RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES1004, doi:10.2205/2007ES000267, 2008

The Relation Between Damage Pattern Caused by Earthquakes and Social-Economic Development of the Society

[20]  It is obvious, that the death toll from any disaster cannot exceed population of the Earth, while material damage cannot be higher than the total cost of technosphere. It means, that the power law of damage distribution cannot be realized in case of very great damage. A real pattern of damage distribution will not satisfy the power-law distribution at b<1 for events x>A, where A is necessarily not above an event of the "doomsday'' type. An event with an extent of xcong A will be named characteristic maximally possible disaster. For interval larger than that of recurrence of such an event, the growth damage pattern changes qualitatively. The total damage amounts will be linearly time dependent, and the use of mean values becomes justified. It means, that it is important to determine a quantity of characteristic maximal event A, and what is the time interval when such a change in the damage distribution pattern takes place.

[21]  A number of approaches to characterization of maximal possible event A and the recurrence period of such event Ta have proposed and verified, using the data of the Harvard Catalogue of Seismic moments, in the works [Pisarenko and Rodkin, 2003b; Rodkin, 2003b; Rodkin and Pisarenko, 2007]. To more correctly determine these parameters it is better to divide the available data aggregate into the uniform groups. Further we will discuss a relation between statistical characteristics of natural disaster pattern and social-economic parameters, therefore we will deal with damage amounts, so breaking is to be accounted for social-economic development. Namely, let us compare a pattern of losses from seismic disasters in different regions: in North America, Europe, Japan, Latin America, Asia, Indochina (Table 1). To determine a value of a characteristic maximally possible disaster A and time of its recurrence Ta will combine the selected regions into two groups with respect to higher (North America, Europe, Japan) and lower (Latin America, Asia, Indochina) level of economic development. Such a distribution complies with the commonly accepted subdivision into developed and developing countries.

[22]  To find changes in the disaster pattern due to rapid growth of the social-economic development in the XX century, we will discuss separately data for 1900-1959 and 1960-1999; because of differences in catalogue accumulation, a number of events within these two time intervals are almost the same. Assuming the distribution stationarity of the death toll during these periods of time, we estimate specific quantities of cumulative death toll sum V(t) over a time period from 1 to 60 and from 1 to 40 years, respectively. In this case, it is possible to use the analytical approach based on relations (2) and (3) along with numerical simulation (to do this we randomly accumulate sums of the death toll for 1 to t years from the observed aggregate of an annual number of casualties, so we take the median of these random realizations).

2007ES000267-fig06
Figure 6
[23]  Figure 6 shows simulation results strongly implying the change in growth pattern of the total death toll caused by earthquakes with time: i.e. from nonlinear growth law corresponding to the power distribution at b<1 to linear growth law adequate to some (unknown) distribution at final value of mathematical expectation. Based on the distribution with finite mean value obtained sum V(t) we find the length of the time interval Ta of the change from nonlinear to linear growth pattern sum V(t). A maximally characteristic disaster A is defined as an event with specific times of recurrence in Ta years. Table 2 presents the obtained parameters Ta and A along with the data on the maximal death toll Max from one earthquake. Figure 6 and Table 2 show that characteristic cumulative death toll and extent (size) of maximal seismic disaster A decreased essentially during the second half of the XX century in the developed countries.

[24]  A similar estimate was based on a less representative data on flood losses from the database EM-DAT: The International Disaster Database http://www.em-dat.net. Table 2 presents also the estimate suggesting the decrease in the death toll in the developed countries from the floods.

[25]  The described approach gives an answer to the first of the above stated question, i.e. to evaluate the limits of application of the power-law distribution with exponent of power b<1. As a result, the length of time when such an approach was used is given by time interval Ta, and maximal disaster described by this relation is defined by characteristic maximal disaster A. At the same time it implies a probable characteristic relation between a disaster pattern and social-economic development.

[26]  Now let us consider the relation between damage from seismic disasters and social-economic parameters. The population of the world is known to have increased four-fold during the XX century. However, the growth of disasters with casualties numbered more than a 100 persons has not been reported (Figure 2). This makes it possible to assume the presence of a factor compensating for potential growth of vulnerability of society with increase of population. It would appear natural to attribute such a compensation to the advancement of technosphere. If it is really associated with the above factor, then with due account for difference in the technical development in the developed and developing countries, one should assume overcompensation and undercompensation in the first and second case, respectively.

2007ES000267-fig07
Figure 7
[27]  Let us verify this assumption. Figure 7 shows a number of disasters with casualties more than 100 persons, that took place in developed and developing countries. It presents also a linear extrapolation to intensity of flow of a number of major disasters inferred from the data over the period of 1900-1939. We notice that the major seismic disasters of the second half of the century differs greatly from results of extrapolation. An actual number of major seismic disasters turned to be less than that to be expected in developed countries and slightly higher than that of developing countries.

[28]  Now let us compare data from different regions (Table 1). The relation between the damage characteristics and social-economic parameters follows from the comparison of data on damages and those of per capita national product (information from database http://unescostat.unesco.org/database). There is correlation between an average ratio of material damage per dead ("damage/casualties'') and a national product per head ("per capita product''). This ratio shows a relatively constant value of 5.2 pm 2. Minimal and maximal ratios differ only by factor 3, whereas the scatter of "damage/casualties'' and "per capita product'' parameters by in order of magnitude higher when taken separately. It means that a characteristic material damage to the death toll ratio shows a regular change in the course of economic development, remaining roughly proportional to the annual per capita product.

[29]  Now material damage from earthquake is to be discussed. Material earthquake losses are known to increase with time. However, to understand the impact of natural disasters on the development of the society one should envisage not this particular effect (fairly expected), but changes of relative losses normalized to current level of national wealth. An annual per capita product - comparison of man-years required to compensate for damage - is taken as the unit of measurement. Damage from major earthquakes in different regions measured in this units turned to be almost the same, namely (200 pm 50) thousand man-years (column 7, Table 1). Such a result might be interpreted in terms of quasi-stationarity of an amount of a relative material damage from earthquakes in the history of mankind.

2007ES000267-fig08
Figure 8
[30]  Damage from seismic disasters increases greatly (and often more accurately estimated) if it occurs in a megapolis area. In this case, important changes in the damage pattern may be caused by the difference in the economic development in different countries. For comparison we shall use a set of data on destructive earthquakes in the largest cities of the world over a period of 1971-1995 [Kronrod and Nekrasova, 1996] along with the above mentioned UN database (http://unescostat.unesco.org/database). We were able to get a required minimal set of data (magnitude, population number of casualties, material damage, per capita national product) only for several events. Figure 8 shows a dependence between material damage per capita and a level of per capita national product as inferred from these data. There is a close correlation between the parameter J - "damage/casualties'' - and an annual per capita national product Q. The coefficient of correlation is r = 0.94 (at a double logarithmic scale of 0.83) at the significance of relation of more than 99%.

[31]  Considering the relation between natural disaster pattern and social-economic development it is pertinent to ask how short a time interval should be for such a relation to be realized. The fastest and more important changes in social-economic situation take place during the periods of social-economic cataclysms. Hence, the question, whether such cataclysms can give rise to changes in vulnerability of the society resulted from natural disasters. To preliminary discuss this issue we made an attempt to compare changes in disaster pattern in such large countries as Russia and China who have undergone staggering social-economic shock.

2007ES000267-fig09
Figure 9
[32]  As to China (area of fairly height seismic activity), it is possible to compare changes in vulnerability to seismic impact and main milestones in the social-economic history of the stormy XX century. The first-third of the XX century is known to be marked in China by the development followed by a period of intervention and civil war. The time of a relatively successful development after the Second World War gave place to the years of the Cultural Revolution. Since the early 1980s China witnessed a stable and fast economic growth. Such a history of development was reflected in the seismic disaster pattern. Plots in Figure 9 show the death toll during strong earthquakes normalized to earthquake energy and to a current number of people in China. As a whole, there is a tendency to decrease in relative losses from seismic disasters, but it was complicated by a relative increase in vulnerability during the 1970s and early 1980s. Since the mid-1980s there was observed some growth in a number of events but consequences were not that grave. The growth in number of events can be explained by a more complete record, whereas a decrease in normalized number of the death toll would be reasonably to attribute to a fast economic growth of China.

[33]  There is just a few earthquakes in Russia, therefore the database created in the Laboratory of the geological risk analyzes of IGE RAS was used to analyze the disaster pattern; this database includes data on natural and natural-technogenic disasters that have taken place in the present territory of Russia since the X century till resent [Ragozin et al., 2003]. The database contains more than 1300 extreme events differing in genesis, negative consequences and in other characteristics. 193 cases of most hazardous events: earthquakes, landslides, mudflows, floods, avalanches, hurricanes, tsunami, and other abiotic disasters have been chosen. All the above cases according to the rules of the EMRCOM (Provisions on classification of emergency situations of natural and technogenic character. Adopted by the Decree of the Government of RF no. 1094 of 13.09.1996) meet the provisions on emergency situations of the federal level. According to the database compilers such a selection provides acceptable completeness and uniformity of data on a number of disasters [Ragozin et al., 2004].

2007ES000267-fig10
Figure 10
[34]  Figure 10 shows an annual number of strong disasters (dots) and moving modified for five years average dependence of a number of disasters. Apparently, during this period of time the society became anomalously vulnerable to potentially hazardous natural and natural technogenic impact due to the change for the worse of social-economic situation. The inobservance of production discipline and incompliance with work performance can strongly affect a probability of occurrence and strength of natural and technogenic disasters, and might well play an important role. Long delay in wages and salaries could not strengthen the labor discipline and work performance rules. In the time of crisis there were also no means for preventive maintenance and safety measures.

[35]  Figure 10 also shows (may be accidental) decrease in average number of disasters in the mid-1990s and a new much weaker peak during 1998-1999. Hypothetically, it is possible to associate these peculiar features with economic revival in the mid-1990s and with the crisis of the 1998, that also resulted in delay of wages and salaries, and freezing of many projects.

[36]  A hypothesis about the relation between changes in number of disasters and short-term changes in a social-economic situation seems quite realistic, and the data of analysis for Russia and China strongly support the hypothesis. If we assume, that even extensive preventive engineering measures cannot be accomplished during a short time interval, still infrastructure, management, and communication systems might be markedly improved; as a result all the above can lessen the burden from disasters. One has to remember, that the Emergency Committee (EMRCOM), powerful in resources available, was set up in Russia during the time interval in question.

[37]  The above presented conclusions about the relation between seismic losses and social-economic conditions are in good agreement with results obtained by other authors. A statement that regions with a fairly low level of economic development are less resistant to earthquake impact was published in [Sobolev, 1997]. Similar conclusions about the relation between characteristics damage amount from natural disasters and a level of social-economic development are presented in the work by Kahn [2003]. The study provides an analysis of data on 225 strong (major) natural disasters over a period of 1990-2001. The author presents relation between a characteristic death toll from natural disasters and social-economic situation in different countries. As a result, the analysis revealed a number of empirical relations. For example, the growth of gross national product (GNP) since the year 2000 will amount to 15000 dollars per capita per year will correspond meanly to decrease in a number of casualties by 500 people in year for a 100 million of population. Another important factor affecting an average death toll from disasters is a management structure; countries with less developed democratic institutions turned to be relatively less vulnerable (in terms of normalized casualties from natural disasters).


RJES

Citation: Rodkin, M. V., and V. F. Pisarenko (2008), Damage from natural disasters: Fast growth of losses or stable ratio?, Russ. J. Earth Sci., 10, ES1004, doi:10.2205/2007ES000267.

Copyright 2008 by the Russian Journal of Earth Sciences

Powered by TeXWeb (Win32, v.2.0).