Bayesian three-dimensional seismic travel-time tomography for active- and passive-source seismic data using physics-informed neural network
Pith reviewed 2026-06-26 12:11 UTC · model grok-4.3
The pith
A neural representation of velocity structure enables tractable Bayesian 3D seismic travel-time tomography with active and passive sources.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central claim is that the neural velocity representation combined with function-space particle-based variational inference makes full Bayesian estimation tractable and data-efficient for three-dimensional travel-time tomography, while analytical marginalization of passive-source parameters allows joint use of active- and passive-source data without explicit joint sampling. Synthetic tests confirm recovery of known structures, and application to marine active-source and earthquake data off the Kii Peninsula yields an ensemble that resolves geological features, supplies spatially varying uncertainty, and reduces storage for the full posterior.
What carries the argument
Meshless neural representation of the velocity structure together with function-space particle-based variational inference and analytical marginalization of passive-source parameters.
If this is right
- The method recovers key geological features from a real marine dataset off the Kii Peninsula.
- It produces spatially varying, data-consistent uncertainty maps across the velocity volume.
- Posterior hypocenters shift 10-15 km mainly in the vertical direction, consistent with prior relocation studies.
- Storage cost for the entire ensemble of velocity models drops dramatically compared with grid-based storage.
Where Pith is reading between the lines
- The storage reduction from the neural representation could make ensemble modeling feasible at regional or global scales where grid storage is prohibitive.
- The analytical marginalization step might transfer to other geophysical inverse problems that treat source or instrument parameters as nuisance variables.
- Joint inversion with additional data types such as gravity could be tested by extending the same neural representation and inference scheme.
Load-bearing premise
The neural network must be expressive enough to capture the true velocity structure and the variational approximation must be close enough to the true posterior for the reported uncertainties to be reliable.
What would settle it
A side-by-side comparison, on a known synthetic 3D velocity model, of the posterior mean and credible intervals obtained by this method versus those obtained by a conventional grid-based Bayesian tomography code.
Figures
read the original abstract
Accurate 3D seismic velocity modeling through seismic travel-time tomography using both active- and passive-source data provides critical underpinning models for seismicity monitoring and hazard assessment. Because travel-time tomography is an inherently ill-posed inverse problem, UQ of the estimated models using Bayesian methods is also important for reliable downstream interpretations and analyses. However, Bayesian inference for 3D tomography based on conventional grid-based representations faces the ``curse of dimensionality'' and severe computational bottlenecks. Consequently, rigorous Bayesian UQ for margin-wide 3D travel-time tomography has remained largely unexplored. In this study, we propose a meshless 3D Bayesian travel-time tomography method that combines PINNs with a neural representation of the velocity structure, enabling tractable and data-efficient Bayesian inference through function-space particle-based variational inference. To efficiently integrate passive-source data into the Bayesian estimation of the velocity structure, we conduct analytical marginalization treating uncertain source parameters as nuisance parameters, with passive-source relocation carried out in post-processing. We validated the capability of our approach for 3D problems through synthetic experiments. Furthermore, we applied the method to a real-world dataset from marine active-source surveys and natural earthquakes off the Kii Peninsula, Nankai Trough. Our probabilistic 3D ensemble successfully resolves key geological features and provides data-consistent uncertainty maps. The posterior mean hypocenters shifted mainly in the vertical direction by 10-15 km, consistent with a previous relocation result. Finally, the neural representation drastically reduces storage requirements for the entire ensemble velocity model, highlighting the scalability and data efficiency of the proposed framework.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper claims to introduce a meshless 3D Bayesian travel-time tomography method that represents velocity structure via a neural network within a PINN framework, performs tractable Bayesian inference using function-space particle-based variational inference, and analytically marginalizes over uncertain passive-source parameters (with post-processing relocation). Synthetic experiments validate the approach for 3D problems, and application to marine active-source and earthquake data from the Nankai Trough yields an ensemble that resolves key geological features, supplies data-consistent uncertainty maps, and produces hypocenter shifts of 10-15 km vertically that match prior results; the neural representation is also noted to reduce ensemble storage requirements.
Significance. If the central claims hold, the work is significant because it provides a scalable route to rigorous Bayesian UQ for margin-scale 3D tomography, directly addressing the curse of dimensionality that has limited such analyses. Credit is due for the synthetic experiments that test the full pipeline and the real-data application to the Nankai Trough that demonstrates consistency with independent relocation results; the neural representation's storage reduction is a practical strength for ensemble dissemination.
minor comments (3)
- [§4.2] §4.2: the convergence diagnostics and sensitivity tests for the particle-based VI (e.g., number of particles, learning-rate schedules) are only summarized; explicit reporting of these choices and their effect on posterior spread would strengthen reproducibility.
- [Figure 7] Figure 7 and associated text: the vertical hypocenter shifts are stated as 10-15 km but the figure panels do not include error bars or the full posterior marginals for the relocated events; adding these would clarify the uncertainty quantification.
- [§3] The notation for the neural velocity field (e.g., the precise form of the PINN loss and the parameterization of the velocity network) is introduced in §3 but the explicit functional form is not restated when the marginalization step is derived; a short equation block linking the two would improve clarity.
Simulated Author's Rebuttal
We thank the referee for the constructive and positive review, which recognizes the significance of the meshless Bayesian PINN framework for 3D travel-time tomography and its application to the Nankai Trough dataset. The recommendation for minor revision is appreciated. No specific major comments are listed in the report, so we have no individual points requiring response or revision at this stage.
Circularity Check
No significant circularity
full rationale
The paper proposes a meshless Bayesian tomography method using PINNs for neural velocity representation and function-space particle-based variational inference, with analytical marginalization for passive sources. All load-bearing steps rely on standard PINN physics constraints and VI approximations that are validated directly against synthetic experiments and independent real-world Nankai Trough data; no derivation reduces by construction to fitted inputs, self-citations, or renamed ansatzes within the manuscript. The approach is self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
Reference graph
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