DEPARTMENT OF GEOGRAPHY NAME: REG NO* PROGRAMME COURSE NARRATION: COURSE CODE: LECTURER DUE DATE ASSIGNMENT QUESTION: EXPLAIN WHY EARTHQUAKE MAGNITUDE CAN BE A POOR GUIDE TO SEISMIC IMPACT ASSESSMENT? (25). DENNIES MAUYA B1128076 DEVELOPMENT STUDIES ENVIRONMENTAL HAZARDS DG213 MR MAVHURA 12 OCTOBER 2012
An earthquake, which may be termed as a quake, tremor or temblor is the result of a sudden release of energy in the earth’s crust that creates seismic waves that cause a lot of destruction in the social and economic environment and the natural environment itself. The seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. In its most general sense, the word earthquake is used to describe any seismic event, whether natural or caused by humans that generate seismic waves. The earthquake magnitude is a number that characterizes the relative size of an earthquake., (Guinness and Nagle 2002). The seismic hazard maps, which provide the basis of risk estimates, lead to underestimates of the casualties by more than two orders of magnitude. Hence, relying on these maps, communities were unprepared in Kashmir, India and Wenchuan of China where killer earthquakes wiped out schools, hospitals and residences, killing and injuring hundreds of thousands of people. How serious the earthquake problem is for megacities like Lima in Peru can be understood when one considers that the population is about 12 million, and, depending on the building quality, the soil conditions, and the distance from the earthquake, the number of fatalities in different districts may range from 0.5 to 4 percent— a potential death toll of 60,000 to 480,000. The looming problem is most dramatically demonstrated by our calculations of the likely fate of the children: In a worst-case scenario of a magnitude-8.5 earthquake close to the city, one must expect that about 20,000 children, about 2 percent of the 1 million school-aged populations, will probably die, and a multiple of this number will be maimed for life, (Max 2012). Earthquake magnitude only gives the size of the quake and nothing else about where the earthquake has happened, the population of economic activities near the epicentre and how prepared were the people to the earthquake. So as a guide to impact assessment, the magnitude is proved to be poor because there are other factors which can be used on measuring the seismic impact assessment such as the distribution of economic activities, density of buildings in an area and even location of the affected area. Although seismologists and engineers have generated a world map of seismic hazard, which shows the level of ground shaking likely not to be exceeded, all of these disasters are always surprising: The ground motions and death tolls far exceeded expectations, causing consternation among the scientific community. The standard method to estimate seismic
hazard has been brought into question and its assumptions and calculation methods have
come under scrutiny, to mean even magnitude can be nothing, except a figure of no use in the seismic impact assessment. The amount of damage and loss of life associated with earthquakes depends largely on the population density, the nature of the buildings, the nature of the bedrock, building density, and the accessibility or isolation of the region. The relative importance of these factors varies in a great deal. For example, the Kobe earthquake of January 1995 had a magnitude of 7.2 and caused over 5000 deaths. By contrast, the Northridge earthquake, which affected part of Los Angeles in January 1994, was 6.6 on the Richter scale but caused only 57 deaths. Yet an earthquake of force 6.6 at Mahashtra in India in September 1993 killed over 22000 people. So the magnitude in this respect can be a poor guide to impact assessment. Kobe and Los Angeles are known earthquake zones, buildings are...