Test-sites for earthquake prediction experiments within the Colli Albani region

Abstract

In this paper we discuss some geochemical data gathered by discrete and continuous monitoring during the 1995–1996 period, carried out for earthquake prediction test-experiments throughout the Colli Albani quiescent volcano, seat of seismicity, selecting some gas discharge sites with peri-volcanic composition. In particular we stressed the results obtained at the continuous geochemical monitoring station (GMS I, BAR site), designed by ING for geochemical surveillance of seismic events. The 12/6/1995 (M=3.6–3.8) Roma earthquake together with the 3/11/1995 (M=3.1) Tivoli earthquake was the most energetic events within the Colli Albani - Roma area, after the beginning of the continuous monitoring (1991) up today: strict correlation between these seismic events and fluid geochemical anomalies in groundwater has been discovered (temperature, Eh, 222Rn, CO 2, NH 3). Separation at depth of a vapour phase, rich in reducing-acidic gases (CO 2, H 2S, etc...), from a hyper-saline brine, within the deep geothermal reservoir is hypothesised to explain the geochemical anomalies: probably the transtensional episodes accompanying the seismic sequences caused an increasing and/or triggering of the phase-separation process and fluid migration, on the regional scale of the Western sector of the Colli Albani, beyond the seismogenic depth (2–4 Km) up to surface. We draw the state of art of GMS II monitoring prototype and the selection criteria of test-sites for earthquake prediction experiments in the Colli Albani region.