Improving Back-Projection Imaging with a Novel Physics-Based Aftershock Calibration Approach

大地震涉及复杂的滑动模式，沿着断层表面，本身是复杂的。 这些复杂性对预测大地震的预期地面运动有重大影响，因此对估计此类事件的危险性有重大影响。 理解这些复杂性是关键，但由于目前成像方法的分辨率有限，这一目标的进展已经放缓。 该项目正在通过一种新的方法提高这种图像的分辨率和准确性，该方法利用密集的地震仪群记录的相对运动来解析大地震的破裂过程。 该技术类似于用天线定位和跟踪移动源的过程。所提出的方法的增强分辨率允许测试改进的基于物理的地震破裂模型，并提高我们的能力，模拟地震灾害。 该项目充分利用包括Earthscope USAray在内的全球密集地震网络日益增加的可用性，并支持一名女研究生的博士工作。 研究成果通过会议和期刊，以及通过向公立学校和本科生班级的推广而被分享。地震阵列处理，也被称为反向投影（BP）成像，是一种新兴的技术，它利用高频（HF）地震波形提供有关地震震源过程的详细信息。尽管该技术提供了独特的高分辨率观测，但已被证明存在缺陷。虽然来自位于各大洲的每个阵列的BP图像能够揭示地震破裂过程的细节，但HF源的确切位置并不一致，导致破裂长度和速度等属性的差异。该团队开发了一种新的余震校准方法，以减轻阵列的震源位置不确定性，并在2015年尼泊尔-廓尔喀7.8级地震中进行了测试。 该团队目前正在将他们的方法应用于2004年苏门答腊M9.2，2010年智利M8.8和2011年日本M9.1地震的数据，并开发出在多个阵列中相互一致的BP图像，并揭示有关地震过程的其他细节。 这项工作正在缩小地震观测和地震模拟之间的差距，并提供关键信息，以改善对大地震地面运动的预测，从而降低地震风险。

Large earthquakes involve complex patterns of slip along fault surfaces that themselves are complex. These complexities have significant impacts on predicting expected ground motions from major earthquakes, and thus on the estimated hazard from such events. Understanding these complexities is key, but progress towards this goal has been slowed by the limited resolution of current imaging methods. This project is improving the resolution and accuracy of such images through a novel method that uses the relative motions recorded by dense clusters of seismometers to resolve the rupture process of large earthquakes. The technique is analogous to procedures used to locate and track moving sources with antennas. The enhanced resolution of the proposed method allows testing of improved physics-based earthquake rupture models, and is improving our capacity to model earthquake hazards. The project takes full advantage of the increasing availability of global dense seismic networks including the Earthscope USArray, and supports the PhD work of a female graduate student. The research results are being shared via conferences and journals, as well as via outreach to public schools and in undergraduate classes.Seismic array processing, also known as back-projection (BP) imaging, is an emerging technique that utilizes high-frequency (HF) seismic waveforms to provide detailed information about source processes of earthquakes. Even though the technique offers unique, high-resolution observations, it has been shown to have shortcomings. While BP images from each array located on various continents are capable of revealing fine details of the earthquake rupture processes, the exact locations of HF sources do not align, leading to discrepancies regarding such properties as rupture length and speed. The team has developed a novel aftershock calibration to mitigate the source location uncertainties of the arrays and tested it on the 2015 M7.8 Nepal-Gorkha earthquake. The team is now applying their method to data from the 2004 M9.2 Sumatra, 2010 M8.8 Chile, and 2011 M9.1 Japan earthquakes, and developing BP images that are mutually consistent across multiple arrays and reveal additional fine detail about the earthquake processes. This work is narrowing the gap between seismic observations and earthquake simulations, and providing key information to improve predictions of ground motions from large earthquakes and thus reduce seismic risk.