Publication Date:
2017-04-04
Description:
The influx of fluids into fault zones can trigger two main types of weakening
processes that operate over different timescales and facilitate fault movement and
earthquake nucleation.
Short-term 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 (∼12,160 t d-1) 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 (μ 〈
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.
Description:
Submitted
Description:
4.5. Degassamento naturale
Description:
N/A or not JCR
Description:
open
Keywords:
Northern Apennines
;
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
;
04. Solid Earth::04.08. Volcanology::04.08.01. Gases
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
manuscript
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