The geometry and stresses of a fault zone often determine where fractures start, how they grow, and where they stop.
In a new study¹, we used deep-learning polarity picks and SKHASH to build a dense catalog of over 16,000 well-constrained focal mechanisms for the 2016–2017 Amatrice-Visso-Norcia sequence in central Italy. We were able to show that normal fault kinematics dominate at shallower depths (2-9 km), with a ~2 km thick near-horizontal basal shear zone with highly variable kinematics at 8-10 km depth. The mainshocks nucleated near intersections between this zone and the steep normal faults.
Building on this, our next work² translates that kinematic mosaic into a finely resolved stress field. We inverted more than 13,000 of the best mechanisms in space and time and find strong small-scale heterogeneity, local rotations of SHmax, and a depth-dependent admixture of transtensional components. These patterns follow the two structural elements above and matter for hazard models: mapping structural boundaries and depth helps constrain rupture development and expected ground motion.
The papers can be accessed here:
[1] Meier, M.-A., Lanza, F., Martínez-Garzón, P., & Chiaraluce, L. (2025). Insights into Extensional Tectonics from a Large Deep Learning Focal Mechanism Catalog. Bulletin of the Seismological Society of America, 1–15. https://doi.org/10.1785/0120250103
[2] Martínez-Garzón, P., Meier, M.-A., Collettini, C., Lanza, F., & Dresen, G. (2025). Stress Heterogeneities Governed by Fault Structure and Stress Transfer: The 2016–2017 Central Italy Seismic Sequence. Journal of Geophysical Research: Solid Earth, 130, e2024JB029763. https://doi.org/10.1029/2024JB029763