A High-Frequency Distance Metric in Ground-Motion Prediction Equations Based on Seismic Array Backprojections

Abstract

Typical ground-motion prediction equations (GMPEs) measure source-to-site distances relative to the closest point on the rupture plane (Rrup). However, for megathrust earthquakes (Mw > 8), the oversimplification of the earthquake source characteristics in distance metrics results in significant bias. Recent studies suggest that the high-frequency (HF) and low-frequency (LF) energy tend to emanate from different portions of the megathrusts. This phenomenon motivates an alternative distance metric based on the array backprojection imaging technique that effectively captures regions releasing HF energy. Herein, we define an HF distance metric (Rhf) as the distance from the site to the high-frequency radiation zone. We study five Mw > 7.2 megathrust earthquakes in Japan and Chile and find that Rhf outperforms Rrup in predicting the ground shaking intensity between 0.5 and 4 Hz. We consider Rhf as a complementary measure to conventional GMPE distance metrics and a more accurate ground-motion predictor in many cases.