Fault Surface Bumps: Prevalence, Causes and Consequences

断层表面的几何形状影响着地震力学的方方面面，但直到最近，地震滑动尺度下断层形态的定量现场数据一直很少。我们已经开始结合地面激光测距和实验室分析来解决这个问题。这项初步工作已经将断层表面的可用数据增加了几个数量级，并产生了新的地质观测结果。数据定量地表明，大滑动断层比小滑动断层更平缓。更引人注目的是，到目前为止测量到的所有原始的、大规模的成熟断层暴露在10‘S米级上都有明显的准椭圆形凸起。这些三维凸起在断层力学中被称为凹凸体，是一种新的现场观测，也是本研究的重点。具体地说，研究人员现在正在确定这类凸起在各种断层上发生的频率，测量凸起发生情况与围岩类型之间的关系，通过测量凸起附近磨损的岩粉总量来限制凸起的来源，绘制凸起附近岩石破坏的发生图，对凸起在围岩上的应力场进行数值模拟，并使用地震数据来确定成熟、光滑断层上的地震是否与不成熟、粗糙的断层上的地震不同。

Fault surface geometry affects all aspects of earthquake mechanics, yet until recently quantitative field data of fault shapes at the scale of earthquake slip has been scarce. We have begun to attack the problem using a combination of ground-based laser distance measurements and laboratory analyses. This initial work has already increased the available data on fault surfaces by several orders of magnitude and produced new geological observations. The data quantitatively shows that large-slip faults are smoother than small-slip ones. More strikingly, all pristine, large-scale exposures of mature faults that have been measured thus far have distinct quasi-elliptical bumps at the 10's of meter scale. These 3D bumps, known in fault mechanics as asperities, are a new field observation and the focus of the present study. Specifically, the investigators are now determining how commonly such bumps occur on a variety of fault, measuring the relationship between the bump occurrence and surround rock types, constraining the origin of bumps by measuring the total amount abraded rock powder in the bump's vicinity, mapping the occurrence of rock damage near bumps, numerically modeling the bump's stress field on the surround rocks and using seismic data to determine if the earthquakes on mature, smooth faults are different than those on immature, rough ones.