Role of lateral mantle flow in the evolution of subduction systems: insights from laboratory experiments

We present 3-D laboratory experiments constructed to investigate the pattern of mantle flow around a subducting slab under different boundary conditions. In particular we present a set of experiments, characterized by different conditions imposed at the trailing edge of the subducting plate (that is, plate fixed in the far field, plate detached in the far field, imposed plate motion). Experiments have been performed using a silicone slab floating inside a honey tank to simulate a thin viscous lithosphere subducting in a viscous mantle. For each set, we show differences between models that do or do not include the possibility of out-of-plane lateral flow in the mantle by varying the lateral boundary conditions. Our results illustrate how a subducting slab vertically confined over a 660-km equivalent depth can be influenced in its geometry and in its kinematics by the presence or absence of possible lateral pathways. On the basis of these results we show implications for natural subduction systems and we highlight the importance of suitable simulations of lateral viscosity variations to obtain a realistic simulation of the history of subductio

Unraveling topography around subduction zones from laboratory models

International audienceThe relief around subduction zones results from the interplay of dynamic processes that may locally exceed the (iso)static contributions. The viscous dissipation of the energy in and around subduction zones is capable of generating kilometer scale vertical ground movements. In order to evaluate dynamic topography in a selfconsistent subduction system, we carried out a set of laboratory experiments, wherein the lithosphere and mantle are simulated by means of Newtonian viscous materials, namely silicone putty and glucose syrup. Models are kept in their most simple form and are made of negative buoyancy plates, of variable width and thickness, freely plunging into the syrup. The surface of the model and the top of the slab are scanned in three dimensions. A forebulge systematically emerges from the bending of the viscous plate, adjacent to the trench. With a large wavelength, dynamic pressure offsets the foreside and backside of the slab by ~500 m on average. The suction, that accompanies the vertical descent of the slab depresses the surface on both sides. At a distance equal to the half-width of the slab, the topographic depression amounts to ~500 m on average and becomes negligible at a distance that equals the width of the slab. In order to explore the impact of slab rollback on the topography, the trailing edge of the plates is alternatively fixed to (fixed mode) and freed from (free mode) the end wall of the tank. Both the pressure and suction components of the topography are ~30% lower in the free mode, indicating that slab rollback fosters the dynamic subsidence of upper plates. Our models are compatible with first order observations of the topography around the East Scotia, Tonga, Kermadec and Banda subduction zones, which exhibit anomalous depths of nearly 1 km as compared to adjacent sea floor of comparable age

Opposite subduction polarity in adjacent plate segments

Active and fossil subduction systems consisting of two adjacent plates with opposite retreating directions occur in several areas on Earth, as the Mediterranean or Western Pacific. The goal of this work is to better understand the first-order plate dynamics of these systems using the results of experimental models. The laboratory model is composed of two separate plates made of silicon putty representing the lithosphere, on top of a tank filled with glucose syrup representing the mantle. The set of experiments is designed to test the influence of the width of plates and the initial separation between them on the resulting trench velocities, deformation of plates, and mantle flow. Results show that the mantle flow induced by both plates is asymmetric relative to the axis of each plate causing a progressive merging of the toroidal cells that prevents a steady state phase of the subduction process and generates a net outward drag perpendicular to the plates. Trench velocities increase when trenches approach each other and decrease when they separate after their intersection. The trench curvature of both plates increases linearly with time during the entire evolution of the process regardless their width and initial separation. The interaction between the return flows associated with each retreating plate, particularly in the interplate region, is stronger for near plate configurations and correlates with variations of rollback velocities. We propose that the inferred first-order dynamics of the presented analog models can provide relevant clues to understand natural complex subduction systemsPeer ReviewedPostprint (published version

The two-sided continental subduction of the Adria microplate (Mediterranean)

The recycling of the continental lithosphere back into the mantle significantly impacts the structure and dynamics of orogens, particularly in the central Mediterranean region. We demonstrate that variations in the rheological properties of the continental lithosphere, as revealed by high-resolution regional tomography, influence the style of continental subduction. We explain the geometry and evolution of the oppositely verging Apennines and Dinarides orogens, as given by contrasting subduction processes, such as underplating and continental delamination, affecting the same plate (the Adriatic microplate, or Adria). In the case of the Apennines, slab peel-back predominates during subduction, resulting in a steeply dipping slab. In contrast, the Dinarides experience flat subduction due to the underplating of continental material. These different mechanisms, influencing kinematics and surface processes, are governed by rheological heterogeneities and different buoyancies of the continental lithosphere

Tsunami at school. An experimental strategy to increase students’ risk perception

We tested a methodology for assessing high school students' tsunami risk perception and knowledge to improve their tsunami awareness. Our objective was to test whether the use of a structured questionnaire on tsunami risk perception could be used as a tool to assess students' improvement after a lesson on tsunamis. For this purpose, we involved about 100 students from four classes of a high school (Polo Liceale Statale "Lazzaro Spallanzani") in the town of Tivoli, in central Italy, about 20 km from Rome and 40 km from the seaside. We administered the questionnaire in three subsequent surveys (to 94, 96, and 109 students, respectively), the first of which without providing any information on which subject they would be dealing with. Students were asked to answer the 31 questions individually, each using her/his mobile phone during science class. After two months, all four classes were trained with a frontal lesson and a discussion on tsunami risk. Afterwards, we administered the questionnaire again and ran the second survey. Finally, we met the students one year later and administered the questionnaire again, then we compared the three survey results. The comparison shows that the students' risk knowledge and perception, which was generally very low in the first survey, improved significantly after the lesson and the relative discussion. Although this result was somewhat expected, it has been possible to confirm and quantify the improvement. According to studies conducted using similar methods [Gray and Di Loreto, 2016; Ayll & oacute;n et al., 2019], the active participation of students, the collaborative approach provided by teachers and researchers, and the use of a survey tool such as a questionnaire - which, despite being completed individually, fosters an environment of emotional sharing - all contribute to stimulating students' curiosity and facilitating their learning in traditional educational settings. We then administered the questionnaire to the same classes one year later. The outputs of the third survey show a partial decrease in students' awareness that nevertheless remains significantly better than in the first survey. This suggests that the students' involvement in the learning process through the questionnaire and through an active discussion after watching videos and pictures works well, but also that a periodic reminder by the science teachers is needed to maintain a constant level of risk awareness and perception. We propose to replicate this approach by involving teachers in the survey, providing them with a recorded lesson with all the basic elements, to be shown between the first and second administration of the questionnaire, and with periodic (yearly) reminders

Scaled seismotectonic models of megathrust seismic cycles through the lens of dynamical system theory

We investigate the physics of laboratory earthquakes in scaled seismotectonic models of megathrust seismic cycles. We study models of different sizes, materials, deformation rates, and frictional configurations. We use nonlinear time-series analysis tools to characterize the dynamics of the models. Observations are described, on average, by a low-dimension (<5), similar to slow slip episodes in nature and friction experiments performed with quartz powder. Results seem insensitive to the along-strike frictional segmentation of the megathrust. Using displacement as an input variable, the instantaneous dimension and the instantaneous extremal index vary through the seismic cycles. We notice the highest values of the instantaneous dimension associated with slip phases. Under specific circumstances, clear drops of the instantaneous extremal index can serve as an early indicator of slip episodes. Prediction horizons in the order of slip duration mirror similar predictability as for slow slip episodes in nature. We conclude that seismotectonic models are effective tools to study frictional physics despite their different spatio-temporal scales

Empirical Analysis of Global-Scale Natural Data and Analogue Seismotectonic Modelling Data to Unravel the Seismic Behaviour of the Subduction Megathrust

Subduction megathrusts host the Earth’s greatest earthquakes as the 1960 Valdivia (Mw9.5, Chile), the largest earthquake instrumentally recorded, and the recent 2004 Sumatra-Andaman (Mw9.2, Indonesia), 2010 Maule (Mw8.8, Chile), and 2011 Tohoku-Oki (Mw9.1,Japan) earthquakes triggering devastating tsunamis and representing a major hazard tosociety. Unravelling the spatio-temporal pattern of these events is thus a key for seismichazard assessment of subduction zones. This paper reviews the current state ofknowledge of two research areas–empirical analysis of global-scale natural data andexperimental data from an analogue seismotectonic modelling—devoted to study cause-effect relationships between subduction zone parameters and the megathrustseismogenic behavior. The combination of the two approaches overcomes theobservational bias and inherent sampling limitations of geological processes(i.e., shortness of instrumental and historical data, decreasing completeness andresolution with time into the past) and allows drawing appropriately from multipledisciplines with the aim of highlighting the geodynamic conditions that may favor theoccurrence of giant megathrust earthquakes

Transnational Access to Research Facilities: an EPOS service to promote multi-domain Solid Earth Sciences in Europe

Transnational access (TNA) allows cross-border, short-term and frequently free-of-charge access to world-class research facilities, to foster collaborations and exchanges of experience. Specifically, TNA aims to encourage open science and innovation and to increase the efficient and effective use of scientific infrastructure. Within EPOS, the European Plate Observing System, the Volcano Observatories and Multi-scale Laboratories communities have offered TNA to their high-quality research facilities through national and European funding. This experience has allowed the definition, design, and testing of procedures and activities needed to provide transnational access inn the EPOS context. In this paper, the EPOS community describes the main objectives for the provision of transnational access in the EPOS framework, based on previous experiences. It includes practical procedures for managing transnational access from a legal, governance, and financial perspective, and proposes logistical and technical solutions to effectively execute transnational access activities. In addition, it provides an outlook on the inclusion of new thematic communities within the TNA framework, and addresses the challenges of providing market-driven access to industry.publishedVersio

Use of Remdesivir in children with COVID-19: report of an Italian multicenter study

Background: COVID-19 is generally milder in children than in adults, however severe infection has been described in some patients. Few data are available on use of Remdesivir (RDV) in children, as most clinical trials focused on adult patients. We report a multicenter study conducted in 10 Italian Hospitals to investigate the safety of RDV in children affected by COVID-19. Methods: We collected the clinical data of children with COVID-19 treated with RDV between March 2020 and February 2022 in 10 Italian hospitals. Clinical data were compared according to a duration of RDV therapy more or less than 5 days. Linear regression model was used to determine the association of significant variables from the bivariate analysis to the duration of RDV therapy. Results: A total of 50 patients were included, with a median age of 12.8 years. Many patients had at least one comorbidity (78%), mostly obesity. Symptoms were fever (88%), cough (74%) and dyspnea (68%). Most patients were diagnosed with pneumonia of either viral and/or bacterial etiology. Blood test showed leukopenia in 66% and increased C-reactive protein (CRP) levels in 63% of cases. Thirty-six patients received RDV for 5 days, nine patients up to 10 days. Most children who received RDV longer were admitted to the PICU (67%). Treatment with RDV was well tolerated with rare side effects: bradycardia was recorded in 6% of cases, solved in less than 24 h after discontinuation. A mild elevation of transaminases was observed in 26% of cases, however for the 8%, it was still detected before the RDV administration. Therefore, in these cases, we could not establish if it was caused by COVID-19, RDV o both. Patients who received RDV for more than 5 days waited longer for its administration after pneumonia diagnosis. The presence of comorbidities and the duration of O2 administration significantly correlated with the duration of RDV therapy at the linear regression analysis. Conclusion: Our experience indicates that RDV against SARS-CoV-2 is safe and well-tolerated in pediatric populations at high risk of developing severe COVID-19. Our data suggest that delaying RDV therapy after diagnosis of pneumonia may be associated with a longer duration of antiviral therapy, especially in patients with comorbidities