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| Titel |
Radon and thoron emission from high and low porosity rocks under increasing deformation: An experimental study |
| VerfasserIn |
Sergio Vinciguerra, Silvio Mollo, Paola Tuccimei, Michael Heap, Michele Soligo, Mauro Castelluccio, Piergiorgio Scarlato, Donald Dingwell |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051362
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| Zusammenfassung |
| Cracking of a medium, observed before earthquake ruptures and/or volcanic eruptions, can
produce anomalous increases in the rate of radon emission, as new exhaling surfaces enhance
its mobility towards the surface. However, in several cases radon emission rate decreases or
does not change significantly before seismic activity and hence the interpretation of such
anomalies remains speculative. Quantitative assessment of the rate of radon emission in
different rock types with increasing deformation is therefore required to address this
problem.
Here we present a new experimental dataset where measurements of radon (222Rn) and
thoron (220Rn) emissions were carried out on lithophysae-rich tuff (initial porosity = 47.01
%) and crystalline lava flow samples (initial porosity = 3.6 %) uniaxially loaded with the aim
of analysing the relationships between incremental damage and the rate of radon
emission.
Our results show that deformation in the high-porosity tuff resulted in a decrease in the
rate of radon emission and can be explained by the fact that compactive pore collapse is the
dominant deformation mechanism. On the other hand, the low porosity lava flow only showed
a small change in radon emission rate with increasing deformation upon macroscopic failure.
This indicates that microcrack damage, as evidenced by the output of acoustic emissions
during deformation, did not improve exhalation surfaces and pathways sufficiently to result in
an increase in radon emission rate. However, when microcracks coalesce to form a
discrete fault plane, new exhaling surfaces are formed and radon emission rates
increase.
It is now clear that the initial physical properties (e.g. porosity) of the rock appear crucial
for understanding of radon emission anomalies. The interplay of the contrasting styles of
deformation (compaction and fracturing) controls the formation/reduction of exhaling
surfaces and thus the rate radon emission. These new experimental data can therefore help
explain the complex trends seen in the field. |
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