Abstract
Under critical conditions where experimental fault slip exhibits self-sustained oscillation, effects of normal stress oscillation (NSO) on fault strength and stability remain poorly understood, as do potential effects of NSO on natural and induced seismicity. In this study, we employed double direct-shear testing to investigate the frictional behavior of a synthetic, slightly velocity-weakening (SVW) fault gouge (characterized by self-sustained oscillation under quasi-static shear loading), when subjected to NSO at different amplitudes (5%–20% of 5 MPa) and frequencies (0.001–1 Hz). During the experiment, fault displacement and gouge layer thickness were measured. Transmitted ultrasonic waves were also employed to probe grain contact states within the gouge layer. Our results show that fault weakening and unstable slip can be triggered at NSO frequencies ranging from 0.03 to 0.1 Hz and amplitudes exceeding 5%. Interestingly, an amplified shear stress drop and weakening effect were observed when the NSO frequency fell in 0.05–0.1 Hz. Analysis of transmitted ultrasonic waves in tests on the SVW gouge revealed fault dilation, accompanied by unstable slip and weakening. By extending an existing microphysical model (the “Chen-Niemeijer-Spiers [CNS]” model), to account for elastic effects of NSO on gouge microstructure and grain contact state, the mechanical and wave data obtained in our experiments on the SVW gouge was reproduced, suggesting an approach for modeling fault instability under upper crustal (SVW) conditions where normal stress is perturbed by subsurface operations, such as periodic gas storage stimulation of reservoir formations.
Original language | English |
---|---|
Article number | e2024JB029521 |
Journal | Journal of Geophysical Research: Solid Earth |
Volume | 129 |
Issue number | 9 |
DOIs | |
Publication status | Published - 1 Sept 2024 |
Bibliographical note
Publisher Copyright:© 2024. American Geophysical Union. All Rights Reserved.
Funding
This study was supported by the National Natural Science Foundation of China (Grants U1839211 and U2239204 to Shengli Ma, Grant 42174224 to Jianye Chen). The work was also supported in part by the DeepNL research programme (Science4Steer Project, project number DEEP.NL.2018.046), financed by the Dutch Research Council (NWO). B. Yu acknowledges the China Scholarship Council for providing funding to perform the theoretical part of this study at Utrecht University. We thank Yanshuang Guo, Jiahui Feng and Qingbao Duan for the technique help in running the friction experiments and the compaction test. We thank the editor Prof. Alexandre Schubnel, an anonymous associated editor, an anonymous reviewer, and Prof. John W. Rudnicki for the constructive suggestions on this work.
Funders | Funder number |
---|---|
Nederlandse Organisatie voor Wetenschappelijk Onderzoek | |
Universiteit Utrecht | |
China Scholarship Council | |
National Natural Science Foundation of China | 42174224, U2239204, U1839211 |
DeepNL | DEEP.NL.2018.046 |
Keywords
- fault friction
- induced seismicity
- microphysical model
- normal stress oscillation
- slightly velocity-weakening gouge