Tectonics and seismicity in the Northern Apennines driven by slab retreat and lithospheric delamination

Understanding how long-term subduction dynamics relates to the short-term seismicity and crustal tec tonics is a challenging but crucial topic in seismotectonics. We attempt to address this issue by linking long-term geodynamic evolution with short-term seismogenic deformation in the Northern Apennines. This retreating subduction orogen displays tectonic and seismogenic behaviors on various spatiotemporal scales that also characterize other subduction zones in the Mediterranean area. We use visco-elasto-plastic seismo-thermo-mechanical (STM) modeling with a realistic 2D setup based on available geological and geophysical data. The subduction dynamics and seismicity are coupled in the numerical modeling, and driven only by buoyancy forces, i.e., slab pull. Our results suggest that lower crustal rheology and lithospheric mantle temperature modulate the crustal tectonics of the Northern Apennines, as inferred by previous studies. The observed spatial distribution of upper crustal tectonic regimes and surface displacements requires buoyant, highly ductile material in the subduction channel beneath the internal part of the orogen. This allows protrusion of the asthenosphere in the lower crust and lithospheric delamination associated with slab retreat. The resulting surface velocities and principal stress axes generally agree with present-day observations, suggesting that slab delamination and retreat can explain the dynamics of the orogen. Our simulations successfully reproduce the type and overall distribution of seismicity with thrust faulting events in the external part of the orogen and normal faulting in its internal part. Slab temperatures and lithospheric mantle stiffness affect the cumulative seismic moment release and spatial distribution of upper crustal earthquakes. The properties of deep, sub-crustal material are thus shown to influence upper crustal seismicity in an orogen driven by slab retreat, even though the upper crust is largely decoupled from the lithospheric mantle. Our simulations therefore highlight the effect of deep lower crustal rheologies, self-driven subduction dynamics and mantle properties in controlling shallow deformation and seismicity

Morpho-chemical characterization of individual ancient starches retrieved on ground stone tools from Palaeolithic sites in the Pontic steppe

Despite the extensive literature on the retrieval of digestible starches from archaeological contexts, there are still signifcant concerns regarding their genuine origin and durability. Here, we propose a multi-analytical strategy to identify the authenticity of ancient starches retrieved from macrolithic tools excavated at Upper Paleolithic sites in the Pontic steppe. This strategy integrates the morphological discrimination of starches through optical microscopy and scanning electron microscopy with single starch chemo-profling using Fourier transform infrared imaging and microscopy. We obtained evidence of aging and biomineralization in the use-related starches from Palaeolithic sites, providing a methodology to establish their ancient origin, assess their preservation status, and attempt their identifcation. The pivotal application of this multidisciplinar approach demonstrates that the macrolithic tools, from which starches were dislodged, were used for foodprocessing across the Pontic Steppe around 40,000 years ago during the earliest colonization of Eurasia by Homo sapien

Coupled, Physics-Based Modeling Reveals Earthquake Displacements are Critical to the 2018 Palu, Sulawesi Tsunami

The September 2018, Mw 7.5 Sulawesi earthquake occurring on the Palu-Koro strike-slip fault system was followed by an unexpected localized tsunami. We show that direct earthquake-induced uplift and subsidence could have sourced the observed tsunami within Palu Bay. To this end, we use a physics-based, coupled earthquake–tsunami modeling framework tightly constrained by observations. The model combines rupture dynamics, seismic wave propagation, tsunami propagation and inundation. The earthquake scenario, featuring sustained supershear rupture propagation, matches key observed earthquake characteristics, including the moment magnitude, rupture duration, fault plane solution, teleseismic waveforms and inferred horizontal ground displacements. The remote stress regime reflecting regional transtension applied in the model produces a combination of up to 6 m left-lateral slip and up to 2 m normal slip on the straight fault segment dipping 65∘ East beneath Palu Bay. The time-dependent, 3D seafloor displacements are translated into bathymetry perturbations with a mean vertical offset of 1.5 m across the submarine fault segment. This sources a tsunami with wave amplitudes and periods that match those measured at the Pantoloan wave gauge and inundation that reproduces observations from field surveys. We conclude that a source related to earthquake displacements is probable and that landsliding may not have been the primary source of the tsunami. These results have important implications for submarine strike-slip fault systems worldwide. Physics-based modeling offers rapid response specifically in tectonic settings that are currently underrepresented in operational tsunami hazard assessment

Toward Recognizing the Waveform of Foreshocks

Abstract The identification of seismic precursors remains a fundamental challenge. Foreshocks are often indistinguishable from regular seismic sequences, making it difficult to determine whether they precede a larger rupture. We show that the ground velocity envelope recorded after several Mw6+ foreshocks exhibits an anomalous sawtooth pattern, distinct from typical post‐mainshock signals. This pattern suggests the presence of rate‐weakening fault patches approaching instability, promoting stress transfer and aftershock migration into neighboring critically stressed regions. A similar signature was observed in multiple events, including the 2011 Mw9.1 Tohoku earthquake and the 2014 Mw8.1 Iquique sequence. To assess the systematic occurrence of this anomaly, we introduce an index Q based on the first 45 min of waveform data. Analyzing 68 M6+ earthquakes in selected regions since 2011, we find that 10 of 11 foreshocks preceding a larger event exhibit anomalous Q values, while only 4 of 57 other events show similar behavior. These findings suggest that foreshock waveform characteristics may provide insight into seismic rupture processes

Slab Rollback Orogeny Model: A Test of Concept

Buoyancy forces associated with subducting lithosphere control the dynamics of convergent margins. In the postcollisional stage these forces are significantly reduced, yet mountain building and seismicity are ongoing, albeit at lower rates. We leverage advances of a newly developed seismo‐thermo‐mechanical modeling approach to simulate tectonic and seismicity processes in a self‐driven subduction and continental collision setting. We demonstrate that the rearrangement of forces due to slab breakoff, in the postcollisional stage, causes bending and rollback of the residual slab, suction forces, and mantle traction at the base of the upper plate, while stress coupling transfers to the shallow crust. Our results provide an explanation for the postcollisional evolution of the Central Alps, where the so‐called Slab Rollback Orogeny model explains the slow yet persistent upper plate advance, the height of the mountain range, and a seismicity pattern consistent with the different tectonic regimes throughout the orogen

Are terrestrial plumes from motionless plates analogues to Martian plumes feeding the giant shield volcanoes?

On Earth, most tectonic plates are regenerated and recycled through convection. However, the Nubian and Antarctic plates could be considered as poorly mobile surfaces of various thicknesses that are acting as conductive lids on top of Earth's deeper convective system. Here, volcanoes do not show any linear age progression, at least not for the last 30 myr, but constitute the sites of persistent, focused, long-term magmatic activity rather than a chain of volcanoes, as observed in fast-moving plate plume environments. The melt products vertically accrete into huge accumulations. The residual depleted roots left behind by melting processes cannot be dragged away from the melting loci underlying the volcanoes, which may contribute to producing an unusually shallow depth of oceanic swells. The persistence of a stationary thick depleted lid slows down the efficiency of melting processes at shallow depths. Numerous characteristics of these volcanoes located on motionless plates may be shared by those of the giant volcanoes of the Tharsis province, as Mars is a one-plate planet. The aim of this chapter is to undertake a first inventory of these common features, in order to improve our knowledge of the construction processes of Martian volcanoes