With Reference To At Least Two Case Studies, One Each From An MEDC and An LEDC, Explain Why LEDC's are More Vulnerable Than MEDC's to Earthquake Hazards.

Table 1

The importance of building design, construction, and the nature of the rock or sediments they are built on, is clearly shown when earthquake statistics are compared. The 1988 Armenian earthquake (an LEDC), of magnitude 6.9, killed 25,000 people, injured 31,000 and made 500,000 homeless. Some 700,000 people lived within a 50km radius epicentre. See figure 2. Compared to the 1989 Californian earthquake, which was twice as powerful, where 1.5 million people lived within a 50km radius of the earthquake epicentre. In the Californian earthquake, 0.1 percent as many people were killed as in the Armenian earthquake. The building design is crucial in explaining the differences. In Armenia, the older stone building were destroyed by the ground shaking, with 88 percent destroyed in Spitak, only 5km from the epicentre. However in Leninakan, 95 percent of the more modern buildings were constructed on soft sediments, which cause eight times the displacement for three times longer.

Figure 2: A map of Armenia showing the epicentre of the 1988 earthquake.

The collapse of buildings and structures is responsible for the majority of deaths, injuries and economic losses resulting from an earthquake. Therefore the damage caused and the number of deaths can be reduced by developing the construction techniques of buildings. The incorporation of aseismic, earthquake resistant, features can strengthen the building incredibly reducing the chance of collapse. Developing structural designs that are able to resist the forces generated by seismic waves can be achieved either by following building codes based on risk maps or by appropriate methods of analysis. Many countries reserve theoretical structural analyses for the larger, more costly or critical buildings to be constructed in seismically active regions, while simply requiring that ordinary structures conform to local building codes. Economic realities usually determine the goal, not of preventing all damage in all earthquakes, but of minimizing damage in moderate, more common earthquakes and ensuring no major collapse at the strongest intensities. An essential part of what goes into engineering decisions on design and into the development and revision of earthquake-resistant design codes is therefore seismological, involving measurement of strong seismic waves, field studies of intensity and damage, and the probability of earthquake occurrence.

The training and experience that emergency services have is also a major factor to assessing how vulnerable LEDC’s are to earthquake hazards. This needs careful organisation and planning, with a clear specification of the role of each group of people. Responsibility for decision-making needs to be identified. One of the key issues for emergency services is where to deploy their people and equipment in an area, which may have suffered disruption of transport and communication lines. New computer developments are helping to make emergency response more effective. The Tokyo Gas Company has a seismic network, which transmits information to a computer using a radio network. This informs the company about pipeline damage so that gas can be switched off and fires and explosions reduced. Individual houses in Tokyo have “smart metres” which cut off the gas if an earthquake over magnitude 5 on the Richter scale occurs.  If the emergency services are adequately trained to dealing with earthquakes and the aftermath, then this radically reduces the number of deaths and injuries. The 1976 Tangshan earthquake demonstrates the problems that rescue services face. The Tangshan earthquake occurred under the city of Tangshan, China, on July 28, 1976. When the dust settled, a quarter of a million people had died, and only a small handful of buildings were left standing. The stations around the quake fault (seismic stations) practically predicted it but they never knew for sure when or it would ever happen.

On the surface, this quake's destruction was worsened by the fact that it struck in the middle of the night. Almost everyone in the city was asleep, and many people were probably crushed to death without even waking up. Many more that lay injured in the rubble died before they could be rescued. The quake knocked out power through the city, making rescue efforts by shocked residents of the city impossible in the dark. A smaller number of people were trapped in nearby coalmines. Many were rescued, but not until hours or days later. Perhaps with better training the rescue services may have been able to rescue more people much quicker and not have to wait for the power to be restored.

Predicting an earthquake and then warning the population is a serious issue, and one that LEDC’s are disadvantaged at. The cost of predicting earthquakes is large, which is why MEDC’s can take advantage of this, and warn people of when and where an earthquake could happen. This is still in its early stages and is not as accurate as it could be in the future. However a little warning is better than no warning at all. Predicting and warning could also be a major factor why LEDC’s are more vulnerable to earthquake hazards. Less advanced technology would certainly not benefit an LEDC in predicting an earthquake, and lack of decent communication in an LEDC would certainly slow down any warning that could have been given. Considerable work has been done in seismology to explain the characteristics of the recorded ground motions in earthquakes. Such knowledge is needed to predict ground motions in future earthquakes so that earthquake-resistant structures can be designed. Although earthquakes cause death and destruction through such secondary effects as landslides, tsunamis, fires, and fault rupture, the greatest losses, both in lives and property, result from the collapse of man-made surface and subsurface structures during the violent shaking of the ground. Accordingly, the most effective way to mitigate the destructiveness of earthquakes from an engineering standpoint is to design and construct structures capable of withstanding strong ground motions.

The factors listed above all help to explain why LEDC’s are more vulnerable to earthquake hazards, although they also affect MEDC’s. This was true for the 1995 Kobe earthquake, which killed 5,500 people. All the modern earthquake prediction techniques and machines did not help to predict this earthquake. The earthquake caused buildings to collapse, railways and roads to split and fires to break out. All the modern techniques for protecting an MEDC, and reducing the hazards, only helped to reduce the impact, which was still enormous. Japan is positioned on the margin of the Eurasian Plate. The Philippine Sea Plate is subducted below the Eurasian plate, resulting in Japan having greater than average seismic and volcanic activity. Immediately south of Osaka Bay is a fault called the Median Tectonic Line, and it was sudden movement along this fault that triggered the earthquake that hit Kobe.

The cost of the 1995 earthquake was estimated at being about $200 million. It could be true to say that loss of life is greater in LEDC’s but the loss of capital is much greater in an MEDC.