Abstract of my project submitted to the ERC-STG-2017 call The ever-increasing amount of geophysical data continuously opens new perspectives on fundamental aspects of the seismogenic behavior of active faults. In this context, studying the interrelation between seismic and aseismic fault slip is essential to understand what causes and what triggers earthquakes. Despite significant advances in the last 15 years, a number of key questions still remain. How is aseismic slip related with the spatial and temporal distribution of earthquakes? Is there a unified physical mechanism explaining the occurrence of seismic and aseismic slip? The problem is that fault processes span a tremendous range of time-scales. Earthquakes propagate during seconds to minutes while inter-seismic strain accumulates for decades, centuries and even millenniums in regions of low strain rate. While different modeling strategies are used to infer seismic or aseismic slip, only a joint interpretation of inter-, co- and post-seismic datasets can allow us to fully explore the interactions between these two slip modes. The proposed work is to develop an entirely new approach, where all available datasets are assimilated to produce a unified model describing seismic and aseismic slip at all resolvable scales of the earthquake cycle. Such model will describe the evolution of inter-seismic and post-seismic slip with a resolution of a few days but also seismic ruptures propagating for tens to hundreds of seconds. In Chile, where various datasets are available, we will produce a new generation of time-dependent slip models, by jointly inverting geodetic, seismological and tsunami observations. This will allow us to address key questions on the seismogenic behavior of faults and to investigate the preparatory process of aseismic slow-slip events observed before some large megathrust earthquakes. Our time-dependent slip models will also be updated in near real time and used to automatically detect anomalous departures from steady-state inter-seismic fault slip.

The HighLand project proposes to combine seismology, remote sensing and machine learning to quantify the impact of climate on mass-wasting activity in regions of high latitude or altitude. The first objective of the project is the development of new processing chains to build, from the continuous recordings produced by regional seismological networks, instrumental catalogs of landslides. The systematic exploration of these seismological chronicles will be made possible by the use of machine learning algorithms and will enable the production of catalogs offering unparalleled spatio-temporal resolution. The seismological detection will be confronted with satellite observations with high temporal repetition possible thanks to the constellations of Sentinel and Landsat satellites. Three regions of the world will first be targeted by this new processing chain: Alaska, the Alps and Nepal. This multi-disciplinary approach will make it possible to produce the necessary observations and to build and constrain models to better understand the long and short-term links between climate and mass wasting activity. The prototype of the processing chain will serve as the basis for a system for observing and listening to the landside activity in near real time in these regions of the world and then on a global scale.

How and when the Tibetan plateau developed has long been a puzzling question with implications for the current understanding of the behavior of the continental lithosphere in convergent zones. The Central Tibetan plateau provides the ideal existing laboratory to understand the evolution of a large scale collisional orogen. Its evolution is now well constrained by an increasing amount of high quality surface and subsurface data. The integration of these data has led to the proposition of the achetypical models of orogenic evolution. Some models focus on the importance of the underthrusting of the rigid Indian and Asian plates beneath Tibet, others argue that the crust and lithosphere are weak and the thickening of the Asian lithosphere is distributed. In this project, we target Central Tibet. Although it remains the least studied part of the collision zone, it constitutes a key element for reconstructions and models involving processes such as continental subduction, underplating or extrusion to be evidenced there. We will provide detailed quantitative data on rates and mechanisms of thickening processes in central Tibet based on an integrate petrologic study of volcanic rocks and associated mantle and lower crustal xenoliths, paleomagnetic data acquired on volcanic rocks, reappraisal of available geophysical data (tomography, heat flow, Bouguer anomaly, refraction and reflection seismicity) and numerical modeling. The comparison with the geometry, lithology and evolution of the Bohemian massif will offer an overarching vision of the evolution of large scale orogens through time. These different approaches, although highly complementary, are rarely integrated within a single project to study a particular mountain belt. We propose to develop an integrated study of deep and surface processes evolution in the core of the orogen. Our aim is to focus on the Central part of the Tibet, Qiangtang Terrane and to compare it with the Moldanubian zone in the Bohemian massif as these zones correspond to the core of the orogen far away from the preserved continental subductions zones that rejunavated the initial orogenic recordings. The interest to compare the Bohemian massif with the Qiangtang Terrane is that the former offers the opportunity to observe directly in the field the root of the orogen while the second is a still active unroofed orogenic zone.

Slow slip events (SSE) are transient processes releasing stress at faults without significant earthquake. Their discovery about two decades ago in subduction zones demonstrates a complex dynamics of the megathrust controlled by spatially variable friction at the plate interface. While deep SSEs occurring downdip of highly locked areas have been extensively studied, other subduction zones highlight another transient process where slip occurs at the same depths as large earthquakes and is synchronous to intense micro-seismicity. We refer to this type of transient as S5 for Synchronous Slow Slip & Seismic Swarm, which is the focus of our proposal. With recurrence time of a few years, S5 periodically induce stress perturbation at the megathrust and might be precursors to an incipient large earthquake, as observed for the 2011 Japan giant earthquake. However, most S5 are not followed by a large earthquake. A major challenge is to know whether some characteristics (e.g. seismicity increase, acceleration of slip, penetration of slip into highly locked areas) could be indicators of the nucleation phase of an incipient large earthquake. As a step required to answer this question, this project aims at (1) precisely observing S5 (2) using novel analysis methodologies to better document the slip and the seismicity during S5 and (3) developing new modelling approaches to consistently integrate the different observations to decipher the underlying physics. We selected four areas along the South America subduction zone where (1) the probability of observing S5 during the duration of the project is high (2) thanks to previous efforts and partnerships with local institutes, existing seismological and geodetic infrastructure enables to deploy a dense network at a lower cost. Two areas are located in the northern Andes in Ecuador and Peru and two are in Central Chile. At each targeted area, we will install additional continuous GNSS stations and broadband seismometers that will be recording during the 4 years of the project. In addition, we will regularly survey dense networks of GNSS benchmarks and perform a 6-months long seismological experiment with 10 additional broadband seismometers at both targeted areas in Chile. Together with existing data sets from dense seismological networks that recorded S5 in Ecuador and Peru, this observational effort will provide spatially and temporally high resolution data to apply novel methods. We will process the GNSS data and investigate new methods to separate non-tectonic contributions in GNSS time series. Then we will derive a velocity field used to perform refined modelling of the interseismic coupling to understand the environment of S5. A novelty is that we will develop a generalized full time-dependent slip inversion from GNSS time series opening the way for a kinematic imaging of slip and slip rate at the subduction interface. For the seismological data, we will (1) search for repeating earthquakes (2) search for tremors and low frequency earthquakes (3) systematically calculate focal mechanisms and source time functions for the largest events. An additional novelty of our proposal is to use Machine Learning (ML) techniques in order to speed up and to improve micro-seismicity analysis. Finally, we will integrate the geodetic and seismological results in a modelling approach where the spatial and temporal evolution of the seismicity and recurrence time for repeating earthquakes are consistent with the stress evolution induced by the slip developing through time at the plate interface. Simultaneously, forward numerical modelling of a frictionally heterogeneous fault will provide a synoptic view of the relations between friction parameters and observable slip behaviors. Finally, physical modelling will examine the physical conditions and characteristics required for an S5 to lead to a large earthquake.

The aim of the PRISMS project is to develop a tool for modelling and predicting the effects on the Earth's ionized environment of electromagnetic emissions and particle ejection from the Sun. Through the PRISMS project, we ambition, by coupling individually validated models, to build an integrated model that will be able to propagate electromagnetic emissions from the Sun and plasma emissions from the solar wind, at the L1 Lagrange point, to the ionized space environment of Earth, with coupling functions adapted to ensure the delicate transmission at the interface between the solar wind and the terrestrial environment. This global model will be constrained by space observations, which will condition the coupling functions in order to better characterize the perturbation and its propagation. The model will evaluate the effects on the ionosphere dynamics of electromagnetic disturbances during solar flares and the effects associated with magnetic storms (corotating interaction regions and coronal mass ejections) and thereby the impact on radio communications through the propagation of electromagnetic waves in this environment. In addition, by developing a suitable module, the model will calculate the ground magnetic trace of these disturbances. At the end of the project, we will have implemented a prototype operational system that will have the ability to follow in near real-time the variations of electromagnetic solar emissions and of thje properties from the solar wind and to describe the disturbances induced by solar activity on the propagation of radio waves. This effort is part of a strategy of national independence with respect to modeling of the damaging effects of the Sun on the industrial, societal and military activities in France and more broadly on an European level.