Challenges of interpreting geodetic deformation in low strain rate regions: Insights from the 2021 M W 7.4 Maduo earthquake

Interseismic deformation and strain rates derived from Global Navigation Satellite Systems (GNSS) or Interferometric Synthetic Aperture Radar (InSAR) data are often used to assess a fault’s earthquake potential. Deformation rates, commonly derived from short-term geodetic observations, are assumed to be indicative of long-term strain accumulation, and variations in strain rate throughout the interseismic period are poorly studied. Many regions have limited spatial and temporal coverage of GNSS data, and using InSAR presents challenges on low strain rate faults, where the signal-to-noise ratio is low. As a case study, we examine the interseismic period prior to a large intraplate left-lateral strike-slip earthquake: the 2021 M W 7.4 Maduo Earthquake. Using InSAR, we derive eastward velocities and maximum shear strain rates, whilst minimising the influence of near-field GNSS data, for two-year, three-year and six-year time periods. We investigate the sensitivity of geodetic deformation rate to the temporal observation window, and find that transient variations in deformation vary in a spatial pattern that cannot be unequivocally attributed to tectonic motion, given the uncertainty of InSAR data in the region. We do, however, observe a consistently low strain rate on the seismogenic fault. This study highlights the challenges faced when trying to obtain meaningful geodetic measurements on low strain rate faults, bringing to question the utility of strain rate as a proxy for seismic hazard in continental block interiors. • InSAR and GNSS data constrain strain rate in several observation windows prior to the 2021 Maduo earthquake. • Low strain rates are consistently observed on the seismogenic fault, irrespective of observation window. • Changing the observation window leads to fluctuations in deformation rates that can not be unequivocally attributed to tectonic motion given the signal-to-noise ratio of InSAR in the region.