Large-scale high-resolution deformation of tectonic and volcanic regions

Satellite geodesy provides critical insights into tectonic deformation, fault activity, and seismic hazard. However, in regions of widespread continental deformation, observational coverage has until recently relied on sparse GNSS measurements, limiting the resolution of short-wavelength deformation features. By integrating InSAR we can greatly improve the resolution, and we have recently constructed a transnational velocity field for the entire Alpine-Himalayan Belt at 1 km spacing, from over 222,000 Sentinel-1 SAR images (2016–2024) and a new compilation of GNSS velocities [Elliott et al., in review]. This dataset spans more than 11,000 km from southwestern Europe to eastern China, covering over 20 million km², and is referenced consistently to the Eurasian frame.

From these velocities, we derive horizontal strain rates, providing near-continuous deformation mapping across the planet’s largest actively deforming region. Results reveal a bimodal pattern of tectonic strain, which is concentrated along major faults in some regions but distributed across broader zones in others. Vertical motions, in contrast, exhibit shorter-wavelength signals dominated by non-tectonic processes, particularly groundwater depletion.

Satellite geodesy also provides critical insights into volcanic deformation and hazard, and we have processed InSAR data for the ~1300 subaerial volcanoes most likely to erupt. Scale is less of an issue for volcanoes, with volcanic activity usually confined to within 40 km of each volcanic centre, but timeliness is important for hazard monitoring, and we process data in near-real time form a subset of volcanoes. For historical analyses we have integrated our InSAR results with local GNSS networks [Bedon et al, in prep], but it remains a challenge to incorporate GNSS from multiple disparate networks for ongoing monitoring on a global basis.

The spatial resolution of InSAR measurements is better than GNSS by orders of magnitude, but inclusion of GNSS is key for two reasons: firstly, for tying InSAR to a global reference frame and secondly, to provide a third component of the velocity field, which allows the full 3-D field to be constrained. However, the combination leads to very different resolutions in the north-south direction, constrained predominantly by GNSS, and the east-west direction, where InSAR dominates. When estimating the strain rate this leads to non-localisation of strain for north-south trending strike-slip faults and east-west trending dip-slip faults but also leads to short wavelength shear strain (e.g., from near-surface creep) being wrongly attributed to dilatation on faults of any orientation [Fang et al., 2024].

We are addressing this issue in two ways. Firstly, by inclusion of along-track velocity estimates from Sentinel-1 burst overlap regions [Nergizci et al., 2024] and secondly by the addition of InSAR velocity measurements from NISAR. The left-looking nature of NISAR acquisitions will provide two more independent velocity measurement vectors that will enable full 3-D estimation at high resolution. Whilst the accuracy in the north-south direction will be ~4 times worse than in the east-west direction, the improvement in resolution will be by orders of magnitude.

References

Elliott et al. (in review). Preprint: doi:10.31223/X5GX6B.

Fang et al (2024). doi:10.1029/2024GL111199.

Nergizci et al. (2024). doi:10.1016/j.procs.2024.06.401.