Large-scale biaxial experiments on gypsum-gouge faults and a bare PMMA fault: Mechanical data and selected strain and image data

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 nucleation, we performed a biaxial shearing experiment on a 350 mm long saw-cut fault filled with gypsum gouge, at room temperature and σ2 = 0.3 - 5 MPa. The gouge layer was sandwiched between polymethylmethacrylate (PMMA) plates that were densely instrumented with strain gauges. Digital Image Correlation (DIC) was used to obtain the deformation field at the top surface of the plates. For reference also a fault without gouge was deformed. 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 80 mm from one of the fault ends, but nucleation on the gouge-filled fault was more complex, nucleating at the ends and/or at 120 mm from the end, with precursory slip occurring over a large fraction of the fault. Nucleation correlated to regions of high fault stress ratio τ/σn. Complexities in nucleation on the gouge-filled fault were related 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 continued when σ2 was lowered, and the nucleation zone increased and interacted with the sample ends before transitioning into instability. The data is provided in a folder with 3 subfolders for 3 experiments. Detailed information about the files in these subfolders as well as information on how the data is processed is given in the explanatory file Buijze_2019_Data_description_sheet.docx. Contact person is Loes Buijze - TNO - loes.buijze@tno.n