Rockfalls triggered by the AD 1356 Basle Earthquake

In the Basle region of Switzerland we demonstrate that rockfall blocks can be dated accurately using the radiocarbon method. Soil beneath rockfall blocks containing organic macro-remains was sampled at four cliff sites in the Tabular Jura south-east of Basle. A lightweight drilling rig drills a 101-mm-diameter hole through rockfall blocks up to 6 m in height. A downhole sampler is used to recover soil samples from below the blocks. Eighteen radiocarbon dates on charcoal, wood, needles of conifers and organic macro-remains from 11 blocks gave dates between 970 and 440 bp. Calibrated ages range between ad 1210 and ad 1450. These results, along with field observations and historical research, suggest that a large number of blocks toppled as rockfalls within a short time interval in the epicentral area of the ad 1356 Basle earthquake.