are in
Zone-IV. Much of the Gangetic plains, most of Gujarat, western Rajasthan and the western
ghats region are classified as Zone-III. Much of the plateau regions in central and
eastern India along with the Deccan lie in Zone I with border regions in Zone II. The
intensity of the quake centred around Bhuj does not cause surprise since the region in
known to be among the most active in India. In contrast, the quake in Latur, Maharashtra,
a few years ago came as a shock since it lies in a region placed in Zone-II.
MEASURING EARTHQUAKES
Earthquake measurement is usually done
using an instrument called a seismograph which physically records tremors by using the
movements of a stylus against paper in both horizontal and vertical directions so as to
reflect tremors in both dimensions. The most popularly used measurement is of the
magnitude of earthquakes using the Richter scale, named after the American scientist who
invented it close to a century ago, the magnitude calculated reflecting the energy
released by the earthquake. The Richter scale is a 10- point scale in which 7.0 is a
severe quake and 8.0 a devastating one. Quakes with magnitude less than 2.0 cannot be felt
but can only be instrumentally measured. Since 1904 when seismometers were first used,
very few earthquakes have exceeded 8.4 and the highest recorded was 8.9 in Japan in 1935.
Originally, Richters calculations used only the deflections of the stylus in a
seismograph and its distance from the epicentre of the quake whereas subsequently
correction factors incorporating the strength of the rocks in the earthquake zone and on
which the instrument stands as well as other factors. The scale is logarithmic not linear
which, along with the correction factors, means that for each point higher on the Richter
scale, the earthquake is about 32 times stronger.
The dispute regarding the strength of
the Gujarat quake, where Indian authorities reported a magnitude of 6.9 and US authorities
reported 7.9, is therefore quite significant. Part of the explanation of this discrepancy
lies in the way the respective measurements were made.
When rocks are unable to bear the
pressure of crust movements in an earthquake, they break down thus releasing the pressure
which spreads out in shock waves. These waves travel at about 3 km per second and can
cover more than 500 km in less than 3 minutes. There are different types of seismic waves
falling under two broad categories: body waves move through the earth and are faster,
while surface waves are slower. Compressional or horizontal waves can cause buildings to
expand and contract while shear or vertical waves cause maximum destruction to buildings,
both these being body waves. L-waves (so named after the British scientist James Love who
classified them) when the ground moves from side to side, and Rayleigh-waves in which the
surface rolls like ocean waves, are both surface waves and usually cause much less damage.
In the Gujarat quake, the Indian
instruments monitored the “body wave” while the US monitoring stations measured
the surface wave resulting in the higher figure both essentially being technically correct
but different ways of reflecting the strength of the quake. It is generally acknowledged
that in major quakes, the surface wave reading gives a better idea of the severity of the
quake and, given the havoc wreaked in Gujarat, a near-8 reading on the Richter scale would
seem to reflect the reality better.
Because of anomalies of this kind,
scientists often prefer to measure the intensity rather than the magnitude of an
earthquake using the 12-point Mercalli Scale (named after Italian seismologist Giuseppe
Mercalli) which measures the local effect and varies both according to the strength of the
quake and the distance from the source. For quakes greater than 7.0 on the Richter scale,
scientists prefer Moment Magnitude measurements which directly measure the energy released
without dependence on the measuring device or its location. Figures on these scales have
not been reliably made available for the Gujarat quake.
Areas with soft, wet soils experience
liquefaction intensifying e q damage, when soils behave like fluids; anything on top can
sink, and liquified soil may itself flow towards lower ground like a mudslide. In Delhi,
the trans-Yamuna area typifies this and the entire area is susceptible to widespread
damage in a major earthquake, especially since no special earthquake-resistant
construction has been undertaken here.
EARTHQUAKE PREDICTION
Many critical comments have appeared in
the media about the failure of authorities to predict the Gujarat quake. Both history and
science indicate that accurate prediction of an earthquake as to location, time and
strength is not only extremely difficult but close to impossible, certainly from
contemporary knowledge and instrumentation. One approach is to study history and geology
of area to look for patterns, but regular patterns usually do not exist. Physical factors,
such as rock composition, shape of ground and even animal behaviour are also taken into
account but are usually not useful for short-term prediction. Long-term predictions can be
reasonably accurate but only as regards broad regions of occurrence, possible magnitudes
and a range of time usually in decades.
For instance, seismic studies indicate
possible 20-year cycles of earthquakes in the Himalayan region and a great quake has not
occured there in more than 50 years even including the Uttarkashi quake of a few years
ago. Experts feel that therefore stresses are accumulating in the Himalayan rocks and are
building up energy which can burst any time. Seismologists have therefore been pointing
out that a massive earthquake, with magnitude of between 7.8-8.3 Richter is overdue in the
Himalayan region, but a more accurate prediction has not been offered as regards either
time or place. Similarly, in many parts of the San Andreas in California, stresses
accumulate over only small areas before they are released in small earthquakes but around
San Francisco, where the faults are “locked”, stresses accumulate and
eventually, but nobody knows exactly when, the breakdown will occur as in 1906 when a huge
8.3 Richter-magnitude quake hit the city.
Till the great SanFrancisco earthquake,
both the US and Japan, especially the latter, being vulnerable to and having suffered
large earthquakes, spent enormous amounts of research time and money on earthquake
prediction. But both countries, Japan somewhat later than the US, virtually abandoned this
goal in favour of one which could yield perceptible benefits viz. putting in place
strategies to prevent or minimise damage caused by earthquakes, putting in place permanent
earthquake monitoring and crisis management set-ups in earthquake-prone regions and
carrying out regular exercises and drills to prepare local populations and concerned
authorities for such crises as may occur. Japan today spends 10 times as much as the US on
earthquake engineering. But this is where India has been found most wanting as so visibly
demonstrated in Gujarat.
PRECAUTIONS AND DAMAGE
MINIMISATION
It is a truism, repeated in virtually
every document or article on earthquakes that, except in hilly areas by causing landslides
or by causing large fissures or other features on the land (such as in the Bhuj region of
Kutch where the massive 1816 quake created a huge scarp or ridge many kilometres long
which resulted in diverting the course of the Indus away from Kutch into what is now
Pakistan), quakes themselves rarely kill people or cause extensive damage but it is
man-made structures that do so.
Structures collapse during earthquakes
when they are not strong enough or are too rigid to absorb the stresses of strong, rocking
forces. In areas where earthquakes are likely, knowing where and how to build can save
many lives and significantly reduce injuries and damage to property. In traditional
construction, softer and more yielding materials such as as mud in Indian plains, wood in
Japan, carefully chosen and laid stones in the sub-Himalayan region in North India and
bamboo structures in the North-East were used to minimise damage caused by collapsing
structures.
In the US and Japan, most modern
buildings, especially in identified seismically-active zones, are built robustly and
carefully to withstand earthquakes.
Earth scientists try to identify areas
likely to suffer great damage due to earthquakes and develop maps showing sites of past
earthquakes, fault zones, flood plains and areas prone to landslides or soil liquefaction
(a condition during earthquakes when normally solid soil is shaken up so much that it
begins to behave as a fluid and thus permits structures above it to sink). Based on these,
land-use planners develop zoning restrictions for unsafe structures in earthquake-prone
areas. Much of the damage in Ahmedabad to recently constructed high-rise buildings is
believed to have been caused, besides poor construction, by the hasty construction over
land reclaimed by filling in local ponds and other water bodies by greedy real estate
developers. In Delhi, even though the trans-Yamuna areas are prone to such
liquefaction, no precautionary measures have been prescribed for building multi-storeyed
buildings or other residential complexes which are today mushrooming in the area.
Engineers have devised several
techniques and have worked out ways to reduce earthquake damage to buildings and
structures of all sizes and shapes. These are very much in evidence in US and Japanese
cities especially San Francisco and Tokyo with their skyscrapers and other high-rise
buildings.
There are a number of ways, ranging from
simple to complex, to build earthquake-resistant structures. Simpler techniques for small
and medium-size buildings include bolting buildings to their foundations, providing
support walls call shear walls made of concrete reinforced with steel bars or rods. Shear
cores made up of shear walls in the building centre, around a stairwell or lift shaft, are
also common in larger buildings. Walls can also be reinforced by cross-bracing with
diagonal steel beams or even with steel mesh or rods forming a cage around brick walls to
keep them from falling. Medium-size buildings are also provided base isolators, kind of
shock-absorbers between the building and the foundation made of alternative layers of
concrete and an elastic material such as synthetic rubber, to absorb some of the sideways
motion that would otherwise damage a building. Base-plates or concrete flat platforms on
which the building rests are also sometimes used. Moats around the building also provide
shock-absorbing capabilities besides isolating buildings from other structures around.
Skyscrapers are specially constructed with deep and secure anchoring, and reinforced
framework with stronger jointing to provide greater flexibility. Provisions are also made
within buildings such as schools, hospitals and workplaces with heavier appliances,
furniture etc fastened down, water and gas lines specially reinforced with flexible
jointing to prevent breaking.
None of these measures were visible in
Gujarat or almost anywhere in India. After the Uttarkashi earthquake, new buildings are at
least required to have lintel beams or steel bands above lintels on doors and windows to
prevent walls from collapsing during earthquakes, but there is little enforcement of this
measure nor has this practice been extended elsewhere in India. Over 170 high-rise
buildings are reported to have collapsed in Ahmedabad alone. Seismic hazard maps and
guidelines for earthquake-resistant housing have been available in India from different
agencies since the 1970s but these are hardly followed anywhere and, worse, are neither
enforced as a condition for approval of building plans nor monitored in any manner. It is
to the credit of the much-maligned public sector agencies, including the PWD, that
numerous buildings including Gujarat Housing Board flats have suffered much less damage
than privately-built housing in Ahmedabad, Bhuj and elsewhere, presumably because there
were at least some bureaucratic norms which were laid down and followed for construction
designs and methods. In the face of this, the Central authorities were said to be
contemplating new regulations requiring self-certification by architects or builders for
earthquake-proofing, even further abandoning the already miniscule role of the state.
Looking ahead India toms-toms its
success in Information Technology, its 4th largest scientific and technical
manpower in the world, its 9th position globally in industrial production. But
only European, Israeli, Turkish and other teams could provide properly equipped mobile
hospitals to treat the injured, communication equipment such as satellite phones which
were brought in by Swiss teams or ultra-sound equipment to detect movements, thermal
imaging equipment to sense warm bodies or fibre-optic linked cameras to peer into
unreachable places, all to detect survivors beneath rubble. The administration did not
know where and how to locate any available generators, earth-moving equipment, cranes and
gas-cutters. Civilian administration collapsed totally for the vital first few days and
only the Army was well-equipped in terms of infrastructure, communications and efficient
manpower deployment and coordination.
After the Latur quake, fully equipped
and trained rapid-action “commando squads” were promised, but the Uttarkashi
quake came and went without it, and now Gujarat. After the Orissa cyclone, a National
Disaster Commission was promised but never came. In the immediate aftermath of Gujarat,
one such has been assured with representatives of all political parties whose major role
becomes clear when one sees the blatantly partisan manner in which relief and
rehabilitation have been organised and centrally funded in the disasters different parts
of India have faced as the victims of the Orissa super-cyclone, the West Bengal and Andhra
Pradesh floods well know. The days to come will show the fate of those in Gujarat.
The least that one can hope for is a full and independent audit of all the funds received
for relief and rehabilitation work, which has never been done for Kargil, Orissa or other
fund-raising causes.
Clearly, a series of institutionalised
measures are needed for both disaster mitigation and disaster management. But will this
come about? In light of all the above, past experiences and the response of the
Gujarat and central administrations to the quake, the future prospects certainly look
bleak.
