The Motu River earthquake of 8 March 1984
DOI:
https://doi.org/10.5459/bnzsee.18.1.41-54Abstract
The Motu River earthquake of 8 March 1984 (M = 6.4) was the largest event to occur at the Hikurangi Margin of New Zealand since 1973. It originated in the upper part of the subducted Pacific plate at a depth of 73 kilometres, and appears typical of previous larger events in the region. The earthquake was widely felt, and has provided valuable data on the spatial distribution of intensity from intermediate depth events.
The earthquake produced records of strong ground motion at nine sites within 152 kilometres of the epicentre, though the accelerograms of only one site were of sufficient amplitude to permit digitisation. The distribution of recorded peak accelerations correlates reasonably well with the pattern of S-wave radiation expected from a double-couple point source. A strong-motion instrument near the mouth of the Motu River recorded a relatively short-duration, moderate amplitude motion of extremely monochromatic frequency content. It is likely that a site resonance dominates the data at this location, thus severely limiting the usefulness of the accelerograms for earthquake source studies.
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