Synopsis: Cathedral’s invisible earthquake damage

Properties of vibrations in a pillar in a $1400$-year-old Sicilian cathedral correlate with those of very small, nearby earthquakes, suggesting new ways of monitoring the gradual damage that such quakes can inflict on old buildings.

Researchers in Italy are concerned that the $7$th century Cathedral of Syracuse in Sicily may be gradually losing structural integrity because of many small, nearby earthquakes. To assess its current state and the relationship with earthquakes, Gianni Niccolini of the National Institute of Metrological Research in Turin and his colleagues monitored so-called acoustic emissions—high-frequency vibrations that are emitted sporadically as tiny cracks develop inside materials such as stone or concrete.

The team wired up a single pillar for four months and then compared the data with earthquake records. As they report in their paper in Physical Review Letters, they found that the distribution of times between events—whether earthquakes or acoustic emissions—fell onto the same curve, over a wide range of timescales and energies, when scaled appropriately. A similar “universal scaling law” has been shown for collections of earthquakes of a range of sizes in different regions, so the new results appear to extend the law to the much smaller energy scales of a single pillar. The correlation suggests that similar mechanisms may underlie both earthquakes and small fractures in the pillar, according to the authors, and that more careful monitoring of the cathedral is warranted. – David Ehrenstein

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