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GEOREF RECORD

A fall in P-wave velocity before the Gisborne, New Zealand, earthquake of 1966

D. J. Sutton
A fall in P-wave velocity before the Gisborne, New Zealand, earthquake of 1966
Bulletin of the Seismological Society of America (1974) 64 (5): 1501-1507

Abstract

A fall in P-wave velocity before the Gisborne earthquake of March 4, 1966 is indicated by arrival-time residuals of P waves from distant earthquakes recorded at the Gisborne seismograph station. Residuals were averaged over 6-month intervals from 1964 to 1968 and showed an increase of about 0.5 sec, implying later arrival times. The change began about 480 days before the earthquake. This precursory time interval is about that expected for an earthquake of this magnitude (ML = 6.2), but unlike most other reported instances, there was no obvious delay between the return of the velocity to normal and the occurrence of the earthquake. Similar analyses were carried out over the same period for two other New Zealand seismograph stations; at Karapiro there was no significant variation in mean residuals, and at Wellington the scatter was too large for the results to be meaningful. The Gisborne earthquake has a focus in the lower crust, about 25 km deep and was deeper than other events for which such precursory drops in P-wave velocity have been reported.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 64
Serial Issue: 5
Title: A fall in P-wave velocity before the Gisborne, New Zealand, earthquake of 1966
Author(s): Sutton, D. J.
Pages: 1501-1507
Published: 1974
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
Accession Number: 1975-006005
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. (incl. sketch map)
S38°40'60" - S38°40'60", E178°01'60" - E178°01'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2024, American Geosciences Institute. Reference includes data supplied by Institute of Geological and Nuclear Sciences Limited (GNS Science), Lower Hutt, New Zealand
Update Code: 1975
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