The October 31 (Ml 5.4) and November 1 (Ml 5.0) Molise earthquake (southern Italy): first results from geochemistry.

Two geochemical surveys have been performed in November and December 2002 in the Molise region (southern Italy) and surrounding areas struck by two moderate size earthquakes on October 31 (M_l 5.4) and on November 1 (M_l 5.3). The main goals of this study were: i) to highlight eventual variations either in the physico-chemical features or in the chemistry of thermo-mineral and cold springs (already sampled in 1997) discharging in an area located 50 km far from the epicentral one (Sannio-Matese, Campania region),; ii) to determine the chemical features of the groundwater discharging in the epicentral area, identifying the location and the extension of the various existing aquifers; iii) to collect information about eventual changes occurred in springs and wells (variations in flows, groundwater level in wells, etc.). Moreover, twice a week samplings have been carried out for two months at two important sulphurous springs (Larino spring, in the epicentral area and Telese thermo-mineral spring, in the Sannio area) in order to gather temporal chemical trend during the ongoing seismicity. We sampled a total of 35 sites (8 springs and wells in the Sannio-Matese area and 27 in the epicentral one) measuring in the field: temperature, pH, Eh, electrical conductivity, as well as radon, bicarbonate and H_2S contents. In laboratory, analyses of major, minor and trace elements have been performed, together with dissolved gas compositions. On 10 selected samples δ13C and 87/86Sr analyses are in progress. Data collected in the second survey show, for springs and wells located in the epicentral area, an evident pH and Eh increase (probably they returned to normal pre-earthquake values) together with some chemical variations; on the contrary, springs located in the Sannio-Matese area showed no variations. Local people observed sin-earthquake flow increases and variations in turbidity in two springs discharging in the epicentral area. All detected groundwater changes are discussed either with the seismological features of the two main shocks (depth, style of faulting) or with the geological setting of the hit area.