SCEC Award Number 15090 View PDF
Proposal Category Travel Only Proposal (SCEC Annual Meeting)
Proposal Title Near source broadband ground-motion modelling of the Canterbury aftershocks and implications for assessing engineering metrics
Investigator(s)
Name Organization
Caroline Holden GNS Science (New Zealand) Anna Kaiser GNS Science (New Zealand)
Other Participants
SCEC Priorities 6e, 6c, 6d SCEC Groups GMSV, Simulators, SIV
Report Due Date 10/16/2015 Date Report Submitted 10/14/2015
Project Abstract
 The large September 2010 and the tragic February 2011 Canterbury earthquakes caused widespread damage in Canterbury despite a magnitude that is much smaller than that expected from the Alpine Fault (Mw=8.2). Recent advances in earthquake mechanics allow us to compute seismograms for realistic earthquake scenarios, at specific locations, and with specific site conditions. Such simulations can provide very useful alternative estimates of possible ground motions from large faults for major population centres in the South Island (NZ).
Synthetic broadband strong-motion records are produced for a possible large Alpine Fault earthquake (Mw8.2) at selected population centres that may be strongly affected. We compute seismograms using a hybrid approach combining a simple discrete wavenumber approach and a stochastic method. To define the earthquake sources, we apply the validated recipe based on a characterised source model for large crustal earthquakes developed by Irikura and Miyake (2011). The synthetic rock site motions are then used as the input motion for a frequency-dependent site amplification function.
The synthetic records show that near-source ground motion accelerations in main West-Coast towns of the South Island are expected to exceed 20%g during an Alpine fault earthquake, while ground motions in Christchurch are expected to be moderate, with peak ground accelerations (PGAs) of 8%g. This high near-source PGA will need further modelling as it is likely due not only to non-linear soil response not accounted for in this study but also to the presence of a modelled asperity nearby and to strong directivity effects.
Intellectual Merit - The research in this project on ground motion modeling for New Zealand is directly relevant to ongoing research in Southern California: approach, methodology, impact of the modeled events, learning form the Canterbury earthquake sequence etc …
- The lead author of this report is also an active participant in the GMSV TAG
Broader Impacts - The research in this project on ground motion modeling for New Zealand is directly relevant to ongoing research in Southern California: approach, methodology, impact of the modeled events, learning form the Canterbury earthquake sequence etc …
- In a broader picture, this project encourages the presence of New Zealand research in an international key platform such as SCEC, but also brings to New Zealand new ideas/input/learning/collaboration from SCEC.
Exemplary Figure Figure 1: (left top and bottom) Mw 8.2 Alpine Fault heterogeneous slip model scenario employing RUPGEN toolkit developed by Mai et al. (2000) and Mai et al. (2002); (right) Peak ground Accelerations computed for an heterogene-ous slip Alpine Fault Scenario plotted against distance to the rupture plane. The black and purple lines are respec-tively extracted from the McVerry et al. (2006) and Chiou and Youngs (2008) models using OpenSHA (Field et al. 2003). It is interesting to note that the simulations match the empirical estimates at short distances but are constantly smaller at increasing distances. This can be explained by the unique narrow fault geometry of the Alpine fault.