Analysis of the Shallow Slip Deficit Using Sub-Pixel Image Correlation: Implications for Fault Evolution, Slip Rates, and Seismic Hazards

这个研究项目的重点是通过使用一种强大的新技术（COSI-corr亚像素图像相关）来了解地震期间地球表面附近断层滑动的分布，这种技术有助于比以前可用的方法更详细地跟踪断层沿线和周围的地表变形的位置和数量。以前的研究表明，地震期间沿断层发生的滑动在深处比在地表附近更大，导致了所谓的地表滑动赤字。确定这种表面滑移缺陷的原因为本研究提供了基本的理论依据。南加州大学和加州理工学院的科学家们将利用COSI-corr图像相关技术，研究过去几十年里发生的十几次大地震的地表附近滑动分布。这些结果将有助于绘制地震中断层上与断层外的变形模式，允许将这些观测结果与断裂带的基本特征相关联，例如断层在其生命周期中所容纳的总滑动量，这可能被证明是未来地震中断层上发生滑动百分比的良好预测指标。研究结果对认识主要断层系统的地震危险性具有重要意义。目前，对未来地震发生概率的预测主要是基于断层的滑动速率，即在许多地震过程中，断层两侧的块体相互滑动的速率。这种速率主要来自于对偏移地表特征的分析，通常不包括可能分布在主断层周围的任何变形。因此，严重的断层外变形可能会导致对断层上运动速率的低估，从而导致对地震危险性的低估。此外，这些数据将使研究人员能够测试地震破裂可能首选传播方向的模型，这对于提前确定强地面运动的区域分布具有深远的意义。预期的结果还可以用来评估地震破裂会（或不会）沿着断层的复杂结构传播的可能性模型，这是提前估计未来地震规模的一个基本重要问题。因此，研究结果将为断层与非断层滑动和破裂行为的统计测量提供基础，这些测量将用于下一代灾害评估策略，以提供对未来地震灾害的更准确估计。

This research project is focused on understanding the distribution of fault slip near the Earth's surface during earthquakes through the use of a powerful new technology (COSI-corr sub-pixel image correlation), which facilitates tracking of the location and amount of surface deformation along and around faults in much more detail than was possible using previously available methods. Previous studies suggest that the slip that occurs along faults during earthquakes is larger at depth than near the surface, leading to what has been termed a surface slip deficit. Determining the cause(s) of this surface slip deficit provides the basic rationale for this research. Using the COSI-corr image correlation technique, scientists from the University of Southern California and Caltech will examine the distribution of slip near the surface along more than a dozen large-magnitude earthquakes that occurred during the past few decades. The results will facilitate the mapping of on-fault versus off-fault deformation patterns in earthquakes, allowing correlation of these observations with basic features of the fault zone, such as the amount of total slip a fault has accommodated in its lifetime, which may prove to be good predictors of the percentage of slip that will occur on faults during future earthquakes.The results of this research have basic implications for the understanding of the seismic hazards posed by major fault systems. Currently, forecasts of the probability of the future occurrence of earthquakes are based largely on the slip rate of the fault, that is, the rate at which the blocks on either side of the fault slide past each other over the course of many earthquakes. Such rates are mainly derived from the analysis of offset surface features, and usually do not include any deformation that might be distributed around the main fault trace. Thus, significant off-fault deformation may yield underestimates of the rate of movements on faults, and thus on seismic hazard. In addition, these data will allow the researcher to test models of possible preferred propagation direction of seismic ruptures, which will be of profound importance for determining in advance the regional distribution of strong ground motions. The anticipated results will also allow assessment of models for the likelihood that seismic ruptures will (or will not) propagate through structural complexities along the fault, an issue of basic importance for estimating in advance the sizes of future earthquakes. The results will thus provide the basis for the development of statistical measures of on-fault versus off-fault slip and rupture behavior that will be used in next-generation hazard assessment strategies to provide more accurate estimates of future seismic hazard.