Gauging Earthquake Hazards with Precariously Balanced Rocks
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Science has so far failed to provide any way to predict earthquakes
on a timescale of days, weeks or months. But geologists are able to
determine, at least roughly, the probability that an earthquake of a
certain size might strike a given area within, say, decades to
centuries. Such predictions are useful for establishing
seismic-safety requirements in building codes, for example. The
problem is that there are few ways to test such evaluations of local
seismic hazard. One novel system uses precariously balanced
boulders. If one can be found, it serves as an indicator that an
earthquake of sufficient size to topple the tippy rock has not
occurred—at least not for a very long time. This
commonsensical observation has blossomed into a quantitative
technique for testing more conventional seismic-hazard assessments.