Frequency Distributions of Earthquake Intensities on Oahu, Hawaii

Abstract

The record of intensities of historic earthquakes felt on Oahu compiled in a companion report has been subjected to tests for completeness and for the validity of the intensity estimates. The record from 1859 through 1983 seems to be essentially complete for quakes with Modified Mercalli intensities of V or greater at Honolulu, and that since about 1910 essentially complete for quakes with Honolulu intensities of IV or greater. No evidence of systematic bias of the intensity estimates was found. A composite record, including all earthquakes with Honolulu intensities of IV or greater occurring during the 74-year period from 1910 through 1983 and the single quake occurring prior to 1910 that had a Honolulu intensity larger than any in the 74-year period, was subjected to frequency analysis. Frequency distributions of both exponential form and of power-law form were found to fit the composite record well. From these frequency distributions, it is estimated that the return interval for earthquakes with intensities of VII or greater in Honolulu lies almost certainly between 74 and 255 years and probably between 125 and 158 years. The records of intensities at places in the western part of Oahu are much less complete, but it appears that, at those places, the return intervals for earthquakes of VII or greater are probably between 480 and 610 years.