Information message about seismic process development in Koryak region within last month since main strike on April 20, 2006 | | Geophisical Survey of GS RAS reports about continued seismic activity in Koryak region. Within last month since the main strike, which happened on April 20, 2006 with magnitude М=7.8 73 aftershocks with magnitudes М>4.0 have been registered here, two of them with М=7.0 (on April 29 and May 22 мая), three - with М >=5.6 (April 21 at 04:32, April 21 at 11:14, May 9 at 11:02 GMT). Aftershock on May 22 has been felt in nine settlements of Olutorsk region, and in Tilichiki settlement being the nearest to the epicenter with intensity 7-8 on МСК-64 scale. | | 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 28 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). | | Preliminary processing has been done with data from 46 stations, accurate processing - with data 50 stations. | | Fig. 1 presents fragments of records obtained from digital stations Bilibino (∆ 7.3º),Petropavlovsk (∆ 8.8º), Yakutsk (∆ 17.1º), Tiksi (∆ 18º), Yuzhno-Sakhalinsk (∆ 19.2º), College Outpost (∆ 21.2º). Fig. 2 presents fragments of records obtained from digital stations Borovoe (∆ 48º), Arti (∆ 50º), Ala-Archa (∆ 54.5º), Obninsk (∆ 57.6º), Kislovodsk (∆ 65.8º), Garni (∆ 68.6º). |
Figure 1
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Figure 2
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| | 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 |
11-11-58.3 |
60.84 |
165.75 |
15 |
50 |
7/17 | 6.5/18 | 9-9.5 | 68 | IPC GS RAS (Accurate) | | 2 |
11-11-58.5 |
60.85 |
165.72 |
15 |
46 |
7/16 | 6.5/15 | 9-9.5 | 68 | IPC GS RAS (Preliminary) | | 3 |
11-11-57.2 |
60.84 |
165.9 |
10 |
393 |
6.7Mw | | | 29 | CSEM | | 4 |
11-11-59.6 |
60.75 |
165.88 |
11 |
78 |
6.6Mw | 6.1/49 | | 47 | NEIC | | 5 |
11-12-54.3 |
60.65 |
166.91 |
10 |
|
7.0 | | | | KRIPC (Preliminary) | | | 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 | | KRIPC - Regional Informational Processing Center of Kamchatka | | Aftershock | | Geophysical Survey of GS RAS has registered 73 aftershocks within the month after the main strike. В Information message about the strong earthquake which happened on territory of Koryak autonomous area of Kamchatka Region on April 20, 2006 described 18 aftershocks, which happened within one day after the main strike. Below one can see the following afterashocks with М>=5. |
| 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 |
| 20061134 | 2006-04-21 11:19:49.0 | 61.34 | 167.67 | 33 | 15 | - | 5.1/ 2 | 3.5-4 | Eastern Siberia, Russia | | 20061140 | 2006-04-21 16:17:19.0 | 60.69 | 165.82 | 33 | 24 | - | 5.3/ 7 | 4-4.5 | Eastern Siberia, Russia | | 20061144 | 2006-04-21 20:50:06.0 | 60.94 | 166.85 | 33 | 28 | - | 5.3/ 10 | 4-4.5 | Eastern Siberia, Russia | | 20061147 | 2006-04-21 23:36:15.0 | 61.04 | 166.91 | 20 | 25 | - | 5.2/ 7 | 4.5-5 | Eastern Siberia, Russia | | 20061150 | 2006-04-22 07:22:00.0 | 61.25 | 167.27 | 40 | 47 | 5.2/ 15 | 5.8/ 12 | 5-5.5 | Eastern Siberia, Russia | | 20061161 | 2006-04-23 01:39:24.0 | 61.44 | 167.79 | 33 | 17 | - | 5.2/ 8 | 4-4.5 | Eastern Siberia, Russia | | 20061168 | 2006-04-23 23:26:58.0 | 61.64 | 168.35 | 33 | 28 | - | 5.3/ 10 | 4-4.5 | Eastern Siberia, Russia | | 20061205 | 2006-04-26 16:37:02.0 | 61.06 | 166.53 | 33 | 32 | 4.8/ 4 | 5.2/ 8 | 4.5-5 | Eastern Siberia, Russia | | 20061235 | 2006-04-29 12:57:57.0 | 60.96 | 165.81 | 33 | 28 | 5.0/ 11 | 5.5/ 12 | 5-5.5 | Eastern Siberia, Russia | | 20061236 | 2006-04-29 16:58:08.0 | 60.57 | 167.47 | 40 | 39 | 7.0/ 14 | 6.3/ 14 | 7.5-8 | Eastern Siberia, Russia | | 20061241 | 2006-04-29 23:42:35.0 | 60.63 | 166.22 | 33 | 30 | 5.0/ 11 | 5.3/ 13 | 5-5.5 | Eastern Siberia, Russia | | 20061269 | 2006-04-30 23:04:16.0 | 60.72 | 167.06 | 20 | 22 | - | 5.0/ 8 | 4-4.5 | Eastern Siberia, Russia | | 20061271 | 2006-05-01 00:02:18.0 | 60.6 | 167.11 | 45 | 28 | - | 5.3/ 8 | 3.5-4 | Eastern Siberia, Russia | | 20061282 | 2006-05-01 12:59:25.0 | 61 | 166.05 | 50 | 14 | - | 5.0/ 7 | 3 | Eastern Siberia, Russia | | 20061390 | 2006-05-09 11:02:23.0 | 60.79 | 165.87 | 33 | 26 | 5.6/ 9 | 6.2/ 9 | 6 | Eastern Siberia, Russia | | 20061445 | 2006-05-14 05:16:48.0 | 60.76 | 166.07 | 15 | 11 | - | 5.1/ 4 | 5 | Eastern Siberia, Russia | | 20061496 | 2006-05-18 19:30:28.0 | 60.89 | 165.95 | 33 | 15 | 4.5/ 6 | 5.3/ 6 | 4-4.5 | Eastern Siberia, Russia | | 20061529 | 2006-05-22 11:11:58.0 | 60.84 | 165.75 | 15 | 50 | 7.0/ 17 | 6.5/ 18 | 9-9.5 | Eastern Siberia, Russia | | 20061530 | 2006-05-22 11:50:30.0 | 60.94 | 165.7 | 10 | 18 | - | 5.2/ 5 | 5.5-6 | Eastern Siberia, Russia | | 20061531 | 2006-05-22 12:04:53.0 | 61.01 | 165.9 | 20 | 22 | - | 5.3/ 6 | 5-5.5 | Eastern Siberia, Russia | | 20061532 | 2006-05-22 12:30:12.0 | 60.82 | 165.64 | 20 | 21 | - | 5.1/ 7 | 4.5-5 | Eastern Siberia, Russia | | 20061533 | 2006-05-22 13:03:07.0 | 60.84 | 165.99 | 10 | 23 | - | 5.6/ 10 | 6.5-7 | Eastern Siberia, Russia | | | Macroseismic manifestations | | Aftershock on May 22 has been felt in 9 settlements of Olutorsk region of Koryak autonomous area, in Tilichiki settlement being the nearest to the epicenter with intensity 7-8 on МСК-64 scale. In accordance with “Interfax” agency no victims have been reported here. At night time some residents have been moved to tent camp. New infrastructure destructions are observed in this settlement, which has been destroyed on April 20. Water pupm station is broken in Tilichiki, electricity power supply substation is stopped, electricity supply lines are damaged. | 
Figure 3 | 
Figure 4 |
| | Focal mechanism and seismic moment of the earthquake | | Focal mechanism of the earthquake 22.05.2006 has been calculated by GS RAS with the first signs of Р-wave arrivals at 59 stations, 21 of these stations registered waves of compression (symbol plus), 28 stations registered waves of expansion (symbol minus). These stations are located in epicentral distance of 7-97 degrees with rather uniform distribution along azymuths. Focal mechanism solution in stereographical projection on lower hemisphere is shown on figure 5, elements of focal mechanism are presented in table 2. On fig. 6, 7 one can see focal mechanism solution calculated with TMC method by National Earthquakes Information Center of Geological Service, USA (NEIC) and with CMT method by Harvard Center, USA (HARVARD) for the same event. As one can see, these two solutions obtained from different methods are close. This earthquake has happened under the action of almost equal by value compression and expansion strengths oriented to the south-west and south-east directions respectively. Type of motion – shift along both nodal planes: left side shift along NP1 plane and right side shift along NP2 plane. NP1 plane has latitudional direction of propagation, NP2 plane has longitudional direction of propagation. Both planes have rather steep falling angle.
It is necessary to note that shift character was observed and for the earthquake on May 9, 2006. Thus, focal mechanisms of the earthquakes on May 9 and May 22, 2006 differ from focal mechanism of the main strike on April 20, 2006, which was characterized by the motion in origin of reverse type. This reverse type of motion was observed for the initial three strongest aftershocks of 2006 (21.04 at 04:32; 21.04 at 11:14, 29.04 at 16:58), as well as for Koryak earthquake, which happened on March 8, 1991. Thus, within the period of April-May 2006 the character of motion in origin has changed in Koryak region. Moreover, for the earthquakes on April 20, 21 and 29, 2006 the rupture plane had Noerth-Eastern direction corresponding with spread direction of the series of aftershocks, while for the earthquake on May 9 and May 22, 2006 the plane of rupture corresponded with different bunch of aftershocks, transversely to Kurilo–Kamchatka direction. At fig. 8 one can see the map with aftershocks and diagrams of focal mechanisms for: Koryak earthquake of 1991, main strike on April 20, 2006 and five strongest aftershocks.
Seismic moment Мо for the earthquake 22.05.2006 has been determined from Р-wave spectra registered by IRIS digital equipment at three seismic stations: Arti (ARU), Obninsk (OBN), Kislovodsk (KIV) located at distances of 50-66 degrees. Averaged value of Мо makes 6.1 Е 18 n*m. The value of moment magnitude Mw calculated from Kanamori formula makes Мw=6.4. The value of Мо from NEIC data makes 7.3 Е 18 n*m., Мw=6.5; from data of Harvard seismological center - Мо =1.0 Е 19 n*m., Мw=6.6. As it is seen the values of Мо and Мw obtained from different methods are also close to each other.
| | 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 |
| 10 | 284 | 21 | 28 |
67 | 180 | 69 | 68 | -8 | 162 |
82 | -158 | IPC GS RAS | | 16 | 131 | 6 | 40 |
73 | 291 | 262 | 83 | 16 | 174 |
75 | 172 | NEIC | | 4 | 118 | 0 | 208 |
86 | 301 | 253 | 87 | 2 | 163 |
88 | 177 | HARVARD | | | IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences | | NEIC - National Earthquakes Information Center of US Geological Service | | HARVARD - Harvard Geophysical Center (USA) | 
Figure 5 | 
Figure 6 | | 
Figure 7 | 
Figure 8 |
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