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The seismic potential of active low-angle normal faults (LANFs, <30° dip) remains enigmatic under Andersonian faulting theory, which predicts that normal faults dipping less than 30° should be inactive. The Alto Tiberina fault (ATF) in the northern Apennines, a partly creeping 17°-dipping LANF, has not been associated with any historical earthquakes but could potentially generate earthquakes up to Mw~7. We investigate the mechanical preconditions and dynamic plausibility of large ATF earthquakes using 3D dynamic rupture and seismic wave propagation simulations constrained by multidisciplinary data from the Alto Tiberina Near Fault Observatory (TABOO-NFO). Our models incorporate the complex non-planar ATF fault geometry, including hanging wall secondary faults and a recent geodetic coupling model. We show that potential large earthquakes (up to Mw~7.4) are mechanically viable under Andersonian extensional stress conditions if the ATF is statically relatively weak (μs=0.37). Large earthquakes only nucleate on favorably oriented, steeper fault sections (dip ≥30°), and remain confined to the coupled portion, limiting earthquake magnitude. These ruptures may dynamically trigger an intersecting synthetic branch but are unlikely to affect more distant antithetic faults. Jointly integrating fault geometry and geodetic coupling is crucial for forecasting dynamic rupture nucleation and propagation.
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Effects of Dip Angle on Rupture Propagation Along Branch Fault Systems
ABSTRACT An important consideration in assessing seismic hazards is determining what is likely to happen when an earthquake rupture encounters a geometric complexity such as a branch fault. Previous studies showed parameters such as branch angle, stress orientation, and stress heterogeneity as key factors in the self-determined rupture path on branch faults. However, most of these studies were conducted in 2D or 3D with perfectly vertical faults. Therefore, in this study, we investigate the effects of dipping angle on rupture propagation along a branch fault system. We construct 3D finite-element meshes where we vary the dip angles (nine geometries in total) of the main and secondary faults, the stressing angle (Ψ=20°, 40°, and 65°), and the hypocenter location with nucleation on both the main and secondary segments. We find that for Ψ=40°, a rupture on the main fault is most likely to propagate across the branch intersection when the secondary fault is dipping. In addition, for Ψ=65°, a rupture on the secondary fault is most likely to propagate to the main fault when the secondary fault is shallowly dipping. This is caused by a fast rupture speed on the secondary fault and the dynamic stress effect that develops with the interaction of the free surface and the dipping secondary fault. These results indicate that dip angle is an important parameter in the determination of rupture path on branch fault systems, with potentially significant impact for seismic hazard, and should be considered in future dynamic rupture modeling studies.
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- Award ID(s):
- 2225216
- PAR ID:
- 10610315
- Publisher / Repository:
- Bulletin of the Seismological Society of America
- Date Published:
- Journal Name:
- Bulletin of the Seismological Society of America
- Volume:
- 115
- Issue:
- 1
- ISSN:
- 0037-1106
- Page Range / eLocation ID:
- 54 to 68
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1785/0120240031
