Geodetic Coupling Models as Constraints on Stochastic Earthquake Ruptures: An Example Application to PTHA in Cascadia.

Current stochastic rupture modeling techniques do not consider the potential influence of inter‐seismic coupling, a first‐order property of a megathrust, which can show correlation between areas of high coupling and areas of greater slip as seen in recent large ruptures globally. Therefore, it is reasonable to assume that it should be considered as prior information in rupture modeling. Here, we first present a mathematical formalism to introduce coupling models as prior information into stochastic rupture modeling. We then focus on how introducing slip deficit information into the stochastic rupture models influences slip distributions for the Cascadia subduction zone (CSZ). We compare rupture models created with two end member models of coupling, one with a shallow coupling and another with coupling deeper downdip. We also discuss the comparison to models created without assuming knowledge of the coupling distribution except for variation in the downdip limit of slip. Variations occur and correlate well with areas with the largest differences in slip deficit rates. The ruptures are then used for regional probabilistic tsunami hazard assessment. Overall, the tsunami amplitudes generated are much more hazardous in the northern extent of the CSZ where differences in coupling distribution are more prevalent. Models obtained from assuming a shallower downdip limit have tsunami amplitudes more similar to those from the geodetic coupling models. Although uncertainties are present in the accuracy of coupling, imposing either constraint created different hazard estimations when compared to those where no prior coupling information was used. Plain Language Summary: Uncertainties are often present when trying to determine future earthquake rupture potentials and their associated hazards. We present here a means of including a first‐order property of a megathrust, a fault's pattern of the current ability to slip (coupling), in a current rupture modeling technique often applied to hazard assessments. We model ruptures classes constrained by two different coupling models for the Cascadia subduction zone (CSZ), as well as two other classes without imposed coupling. These ruptures are then used to determine associated tsunamis and the total probabilistic tsunami hazards for the Cascadia region. Overall, the tsunami amplitudes generated are much more hazardous in the northern extent of the CSZ where differences in coupling distribution are more prevalent. Models obtained without coupling but constrained by a shallower limit of slip have tsunami amplitudes more similar to those from the geodetic coupling models. Although uncertainties are present in the accuracy of coupling, imposing either constraint created different hazard estimations when compared to those where no prior coupling information was used. Key Points: Including fault coupling produces considerable variations for stochastic slip rupture models as well as the resultant probabilistic tsunami hazardsThe coupling models produced similar patterns of tsunami hazards for the central Cascadia region and more dissimilar hazards in the northern and southern coastal Cascadia regionsExpanding seafloor observations is necessary for a more accurate understaning of the Cascadia tsunami hazard [ABSTRACT FROM AUTHOR]