Monday, 4 July 2011

Case Study: A Tale of Two Cities...

How can two earthquakes of the same magnitude hit two different countries, resulting in two very different situations? Although no two earthquakes are identical - with some parameters differing and thus making them difficult to contrast - this case study highlights a crucial reminder of the vulnerability to natural hazards in the developing world:

Case Study 1: Northridge, California, United States of America 
Sitting adjacent to the San Andreas Fault, a location on the earth where two tectonic plates are sliding past each other, the state of California is prone to earthquakes. However, there are also a number of other faults, including reverse and thrust faults, in this area which have caused significant earthquakes throughout recent history. 

On the 17th January 1994, an earthquake with Moment Magnitude 6.7 struck the Southern Coast of California, close to Los Angeles. The Northridge earthquake occurred in the early hours of the morning meaning that many people were still asleep and indoors. The earthquake caused an unusually strong ground acceleration which resulted in significant damage and became one of the costliest disasters in the history of the USA. The earthquake resulted in 57 people killed, and over 5000 injured. The earthquake occurred relatively close to densely populated areas (compared to the 2003 San Simeon Earthquake, for example, which killed 2 people). Although California had strict building codes some buildings and roads collapsed. Landslides also occurred, fires broke out and there was also an outbreak of the disease Valley Fever. 

Case Study 2: Bam, Iran  
The city of Bam, in the Islamic Republic of Iran suffered a devastating earthquake in 2003. Iran is part of the Arabian Plate, which moves northwards into the Eurasian Plate. This tectonic activity means Iran is prone to large earthquakes.

On the 26th December 2003, an earthquake with Moment Magnitude 6.6 occurred at a depth of around 10km. This earthquake also occurred in the early hours of the morning, meaning many people were indoors and asleep. Fatalities of this earthquake totaled 26,271 and casualties around 30,000. The city, primarily composed of mud-brick building, was devastated in the earthquake. Large amounts of the city did not comply with earthquake regulations set out in the country, which meant that many buildings failed. 


The differences between the two earthquakes are stark, they were similar in size and other factors and yet the Bam earthquake killed 460 times more people than the Northridge earthquake. There were a number of factors which led to this contrast, and the immense vulnerability of the people in Iran.

(1) Adherence to Building Standards
As mentioned above, there are strict building codes in place in California. These were reviewed and updated following the earthquake in Northridge. In Bam, however, the building codes existed but were not adhered to in many cases. Poverty meant that many people built their own houses, or used local builders. This resulted in little notice of national regulations and hence buildings collapsing and many people being buried beneath rubble. It was estimated that around 75% of all buildings in Bam were completely destroyed, and 85-90% of all buildings and infrastructure being damaged or destroyed.  

(2) Urban Planning
Urban planning is also linked to vulnerability. Southern California was developed in a methodical and structured way, whereas Bam did not have this methodical urban planning. Lack of urban planning increases vulnerability as the infrastructure can not be designed to withstand earthquakes, escape routes can not be put into place, and detailed geotechnical analyses of soil types can not be undertaken to ensure areas of ground that are particular vulnerable are avoided.

(3) Education
Even though both California and Iran are prone to earthquakes, the differences in education about earthquakes again contrast hugely. In California people were much more aware of what was happening and how to respond. In Bam, there was very little education with many people holding traditional religious views about earthquakes - views described as poisonous by one Tehran based Geophysics Professor. A lack of understanding about the dynamics of earthquakes and how to respond can significantly increase vulnerability to a hazard.


According to the CIA figures for 2003 Iran is ranked 97th in a list of countries of GDP per Capita, compared to the USA at 2nd. This differences in their economic development meant there was less money to invest in infrastructure, development and education.    

Vulnerability existed in both Iran and the USA, leading to tragic disasters that impacted people in both countries. In Iran however, the human cost of the disaster was 460 times higher than California as a result of increased vulnerability. The impacts of good urban planning, good structural and earthquake engineering and good education are evident.