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Optimized experimental design strategies for ERT monitoring of transient flow processes

Geophysical Journal International - Thu, 12/18/2025 - 00:00

SummaryMonitoring subsurface fluid transport processes using electrical resistivity tomography (ERT) gained attention due to its sensitivity to variations in fluid content and temperature. Capturing these dynamic processes, such as tracer transport or pollutant dispersion, requires not only advanced imaging techniques but also efficient data acquisition strategies to ensure high-resolution and cost-effective monitoring. This study advances Optimal Experimental Design (OED) for transient flow monitoring using ERT. We developed three different strategies based on the Compare-R algorithm, and present as well as compare their results. By optimizing the selection of measurement configurations, these strategies aim to maximize the information content of the acquired data while minimizing redundancy and acquisition costs. The data-driven approach uses data from prior time steps to generate focusing masks. The model-driven approach incorporates transport models to target critical areas, and the hybrid approach combines both methods, iteratively refining the transport model based on the acquired data. We use synthetic studies to demonstrate the model-driven strategy”s advantage in identifying transport-affected areas, especially for rapid processes or longer monitoring intervals. The data-driven approach performs well when masked and process-affected areas overlap, but struggles with spatial delays otherwise. The hybrid OED effectively combines the strengths of both methods, detecting discrepancies between modeled and observed fluid flow, and refining transport simulations for subsequent steps, thereby ensuring reliable optimization for dynamic monitoring scenarios.

Splitting constraints in regions with sparse coverage: Uniformly processed PS measurements from a massive global dataset

Geophysical Journal International - Thu, 12/18/2025 - 00:00

SummaryShear wave splitting, caused by seismic anisotropy, provides insights into convective processes in the mantle. While upper mantle anisotropy beneath the continents is well-resolved with high lateral resolution, its characterization beneath the oceans remains limited due to the paucity of seismic stations. In this study, we leverage the sensitivity of P waves that convert to S upon reflection at the surface (PS) to infer seismic anisotropy near their bounce point. We measure PS splitting automatically from a global dataset that includes all earthquakes with magnitudes ≥5.9 from January 1995 to present, collected from 25 datacenters, totaling approximately 5,800 events and 18 million three-component seismograms. After careful quality control, we obtain 889 PS splitting measurements from this dataset, mostly for regions without other splitting constraints. These regions include the South China Sea, the Philippine Sea, the western Pacific Ocean, the western Atlantic Ocean near the Caribbean, and the South Atlantic Ocean. Where independent SKS constraints are available, these are in general agreement with our PS results. Comparisons of PS fast directions to azimuthal seismic anisotropy derived from surface waves and the direction of absolute plate motion (APM) show a dominant contribution of asthenospheric deformation to the measurements. This agreement is particularly pronounced beneath the oceans, away from subduction zones, for instance, across much of the Pacific basin. In contrast, splitting patterns near subduction zones are generally more complex: fast directions are most often trench-parallel or oblique, and only rarely trench-perpendicular, suggesting that a trench-parallel component of shear deformation is commonly generated in subduction settings, as commonly inferred from SKS splitting. We make all measurements publicly available as a data product, along with detailed metadata to enable future work.

Satellite data reveals new insights into sustainable groundwater usage in the Hollywood Basin

Phys.org: Earth science - Wed, 12/17/2025 - 20:37

Groundwater is a critical resource in Southern California, where long-term drought and climate change place increasing pressure on local aquifers. Some regions, like the Hollywood Basin (a small region in and around the West Hollywood neighborhood), are increasing their reliance on these aquifers in order to reduce the amount of water imported from elsewhere. A new Caltech-led study provides the most detailed picture to date of how the Hollywood Basin responds to groundwater usage, revealing that current estimates of sustainable groundwater yield may be too high.