Basalt is a major component of the earth and moon crust. 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 of 100–400 °C and with varied obsidian mass fractions of 0–100% 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 temperatures >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 seismic response of basaltic faults with the effect of temperature controlling the range of seismogenic depths. Thus, shallow moonquakes tend to occur in the lower lunar crust due to the corresponding anticipated higher glass content and a projected temperature range conducive to velocity-weakening behavior. These observations contribute to a better understanding of the nucleation mechanism of shallow seismicity in basaltic faults.

中文翻译：

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玄武岩断层中受温度升高和黑曜石添加控制的凿孔稳定性及其对月震的影响


玄武岩是地球和月球地壳的主要组成部分。矿物成分和温度会影响摩擦不稳定性，从而影响玄武岩断层发生地震的可能性。我们在 100 MPa 的围压、100-400 °C 的温度范围内和湿/干条件下黑曜石质量分数为 0-100% 的玄武岩凿孔进行了速度步进剪切实验，以研究玄武岩断层的摩擦强度和稳定性。我们观察到，随着黑曜石含量的增加，从速度中性行为转变为速度减弱行为。黑曜石/玄武岩混合凿孔的摩擦稳定性响应的特点是在 200 °C 时从速度增强转变为速度减弱，在温度 >300 °C 时又转变为速度增强。 相反，含黑曜石凿子的摩擦强度对温度和湿/干条件不敏感。这些结果表明，黑曜石含量在玄武岩断层的潜在地震响应中占主导地位，其影响是温度控制地震深度范围的影响。因此，浅层月震往往发生在月壳下部，因为相应地预期较高的玻璃含量和有利于速度减弱行为的预计温度范围。这些观测结果有助于更好地理解玄武岩断层中浅层地震活动的成核机制。