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

该项目的目标是以圣安德烈亚斯南部断裂带为天然实验室，增进我们对地壳尺度结构与岩石圈动力学和现今地壳应变场之间关系的理解。具体地说，这项研究集中于确定加州圣贝纳迪诺附近圣安德烈亚斯断裂带的各种断层的位移速率变化的时间尺度。一种新的基于光滑样条理论的建模技术正在开发中，用于从大地测量和地质研究中获得的可用位移速率平均值推断瞬时断层位移速率。在一组断层上的总位移随时间保持不变的条件下，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速率在百万年、十万年和一万年的时间尺度上存在明显的差异。尽管随着时间的推移有很大的变化，但现有的数据与恒定的总移位率的概念是一致的。加州东部剪切带断层的贡献也在探索中。圣哈辛托断裂的诞生与圣安德烈亚斯断裂中一个主要的限制弯曲的发育有关。瞬时位移速率估计表明，圣安德烈亚斯断层的速率减慢了约80%，这与圣哈辛托断层的形成相吻合。这些断层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2D和3D数值模型，其中包括脆性弹塑性和粘弹性流变学，以了解观测到的位移速率变化背后可能的动态过程。正在利用数值实验来探索控制断裂带形成和演化的参数，包括评估地壳增厚的相对重要性、斜向断裂段上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.