美国地质调查局Devin McPhillips的研究组近日取得一项新成果。他们报道了美国加利福尼亚州库卡蒙加断层地质滑动速率的时空分析，即对沿走向应用和多断层破裂的影响。该项研究成果发表在2023年2月21日出版的《JGR地球》上。

课题组研究人员调查了库卡蒙加断层的滑动速率。库卡蒙加断层位于横向断层系统与圣安德烈亚斯断层和圣哈辛托断层的交界处，据推测，它与这些断层相连，促进了大型多断层地震的传播。先前的研究表明，晚第四纪冲积扇表面上的库卡蒙加断层位移沿走向变化很大。研究团队从冲积扇的深度剖面提出了两个新的¹⁰Be地表暴露年龄。滑动速率一致，平均速率为1.4±0.3 m/kyr，时间间隔为约20、约30和约40 kyr。如果库卡蒙加断层参与了多断层破裂，那么这些地震要么很少发生，要么有足够的规律性，在多个区间内保持明显的稳定频率。

该课题组也探讨了沿走向断层位移可变性为主题的一个校准的形态学模型。该模型成功地再现了陡坎剖面，并表明断层位移可变性可部分由陡坎年龄而不是用抬升速率来解释。该团队推断，短暂沟蚀和分布变形都导致了断层位移的变化，尽管在没有跨越陡坡挖掘的情况下，这两者都很难有把握地探测到。研究结果表明，更好地描述沿走向的累积滑移可变性可以提高滑动速率的准确性和精度。不考虑认知不确定性的滑动速率可能不适用于较长断层段的外推。

据了解，为了约束断层发生的过程和危险程度，可以在不同的断层长度或时间间隔上外推断层的滑动速率。

附：英文原文

Title: Spatial and temporal analysis of geologic slip rates, Cucamonga Fault, California, USA: Implications for along-strike applications and multi-fault rupture

Author: Devin McPhillips, Katherine Scharer

Issue&Volume: 2023-02-21

Abstract: To constrain fault processes and hazard, fault slip rates may be extrapolated over different fault lengths or time intervals. Here, we investigate slip rates for the Cucamonga Fault. The Cucamonga Fault is located at the junction of the Transverse Range fault system with the San Andreas and San Jacinto Faults, and it is hypothesized to connect with these faults, promoting the propagation of large, multi-fault earthquakes. Previous work has shown that Cucamonga Fault displacements on late Quaternary alluvial fan surfaces are highly variable along strike. We present two new ¹⁰Be surface exposure ages from depth profiles on the alluvial fans. Slip rates are consistent, with an average rate of 1.4 ± 0.3 m/kyr, over time intervals of ～20, ～30, and ～40 kyr. If the Cucamonga Fault participates in multi-fault ruptures, then these earthquakes occur either rarely or with sufficient regularity to maintain apparently steady rates over multiple intervals. We also explore along-strike fault displacement variability using a calibrated morphological model. The model successfully reproduces scarp profiles and indicates that fault displacement variability can be explained in part by scarp age but not uplift rate. We infer that both erosion by ephemeral gullying and distributed deformation contribute to fault displacement variability, although both are difficult to detect confidently without excavations across the scarp. These investigations show that better characterization of cumulative-slip variability along strike may improve accuracy and precision of slip rates. Slip rates that do not consider epistemic uncertainties may not be suitable for extrapolation over longer fault sections.

DOI: 10.1029/2022JB024942

Source: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JB024942