According to the latest global seismic risk map (developped in GEM project, 2018) there are currently 17 megacities around the world with a population of more than 10 million that are placed at the highest risk level, including Tokyo, Jakarta, Delhi, Beijing, Manila, Mexico City, Osaka, Los Angeles, Dhaka, Chengdu, Karachi, Tehran, Istanbul, Lahore, Nagoya, Bogota, and Lima. One of the best efforts to address the impact of earthquakes on a region, especially in densely populated urban areas, is to conduct earthquake risk assessments. The megacities has normally a changing day/nith population. The population increases even up to 50% during working day time. This means that there are specially the periferal and suburban marginal towns around these megapoles. Therefore these towns are mostly the resting locations for the worker in the megapoles. The assessment of earthquake risk is mostly complicated specially in the megapoles in the underdevelopping countries. What are the major peririties for such assessments?
This is a very interesting question to which I do not have an answer. But quite clearly, some cities have millions of people coming in the morning and leaving in the evening. As you know, Tehran is a good example.
I would think that one has to collect data on weight variables, among others. That is, the difference in weight during working day and night for commuting population, the weight of transport vehicles for people, configuring whether the commuting population spreads radially or in some particular direction after leaving the megapolis, etc. One also has to carefully monitor the fate of the used water in this regard@. I heard from someone that much of Karachi sewerage water is flushed down, without bothering about consequences.
Good afternoon Professor Zare,
You are quite right that it is a very important question, as well as an exceptionally difficult one to respond to. Even more so, one would expect that a country specific approach would be required to come with some relevant answers.
I would suggest that one possible approach would be to consider first the earthquake risk associated with the existing buildings stock in this megacities with a view to identify where the major risk lies. The second tier would be the risk assesment associated with the public spaces and associated infrastructure. Both of these would have to be considered in the light of the time and day specific analysis.
I recall that there is a book from the 1980s which listed the daily life pattern in different countries. If exist, an updated version of the book or a sample survey in the optimal periods might provide a good indication of the distribution of people within certain period of time during each day of the week.
Combining the building, infrastructure and environment risk analysis with the daily living pattern should provide snapshots of risk for different time of the day in the week. This should allow to identify how the earthquake risk shifts within a day. Naturally this should assit in identifiying locations and periods where the highest risk exist which could be used to develop relevant mitigation policies.
With Best Wishes
Vladimir
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