Diagram from the paper.
The developed methodology was able to identify the fault structures associated with the rupture of two earthquake sequences with mainshocks ML 3.2-3.3. This schematic illustration shows the difference between the reactivated Y-shears representing the main fault planes (illuminated by dark blue hypocenters) and P-shears, associated with a contractional stepover (illuminated by orange hypocenters). The method adjusts the structures and geometries by evaluating a number of fault properties. The variation of selected fault properties for the different parts of the faults are shown to the right, generally matching the observations for both sequences. Credit: Truttmann et al. [2023], Figure 10
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Solid Earth

Accurate information about the geometry of faults at depth is of high importance for addressing several geophysical applications, from obtaining details about earthquake rupture and arrest to monitoring hydraulic stimulations. And yet, imaging fault structure in 3D remains a challenge, with the current existing methods not achieving detailed spatial resolution.

Truttmann et al. [2023] present a new methodology to image in high resolution the 3D architecture of seismically active faults. Their methodology employs high resolution seismicity catalogs containing the hypocentral locations of seismic events together with their magnitude, and combines nearest neighbor learning with principal component analysis to find the best fault geometries fitting the seismicity. The applications of this methodology to two seismic sequences, including mainshocks of ML 3.2-3.3, show that fault step-overs are governed by lower seismic migration velocities and fault locking processes.

The systematic application of such methodology to different seismicity sequences could significantly improve our understanding of how the 3D fault architecture affects earthquake behavior, fault deformation processes, and fault reactivation.

Citation: Truttmann, S., Diehl, T., & Herwegh, M. (2023). Hypocenter-based 3D Imaging of Active Faults: Method and Applications in the Southwestern Swiss Alps. Journal of Geophysical Research: Solid Earth, 128, e2023JB026352. https://doi.org/10.1029/2023JB026352

—Patricia Martínez-Garzón, Associate Editor, JGR: Solid Earth

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