Tuesday, September 03, 2013

Tectonic plates, building codes, and cities in South Asia

by Salman Hameed

I was struck by a graphic from a recent article in Science. It shows different tectonic plates, cumulative deaths from earthquakes from 900-1900 CE, deaths from earthquakes since 1900, and the sizes of major cities. As an aside, for those who believe that earthquakes are God's punishment, we have a good idea where most of the evildoers live - we are looking at you, Iran!

Here is the figure:

As can be seen from the histogram, Iran has indeed suffered most fatalities from these earthquakes. However, the deaths south asia has more deaths since 1900 than for prior 1000 years. It is this point that the authors want to highlight:
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 (see the figure, panel A) . The collision occurs mid-continent and, as a result, earthquakes have historically destroyed many settlements, especially in Iran (1). 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 (see the figure, panel B). 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. 
Since I grew up in Karachi, I'm well aware of the explosive growth of the city as well as its rows and rows of cement buildings. The late columnist Ardeshir Cowasjee wrote in 1999 a series of articles about the earthquake scenario in Pakistan and concluded that:
The people of Karachi should know that all the commercial and residential high-rises are unsafe and dangerous to live in. Most of the builders and contractors, their attorneys or the entity they have established to construct a particular building, disappear from the scene as soon as a building is semi-complete and all spaces sold. The majority are members of the Association of Builders and Developers (ABAD), the body which makes the most noise when any building is ordered to be demolished and accepts no responsibility for the conduct of its members.
The authors of the Science article reach a similar conclusion and offer a modest proposal for the enforcement of existing building codes to save lives:
Earthquake hazard maps characterizing potentially active faults (in India, few active faults are exposed at Earth's surface) are in their infancy, and there are almost no data on the attenuation of strong shaking with distance in large earthquakes or the local amplification of seismic waves in cities. The establishment and implementation of credible earthquake-resistant building codes thus remains a data-gathering challenge for scientists, engineers, and planners of South Asia.  
These studies will take many decades to complete, yet immediate and crucial decisions must also be made by those responsible for the safety of critical facilities. Nuclear power plants can be constructed to withstand the largest of earthquakes, but engineers need trustworthy estimates of potential future accelerations. India has adopted a routine approach to calculating these accelerations (14) but unsubstantiated claims for low seismic hazards at a planned nuclear power plant at Jaitapur south of Mumbai have left many uneasy (15). The plant will be constructed on a coastal plain crossed by a fault that since 50,000 years ago may have lowered (11) the planned plant site by more than 20 m. The timing of earthquakes that permitted the fault to slip, and therefore its earthquake hazard, is unknown (11, 15). 
However, 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. Deaths from future earthquakes could be vastly reduced, with no additional scientific input, were governments to enforce existing construction codes. Conversely, the development of improved estimates of seismic risk will be futile if governments permit unauthorized and unsound construction practices to continue (3, 4). 

Read the full article here (you may need subscription to access the full text).


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