Information message about the strong earthquake near the western coast of South Island, New Zeeland, July 15, 2009.

     The strong earthqauke with М=7.6 has occured on July 15, 2009 at 09:22 GMT (13:22 Moscow time) near the western coast of South Island, New Zeeland.
     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 37 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 30 stations, accurate processing - with data 41 stations.
     Fig. 1 presents fragments of records obtained from digital stations Tennant Creek (∆ 36.9º), Sanae (∆ 62.8º), Erimo (∆ 89.8º), Vladivostok (∆ 93.6º), Petropavlovsk (∆ 98.5º). Fig. 2 presents fragments of records obtained from digital stations Talaya (∆ 111.1º), Bilibino (∆ 113.4º), Tiksi (∆ 120º), Borovoe (∆ 128º), Arti (∆ 135.5º).

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 09-22-31.8 -45.65 166.66  33  41  7.6/246.4/119 115 IPC GS RAS (Accurate)
2 09-22-31.8 -45.62 166.7  33  30  7.6/226.2/89 200 IPC GS RAS (Preliminary)
3 09:22:30.5 -45.721 166.595  2  77  7.7 Mw   80 CSEM (Preliminary)
4 09:22:29.6 -45.73 166.573  2  201  7.8Mw   27 CSEM (Accurate)
5 09:22:29.0 -45.75 166.577  12  209  7.6Mw 6.6/45 25 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 depicts with red star epicenter of this earthquake, which was located near the western coast of South Island, New Zeeland, at the depth of 33 km, in 157 km. N-W from Invercargill, in 295 km. West from Dunedin, in 527 km. S-W from the Capital of South Island Christchurch and in 811 km S-W from New Zeeland capital Wellington.

    Figure 3
    Aftershock
         GS RAS has registered: 8 aftershocks with magnitudes М>4.8 (within the day 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
    200922572009-07-15 09:41:57.0-46.11166.13316-5.8/ 65.5 Off w. coast of S. Island, N.Z.
    200922582009-07-15 09:52:20.0-45.49165.463311-5.3/ 44-4.5 Off w. coast of S. Island, N.Z.
    200922602009-07-15 13:50:42.0-45.27166.843315-5.4/ 54.5 Off w. coast of S. Island, N.Z.
    200922652009-07-15 23:41:18.0-45.57167.21709-5.3/ 43-3.5 South Island, New Zealand
    200922672009-07-16 00:24:08.0-46.33165.893310-5.3/ 44-4.5 Off w. coast of S. Island, N.Z.
    200922682009-07-16 00:44:50.0-46.33166.053310-5.3/ 44-4.5 Off w. coast of S. Island, N.Z.
    200922692009-07-16 02:13:11.0-45.33166.753310-4.8/ 53-3.5 Off w. coast of S. Island, N.Z.
    200922722009-07-16 06:30:02.0-45.79166.51336-5.0/ 43.5-4 Off w. coast of S. Island, N.Z.
    Macroseismic manifestations
          In accordance with NEIC this earthquake was felt all around the South Island with intensity 6 MSK. A few buildings were damaged, communication lines to some settlements interrupted, no victims registered. Fig. 4 shared from NEIC , presents the map with intensities composed from phone calls made by 325 respondents living in 51 local places.

    Figure 4
    Historical records
         New Zeeland is part of so called Fire Ring, which includes seismic active zones and volcanoes, including sea volcanoes. Nearly 14 thousand earthquakes are registered annually on the North and South Islands and adjacent Pacific Ocean territories. On August 21, 2003 in the region of south-western coast of the South Island it was registered the earthquake with Ms=7.3. Fig.5 presents the map with epicenters.

    Figure 5
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solutions of the earthquake which happened on July 15, 2009 at 09:22 GMT were obtained with CMT method in NEIC, USGS Harvard Center USA, HRVD (Global CMT Catalog), they are presented in table 2 and shown on fig. 6,7. These solutions are almost identical. This earthquake has happened under prevailing action of compression forces oriented to the west. One nodal plane NP1 has S-E direction of propagation and is steeply falling (DP=64-75º), another plane NP2 has N-N-E direction of propagation and lays plain more (DP=24-33º). The type of motion for steeply falling nodal planes – uplift (with left side drift components), for plain laying planes in case of USGS – uplift, in case of HRVD – thrust (with right side drift components). The value of seismic moment Мо of the earthquake which happened on 15.07.2009 at 09:22 in accordance with USGS makes Мо=3.1* 10** 20 n*m, in accordance with HRVD Мо = 6.01* 10** 20 n*m; the value of moment's magnitude makes Mw = 7.6 in accordance with USGS and Mw=7.8 in accordance with HRVD.
    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
    644016271 181752733126166 6469NEIC
    564027259 181592624140154 7471HARVARD
  • NEIC - National Earthquakes Information Center of US Geological Service
  • HARVARD - Harvard Geophysical Center (USA)

    • Figure 6
    Figure 7


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