Magnitude 7 Earthquake Hits Kermadec Islands

Region: KERMADEC ISLANDS, NEW ZEALAND

10-degree Map Centered at 30°S,180°E – 2 Earthquakes on the Map. USGS

Raoul Island, Kermadec Islands, Global Reference Map. USGS

Magnitude:    7.0
Date-Time: Tuesday, September 30, 2008 at 03:19:31 AM at epicenter
Location: 29.872°S, 177.684°W
Depth: 35 km  set by location program
Distances:

• 70 km  SSE of Raoul Island, Kermadec Islands
• 210 km  NE of L’Esperance Rock, Kermadec Islands
• 1050 km  NE of Auckland, New Zealand
• 1440 km  NNE of WELLINGTON, New Zealand

Location Uncertainty: horizontal +/- 6.8 km ; depth fixed by location program
Source: USGS NEIC

Aftershocks: Magnitude 5.2 [Tuesday, September 30, 2008 at 04:10:38 AM at epicenter at T+ 51 min.]

FEWW Comments:

• Another 6.8+ quake in the area within 200km radius of Raoul Island, as well as more aftershocks of magnitude 4+ can be expected in the next 18-24 days.

• The mean center of earthquake cluster incidence along the Tonga – Kermadec subduction zone that has produced about 50 earthquakes of magnitude 6 or larger [USGS data] and includes the epicenter of the September 30 quakes detailed above, is shifting in a southerly direction, along the interaction line between the Pacific and Australia plates, toward New Zealand.

Implication for New Zealand Islands:

• A substantial increase in the frequency of earthquake striking the twin islands.
• More earthquakes with magnitude 6 or larger.
• A marked increased in large explosive volcanic eruptions, especially in the following zones [also include ‘extinct’ volcanoes]
  • Taupo Volcanic Zone
  • Bombay Hills
  • Auckland volcanic field
  • Mount Taranaki
  • Mt Horrible volcano
  • Mount Taranaki
  • Mount Cargill

Worst Case Condition for New Zealand Islands:

• Large earthquakes and massive volcanic eruptions could potentially destroy much of New Zealand structures and claim many lives.
• Earthquake and volcano-triggered waves could also give rise to 40 to 50-meter tsunami that would engulf the coastal areas and low-lying lands throughout New Zealand [could also affect parts of Australia’s eastern seaboard,] compounding the damage.
• A super/mega colossal Plinian/Ultra-Plinian eruption occurring in New Zealand’s North Island simultaneously [or within a short period of time] with a magnitude 9.8 earthquake off the eastern coast of New Zealand could claim many lives.
• Probability of occurrence:
  1. Event 1.  A magnitude 9.8 earthquake striking off the eastern coast of New Zealand with (i) the foreshocks ripping through Auckland, Hamilton, Taupo areas, (ii) the mainshock leveling Wellington, Palmerstone North, Marlborough, Nelson and Christchurch, and (iii) the aftershock causing substantial damage as far south as Invercargill: 85%
  2. Event 2. A super/ mega colossal Plinian/Ultra-Plinian eruption in the North Island: 72%  [South Island: 57%]
  3. Event 1 and Event 2 occurring simultaneously, or within a short period of time: 64 %

Related Links:

• Earthquake Cluster Zone Closing in on New Zealand
• Mt Ruapehu Eruption Alert

Seismicity in 2008. USGS

Magnitude 7 and higher since 1900. USGS

All Images Credit: USGS

PDF version ; Image

DISCUSSION [Source: USGS]

The September 29, 2008, M7.0 earthquake occurred in the Tonga – Kermadec subduction zone. The subduction zone extends north-northeast from the North Island of New Zealand for over 2500 km through Tonga to within 100 km of Western Samoa. At a broad scale, tectonics of the subduction zone reflect the motion of the Pacific plate westward with respect to the interior of the Australia plate at a velocity of about 60 mm/y in the epicentral region of the earthquake. The Pacific plate subducts beneath the Australia plate at the Tonga and Kermadec trenches, and dips to the west. In detail, the eastern edge of the broad Australia plate may itself be viewed as a collection of small plates or microplates that move with respect to each other and with respect to the Pacific plate and the Australia plate interior. The location and focal-mechanism of the earthquake are consistent with it occurring as thrust faulting on the interface between the subducting Pacific plate and the overriding Australia plate (in detail, the overriding Kermadec microplate).

The interaction between the Pacific and Australia plate creates one of the most active tectonic environments in the world, with a high level of associated earthquake activity. Since 1976, a 200-km long section of the Tonga – Kermadec subduction zone that includes the epicenter of the September 29 earthquake has produced over 50 earthquakes of magnitude 6 or larger, with the largest having magnitude 7.9.