Information message about destructive earthquake in the Eastern Sichuan, China, May 12, 2008 |
| The earthquake with M=8 which caused victims and distractions has occurred on May 12, 2008 at 6:28 GMT (10:28 Moscow time) in the Eastern Sichuan, China. |
| 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 55 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). |
| Preliminary processing has been done with data from 33 stations, accurate processing - with data 55 stations. |
| Fig. 1 presents fragments of records obtained from digital stations Talaya (∆ 20.5º), Ala Archa (∆ 25.6º), Kurchatov (∆ 26.8º), Borovoe (∆ 32.4º), Arti (∆ 40º). Fig. 2 presents fragments of records obtained from digital stations Seimchan (∆ 44.4º), Diego Garcia (∆ 48.4º), Kislovodsk (∆ 48.7º), Lovozero (∆ 53.5º), Pulkovo (∆ 55.2º) |
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 |
06-28-00.0 |
31.16 |
103.33 |
10 |
55 |
8/20 | 7.1/33 | 11.5 | 108 | IPC GS RAS (Accurate) | | 2 |
06-27-59.3 |
31.11 |
103.41 |
10 |
33 |
8/14 | 7.1/27 | 11.5 | 147 | IPC GS RAS (Preliminary) | | 3 |
06-27-59.0 |
31.12 |
103.24 |
10 |
695 |
7.8Mw | | | 20 | CSEM | | 4 |
06-28-00.8 |
31.08 |
103.27 |
10 |
228 |
7.8Mw | | | 29 | 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 downloaded from NEIC USA depicts epicenter of this earthquake, which was located in the mountainous area of Sichuan province of China, in 1540 km to the south-west from Beijing. |
Figure 3 |
|
| Aftershock |
| This earthquake has been accompanied with numerous aftershocks. Below one can see the strongest of these aftershocks determined with GS RAS data: |
| 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 |
| 20081537 | 2008-05-12 06:43:12.0 | 31.31 | 103.92 | 10 | 8 | - | 6.0/ 4 | 7.5-8 | Sichuan, China | | 20081538 | 2008-05-12 06:54:18.0 | 31.87 | 104.81 | 33 | 8 | - | 5.6/ 7 | 5 | Sichuan, China | | 20081549 | 2008-05-12 09:42:26.0 | 31.54 | 104.1 | 33 | 30 | - | 5.7/ 16 | 5-5.5 | Sichuan, China | | 20081556 | 2008-05-12 11:11:00.0 | 31.26 | 103.58 | 10 | 48 | 6.2/ 24 | 6.0/ 25 | 8.5-9 | Sichuan, China | | 20081583 | 2008-05-12 20:08:46.0 | 31.32 | 103.98 | 10 | 41 | 5.6/ 17 | 6.0/ 21 | 7.5-8 | Sichuan, China | | 20081584 | 2008-05-12 20:45:33.0 | 31.77 | 104.51 | 33 | 32 | - | 5.5/ 15 | 4.5-5 | Sichuan, China | |
| Macroseismic manifestations |
| After ITARR TASS information the powerful underground shock has turned Sichuan province of China into the zone of disaster. The number of killed people reached 12 thousand and the same number is under the debris. The destiny of 30 thousand people is unknown. Buildings in Venchuan district of Sichuan Province have 80% damage. Ground shocks were felt on a vast territory – at the top of high buildings of Beijing, which is located in 1540 km from the earthquake’s place, and it was also felt in Sri Lanka, Vietnam and Korea. |
| Focal mechanism and seismic moment of the earthquake |
| Focal mechanism solutions of the earthquake 12.05.2008 have been obtained with TMC method in NEIC USA and in Harvard Center USA, HRVD (Global CMT Catalog), they are presented in table 2 and shown on figures 4, 5. All mechanisms obtained have both the same and different features.
From these solutions this earthquake has occurred under the action of prevailing action of compression forces oriented in accordance with NEIC to the north-west, and in accordance with HRVD – to the east-south-east. In both cases one nodal plane (NP1) is flat (DP=23◦ and 33) of north-eastern direction of propagation, the other plane (NP2) is steeply falling (DP=67◦ and 70◦) propagating in accordance with NEIC to the north-east, in accordance with HRVD in parallel with meridian direction. The motion along flat plane with NEIC is characterized by the thrust (with components of left side drift), with HRVD – by right side drift (with components of uplift). Along the steeply falling plane the motion in both solutions is characterized by uplift with shift components (right side from NEIC and left side from HRVD).
The avaraged seismic moment Мо=3.6* 10** 20 n*m has been calculated in IPC GS RS with P-wave spectra obtained at three stations: "Arti" - delta 40 degrees, "Obninsk" - delta 52.1 degrees, "Kislovodsk" - delta 48.8 degrees. The avaraged moment magnitude Mw has been calculated from Kanamori formula and makes Mw=7.7;
The value of seismic moment Мо of the earthquake 12.05.2008 in accordance with NEIC makes 6.7* 10** 20 n*m, in accordance with HRVD Мо=9.43* 10** 20 n*m. The value of moment magnitude Мw calculated from Kanamori formula in accordance with NEIC makes Мw=7.8, in accordance with HRVD – Мw=7.9.
|
| 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 |
| 67 | 135 | 21 | 304 |
4 | 35 | 26 | 23 | 80 | 218 |
67 | 94 | NEIC | | 57 | 227 | 25 | 2 |
20 | 103 | 229 | 33 | 141 | 352 |
70 | 63 | HARVARD | |
| NEIC - National Earthquakes Information Center of US Geological Service |
| HARVARD - Harvard Geophysical Center (USA) |
Figure 4 | 
Figure 5 |
|
