A revision of attenuation relationships for Modified Mercalli intensity in New Zealand earthquakes

  • D. J. Dowrick Department of Scientific and Industrial Research, Lower Hutt, New Zealand

Abstract

This study of attenuation of Modified Mercalli intensity in New Zealand earthquakes used a carefully selected set of isoseismal maps from 30 events with magnitudes ranging from ML= 5.0 to Ms = 7.8, and depths ranging from very shallow to 65 km. A completely revised set of magnitudes was used. A two-step stratified regression analysis was used to evaluate the coefficients of the expression for intensity

I = a + bM + cr + dlog10r

where r is the mean slope radius corresponding to the distance from the isoseismal to the centroid of the fault rupture surface. The resulting expressions model events of all depths very well, and completely revise the attenuation curves of earlier work done in the 1970’s in which depth was not taken into account. The earlier proposals for regional variations in attenuation were not substantiated, the apparent differences for most of the country being explained by the effects of depth and source mechanism rather than path characteristics. The attenuation character of the Central Volcanic Region and Fiordland remain to be properly established. Attenuation of intensity in New Zealand was found to be very similar to that for Turkey, the two regions being dominated by strike-slip faulting.

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Published
1991-09-30
How to Cite
Dowrick, D. J. (1991). A revision of attenuation relationships for Modified Mercalli intensity in New Zealand earthquakes. Bulletin of the New Zealand Society for Earthquake Engineering, 24(3), 210-224. https://doi.org/10.5459/bnzsee.24.3.210-224
Section
Articles