Earthquake ruptures and topography controlled by plate interface deformation

What controls the location and segmentation of mega-earthquakes in subduction zones is a long-standing problem in earth sciences. Prediction of earthquake ruptures mostly relies on interplate coupling models based on Global Navigation Satellite Systems providing patterns of slip deficit between tectonic plates. We here investigate if and how the seismic and aseismic patches revealed by these models relate to the distribution of deformation along the plate interface, i.e. basal erosion and/or underplating. From a mechanical analysis of the topography applied along the Chilean subduction zone, we show that extensive plate interface deformation takes place along most of the margin. We show that basal erosion occurs preferentially at 15 km depth while underplating does at 35 ± 10 and 60 ± 5 km depth, in agreement with P-T conditions of recovered underplated material, expected pore pressures, and spatial distribution of marine terraces and uplift rates. Along southern Chile, large sediment input favors shallow accretion and underplating of subducted sediments, while along northern Chile, extensive basal erosion provides material for the underplating. We then show that all major earthquakes of southern Chile are limited along their down-dip end by underplating while, along northern Chile, they are surrounded by both basal erosion and underplating. Segments with heterogeneously distributed deformation largely coincide with lateral earthquake terminations. We therefore propose that long-lived plate interface deformation promotes stress build-up and leads to earthquake nucleation. Earthquakes then propagate along fault planes shielded from this long-lived permanent deformation, and are finally stopped by segments of heterogeneously distributed deformation. Slip deficit patterns and earthquake segmentation therefore reflect the along-dip and along-strike distribution of the plate interface deformation. Topography acts as a mirror of distributed plate interface deformation and should be studied systematically to improve the prediction of earthquake ruptures.

Earthquake ruptures tied to long-lived plate interface deformation

<p>Predicting the spatial extent of mega-earthquakes is an essential ingredient of earthquake hazard assessment. In subduction zones, this prediction mostly relies on geodetic observations of interseismic coupling. However, such models face spatial resolution issues and are of little help to predict full or partial ruptures of highly locked patches. Coupling models are interpreted in the framework of the rate-and-state friction laws. However, these models are too idealized to take into account the effects of a geometrically or rheologically complex plate interface. In this study, we show, from the critical taper theory and a mechanical analysis of the topography, that all recent mega-earthquakes of the Chilean subduction zone are surrounded by distributed interplate deformation emanating from either underplating or basal erosion. This long-lived plate interface deformation builds up stresses ultimately leading to earthquake nucleation. Earthquakes then propagate along a relatively smooth surface and are stopped by segments of heterogeneously distributed deformation. Our results are consistent with long-term features of the subduction margin, with observed short-term deformation as well as physical parameters of recovered subducted fragments. They also provide an explanation for the apparent mechanical segmentation of the megathrust, reconciling many seemingly contradictory observations on the short- and long-term deformation. Consequently, we propose that earthquake segmentation relates to the distribution of deformation along the plate interface and that slip deficit patterns reflect the along-dip and along-strike distribution of the plate interface deformation. Topography would therefore mirror plate interface deformation and could serve to improve earthquake rupture prediction.</p>

Numerical Investigation of Two-Phase Flows in Corrugated Channel with Single and Multiples Drops

This work aims at investigating numerically the effects of channel corrugation in two-phase flows with single and multiples drops subject to buoyancy-driven motion. A state-of-the-art model is employed to accurately compute the dynamics of the drop’s interface deformation using a modern moving frame/moving mesh technique within the arbitrary Lagrangian–Eulerian framework, which allows one to simulate very large domains. The results reveal a complex and interesting dynamics when more than one drop is present in the system, leading eventually in coalescence due to the amplitude of the corrugated sinusoidal channel and distance between drops.