Effects of temperature and obsidian content on the friction and stability of simulated basalt gouges: Implications for shallow moonquakes

Basalt is a major component of crust on both the Earth and Moon. Mineral composition and temperature influence frictional instability and thus the potential for seismicity on basaltic faults. We performed velocity-stepping shear experiments on basalt gouges at a confining pressure of 100 MPa, temperatures in the range 100-400°C and with varied obsidian contents of 0-100 wt.% under wet/dry conditions to investigate the frictional strength and stability of basaltic faults. We observe a transition from velocity-neutral to velocity-weakening behaviors with increasing obsidian content. The frictional stability response of the mixed obsidian/basalt gouges is characterized by a transition from velocity-strengthening to velocity-weakening at 200°C and another transition to velocity-strengthening at >300°C. Conversely, frictional strengths of the obsidian-bearing gouges are insensitive to temperature and wet/dry conditions. These results suggest that obsidian content dominates the potential s..., ,