Ground motion simulation

Sponsors: Rutherford Discovery Fellowship (RSNZ), Marsden Fund (RSNZ), NZ Earthquake Commission (EQC), NZ Natural Hazards Research Platform (NHRP)

Collaborators: Rob Graves (USGS Pasadena), Jarg Pettinga (UC), Misko Cubrinovski (UC), Matthew Hughes (UC), Chris McGann (UC), Brady Cox (UTexas), Liam Wotherspoon (UAuckland), Hoby Razafindrakoto (UC), Ahsan Nazer (UC), Seokho Jeong (UC)

Postgraduate researchers: Robin Lee, Ethan Thomson

Videos: Have a look at animations of our latest simulations of various New Zealand earthquakes here.

Canterbury earthquakes

The 2010-2011 Canterbury earthquakes produced severe ground motions in the Christchurch urban area, and consequently extensive liquefaction and damage to structures and infrastructure. As a result of unique datasets which have been collected, these earthquakes provide numerous opportunities to understand fundamental phenomena related to: (1) severe earthquake-induced ground motions and; (2) the seismic response of near-surface soil deposits. We are using state-of-the-art analyses to shed light on several profound ground motion observations which remain unresolved. As a result, this work will develop a unified understanding of the seismic response of urban areas residing on sedimentary basins with liquefiable soils.

Seismic velocity model

To date our efforts have largely focused on the development of a comprehensive 3D seismic velocity model for the Canterbury region. Numerous sources of data are utilized in the model formulation to provide adequate resolution where necessary. The available data sources include: 3D regional tomography, seismic reflection survey lines, geotechnical boreholes and well logs, spectral analysis of surface waves, and cone penetration test (CPT) results, each of which provide velocity constraints over their respective ranges of application.

See our recent 2015 Seismological Society of America (SSA) Annual Meeting presentation.

Various data sources used to develop a 3D seismic velocity model for Canterbury

Because of the significant nonlinear response of surficial soils in the Canterbury earthquakes, particular attention has been given to accurately describing the near-surface soil conditions. As part of this project, we have developed a region-specific CPT-Vs correlation. In combination with >15,000 CPT logs which exist in the Canterbury region this correlation has allowed us to develop high resolution maps of Vs30 (30m averaged near surface shear wave velocity) and Vs with depth.

Comparison of measured and predicted Vs values from the Christchurch-specific CPT-Vs correlation

Hybrid broadband ground motion simulation

Using the 3D seismic velocity model for the Canterbury region we are performing hybrid broadband ground motion simulations of the major events in the 2010-2011 Canterbury earthquake sequence. In particular, we are utilizing the Graves and Pitarka (2010) simulation methodology, and several different models for the causative fault ruptures.

Animations that have been created using 3D velocity models can be found https://www.youtube.com/channel/UCNuhhSRyueqB5PBIRfoM-qQ:

Broadband simulated ground motions from the 2010-2011 Canterbury Earthquakes