Rock mass strength is recognized as an important control on landscape morphology and evolution. However, the controls on rock strength in mountainous topography remain poorly characterized, in part because strength remains challenging to quantify at spatial scales relevant to geomorphology. Here we quantify the mechanical properties of rock masses using subsurface S‐wave velocities, Schmidt hammer hardness values, and Geological Strength Index (GSI) observations. We produce shallow depth profiles of rock mass shear strength using intact rock hardness as measured from a Schmidt hammer, and assessment of the structure and surface conditions of fractures using GSI. We apply these techniques to the Western Transverse Ranges, southern California, USA, where gradients in stratigraphic age and erosion rate allow us to evaluate our methodology. We resolve strength differences of 200 kPa to ∼5 MPa that appear to be related to diagenetic changes associated with the maximum burial depth of young clastic sedimentary rocks. For rocks of the same lithologic type, stratigraphic age, and inferred burial histories, we resolve smaller differences in strength (300 kPa–1.5 MPa) that appear to be positively correlated with mean erosion rates. We suggest that the increase in strength with increasing erosion rate reflects decreased residence time in the weathering zone for ranges experiencing faster fault slip rates. These findings demonstrate up to an order of magnitude variability in strength with respect to burial, erosion, and time for lithologically similar rocks. As such, lithology alone is unlikely to adequately capture the role of rock strength in landscape evolution.

中文翻译：

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埋藏，侵蚀和时间跨梯度的近地表岩体强度剖面

岩体强度被认为是对景观形态和演化的重要控制。但是，山区地形对岩石强度的控制仍然欠佳，部分原因是强度仍然难以在与地貌相关的空间尺度上进行量化。在这里，我们使用地下S波速度，施密特锤硬度值和地质强度指数（GSI）观测值来量化岩体的力学性能。我们使用从Schmidt锤测得的完整岩石硬度生成岩体抗剪强度的浅深度剖面，并使用GSI评估裂缝的结构和表面状况。我们将这些技术应用于美国加利福尼亚南部的西部横向山脉，在这里地层年龄和侵蚀速率的梯度使我们能够评估我们的方法。我们解决了200 kPa至〜5 MPa的强度差异，这似乎与与年轻碎屑沉积岩的最大埋藏深度有关的成岩作用有关。对于相同岩性类型，地层年龄和推断的埋藏历史的岩石，我们解决了较小的强度差异（300 kPa–1.5 MPa），这些差异似乎与平均侵蚀速率呈正相关。我们建议，随着侵蚀速率的增加，强度的增加反映出在经历更快断层滑移率的范围内，在风化带中的停留时间减少了。这些发现表明，岩性相似的岩石在埋藏，侵蚀和时间方面的强度变化幅度最大。因此，仅岩性不可能充分捕捉岩石强度在景观演化中的作用。