Yujiang Xie

Dr. Yujiang Xie is a Research Fellow Scientist at the Institute for Geophysics (UTIG), Jackson School of Geosciences, The University of Texas at Austin. He previously served as a Research Fellow at the University of Southampton (UK) and received his Ph.D. from the University of Hamburg (Germany) in 2017.

His work spans theoretical and computational seismology and applied mathematics, with an emphasis on partial differential equations, seismic wave propagation, full-waveform modeling and inversion (FWI), and high-performance scientific computing. Early contributions include advances in 3-D common-reflection-surface imaging via global optimization (Xie & Gajewski, 2018, 2019), seismic data enhancement using wavefront attributes (Xie & Gajewski, 2017), and wavefront tomography grounded in ray theory and wavefront attributes (Xie et al., 2018). He developed the packages to compute 3-D wavefront attributes using global optimization and verified these attributes with kinematic and dynamic ray tracing. These wavefront attributes are useful, for instance, for prestack seismic data enhancement, reflection and diffraction separation, seismic wavefront tomography, and seismic source localization. Since 2018, Dr. Xie has focused on finite-difference FWI, adjoint-state methodology, and spectral-element adjoint tomography. He developed an on-the-fly second-order adjoint-state method within a spectral-element framework (Xie et al., 2021) that simultaneously computes gradients and full Hessian kernels on the fly, substantially reducing disk space and I/O requirements (e.g., from 1000 TB down to 1 TB). He presented the Quad spectral-element method (QuadSEM). Building on spectral-element theory, he formulated shifted Fréchet and Hessian-kernel expressions for anelastic media (Xie et al., 2023), which support both frequency-dependent and frequency-independent Q Fréchet and Q Hessian kernel calculations. Beginning in 2024, his research expanded to anisotropic FWI at the reservoir scale and anisotropic adjoint tomography at the continental and global scales, exploring parameterizations and sensitivity analyses to mitigate trade-offs, enhance imaging fidelity, and derive full Hessian-kernel expressions for anisotropic media. In 2025, he extended his work to the mathematical foundations of deep learning in seismology, aiming to rigorously establish the mathematical and numerical equivalence between selected machine-learning approaches and classical inverse methods. Dr. Xie collaborates actively with PIs at Oxford, Toronto, Princeton, Berkeley, MIT-WHOI, and numerous institutions.

Collaborators:
1. Prof. Dirk Gajewski, University of Hamburg, PhD supervisor (Germany)
2. Prof. Catherine A. Rychert, MIT-WHOI, Postdoc PI (USA)
3. Prof. Nicholas Harmon, MIT-WHOI, Postdoc PI (USA)
4. Prof. Mike Kendall, University of Oxford, Postdoc Co-PI (UK)
5. Prof. Qinya Liu, University of Toronto, Postdoc Co-PI (Canada)
6. Prof. Barbara A. Romanowicz, UC Berkeley (USA)
7. Prof. Mrinal K. Sen, UT Austin (USA)
8. Prof. Jeroen Tromp, Princeton University (USA)
9. Many others

Recommended books:
1. Cerveny, V. (2001). Seismic Ray Theory. Cambridge University Press.
2. Dahlen, F. A., & Tromp, J. (1998). Theoretical Global Seismology. Princeton University Press.
3. Igel, H. (2016). Computational Seismology: A Practical Introduction. Oxford University Press.

Selected work:
Xusong Yang, Yujiang Xie, Catherine A. Rychert, Nicholas Harmon, Saskia Goes, Andreas Rietbrock, Lloyd Lynch, and VoiLA Working Group, 2025. Seismic imaging of a basaltic Lesser Antilles slab from ancient tectonics, Nature, 640, 697-701. https://doi.org/10.1038/s41586-025-08754-0
Media coverage: https://nature.altmetric.com/details/175978347/news

Tianshi Liu, Kai Wang, Yujiang Xie, Bin He, Ting Lei, Nanqiao Du, Ping Tong, Yingjie Yang, Catherine A. Rychert, Nicholas Harmon, Giovanni Grasselli, Qinya Liu, 2024. Cube2sph: A Toolkit Enabling Flexible and Accurate Continental-scale Seismic Wave Simulations using the SPECFEM3D Package, Computers & Geosciences, 190, 105644. https://doi.org/10.1016/j.cageo.2024.105644

Yujiang Xie, Catherine Rychert, Nicholas Harmon, 2023. Elastic and anelastic adjoint tomography with and full Hessian kernels, Geophysical Journal International , 234, 1205-1235. https://doi.org/10.1093/gji/ggad114

Peng Yang, Dirk Gagewski and Yujiang Xie, 2023. Gaussian-weighted cross-correlation imaging condition for microseismic source localization, Geophysics, 88, 1-96. https://doi.org/10.1190/geo2022-0455.1

Nicholas Harmon, Catherine Rychert, Yujiang Xie and Bogiatzis Petros, 2022 Analytic P-to-S and S-to-P scattered wave sensitivity kernels, Geochemistry, Geophysics, Geosystems , 23, e2021GC010290. https://doi.org/10.1029/2021GC010290

Bogiatzis Petros, Catherine Rychert, Nicholas Harmon and Yujiang Xie, 2022. Fast calculation of spatial sensitivity kernels for converted waves in arbitrary heterogeneous media using graph theory, Geophysical Journal International , 230, 654-672. https://doi.org/10.1093/gji/ggac078

Yujiang Xie, Catherine Rychert, Nicholas Harmon, Qinya Liu and Dirk Gajewski, 2021. On-the-fly Full Hessian Kernel Calculations Based upon Seismic Wave Simulations, Seismological Research Letters , 92(6), 3832-3844. https://doi.org/10.1785/0220200410

Lei Li, Jingquan Tan, Dazhou Zhang, Ajay Malkoti, Ivan Abakumov and Yujiang Xie, 2021. FDwave3D: A MATLAB solver for the 3D anisotropic wave equation using the finite-difference method, Computational Geosciences, 25, 1565-1578. https://doi.org/10.1007/s10596-021-10060-3

Yujiang Xie and Dirk Gajewski, 2019. Reliability of data-driven wavefront attributes in laterally heterogeneous media, Geophysics, 84(3), O49-O62. https://doi.org/10.1190/geo2018-0382.1

Lei Li, Jingquan Tan, Yujiang Xie, Yuyang Tan, Jan Walda, Zhengguang Zhao and Dirk Gajewski, 2019. Waveform-based microseismic location using stochastic optimization algorithms: A parameter tuning workflow, Computers & Geosciences, 124, 115-127. https://doi.org/10.1016/j.cageo.2019.01.002

Yujiang Xie and Dirk Gajewski, 2018. 3-D wavefront attribute determination and conflicting dip processing, Geophysics, 83(6), V325-V343. https://doi.org/10.1190/geo2017-0792.1

Yujiang Xie and Dirk Gajewski, 2017. 5-D interpolation with wavefront attributes, Geophysical Journal International, 211, 897-919. https://doi.org/10.1093/gji/ggx334

Yujiang Xie and Gao Liu, 2015. Resolution enhancement of non-stationary seismic data using amplitude-frequency partition, Geophysical Journal International, 200, 773-778. https://doi.org/10.1093/gji/ggu401

Yujiang Xie and Gao Liu, 2014. Predicting the distribution of reservoirs by combining variable wavelet model of seismograms with wavelet edge analysis and modeling, Journal of Applied Geophysics, 101, 116-123. https://doi.org/10.1016/j.jappgeo.2013.12.005