New Zealand Journal of Geology and Geophysics abstracts

---

The Ormond, New Zealand, earthquake of 1993 August 10: rupture in the mantle of the subducted Pacific plate

MARTIN REYNERS
PETER MCGINTY
KEN GLEDHILL

Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand

Abstract  Data from temporary seismographs installed immediately after the ML 6.3 Ormond earthquake of 1993 August 10 have been used to determine the nature of faulting which took place during the event. The rupture began at 37 km depth, within the mantle of the subducted Pacific plate, and aftershocks extended from near the base of the subducted crust to c. 20 km into the subducted mantle. Aftershocks in the mantle decayed exceptionally rapidly compared with those in the crust of the subducted plate. This may reflect a hotter, more ductile mantle and/or relatively homogeneous rupture within the mantle during the mainshock. Aftershocks within the mantle show a variety of thrusting mechanisms. Focal mechanisms of aftershocks within the subducted crust indicate that compression along strike dominates over slab pull, and that the down-dip stress has a similar magnitude to the vertical stress. This suggests that, at least after the Ormond earthquake, the tectonic stress coupled across the plate interface is rather low.

Keywords  Ormond earthquake; subduction; aftershocks; focal mechanisms; plate coupling

New Zealand Journal of Geology and Geophysics, 1998, Vol. 41: 179-185

0028-8306/98/4102-0179 $7.00/0 (c) The Royal Society of New Zealand 1998

PDF file of entire paper: medium quality (598K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page