Scientists To Look Closer At Fiordland Aftershocks

MEDIA RELEASE from GNS Science
16 OCTOBER 2007
Scientists To Take Close Look At Fiordland Aftershocks

Seismologists plan to install portable instruments in Fiordland later this week to record aftershocks in the wake of today’s magnitude 6.7 quake west of Milford Sound.

The six battery-powered seismometers will enable pinpoint accuracy in recording the size, depth, and location of aftershocks.

Close study of aftershocks enables seismologists to determine the size and orientation of the “fault break” in the crust. This helps in indicating if the main shock has had any affect on nearby faults.

GNS Science seismologist Bryan Field said aftershocks could continue for several weeks after a large earthquake.

“ Aftershocks occur as the earth’s crust adjusts to stresses caused by the main shock. No two aftershock sequences are exactly the same,” Mr Field said.

“ This looks to be a particularly rich aftershock sequence that should yield useful information about stresses in the earth’s crust in the Fiordland region.”

In the hours following this morning’s main shock, there were dozens of aftershocks with half-a-dozen big enough to be felt widely in the southern part of the South Island.

Mr Field said the portable instruments would record aftershocks continually for several weeks before scientists would recover them and analyse the data they had captured.

Today’s magnitude 6.7 quake is the biggest in New Zealand since a magnitude 7.2 quake struck near Secretary Island off the Fiordland coast on 22 August 2003. Scientists recorded about 5000 aftershocks over several months after the 2003 quake.

ENDS

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