Assessment of seismic intensities resulting from the 1987 Edgecumbe earthquake, New Zealand, and implications for modernising the intensity scale

The intensity of shaking caused by the main shock of the M L 6. 3 Edgecumbe earthquake of 1987, as shown by ground deformation, property damage and the impressions of witnesses, and the distribution of intensities about the epicentre, is compared with expectations based on models assumed by Smith. Agreement with one of Smith's regional models is found to be good outside the epicentral area but less good within it, possibly because of the unusually shallo, depth of the source. Limitations of the Modified Mercalli (MM) scale used to classify seismic intensities in New Zealand are discussed, and the possibility that a change to the Medvedev-Sponheuer-Kárník (MSK) scale would be advantageous is considered but rejected. Sugge~tions are made for minor revision of the New Zealand versIOn of the MM scale to improve discrimination between intensities X and XI and to allow for changes in building standards since the current version was published. A need for more systematic archiving of intensity data to facilitate therecovery of specific classes of information is identified.