Evidence of kilometer-wide shallow bulk plastic yielding along the 2021
Maduo, Tibet, surface rupture, and its relation with the dynamic rupture
process
Abstract
Surface deformation associated with continental earthquake ruptures
includes localized deformation on the faults, as well as deformation in
the surrounding medium though distributed and/or diffuse processes.
However, the connection of the diffuse part of the surface deformation
to the overall rupture process, as well as its underlying physical
mechanisms are not yet well understood. Computing high-resolution
optical image correlations for the 2021/05/21 Mw7.4 Maduo, Tibet,
rupture, we highlight a correlation between the presence of faults and
fractures at the surface, and variations in the across-fault
displacement gradient, fault zone width, and amplitude of surface
displacement. We show that surface slip along primary faults is
systematically associated with gradients greater than 1%, and is
dominant in regions of greater coseismic surface displacement.
Conversely, the diffuse deformation is associated with gradients ≤0.3%,
and is dominant in regions of lesser surface displacement. The
distributed deformation then occurs for intermediate gradients of
0.3-1%, and at the transition between the localized and diffuse
deformation regions. Such patterns of deformation are also described in
laboratory experiments of rock deformation, themself supported by field
observations. Comparing these experiments to our observations, we
demonstrate that the diffuse deformation along the 2021 Maduo rupture
corresponds to kilometer-wide plastic yielding of the bulk medium
occurring in regions where surface rupture is generally missing. Along
the 2021 Maduo rupture, diffuse deformation occurs primarily in the
epicentral region, where the dynamic stresses associated with the
nascent pulse-like rupture could not overcome the shallow fault zone
frictional strength.