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| Titel |
Scaling the sandbox: New insights from detailed mechanical testing and quantitative comparison to nature |
| VerfasserIn |
Malte C. Ritter, Karen Leever, Matthias Rosenau, Onno Oncken  |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128696
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| Publikation (Nr.) |
 EGU/EGU2016-8706.pdf |
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| Zusammenfassung |
| Analogue sandbox experiments are an important tool to understand tectonic deformation. In
combination with modern imaging techniques they provide a spatio-temporal resolution no
other method can achieve. The downside is that information on stress distribution within the
sandbox model is not readily available, which is the reason for most experiments to date
being interpreted kinematically only. However, with the advent of reliable force sensors
with a suitable dynamic range the dynamic evolution of sandbox models becomes
available for analysis, offering new insights into the transient evolution of tectonic
systems.
The interpretation of sandbox dynamics and its transfer to natural systems requires a
much stricter scaling approach than usually considered. In particular it requires that not only
the strength of the model material, but also its transient strength evolution, i.e. its
weakening, be properly scaled to that of the natural prototype. No such scaling of
transient strength exists up to now. Furthermore, published mechanical test data have
mostly been obtained under normal load conditions not representative for analogue
experiments.
To derive a scaling of transient strength we therefore measured and analysed two standard
analogue model materials (quartz sand and glass microbeads) using ring-shear tests at low
normal loads similar to common analogue experiments. We find that strain weakening under
these conditions ( < 1 kPa normal load) is governed by a reduction of cohesion, not
friction, which is the case for higher normal loads ( > 1 kPa) only. We show that this
basically restricts proper scaling of transient strength of the tested materials to crustal
scale models, with a length scaling factor of (nature/model) = 106. For this scale
range we quantitatively compare the model materials’ transient strength evolution
both laboratory measurements of natural rocks and to estimates for the earth’ crust.
Accounting for lithostatic and hydrostatic conditions, respectively, we find that
proper dynamic scaling – also of transient properties – is achieved in either case. |
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