The loading and unloading of stress on a continental scale has completely changed in recent years.
More people have been killed by earthquakes in Asia this past century than in all previous years put together, with India and Pakistan together accounting for over 2,00,000 deaths after 1900, says a paper in Science.
And this staggering loss of life in the two countries owes to “the fragility of construction methods introduced there in the past century,” says the paper provocatively titled ‘Buildings as Weapons of Mass Destruction.’
The “spontaneous collapse” of multi-storey structures is getting all too frequent in South Asia’s major cities, and the “shoddy construction” could be attributable to “poverty and ignorance, or to covert avoidance of building codes” by contractors, say the authors Roger Bilham of the Department of Geological Sciences, University of Colorado, USA and Vinod Gaur of the Centre for Mathematical Modelling and Computer Simulation, Bangalore.
Earthquake-resistant design codes in these countries are often only applied to civic structures, ignoring dwellings, it adds. “Deaths from future earthquakes could be vastly reduced, with no additional scientific input, were governments to enforce existing construction codes,” add the geophysicists who had, a decade ago in Science predicted a “great Himalayan earthquake.” “Conversely, the development of improved estimates of seismic risk will be futile if governments permit unauthorized and unsound construction practices to continue.”
But the creation and enforcement of earthquake-resistant building codes poses a big challenge in terms of data collection, and could take “many decades to complete.”
The seismologists, who have often expressed their scepticism over the proposed nuclear power plant at Jaitapur however state that “by far the greatest risk from earthquakes in south Asia is currently not from its nuclear facilities but from its fragile dwellings that will collapse in quite modest future shaking.”
A major earthquake appears to prompt revisions to seismic risk maps of India and Pakistan, thereby “endorsing a perception of increased seismic risk in the region of a recent earthquake.” While revising the hazards maps is indeed desirable, the authors drive home the point that in light of the seismic history of most of the region being short, such revisions may not serve the desired purpose. Even if India’s historical record were to be known, it may not be a “reliable key to its seismic future.”
The reasoning for this is that, the loading and unloading of stress on a continental scale has completely changed in recent years. While there has been some unloading of stress in the north due to groundwater withdrawal, there has been a concomitant increase in the south in the form of reservoirs. While these loading changes are small, they could end up proving “fatal because they act on a system close to failure,” they warn.
“There are several unknowns in terms of seismic vulnerability,” Prof Gaur told The Hindu. “But the location of critical facilities must be subject to specific site investigations targeted at reducing these uncertainties. Large critical facilities, must be designed to withstand the maximum credible earthquake.”
While populations in the Himalayas “face a clear risk” from great earthquakes in the future, even a moderate earthquake in the continental collision zone (where the Arabian and Indian Plates collide with the southern margin of the Eurasian plate) would “threaten a far greater population.” This tectonic collision zone — comprising Iran, Afghanistan, Pakistan, India, Nepal, Bhutan, Bangladesh, Sri Lanka, and Myanmar — accounts for a quarter of the world’s population, says the paper.