Calibration of a probabilistic fatigue model for predicting plaster cracks on unreinforced masonry walls caused by induced seismic hazard

In Switzerland, in the city of Basel and in the canton of St Gallen, two pilot Enhanced Geothermal System (EGS) projects caused two sequences of induced earthquakes with magnitude up to 3.5. Only in Basel, after the largest seismic event, the damage claims were of the order of 7-10 million of Swiss Francs. These claims were associated with nonstructural damage, mainly hairline cracks on wall plaster. It follows that quantification of nonstructural damage due to induced ground motions is central for estimating related financial risk. It is important to stress that small amplitude and large number of cycles characterize induced seismic loading. Therefore, fatigue drives plaster deterioration, which shows a remarkable variability. This standpoint motived the authors to develop a probabilistic fatigue model for predicting the amount of plaster hairline cracks on Unreinforced Masonry Walls (UMW) produced by induced seismic load. The developed probabilistic fatigue model is calibrated on low amplitude cyclic tests and can, potentially, be used for estimating nonstructural damage and financial losses for new projects where induced seismicity is of concern.