Authors:	Martina, Kirilova Toy, Virginia Sauer, Katrina Renard, François Gessner, Klaus Wirth, Richard Xiao, Xianghui Matsumura, Risa
Title:	Micro- and nano-porosity of the active Alpine Fault zone, New Zealand
Online publication date:	28-Jan-2021
Year of first publication:	2020
Language:	english
Abstract:	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.
DDC:	550 Geowissenschaften 550 Earth sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-5605
Version:	Published version
Publication type:	Zeitschriftenaufsatz
License:	CC BY
Information on rights of use:	https://creativecommons.org/licenses/by/4.0/deed.en
Journal:	Solid earth 11 6
Pages or article number:	2425 2438
Publisher:	Copernicus Publ.
Publisher place:	Göttingen
Issue date:	2020
ISSN:	1869-9529
Publisher URL:	https://doi.org/10.5194/se-11-2425-2020
Publisher DOI:	10.5194/se-11-2425-2020
Appears in collections:	JGU-Publikationen