Abstract:
The co-seismic rupture of subduction megathrust earthquake exerts a major
control on the earthquake magnitude and size of resulting tsunami,
understanding what factors control the co-seismic rupture is thus essential to
assess a margin’s ability to generate large earthquakes and tsunamis. The
morphology and frictional strength of the plate boundary fault at subduction
zones have long been proposed to control the seismic rupture propagation
during megathrust earthquakes, but with controversial views. This is largely
because there is very few the direct observation of the spatial relationship
between these key parameters. The eastern Markan Subduction Zone has
favorable conditions for large earthquakes, such as the 1945 Mw 8.1 and 2017
Mw6.3 earthquakes. Rupture of these two events have been well constrained to
a relatively concentrated spatial distribution. Along strike, the Little Murray
Ridge has been subducted partially beneath the Makran wedge, adding
structural complexes. Here, we used the high-resolution seismic profiles,
multibeam bathymetry along the eastern Makran accretionary wedge to map the
fine structure of plate interface fault, which is combined with the Critical Taper
Theory to estimate the spatial variation of basal strength. We then compared
these structural and mechanical variations along the megathrust with the
distribution of the two historical ruptures. We observed that low shear strength
in non-ridge subducted segments facilitates the 1945 and 2017 rupture
propagation, contrasting with high-strength area associated with the ridge
subduction impeding them. The research underscores the significant control of
fault morphology and strength in seismic rupture behavior, offering insights for
seismic hazard assessment in subduction zones.
