Research News

Improving Earthquake Maps to Save Lives, Minimize Damages

IPR’s Seth Stein and Bruce Spencer offer statistical solutions for hazard maps

Tohoku Earthquake

Damage from the 2011 Tohoku earthquake and tsunami, as seen above, caused nearly $300 billion in damages.

In 2011, the 9.0-magnitude Tohoku earthquake and the resulting tsunami killed more than 15,000 people and caused nearly $300 billion in damages. The shaking from the earthquake was significantly larger than Japan’s national hazard map had predicted, devastating areas forecasted to be relatively safe. 

Such hazard-mapping failures prompted three Northwestern researchers—geophysicist and IPR associate Seth Stein, IPR statistician Bruce Spencer, and graduate student Edward Brooks—to search for better ways to construct, evaluate, and communicate the predictions of hazard maps.

Seth Stein

“From a policy standpoint, a map that’s good in California but a disaster in the oceans is probably not that bad,” Stein explained. “But the reverse—a map that was completely accurate in the oceans, but wrong in California—would be very bad for people.” 

Bruce Spencer

In two recent IPR working papers, the scholars point out several critical problems with current hazard maps and offer statistical solutions to improve mapping. 

Currently, no widely accepted metric exists that can gauge how well one hazard map performs compared with another. In the first working paper, the researchers use 2,200 years of Italian earthquake data to highlight several different statistical models that could be used to compare how well maps work and improve future maps. 

Since underestimating an earthquake’s impact can leave areas ill-prepared, the scholars developed asymmetric models that weigh underprediction heavily and can account for the number of affected people and properties.

In a second working paper, the scholars offer further methodological guidance on when—and how—to revise hazard maps using Bayesian modeling, which allows multiple probabilities to stack up with evidence. 

While forecasting is never an exact science, improving these seismological maps would allow governments to be better prepared, especially in the most populous areas where the risk for death and destruction is greatest, and could help ensure the viability of costly earthquake-resistant construction projects.

While making seismological models more accurate is hugely important, Stein also calls for greater outreach regarding their implementation and use. “We need to get much better at communicating to potential users of this information—urban planners, state legislators—and tell them what we know and what we don’t know,” Stein said. “We want to help them make sensible policies given the limitations of what we can forecast.”

Seth Stein is William Deering Professor of Earth and Planetary Sciences and an IPR associate. Bruce Spencer is professor of statistics and an IPR fellow. Edward Brooks is a Northwestern graduate student. For more, read “Metrics for Assessing Earthquake Hazard Map Performance” (WP-14-13) and “Bayes and BOGSAT: Issues in When and How to Revise Earthquake Hazard Maps” (WP-14-14).

Top photo by Héctor García