Quantifying co-seismic and post-seismic slip on fault scarps and their erosional modification using high-resolution Pleiades optical satellite data and repeat Terrestrial Laser Scanning: the 2016 Mw 6.6 Norcia earthquake (Central Italy)

Abstract

Fault scarps are a topographical expression of sharp gradients in ground movements in an active tectonic region. However, inferences of slip history and causative earthquake sizes may be biased by co-seismic slip gradients, near-fault deformation, afterslip and erosional processes.
To address these biases, I investigate co-seismic and continuing post-seismic deformation of near-fault areas and degradation of fault scarps, using high resolution Pleiades optical satellite images and repeat Terrestrial Laser Scans (TLS). The study area is Monte Vettore in the Apennines, Cental Italy, which has extensive surface ruptures associated with the Mw 6.6 30th October 2016 Norcia earthquake, part of the Central Italy Earthquake Sequence.
I combine image correlation techniques with novel median-based filtering to effectively de-noise the Pleiades data, creating Digital Elevation Models (DEMs) from before and after the Norcia earthquake. Those DEMs are then differenced horizontally and vertically. The results identify detail of near-fault co-seismic surface deformation. I jointly invert those data with far-field InSAR (Interferometric Synthetic Aperture Radar) and GNSS (Global Navigation Satellite System) datasets to model co-seismic slip at depth. My model reveals detail of slip transfer from the Monte Vettore fault at shallow depth. This provides insights into the distribution of near-fault co-seismic slip in an area of complex faulting by slip being partitioned onto minor near-surface hanging wall structures, with slip vectors diverging from those at greater depth.
The causes of post-seismic alteration or degradation of fault scarps are expected to be tectonic-related after-slip and/or erosion. Combining careful alignment of repeat TLS, use of an ICP (Iterative Closest Point) algorithm, filtering and detrending techniques, I characterise post-seismic deformation at 6 individual sites at ~centimetre scale. This provides insights into how individual factors (e.g. underlying geology, topography, and co-seismic slip gradients and distribution) influence which causes dominate and how degradation develops spatially and temporally. I show that fault scarps are highly variable records of a fault’s slip history. Any assessment of previous slip history using fault scarps as evidence needs to have regard to all those factors.