169 Advances and Challenges in Seismotectonic Studies in Slow-Deforming Regions

This session explores advances and challenges in understanding tectonic deformation in slow-deforming regions, integrating geodetic, geological, and modeling approaches to address earthquake hazards in seemingly stable yet vulnerable intraplate settings.

Tuesday, 21 October 2025
8:00 AM - 12:00 PM
HBGCC, 217D

Lithospheric Dynamics of Italy and Its Surrounding Regions

Paper number: 169-5
Program: Technical Sessions
Time: 9:10 AM – 9:25 AM

Authors

Abstract

The Italian Peninsula lies within a tectonically complex region where African-Eurasian convergence persists along with the motion of the Adria microplate, bounded by opposing subduction systems beneath the Apennines and the Dinarides. Although kinematics across the region has been well characterized, the relative contributions of different mechanical processes to present-day deformation remain uncertain. In this study, we investigate the extent to which gravitational potential energy (GPE) variations in the lithosphere and far-field tectonic loading contribute to observed deformation. We first modeled the present-day horizontal strain-rate field using GPS velocity data sets from 23 published works. This strain rate field aligns well with focal mechanism solutions, indicating that the kinematic model captures broad features of present-day crustal deformation. We then applied a thin viscous sheet approach to compute the vertically averaged deviatoric stress field associated with GPE variations. We also solved for a best-fit boundary condition solution that when added to the GPE contribution provides a best fit with the stress indicators. The sum of these two deviatoric stress field solutions forms our total dynamic model. The model predicts NE-SW tensional stresses along the Apennines driven by gravitational collapse. To the east, the regime transitions to ENE-WSW compression across the Adriatic Sea and western Dinarides, primarily from GPE gradients, with additional far-field tectonic contributions. Tensional stresses along the Apennine continue south into Calabria, where the principal stresses rotate clockwise toward E-W, and further into eastern Sicily as a trans-tensional field, consistent with moment tensors there. Offshore northern Sicily, GPE and far-field stresses predict NNE-SSW and NW-SE compression, respectively, summing to near due N-S compression consistent with thrust focal mechanisms there. In the Po Plain, the model predicts reverse-faulting earthquakes with strikes ~N90°E. While our dynamic model broadly explains the kinematics, some discrepancies remain. For instance, GPE-associated stress peaks lie slightly west of the Apennine crest, offset from zone of highest extensional strain. We interpret this as evidence for a weaker lower crust beneath the Apennines, where extension is concentrated due to thick crust and elevated horizontal thermal gradients. From the stress and strain-rate fields, we estimate effective lithospheric viscosity, revealing low-viscosity zones that correlate with the thickest crust beneath the Apennines, suggesting that the weak rheological structure there controls where extensional strain is accommodated.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412749

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