Extremely Large Off-Fault Deformation during the 2021 Mw 7.4 Maduo, Tibetan Plateau, Earthquake

Abstract

Abstract The 21 May 2021 Mw 7.4 Maduo earthquake ruptured a 170 km long immature strike-slip fault within the eastern Tibetan plateau. Based on pixel correlation of pre- and postevent Sentinel-2 optical satellite images (band 8; pixel = 10 m), we determine the coseismic horizontal displacement and deformation-zone width at the surface. These results, compared with the on-fault slip from geological measurements, document that <20% of the fault displacement is localized on the fault plane, whereas as high as >80% of the fault displacement occurred as off-fault deformation (OFD), over a mean deformation-zone width of 835 m (ranging from 60 to 1670 m). The OFD% of the Maduo earthquake is significantly larger than the OFD% (28%–64%) of all other (eight in total) previously documented earthquakes occurring on immature strike-slip faults, amongst which five earthquake faults have a structural maturity (cumulative displacement) even lower than the Maduo earthquake fault. These observations may be explained by that (1) the fault maturity is not the only factor controlling the behavior of OFD or the degree of strain localization during an earthquake, or that (2) the calculated OFD includes some elastic deformation due to fault slip reduction in the shallow depth. Our results have an implication that the seismic hazard assessment of immature strike-slip faults is more challenging than previously thought.