The Mw 7.2 Fiordland earthquake of August 21, 2003
Background and preliminary results
The Mw 7.2 Fiordland earthquake of August 21 2003 was the largest shallow earthquake to occur in New Zealand for 35 years. Because of its location in an unpopulated area, it caused only minor damage to buildings, roads and infrastructure. It triggered numerous landslides on steep slopes in the epicentral region, where intensities reached MM9. Deployments of portable seismographs, strong motion recorders and GPS receivers in the epicentral region immediately after the event have established that the earthquake involved thrusting at the shallow part of the subduction interface between the Australian and Pacific plates. Recently installed strong motion recorders of the GeoNet network have ensured that the earthquake is New Zealand's best recorded subduction interface event. Microzonation effects are clear in some of the records. Current peak ground acceleration attenuation relationships for New Zealand subduction interface earthquakes underprediet the ground motions recorded during the earthquake, as was the case for previous large events in Fiordland in 1993 and 1989. The four portable strong motion recorders installed in the epicentral region have provided excellent near-field data on the larger aftershocks, with recorded peak ground accelerations ranging up to 0.28g from a nearby ML 6.1 event.
Beavan, J. & Haines, J., (2001). Contemporary horizontal velocity and strain-rate fields of the Pacific-Australian plate boundary zone through New Zealand. Journal of Geophysical Research, 106: 741-770.
Darby, D. J. & Beavan, J., (2001). Evidence from OPS measurements for contemporary plate coupling on the southern Hikurangi subduction thrust and partitioning of strain in the upper plate. Journal of Geophysical Research, 106: 30,881-30,891.
DeMets, C., Gordon, R. G., Argus, D. F. & Stein, S., (1994). Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions. Geophysical Research Letters, 21: 2191-2194.
Doser, D. I., Webb, T. H. & Maunder, D. E., (1999). Source parameters of large historical (1918-1962) earthquakes, South Island, New Zealand. Geophysical Journal International, 139: 769-794.
Eberhart-Phillips, D. & McVerry, G. H., in press. Estimating slab earthquake response spectra from a 3-D Q model. Bulletin of the Seismological Society of America.
Eberhart-Phillips, D. & Reyners, M., (2001). A complex, young subduction zone imaged by three-dimensional seismic velocity, Fiordland, New Zealand. Geophysical Journal International 146: 731-746.
Hancox, G. T., Cox, S., Turnbull, I. M. & Crozier, M. J., (2003). Reconnaissance studies of landslides and other ground damage caused by the M7. l Fiordland earthquake of 22 August 2003. Institute of Geological and Nuclear Sciences science report 2003/30.
Hancox, G.T., & Perrin, N.D., (1994). Green Lake landslide: a very large ancient rock slide in Fiordland, New Zealand. Proceedings of the VIIth I.A.E.G. International Congress, Lisbon, Portugal, 5-9 Sept 1994, p 1677 - 1689.
Hancox, G.T., Perrin, N.D., & Dellow, G.D., (2002). Recent studies of historical earthquake-induced landsliding, ground damage, and MM intensity in New Zealand. Bulletin of the New Zealand Society for Earthquake Engineering, 35: 59-95.
INQUA, (2003). An innovative approach for assessing earthquake intensities: The proposed INQUA Scale based on seismically-induced effects in the environment. Report of Working Group under the INQUA Subcommission on Palaeoseismicity. 16th INQUA Congress, Reno, USA, July 2003.
McVerry, G.H., Zhao, J.X., Abrahamson, N.A. & Somerville, G.H., (2000). Crustal and subduction zone attenuation relations for New Zealand earthquakes. Paper No. 1834, Proceedings 12th World Conference on Earthquake Engineering, Auckland, New Zealand.
Reyners, M., Gledhill, K. & Waters, D., (1991). Tearing of the subducted Australian plate during the Te Anau, New Zealand, earthquake of 1988 June 03. Geophysical Journal International 104: 105-115.
Reyners, M., Robinson, R., Pancha, A. & McGinty, P., (2002). Stresses and strains in a twisted subduction zone - Fiordland, New Zealand. Geophysical Journal International 148, 637-648. DOI: https://doi.org/10.1046/j.1365-246X.2002.01611.x
Reyners, M. & Webb. T, (2002). Large earthquakes in Fiordland, New Zealand, 1989-93. New Zealand Journal of Geology & Geophysics 45: 109-120.
Robinson, R., Webb, T., McGinty, P., Cousins, J. & Eberhart-Phillips, D., (2003). The 2000 Thompson Sound earthquake, New Zealand. New Zealand Journal of Geology & Geophysics 46: 331-341.
Saiki, T., Okada, H., Takahashi, T., Irikura, K., Zhao, J. X., Zhang, J., Thio, H.K., Somerville, P.G., & Fukushima, Y., (2003). Attenuation models for response spectra derived from Japanese strong-motion records accounting for tectonic source types. Abstract submitted to 13th World Conference on Earthquake Engineering, Vancouver, Canada 2004.
Van Dissen, R., Cousins, J., Robinson, R. & Reyners, M., (1994). The Fiordland earthquake of 10 August 1993. Bulletin of the New Zealand National Society for Earthquake Engineering 27: 147-154.
Youngs, R. R., Chiou, S.-J., Silva, W. J. & Humphrey, I. R., (1997). Strong ground motion attenuation relationships for subduction zone earthquakes. Seismological Research Letters 68: 58-73.
Copyright (c) 2003 Martin Reyners, Peter McGinty, Simon Cox, Ian Turnbull, Tim O'Neill, Ken Gledhill, Graham Hancox, John Beavan, Dion Matheson, Graeme McVerry, Jim Cousins, John Zhao, Hugh Cowan, Grant Caldwell, Stewart Bennie, GeoNet team
This work is licensed under a Creative Commons Attribution 4.0 International License.