metropolitan areas in developing countries and those mixed with inner cities in developed countries. Under the large difference of vulnerability in every local area, the areas with the largest vulnerability are firstly damaged through collapsed of poorly-made houses, eruption of fires and troubles of old lifeline networks. The damage will be easily enlarged in neighboring areas. The classification of natural disasters is shown in Table 1. Natural disasters are divided into four categories from the view points of population and infrastructures following as:
1) Rural disasters: The largeness of hazard decides the scale of human and property damage.
2) Urbanizing disasters: At first stage of urbanization, population rapidly increases at newly developed areas such as flood-prone lowlands and foot of cliff and hill.
3) Urbanized disasters: The increase rate of population becomes small after rapid urbanization. The construction of countermeasures against natural disasters can contribute to redaction of human damage, but many infrastructures such as various lifeklines were severely damaged.
4) Urban disasters: Even if hazard is not enough large, phase shift occurs under densely populated condition in metropolitan areas. Human and property damage become huge. Some characteristics of the disasters are summarized in Table 1. In urban disasters, the damage much depends on human factors so that characteristics of man-made disaster are included.
The revolution of natural disasters is shown in Fig. 1 in which the horizontal axis corresponds to length of affected time and the vertical one represents the largeness of damaged area. We defined that the secondary disaster has very long affected time and complex disaster has very wide damaged area. In this figure, some typical natural disasters are plotted. Disaster lessons are changed in every kind of natural disasters. If huge hazard will attack on metropolitan areas, we have all kind of natural disasters because in the city center urban disasters occur
Fig. 1 Revolution of natural disasters
and in the suburbs urbanizing or rural natural disasters may rise up. This situation depends on the locality and the history of formation of metropolitan areas.
2.2 Process of damage enlargement and its measures
Flow charts of required measures against various kind of themes are shown in Fig. 2 in which the horizontal axis represents a timeline divided into two sections, separated by the occurrence of the 1995 Great Hanshin-Awaji Earthquake Disaster. To the left of the occurrence of the earthquakes are the pre-disaster risk management and to the right are post-disaster crisis management. Depicted in the vertical axis are themes related to physical attributes (Natural World) in the
