Department of Earth and Environmental Sciences
In the aftermath of the March 2011 earthquake and tsunami in Japan, there is heightened interest (and fear) regarding the seismic safety of nuclear power plants in the United States. Of particular interest is the Indian Point nuclear power plant in Westchester County just north of New York City, and the question of whether a large earthquake is likely to occur there. Seismologists are expected to provide definitive answers to such questions, but unfortunately life — and Earth processes — are not so simple.
A recent report from msnbc.com described how, based on their analysis of the Nuclear Regulatory Commission’s assessment of nuclear power plants in the US, one of Indian Point’s reactors is No. 1 for risk of damage from an earthquake. Furthermore, a number of other eastern US plants are also higher on the list than nuclear power plants in California. The reason for this surprising result is that California power plants were designed to withstand larger earthquakes than these eastern US plants.
It is important not to minimize the real risk of earthquakes hitting nuclear power plants in the eastern US. It is certainly true that there is a real earthquake hazard in the eastern US, albeit significantly less than the hazard in California. The challenge is that unlike the California situation — where relatively well-understood plate tectonic processes dominate the hazard and thus large earthquakes are more likely to occur in places we expect — it is not clear where to expect the next large eastern earthquakes. In spite of advances in our research, there still remains great uncertainty about the fundamental question of where future large earthquakes are (and are not) likely to occur in the eastern US. Any attempt to discern whether or not any particular location is more prone to future large earthquakes than any other location is still fraught with uncertainty. We have a long way to go before we will be able to say (if ever) that a given location on a map of the eastern US is really more prone to future large earthquakes than any other location.
A 2008 study by seismologists at Columbia University’s Lamont-Doherty Earth Observatory argued that Indian Point is located at the intersection of two active seismic zones, and is thus one of the least favorable sites in the New York City area from an earthquake hazard and risk perspective. My own assessment of the situation is that the distribution of epicenters lends itself to many possible conjectures of hypothetical fault zones, all of which are based on circumstantial evidence. None of these hypotheses can be considered as concrete evidence that the Indian Point site is necessarily any more prone to future large earthquakes than many other sites in the New York City area.
It would of course be comforting if seismology could tell us which of these two assessments is right. In my many years of experience of being asked to respond to these types of questions, I am often struck by how uncomfortable people generally are with uncertainty. Many people are so desperate for certainty in an uncertain world that they seem to be more comforted being told “Yes, a tragic earthquake is certain to occur in your town next week” than to be told “We just don’t know.” But, the truth is that we just don’t (yet?) have definitive answers to the question of what the level of risk is to nuclear power plants in the eastern US.
California does have a higher earthquake hazard, but eastern US power plants have not been built to withstand earthquakes as well as those in California. Hopefully, over time seismologists will be able to reduce the uncertainty and more accurately assess the balance between these two effects. But for now, this will remain a matter of deciding the level of uncertainty that we are willing to accept in order to provide us with energy for our chosen lifestyle. The tragic earthquake and tsunami in Japan provide a stark reminder that seismic risk assessment is both a science and an art.