Source considerations for moderate magnitude earthquake ground motion simulation validation

Abstract

In New Zealand, previous hybrid broadband ground motion simulation validation efforts were initially focussed on large magnitude (Mw) earthquakes, and more recently on small magnitude earthquakes (3.5<Mw≤5.0). Both regional and nation-wide validation exercises have led to improvements to the Graves and Pitarka (2010,2015) simulation methodology and/or velocity modelling, both crustal and shallow. Naturally, the next step is to consider moderate magnitude earthquakes (5.0<Mw≤6.0) which bridge the gap between previous studies. This study presents preliminary results on the validation of moderate magnitude active shallow crustal earthquakes in New Zealand with emphasis on source modelling considerations. 62 earthquakes are considered with 1726 ground motions across 202 recording stations. The earthquake fault ruptures are kinematically modelled as single plane finite faults given there are no detailed source inversion studies for these events (with few exceptions). The effect of kinematic slip generator, fault dimension aspect ratio and choice of centroid moment tensor nodal plane on the simulated ground motions are examined. The simulations are compared against observed records to quantify their predictive capability for moderate magnitude earthquakes, identify aspects for future improvement and provide insights into the salient ground motion characteristics observed.