04 September 2010

Earthquake in Christchurch, NZ

Christchurch, New Zealand suffered a 7.1 earthquake yesterday. It appears, remarkably, there there have been injuries but no fatalities. Christchurch is a lovely city on the Canterbury Plains next to the Pacific Ocean. I have found memories of many visits to the city, and have close friends living there. We have been in contact and other than bad damage to their house and the neighbours, all are safe and uninjured.

GNS Science, a New Zealand government-owned research organisation released the following Media Release.

As background, the Hawke's Bay earthquake of 1931 killed hundreds, and raise the port of Napier far enough that the port was too shallow for ships and it silted over. There is now an airfield over what was a port. In addition, the rebuilding that took place in Napier after that quake followed the style of the day, making Napier a center of Art Deco buildings.

Christchurch will recover (quickly), and will continue to be a beautiful city on the plains of the South Island.

At the same time, this is a reminder to all New Zealanders of the importance of earthquake preparedness. Especially in Wellington!





The magnitude 7.1 earthquake that hit Canterbury early today is expected  to be the most damaging since the 1931 magnitude 7.8 Hawke's Bay  earthquake.

The earthquake, which jolted Cantabrians awake at 4.35am on Saturday, was  located 30km west of Christchurch near Darfield at a depth of 10km. It was  felt throughout the South Island and as far north as New Plymouth. Damage  to buildings and infrastructure in Christchurch and surrounding areas is  considerable.

Dozens of aftershocks occurred in the first few hours after the quake and  it is likely they will continue for weeks.   GNS Science duty seismologist, John Ristau, said typically the largest  aftershocks occurred within the first 48 hours of a large earthquake. They  generally declined in frequency and size over time.

"A rule of thumb for a large earthquake at a shallow depth such as this is  that the largest aftershock will be about one unit of magnitude lower than  the main shock," Dr Ristau said.   Seismologists say a foreshock of about magnitude 5.4 occurred a few  seconds before the main shock. Both shocks occurred in slightly different  locations. Seismic energy from the two shocks became entangled making it  difficult to pinpoint the size, location, and depth of the main shock.   There are several known active faults under the Canterbury Plains and in  the Canterbury foothills, but at this stage it appears the earthquake has  not occurred on a known fault.   Scientists from GNS Science, Victoria University of Wellington and  Stanford University in the US have joined colleagues from Canterbury  University to deploy about 40 portable earthquake instruments to record  aftershocks over the next few weeks.

The GNS Science contingent hopes to have most of their portable  instruments deployed around Canterbury by Sunday night. This will mean  approaching landowners and seeking permission, as they hope to place some  of the instruments on private land.   They will concentrate their deployment on the areas where most of the  aftershocks have already occurred.

 The battery-powered instruments will be left unattended for about three  weeks to record aftershocks. Seismologists study aftershock sequences to  find out more about the mechanics of the main shock and rupture, and to  ascertain if stress in the earth's crust has been transferred onto other  faults in the region.

Scientists will also study satellite data to investigate surface  deformation in Canterbury as a result of the earthquake. Geologists from  GNS Science have travelled to Canterbury to investigate the geological and  environmental impacts of the quake, and to undertake a detailed ground  study.   Engineering seismologists from GNS Science will join colleagues from the  Building Research Association of NZ and Canterbury and Auckland  Universities to investigate the impacts on buildings and infrastructure in  Canterbury to find out how different construction types performed.

The information they gather will be fed into the engineering community to  help ensure structures are built appropriately to cope with stresses  caused by strong ground shaking. It will also help as older buildings and  structures are retro-fitted to improve their ability to withstand  earthquake shaking.

Much of the scientific response to the earthquake is being coordinated  under the GNS Science-led Natural Hazards Research Platform, set up by the  government a year ago to provide long-term funding for natural hazards  research.   Manager of the Platform, Kelvin Berryman, said post-earthquake  reconnaissance was one of the roles of the Platform, as well as developing  quantitative estimates of earthquake, volcano, landslide, tsunami, flood,  snow, and wind hazards in New Zealand.

"We have an obligation to learn as much as we can from this event to help  improve our understanding of earthquakes and their impact on society, and  to help ensure that New Zealand is well prepared for future earthquakes,"  Dr Berryman said.   To see more information on the earthquake go to our GeoNet site.

http://www.geonet.org.nz/ Specific information on the Darfield quake can be found here.


No comments:

Post a Comment