R.L. Lee

Ground motion simulations of great earthquakes on the Alpine Fault: effect of hypocentre location and comparison with empirical modelling

ABSTRACT This paper discusses simulated ground motion intensity, and its underlying modelling assumptions, for great earthquakes on the Alpine Fault. The simulations utilise the latest understanding of wave propagation physics, kinematic earthquake rupture descriptions and the three-dimensional nature of the Earths crust in the South Island of New Zealand. The effect of hypocentre location is explicitly examined, which is found to lead to significant differences in ground motion intensities (quantified in the form of peak ground velocity, PGV) over the northern half and southwest of the South Island. Comparison with previously adopted empirical ground motion models also illustrates that the simulations, which explicitly model rupture directivity and basin-generated surface waves, lead to notably larger PGV amplitudes than the empirical predictions in the northern half of the South Island and Canterbury. The simulations performed in this paper have been adopted, as one possible ground motion prediction, in the ‘Project AF8’ Civil Defence Emergency Management exercise scenario. The similarity of the modelled ground motion features with those observed in recent worldwide earthquakes as well as similar simulations in other regions, and the notably higher simulated amplitudes than those from empirical predictions, may warrant a re-examination of regional impact assessments for major Alpine Fault earthquakes.

3D models of Quaternary-aged sedimentary successions within the Canterbury, New Zealand region

ABSTRACT A 3D high-resolution model of the Quaternary geological stratigraphic sequence in the Canterbury, New Zealand region is developed utilising datasets of over 500 high-quality water well logs from a database of 29,985, and over 370 near-surface cone penetration test (CPT) records from a database of 13,670. The model, developed using geostatistical Kriging, represents the complex interbedded regional Quaternary geology by characterising the boundaries between significant interbedded geological formations as 3D surfaces. The model is examined in the form of both geological surface contour maps and vertical cross sections, where the most evident trend identified is the easterly dip caused by the dominant alluvial deposition of terrestrial sediments. The developed 3D interbedded Quaternary stratigraphy model has several applications for hydrologic modelling, earthquake-induced ground motion simulations and seismic site characterisation. For the latter case, the role of the model in constraining surface wave analysis-based shear wave velocity profiling is illustrated.