Deep mass redistribution prior to the 2010 Mw 8.8 Maule (Chile) Earthquake revealed by GRACE satellite gravity

Subduction zones megathrust faults constitute a considerable hazard as they produce most of the world's largest earthquakes. However, the role in megathrust earthquake generation exerted by deeper subduction processes remains poorly understood. Here, we analyze the 2003 - 2014 space-time variations of the Earth's gravity gradients derived from three datasets of GRACE geoid models over a large region surrounding the rupture zone of the Mw 8.8 Maule earthquake. In all these datasets, our analysis reveals a large-amplitude gravity gradient signal, progressively increasing in the three months before the earthquake, North of the epicentral area. We show that such signals are equivalent to a 60 km(3) water storage decrease over 2 months and cannot be explained by hydrological sources nor artefacts, but rather find origin from mass redistributions within the solid Earth on the continental side of the subduction zone. These gravity gradient variations could be explained by an extensional deformation of the slab around 150-km depth along the Nazca Plate subduction direction, associated with large-scale fluid release. Furthermore, the lateral migration of the gravity signal towards the surface from a low coupling segment around -32.5 degrees North to the high coupling one in the South suggests that the Mw 8.8 earthquake may have originated from the propagation up to the trench of this deeper slab deformation. Our results highlight the importance of observations of the Earth's time-varying gravity field from satellites in order to probe slow mass redistributions in-depth major plate boundaries and provide new information on dynamic processes in the subduction system, essential to better understand the seismic cycle as a whole. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

Subduction zones megathrust faults are a major cause of the world's largest earthquakes. However, the role of deeper subduction processes in earthquake generation is poorly understood. In this study, the variations of the Earth's gravity gradients derived from GRACE geoid models are analyzed from 2003 to 2014. The analysis reveals a large-amplitude gravity gradient signal north of the epicentral area in the three months prior to the earthquake. The results suggest that these signals are related to mass redistributions within the solid Earth on the continental side of the subduction zone. The study highlights the importance of monitoring the Earth's time-varying gravity field to better understand the seismic cycle and dynamic processes in subduction zones.