Announcement of the severe earthquake in the Kermadec Islands, New Zealand, July 6, 2011

     A powerful earthquake with M = 7.8 has occurred on July 6, 2011 at 19:03 UTC (23:03 Moscow time) near the Kermadec Islands, New Zealand.
     Parameters of the earthquake have been determined in the Alert Service (AS) of Information Processing Center (IPC) of Geophysical Survey of RAS in Obninsk with station data obtained from digital and analog seismic stations of Russia, countries of CIS and from abroad. Alert message on this earthquake has been delivered in 21 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 37 stations, accurate processing - with data 74 stations.
     Fig. 1 presents fragments of records obtained from digital stations Port Moresby (∆ 39.6º), Tennant Creek (∆ 45.6º), Кipapa (∆ 53.4º), Petropavlovsk (∆ 84.9º), Mys Shultsa (∆ 86.4º). Fig. 2 presents fragments of records obtained from digital stations Kuldur (∆ 90.9º), Magadan (∆ 92.7º), Seimchan (∆ 95.3º), Bilibino (∆ 97.9º), Yakutsk (∆ 100.8º).

Figure 1
 

Figure 2
 
     IPC GS RAS also has obtained information with parameters of this event from some seismological centers, these data are given in table 1:
Table 1
NN Time in origin h-min-s (GMT) Lat degr. Lon degr. Depth km N s/st Ms/ N mb/ N I0 calc GAP Center
1 19-03-17.9 -29.32 -176.25  20  74  7.8/257.2/2810-10.5 43 IPC GS RAS (Accurate)
2 19-03-18.4 -29.29 -176.31  20  37  7.8/237.1/1010-10.5 76 IPC GS RAS (Preliminary)
3 19-03-22.7 -29.27 -176.28  40  673  Mw 7.6   19 CSEM
4 19-03-16.7 -29.31 -176.2  20  620  Mw 7.8 7/341 18 NEIC
  • IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences
  • CSEM - European - Mediterranean seismological center
  • NEIC - National Earthquakes Information Center of US Geological Service
    • Epicenter
         Fig.3 presents with red star epicenter of this earthquake, which origin was located in the region of Kermadec Islands, New Zealand, at the depth of 20 km, 913 km S-S-W off Nuku'alofa town - the Capital of Tonga and 1184 km N-E off Auckland, New Zealand.

    Figure 3
    Aftershock
         GS RAS registered 10 aftershocks with М>=5.1 within 15 after the main shock.
    N Date   &   Time (GMT)
    yy-mm-dd hh:mm:sec    		 Lat
    degr.    		 Lon
    degr.    		 Depth
    km    		 N
    station    		 Ms/ N mb/ N Io
    calc.    		 Region
    201131052011-07-06 20:35:39.0-29.46-176.342021-5.8/ 56-6.5 Kermadec Islands region
    201131062011-07-06 21:04:01.0-29.18-176.382011-5.6/ 45.5-6 Kermadec Islands region
    201131082011-07-06 22:31:22.0-29.2-177.17209-5.1/ 24.5-5 Kermadec Islands, New Zealand
    201131092011-07-07 00:33:34.0-28.9-176.782010-5.5/ 55.5 Kermadec Islands region
    201131102011-07-07 01:26:36.0-29.18-176.292013-5.3/ 45-5.5 Kermadec Islands region
    201131122011-07-07 02:10:19.0-29.12-177.092018-5.3/ 55-5.5 Kermadec Islands, New Zealand
    201131132011-07-07 03:41:40.0-29.67-176.493314-5.2/ 34-4.5 Kermadec Islands region
    201131152011-07-07 04:40:14.0-29.66-176.312019-5.6/ 85.5-6 Kermadec Islands region
    201131182011-07-07 09:10:52.0-29.06-176.783323-6.0/ 86 Kermadec Islands region
    201131192011-07-07 09:29:58.0-29.15-176.933327-5.8/ 55.5 Kermadec Islands region
    Macroseismic manifestations
         According to RIA-Novosti no messages about casualties or damage were received. It was expected that quite a powerful tsunami could reach New Zealand's East Cape for two hours after the earthquake, and the Auckland Islands - in three. However, the office of civil defense of New Zealand stated that the threat of a major tsunami had passed, but the people living in coastal areas, is still worth to stay away from the coast due to strong currents.
    Historical records
         The earthquake of July 6, 2011 took place near the Kermadec trench. This area is a zone of subduction of the Pacific and Australian plates, which is experiencing high levels of seismic activity. Over the past 38 years have seen 50 events with M> = 6.5 and 4 events with M> = 7.5. Two of them with M = 7.8 and M = 8.2 occurred on January 11 1976 in 150 km west-north-west of the present case, an earthquake with M = 7.8 occurred February 9 1978 in 200 km to the southwest, and with M = 8.3 - on October 20, 1986 about 130 km to the north. Neither one of these events were observed damage or casualties.
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution of the origin for this earthquake which occurred on July 6, 2011 at 19:03 UTC was calculated using long-period waves (WPhase) at the National Earthquake Information Center U.S. Geological Survey, USGS, and the method of centroid moment tensor in the Global CMT Catalog , USA. Focal mechanisms in the stereographic projection on lower hemisphere are shown in Figures 4-5, the elements are presented in Table. 2. Solutions are practically identical. The earthquake occurred under the influence of tensile stresses oriented nearly along latitude. Both nodal planes are circum-meridian stretch. Type of movement in both planes - fault components with left hand shift components on the flatter plane NP1 (DP = 33 º -40 º) and right hand shift for the steeper NP2 (DP = 52 º -58 º). The value of seismic moment for this quake of July 6, 2011 according to the USGS is Mo = 2.8 * 10 ** 20 n * m, the value of moment magnitude Mw = 7.6. The value of seismic moment for this quake of July 6, 2011 according to the Global CMT Mo = 2.92 * 10 ** 20 n * m, moment magnitude Mw = 7.6.
    Table 2
    Axes of main strengths Nodal planes Center
    T P N NP1 NP2
    Pl Azm Pl Azm Pl Azm Stk Dp Slip Stk Dp Slip
    62707627 111791440-71170 52-105NEIC
    139274304 8183859-80171 33-105Quick CMT
  • NEIC - National Earthquakes Information Center of US Geological Service
  • Quick CMT - Quick CMT catalog

    • Figure 4
    Figure 5


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