Prediction of subduction earthquakes mostly relies on interplate coupling models providing patterns of slip deficit between tectonic plates. These coupling patterns are interpreted in the framework of elasto-dynamics and rate-and-state friction laws. However, this framework has been challenged by recent observations, showing that rheological and geometrical complexities have to be taken into account to understand the megathrust mechanics. To account for these complexities, dynamic thermo-mechanical simulations, incorporating equivalent rate-and-state friction laws have emerged. However, they were run at the whole subduction scale impeding a precise study of the forearc deformation to be compared with its short-term deformation. To understand how these complexities affect the megathrust behaviour, we here propose to develop a visco-elasto-plastic thermo-mechanical model at forearc scale. This model will incorporate thermal evolution and its feedback on rock rheology, and will be able to drop the time steps at key geological moments of the simulations to capture slow motion of earthquake cycle conditioned by loading and structures that are self-consistent with long-term deformation. After the model development, we will explore the effect of different initial conditions (such as thermal state, sediment cover thickness, mineralogy transitions, accretion vs erosive prism, subducting features) on the short- and long-term deformation of the forearc. We will then investigate selected profiles along well-instrumented subduction zones, to provide mechanical explanations to the observed short-term deformation. We will run simulations at the seismic cycle scale in these regions and then along less constrained subduction zones to improve their seismic hazard assessment.

The Alboran Sea is one of the most geologically active areas in the Mediterranean where submarine landslides with a tsunamigenic potential are present. The links between landslides, seismicity and tectonic movements are not obvious: the distribution of epicentres does not reflect the distribution of landslides; the mobilised material of target landslides is larger on gentle slopes. The stability of slopes seems to be controlled by interactions between several factors. The target area holds a variability in the distribution and type of slope instabilities. It therefore constitutes an appropriate key area to investigate how factors such as bottom current contourite deposition, fluid seepage and tectonic uplift precondition the stability of slopes and their link with seismic activity. The ALBAMAR project aims at understanding submarine landslides occurrence and frequency, to constrain the probability of future slope failures in the southern part of the Alboran Sea, for assessing landslide and tsunami hazard in this densely coastal populated region.

Over the past decades, it has become clear that the deadliest and the costliest earthquakes are related to poor hazard assessment. Understanding what is an earthquake, when and where it may strike is a fundamental step to mitigate seismic risk all over the world. To be predictive, two pieces of information are compulsory: we need to know the physical properties of the fault and how much energy, ready to be released seismically, is stored in the surrounding rocks. While, since the 1960’s, a thorough effort has been made to understand the frictional behavior of faults in the brittle crust, surprisingly very little has been undertaken to assess the energy build up and how it may vary through time. Indeed, in seismotectonics, out of simplicity, the host medium is considered elastic, i.e. it never evolves. Yet geological and geophysical observations of fault zones tell a different story. They suggest that on top of the ``seismic cycle” there is a superimposed ``cycle” where the properties of the surrounding rocks evolve according to the fault slip dynamics. Hence, in turn, it influences how much energy can be stored and how it is released (seismically or aseismically). Yet, the models we use nowadays do not take into account this INTERTWINEd dynamics. To fully address this shortcoming, a multidisciplinary approach is necessary. I propose to develop the next generation of models that will account for this variation of energy build up over the seismic cycle. I will bring a particular attention on off-fault fracture growth and healing, and on fluids circulation. Conjointly, acquisition of geodetic and field data will help to constrain and cross-validate the numerical models. For accessibility, we will focus on continental faults in Taiwan, India and USA. For too long, communities have been analyzing the same problem separately. Upon completion, this project will provide a unified framework to study active fault zones and provide a physics-based tool to assess seismic risk.

Earthquakes are the natural hazard with greatest impact on the world's populations, yet predicting when and where they will occur remains a key challenge. This is because earthquake triggering, and the consequent seismic and tsunami hazard potential, depends on the interplay of a range of regional and local factors that remain poorly constrained. This is particularly the case in broad zone of slow deformation of continental crust, such as along the African-Eurasian plate boundary (e.g. Alboran Sea; < 5 mm/a). In such intracontinental contexts of slow deformation, it is difficult to precisely constrain where elastic energy accumulates, when and how it is released and thus the resulting seismic hazard. The purpose of the ALBANEO project is to address key open questions regarding the functioning over time of an intra-continental fault system along an incipient plate boundary in the Alboran Sea, and its potential future evolution and implication for regional seismic and tsunami hazards. The project focuses on the Al Idrissi active Fault System in the Alboran Sea as a case study. The ALBANEO project proposes to use data from the 2021 ALBACORE oceanographic cruise (R/V Pourquoi Pas?, 2021) to obtain results on the distribution and style of deformation at and near the seafloor, on the mechanical and thermal properties of fault compartments, on their dynamic interactions with sedimentation, on seismic activity through time, and on past and present-day fluid flow through faults. The cruise targeted active fault segments hosted within Quaternary sedimentary systems including deep sea contourites and shelf sedimentary wedges. Specific questions to be addressed using data acquired during ALBACORE are: • What insights can be obtained from the sedimentary record about the tectonic control of depositional processes and seafloor morphology, slip rates and fault activity, and to build an accurate age model? • Over Quaternary timescales, where, when and how is the accumulated elastic energy released during earthquakes? • What are the physical properties of sediments and the dynamics and history of fluid flow of fault segments within the strike-slip system? Addressing these questions require a multidisciplinary and multi-scale approach. The ALBANEO project will use geophysical, geological, geotechnical, geochemical and geothermal data acquired during the ALBACORE oceanographic cruise. During ALBANEO, analyses of seismic profiles correlated to available sediment cores and in-situ data will allow us to construct the first accurate age model to evaluate slip rate and date co-seismic events that have affected the Alboran region during the last 130ka, as well as define a sequence stratigraphy model for the shelf wedge (Tasks #1 and #3). Geophysical, geochemical and geotechnical data will be used to constrain physico-chemical properties and fluid dynamics along the Al Idrissi Fault segments (Task #2). These analyses will provide inputs to kinematic and mechanical modelling of fault dynamics and strain partitioning (Task #4). Project results will be disseminated through a data management plan (Task #5). The results of ALBANEO will afford an improved understanding of earthquake triggering in a slow-slip and diffuse deformation setting. The study has strong societal interests for coastal communities and infrastructure as it will result in improved assessments of the risks related to earthquake, tsunamis and submarine landslide hazards.

Active fault zones are complex objects with physical properties and slip behavior constantly evolving in response to external mechanical constraints. In the brittle part of the crust, the deformation is rather localized, and the accumulated stresses are released by slip along the fault plane. Geodetic techniques, combined with seismology, have documented the spatial and temporal variability of slip modes at seismogenic depth (0-40 km). Slip rate on faults span a continuum ranging from mm/yr to m/s, and these seismic and aseismic conditions are not necessarily stable over time. Additionally, numerous studies have highlighted the strong coupling existing between the main fault plane and the surrounding medium. They suggest that on top of the “seismic cycle” there is a superimposed “cycle” where the properties of the fault zone evolve according to the sliding dynamics, which in turn influences the mode of deformation. However, the physics of the processes that controls these behaviors, and how it evolves in space and time, remains poorly understood. This severely limits our ability to assess the potential size, magnitude and recurrence of earthquakes on active faults. Therefore, to improve our understanding of active fault zones, seismic/aseismic slip and the evolving physical properties of the bulk must be studied as a unique system of stress accommodation and no longer as two distinct entities. However, to address this problem, the current numerical models of seismic cycle cannot be used. Deformation in the brittle crust is modeled by two planes, sliding one against the other and whose behavior is controlled by the properties of the interface only. Moreover, such models usually require to attribute constant properties (pressure, temperature, petrology, microstructure), that do not evolve with the deformation. Therefore, by ignoring the contribution of the evolving medium, the complex feedback, as described above, is not taken into account. It calls for a thorough research effort directed towards the development of a new generation of models that includes this entangled dynamic. With the help from the ANR program, we propose to study the evolution of the thermo-hydro-mechanical (THM) properties as a function of sliding and the counter-impact on the deformation mode. This project will provide a concerted view on fault behavior using a combined observational and theoretical approach. Developing new numerical tools, we will determine the first-order effect of the spatiotemporal variations of temperature, elastic properties and pore pressure by studying them separately. The theoretical development will be tested according to their ability to reproduce field data. For this part of the project, we will highly rely on previously published work and current projects the team-members are involved in (Taiwan, Philippines, Aegean region). Models will also help to identify the relevant parameters to document in the field or using geodesy, thus applying a true back-and-forth approach between numerical models and observations. This unique study will bring together knowledge from fracture mechanics, structural geology, laboratory experiments and geodetic analysis of active faults inside one project. It will add to our understanding of earthquake physics and aseismic deformation, therefore providing a much- needed mechanistic interpretation of fault slip behavior.