Abstract
With the availability of better estimates of magnitudes for large historical earthquakes, a 1978 study to model the Modified Mercalli intensities in large earthquakes in New Zealand has been revised. While instrumental measures of strong ground motion are obviously valuable, intensities will always be important because most of our large historical events predate the installation of accelerographs, and because intensity does seem to give a measure of the degree of damage. Crustal earthquakes in the Main Seismic Region have been divided into two classes on the basis of known or apparent focal depth. Events in the volcanic region are treated separately. No revision is attempted for shallow earthquakes in Fiordland or for events at greater than crustal depths anywhere in the country, the data base being too poor. Detailed goodness-of-fit statistics are presented: they compare favourably with those for the 1978 model and also for another model developed recently. The model is for the far field, so is useful for regional estimation of hazard but not for fault-specific studies at short distances. A companion paper addresses near-source modelling. Intensity is often assumed to be linearly related to the logarithm of ground motion parameters such as displacement or acceleration. This study shows that that assumption cannot hold over a range of distances. It may be possible to formulate a linear relationship at any particular distance, but the parameters of that relationship will change as distance is varied.
Highlights
One of the essential tools in earthquake hazard analysis is a model for the attenuation of strong ground motion with distance from the source
While it is clearly desirable to have instrumental records of strong motion, because of the shortcomings of the intensity scale, the fact remains that most of our large earthquakes occurred before accelerographs were in operation
The present study develops a function which has a similar curvature for the two regions, but in Region A that curvature is only evident at distances less than about 20 km, where we have very little data
Summary
One of the essential tools in earthquake hazard analysis is a model for the attenuation of strong ground motion with distance from the source. The strong motion data available from most of New Zealand's important earthquakes are in the form of intensities. While it is clearly desirable to have instrumental records of strong motion, because of the shortcomings of the intensity scale, the fact remains that most of our large earthquakes occurred before accelerographs were in operation. It was used in a hazard analysis [Smith 1978b], and a summary of these two papers was presented as soon as the results were to hand [Smith, 1976]. Smith & Berryman [1983,1986] used the results of the 1978 study to estimate earthquake hazard Because the 1976 paper presented only a summary and not the full detail of the analysis, the study will be referred to as the 1978 study. Smith & Berryman [1983,1986] used the results of the 1978 study to estimate earthquake hazard
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
