Earthquake-related elemental and isotopic lead anomaly in a springwater

Elemental and isotopic analyses of lead present at ultra-trace levels were obtained with a double focusing inductively coupled plasma mass spectrometer on a Pyrenean springwater. The sampling was carried out across a time series of 598 days encompassing an earthquake of magnitude 5.2. Lead concentrations show a tenfold increase and isotopic compositions shift toward anthropogenic values four days prior to the quake. The time lag between these geochemical anomalies and the earthquake, combined with hydrogeological constraints, are then used to infer where and when strain changes during earthquake preparation processes went beyond the threshold required to temporarily mix waters from normally independent aquifers. The occurrence of pre-seismic centrifugal strain waves propagating from the epicenter area is proposed on the basis of the observed geochemical anomalies.