On the relationship between offshore geodetic coverage and slip model uncertainty: Analog megathrust earthquake case studies.

Abstract

We apply a geodetic slip inversion technique to analog subduction megathrust earthquakes to demonstrate how limited offshore geodetic coverage affects coseismic slip models. We analyzed two archetypical megathrust earthquakes: trench‐breaking and non‐trench‐breaking earthquakes. Slip inversion models of analog earthquakes show quantitative and qualitative changes as a function of offshore coverage. Shallow slip cannot be resolved if the observation coverage of the offshore segment is <50%. Moreover, the slip pattern of shallow event flips from landward to trenchward skewed as offshore coverage reduces to <40%. The estimated slip for both event types converges to a similar unimodal pattern when there is no offshore coverage. We infer 5‐20% slip overestimation when the observations are above the high slipping zone during trench‐breaking events versus 5‐10% underestimation during non‐trench‐breaking events if observations are land‐limited. The moment magnitude derived for trench‐breaking ruptures might be significantly affected (ΔM w ~ 0.5).