Wellington Fault modelling

Modeling strong ground motion in the Wellington metropolitan area by Benites and Olsen (2005).

Numerical modeling of M 6.7 earthquakes due to ruptures on this fault, intended to characterize the 3D effects of the
region’s main geological features on the ground motion, are performed by using a finite-differences scheme with staggered grid, for frequencies up to 1.5 Hz.

When the fault ruptures from south to north, resonance occurs within a small area close to the harbor, where the depth of the basin is largest.The combined focusing effects produce amplification factors in the valley of about 5 between 0.5 Hz and 0.7 Hz. In Wellington City the amplification factors are between 0.5 (deamplification) and 2, except for an area on reclaimed land in the harbor, which shows an amplification factor as large as 9. After the rupture has stopped, higher frequency waves, between 1 and 1.2 Hz, appear trapped (reverberating) in the harbor for the remaining duration of the seismograms, up to 60 sec.

When the rupture is from north to south, none of the focusing effects occur. Only the long-lasting reverberations in the harbor seem a characteristic of the wave propagation common to both rupture directions. Nevertheless, the amplification factors in this north-to-south scenario are about the same as for the south-to-north rupture.

Figure 9: ground motion modelling from a Wellington Fault rupture (Benites and Olsen, 2005)

Ground motion modelling from a Wellington Fault rupture (Benites and Olsen, 2005)