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 spectromete r on a Pyrenean springwater. The sampling was carried out across a time ser ies of 598 days encompassing an earthquake of magnitude 5.2. Lead concentra tions show a tenfold increase and isotopic compositions shift toward anthro pogenic values four days prior to the quake. The time lag between these geo chemical anomalies and the earthquake, combined with hydrogeological constr aints, are then used to infer where and when strain changes during earthqua ke preparation processes went beyond the threshold required to temporarily mix waters from normally independent aquifers. The occurrence of pre-seismi c centrifugal strain waves propagating from the epicenter area is proposed on the basis of the observed geochemical anomalies. (C) 1999 Elsevier Scien ce B.V. All rights reserved.