Trends in systematic site residuals with geomorphic categories for New Zealand ground-motion instrument sites

Abstract

This study investigates systematic site-effects from prediction residuals of physics-based ground-motion simulations for a database of small magnitude (i.e., 3.5 ≤ MW ≤ 5) shallow crustal earthquakes in New Zealand. The database includes 5,218 ground motions from 496 earthquakes recorded at 382 sites, providing a wide range of site and basin conditions at which to evaluate systematic site-effects and within-site variability in residuals. Sites displaying large systematic site residuals and within-site variability are identified and scrutinised to study the site and path characteristics that contribute to these effects with an overarching goal of improving how these phenomena are modelled. Sites in major urban areas overlying sedimentary basins are of particular interest to assess the quality of site characterisation data, basin models, and site response modelling techniques on a nation-wide scale. Results indicate that predictions at sites with strong site/basin amplification can be improved with site-specific site characterisation data and modelling, and more refined basin models.