Group B, Poster #222, Ground Motions

Low Frequency Non-Ergodic Synthetic Modeling of Earthquake Basin Effects in Wellington, New Zealand

Morgan O. Newton, John N. Louie, Tim Stern, & Aasha Pancha
Poster Image: 

Poster Presentation

2022 SCEC Annual Meeting, Poster #222, SCEC Contribution #12218 VIEW PDF
The 2016 7.8 magnitude Kaikōura earthquake in the South Island of New Zealand consisted of a complex sequence of ruptures, lasting approximately two minutes. During the earthquake, the Wellington capital region experienced unexpected localized zones of damage due to focused seismic energy within its sedimentary basin. Some modern buildings adjacent to Wellington Harbour sustained devastating damage, while historical districts of low-rise unreinforced masonry sustained little to no damage. As seismic waves travel through soft sediments in basins like those underlying Wellington, energy moves at slower velocities and produces elevated shaking amplitudes. These effects accompany prolonged durat...ion of ground shaking and are factors in the Kaikōura damage and the increased risk of damage and injury citywide. In order to understand how waves propagate through the basins of the Wellington region, we computed 27 low frequency (<0.6 Hz) 3D shaking models using SW4 software from Three 3D velocity models were tested, one which contrasts an older geologically-based GNS Science basin model having a maximum sediment thickness under the city of 250 m, a second that included newly developed gravity-based model by Stronach and Stern with a maximum thickness of 540 m under the city, and a 1D model with no basins at all. Each scenario run took about 3 hours on an Intel MacBook. Our research aims to determine if the adjustments of sedimentary basin thickness under the city made by Stronach and Stern produce a substantial difference in how seismic waves travel. Not only will these results help us to understand focused seismic energy within sedimentary basins, it will also help inform hazard planning and preparation for expected seismic events.