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1. Forecasting 3D Rupture Dynamics of the Alto Tiberina Low-Angle Normal Fault, Italy

   https://doi.org/10.26443/seismica.v4i2.1603  

   Marchandon, Mathilde; Gabriel, Alice-Agnes; Chiaraluce, Lauro; Tinti, Elisa; Casarotti, Emanuele; Biemiller, James (July 2025, Seismica)

   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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2. Fault valving and pore pressure evolution in simulations of earthquake sequences and aseismic slip

   https://doi.org/10.1038/s41467-020-18598-z  

   Zhu, Weiqiang; Allison, Kali L.; Dunham, Eric M.; Yang, Yuyun (December 2020, Nature Communications)

   null (Ed.)

   Abstract Fault-zone fluids control effective normal stress and fault strength. While most earthquake models assume a fixed pore fluid pressure distribution, geologists have documented fault valving behavior, that is, cyclic changes in pressure and unsteady fluid migration along faults. Here we quantify fault valving through 2-D antiplane shear simulations of earthquake sequences on a strike-slip fault with rate-and-state friction, upward Darcy flow along a permeable fault zone, and permeability evolution. Fluid overpressure develops during the interseismic period, when healing/sealing reduces fault permeability, and is released after earthquakes enhance permeability. Coupling between fluid flow, permeability and pressure evolution, and slip produces fluid-driven aseismic slip near the base of the seismogenic zone and earthquake swarms within the seismogenic zone, as ascending fluids pressurize and weaken the fault. This model might explain observations of late interseismic fault unlocking, slow slip and creep transients, swarm seismicity, and rapid pressure/stress transmission in induced seismicity sequences. 

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3. Geodetic Resolution of the Interplay Between Earthquakes and Slow Slip in the Hikurangi Margin

   https://doi.org/10.1029/2025JB033143  

   Maubant, Louise; Wallace, Laura M; Williams, Charles A; Michel, Sylvain; Klein, Emilie; Frank, William B (May 2026, Journal of Geophysical Research: Solid Earth)

   Abstract Interactions between slow slip and earthquakes remain poorly understood. We examine such an interaction in the central Hikurangi subduction zone where several moderate (Mw 4–5+) earthquakes occurred during a deep, 2‐year M7 slow slip event that started in 2021. We apply three different geodetic inversion methods to 6 years (2018–2024) of continuous GNSS data from 97 stations across New Zealand's North Island to retrieve the time‐dependent evolution of fault slip at depth: (a) a fixed‐window (1, 3, 6 months) static offset approach; (b) an Independent Component Analysis‐based inversion Method (ICAIM); and (c) an elastic block modeling approach utilizing TDefnode. All three methods yield a consistent, high‐resolution slip history in time and space. The 2021–2024 long‐term, deep slow slip event (equivalent 7.1–7.2) evolved with five to six distinct sub‐events, three of which represent an increase in slow slip event moment release within weeks after 4+ normal mechanisms (intraslab) earthquakes. In contrast, plate interface events ( 5) during this period do not seem to impact the slow slip event evolution. Static Coulomb modeling shows that cumulative slow slip increased stress by 40–60 kPa at the hypocenters of two plate‐interface earthquakes, suggesting that slow slip may have contributed to bringing these faults closer to failure. Our results reveal an asymmetric interplay between slow slip and seismicity: intraslab earthquakes modulate ongoing slow slip, while slow slip loading may trigger interface events, demonstrating two‐way interactions at considerably lower magnitudes than typically documented at other subduction zones. 

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4. Afterslip and Triggered Slip Following the 6 Feb 2023 Kahramanmaraş Earthquake Sequence, East Anatolian Fault, Türkiye

   https://doi.org/10.1007/978-3-031-87558-8_84  

   Bilham, Roger; Ayruk, Efe Turan; Turğut, Muhammed; İrgüren, Recep; Köküm, Mehmet; Elhisso, Abdulrahman; Farımaz, İlay; Doğan, Uğur (January 2025, Springer Nature Switzerland)

   The Mw7.8 and Mw7.6 Kahramanmaraş earthquakes of 6 Feb 2023 in SW Türkiye resulted in more 10 than 500 km of surface rupture with surface offsets locally exceeding 5 m. The earthquakes induced 5 mm of 11 triggered slip on the North Anatolian Fault at Ismetpasa, but only 1 mm of slip on the East Anatolian Fault at 12 Sivrice. The amplitude of both triggered slip events corresponds to the release a local creep slip-deficit that 13 had developed prior to the earthquakes. In March we installed ten carbon-rod extensometers across segments 14 of these faults to investigate whether surface-slip continues. Of these, seven recorded less than a few mm of 15 slip in the 6 months since the mainshocks revealing that the fault in these locations was now locked. The 16 remaining instruments identified two segments where fault slip continues. At Goksun near the northwestern 17 end of the Mw 7.6 rupture we recorded surface slip preceding local aftershocks, including a unique record of 18 accelerating slip preceding a local Mw4.7 aftershock. A second region of continued slip is found at the eastern 19 end of the Mw 7.8 rupture known as the Puturge gap, a segment of the fault that also arrested coseismic slip in 20 the Elazığ-Sivrice 2020 Mw 6.8 earthquake. The array of five extensometers installed here, including one 52 m 21 long, reveals >3.8 mm/yr of slip to be continuing at depth. In September, creepmeters 45 km apart recorded 22 what appears to be an eastward propagating creep event in the subsurface. To investigate the evolution of 23 subsurface slip here the five creepmeters have been supplemented with a 3-component 1-km-scale cGPS array 24 recording at 5Hz. 

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5. Episodic creep events on the San Andreas Fault caused by pore pressure variations

   https://doi.org/10.1038/s41561-018-0160-2  

   Khoshmanesh, Mostafa; Shirzaei, Manoochehr (June 2018, Nature Geoscience)

   Recent seismic and geodetic observations indicate that interseismic creep rate varies in both time and space. The spatial extent of creep pinpoints locked asperities, while its temporary accelerations, known as slow-slip events, may trigger earthquakes. Although the conditions promoting fault creep are well-studied, the mechanisms for initiating episodic slow-slip events are enigmatic. Here we investigate surface deformation measured by radar interferometry along the central San Andreas Fault between 2003 and 2010 to constrain the temporal evolution of creep. We show that slow-slip events are ensembles of localized creep bursts that aseismically rupture isolated fault compartments. Using a rate-and-state friction model, we show that effective normal stress is temporally variable on the fault, and support this using seismic observations. We propose that compaction-driven elevated pore fluid pressure in the hydraulically isolated fault zone and subsequent frictional dilation cause the observed slow-slip episodes. We further suggest that the 2004 Mw 6 Parkfield earthquake might have been triggered by a slow-slip event, which increased the Coulomb failure stress by up to 0.45 bar per year. This implies that while creeping segments are suggested to act as seismic rupture barriers, slow-slip events on these zones might promote seismicity on adjacent locked segments. 

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