Informational message about the strong earthquakes in the Solomon Islands, April 12 and 13, 2014

     The strong earthquake M=7.7 has occurred on April 12, 2014 at 20:14 GMT (April 13 at 00:14 Moscow time) in the Solomon Islands. Another shock M=7.4 has occurred in less than 17 hours on April 13 at 12:36 GMT (16:36 Moscow time).
     Alert messages about these earthquakes were sent to EMERCOM operational staff in 14 and 16 minutes after their occurrence respectively.
      Fig. 1 presents fragments of non filtered records obtained from digital stations Monsavu (∆ 16.6º), Tennant Creek (∆ 28.2º), Erimo (∆ 55.8º), Yuzhno-Kurilsk (∆ 57º), Taejon (∆ 57.7º). Fig. 2 presents fragments of filtered records used for extraction of initial arrivals from digital stations Kurilsk (∆ 57.7º), Mys Shultsa (∆ 60.7º), Vladivostok (∆ 60.8º), Severo-Kurilsk (∆ 61.9º), Petropavlovsk (∆ 64.1º).

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 12-36-17.7 -11.18 161.86  33  53  7.4/286.9/238.5-9 71 IPC GS RAS ([2])
2 20-14-34.6 -11.25 162.29  10  38  7.7/197.2/1811 134 IPC GS RAS ([1])
3 20-14-39.1 -11.284 162.254  20  159  Mw 7.8   35 CSEM ([1])
4 12-36-16.8 -11.46 161.99  10  63  Mw 7.6   50 CSEM ([2])
5 20-14-39.6 -11.315 162.211  29.3  88  Mw 7.6 6.9/214 28 NEIC ([1])
6 12-36-18.7 -11.451 162.069  35  130  Mw 7.4 6.8/421 17 NEIC ([2])
  • 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
         The epicenter of the first earthquake is shown in Fig. 3 with red star, which origin was located in the Solomon Islands at the depth of 10 km, 324 km S-E of the capital city of the Solomon Islands, Honiara. The epicenter of the second earthquake is shown with yellow star, its origin was located at a depth of 33 km, 48 km W-N-W of the first shock.

    Figure 3
    Aftershock
         Increased seismic activity in the area was registered since April 11, when it was recorded the earthquake M=6.8 at 07:07 GMT, it was located 945 km S-W of the currently reported earthquake of April 12 and it was accompanied with 19 aftershocks М>=4.6. Origins of these earthquakes were located at a depth of 50-60 km. After the strong shock M=7.7 GS RAS registered 17 aftershocks M>=4.7 within the next 16 hours. Another strong shock M=7.4 was registered less than 16 hours after the first one, then it was accompanied with 18 aftershocks M>=4.7 within the next 17 hours. About 60 events were registered for 3 days in the area of Solomon Islands. The strongest aftershocks M>5.5 are shown 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
    201413052014-04-12 20:24:42.0-11.18162.151031-5.8/ 227-7.5 Solomon Islands
    201413092014-04-12 21:39:00.0-11.01162.081032-5.5/ 166.5-7 Solomon Islands
    201413342014-04-13 12:46:42.0-11.2162.383324-5.9/ 135.5-6 Solomon Islands
    201413362014-04-13 13:12:20.0-11.03161.943325-6.0/ 136 Solomon Islands
    201413382014-04-13 13:25:02.0-11.06161.893349-5.9/ 225.5-6 Solomon Islands
    Historical records
         The region of the reported earthquake of April 12, 2014 is seismic active. According to USGS NEIC since 1900 in this area within the margins of 500 km about 62 earthquakes with М>=7 were registered. Most famous of them have occurred in radius about 100 km: doublet with М=7 in November 1978, the earthquakes М=7.1 in 1931 and 1937 and another one with М=7.2 in 1910. The last strong earthquake in the area of Solmons has occurred on February 6, 2013 М=6.7 in 295 km E of current epicenter, and destructive earthquake which caused tsunami wave with height of about 5 meters has occurred on April 1, 2007 М=7.8- in 670 km N-W of current epicenter.
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution of the origin for the earthquake of April 12, 2014 was obtained in IPC GSRAS with signs of initial arrivals of P waves at 95 stations, including 58 stations which registered the waves of compression (plus signs), and 36 stations which registered the waves of expansion (minus signs). These stations are located in the interval of epicentral distances of 2–99º are evenly dispersed along the azimuth. Focal mechanism solution in stereographic projection at the lower hemisphere is presented at fig. 4, elements of mechanism are presented in table 2. Fig. 5, 6 and table. 2 present focal mechanism solutions obtained in USGS NEIC with tensor moment Mww technique and in Quick CMT Catalog, USA with CMT technique. Both solutions are close. The earthquake has occurred under the action of compression stresses N-E–S-W oriented. Transverse stresses were oriened to the north. Nodal plane NP1 strikes N-E (STK=15-29º) and is steeply dipping (DP=57–78º). Nodal plane NP2 strikes S-E (STK=115-124º) and is dipping to the horizon under the significant angles (DP=70–75º). The type of motion along both planes – slips (right latteral for NP1, left latteral for NP2) with reverse fault components. Seismic moment of the earthquake 12.04.2014 was obtained in IPC GS RAS with Р-wave spectra obtained at «Talaya» station (∆80.41º), Mo=1.9*10**20 N*m, Mw=7.5; according to USGS NEIC – Mo=2.72*10**20 N*m, Mw=7.6, according to Quick CMT – Mo=3.48*10**20 N*m, Mw=7.6. Focal mechanism solution of the origin for the earthquake of April 13, 2014 was obtained in IPC GS RAS with signs of initial arrivals of P waves at 93 stations, including 82 stations which registered the waves of compression (plus signs), and 11 stations which registered the waves of expansion (minus signs). These stations are located in the interval of epicentral distances of 2–99º and are dispersed rather uniformly along the azimuth. Focal mechanism solution of the origin in stereographic projection at the lower hemisphere is presented at fig. 7, elements of mechnism are presented in table 2. Fig. 8, 9 and table 2 present focal mechanism solutions obtained in USGS NEIC with tensor moment Mww technique and in Quick CMT Catalog, USA with CMT technique. Both solutions are close. The earthquake has occurred under the action of compression stresses oriented almost along meridian. Both nodal planes have nearly the same dip angle (DP=40–52º) and have latitudional (STK=90-105º) and N-W (STK=279-299º) strike directions. The type of motion along both planes – reverse faults with slip components. Seismic moment of the earthquake of 13.04.2014 was obtained in IPC GS RAS with Р-wave spectra registered at «Talaya» station (∆80.13º), Mo=9.6*10**19 N*m, Mw=7.3; according to USGS NEIC – Mo=1.59*10**20 N*m, Mw=7.4, according to Quick CMT – Mo=1.76*10**20 N*m, Mw=7.4. As one can see focal mechanisms of these two origins are different. Both earthquakes have occcurred in the same seismic region, but in different tectonics conditions. The earthquake of April 12, 2014 with М=7.7 has occurred close to transform rupture oriented N-W-S-W, this is at the border between Australian and Pacific Ocean plates. The type of focal mechanism of the origin – slip. The earthquake of April 13, 2014 with М=7.4 has occurred to the south from Australian plate, close to ocean trench which adumbrates the border between Australian and Pacific Ocean plates, in the zone of subduction characterized by sheer change of interaction between the plates. The type of focal mechanism of the origin – reverse fault.
    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
    23346578 661802978160124 7013IPC GS RAS [1]
    792890199 11109984675299 46105IPC GS RAS [2]
    283395246 61148116742419 67163NEIC [1]
    87120112 32821054494279 4686NEIC [2]
    3534011242 53137115753415 57162Quick CMT [1]
    78249611 10102904075289 52102Quick CMT [2]
  • IPC GS RAS [1] - IPC GS RAS [1]
  • IPC GS RAS [2] - IPC GS RAS [2]
  • NEIC [1] - National Earthquakes Information Center of US Geological Service[1]
  • NEIC [2] - National Earthquakes Information Center of US Geological Service [2]
  • Quick CMT [1] - Quick CMT catalog [1]
  • Quick CMT [2] - Quick CMT catalog [2]

    • Figure 4
    Figure 5

    Figure 6
    Figure 7

    Figure 8
    Figure 9


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