Information message about destructive earthquake in China on April 20, 2013 |
| The destructive earthquake with M=7 has occurred in China on April 20, 2013 at 00:02 GMT (4:02 Moscow time). |
| 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 14 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). |
| Preliminary processing has been done with data from 40 stations, accurate processing - with data 63 stations. |
| Fig. 1 presents fragments of records obtained from digital stations Taijon (∆ 21.2º), Talaya (∆ 21.4º), Mys Shultsa (∆ 25.6º), Ala-Archa (∆ 25.9º), Vladivostok (∆ 26.3º). Fig. 2 presents fragments of records obtained from digital stations Borovoe (∆ 32.9º), Erimo (∆ 34.2º), Arti (∆ 40.5º), Tiksi (∆ 43.7º), Obninsk (∆ 52.5º) |
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 |
00-02-46.2 |
30.29 |
103.03 |
20 |
63 |
7/36 | 6.7/36 | 8.5-9 | 57 | IPC GS RAS (Accurate) | | 2 |
00-02-45.3 |
30.16 |
102.97 |
10 |
40 |
| 6.5 | 9-9.5 | | IPC GS RAS (Preliminary) | | 3 |
00-02-48.7 |
30.327 |
102.99 |
20 |
401 |
Mw 6.6 | | | 25 | CSEM | | 4 |
00-02-47.3 |
30.284 |
102.956 |
12.3 |
161 |
6.8/50 | 6.5 /370 | | 14 | 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 epicenter of this earthquake, which origin was located on the territory of Chinese, Sichuan Province, at the depth of 20 km, 105 km W-S-W of Chengdu City and 350 km W-N-W of Chongqing. |
Figure 3 |
|
| Aftershock |
| GS RAS registered 12 aftershocks with M≥4.5 within the 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 |
| 20131439 | 2013-04-20 01:02:56.0 | 30.34 | 102.97 | 20 | 25 | - | 4.9/ 14 | 4-4.5 | Sichuan, China | | 20131440 | 2013-04-20 01:11:50.0 | 30.18 | 102.89 | 20 | 23 | - | 5.1/ 16 | 4.5-5 | Sichuan, China | | 20131441 | 2013-04-20 01:37:28.0 | 30.18 | 102.76 | 20 | 24 | - | 5.1/ 17 | 4.5-5 | Sichuan, China | | 20131442 | 2013-04-20 02:19:10.0 | 31.11 | 103.05 | 20 | 10 | - | 4.5/ 5 | 3-3.5 | Sichuan, China | | 20131443 | 2013-04-20 02:38:32.0 | 30.07 | 103.19 | 20 | 14 | - | 4.5/ 12 | 3-3.5 | Sichuan, China | | 20131444 | 2013-04-20 03:34:15.0 | 30.05 | 102.89 | 20 | 31 | - | 5.2/ 17 | 4.5-5 | Sichuan, China | | 20131451 | 2013-04-20 07:18:32.0 | 30.54 | 103.1 | 20 | 15 | - | 4.6/ 12 | 3-3.5 | Sichuan, China | | 20131452 | 2013-04-20 10:58:59.0 | 30.4 | 103.24 | 20 | 14 | - | 4.6/ 13 | 3-3.5 | Sichuan, China | | 20131453 | 2013-04-20 11:12:49.0 | 30.36 | 103.02 | 20 | 17 | - | 4.8/ 16 | 3.5-4 | Sichuan, China | | 20131466 | 2013-04-20 18:32:10.0 | 30.35 | 103.09 | 33 | 14 | - | 4.5/ 11 | 2-2.5 | Sichuan, China | | 20131469 | 2013-04-20 19:54:43.0 | 30.25 | 103.15 | 20 | 16 | - | 4.5/ 13 | 3-3.5 | Sichuan, China | | 20131470 | 2013-04-20 20:53:43.0 | 30.34 | 103.1 | 20 | 26 | - | 5.3/ 16 | 5-5.5 | Sichuan, China | |
| Macroseismic manifestations |
| In accordance with RIA-Novosti 208 persons were killed and 11800 injured after this earthquake. More than 1,5 million people suffered more or less from this earthquake in Sichuan Province.
|
Figure 4 |
|
| Historical records |
| Epicenter of this earthquake is located in 103 km N-N-W from catastrophic earthquake of May 12, 2008 with М=8, which killed more than 80000 people.
The strongest earthquake of last time has occurred in this area in the neighboring Yunnan Province on September 07, 2012 in 328 km S-S-E of currently reported epicenter of April 20, 2013. |
| Focal mechanism and seismic moment of the earthquake |
| Focal mechanism of the origin for this earthquake which occurred on April 20, 2013 at 00:02 was calculated in IPC GS RAS with signs of initial arrivals of P waves at 217 stations, including 204 stations which registered the waves of compression (plus signs), and 13 stations which registered the waves of expansion (minus signs). These stations are located in the interval of epicentral distances of 5–99º and dispersed rather evenly along the azimuths. Focal mechanism solution in stereographic projection at the lower hemisphere is presented at figure 5, elements of this mechanism are presented in table 2. Fig. 6, 7 present focal mechanism obtained in USGS NEIC with USGS Centroid Moment Solution method and solution obtained in Quick CMT Catalog, USA with CMT technique.
Both solutions are close. The earthquake has occurred under the action of S-E oriented compression strengths. Both nodal planes have N-E – S-W direction of propagation. One nodal plane is rather vertical (DP=52-59º), another plane - is more flat (DP=32-38º. The type of motion along both planes – uplift with minor slip components.
Seismic moment of the earthquake was obtained in IPC GS RAS with spectra of Р waves at two stations: «Arti» (∆40.52) and «Obninsk» (∆52.47), it makes Mo=2.2*10**19 N*m, averaged value of moment magnitude Mw was calculated with Kanamori formula and makes Mw=6.8. In accordance with USGS NEIC Mo=1.0*10**19 N*m, Mw=6.6, in accordance with Quick CMT – Mo=1.06*10**19 N*m, Mw=6.6. |
| 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 |
| 76 | 277 | 13 | 118 |
5 | 27 | 24 | 58 | 84 | 214 |
32 | 99 | IPC GS RAS | | 73 | 340 | 14 | 122 |
10 | 214 | 40 | 59 | 102 | 198 |
33 | 71 | NEIC | | 82 | 268 | 7 | 116 |
4 | 25 | 22 | 53 | 85 | 210 |
38 | 96 | 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 |
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