The Fiordland earthquake of 10 August, 1993

A reconnaissance report covering
 tectonic setting, peak ground acceleration,
 and landslide damage

  • R. Van Dissen GNS Science, Lower Hutt, New Zealand
  • J. Cousins GNS Science, Lower Hutt, New Zealand
  • R. Robinson GNS Science, Lower Hutt, New Zealand
  • M. Reyners GNS Science, Lower Hutt, New Zealand

Abstract

On 10 August, 1993, a ML 6.7 (Ms 7.1, Mw 7.0) earthquake occurred c. 10 km offshore of western Fiordland, New Zealand (45.2° S, 166.7° E). Its hypocentre is approximately 20 km deep which places it on, or close to, the interface between the subducted Australian plate and the overriding Pacific plate. The focal mechanism for the mainshock indicates reverse faulting on either a steep west-dipping, or shallow southeast-dipping plane. Analysis of a subset of the over 7,000 recorded aftershocks defines a shallow (c. 15°) southeast-dipping plane, roughly 25 km long and 15 km wide, that probably represents the rupture surface of the mainshock.

The earthquake was strongly felt by fishermen offshore in the epicentral region. Onshore, there were no reports of damage to man-made structures. The maximum peak ground acceleration recorded was 0.08 g at Te Anau, about 73 km from the epicentre. The attenuation of peak horizontal ground acceleration for this event is similar to the attenuation of other shallow crustal earthquakes in New Zealand.

The number of landslides triggered by this event is at least an order-of-magnitude less than the number of pre-existing landslide scars. The highest concentration of new slides appears to be in the Vancouver Arm/Hall Arm region, c. 45 km south-southeast from the epicentre. Many of the new slides were narrow, shallow seated failures, or small reactivated portions of older slides. The two largest earthquake-triggered landslides observed are located near Hall Arm, and in the Freeman Burn north of Lake Manapouri. Except perhaps for these two slides, all other observed earthquake-triggered slides will be indistinguishable from storm-generated slides once re-vegetated.

References

Carver, G.A., Jayko, A.S., Valentine, D.W. and Li, W.H. 1994. Coastal uplift associated with the 1992 Cape Mendocino earthquake, northern California. Geology 22:195-198. DOI: https://doi.org/10.1130/0091-7613(1994)022<0195:CUAWTC>2.3.CO;2

Cousins, W.J., Porritt, T.E., Hefford, R.T., O'Kane, S.M., Baguley, D.E. and McVerry, G.H. 1993. Peak accelerations from New Zealand earthquake accelerograms. Institute of Geological & Nuclear Sciences Science Report No. 93/43.

Kinugasa, Y., Yamazaki, H., Mizuno, K., Tsukuda, E., Okumura, K. and Hikita, Y. 1993. Crustal movement associated with Hokkaido earthquake of 1993. Proceedings, Eighth International Symposium on Recent Crustal Movements. Kobe, Japan, Dec 6-11.

McVerry, G.H. and Sritharan, S. 1991. Earthquake site response effects demonstrated by New Zealand strong-motion records. Proceedings, Pacific Conference on Earthquake Engineering 3:205-216.

McVerry, G.H. and Dowrick, D.J., Sritharan, S., Cousins, W.J., Porritt, T.E. 1993. Attenuation of peak ground accelerations in New Zealand. Presented at, Japan-US Workshop on Strong-Motion Data, Menlo Park, California, Dec 10-17.

Oppenheimer, D., Beroza, G., Carver, G., Dengler, L., Eaton, J., Gee, L., Gonzalaz, F., Jayko, A., Li, W.H., Lisowski, M., Magee, M., Marshall, G., Murray, M., McPherson, R., Romanowicz, B., Satake, K., Simpson, R., Somerville, P., Stein, R. and Valentine, D. 1993. The Cape Mendocino, California, earthquake of April 1992, subduction at the triple junction. Science 261:433-438. DOI: https://doi.org/10.1126/science.261.5120.433

Perrin, N.D. and Hancox, G.T. 1991). Landslide-dammed lakes in New Zealand - preliminary studies on their distribution, causes and effects. Proceedings, Sixth International Symposium on Landslides 1457-1466.

Reyners, M., Gledhill, K. and Waters, D. 1991. Tearing of the subducted Australian plate during the Te Anau, New Zealand, earthquake of 1988 June 3. Geophysical Journal International 104:105-115. DOI: https://doi.org/10.1111/j.1365-246X.1991.tb02497.x

Reyners, M. and Robinson, R. 1993. Seismicity and structure of the Fiordland subduction zone, New Zealand EOS, Transactions of the American Geophysical Union. 74(43): 96.

Published
1994-06-30
How to Cite
Van Dissen, R., Cousins, J., Robinson, R., & Reyners, M. (1994). The Fiordland earthquake of 10 August, 1993. Bulletin of the New Zealand Society for Earthquake Engineering, 27(2), 147-154. https://doi.org/10.5459/bnzsee.27.2.147-154
Section
Articles

Most read articles by the same author(s)