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| Titel |
Insights to caving processes from localization of microseismic swarms induced by salt solution mining |
| VerfasserIn |
Jannes Lennart Kinscher, Pascal Bernard, Isabelle Contrucci, Anne Mangeney, Jack Pierre Piguet, Pascal Bigarre |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093197
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| Publikation (Nr.) |
 EGU/EGU2014-7706.pdf |
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| Zusammenfassung |
| In order to improve our understanding of hazardous ground failures, caving processes, and
collapses of large natural or man-made underground cavities, we studied microseismicity
induced by the development and collapse of a salt solution mining cavity with a diameter of
~ 200 m at Cerville-Buissoncourt in Lorraine, France. Microseismicity was recorded as part
of a large geophysical, multi-parameter monitoring research project (GISOS) by a local, high
resolution, triggered 40 Hz geophone monitoring system consisting of five one-component
and four three-component borehole stations located around and in the center of the cavity.
The recorded microseismic events are very numerous (~ 50.000 recorded event files) where
the major portion (~ 80 %) appear in unusual swarming sequences constituted by complex
clusters of superimposed microseismic events. Body wave phase based routine
tools for microseismic event detection and localization face strong limitations in
the treatment of these signals. To overcome these shortcomings, we developed
two probabilistic methods being able to assess the spatio-temporal characteristics
in a semi-automatic manner. The first localization approach uses simple signal
amplitude estimates on different frequency bands, and an attenuation model to
constrain hypocenter source location. The second approach was designed to identify
significantly polarized P wave energies and the associated polarization angles. Both
approaches and its probabilistic conjunction were applied to the data of a two months
lasting microseismic crisis occurring one year before the final collapse that was
related to caving processes leading to a maximal growth of ~ 50 m of the cavity
roof.
The obtained epicenter locations show systematic spatio-temporal migration
trends observed for different time scales. During three phases of major swarming
activity, epicenter migration trends appear in the order of several seconds to minutes,
are spatially constrained, and show partially a reversal and cyclic spatio-temporal
behavior. Similar epicenter migration trends are observed in the order of hours,
and days from the spatio-temporal distribution of epicenter clusters in the cavity
zone. From these observations and other geophysical parameters we conclude that
microseismicity mainly represents detachment cracking at the cavity roof which is
in a critical state of stress. Furthermore, we assume that the systematic epicenter
migration trends represent chain reaction failures initiated by partial fracturing
and subsequent stress redistribution processes. These preliminary results give first
evidence that local microseismic monitoring can be a very powerful tool in order to
survey and study hazardous caving processes. In future work, these hypotheses
will be further tested and specified by detailed analysis of the spectro-energetic
mircoseismic signal characteristics and comparison to local geodetic deformation data. |
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