The Mw 6.6 Gisborne earthquake of 2007

Preliminary records and general source characterisation


  • Caroline François-Holden GNS Science, Lower Hutt, New Zealand
  • Stephen Bannister GNS Science, Lower Hutt, New Zealand
  • John Beavan GNS Science, Lower Hutt, New Zealand
  • Jim Cousins GNS Science, Lower Hutt, New Zealand
  • Bryan Field GNS Science, Lower Hutt, New Zealand
  • Rob McCaffrey GNS Science, Lower Hutt, New Zealand
  • Graeme McVerry GNS Science, Lower Hutt, New Zealand
  • Martin Reyners GNS Science, Lower Hutt, New Zealand
  • John Ristau GNS Science, Lower Hutt, New Zealand
  • Sergey Samsonov GNS Science, Lower Hutt, New Zealand
  • Laura Wallace GNS Science, Lower Hutt, New Zealand



Gisborne city experienced recorded peak ground accelerations exceeding 0.25g for the third time since 1966 in the magnitude Mw 6.6 earthquake at 075516 UT (8:55 pm local time) on 20 December 2007. The earthquake was at a hypocentral distance of 64 km from Gisborne at a depth of 40 km, well within the mantle of the subducted slab of the Pacific plate as it dips beneath the North Island of New Zealand. At this location the plate interface is about 10-15 km deep. The main event was followed by sparse aftershocks consistent with a rupture of the subducted plate, with the largest aftershock of magnitude 4.6 occurring on December 22nd. The GeoNet website received 3,257 felt reports, with a strongest intensity of MM8 (heavily damaging) assigned to the main shock.

The 122 strong motion records of this event show a clear regional directional variation in the wave propagation, as well as a distinct 2 Hz peak widely observed throughout the country. At a local scale, three sites in the Gisborne region recorded accelerations around 0.2g. Recordings in Gisborne city also revealed a predominant displacement direction, parallel to the main street where most of the damage occurred.

Source studies from moment tensor solution, aftershock relocations, GPS and strong motion data showed that the earthquake occurred within the subducted plate on a 45 degree eastward dipping fault plane. The mainshock rupture area is about 10 km2 reaching a maximum slip of 2.6 m. The computed high stress drop value of 17 MPa is as expected for an intraslab event and consistent with observations of very energetic seismic waves as well as heavy structural damage.

GPS data recorded by continuous GPS instruments have also shown that slow slip occurred for about three weeks after the main shock. The slow slip was triggered on the subduction interface, rather than on the same fault plane as the aftershocks. This is the first clear-cut case worldwide of triggered slow slip, although three non-triggered slow-slip events have occurred in the same region since 2002.


Reyners, M. and McGinty, P., 1999. Shallow subduction tectonics in the Raukumara Peninsula, New Zealand, as illuminated by earthquake focal mechanisms. Journal of Geophysical Research B: Solid Earth, 104(B2): 3025-3034. DOI:

Barker, D.H.N., Sutherland R., Henrys S. and Bannister S., manuscript submitted to Tectonics. Geometry of the Hikurangi subduction thrust and upper plate, North Island, New Zealand.

Wallace, L.M., Beavan, J., McCaffrey, R. and Darby, D., 2004. Subduction zone coupling and tectonic block rotation in the North Island, New Zealand, Journal of Geophysical Research, 109, doi:10.1029/2004JB003241. DOI:

Doser, D.I. and Webb, T.H., 2003. Source parameters of large historical (1917-1961) earthquakes, North Island, New Zealand. Geophys. J. Int., 152, 795-832. DOI:

Webb, T. and Anderson, H., 1998. Focal mechanisms of large earthquakes in the North island of New Zealand : slip partitioning at an oblique active margin. Geophys. J. Int., 134, 40-86. DOI:

Reyners, M., McGinty, P. and Gledhill, K., 1998. The Ormond, New Zealand earthquake of 1993 August 10: rupture in the mantle of the subducted Pacific plate, New Zealand Journal of Geol. and Geophys., 41, 179-185. DOI:

Douglas, A., Beavan, J., Wallace, L., Townend, J., 2005. Slow slip on the northern Hikurangi subduction interface, New Zealand Geophysical Research Letters, 32, doi:10.1029/2005GL023607. DOI:

McVerry, G.H., Zhao, J.Z., Abrahamson, N.A. and Somerville, P.G. 2006. New Zealand acceleration response spectrum attenuation relations for crustal and subduction zone earthquakes. Bulletin of the New Zealand Society for Earthquake Engineering, 39(1): 1-58. DOI:

Eberhart-Phillips, D., Reyners, M. Chadwick, M. Stuart, G., 2008. Three-dimensional attenuation structure of the Hikurangi subduction zone in the central North Island, New Zealand. Geophys. J. Int., 174, 418-434. DOI:

Strachan, C.M., and Glogau O.A., 1969. Report on damage in the Gisborne earthquake 1966, Bulletin 194, New Zealand Department of Scientific and Industrial Research.

Eberhart-Phillips, D. and Reyners, M., 1999. Plate interface properties in the northeast Hikurangi subduction zone, New Zealand, from converted seismic waves. Geophys. Res. Lett., 26: 2565-2568. DOI:

Ristau, J., 2008. Implementation of routine regional moment tensor analysis in New Zealand, Seism. Res. Lett., 79, 400-415, doi: 10.1785/gssrl.79.3.400. DOI:

Zhang, H. and Thurber, C., 2003. Double-difference tomography: the method and its application to the Hayward Fault, California, Bull. Seismol. Soc. Am. 93 (2003), pp. 1875-1889.

Waldhauser, F. and Ellsworth, W. L. 2000. A doubledifference earthquake location algorithm: Method and application to the northern Hayward fault, California, Bull. Seismol. Soc. Am., 90, 1353-1368.

Reyners, M.E., Eberhart-Phillips, D., Stuart, G., Nishimura, Y., 2006. Imaging subduction from the trench to 300 km depth beneath the central North Island, New Zealand, with Vp and Vp/Vs. Geophysical journal International, 165(2), 565-583. DOI:

Beavan, J., Wallace, L., Douglas, A., Fletcher, H., and Townend, J., Slow slip events on the Hikurangi subduction interface, New Zealand, Dynamic Planet, Monitoring and Understanding a Dynamic Planet with Geodetic and Oceanographic Tools, IAG Symposium, Cairns, Australia, 22-26 August, 2005, Series: International Association of Geodesy Symposia, Tregoning, Paul; Rizos, Chris (Eds.), Vol. 130, 438-444, (2007).

Francois-Holden, C., Di carli, S., Sladen A. and Madariaga R., 2008. Non linear kinematic source inversion of the 2000 Tottori, Japan earthquake - submitted Geophys. Res. Letters.

Peyrat, S. and Favreau, P. Kinematic and spontaneous rupture models of the 2005 tarapaca intermediate depth earthquake -submitted. Geophys. J. Int.

Massonnet, D. and FEIGL, K., 1998, Radar interferometry and its application to changes in the Earth surface: Reviews of Geophysics, 36, 441-500. DOI:

Rosen, P., Hensley, P., Joughin, I., Li, F., Madsen, S., Rodriguez, E. and Goldstein, R., 2000, Synthetic aperture radar interferometry: Proceedings of the IEEE, 88, 333-382. DOI:

OKADA, Y., 1992, Internal deformation due to shear and tensile faults in a half-space: Bulletin of the Seismological Society of America, 82, 1018-1040.

Internet resource for sand boils observations:




How to Cite

François-Holden, C., Bannister, S., Beavan, J., Cousins, J., Field, B., McCaffrey, R., McVerry, G., Reyners, M., Ristau, J., Samsonov, S., & Wallace, L. (2008). The Mw 6.6 Gisborne earthquake of 2007: Preliminary records and general source characterisation. Bulletin of the New Zealand Society for Earthquake Engineering, 41(4), 266–277.