There are a diverse variety of both physical (geological and geographic) and human (economic, political and historical) factors that influence how significant an earthquake can be. The magnitude of the earthquake can be measured by seismographs using a logarithmic Richter scale, measuring the earthquake strength. However this often bears little resemblance to the actual impact of the earthquake, (which can be measured using the descriptive / qualitative Modified Mercalli scale which measures the physical effect of the earthquake) for the following reasons…
One of the ideas that must be considered is how the magnitude of the earthquake is not directly proportional to the intensity of the earthquake as there is a considerable distance between the focus (point of fracture) and epicentre (point on surface vertically above focus on earth surface). If the focal point is ‘shallow’ (under 70km deep) then the impact of the earthquake is greatest, but if the point is e.g. 500km deep then potential impact is reduced. However it is usually accepted as a generalisation that a more powerful earthquake can potentially cause greater damage. Evidence clearly shows how this is not an accurate generalisation – whilst a 1989 Loma Prieta, USA earthquake of Richter Scale magnitude 7.1 caused 67 deaths, a 1988 Spitak, Armenia quake with magnitude 6.9 caused 25000; many other factors must be considered…
Proximity of the epicentre to larger built up urbanised areas poses greater potential human damage – the epicentre being vertically above a CBD is obviously going to result in many more deaths (and less importantly financial disaster) than one of equal magnitude in a sparsely populated region. Distribution of population can significantly vary the impact of an earthquake – rapid urbanisation in ‘ring of fire’ regions due to industrial development / scientific advancement is making the potential problems worse, with Tokyo, one of the largest cities out of all MEDCs, being one of the most vulnerable.
Tied in with manmade buildings causing variation in earthquake impact is the natural geology of the location. Responses to earthquakes vary depending upon the land material, with different rates of liquefaction (the speed at which a material such as sand or clay converts to liquid) can cause the collapse of high-rise structures as well as promote landslides. An example of this is the 1989 Loma Prieta earthquake where the area most damaged was that where housing had been built on unstable dumped landfill material.
Finally, the wealth and status of the nation in question is highly influential. As a generalisation, a more wealthy country can respond more effectively to an earthquake, and have stronger building structures which reduce damage in the first place. For poorer countries, the ‘secondary’ impact of earthquakes is exacerbated due to government under funding and lack of appropriate resources resulting in inability to cope emotionally, economically… However, death tolls can be still potentially high regardless of a country’s wealth if, as was evident in Kobe in 1995, building regulations which are set out in order to save lives, are dismissed for economic benefit.
2. Discuss the management strategies used to manage the impact of earthquakes.
Management strategies carried out vary widely depending upon government intervention and availability of finance & resources. The potential earthquake hazard can be reduced by modifying people’s vulnerability, use of hazard-resistant design plus modifying the loss…
Particularly when earthquakes strike heavily urbanised areas, a sizeable number of deaths result (especially during working hours) from high rise structures which collapse or sink due to liquefaction. Improving building design reduces the hazard to human life and also can potentially minimise financial loss.
Engineers work at improving aseismic (earthquake resistant) design, and there are currently three main types of this kind of building – in the Northridge LA 1994 earthquake most family homes remained safe as they followed regulations that specified aseismic design. (Buildings must have steel frames & must be able to sway; Bricks are not used; Fire resistant materials & shatterproof glass are compulsory).
Ideas for reducing the hazard of buildings if an earthquake occurs include reinforced latticework foundations, deep in the bedrock; Steel cables attached to bridge girders / columns to restrain movement; adding eccentric cross-bracings to the structure of high rise buildings increasing ductility.
Although it is still a technological impossibility to accurately predict earthquakes, there have been some scientific advances in nations such as Japan, China & USA. However, the plate tectonics theory can be used at a global scale, and regionally previous data could be used to predict forthcoming quakes. However it is not possible to predict the exact date or intensity of these –
Predicting an earthquake hours before its occurrence is based on e.g. changes in groundwater levels, radon gas emission (by measuring the rate of decomposition in boar holes) and animal behaviour. Particularly in the United States, complex GIS systems are being used to create hazard maps, taking the likes of liquefaction and landslide potential into consideration (Californian “Earthworm” mentioned below).
Community preparedness is a key factor in managing the hazard, and there are two levels – Public preparedness as well as Government / emergency services preparedness.
Authorities make sure the most appropriate action is taken by analysing previous experiences. A general initial public response that is requested in the event of an earthquake is to have emergency supplies in stock, move under protective furniture and then await rescue – a strategy obviously aimed at minimising potential risk. In addition, knowledge of basic first aid is recommended, accounting for possible delays of emergency services due to potential breakdown of communication and infrastructure.
Earthquake prone cities of Tokyo, LA and San Francisco have public earthquake awareness days, with even toddlers participating in role-playing an earthquake situation.
Emergency services are able to respond more effectively thanks to technological advances in IT, with a Tokyan gas company being able to rapidly be notified of pipeline damage and gas supplies are cut off by “smart meters” in event of an earthquake where magnitude > 5.
In California, “Earthworm” is a seismic computer that is able to detect earthquake activity by monitoring ground levels. In future a complex GIS is being considered, interlinking diverse factors such as service lines, locations of hospitals & schools etc to pinpoint areas which greatly require help. “Readicube” is the most up-to-date GIS, taking social and demographic data into account too.
The government being able to efficiently enable aid to pass through following an earthquake is essential and a management strategy for this is likely to be (briefly) prepared in advance.
c. Assess the success of such management strategies.
The success rates of these various management strategies has been diverse depending upon geographical location and type of strategy…
Although the concept of well built, aseismic structures is highly beneficial for essential public resources such as hospitals, a problem arises as the high cost of aseismic design fails to reduce the vulnerability of the poorer people. This can result in so-called “classquakes” such as Guatemala 1976 where 22000 people in poorer standard housing were killed whilst those with more earthquake-resistant structures remained unaffected.
Regardless of complex technology used to predict earthquakes, the Northridge quake showed that even all this was not useful as it did not account for movement along minor or unknown faults (they had no idea that the Northridge fault even existed). Although they had prepared the emergency services for such an event, they had not considered the freeway collapsing making it impossible for the services to get through.
Attempting to use events such as unusual animal behaviour has proven to be successful – 90000 people were evacuated 51/2 hours before the 1975 Haicheng earthquake in China due to successful forecasting. However the Tangshan quake the next year caused 250000 deaths due to complete unexpectedness.
In Japan by 1995, so much money had been spent developing earthquake prediction technology, that was of no use for the Kobe disaster, which as worse than expected due to liquefaction & unconsolidated clays. The Kobe citizens had been given much training beforehand but in the real situation many panicked and could not cope. Resultantly there were 5400 fatalities (from both primary and secondary effects) as arguably many citizens had a false sense of security – although they knew that the fault was under stress they did not believe it would strike in their lifetime.
Although the Californian GIS system appears to be very impressive and enable a near instant response to earthquakes, these are simply future plans and technology is still being developed; little of the aims have yet been implemented.
In 1990, the Japanese government allowed transference of some of Tokyo’s power to other, less earthquake-prone regions such as North Honshu. Whilst this is a good idea as it reduced potential economic / administrative difficulty be there an earthquake in Tokyo, realistically a quake in Tokyo would affect the global economy.
Although one would think that a government would try and help the citizens as much as possible following a disaster, aid movements in the past have been hindered. After the 1995 Kobe quake, Japan initially adamantly refused to accept foreign aid (although it had a shortage of e.g. medical teams). After the Izmit disaster in Turkey 1999 the government slowed down Aid transfers by imposing import duty on them, and also refusing to accept Greek blood although many were in desperate need for blood. In Mexico 1985, the government hindered aid movement for the first few days by believing they could cope with the crisis without any external help. In such examples governments have prioritised pride over the welfare of their citizens. Muppets.