Combined analysis of the 2016 Kaikoura earthquake (New Zealand) : Constraining surface deformation using optical image correlation and modeling incorporating realistic elastic structure and topography

Titre : Combined analysis of the 2016 Kaikoura earthquake (New Zealand) : Constraining surface deformation using optical image correlation and modeling incorporating realistic elastic structure and topography

Laboratoire de rattachement : ISTerre

Encadrant : Mathilde Radiguet
Co-Encadrant : James Hollingsworth

Téléphone : +33 (0)4 76 63 51 19

Mots clés : corrélation d’images optiques, déformations co-sismiques, fonction de Green 3D, inversion du glissement.

serpentine ; mécanique des roches ; endommagement co-sismique ; pétrophysique ; analyse microstructurale

Contexte et objectifs de la mission de stage :
On November 13, 2016, the magnitude Mw 7.8 Kaikoura earthquake struck the northeastern coast of
the South Island, New Zealand. Despite high levels of seismic activity in the region, this earthquake is
the largest to have occurred since the 1848 Blenhaim earthquake (Mw 7.5). The Kaikoura earthquake produced a highly complex pattern of surface deformation, as revealed by InSAR and GPS data, optical satellite image correlation and field mapping, which all indicate that multiple faults segments were involved in the rupture process. In this project, we aim at refining the Kaikoura earthquake slip model with a geodetic analysis and modeling using realistic 3D Greens functions.

The student will focus on two aspects : the production of high-resolution deformation map using optical satellite imagery and the modeling of these data (in addition with others available datasets) using a forward model (Greens functions), which account for both topography and elastic structure.

First, we propose to extract 3D displacements in the near-fault region using pre- and post-earthquake stereo Pleiades optical satellite data. These data provide constraint on near fault surface deformation, and will be combined with other existing data sets (GPS and InSAR) to produce a deformation map of the Kaikoura earthquake.

Then, we will model these surface slip distribution using realistic 3D Greens functions. The originality
of our approach is to account for topographic effects and variability in the elastic structure in our forward model (Green’s function) computation. These effects are usually neglected in the modeling of surface displacements, as most studies consider layered or homogeneous half space. However, important topographic variations, as observed in New-Zealand, can have a significant effect on the expression of surface displacement, and should not be overlooked. The 3D Greens function will be computed using the finite element code Pylith. A quantitative analysis of the discrepancy between homogeneous and 3D Greens functions will be performed. Then, the surface deformation data will be inverted using the estimated 3D Greens function.

The present study will help to constrain the source model of this complex earthquake.