Collaborative Research: Reconciling Geologic and Geodetic Rates of Deformation: The Role of Distributed Strain in the Upper Crust

了解地表形变在不同时间尺度上的时空分布，可以深入了解岩石圈的流变性、破裂行为和沿断层网络的滑动转移的性质。然而，GPS提供的新见解带来了新的挑战：尤其是，在大地测量时间尺度(不到10年)上测量的弹性应变累积如何与在更长时间尺度(10,000-1,000,000年)上推断的地质滑动有关？在过去的几年里，许多工作都集中在东加州剪切带上地表形变的大地速率和断层滑动的地质速率之间的明显差异上。最近对这种差异的假设集中在应变场的时间变化上，其原因是：1)地震应变释放的聚集，2)共轭断层系统的振荡应变释放，或3)近期地震后的粘弹性变形。然而，为了充分了解断层系统行为变化的速度和节奏，需要对地质时期的断层滑动进行完整的表征。这个研究小组正在收集必要的基本地质和地貌数据，以严格评估加利福尼亚州欧文斯山谷的断层位移速率。特别是，该项目旨在了解弥漫排列的小断层在调节整个地区的应变方面所起的作用。目前对大地测量数据的解释没有考虑到这些断层网络可能是地质滑动的重要组成部分，这一假设正在通过确定断层滑动速率(利用分布在欧文斯河谷中部和北部的许多断层阵列的断层滑动速率(利用冰川冰川、河流阶地和冲积扇等地貌标志)进行检验。此外，另一种假设认为，地质和大地测量数据之间的差异可能反映了应变释放速度的时间变化。通过利用具有不同时代的偏移标记的场地，正在对整个区域分布的断层的速度和节奏进行精细的了解。该项目通过改进对跨越扩散的北美-太平洋板块边界的大地测量数据的解释，以及通过对断层滑动的时间变化问题的新的见解，促进实现更广泛的地质/地球物理界所阐述的更大的目标。

Understanding the spatial and temporal distribution of surface deformation over various timescales can yield insight into lithospheric rheology, rupture behavior, and nature of slip transfer along fault networks. However, new insights provided by GPS bring new challenges: in particular, how does elastic strain accumulation measured over geodetic timescales (less than 10 yr) relate to geologic slip inferred over longer timescales (10,000 - 1,000,000 yr)? Over the past few years, much effort has been focused on an apparent discrepancy between geodetic rates of surface deformation and geologic rates of fault slip across the Eastern California Shear Zone. Recent hypotheses for this discrepancy center on temporal variations in the strain field which result from: 1) clustering of seismic strain release, 2) oscillatory strain release on conjugate fault systems, or 3) viscoelastic deformation following recent earthquakes. In order to fully understand the pace and tempo of variations in fault system behavior, however, a complete characterization of fault slip over geologic time is required.This investigator team is collecting the basic geologic and geomorphic data necessary to critically assess rates of fault displacement across Owens Valley, California. In particular, the project is aimed at understanding the role played by diffuse arrays of small faults in accommodating strain across the region. The hypothesis that these fault networks may account for a significant component of geologic slip not considered by current interpretations of geodetic data is being tested by determining fault slip rates (exploiting geomorphic markers such as glacial moraines, river terraces and alluvial fans) on numerous fault arrays distributed throughout central and northern Owens Valley. Moreover, an alternative hypothesis holds that the discrepancy between geologic and geodetic data may reflect temporal variation in the rate of strain release. A refined understanding of the pace and tempo of distributed faulting across the region is being developed by exploiting sites with offset markers of varying age.This project contributes towards larger goals articulated by the broader geologic/geophysical community by improving interpretations of geodetic data across the diffuse North American - Pacific plate boundary, and by developing new insight into the problem of temporal variations in fault slip.