  162173 Ryugu, the target of Hayabusa2, has a round shape with an equatorial
ridge, which is known as a spinning top-shape. A strong centrifugal force is a
likely contributor to Ryugu's top-shaped features. Observations by Optical
Navigation Camera onboard Hayabusa2 show a unique longitudinal variation in
geomorphology; the western side of this asteroid, later called the western
bulge, has a smooth surface and a sharp equatorial ridge, compared to the other
side. Here, we propose a structural deformation process that generated the
western bulge. Applying the mission-derived shape model, we employ a finite
element model technique to analyze the locations that experience structural
failure within the present shape. Assuming that materials are uniformly
distributed, our model shows the longitudinal variation in structurally failed
regions when the spin period is shorter than ~3.75 h. Ryugu is structurally
intact in the subsurface region of the western bulge while other regions are
sensitive to structural failure. We infer that this variation is indicative of
the deformation process that occurred in the past, and the western bulge is
more relaxed structurally than the other region. Our analysis also shows that
this deformation process might occur at a spin period between ~3.5 h and ~3.0
h, providing the cohesive strength ranging between ~4 Pa and ~10 Pa.
