Karela Fry

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Buildings as Weapons of Mass Destruction

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Science carries a perspectives article about geoscience with the title which I have plagiarized above:

A quarter of the world’s population inhabits the nations of Iran, Afghanistan, Pakistan, India, Nepal, Bhutan, Bangladesh, Sri Lanka, and Myanmar. These countries lie on or near the northern edge of the Arabian and Indian Plates that are colliding with the southern margin of the Eurasian Plate. The collision occurs mid-continent and, as a result, earthquakes have historically destroyed many settlements, especially in Iran. Deaths from earthquakes since 1900 have exceeded those in all previous centuries, and earthquake deaths to the east of Iran have far outnumbered those in Iran. We ascribe this to the recently increased population at risk in Pakistan and India and to the fragility of construction methods introduced there in the past century.

After each damaging earthquake, engineers tasked with reconstruction confront two questions: Why did so many structures collapse? And to what potential future accelerations will new construction be exposed?

Postseismic investigations reveal that structural collapse is typically attributable to shoddy construction resulting from poverty and ignorance, or to covert avoidance of building codes by contractors. Moreover, earthquake-resistant design codes, where they exist, are generally applied to civic structures only, and not to the dwellings where most of the people of South Asia live. Pervasive building fragility is all too frequently highlighted by the spontaneous collapse of multistory structures in the major cities of south Asia. During strong earthquakes, widespread building collapse is not only expected but also statistically quantifiable within minutes of the mainshock and is used to aid search and rescue.

Does this mean that the non-state actors who are responsible for the proliferation of these WMDs are the builders? What would that make the governments which have been hand in glove with builders?

But equally worryingly, the article goes on to record some basic facts about seismic risks in India:

The front [northern] edge of India is bent downward by about 4 km by the weight of Tibet. This flexural loading stretches the surface and compresses the base of the Indian Plate in northern India and does the reverse in southern India, with a stress intensity that diminishes with distance from the Himalaya. Local extremes in compression or tension result in earthquakes throughout the subcontinent. Additional stresses arise from sedimentary loads along India’s rifted shorelines. These stresses and their slow variation with time are the reason that much of the continental Indian Plate is close to seismic failure; their spatial distribution provides a foundation for maps of future seismic risk.

There remains the disquieting possibility that India’s historical record—even if it were known precisely—may not be a reliable key to its seismic future. Reservoirs have triggered earthquakes in Koyna, Warna, and, debatably, Latur. On a continental scale, the unloading of the flexural depression in the north by depletion of subsurface reservoirs in the Punjab and Ganges plains and the corresponding increase in loading from new reservoirs in the south have adversely perturbed the preindustrial flexural loading of the Indian Plate. Although these stresses are small, they could prove fatal because they act on a system close to failure.

The article is not very long, and certainly worth reading in full.

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Written by Arhopala Bazaloides

August 12, 2013 at 7:50 pm

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