Detection of pre-seismic signals in GRACE geoid models: application to the 2011 Tohoku Mw9.0 Earthquake
Abstract
Retrieving pre-seismic signals before the occurrence of great earthquakes is a critical challenge of Earth's sciences. Space geodetic observations of ground displacements and seismic data provide monitoring of seismic events and shallower aseismic motions, but the full spectrum of deformations of the subducted slab at depth remains difficult to constrain. Yet, the pulling force of the slab plays an important role in driving plate motions. Time-varying satellite gravity can overcome this observational limit, thanks to a unique sensitivity to mass redistributions at all depths and a global coverage. Taking the example of the 2011 Tohoku earthquake, we develop here a global and systematic analysis of time series of GRACE-reconstructed gravity gradients, to test whether the deep gravity signals preceeding the earthquake (Panet et al., 2018 ; Bouih et al. 2022) can be detected before the event as a specific feature originating from solid Earth. Our approach is based on a refined detection of short-term gravity variations aligned with the subduction direction, and consistency tests between signals shared by different GRACE geoid models. These tests allow us to evaluate the signals robustness with respect to errors and oceanic corrections in the GRACE gravity solutions. Our results underline the unique character of the deep pre-Tohoku gravity variations compared to the usual variability of gravity. Beyond the case of the Tohoku earthquake, our approach can be applied to the systematic monitoring of the Pacific subduction belt, to detect gravity variations potentially linked with sudden changes in slab motions in-depth these plate boundaries.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.T32D0150P