Breaking the High-Frequency Barrier in Earthquake Source Imaging With a Network of Seismic Antennas

由于地壳的非均质性，传统震源成像技术的时空分辨率有限，无法吸收高频波场，这阻碍了地震学对地震物理的深入研究。该项目旨在开发新一代地震台网，专门用于大地震破裂的高分辨率成像。如果地震记录在由多个小孔径阵列组成的高度聚集的强震网络上，则可以实现非参数震源成像：使用高分辨率到达方向估计技术处理阵列数据可以提供高频震源辐射“亮点”的时空分布，从而直接了解破裂复杂性。提出的研究包括系统设计和规范的各个方面，可以通过实际地震场景的计算建模，优化实验设计问题的数值解决方案，阵列信号处理技术的发展和可用数据集的分析来解决。研究人员将在具有真实震源复杂性、地壳非均质性和地形的地震情景中生成震源动力学和波传播，以提供概念验证，以评估多阵列成像复杂震源过程的鲁棒性和分辨率。通过将散射对波形相干性的影响量化为频率和站间距离的函数，并通过确定波场相干性的适当地貌代用物，这些综合情景还将指导确定阵列选址的实际指导方针。优化技术将用于寻找网络和阵列几何形状，以最大限度地提高源成像分辨率和鲁棒性，同时最小化要部署的传感器总数。世界上许多大城市在靠近活动断层的地方都有地震危险，在这些地方，震源复杂性的影响主导了地面震动的幅度和变异性。提高我们对地震动力学的理解将巩固基于物理的地震危险性评估方法的新兴趋势。该项目旨在通过设计由活跃断层附近的多组强运动传感器组成的新一代地震网络，实现我们对大地震破裂传播细节成像能力的革命性发展。这一发展的目的是在地震破裂过程的时空分辨率方面进行数量级的改进，这将允许测试关于地震物理的竞争性假设，从而将推进我们对地震危害的定量理解。该概念及时建立在2004年帕克菲尔德地震单阵列记录的最新经验之上，并利用了最近的技术发展，例如低成本MEMS加速度计和无线通信的可用性日益增加。提出的概念将在地震工程、常规地震台网分析和构造地震监测等多个额外应用中做出贡献。

Seismological insight into the physics of earthquakes is hampered by the limited spatio-temporal resolution of conventional source imaging techniques which, due to the heterogeneity of the Earth's crust, are incapable of assimilating the high-frequency wavefield. This project aims at enabling the development of a new generation of seismic networks specially designed for high-resolution imaging of large earthquake ruptures. Non-parametric source imaging can be achieved if an earthquake is recorded on a highly clustered strong motion network, composed of multiple small aperture arrays: processing array data with high resolution direction-of-arrival estimation techniques can provide the spatio-temporal distribution of "bright spots" of high-frequency source radiation, a direct insight on rupture complexity. The proposed research encompasses aspects of the system design and specifications that can be addressed through computational modeling of realistic earthquake scenarios, numerical solution of optimal experiment design problems, developments in array signal processing techniques and analysis of available datasets. The researchers will generate source dynamics and wave propagation in earthquake scenarios with realistic source complexity, crustal heterogeneities and topography to provide a proof of concept, to assess the robustness and resolution of imaging complex source processes with multiple arrays. These synthetic scenarios will also guide the definition of practical guidelines for array site selection, by quantifying the effect of scattering on waveform coherency as a function of frequency and inter-station distance and by identifying adequate geomorphological proxies for wavefield coherency. Optimization techniques will be employed to find the network and array geometries that maximize the source imaging resolution and robustness while minimizing the total number of sensors to be deployed.Many large urban areas around the world are exposed to earthquake hazard in close proximity to active faults, where the effects of the earthquake source complexity dominate the amplitude and variability of ground shaking. Improving our understanding of earthquake dynamics will consolidate the emerging trend of physics-based approaches for earthquake hazard assessment. This project aims at a transformative development of our capabilities to image the details of the rupture propagation of large earthquakes through the design of a new generation of seismic networks made of multiple clusters of strong motion sensors near active faults. This development aims at an order-of-magnitude improvement in the spatio-temporal resolution of earthquake rupture processes that will allow testing of competing hypothesis about the physics of earthquakes and hence will advance our quantitative understanding of earthquake hazards. The concept timely builds upon recent experience with single-array recordings of the 2004 Parkfield earthquake and takes advantage of recent technological developments, such as the increasing availability of low cost MEMS accelerometers and wireless communication. The proposed concept will be designed to allow contributions to multiple additional applications in earthquake engineering, analysis of conventional seismic networks and monitoring tectonic tremor.