December 20, 2007 Gisborne Earthquake

Response Spectra

A set of acceleration spectra for the GeoNet site closest to the Gisborne CBD have been processed by Jim Cousins and Graeme McVerry of GNS Science. These were compared with the design spectra from NZS 1170.5, the seismicity model (to test the attenuation model), and from the hazard spectra. The comparisons and some salient points of interest are available in an accompanying document: Gisborne Spectra.

The notable features are the high acceleration levels (around 0.5 ULS) in the 0.2 to 0.8 sec period range and a specific spike at around 0.35 sec. (nearly to ULS level), which diminishes rapidly beyond that range. (Note that the spectra were reoriented to be true N/S and E/W, which differs from the instrumentation orientation as shown on the GeoNet website).

Work continues and more information will be provided as it comes to hand.

See the GNS Science News Release BIG FINISH TO THE EARTHQUAKES OF 2007 (9 Jan 2008) for more details about the earthquake.

The earthquake will be the topic at a special session of the 2008 NZSEE Conference.