Constraints on Long-Term Seismic Hazard From Vulnerable Stalagmites

As for any model/theory, a probabilistic seismic hazard analysis (PSHA) model is best tested by comparing its predictions with observations that are independent, e.g. which have not been used for creating the model. Arguably, the most valuable information in the context of seismic hazard analysis is information on long-term hazard, namely maximum intensities (or magnitudes) occuring over time intervals that are at least as long as a seismic cycle. Such long-term information can in principle be gained from intact stalagmites in natural caves, and we outline the approach here. Sensitive stalagmites have survived all earthquakes that have occurred over their long time span, e.g. over thousands of years or more depending on the age of the stalagmite. Their “survival” requires that the horizontal ground acceleration has never exceeded a certain critical value within that period. Such information is very valuable, even if it concerns only a single site, namely that of a particularly sensitive infrastructure.