Alternative rupture-scaling relationships for subduction interface and other offshore environments

Alternative fault-rupture-scaling relationships are developed for Mw 7.1–
9.5 subduction interface earthquakes using a new database of consistently derived finitefault
rupture models from teleseismic inversion. Scaling relationships are derived for
rupture area, rupture length, rupture width, maximum slip, and average slip. These relationships
apply width saturation for large-magnitude interface earthquakes (approximately
Mw >8:6) for which the physical characteristics of subduction zones limit the
depth extent of seismogenic rupture, and consequently, the down-dip limit of strong
ground motion generation. On average, the down-dip rupture width for interface earthquakes
saturates near 200 km (196 km on average). Accordingly, the reinterpretation of
rupture-area scaling for subduction interface earthquakes through the use of a bilinear
scaling model suggests that rupture asperity area is less well correlated with magnitude
for earthquakes Mw >8:6. Consequently, the size of great-magnitude earthquakes appears
to be more strongly controlled by the average slip across asperities.
The sensitivity of the interface scaling relationships is evaluated against geographic
region (or subduction zone) and average dip along the rupture interface to
assess the need for correction factors. Although regional perturbations in fault-rupture
scaling could be identified, statistical significance analyses suggest there is little
rationale for implementing regional correction factors based on the limited number
of interface rupture models available for each region.
Fault-rupture-scaling relationships are also developed for intraslab (within the
subducting slab), extensional outer-rise and offshore strike-slip environments. For
these environments, the rupture width and area scaling properties yield smaller dimensions
than interface ruptures for the corresponding magnitude. However, average and
maximum slip metrics yield larger values than interface events. These observations
reflect both the narrower fault widths and higher stress drops in these faulting environments.
Although expressing significantly different rupture-scaling properties from
earthquakes in subduction environments, the characteristics of offshore strike-slip
earthquake ruptures compare similarly to commonly used rupture-scaling relationships
for onshore strike-slip earthquakes.