Abstract
The 2016 Mw 7.8 Kaikōura earthquake represents an extremely complex event involving over ten major crustal faults, altering conventional understanding of multi-fault ruptures. Although evidence for coseismic slip on the Hikurangi subduction interface is controversial, we present afterslip on the subduction zone beneath Marlborough using 13 months of Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) observations. The spatially and temporally correlated atmospheric errors in SAR interferograms are problematic, and hence a new InSAR time series approach, combining the Generic Atmospheric Correction Online Service (GACOS) with a spatial-temporal Atmospheric Phase Screen (APS) filter to facilitate the InSAR time series analysis, is developed. For interferograms with over 250 km spatial extent, we achieve a 0.77 cm displacement RMS difference against GPS, improving 61% from the conventional InSAR time series method (TS). Comparisons between the overlapping region of two independent tracks show an RMS difference of 1.1 cm for the TS-GACOS-APS combined method, improving 54% from the TS method and 27% from using TS with an APS filter only. The APS filter reduces the short wavelength residuals substantially, but fails to remove the long wavelength error even after the ramp removal, revealing that the GACOS correction has played a key role in mitigating long wavelength atmospheric effects. The resultant InSAR displacements, together with the GPS displacements, are used to recover the time-dependent afterslip distribution on the Hikurangi subduction interface, which provides insights for reviewing the co-seismic slip sources, the present status of the subduction plate boundary and future seismic hazards.
Highlights
The 2016 Mw 7.8 Kaikōura earthquake, which struck the northern South Island of New Zealand on 13 November 2016, ruptured over ten major faults with up to 10 m surface displacements, generating a re gional tsunami which peaked at ~7 m (Bai et al, 2017), and triggered numerous landslides (Massey et al, 2018)
In this paper we propose a time series (TS) analysis method that takes advantage of the Generic Atmospheric Correction Online Service (GACOS; Yu et al (2018)) to reduce the long wavelength and elevation dependent atmospheric errors from each in terferogram, resulting in a more randomised error distribution of the phase measurements and which helps satisfy the fundamental assumptions of Interferometric Synthetic Aperture Radar (InSAR) time series analysis
Sentinel-1 line-of-sight range changes and Global Positioning System (GPS) displacements were used to recover the time-dependent afterslip on the Hikurangi mega thrust beneath the Marlborough Fault System following the Mw 7.8 Kaikōura earthquake
Summary
The 2016 Mw 7.8 Kaikōura earthquake, which struck the northern South Island of New Zealand on 13 November 2016, ruptured over ten major faults with up to 10 m surface displacements, generating a re gional tsunami which peaked at ~7 m (Bai et al, 2017), and triggered numerous landslides (Massey et al, 2018). Holden et al (2017) proposed kinematic models based on local strong-motion and high-rate GPS data, suggesting that the rupture propagated from south to north with half of the moment release occurring at the far north, 60 s after the origin time. None of these models has ruled-out possible slip along the southern Hikurangi subduction interface, which is still debated, and difficult to determine based on the existing coseismic observations None of these models has ruled-out possible slip along the southern Hikurangi subduction interface, which is still debated, and difficult to determine based on the existing coseismic observations (e.g. Holden et al, 2017; Hollingsworth et al, 2017; Xu et al, 2018)
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