Abstract
The geochemical monitoring carried out on fluids released in the Central Apennines (Umbria region) evidenced seismically-induced modifications of the physic-chemical parameters in all the released fluids, including some cold waters circulating in certain carbonate rocks that are exploited for drinking purposes. The results allowed us to recognize the presence of components of diverse origin that changed the chemical composition of the water. These components, potentially dangerous for human consumption, can be considered as being ”secondary effects” on local aquifers, induced by crustal deformation. We would also stress the relationship between the circulating fluids and active tectonic structures, as we detected modifications in some springs that were apparently not located anywhere near the local faults. The temporal variations in the geochemical features of the investigated cold waters are related to the local faulting activity that occurs during seismogenesis. The geochemical monitoring that provided information on fault movements during the seismic crisis, is also able to give us information regarding faulting activity in its earlier stages.
Highlights
This study has investigated the temporal variations that took place in the geochemistry of TAO, Vol 16, No 4, October 2005 some cold waters from the Umbria region (Central Apennines, Italy) with the aim of obtaining a better understanding of the relationship between seismogenic processes and the behaviour of circulating fluids.On September 26, 1997, an earthquake struck the study-area (Fig. 1); this initiated a seismic crisis that lasted for more than six months
The observations made during the geochemical monitoring activity in Umbria allowed us to detect interesting behavior on the part of the circulating fluids during the 1997 - 98 seismic crisis
The ample literature on the subject [see Thomas (1988) and cited references; Toutain and Baubron (1999) and literature therein] and more recently Ramirez-Guzman et al (2005), Song et al (2005) shows that seismogenic-induced geochemical modifications occur in anomalous fluids circulating in seismic-prone areas
Summary
This study has investigated the temporal variations that took place in the geochemistry of. Except for one event that occurred on March 26, 1998, (M 5.3; Castello et al 2005), which was marked by a hypocenter located at the crust-mantle transition (as deep as 51 km; Morelli et al 2000), all the hypocenters of the entire seismic sequence were at a depth of 5 - 10 km in the upper crust, to which the crustal seismicity of the Umbria-Marche region is normally confined (Barchi 2002). The direct faulting activity allowed local permeability to increase and was responsible for the observed geochemical anomalies that were caused by an increased uprising of deep-originated fluids that affected the chemical and isotopic composition of the circulating fluids. The observed modifications provide new information regarding the effects the development of a seismogenic process can have, and highlight the incidence of secondary-induced effects related to the seismicity, that may greatly increase the hazards that could be incurred by earthquake-prone areas
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