Strain Threshold for the Formation of Coseismic Surface Rupture

Abstract

The 2021 M w 7.4 Maduo earthquake (eastern Tibetan Plateau), with a surface deformation zone that is characterized by multiple distinct surface rupture segments separated by segments with no surface ruptures, provides an excellent opportunity to constrain the strain threshold (minimum strain) for the formation of surface ruptures. Through sub‐pixel correlation of pre‐ and post‐event SPOT‐6/7 satellite images (pixel = 1.5 m), we derive surface displacement and shear‐strain fields of the Maduo earthquake. By quantifying the minimum shear strain along the surface rupture segments and the maximum shear strain along the segments with no surface ruptures, we estimate a rupture strain threshold, which ranges from 0.8% to 1.8% and appears to decrease with structural maturity of the causative fault. This threshold is generally consistent with a rupture strain limit (0.5%–1.5%) of intact rocks from laboratory measurements, and is higher than a commonly‐assumed strain threshold (0.5%) for inelastic deformation. During large earthquakes, two sides of the fault dislocate relative to each other and create a narrow surface deformation zone in between. Whether surface rupture can be produced depends on the strain, a unitless measurement of deformation, within the surface deformation zone. For natural earthquakes, the minimum strain that is needed to create surface rupture (the rupture strain threshold) has not yet been determined. Here we investigate such strain for the surface rupture of 2021 M w 7.4 Maduo earthquake at the eastern Tibetan Plateau. By analyzing the Maduo coseismic surface strain field and its correlation with spatial extent of the coseismic surface rupture, we determine that the rupture strain threshold ranges from 0.8% to 1.8%, and it appears to decrease with structural maturity of the causative fault. This threshold is generally consistent with a rupture strain limit (0.5%–1.5%) of intact rocks from laboratory measurements, and is higher than a commonly‐assumed strain threshold (0.5%) for inelastic deformation. Our study, for the first time, provides a direct measurement of rupture strain threshold based on natural earthquake studies. We derive the 2021 Maduo coseismic surface displacement and strain fields through sub‐pixel correlation of SPOT‐6/7 optical images The strain threshold for the formation of Maduo surface rupture is 0.8%–1.8%, and it appears to decrease with the causative fault maturity This value is consistent with a laboratory‐derived rupture threshold 0.5%–1.5% and is higher than a commonly‐assumed inelastic threshold 0.5%