Collaborative Research: Constraining Fault Displacement Histories and Lithospheric Dynamics using Geology and Geophysics

该项目的目标是提高我们对地壳尺度结构与岩石圈尺度动力学和当今地壳应变场之间的关系的理解，利用南部圣安德烈亚斯断裂带作为自然实验室。具体来说，这项研究的重点是确定在加利福尼亚州圣贝纳迪诺附近的圣安德烈亚斯断裂带组成的各种断层上位移率变化的时间尺度。一种新的基于平滑样条理论的建模技术被开发出来，从大地测量和地质研究中得到的可用的位移率平均值来推断瞬时断层位移率。在一组断层的总位移随时间守恒的条件下，估计时变位移率。初步结果表明，圣安德烈亚斯和圣哈辛托断裂带的位移率在100万年、10万年和1万年的时间尺度上有明显的变化。尽管随时间变化很大，但现有数据与总驱替率恒定的概念是一致的。东加利福尼亚剪切带断层的贡献也在探索中。圣哈辛托断层的诞生与圣安德烈亚斯断层中一个主要抑制弯曲的发育有关。瞬时位移率估计表明，随着圣哈辛托断层的形成，圣安德烈亚斯断层速率减慢了约80%。这些断层的形成和位移速率变化数据对岩石圈动力学具有重要意义。该项目的一个重要部分是使用非线性二维和三维数值模型，包括脆性弹塑性和粘弹性流变学，以了解观察到的位移率变化背后可能的动态过程。数值实验用于探索控制断裂带形成和演化的参数，包括对地壳增厚的相对重要性的评估，斜断层段的正应力变化，以及下地壳和上地幔的粘性强度。

The goal of this project is to improve our understanding of how crustal-scale structures relate to lithospheric-scale dynamics and present-day crustal strain fields using the southern San Andreas fault zone as a natural laboratory. Specifically, the research is concentrating on a determination of the time-scales over which displacement rates vary on the various faults composing the San Andreas fault zone near San Bernardino, California. A new modeling technique based on the theory of smoothing splines is being developed to infer instantaneous fault displacement rates from available displacement rate averages from geodetic and geological studies. Time-variable displacement rates are estimated subject to the condition that the total displacement across a set of faults is conserved through time. Preliminary results indicate appreciable variations in displacement rate for the San Andreas and San Jacinto fault zones on million, 100 thousand, and 10 thousand year time-scales. Despite large variations through time, existing data are consistent with the notion of a constant total displacement rate. The contribution of eastern California shear zone faults is also being explored. The birth of the San Jacinto fault correlates with the development of a major restraining bend in the San Andreas fault. Instantaneous displacement rate estimates indicate that the San Andreas fault rate slowed by some 80 percent coincident with the formation of the San Jacinto fault. These fault formation and displacement rate variation data have implications for lithospheric dynamics. An important part of this project is the use of nonlinear 2D and 3D numerical models that include brittle elastic-plastic and visco-elastic rheologies to understand possible dynamic processes underlying the observed displacement rate changes. Numerical experiments are being used to explore the parameters that control fault zone formation and evolution, including an assessment of the relative importance of crustal thickening, variations in normal stress on oblique fault segments, and the viscous strength of the lower crust and upper mantle.