The red marker on the map shows the epicenter of the earthquake, the origin of which was in the Pacific Ocean, S of the Alaska Peninsula, USA, at a depth of 15 km, 76 km SE of Perryville and 151 km E of Sand Point.
|
Time in origin (GMT) |
Latitude, degree |
Longitude, degree |
Depth, km |
Stations number |
Ms/N |
mb/N |
I0 (calculated) |
GAP |
Center |
1
|
06:15:45.0
|
55.54 |
-158.11 |
15.0 |
72
|
8.0/46 |
7.3/55 |
10.5-11 |
70
|
GS RAS(Verified) Federal research center, Geophysical survey of Russian Academy of Sciences
|
2
|
06:15:56.6
|
55.78 |
-158.12 |
100.0 |
13
|
|
6.6/11 |
5.5-6 |
|
GS RAS(Preliminary) Federal research center, Geophysical survey of Russian Academy of Sciences
|
3
|
06:15:50.5
|
55.54 |
-158.01 |
43.4 |
873
|
Mw 8.2 |
|
|
16
|
CSEM European - Mediterranean seismological center
|
4
|
06:15:49.9
|
55.47 |
-157.92 |
46.7 |
82
|
Mw 8.2 |
7.0 |
|
66
|
NEIC National Earthquakes Information Center of US Geological Service
|
Fig. 1 presents fragments of records obtained from digital stations Kodiak Island (∆ 3.8º), College (∆ 10.6º), Petropavlovsk (∆ 25.1º), Seimchan (∆ 25.8º), Severo-Kurilsk (∆ 27.5º). Fig. 2 presents fragments of records obtained from digital stations Tiksi (∆ 33.6º), Kurilsk (∆ 35.1º), Yakutsk (∆ 36.2º), Yuzhno-Sakhalinsk (∆ 37º), Ussuriysk (∆ 44.6º).
Image 1
Image 2
GS RAS registered 23 aftershocks with М>=4.6 within the day after the main shock.
N |
Time in origin (GMT) |
Latitude, degree |
Longitude, degree |
Depth, km |
Stations number |
Ms/N |
mb/N |
I0 (calculated) |
Region |
20213020
|
29/07/2021 06:23:28.0.0 |
55.7 |
-157.81 |
15.0 |
35 |
|
6.6/23 |
8.5-9 |
Alaska Peninsula
|
20213018
|
29/07/2021 06:32:34.0.0 |
55.43 |
-156.98 |
15.0 |
52 |
|
6.2/38 |
7.5-8 |
South of Alaska
|
20213022
|
29/07/2021 06:47:23.0.0 |
55.21 |
-157.82 |
15.0 |
39 |
|
5.5/18 |
6 |
Alaska Peninsula
|
20213019
|
29/07/2021 07:49:57.0.0 |
55.38 |
-157.48 |
15.0 |
39 |
|
5.0/23 |
4.5-5 |
Alaska Peninsula
|
20213021
|
29/07/2021 08:09:43.0.0 |
55.34 |
-157.42 |
15.0 |
32 |
|
5.0/21 |
4.5-5 |
Alaska Peninsula
|
20213023
|
29/07/2021 08:15:45.0.0 |
55.17 |
-157.15 |
15.0 |
27 |
|
4.8/21 |
4-4.5 |
Alaska Peninsula
|
20213024
|
29/07/2021 08:25:21.0.0 |
55.84 |
-156.23 |
15.0 |
24 |
|
4.8/8 |
4-4.5 |
South of Alaska
|
20213027
|
29/07/2021 09:28:21.0.0 |
55.63 |
-157.73 |
15.0 |
50 |
|
5.3/41 |
5.5 |
Alaska Peninsula
|
20213026
|
29/07/2021 09:53:40.0.0 |
55.4 |
-157.02 |
15.0 |
31 |
|
5.0/22 |
4.5-5 |
Alaska Peninsula
|
20213028
|
29/07/2021 10:26:54.0.0 |
55.02 |
-157.08 |
15.0 |
25 |
|
4.6/21 |
3.5-4 |
Alaska Peninsula
|
20213031
|
29/07/2021 11:08:46.0.0 |
55.6 |
-157.73 |
15.0 |
23 |
|
4.7/11 |
4-4.5 |
Alaska Peninsula
|
20213032
|
29/07/2021 12:42:43.0.0 |
55.35 |
-156.48 |
15.0 |
21 |
|
4.8/13 |
4-4.5 |
South of Alaska
|
20213033
|
29/07/2021 13:17:49.0.0 |
56.26 |
-156.43 |
15.0 |
30 |
|
5.1/20 |
5 |
Alaska Peninsula
|
20213035
|
29/07/2021 16:09:09.0.0 |
55.33 |
-157.18 |
15.0 |
57 |
|
5.6/36 |
6-6.5 |
Alaska Peninsula
|
20213037
|
29/07/2021 19:11:31.0.0 |
56.08 |
-157.09 |
15.0 |
25 |
|
4.9/19 |
4.5-5 |
Alaska Peninsula
|
20213038
|
29/07/2021 20:30:31.0.0 |
55.52 |
-157.02 |
15.0 |
48 |
|
5.5/26 |
6 |
Alaska Peninsula
|
20213039
|
29/07/2021 20:32:41.0.0 |
55.37 |
-157.02 |
15.0 |
54 |
|
5.9/36 |
6.5-7 |
Alaska Peninsula
|
20213040
|
29/07/2021 21:00:03.0.0 |
54.86 |
-157.71 |
15.0 |
36 |
|
5.0/25 |
4.5-5 |
South of Alaska
|
20213041
|
29/07/2021 21:39:13.0.0 |
55.11 |
-157.09 |
15.0 |
28 |
|
4.8/22 |
4-4.5 |
Alaska Peninsula
|
20213042
|
29/07/2021 22:18:28.0.0 |
55.5 |
-157.51 |
15.0 |
42 |
|
5.4/28 |
5.5-6 |
Alaska Peninsula
|
20213044
|
29/07/2021 23:38:13.0.0 |
55.16 |
-156.98 |
15.0 |
22 |
|
4.7/12 |
4-4.5 |
South of Alaska
|
20213049
|
30/07/2021 03:52:13.0.0 |
55.6 |
-157.21 |
15.0 |
63 |
5.4/34 |
5.9/40 |
6.5-7 |
Alaska Peninsula
|
20213050
|
30/07/2021 05:32:12.0.0 |
55.44 |
-159.1 |
15.0 |
34 |
|
5.1/21 |
5 |
Alaska Peninsula
|
The focal mechanism solution of the origin was calculated in GS RAS with signs of initial arrivals of P waves at 99 stations, including 84 stations which registered compression waves (plus signs) and 15 stations which registered tensile waves (minus signs). These stations are located in the interval of epicentral distances of 3.6-99.6º and in azimuth range Az=2-358º. The focal mechanism solution in stereographic projection on the lower hemisphere and its elements are presented in the table. The table also contains focal mechanism solutions obtained at the USGS NEIC with WW-phase Moment Tensor (Mww) technique and in Lamont-Dohert Earth Observatory of Columbia University, USA (LDEO GCMT) with СМТ (Centroid moment tensor) technique. Solutions from different centers are close. The earthquake occurred under the action of slight prevalence of compression stresses oriented S-SE (AZ=145-151º). One nodal plane NP1 strikes SW (STK=230-236º) according to GS RAS and LDEO GCMT and W-SW (STK=239º) according to USGS NEIC, another plane NP2 strikes E-NE (STK=54º-65º). NP1 plane lies more horizontally (DP=10-20º) if compared with NP2 (DP=54-65º). The type of motion along NP1 – thrust, along NP2 – reverse fault. The seismic moment according to USGS NEIC makes Mo=2.36 *10**21 N*m, Mww=8.2. According to LDEO GCMT Mo=2.96*10**21 N*m, Mw=8.2
Axes of main strengths |
Nodal planes |
Center |
|
T |
P |
N |
NP1 |
NP2 |
PI: 64
Azm: 343
|
PI: 26
Azm: 151
|
PI: 5
Azm: 243
|
Stk: 230
Dp: 20
Slip: 76
|
Stk: 65
Dp: 71
Slip: 95
|
GS RAS Federal research center, Geophysical survey of Russian Academy of Sciences
|
|
PI: 59
Azm: 323
|
PI: 31
Azm: 145
|
PI: 1
Azm: 54
|
Stk: 239
Dp: 14
Slip: 95
|
Stk: 54
Dp: 76
Slip: 89
|
NEIC National Earthquakes Information Center of US Geological Service
|
|
PI: 55
Azm: 331
|
PI: 35
Azm: 150
|
PI: 1
Azm: 240
|
Stk: 236
Dp: 10
Slip: 86
|
Stk: 60
Dp: 80
Slip: 91
|
GCMT Lamont-Doherty Earth Observatory Global CMT Columbia University, USA
|
|