Information message about the strong earthquake off the southeast coast of Alaska, January 5, 2013 |
| The strong earthquake with M=7.8 has occurred on January 5, 2013 at 08:58 GMT (12:58 Moscow time) off the southeast coast of Alaska. |
| 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 19 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). |
| Preliminary processing has been done with data from 27 stations, accurate processing - with data 52 stations. |
| Fig. 1 presents fragments of records obtained from digital stations Albuquerque (∆ 28.2º), Bilibino (∆ 29.3º), Seimchan (∆ 36.2º), Petropavlovsk (∆ 37.7º), Magadan (∆ 38.3º). Fig. 2 presents fragments of records obtained from digital stations Pulkovo (∆ 64.6º), Arti (∆ 68.1º), Obninsk (∆ 69.7º), Borovoe (∆ 70º), Kislovodsk (∆ 81º).
|
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 |
08-58-18.7 |
55.35 |
-134.77 |
10 |
52 |
7.8/25 | 6.5/26 | 11-11.5 | 166 | IPC GS RAS (Accurate) | | 2 |
08-58-20.0 |
55.4 |
-134.7 |
10 |
27 |
7.5/8 | 6.5/18 | 10-11 | 166 | IPC GS RAS (Preliminary) | | 3 |
08-58-19.9 |
55.28 |
-134.67 |
10 |
387 |
7.5 Mw | | | 129 | CSEM | | 4 |
08-58-19.4 |
55.292 |
-134.728 |
9.6 |
334 |
7.7 Mw | 6.4/276 | | | NEIC (Preliminary) | | 5 |
08-58-19.7 |
55.368 |
-134.621 |
9.8 |
1237 |
7.8/653 | 6.4/576 | | 22 | NEIC (Accurate) | |
| 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 |
| In Fig. 3 red star presents the epicenter of the earthquake off the southeast coast of Alaska, USA, at the depth of 10 km, 102 km SSW of Port Alexander, Alaska, USA, 310 km WNW of Prince Rupert, Canada, 330 km SSW of Juneau, Alaska, USA. |
Figure 3 |
|
| Aftershock |
| GS RAS registered 5 aftershocks with M≥4.6 within one 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 |
| 20130053 | 2013-01-05 09:27:19.0 | 55.53 | -134.62 | 10 | 22 | - | 4.9/ 13 | 5-5.5 | Southeastern Alaska | | 20130054 | 2013-01-05 10:11:20.0 | 55.84 | -135.29 | 10 | 35 | - | 5.2/ 12 | 5.5-6 | Off coast of Southeastern Alaska | | 20130059 | 2013-01-05 11:39:38.0 | 55.62 | -135.58 | 10 | 19 | - | 4.7/ 6 | 4.5-5 | Off coast of Southeastern Alaska | | 20130055 | 2013-01-05 12:28:29.0 | 55.14 | -134.6 | 10 | 33 | - | 5.2/ 20 | 5.5-6 | Southeastern Alaska | | 20130068 | 2013-01-06 08:37:28.0 | 55.67 | -135.38 | 10 | 21 | - | 4.6/ 14 | 4.5 | Off coast of Southeastern Alaska | |
| Macroseismic manifestations |
| Fig. 4 shared from USGS NEIC presents the USGS Community Internet Intensity Map by 933 responses in 40 ZIP codes and 31 cities. Pacific Center of Tsunami Warning announced tsunami alert, tsunami wave with maximum height of 13 cm was registered in Port Alexander, Alaska. |
Figure 4 |
|
| Historical records |
| October 28, 2012, the strong earthquake in the Queen Charlotte Islands region with M=7.7, 340 km S-E of the earthquake. |
| Focal mechanism and seismic moment of the earthquake |
| Focal mechanism solution of this earthquake’s origin was calculated in IPC GS RAS with signs of initial arrivals of P waves at 211 stations, including 161 stations which registered the waves of compression (plus signs) and 50 stations which registered the waves of expansion (minus signs). These stations are located in the interval of epicentral distances of 1–95º along the azimuths and mainly in 1, 2 and 4 quadrants.
Focal solution of the origin in stereographic projection at the lower hemisphere is presented at figure 5, elements of this solution are presented in table.2. Table 2 and figures 6, 7 also present focal mechanism solutions calculated with Centroid Moment Solution method in NEIC USGS, USGS NEIC and in Quick CMT Catalog, USA.
The solutions obtained in IPC GS RAS, USGS NEIC and Quick CMT are identical. This earthquake has occurred under the close in value forces of compression oriented to the south (in case of GSRAS and USGS) and to the north (in case of Quick CMT) and forces of expansion oriented in all cases north-west. Both nodal planes decline rather steeply (DP=57–86º).One of them NP1 has north-east orientation (Stk=63-71º), another NP2 – north-west ((Stk=330-340º). Type of motion along both planes – slips (left side for NP1 and right side for NP2).
Seismic moment of the earthquake obtained in IPC GS RAS with spectra of Р waves obtained at two stations: «Arti» (∆68.05º) and «Obninsk» (∆69.67º) makes Мо=2.2*10**20 N*m. Averaged value of moment magnitude calculated with Kanamori formula makes Mw=7.5. In accordance with USGS NEIC – Мо=2.6*10**20 N*m, Mw=7.5, in accordance with Quick CMT – Мо=2.33*10**20 N*m, Mw=7.5.
|
| 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 | 296 | 5 | 205 |
78 | 90 | 71 | 86 | 11 | 340 |
79 | 176 | IPC GS RAS | | 26 | 292 | 19 | 192 |
57 | 71 | 63 | 85 | 33 | 330 |
57 | 174 | NEIC | | 23 | 288 | 6 | 20 |
66 | 123 | 66 | 70 | 12 | 332 |
78 | 159 | Quick 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 |
|
