Abstract
Geodetic observations and large-scale laboratory experiments show that seismic instability is preceded by slow slip within a finite nucleation zone. In laboratory experiments rupture nucleation is studied mostly using bare (rock) interfaces, whereas upper crustal faults are typically filled with gouge. To investigate effects of gouge on rupture nucleation, we performed a biaxial shearing experiment on a 350 mm long saw-cut fault filled with gypsum gouge, at room temperature and a minimum horizontal stress σ2 = 0.3–5 MPa. The gouge layer was sandwiched between polymethylmethacrylate (PMMA) plates For reference also a fault without gouge was deformed. Strain gauges and Digital Image Correlation were used to monitor the deformation field along the fault zone margins. Stick-slip behavior occurred on both the gouge-filled fault and the PMMA fault. Nucleation of instability on the PMMA fault persistently occurred from one location 2/3 to 3/4 along the fault adjacent to a slow slip zone at the fault end, but nucleation on the gouge-filled fault was more variable, nucleating at the ends and/or at approximately 2/3 along the fault, with precursory slip occurring over a large fraction of the fault. Nucleation correlated to regions of high average fault stress ratio τ/σn, which was more variable for the gouge-filled fault due to small length scale variations in normal stress caused by heterogeneous gouge compaction. Rupture velocities and slip rates were lower for the gouge-filled fault than for the bare PMMA fault. Stick-slip persisted when σ2 was lowered and the nucleation zone length increased, expanding from the center to the sample ends before transitioning into instability.
Original language | English |
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Article number | e2019JB018429 |
Number of pages | 25 |
Journal | Journal of Geophysical Research: Solid Earth |
Volume | 125 |
Issue number | 8 |
DOIs | |
Publication status | Published - Aug 2020 |
Funding
This study was performed in the context of the research program ?Studies on fault (re)activation and dynamic friction and failure behavior? (Research Agreement UI49294) funded by the Nederlandse Aardolie Maatschappij (NAM). This program focuses on a fundamental understanding of the physical mechanisms of production-induced reservoir compaction and induced seismicity in the Groningen gas field. The authors would like to thank Dirk Doornhof (NAM B.V.) for feedback on the manuscript. Also, Gerd-Jan Schreppers of DIANA FEA B.?V. is thanked for his support and discussions on numerical modeling. CEA employees Yuntao Ji, Wenbo Qi, and Yan-Qun Zhuo, and UU employees Thony van der Gon-Netscher and Floris van Oort are thanked in particular for technical assistance in the laboratories at CEA and UU. Andr? Niemeijer is supported by the European Research Council, starting grant SEISMIC (335915) and by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) Vidi-grant 854.12.001. We thank Greg McLaskey and two anonymous reviewers for their reviews and constructive feedback. Vincent Brunst is thanked for his help with data storage and accessibility.
Keywords
- gypsum gouge
- large-scale experimental faults
- nucleation of stick-slip instability
- PMMA
- rupture nucleation