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Durham University

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Publication details for Dr Nicola De Paola

Collettini, C., Cardellini, C., Chiodini, G., De Paola, N., Holdsworth, R.E. & Smith, S.A.F. (2008). Fault weakening due to CO2 degassing in the Northern Apennines: short- and long-term processes. In The Internal Structure of Fault Zones: Implications for Mechanical and Fluid-Flow Properties. Wibberley, C.A.J., Kurz, W., Imber, J., Holdsworth, R.E. & Collettini, C. Geological Society of London. 299: 1-20.

Author(s) from Durham

Abstract

Abstract: The influx of fluids into fault zones can trigger two main types of weakening process
that operate over different timescales and facilitate fault movement and earthquake nucleation.
Short- and long-term weakening mechanisms along faults require a continuous fluid supply
near the base of the brittle crust, a condition satisfied in the extended/extending area of the Northern
Apennines of Italy. Here carbon mass balance calculations, coupling aquifer geochemistry to
isotopic and hydrological data, define the presence of a large flux (c. 12 160 t/day) of deep-seated
CO2 centred in the extended sector of the area. In the currently active extending area, CO2 fluid
overpressures at 85% of the lithostatic load have been documented in two deep (4–5 km)
boreholes. In the long-term, field studies on an exhumed regional low-angle normal fault show
that, during the entire fault history, fluids reacted with fine-grained cataclasites in the fault core
to produce aggregates of weak, phyllosilicate-rich fault rocks that deform by fluid assisted
frictional–viscous creep at sub-Byerlee friction values (m , 0.3). In the short term, fluids can
be stored in structural traps, such as beneath mature faults, and stratigraphical traps such as
Triassic evaporites. Both examples preserve evidence for multiple episodes of hydrofracturing
induced by short-term cycles of fluid pressure build-up and release. Geochemical data on the
regional-scale CO2 degassing process can therefore be related to field observations on fluid
rock interactions to provide new insights into the deformation processes responsible for active
seismicity in the Northern Apennines.