Collaborative Research: Incorporating SPECFEM3D numerical seismograms in the Global CMT Project

这项研究将为改进地震的科学描述奠定基础，有利于地震统计学、地震层析成像、地震危险性、地震识别以及构造解释和分析的研究人员。这是使复杂和昂贵的数值计算结果可供多种应用和广泛用户使用的第一步。这项工作的重点是论证该方法的可行性，但该数据库和方法对于任何需要从任何地点的任意地震准确预测全球地震波场的研究都将是有价值的，而不需要昂贵的计算。两名研究生将接受地震科学、理论地震学和计算地球科学相结合的研究培训。这项为期两年的重点工作将：(1)开发一种计算、存储和访问最先进的地球三维层析模型的高保真长周期合成地震图的新方法；(2)将这些地震图纳入全球质心矩张量(CMT)计划的地震分析。目前，CMT合成地震记录是使用现代3D地球模型计算的，但其精度受到以下因素的限制：模式总和和面波射线理论的路径平均近似的有效性、对地面运动幅度和极化的不准确预测、以及其他未建模的影响、反演地震参数的偏差。在CMT分析中纳入高保真合成地震记录将改善震源的特征，并消除对不确定和偏差的关键来源的担忧。该团队将调整频谱元素波动方程解算器SPECFEM3D_Globe，以在全球震中网格上为大量台站位置生成核心地震图数据库，使用震源-接收器互易性来加快计算速度。网格上的核心地震图将以一种便于快速访问特定震源区域和全球地震台网台站的格式组织和存储。任意质心位置的核心地震图将通过空间内插有效地计算，其方式与完全正演计算的精度相匹配。CMT代码将被修改，以接收内插的SPECFEM3D_GLOBAL地震记录，测试将允许评估该方法和方法的成功。普林斯顿数字地震学小组和拉蒙特地震分析小组将联合评估波形内插的方法和保真度，开发访问(海量)全球波形数据库的实用格式，并评估这些开发的成功。该项目由地球科学部地球物理和仪器与设施计划联合支持。它也是由地球科学理事会和高级网络基础设施办公室合作资助的，以支持人工智能/ML和地球科学领域的开放科学活动。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This research will lay the groundwork for improvements in the scientific description of earthquakes, benefitting researchers in earthquake statistics, seismic tomography, seismic hazard, and seismic discrimination, as well as tectonic interpretation and analysis. This is the first step towards making the results of complex and expensive numerical calculations available for multiple applications and a wide range of users. This work focuses on demonstrating the feasibility of the methodology, but the database and method will be valuable for any research requiring accurate predictions of the global seismic wavefield from an arbitrary earthquake at any location without expensive computation. Two graduate students will be trained in research at the nexus of earthquake science, theoretical seismology, and computational Earth science.This two-year, focused effort will (1) develop a new method for calculating, storing, and accessing high-fidelity long-period synthetic seismograms for state-of-the-art 3D tomographic models of the Earth, and (2) incorporate these seismograms in the earthquake analysis of the Global Centroid-Moment-Tensor (CMT) Project. Currently, the CMT synthetic seismograms are calculated using modern 3D Earth models, but accuracy is limited by the validity of the path-average approximation for mode summation and surface-wave ray theory, inexact predictions of the amplitude and polarization of ground motion, and other unmodeled effects, bias retrieved earthquake parameters. The incorporation of higher-fidelity synthetic seismograms in the CMT analysis will improve the characterization of seismic sources and remove concerns about a key source of uncertainty and bias. The team will adapt the spectral-element wave-equation solver SPECFEM3D_GLOBE to generate a database of kernel seismograms on a global grid of hypocenters, for a large set of station locations, using source-receiver reciprocity to speed up the calculation. Kernel seismograms on the grid will be organized and stored in a format that facilitates rapid access to a particular source region and the stations of the Global Seismographic Network. Kernel seismograms for an arbitrary centroid location will be efficiently calculated by spatial interpolation, in a manner that matches the accuracy of the full forward calculation. The CMT code will be modified to ingest the interpolated SPECFEM3D_GLOBE seismograms and testing will allow the assessment of success of the approach and method. The Princeton numerical seismology group and Lamont earthquake-analysis group will jointly evaluate the approach and fidelity of the waveform interpolation, develop practical formats for accessing the (massive) database of global waveforms, and assess the success of these developments.This project is jointly supported by the Geophysics and Instrumentation and Facilities programs in the Division of Earth Sciences. It is also co-funded by a collaboration between the Directorate for Geosciences and Office of Advanced Cyberinfrastructure to support AI/ML and open science activities in the geosciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.