Total Surface Displacement from Geodetic Imaging Refines Fault Scaling Relations for Continental Strike-Slip Earthquakes: Implications for shallow slip deficits and Constant Stress Drops

Chris Milliner, Jean-Philippe Avouac, Brian Chiou, & Rui Chen

Submitted September 7, 2025, SCEC Contribution #14829, 2025 SCEC Annual Meeting Poster #TBD

Fault scaling relationships underpin seismic hazard estimates of expected magnitudes and source properties and inform fundamental questions about earthquake mechanics—such as whether stress drops are constant across magnitudes (scale invariance) or whether large ruptures behave differently from smaller ones. However, displacement inputs to these relations are commonly derived from field surveys, which can miss distributed off-fault shear, or from finite-fault inversions, which typically lack near-field data, are non-unique and sensitive to data quality, parameterization, and regularization choices. Both approaches potentially risk underestimating the true surface displacement. We address this by using high-resolution geodetic imaging (radar and optical pixel offsets) to measure total surface displacement, including distributed shear, for 21 continental strike-slip ruptures. Distributed shear can contribute up to 40% of the total displacement, and here we discuss how its inclusion could alter displacement–Mw, displacement–rupture length, and rupture width–rupture length scaling. We evaluate whether these revised relations support constant-stress-drop scaling and compare the observed surface displacement to finite fault inversion estimate from >40 published slip models to assess whether a systematic underestimation of surface slip estimates may exist. Residuals from the revised scaling are also analyzed for possible effects of fault maturity, where we assess whether less mature faults host higher-than-expected displacement and stress drops. Finally, we present 3D near-field surface deformation and fault displacement measurements from the 2025 Mw 7.7 Mandalay, Myanmar earthquake from Sentinel-1 radar and Sentinel-2 optical pixel offset data. This rupture, the longest in the historical record, shows an unusually low average displacement (3.34 m), challenging scaling expectations for extreme-length strike-slip earthquakes and providing a new constraint on global fault scaling.

Key Words
Fault Scaling Myanmar

Citation
Milliner, C., Avouac, J., Chiou, B., & Chen, R. (2025, 09). Total Surface Displacement from Geodetic Imaging Refines Fault Scaling Relations for Continental Strike-Slip Earthquakes: Implications for shallow slip deficits and Constant Stress Drops. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy