Information message about the strong earthquake in the Queen Charlotte Islands region on October 28, 2012

     The strong earthquake with M=7.7 has occurred on October 28, 2012 at 03:04 GMT (07:04 Moscow time) in the Queen Charlotte Islands region of Canada.
     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 16 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 48 stations, accurate processing - with data 59 stations.
     Fig. 1 presents fragments of records obtained from digital stations Albuquerque (∆ 25.4º), Bilibino (∆ 32.4º), Hockley (∆ 34.9º), Petropavlovsk (∆ 40.3º), Magadan (∆ 41.3º). Fig. 2 presents fragments of records obtained from digital stations Talaya (∆ 66º), Obninsk (∆ 72.2º), Borovoe (∆ 73º), Kiev (∆ 75.8º), Kislovodsk (∆ 83.6º).

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 03-04-08.1 52.75 -132.06  20  59  7.7/327/329.5-10 79 IPC GS RAS (Accurate)
2 03-04-07.6 52.67 -132.11  20  48  7.7/297.1/269.5-10 79 IPC GS RAS (Preliminary)
3 03-04-08.5 52.624 -132.175  10  486  Mw 7.7   50 CSEM
4 03-04-10.6 52.769 -131.927  17.5  716  7.4/796.5/536 58 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 the epicenter of this earthquake which origin was located at the west coast of the Queen Charlotte archipelago Moresby, Canada, at a depth of 20 km, 211 km S-Wof Prince Rupert, 745 km N-Wof Vancouver.

    Figure 3
    Aftershock
         GS RAS registered 29 aftershocks with М ≥ 4.7 within the day after the main shock. Most signidficant of them are presented in the table.
    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
    201239862012-10-28 06:16:49.052.05-131.751027-5.3/ 176-6.5 Queen Charlotte Islands region
    201239902012-10-28 09:17:26.052.21-132.251028-5.4/ 176-6.5 Queen Charlotte Islands region
    201240062012-10-28 18:54:19.052.54-132.7610436.2/ 245.9/ 198.5-9 Queen Charlotte Islands region
    201240072012-10-28 19:03:20.052.83-132.731029-5.5/ 146.5-7 Queen Charlotte Islands region
    201240082012-10-28 19:09:52.052.34-132.121034-5.6/ 196.5-7 Queen Charlotte Islands region
    201240092012-10-28 19:16:48.052.6-132.581034-5.4/ 156-6.5 Queen Charlotte Islands region
    Macroseismic manifestations
         Fig. 4 shared from USGS NEIC presents the USGS Community Internet Intensity Map by 931 responses in 179 cities. After this earthquake local authorities issued tsunami warning for Hawaii Islands and for Oregon State. Authorities of Hawaii Island announced evacuation for nearly 100 thousand people. However their concerns were in vain: the height of wave which reached Hawaii Islands was significantly lower than the value forecasted by specialists. In accordance with West Coast and Alaska Tsunami Warning Center most significant wave height of 76 cm was noticed at Kahului Maui HI.

    Figure 4
    Historical records
         Within the last 40 years 7 earthquakes with M>6 were registered in this region, the most significant of them was the earthquake on November 17, 2009 with M=6.5 which occurred in 84 km S-E of the reported here earthquake 2012.
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism of the earthquake on October 28, 2012 at 3h 04m is shown in Figures 5-7 in the stereographic projection on the lower hemisphere, the elements of the mechanism are presented in Table 2. Focal mechanism solutions are computed: in IPC GS RAS - according to the P-wave first arrival signs on 248 stations in the range of epicentral distances of 2.8-98º (205 “plus” signs and 43 “minus” signs); using WPhase Moment Solution method (USGS WPhase Moment Solution) at the National Earthquake Information Center OF U.S. Geological Survey (USGS NEIC) and by centroid moment tensor method in Quick CMT Catalog, USA. Solutions according to the different centers are similar. The earthquake occurred under the influence of similar by value compressive stresses of SW orientation and tensile stresses of NNE orientation. One of the nodal planes - NP1 – is steeply dipping (DP = 58-72 º), the other - NP2 - is flat (DP = 18-32º). Type of movement in the source is a reverse fault on NP1 plane and a thrust on NP2 plane. Seismic moment of the earthquake obtained in IPC GS RAS from P-wave spectra at three stations: "Talaya» (Δ 65.95 º), «Obninsk» (Δ 72.18 º) and "Kislovodsk» (Δ 83.64 º) is Mo=2.8*10**20 N*m, Mw=7.6. Seismic moment of the earthquake according to the USGS NEIC is Mo=6.9*10**20 N*m, Mw=7.8, according to the Quick CMT Mo=5.18*10**20 N*m, Mw=7.7.
    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
    76713208 51171145884304 3299IPC GS RAS
    622427215 41231227285317 18105NEIC
    70317215 101221166379320 29111Quick CMT
  • IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences
  • NEIC - National Earthquakes Information Center of US Geological Service
  • Quick CMT - Quick CMT catalog

    • Figure 5
    Figure 6

    Figure 7


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