Jan 12 2012 - December 2011 GeoNet roundup

Additions and upgrades to the geophysical monitoring networks

• In the Canterbury region, two new strong-motion sites were installed at Hillmorton High School (HHSS) and Ouruhia School (OHSS), and two of the temporary sites were made permanent Whitecliffs (WCSS) and Sign of the Kiwi (STKS).
• In the North Island, new strong motion sites were installed at Naenae Bowling Club (LNBS) in Lower Hutt, Opunake Primary School (OPSS) and Monrad Intermediate School (PNMS) in Palmerston North.

Earthquakes summary

• The most reported felt earthquake of the month occurred on Saturday, December 3, magnitude 5.7, 30 km east of Picton at a depth of 60 km. We have received 5,486 felt earthquake reports to date. This is the second-most reported New Zealand earthquake after the M 7.1 Darfield quake (7,552 reports).
• The Darfield aftershock sequence stirred again on Friday, December 23 with the most significant earthquakes being of magnitude 5.8 and magnitude 6.0. We have received 1,778 and 1,243 felt earthquake reports respectively for these.
• The preliminary locations of November's earthquakes located by our analyst team are shown below. Not all events for this month have been fully analysed yet due to the high numbers of earthquakes we are dealing with at this time. These maps will be updated when the month is finalised.

Volcano surveillance update and field trips

Summary

• No eruptive volcanic activity occurred at any of New Zealand's active volcanoes during December.
• Visits to White Island found that the lake level continues to fall.
• The temperature of Ruapehu's Crater Lake fluctuated between 30 to 33 °C.

Thursday December 1 - Gas flight over White Island

The gas flight took place in very unpleasant, bumpy conditions. Unfortunately, due to instrument problems there was no CO₂ result. There has been a increase in SO₂ since the last flight in September, but that was a particularly low result. H₂S was similar to the previous reading in August.

Thursday December 8 - White Island Sampling and Deformation Survey

Spectacular sulphur deposits seen on White Island during the December visits.

The Crater Lake was not sampled as access was difficult. It is much lower compared to the last sampling trip in late September and there has been some minor landslide activity on the lower shelf where we would normally access the lake. The fumaroles temperatures were slightly down and the flows were down a lot since the previous visit in August.

Friday December 9 - White Island Soil Gas Survey and Spring Sampling

The spring temperatures were slightly up and the overall soil flux was down from the previous survey trip in August.

Reported landslides from media sources

Wednesday December 14 - Friday December 16

• Exceptionally heavy rainfall in Nelson and parts of Tasman district resulted in thousands of slips. The worst affected areas were Nelson city and the eastern parts of Golden Bay. Significant slips include:
  • Rocks Road (SH 6) in Nelson closed by rock-falls;
  • Incipient movement of parts of the Tahunanui landslide resulted in the evacuation of several homes;
  • SH 60 at Birds Hill between Takaka and Collingwood – both lanes were taken out by an underslip;
  • Several valleys east of Takaka, including the Pohara Valley, were badly affected by debris flows with many houses damaged and streams changing course;
  • The road to Totaranui will be closed for three months;
  • The Abel Tasman walkway was closed due to slip damage.

Saturday December 31

• Slips closed SH 2 in the Waimana Gorge forcing thousands of travellers to use a detour. The Waioeka Gorge was also affected by slips.

Felt earthquakes of
November 2011
(92 located).

Shallow earthquakes of
November 2011
(421 located to date).

Deep earthquakes of
November 2011
(167 located to date).