Surface Rupture Earthquakes and the Mechanics of Earthquake Faulting

拟议的工作将从历史上的破裂地震中发展新的观测和数据，以提高对地震破裂过程的理解。以前的观测工作已经确定了断层几何形状在破裂传播中的作用，在描述地表破裂滑动分布时解决和忽略了自相似性，清楚地表明断层破裂不是一贯的单向或双向的，地震不是一贯地在最终记录最大滑动的断层部分上发生，大的走滑型地震的平均同震滑动和破裂长度之间的关系似乎需要在孕震层以下逐渐增大的深度处的同震滑动作为破裂长度的函数。以前的工作受到时间和资金的限制，只限于一组大约36次大的大陆地震，这些地震都有以下特点：（1）存在地表破裂痕迹图，（2）存在附近没有破裂的活动断层图，（3）存在沿破裂走向沿着许多点的同震偏移量测量，以确定地表滑动分布。由此产生的汇编已经成为更大的地震物理学界大量引用和广泛使用的资源。这项工作将把以前的分析扩展到一个列表，其中有两倍多的地震产生了地表喷发，但文件可能无法同时满足所有三个标准。这一建议的前提是，在遵循类似的方法并将分析扩展到这些额外的地表破裂地震时，还需要获得许多观察和见解。更广泛的意义：将观察范围放在我们理解地震过程物理学的努力上是量化由活动断层造成的地震危险的核心;这是拟议研究的最广泛和最实际的影响。其他研究人员已经开发了地震破裂行为的数值模型，但要知道它们对地球行为的预测效果如何，取决于来自真实的地面破裂的观测数据。研究问题包括断裂能从一个断层跳到另一个断层多远，断层轨迹的角度偏差如何影响断裂，地壳断裂延伸到多深，以及地表断裂如何与预期的地面运动相关。作为一个实际例子，经验观察将改进确定预期终点的工具，从而确定加州地震的破裂长度。

The proposed work will develop new observations and data from historical groundrupturing earthquakes to improve understanding of the earthquake rupture process. Priorobservations have worked to define the role of fault geometry in rupture propagation, addressedand discounted self-similarity in the description of surface rupture slip distributions, shownclearly that fault rupture is not consistently uni- or bi-lateral, that earthquakes do not consistentlyinitiate on the section of fault ultimately recording maximum slip, and thatthe relationshipbetween average coseismic slip and rupture length for large strike-slip earthquakes appears torequire coseismic slip at progressively greater depths below the seismogenic layer as a functionof rupture length. Previous work was been limited by time and funding to a set of about threedozen large continental earthquakes which shared the characteristics that there existed (1) mapsof the surface rupture trace, (2) maps of the nearby active faults that did not rupture, and (3)measurements of coseismic offset at many points along the strike of the rupture to define thesurface slip distribution. The resulting compilation has already become a heavily cited andwidely used resource for the larger earthquake physics community. This work will extendprevious analyses to a list of more than twice as many earthquakes that have produced surfaceruptures but for which documentation may not simultaneously satisfy all three criteria. Thepremise of this proposal is that many observations and insights are yet to be gained in followinga similar approach and extending the analysis to these additional surface rupturing earthquakes.Broader Significance:Placing observational bounds on our efforts to understand the physics of the earthquakeprocess is at the heart of quantifying earthquake hazard imposed by mapped active faults; this isthe broadest and most practical impact of the proposed research. Other researchers havedeveloped numerical models of earthquake rupture behavior, but knowing how well they predictreal earth behavior depends on observational data from real ground ruptures. Research questionsinclude how far a rupture can jump from one fault to another, how angle deviations in a faulttrace affect rupture, how deep into the crust rupture extends, and how surface rupture correlateswith expected ground motions. As a practical example, the empirical observations will improvetools to define the expected endpoints and thus rupture lengths of earthquakes in California.Funding will also contribute to the training of a graduate-level geoscience student.