Seismology Highlights 2012-13
Greendale Fault trace, September 2010.
New Zealand's plate boundary location means that it is particularly vulnerable to earthquake hazard, especially since several of our large cities are situated close to active faults. From New Zealand's historical record, we also know that earthquakes are an important trigger for local tsunami, landslides, and liquefaction. Earthquake effects possibly represent the most severe, but infrequent, natural hazard in New Zealand, yet are also the most amenable to mitigation via zoning, building codes, and other social measures. For these reasons, earthquake research is critical, and has very high uptake by research users.
A better understanding of earthquake hazard is vital for the development of hazard models, estimation of risk and the development of robust mitigation strategies. An understanding of the earthquake rupture process, seismic energy attenuation and site effects is critical in understanding the conditions necessary for initiation of earthquakes and the associated ground motions. The research is ultimately used to inform and update regional seismic hazard models and building design standards
Canterbury Earthquake Sequence 2010-11
The September 2010 Darfield earthquake generated a 30 km of surface fault rupture along the Greendale Fault. Near the western end of the fault rupture there is a serendipitous coincidence of a number of extremely high quality data sets, including pre- and post-earthquake LiDAR, cadastral surveys, and detailed fault mapping. These data sets have been combined to yield the most comprehensive picture of kinematics and deformation on any stretch of surface fault rupture worldwide and will inform engineering design, and land-use planning with regard to mitigation of the damage and loss resulting from surface fault rupture.
- Duffy, B., Quigley, M., Barrell, D.J.A., Van Dissen, R., Stahl, T., Leprince, S., McInnes, C., Bilderback, E., 2013, Fault kinematics and surface deformation across a releasing bend during the 2010 Mw 7.1 Darfield, New Zealand, earthquake revealed by differential LiDAR and cadastral surveying. Geological Society of American Bulletin 125 (3/4): 420-431. doi: 10.1130/B30753.
Results from spectral inversion of Canterbury earthquake data were presented at the annual Seismological Society America (SSA) workshop in April, and at the New Zealand Society of Earthquake Engineering, also in April. This research is continuing as part of the Natural Hazards Research Platform contestable round in 2012, incorporating site effect work done at GNS Science.
- Kaiser, A.E.; Oth, A.; Benites, R.A. 2013. Source, path and site effects influencing ground motions during the Canterbury earthquake sequence, determined from spectral inversions. Paper 18: Proceedings of the New Zealand Society for Earthquake Engineering Annual Meeting, 26 – 28 April, Wellington.
- Kaiser, A.; Oth, A. 2013. Separating Source, Path and Site Influences on Ground Motion during the Canterbury Earthquake Sequence, New Zealand. Oral presentation at Seismological Society of America Annual Meeting, 17 - 19 April, Salt Lake City.
In collaboration with Brad Aagaard (USGS), we are investigating finite element models of dynamic rupture propagation during the Darfield main earthquake. These models are helping to constrain the range of source parameters ( e.g. background stress field, stress-drops) for the multi-fault-segment rupture during the Darfield earthquake.
- Aagaard, B., C. A. Williams, and B. Fry, Factors Contributing to Multi-Fault Rupture in the 2010 M7.1 Darfield, New Zealand, Earthquake, AGU Fall Meeting, 2012.
Russ van Dissen (centre) in trench dug at Wellington Fault, Upper Hutt (2008).
Wellington Fault
A large earthquake on the southern section of the Wellington Fault is one of the most severe natural hazards that faces the country. Accordingly, the likelihood of rupture of this section of fault is of national significance. In our recently published paper, the rate of movement of the Wellington Fault, and its variability through time, is evaluated. These results are being used to calculate the likelihood of a large earthquake on this portion of the Wellington Fault (about 10-15% in the next 100 years). Related work on the Wairarapa and Ohariu faults has also been undertaken.
- Ninis, D., Little, T.A., Van Dissen, R.J., Litchfield, N.J., Smith, E.G.C., Wang, N., Rieser, U., Henderson, C.M., 2013, Slip rate on the Wellington Fault, New Zealand, during the late Quaternary: Evidence for variable slip during the Holocene. Bulletin of the Seismological Society of America 103 (1): 559-579. doi: 10.1785/0120120162.
- Van Dissen, R., Rhoades, D., Little, T., Litchfield, N., Carne, R., Villamor, P., in press, Conditional probability of rupture of the Wairarapa and Ohariu faults, New Zealand. New Zealand Journal of Geology and Geophysics.
National Seismic Hazard Model
Matt Gerstenberger has developed an expert elicitation process to assess seismic hazard models for the Canterbury region. International experts were invited to a workshop in November 2012, where a number of different models were presented and discussed by the panel. This is an innovative approach to seismic hazard assessments not applied previously in New Zealand, and results are being used for earthquake response and future planning by government. A significant component of our work has been in responding to requests from the Engineering Advisory Group (Building & Housing, MBIE) and other end-users, such as the insurance industry. We developed seismicity information to help end-users understand the modelled seismic hazard for the region and included such things as looking at different magnitudes, time ranges and aftershocks.
NSHM update for 2010 showing peak ground acceleration expected with a 475 year return period on Class C sites. Hazard estimates in units of g.
- McVerry, G.H.; Gerstenberger, M.C.; Rhoades, D.A.; Stirling, M.W. 2012 Spectra and pgas for the assessment and reconstruction of Christchurch. paper 115 (8 p.) IN: Implementing lessons learnt : 2012 Conference, 13-15 April, Christchurch, New Zealand. Christchurch: New Zealand Society for Earthquake Engineering. (Link ♦)
- Gerstenberger, M.C.; Rhoades, D.; McVerry, G.H.; Berryman, K.R.; Christopherson, A.; Nicol, A.; Pettinga, J.R.; Steacy, S.; Stirling, M.W.; Reyners, M.E.; Williams, C.A. 2012 A time-dependent update of the New Zealand National Seismic Hazard Model for the Canterbury earthquake sequence. p. 434 IN: SSA 2012 Annual Meeting announcement. Albany, Calif.: Seismological Society of America. Seismological research letters 83(2).
Our joint collaborative work with Southern California Earthquake Center (SCEC) continues. We work closely with SCEC to advance the testing of earthquake forecasting models - this is a key part of our activities connected with the Collaboratory for the Study of Earthquake Predictabilty (CSEP), a broad international collaboration. Staff attended SCEC sponsored invitation-only CSEP workshops in Palm Springs, California in June 2012 and ETH Zurich in October 2012. Additional collaborations between SCEC and GNS Science include benchmarking exercises for numerical codes used in stress and deformation modelling of coseismic, interseismic, and postseismic behavior. Yoshi Kaneko participated in the SCEC (Southern California Earthquake Centre) code validation benchmark on "Dynamic rupture propagation on a vertical strike-slip fault with a step-over". Kaneko's benchmark results agreed well with those of other modelers - the results are at http://scecdata.usc.edu/cvws/.
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Last updated 26 September 2013.