Micro- and nano-porosity of the active Alpine Fault zone, New Zealand
<p>Porosity reduction in rocks from a fault core can cause elevated pore fluid pressures and consequently influence the recurrence time of earthquakes. We investigated the porosity distribution in the New Zealand's Alpine Fault core in samples recovered during the first phase of the Deep...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-12-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/11/2425/2020/se-11-2425-2020.pdf |
| Summary: | <p>Porosity reduction in rocks from a fault core can cause elevated pore fluid
pressures and consequently influence the recurrence time of earthquakes. We
investigated the porosity distribution in the New Zealand's Alpine Fault core
in samples recovered during the first phase of the Deep Fault Drilling Project
(DFDP-1B) by using two-dimensional nanoscale and three-dimensional microscale
imaging. Synchrotron X-ray microtomography-derived analyses of open pore
spaces show total microscale porosities in the range of
0.1 %–0.24 %. These pores have mainly non-spherical, elongated, flat
shapes and show subtle bipolar orientation. Scanning and transmission electron
microscopy reveal the samples' microstructural organization, where nanoscale
pores ornament grain boundaries of the gouge material, especially clay
minerals. Our data imply that (i) the porosity of the fault core is very
small and not connected; (ii) the distribution of clay minerals controls the
shape and orientation of the associated pores; (iii) porosity was reduced due
to pressure solution processes; and (iv) mineral precipitation in fluid-filled
pores can affect the mechanical behavior of the Alpine Fault by decreasing
the already critically low total porosity of the fault core, causing elevated
pore fluid pressures and/or introducing weak mineral phases, and thus
lowering the overall fault frictional strength. We conclude that the current
state of very low porosity in the Alpine Fault core is likely to play a key
role in the initiation of the next fault rupture.</p> |
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| ISSN: | 1869-9510 1869-9529 |