Systematic Characterization of Morpho-Tectonic Variability Along the Cascadia Convergent Margin: Implications for Outer Wedge Dynamics and Shallow Megathrust Behavior

Assessing Margin-Wide Rupture Behaviors along the Cascadia Megathrust with 3-D Dynamic Rupture Simulations

“…Given this assumption, our results could be interpreted to mean that the slip-rate deficit is not accumulated the same everywhere along the Cascadia megathrust. This is consistent with suggested RI segmentation (e.g., Goldfinger et al, 2017), some of which may be expressed as along-strike changes in fault vergence patterns and outer wedge geometry (Gulick et al, 1998;Watt and Brothers, 2020). There is also the possibility that the coupling models we used in our study overestimated the slip-rate deficit due to inelastic off-fault deformation (e.g., Baker et al, 2013).…”

“…Previously developed 2-D dynamic rupture simulations (Ramos and Huang, 2019) were relative to a specific location in northern Cascadia, which is where we initiate rupture (Figure 3a). Such a laterally uniform dynamic stress drop distribution is unlikely given observations of geophysical and geological megathrust segmentation (e.g., Watt and Brothers, 2020). However, we develop such a simulation to demonstrate 1) what a megathrust event would appear as if there was a strong gradient in shear stress-rate from the locked to gap regions (20 -30 km depth) across the margin and 2) how this scenario would influence coastal subsidence amplitudes.…”

“…We find that placing segment limits near ~46 and 43 degrees latitude (Y ranges from 180 to -350 km; Figure 5a), together with T levels between 200 -250 years (~ 8 -10-m slip deficit), leads to margin-wide rupture. The position of these segment limits corresponds to changes in estimated RI level, tremor patterns and forearc morphology (Figure 1; Goldfinger et al, 2017;Watt and Brothers, 2020). The middle segment encompasses most of the creeping region offshore Oregon.…”

“…Our partitioning of the margin is informed by paleoseismic (Goldfinger et al, 2012(Goldfinger et al, , 2017, ETS (Brudzinski and Allen, 2007), and morphotectonic studies (Watt and Brothers, 2020) in Cascadia. The following dynamic rupture models are parameterized using at least three segments.…”

“…Several geological and geophysical observations suggest the Cascadia megathrust exhibits along-strike segmentation. For instance, there are systematic changes in the accretionary wedge backstop geometry, seismicity, and interseismic slip patterns (e.g., Stone et al, 2018;Bartlow, 2020;Watt and Brothers, 2020) that may indicate coseismic rupture patterns will also be variable along-strike. The strongest observational constraints that may inform our understanding of future great earthquakes come from paleoseismic and geodetic observations.…”