Earthquake in New Zealand
Wednesday, 15. July 2009, 17:46:19
So far only little damage has been reported. The affected region is unpopulated (0 people/km²) and has high resilience for natural disasters. A tsunami warning was in effect for about 2 1/2 hours after the quake, but then dropped. Sea-level readings indicated a tsunami had been generated by the temblor, though there was no report of any substantial impact. At Jackson Bay, the sea had risen 0.17 m. The coastal area near the epicenter is sparsely populated and includes Fiordland National Park. Tectonic Summary from USGS:
“The North and South Islands of New Zealand straddle the boundary between the Australian and Pacific plates. Along this boundary through southern New Zealand, the Australian Plate moves to the northeast at a rate of 35-45 mm/yr relative to the Pacific plate. In Southwestern South Island, this motion is accommodated by oblique convergence at the Puysegur Trench, where the Australian Plate subducts beneath the Pacific Plate. Further north along the South Islands’ west coast, relative motion is accommodated via oblique strike-slip movement along the Alpine Fault, driving the uplift of the Southern Alps.
The recent (09/07/15) thrust earthquake occurred near the southern tip of South Island in a region known as Fiordland, in a complex area of transition in plate boundary structure from Puysegur subduction to Alpine fault strike-slip motion. The preliminary location, depth, and estimate of fault orientation of this event are consistent with the earthquake having resulted from slip on the subduction thrust interface between the Pacific and Australian plates. The deformed Australian plate beneath Fiordland is highly active both along its’ interface with the Pacific plate and internal to the subducted Australian plate. Over the past two decades, several large earthquakes have occurred in Fiordland, predominantly in a cluster to the northeast of today’s earthquake. Though the faulting mechanisms of those events are similar to today’s earthquake, their slip vectors are rotated clockwise with respect to plate motions, and thus may not represent exactly the same style of faulting.
The most recent of these previous large events occurred in August of 2003 when a magnitude 7.2 earthquake approximately 100 km to the northwest caused minor damage in Otago and Southland, and numerous landslides across the Fiordland region. A magnitude 7.0 event on August 10, 1993 caused power outages in the Te Anau area and was felt throughout South Island and as far away as Sydney, Australia. A magnitude 6.4 earthquake struck on May 31, 1989 and was felt strongly in the southwestern part of South Island and a magnitude 6.7 quake struck on June 3, 1988.”
The following map from USGS gives a lot of information about the earthquake:
Another map from the USGS Earthquake Seismicity webpage shows the New Zealand transform faults (Alpine fault) in a greater tectonic perspective. Earthquakes occur regularly in New Zealand . About 14,000 earthquakes, most of them minor, are recorded each year. About 200 of these are strong enough to be felt. Fewer than 10 annually cause damage. Most earthquakes in New Zealand occur along the main ranges running from Fiordland in the southwest to East Cape in the northeast. This axis follows the boundary between the Indo-Australian and Pacific plates. Large earthquakes are less common along the central Alpine Fault, where the plates are not subducting and the forces are accommodated in different ways.Some of the links below are rather short-lived
• http://news.xinhuanet.com/english/2009-07/15/content_11713337.htm
• http://www.bloomberg.com/apps/news?pid=20601087&sid=aB8ek3ijRBiM
• http://www.gdacs.org/reports.asp?eventType=EQ&ID=61348&system=asgard&location=NZL&alertlevel=Green&glide_no=&TsID=1479
• http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009jcap.php
• http://shakingearth.blogspot.com/2009/07/largest-quake-of-year-in-new-zealand.html
• http://news.bbc.co.uk/2/hi/asia-pacific/8151530.stm
• http://tvnz.co.nz/national-news/factbox-new-zealand-s-biggest-earthquakes-2848956
• http://www.huffingtonpost.com/2009/07/15/new-zealand-earthquake-tr_n_232996.html
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