New Zealand Journal of Geology and Geophysics abstracts
The Mw 6.2 Cass, New Zealand, earthquake of 24 November 1995: reverse
faulting in a strike-slip region
KEN GLEDHILL
RUSSELL ROBINSON
TERRY WEBB
RACHEL ABERCROMBIE
JOHN BEAVAN
JIM COUSINS
Institute of Geological & Nuclear Sciences
Gracefield Centre
P.O. Box 30 368
Lower Hutt, New Zealand
DONNA EBERHART-PHILLIPS
Institute of Geological & Nuclear Sciences
Private Bag 1930
Dunedin, New Zealand
Abstract On 24 November 1995 an earthquake of moment
magnitude MW 6.2 struck near the small settlement of Cass in the
Southern Alps, South Island, New Zealand. Body-wave modelling using teleseismic
arrivals gives an oblique reverse focal mechanism for the mainshock, with the
fault plane striking approximately north-south, and a shallow centroid depth of
3-6 km. Aftershock recordings at the station SNZO near Wellington were
used as empirical Green's functions to estimate a source time function duration
of 7 s. A joint inversion for velocity and location of 169 selected events
was used to derive a one-dimensional velocity model with station terms, and
this velocity model was then used to relocate all recorded aftershocks. A
subset of the best 803 events was then selected for further analysis. The
apparent trend of the aftershock zone is NNW-SSE, with the mainshock near the
centre. However, projections of the aftershocks on north-south and east-west
cross-sections show a band of activity shallowing to the south and dipping to
the west. The north-striking, west-dipping nodal plane of the mainshock focal
mechanism is therefore most likely to be the fault plane. Early aftershocks
occurred mainly to the south of the mainshock location, suggesting rupture to
the south, a feature supported by the mainshock modelling. The aftershock focal
mechanisms are mixed but reflect the regional stress field (NW-SE
compression).
Keywords Cass earthquake; focal mechanisms; aftershocks;
strong ground motion
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
255-269
0028-8306/00/4302-0255 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (1778K); (scanned from paper original: notes about this process)
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