Crustal faults in the southern Cascadia forearc help to accommodate strains related to plate interactions near the Mendocino triple junction (MTJ). Geologic work has identified the Little Salmon fault, Mad River fault zone (MRFZ), and Grogan fault as Quaternary-active structures; however, the slip rates on these major fault systems are poorly constrained. This work constructs elastic block models of the MTJ region and leverages GNSS velocity data to better understand how strain is partitioned among these three faults. We evaluate models with various forearc fault structures and apply a bootstrap analysis to provide independent slip rate distributions for each fault. Model results indicate that the Little Salmon fault zone is an important structure that accommodates both thrust and right-lateral shear motion in the forearc. Appreciable right-lateral slip rates on the MRFZ indicate that this system plays an important role in facilitating translation of the forearc and may serve as an extension of the northern San Andreas fault system. In contrast, the models place very little strike-slip motion on the Grogan fault and prefer this structure to mainly host reverse slip. We observe the highest slip rates on the Bear River fault zone, indicating significant strain to the north of the MTJ.

中文翻译：

---

从 GNSS 推断的南卡斯卡迪亚前弧断层的应变分配

卡斯卡迪亚前弧南部的地壳断层有助于适应与门多西诺三合点（MTJ）附近板块相互作用相关的应变。地质工作已将 Little Salmon 断层、Mad River 断层带 (MRFZ) 和 Grogan 断层确定为第四纪活动构造；然而，这些主要断层系统的滑移率受到的限制很差。这项工作构建了 MTJ 区域的弹性块模型，并利用 GNSS 速度数据来更好地了解应变在这三个断层之间的分配方式。我们评估具有各种前弧断层结构的模型，并应用自举分析来为每个断层提供独立的滑移率分布。模型结果表明，Little Salmon 断裂带是一个重要的构造，它同时适应了前弧中的逆冲和右旋剪切运动。MRFZ 上明显的右侧滑移率表明，该系统在促进前弧平移方面发挥了重要作用，并可作为北部圣安德烈亚斯断层系统的延伸。相比之下，模型对 Grogan 断层的走滑运动非常少，并且更喜欢这种结构主要承载反向滑动。我们观察到熊河断层带的最高滑动率，表明 MTJ 以北的应变显着。