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The Seismic Risk in a Mega-City. Emergency planning in Istanbul

Natural phenomena, such as hurricanes, volcanic eruptions, earthquakes, etc., threaten always more often human communities all over the world, frequently causing large-scale disasters. The seismic events are amid the most catastrophic of these phenomena: in few seconds and without any warning, they might strongly shake human settlements causing numerous causalities, changing the anthropic and natural landscape and erasing the historical and cultural heritage. In turn, these direct effects could trigger other secondary consequences not less severe, such as the disruption of economic activities and services of public utility, social problems, etc.
Therefore, an earthquake could be potentially more dangerous when hits a global city. Among them, Istanbul is a megalopolis characterized by one of the highest level of seismic risk in the world :
• by the 2030, it could be hit by a big shock (Magnitude 7 or more) with a 62±15% probability;
• more than 50% of Istanbul inhabitants live in irregular and squatter buildings characterized by precarious structural and functional conditions;
• it is the economic and financial capital of Turkey, an important attractive node of population (in Istanbul live officially more than 13 million of people) and national-international activities and capitals.
Inside each mega-cities, there are several neighborhoods with particular vulnerabilities. They could be characterized by a high density of residential population, economic activities, public services, etc. If they are seriously damaged due to a seismic event, for example, the consequences might have an impact not only at urban scale but probably also at national scale.
Therefore, in this thesis, the seismic risk has been evaluated for one of the numerous highly vulnerable Istanbul’s areas. The zone analyzed is part of the old and historic neighborhood of Pera/Galata: it is a kind of “buffer” around İstiklal Caddesi, famous pedestrian street, which is being visited by nearly 3 million people during the weekends, according to unofficial sources. Furthermore, it is characterized by an important historical, cultural and architectonical heritage and it is the location of several economic activities and public facilities.
In particular, the seismic risk has been assessed confronting two different approaches: one traditional and one experimental (which has been elaborated in this research). The principal differences between them are the temporal dimension (static/dynamic during the day), the exposure (residents/city users) and the vulnerability (general factors/specific factors characterizing the case study area).
So, the case study area, marked by a low level of seismic risk according to the traditional approach, results be at middle-high risk according to the experimental approach. The difference in the evaluation is not due to the hazard component (in both cases not so much relevant) but rather to the specific peculiarities of the urban environment which increase notably the vulnerability: first of, the high presence of city users, not resident in the case study area, during 24 hours a day, 7 days a week. Indeed, the city users do not know very well the zone and, so, their continuative high presence increases the vulnerability as well as the exposure value.
Assessed the seismic risk, some mitigation actions have been proposed and, in particular, an evacuation-mitigation plan has been predisposed for the case study area. If adequately developed and publicized, it would guarantee the reduction of casualties during and in the aftermath the seismic shock.

Mostra/Nascondi contenuto.
CHAPTER 1 - INTRODUCTION 1 CHAPTER 1 - INTRODUCTION A natural disaster is generated by an extreme phenomenon of nature that threatens human lives, activities or property, or the landscape; in other words the entire anthropic environment. However, the natural phenomena are not natural disasters by themselves, but they could become when the place afflicted is highly vulnerable or exposed. Almost always, the disasters are not caused by the hazards but by the “predisposition” of the human communities to be afflicted: the vulnerability. For instance, if two major earthquakes, with same characteristics and magnitude, happen, one in a desert and one in the middle of a settlement, the first one, having no direct consequences on human life, will be considered a natural phenomenon and maybe only the geologist will notice it, while the second one, probably causing many casualties and damages, will be considered a natural disaster, and it has to be faced by the whole community. In the last century, the number of natural catastrophes reported vastly increased. Only in 2011, according to the EM-DAT 1 database, there were more than 302 natural disasters all around the world, costing over 29,780 lives and affecting 2 nearly 206 million others. As Smith (2001) says, “about 25 percent of the world’s population live in areas at risk from natural disasters”, and every year this percentage is increasing. According to Alexander (2010), “the relentless rise in global population, polarization of wealth between rich and poor, marginalization of vulnerable communities, [..] have all contributed to the increasing toll of natural disasters”. All over the world, to meet the insatiable demand for land, communities were built in the more dangerous areas, more prone to natural disasters; those places were systematically spared (or at least only the places at risks different than the geological; see Paragraph 2.1) by the historic settlements which, for obvious reasons, were built in more safe areas. This increased demand for land is first of all due to the world population’s growth (Table 1.1 show that today, in 2010, the world population is more than four times in confront of the beginning of the last century), in parallel with the growth of the urban population, which in 2010, for the first time in history, exceeded the rural population (see Table 1.2). Each day, according to Guha-Sapir et al. (2011), “almost 180,000 people move to cities. While city populations grow faster than city infrastructure can adapt, migrants often encounter a lack of infrastructure, services, housing and property rights. These urban newcomers are forced to live in unsafe [and often informal] places”. However, formal planning has also made some mistakes. Indeed, it often stoops to compromises 1 It is a worldwide database on disasters which is maintained by the Centre for Research on the Epidemiology of Disasters (CRED) of The Catholic University of Louvain in Brussels-Belgium and by the United States Agency for International Development’s Office of Foreign Disaster Assistance (USAID/OFDA). 2 With “affected” it’s meaning the number of people requiring immediate assistance during a period of emergency; so, this may include displaced or evacuated people.

Laurea liv.II (specialistica)

Facoltà: Architettura

Autore: Alessandro Demarchi Contatta »

Composta da 310 pagine.

 

Questa tesi ha raggiunto 251 click dal 06/11/2012.

 

Consultata integralmente una volta.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.