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| Titel |
Poroelastic responses of confined aquifers to subsurface strain and their use for volcano monitoring |
| VerfasserIn |
K. Strehlow, J. H. Gottsmann, A. C. Rust |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 6, no. 4 ; Nr. 6, no. 4 (2015-11-10), S.1207-1229 |
| Datensatznummer |
250115523
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| Publikation (Nr.) |
 copernicus.org/se-6-1207-2015.pdf |
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| Zusammenfassung |
Well water level changes associated
with magmatic unrest can be interpreted as a result of pore pressure changes
in the aquifer due to crustal deformation, and so could provide constraints
on the subsurface processes causing this strain. We use finite element
analysis to demonstrate the response of aquifers to volumetric strain induced
by pressurized magma reservoirs. Two different aquifers are invoked – an
unconsolidated pyroclastic deposit and a vesicular lava flow – and embedded
in an impermeable crust, overlying a magma chamber. The time-dependent, fully
coupled models simulate crustal deformation accompanying chamber
pressurization and the resulting hydraulic head changes as well as flow
through the porous aquifer, i.e. porous flow. The simulated strain leads to centimetres (pyroclastic aquifer) to metres (lava flow aquifer) of hydraulic
head changes; both strain and hydraulic head change with time due to
substantial porous flow in the hydrological system.
Well level changes are particularly sensitive to chamber volume, shape and
pressurization strength, followed by aquifer permeability and the phase of
the pore fluid. The depths of chamber and aquifer, as well as the aquifer's
Young's modulus also have significant influence on the hydraulic head signal.
While source characteristics, the distance between chamber and aquifer and
the elastic stratigraphy determine the strain field and its partitioning,
flow and coupling parameters define how the aquifer responds to this strain
and how signals change with time.
We find that generic analytical models can fail to capture the complex
pre-eruptive subsurface mechanics leading to strain-induced well level
changes, due to aquifer pressure changes being sensitive to chamber shape and
lithological heterogeneities. In addition, the presence of a pore fluid and
its flow have a significant influence on the strain signal in the aquifer and
are commonly neglected in analytical models. These findings highlight the
need for numerical models for the interpretation of observed well level
signals. However, simulated water table changes do indeed mirror volumetric strain, and wells are therefore a valuable addition to monitoring systems that could
provide important insights into pre-eruptive dynamics. |
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