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Quantifying Near‐Surface Rock Strength on a Regional Scale From Hillslope Stability Models
Journal of Geophysical Research: Earth Surface ( IF 3.9 ) Pub Date : 2020-06-09 , DOI: 10.1029/2020jf005665
Kirk F. Townsend 1 , Sean F. Gallen 2, 3 , Marin K. Clark 1
Affiliation  

Rock strength is a fundamental property of earth materials that influences the morphology of landscapes and modulates feedbacks between surface processes, tectonics, and climate. However, rock strength remains challenging to quantify over the broad spatial scales necessary for geomorphic investigations. Consequently, the factors that control rock strength in the near‐surface environment (i.e., the critical zone) remain poorly understood. Here we quantify near‐surface rock strength on a regional scale by exploiting two hillslope‐stability models, which explicitly relate the balance of forces within a hillslope to Mohr‐Coulomb strength parameters. We first use the Culmann finite‐slope stability model to back‐calculate static rock strength with high‐density measurements of ridge‐to‐channel hillslope height and gradient. Second, we invert the Newmark infinite‐slope stability model for strength using an earthquake peak ground acceleration model and coseismic landslide inventory. We apply these two model approaches to a recently inverted sedimentary basin in the eastern Topatopa Mountains of southern California, USA, where a tectonic gradient has exposed stratigraphic units with variable burial histories. Results show similar trends in strength with respect to stratigraphic position and have comparable strength estimates to the lowest values of published direct‐shear test data. Cohesion estimates are low, with Culmann results ranging from 3 to 60 kPa and Newmark results from 6 to 30 kPa, while friction angle estimates range from 24° to 44° from the Culmann model. We find that maximum burial depth exerts the strongest control on the strength of these young sedimentary rocks, likely through diagenetic changes in porosity, cementation, and ultimately, lithification.

中文翻译:

利用坡度稳定性模型对区域近地表岩石强度进行量化

岩石强度是地球材料的基本属性,它会影响景观的形态并调节地表过程,构造和气候之间的反馈。但是,岩石强度仍然难以在地貌研究所需的广阔空间范围内进行量化。因此,对于在近地表环境(即临界区)控制岩石强度的因素仍然知之甚少。在这里,我们通过利用两个山坡稳定性模型对区域近地表岩石强度进行量化,这两个模型将山坡内的力平衡与莫尔库仑强度参数明确相关。我们首先使用Culmann有限边坡稳定性模型,通过对山脊到河道的山坡高度和坡度进行高密度测量来反算静态岩石强度。第二,我们使用地震峰值地面加速度模型和同震滑坡清单反演了纽马克无限边坡稳定模型的强度。我们将这两种模型方法应用于美国加利福尼亚南部东部托帕托巴山脉的最近倒置的沉积盆地,该地区的构造梯度暴露出具有不同埋藏历史的地层单元。结果显示出相对于地层位置的强度趋势相似,并且强度估算值与已发布的直接剪切试验数据的最低值相当。内聚力估计值较低,Culmann模型的Culmann结果范围为3至60 kPa,Newmark结果为6至30 kPa,而摩擦角估计范围为24°至44°。我们发现最大的埋藏深度对这些年轻的沉积岩的强度具有最强的控制作用,
更新日期:2020-07-22
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