CE49 - Planétologie, structure et histoire de la Terre

Active tectonics and deformation mechanisms in fold-and-thrust belt : learning from Southwestern Taiwan – Active-SW

Submission summary

Active-SW project gathers a multidisciplinary team of 25 members from four France partners and three Taiwan partners with balanced scientific and financial contributions and complementary skills. The project aims to gain knowledge on the deformation mechanisms that accommodate tectonic stress in the crust and control seismic hazard and the growth of geological structures and topography in active tectonic areas. We focus on fold-and-thrust belts, which are widespread throughout the world and often associated with significant seismic risks. In this context, a key scientific question is whether aseismic deformation can be the dominant process, rather than deformation by seismic increments. If so, what are the key physical parameters that favor this mode of deformation? This has important implication for seismic hazard assessment and is a fundamental issue for our understanding of the role of lithology and fluids on the seismic cycle and on the rheology of the upper crust and its long-term tectonic deformation. To address these questions, we propose through a multidisciplinary approach (geodesy, seismology, geomorphology, geology, numerical and analogue modelling) an integrative study of the structure and development of the southwestern Taiwan fold-and-thrust belt, at different spatial and time scales: from short-term (few years) to long-term (1 Ma) and from small-scale (i.e. 1-10 km; single geological structure) to large-scale (100 km) processes. Southwestern Taiwan indeed is a rare place where high strain rates (µstrain/yr) can be measured across a fold-and-thrust belt with a very low level of seismicity in the foreland basin, where the fault system is developing. The presence of a thick clayey sedimentary layer with overpressured fluids attested by mud volcanoes makes this area particularly relevant for our project. A first objective of the project is to gather a spatially and temporally dense record of aseismic deformation, including transient signals, to get strong constraints to locate and quantify the deformation at depth and to identify and model the deformation mechanisms. GNSS, levelling, InSAR and image correlation techniques will contribute to this objective and will be complemented by a thorough seismological analysis of the microseismicity and tremor activity that often accompanies this type of deformation. Monitoring of mud volcanoes is proposed as an original approach to get additional information on deep deformation process. Those short-term observations will be confronted to long-term deformation to distinguish between different possible physical processes. This will include (1) analysis the meso- and micro- structures of fault zones (fault gouge and damage zone), in particular those that are creeping, to determine the deformation mechanisms at play, determine fault kinematics, and quantify on-fault potential long-term offsets; (2) identification of geomorphic evidence for rock uplift gradients at the timescale of ~1-10 ka based on the analysis of the landscape (channels and hillslopes) and of denudation rates; (3) estimation of the shortening and 3D geometry on the main geological structures. Numerical and analogue modelling approaches will be used to answer different questions about the deformation mechanism at different timescales. At the timescale of the seismic cycle, time-dependent models will investigate the factors that control surface deformation seen in geodesy. Rheology, basin and basement architecture, surface processes (erosion and sedimentation) and fluid overpressure will be investigated at the timescale of 0.1-1 Ma. Going back and forth from models to observations will eventually lead to deformation mechanisms that are consistent with observations at all spatial and time scales. The knowledge gained on aseismic deformation mechanisms from this project will have a direct impact on seismic hazard assessment in the densely populated area of Taiwan and more widely in other active tectonic contexts.

Project coordination

Erwan PATHIER (Institut des Sciences de la Terre)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

NCU National Central University / Graduate Institute of Applied Geology
NTU National Taiwan University / Institute of Oceanography
NCKU National Cheng Kung University / Departement of Earth Sciences
CNRS DR12_CEREGE Centre National de la Recherche Scientifique Délégation Provence et Corse_Centre européen de recherche et d'enseignement de géosciences de l'environnement
LOG Laboratoire d'océanologie et de géosciences (LOG)
IPGP Institut de physique du globe de Paris
ISTERRE Institut des Sciences de la Terre

Help of the ANR 600,734 euros
Beginning and duration of the scientific project: January 2022 - 48 Months

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