Everyone makes mistakes — and sometimes, those mistakes can be deadly. Flawed hazard maps may be partly blamed for the devastation that accompanied the devastating earthquakes that have struck Japan, Haiti and China in recent years, according to a new study published in the journal Tectonophysics.
Hazard maps are guides to estimate how bad the earthquake danger is in any given area, and seismologists and engineers use them to gauge earthquake risk. But the maps can be oversimplified, largely because the mapmakers don’t have enough data about earthquake history in their areas of interest. As such, the study says, they often work off their own preconceptions — and the maps don’t do too well when those assumptions are wrong.
The study looked at three of the biggest earthquakes in the past five years, and whether the damage had been accurately predicted by the hazard maps:
The Tohoku earthquake of 2011 released 150 times more energy than hazard maps predicted. The maps estimated that an earthquake in the area would probably reach 7.5 on the Richter scale and that the Tohoku area was a lower-risk region than other parts of Japan. That March, the 9.0-magnitude earthquake that ravaged the area left tens of thousands dead, obliterated buildings and led to a meltdown at the Fukushima nuclear power plant.
In 2001, hazard maps predicted low ground motion in Haiti based on recent earthquake data for the region. Had the maps taken a longer-term view of earthquake history, they would have shown that over history Haitian earthquakes are generally more damaging, and the 7.1-magnitude earthquake that ravaged Port-au-Prince in 2010 might have been a little more manageable.
Mapmakers assessed the Longmenshan fault as low risk, but they may not have considered the gradual movement across the fault that would eventually build enough tectonic pressure to cause a 7.9-magnitude earthquake in Sichuan province. This mistake came from a lack of evidence for large earthquakes on the fault over the past thousand years, according to the study.
The researchers who conducted the Tectonophysics study propose two changes to current mapping approaches: communicating the uncertainties of each map to users and checking each map against a reference map. Perhaps most important, however, is the authors’ recommendation that mapmakers approach their jobs with a “sense of humility and caution.” Nature is full of exceptions and surprises, and even the best hazard maps can’t stop the planet from breaking the rules sometimes.