Publication Date:
2017-04-04
Description:
An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
Description:
Radon and thoron emissions from lithophysae‐rich tuff
under increasing deformation are measured to determine
how mechanical damage affects gas emission levels in
tuffs. Mechanical properties of rocks under stresses should
be carefully considered to properly interpret data from
geochemical field monitoring. Two samples are uniaxially
loaded up to failure, while two others are unloaded at the
end of the elastic phase, in order to achieve the highest
compaction of existing pores. Changes in the porosity of
deformed samples are evidenced by helium pycnometer
and microscopy analyses. Radon and thoron exhalation
rates are measured on groups of two samples by alpha
spectrometer technique. Results show that tuff samples
are characterised by a dual porosity consisting of a
macroporosity, given by isolated large pores with sizes
from mm‐ up to cm‐scale and a microporosity ranging
between microns to hundreds of microns. At the end of
the elastic phase pervasive pore collapse is observed, due
to the closure of the cm‐scale macropores. This is
mirrored by a significant decrease of radon and thoron
release. After failure, a further reduction of porosity in the
rock adjacent to the fault planes is observed due to
extensive closure of both macropores and micropores. At
this stage radon and thoron emissions increase. The
formation of new exhaling surfaces is the main carrier of
the bulk increase of radon and thoron exhalations, strongly
prevailing over the densification carried out from the
compaction mechanisms. In terms of volcanic hazard,
negative anomalies in radon emissions should be
considered as indicators of forthcoming ruptures. Key
words: radon and thoron exhalation, tuff deformation,
seismic precursor.
Description:
Published
Description:
L05305
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
JCR Journal
Description:
reserved
Keywords:
Radon
;
Rock deformation
;
04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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