Estimation of Seismic Intensities Based on the Spatial Distribution of Asperities in Megathrust Earthquakes

Earthquake source-to-site distance affects the attenuation of seismic waves in their trajectory, and thus, is a key parameter in the estimation of ground motion (GM). The distance between major slip zones on the fault and the surface represents one of the most common physical concepts that is not usually incorporated into GMPE path term due to the difficulty of identifying these zones. Recent studies have shown that there is a correlation between areas of high interseismic locking and high coseismic slip, information that can be used to infer distances to asperities. Here, we propose a source-to-site distance metric (R-asp) that takes into account an a priori size of potential asperities based on locking models to estimate the slip distribution in the rupture plane. We propose a simple modification to an existing GMPE, which needs an interseismic locking model as input. The metric we propose is aimed at large megathrust earthquakes and was tested in Japan subduction zone. This metric can be used for new ground motion prediction equations (GMPE) but also to improve the results given by existing GMPEs. We find that R-asp produces an improvement in the prediction of ground motion intensities for periods under 1 s. Our results show a reduction in standard deviation and mean of intra-residuals, which could be relevant to deterministic and probabilistic seismic hazard applications.