Maximum earthquake magnitude unlikely to be controlled by subduction interface roughness

Abstract Understanding the controls on seismogenic behaviour at the plate interface in subduction zones is essential to assessing the hazard they pose. The interface topography, or roughness, is widely thought to be an important factor, yet how roughness influences earthquake magnitude is still debated. This debate persists because, generally, studies are limited to individual subduction margins, proxies for roughness are used rather than direct measurements and historical earthquake records are short. Here we show by analysing data from 15 subduction zones globally that there is no relationship between any interface roughness parameter we derive from observations and a proxy for maximum earthquake magnitude. Specifically, for each margin, we use seismic reflection profiles of the plate boundary fault to quantify its roughness at 1–10 km scales, and in the same locations we test whether geodetically constrained interface coupling is an indicator of earthquake potential in lieu of a longer historical record. This analysis shows a strong positive relationship between earthquake magnitude and interface coupling, and that roughness parameters are unrelated to maximum magnitude or coupling. Our findings challenge the prevailing hypothesis that subduction interface roughness is a predominant control on its seismogenic behaviour and imply that interface roughness measured over length scales up to 10 km should not be used to assess a margin’s seismic hazard.