Long-term geochemical monitoring and extensive/compressive phenomena: case study of the Umbria Region (Central Apennines, Italy)
Main Article Content
Abstract
Long-term geochemical monitoring performed in the seismic area of the Umbria-Marche region of Italy (i.e. Central
Apennines) has allowed us to create a model of the circulation of fluids and interpret the temporal chemical
and isotopic variations of both the thermal springs as well as the gas vents. Coincident with the last seismic crisis,
which struck the region in 1997-1998, an enhanced CO2 degassing on a regional scale caused a pH-drop in
all the thermal waters as a consequence of CO2 dissolution. Furthermore, much higher 3He/4He isotope ratios
pointed to a slight mantle-derived contribution. Radon activity increased to well above the ±2 sinterval of the earlier
seismic period, after which it abruptly decreased to very low levels a few days before the occurrence of the
single deep-located shock (March 26, 1998, 51 km deep). The anomalous CO2 discharge was closely related to
the extensional movement of the normal faults responsible for the Mw 5.7, 6.0 and 5.6 main shocks that characterized
the earlier seismic phase. In contrast, a clear compressive sign is recognizable in the transient disappearance
of the deep-originating components related to the Mw 5.3, 51 km-deep event that occurred on March 26,
1998. Anomalies were detected concomitantly with the seismicity, although they also occurred after the seismic
crisis had terminated. We argue that the observed geochemical anomalies were driven by rock permeability
changes induced by crustal deformations, and we describe how, in the absence of any release of elastic energy, the
detection of anomalies reveals that a seismogenic process is developing. Indeed, comprehensive, long-term geochemical
monitoring can provide new tools allowing us to better understand the development of seismogenesis.
Apennines) has allowed us to create a model of the circulation of fluids and interpret the temporal chemical
and isotopic variations of both the thermal springs as well as the gas vents. Coincident with the last seismic crisis,
which struck the region in 1997-1998, an enhanced CO2 degassing on a regional scale caused a pH-drop in
all the thermal waters as a consequence of CO2 dissolution. Furthermore, much higher 3He/4He isotope ratios
pointed to a slight mantle-derived contribution. Radon activity increased to well above the ±2 sinterval of the earlier
seismic period, after which it abruptly decreased to very low levels a few days before the occurrence of the
single deep-located shock (March 26, 1998, 51 km deep). The anomalous CO2 discharge was closely related to
the extensional movement of the normal faults responsible for the Mw 5.7, 6.0 and 5.6 main shocks that characterized
the earlier seismic phase. In contrast, a clear compressive sign is recognizable in the transient disappearance
of the deep-originating components related to the Mw 5.3, 51 km-deep event that occurred on March 26,
1998. Anomalies were detected concomitantly with the seismicity, although they also occurred after the seismic
crisis had terminated. We argue that the observed geochemical anomalies were driven by rock permeability
changes induced by crustal deformations, and we describe how, in the absence of any release of elastic energy, the
detection of anomalies reveals that a seismogenic process is developing. Indeed, comprehensive, long-term geochemical
monitoring can provide new tools allowing us to better understand the development of seismogenesis.
Article Details
How to Cite
Caracausi, A., Italiano, F., Martinelli, G., Paonita, A. and Rizzo, A. (2005) “Long-term geochemical monitoring and extensive/compressive phenomena: case study of the Umbria Region (Central Apennines, Italy)”, Annals of Geophysics, 48(1). doi: 10.4401/ag-3178.
Issue
Section
OLD
Open-Access License
No Permission Required
Istituto Nazionale di Geofisica e Vulcanologia applies the Creative Commons Attribution License (CCAL) to all works we publish.
Under the CCAL, authors retain ownership of the copyright for their article, but authors allow anyone to download, reuse, reprint, modify, distribute, so long as the original authors and source are cited. No permission is required from the authors or the publishers.
In most cases, appropriate attribution can be provided by simply citing the original article.
If the item you plan to reuse is not part of a published article (e.g., a featured issue image), then please indicate the originator of the work, and the volume, issue, and date of the journal in which the item appeared. For any reuse or redistribution of a work, you must also make clear the license terms under which the work was published.
This broad license was developed to facilitate open access to, and free use of, original works of all types. Applying this standard license to your own work will ensure your right to make your work freely and openly available. For queries about the license, please contact ann.geophys@ingv.it.