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 events 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 (ΔMw ~ 0.5).