• Improvements to the popular Quake Search application were released. It features a more straightforward interface and a wider variety of output formats, as well as being more robust "under the bonnet".
• The regional seismic site at Highcliff Hill (HHSZ) near Dunedin was upgraded to full National Network specifications, and has been renamed Otago Peninsula (OPZ). The short-period seismometer has been replaced with a broadband seismometer, capable of measuring seismic waves at a wider range of frequencies, and an accelerometer has been added to measure the amplitude of strong shaking should a large earthquake occur.
• A combined seismic and CGPS site was made operational at Black Hill Station (BHHZ) east of Taihape.
• A down-hole strong-motion array (site code EDAS) was installed and made operational at the Fonterra factory near Edgecumbe in the Bay of Plenty. It features three seismometers at varying depths and a pressure sensor to determine the water-table depth.

• Additional volcano monitoring information was made available on the website. A new section called Current Activity shows a network map, recent earthquakes and links to a representative seismograph for each volcanic centre, plus webcam photographs and movie sequences where these are available.
• Two new combined seismic and CGPS sites were made operational at Arahi (near Wairoa) and Kereru (in southern Hawke's Bay).
• Three more strong-motion recorders, part of the CanNet network, were installed in Christchurch city.

A new section called Current Activity has been added. For each volcanic centre, it shows a network map, recent earthquakes and links to a representative seismograph. For those volcanoes with cameras, we are now regularly constructing short movies from the still photographs.

Images

A big, new gallery of stunning photos.

Monitoring Methods

Lots of detailed information here about how we perform volcano monitoring.

• One new seismic station was completed and brought on line at Post Office Road, on the eastern side of the northern Tararua ranges.
• The web camera watching Ngauruhoe was upgraded; the previous camera had given faithful service since April 2002.
• A VSAT satellite connection was installed on Great Barrier Island and is now transmitting data from a hydrophone array. This will also serve a tsunami gauge and a seismic station that are planned to be built.
• Hazards information is now available in mobile and PDA-friendly form on the "mobile" GeoNet website.
• Sea level data recorded by the New Zealand Tsunami Monitoring Network is now available on the website, and a plot showing the recordings of the last 36 hours can be viewed.

On the website you can find:

• Plots of the relative sea levels on the Tsunami Gauges page.
• Raw data from the gauges.

To get there from the main website, a link has been placed on the home page (the phone icon next to the RSS icon at the top right). There is also user agent detection, so if you attempt to go to www.geonet.org.nz from a mobile device you should get redirected to the mobile content.

The release of this website will allow emergency responders to view geohazard maps and images as well as text information even if they are away from their computers without expensive download costs and difficult site navigation.

Photograph looking north towards the dam crest along the outflow channel, March 4 2008.

Photograph looking north of the Young River landslide, dam and lake, March 4 2008.

In November 2007 GeoNet installed radio communications to the lake-level sensor, allowing data from the dam to be accessed from GNS Science in Avalon near Wellington. These data are proving very useful for both GNS assessing changes in lake level due to rainfall and Otago Regional Council for their management of the hazard.

A second laser-scan survey of the landslide (by GNS on November 1 2007) covered a much larger portion of the landslide and was combined with a control survey using satellite global positioning system (GPS) equipment. This allowed the landslide and lake volumes to be more accurately estimated.

Dam height (maximum) above the original river bed:	70 metres
Landslide volume:	11 million cubic metres
Lake volume (at dam crest level):	21 million cubic metres

Lake water continues to flow over the dam crest and has caused some erosion of material from along the outflow channel during periods of high rainfall. A laser-scan survey of the outflow channel was repeated on March 4 2008 to enable assessment of the amount of this erosion.

When we hear about an earthquake, we often want to know who is going to have been affected by it. ShakeNZ on the GeoNet home page tells us the shaking intensities at individual locations within minutes. What if we want a broad view of the zone of impact? This is where the new isoseismal map can help. Isoseismal contours join up points of equal Modified Mercalli intensity, much like an isobaric map shows the high and low pressure areas on a weather map. A model¹ is used to predict the likely level of shaking caused by an earthquake of a certain magnitude, depth, region and fault rupture type.

A model is necessarily a simple view of the more complex reality, and the contours shown will not exactly correspond to the spot intensities reported by instruments and people. Nevertheless the contours give a quick visual appreciation of the anticipated zone of impact.

The model has been derived from the contours of "felt" reports of many past New Zealand earthquakes. The reports you make after feeling an earthquake add to the data that can be used to improve this model in the future. The model also allows planners to set up "what if?" scenarios and be better prepared for actual earthquakes when they happen.

The accompanying images show two recent examples of isoseismal maps: the top one is a "felt only" earthquake, with damage unlikely; the bottom one is potentially serious, but the structural damage zone is out to sea, and the lesser damage zone is largely in wilderness. We have used three coloured zones to help understand the overall seriousness of the earthquake: green for areas likely to have felt the earthquake, yellow for areas where household contents and fittings may be damaged, and red for areas that may experience damage to buildings.

In the past two years there have been three earthquakes that caused shaking in the red zone: the Fiordland earthquake (shown) and one of its aftershocks, and the December 2007 earthquake off the coast of Gisborne. By using colour to highlight the expected seriousness of shaking, we can better understand whether an earthquake is significant or not.

¹Dowrick, D.J.; Rhoades, D.A. 2005 Revised models for attenuation of Modified Mercalli intensity in New Zealand earthquakes. Bulletin of the New Zealand Society for Earthquake Engineering, 38(4): 185-214.

The twelve active volcanoes in New Zealand are monitored by the GeoNet project using a variety of techniques. The most common and useful is volcano-earthquake monitoring, along with direct observation and water and gas chemistry. Ground deformation surveys are also conducted at some of the volcanoes.

A moderate to large eruption through the active Crater Lake at Mt Ruapehu on September 25 generated a blast and ballistic fall field to the north of the lake, across much of the summit area. It also generated lahars into two catchments draining off the summit of the volcano. The lahar to the north down the Whakapapa Valley reached into the skifield, while the floods down the Whangaehu Valley reached to just beyond the National Park Boundary. The Crater Lake started the year warm, ranging around 23 - 28 ºC cooling through the middle part of the year. The eruption occurred from a cool lake, but the lake has been heating since the eruption, reaching 37 ºC in December. Volcanic tremor and volcanic earthquakes are often recorded at Ruapehu, and were recorded through 2007. Following the September eruption the level of volcanic tremor increased and remained high at year's end.

In March, the tephra dam blocking the natural outlet of the Crater Lake failed during a storm and the much anticipated break-out lahar occurred. This created a unique opportunity for scientists to study a volcanic lahar and test contingency plans.

In late May 2006, a period of seismic unrest began at Ngauruhoe with a several-fold increase in the rate of volcanic earthquake activity. On June 6 2006, in response to the volcanic earthquakes, the Scientific Alert Level was raised from 0 to 1, signifying that there had been a departure from typical background activity and that there were consequently signs of volcano unrest. The signs of volcanic unrest have continued this year; however the program of volcanic gas and temperature monitoring has shown no changes to date. There have been no eruptions at Ngauruhoe since 1977. Volcanic earthquakes are considered a common precursor to volcanic eruptions, particularly when there is a significant increase in the number and/or size of events.

Also since 2000 we have also observed significant numbers of shallow volcanic earthquakes at Tongariro volcano without any other changes in monitored parameters and without an eruption.

New Zealand’s other active volcano is White Island, which has not erupted since 2000, when a scoria eruption occurred, marking the end of an eruption episode that ran from December 1975. Following the eruptions in 2000 the active crater has cooled, allowing a crater lake to form and fill the crater. The water level rose in this lake to reach within about 1 m of overflow in February 2006. Later that year the lake temperature rose to over 60 ºC and the lake level started to fall and by March 2007 the water level had receded 25 m. The fall is due to evaporation of the hot lake water. Through the remainder of the year the water level in the lake remained low.

Only two small hydrothermal eruptions occurred in Rotorua during 2007. The first on May 27 at the mouth of the Puarenga Stream, and a smaller one at the former site of Malfroy's geyser in the Government Gardens in late June. These were smaller than events last year.

The largest and most destructive earthquake in 2007 occurred on the evening of December 20 and was centred offshore, 50 km south-east of Gisborne. The magnitude 6.8 earthquake, the most damaging in New Zealand since the Edgecumbe earthquake in March 1987, was at a depth of 40 km and was felt from Auckland to Dunedin and on the Chatham Islands. At least three buildings collapsed in Gisborne city, and others suffered severe structural damage. Services, including electricity, gas, water and sewerage, were also affected. Because the earthquake was centred within the subducting Pacific plate, few aftershocks followed, with the largest being a magnitude 4.8. GeoNet received over 3,000 felt reports, and preliminary Earthquake Commission estimates for the cost of damage to residential property are around $30 million.

Early on October 16, a magnitude 6.7 earthquake centred 60 km west of Milford Sound caused landslides in the Milford Sound area, and minor to moderate damage, mostly goods falling from shelves, throughout the lower South Island. The depth of the event was 24 km, and it was caused by stresses due to the subduction of the Australian plate beneath the Pacific plate. There were several significant aftershocks, the largest being of magnitude 6.2, which also caused goods to fall from shelves. The Earthquake Commission reports the cost of claims so far at about $1.5 million, and there were close to 1,600 felt reports for the main event.

The largest deep earthquake, a magnitude 5.9 event on November 30, was also in the Fiordland region, centred 50 km north-west of Te Anau at a depth of 115 km. This was felt from Stewart Island to Christchurch, with a few scattered reports of goods off shelves.

Other widely felt earthquakes of interest include a magnitude 5.4 event on January 18, at a depth of 50 km and centred 20 km north of Taihape, which was felt throughout the lower North Island. On May 13, a magnitude 5.4 event near Nelson, with a depth of 90 km, was felt from Marton to Christchurch. On August 25, a magnitude 5.1 event at a depth of 50 km and centred 40 km west of Foxton, was felt from the King Country through to North Canterbury. On October 4, a magnitude 5.6 earthquake centred 40 km north of Hanmer Springs at a depth of 70 km, was felt from Hamilton to Ashburton, with over 2,230 felt reports submitted. And on November 7, a magnitude 5.4 earthquake, 60 km deep, centred 30 km south of Saint Arnaud, was felt from New Plymouth to Christchurch, with 930 felt reports received.

Four earthquakes located outside the New Zealand region were reported felt. The two most significant of these occurred on September 30 and were both shallow events centred about 400 km south-west of Stewart Island. The first had a magnitude of 7.3, the second four hours later was of magnitude 6.4. Both were felt from Stewart Island to Christchurch, with goods off shelves reported at several localities for both. There was a total of over 1,200 felt reports for these events.

Seismic swarm activity in the region close to Matata in the central Bay of Plenty, which began in January 2005, continued intermittently during 2007, with about 1,200 events of depth about 5 km. Six of magnitude 4.0 or greater were located there in the period from March to May. In late September and October there was another period of intense activity during which five events of magnitude greater than 4.0 occurred. The biggest event of the sequence was magnitude 4.7 on September 30, and was felt throughout the Bay of Plenty. A total of about 190 of these swarm events have been reported felt throughout the year. The activity is due to spreading of the earth’s crust in the region, gradually pulling apart at the rate of about one cm per year.

Unusual earthquakes throughout the year include three small shallow earthquakes centred in the Hauraki Gulf east of Orewa that occurred on February 21, the biggest of magnitude 4.5. These were felt widely throughout Auckland and the Coromandel Peninsula, with a few reports of items falling from shelves. Because of its location close to a major urban area, close to 2,000 felt reports were submitted for this relatively minor event.

Another small but unusual event, a magnitude 4.1 earthquake, 10 km deep and centred 20 km south-east of Dunedin, was felt throughout eastern Otago, with some reports of goods falling off shelves in Dunedin. A total of over 630 felt reports were received for this event.