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，无法同化高频波场，这阻碍了对地震物理学的深入了解。该项目旨在开发专门为大地震破裂的高分辨率成像而设计的新一代地震台网。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：利用高分辨率的波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，从而直接了解破裂的复杂性。拟议的研究包括系统设计和规范的各个方面，这些方面可以通过对现实地震情景的计算建模、最优实验设计问题的数值解、阵列信号处理技术的发展和对现有数据集的分析来解决。研究人员将在具有现实震源复杂性、地壳非均质性和地形的地震情景中产生震源动力学和波传播，以提供概念证明，评估用多个阵列成像复杂震源过程的稳健性和分辨率。这些综合方案还将通过量化散射对波形相干性的影响作为频率和台站间距离的函数，并通过确定波场相干性的适当地貌指标，来指导确定阵列选址的实用准则。优化技术将被用来寻找在最大化震源成像分辨率和稳健性的同时最小化要部署的传感器总数的网络和阵列几何形状。世界上许多大城市地区都暴露在活动断层附近的地震危险中，其中震源复杂性的影响决定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以物理为基础的地震危险性评估方法的新趋势。该项目旨在通过设计由活动断层附近的多个强震传感器群组成的新一代地震网络，对我们成像大地震破裂传播细节的能力进行革命性的发展。这一进展旨在提高地震破裂过程的时空分辨率，从而检验关于地震物理的相互竞争的假说，从而促进我们对地震危害的定量理解。这一概念适时地建立在2004年帕克菲尔德地震单阵列记录的最新经验基础上，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日益普及。拟议的概念将被设计为在地震工程、常规地震台网分析和监测构造震动方面的多种额外应用。

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.