Wednesday, July 22, 2009

Earthquake on South Island, NZ

An earthquake occurred at 9:22 PM (9:22 AM GMT) on the evening of Wednesday, July 16th in the Fiordland region of southern New Zealand. At this writing , the earthquake's moment magnitude is reported as 7.6 by the USGS but as 7.8 by the New Zealand's Institute of Nuclear and Geological Sciences. Fiordland is near the southern tip of South Island, where the Australian Plate moves to the northeast at a rate of 35-45 mm/yr relative to the Pacific plate. The yellow area in the above "beach ball" pattern shows the predominantly eastward component of the current thrust within the northeastward plate movement.

The tremor lasted at least a minute and was felt as a rolling motion across New Zealand's South Island, according to the BBC. New Zealand issued a tsunami warning for a string of its coastal towns and cities, but later cancelled it. A tsunami was detected in the Tasman Sea, heading towards the southeast coast of Australia. About an hour after a tsunami warning was issued, Australian officials downgraded it to a "small boat alert" and there was little or no evidence for coastal flooding as a result of the quake.

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