China's Dams

Mapping disaster

(September 14, 2012) This spring, Probe International used the power of hazard mapping to assess the risks of China’s breakneck dam-building along its western rivers. Now, a new study published by the international scientific journal Tectonophysics discusses how flawed hazard maps may have underestimated such risks and been partly to blame for the devastation caused by the 2011 Japan, 2010 Haiti and 2008 China earthquakes. 

Why earthquake hazard maps often fail and what to do about it

By Seth Stein (Department of Earth and Planetary Sciences, Northwestern University, Evanston IL 60208, USA), Robert J. Geller (Dept. of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo 113‐0033, Japan), and Mian Liu (Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA)

Tectonophysics, available online, July 4, 2012

The Chinese 2008 Wenchuan, Haitian 2010, and 2011 Tohoku earthquake on Japan’s coast are striking examples of highly destructive earthquakes that occurred in areas predicted by earthquake hazard maps to be relatively safe. The authors of “Why earthquake hazard maps often fail and what to do about it” examine what went wrong for Tohoku, and how this failure illustrates the limitations of earthquake hazard mapping. They explore examples from several seismic regions to show that earthquake occurrence is typically more complicated than the models used as the basis for hazard map creation, and that the available history of seismicity is almost always too short to reliably establish the spatiotemporal pattern of large earthquake occurrence.

“As a result,” they say, “key aspects of hazard maps often depend on poorly constrained parameters, whose values are chosen based on the mapmakers’ preconceptions. When these are incorrect, maps do poorly.”

Here is more from the authors’ Abstract:

This situation will improve at best slowly, owing to our limited understanding of earthquake processes. However, because hazard mapping has become widely accepted and used to make major decisions, we suggest two changes to improve current practices. First, the uncertainties in hazard map predictions should be assessed and clearly communicated to potential users. Recognizing the uncertainties would enable users to decide how much credence to place in the maps and make them more useful in formulating cost-effective hazard mitigation policies. Second, hazard maps should undergo rigorous and objective testing to compare their predictions to those of null hypotheses, including ones based on uniform regional seismicity or hazard. Such testing, which is common and useful in similar fields, will show how well maps actually work and hopefully help produce measurable improvements. There are likely, however, limits on how well hazard maps can ever be made because of the intrinsic variability of earthquake processes.

To read their full study, see Tectonophysics 562-563 (2012) 1-25.

Read coverage in TIME magazine (Earthquake Damage: Are bad maps to blame? by Tara Thean, originally published on September 3, 2012).

Related interest

The importance of accurate hazard mapping was discussed in Probe International’s study, Earthquake Hazards and Large Dams in Western China, on the seismic risk of dam construction in western China. To illustrate the risks, a Probe International expert overlaid a Chinese map of known dam locations with a United Nations’ seismic hazard map, US Geological Survey earthquake data, as well as Google Earth satellite images to reveal that more than 130 large dams underway in western China could trigger disaster — earthquakes, even tsunamis — due to their construction in seismic hazard zones. Read on

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