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Focal mechanisms of intermediate depth and deep earthquakes in the North Island, New Zealand

dc.contributor.authorHarris, F
dc.date.accessioned2011-08-25T21:16:30Z
dc.date.accessioned2022-10-30T18:57:49Z
dc.date.available2011-08-25T21:16:30Z
dc.date.available2022-10-30T18:57:49Z
dc.date.copyright1975
dc.date.issued1975
dc.description.abstractThe focal mechanisms of 215 intermediate-depth earthquakes between latitudes 38°S and 40°S and 24 deep earthquakes beneath the Bay of Plenty are studied on the basis of P and S wave first motion data. For 155 of the intermediate shocks (group A) a composite focal mechanism solution gives the tension axis parallel to the Benioff zone and inclined in a northward direction at about 30° to the dip of the zone. This orientation is related to the sloping bottom edge of the lithospheric slab, which is sinking through the asthenosphere under its own weight. The compression axis is also parallel to the Benioff zone. For a further 41 intermediate earthquakes (group B) a composite focal mechanism gives the tension axis in the direction of the dip of the Benioff zone and the compression axis normal to the zone. Most of these earthquakes were 150 km to 200 km deep, and it is proposed that at such depths the occurrence of a group A earthquake temporarily removes the effect of the sloping bottom edge of the lithospheric slab on the local stress field. The focal mechanism solution of the deepest well-observed earthquake between latitudes 38°S and 40°S, which was at 274 km, gives a down-dip compression axis, suggesting that at this depth the lithospheric slab has encountered resistance to its downward motion. For 23 of the deep shocks beneath the Bay of Plenty the composite first motion pattern is similar to that for the group B earthquakes, consistent with the bottom edge of the lithospheric slab being horizontal in this region. For the remaining earthquake, which at a depth of 423 km was 52 km below the next deepest, the first motions have opposite polarity to those of the other deep shocks, again suggesting that at the greater depth the lithospheric slab has encountered resistance to sinking.en_NZ
dc.formatpdfen_NZ
dc.identifier.urihttps://ir.wgtn.ac.nz/handle/123456789/25928
dc.languageen_NZ
dc.language.isoen_NZ
dc.publisherTe Herenga Waka—Victoria University of Wellingtonen_NZ
dc.rights.holderAll rights, except those explicitly waived, are held by the Authoren_NZ
dc.rights.licenseAuthor Retains Copyrighten_NZ
dc.rights.urihttps://www.wgtn.ac.nz/library/about-us/policies-and-strategies/copyright-for-the-researcharchive
dc.subjectEarthquakesen_NZ
dc.subjectEarthquakes in New Zealanden_NZ
dc.subjectPhysicsen_NZ
dc.titleFocal mechanisms of intermediate depth and deep earthquakes in the North Island, New Zealanden_NZ
dc.typeTexten_NZ
thesis.degree.disciplinePhysicsen_NZ
thesis.degree.grantorTe Herenga Waka—Victoria University of Wellingtonen_NZ
thesis.degree.levelMastersen_NZ
thesis.degree.nameMaster of Scienceen_NZ
vuwschema.type.vuwAwarded Research Masters Thesisen_NZ

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