Information message about the strong earthquake in Mexico on March 20, 2012. |
| The strong earthquake with M=7.7 and destructions has occurred in Mexico on March 20, 2012 at 18:02 GMT (22:02 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 39 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). |
| Preliminary processing has been done with data from 28 stations, accurate processing - with data 43 stations. |
| Fig. 1 presents fragments of records obtained from digital stations Juntas de Abangares (∆ 14.4º), Albuquerque (∆ 19.7º), College (∆ 58.5º), Falkland Islands(∆ 76.5º), Кingsbay (∆ 77.6º). Fig. 2 presents fragments of records obtained from digital stations Tiksi (∆ 86.4º), Lovozero (∆ 89.1º), Yakutsk (∆ 93º), Erimo (∆ 98.8º), Obninsk (∆ 98.9º).
|
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 |
18-02-47.1 |
16.63 |
-98.25 |
20 |
43 |
7.7/19 | 6.7/18 | 9.5-10 | 96 | IPC GS RAS (Accurate) | | 2 |
18-02-46.5 |
16.72 |
-98.27 |
10 |
28 |
7.7/18 | 6.7/16 | 11 | 96 | IPC GS RAS (Preliminary) | | 3 |
18-02-49.6 |
16.69 |
-98.24 |
19.3 |
475 |
Mw 7.4 | | | 80 | CSEM | | 4 |
18-02-48.9 |
16.66 |
-98.19 |
17.5 |
438 |
Mw 7.6 | 6.6/353 | | 79 | 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 in Mexican state Guerrero at the depth of 20 km, in 171 km W-S-W of Oaxaca, 182 km E-S-E of Acapulco and 326 km S-S-E of Mexico City. |
Figure 3 |
|
| Aftershock |
| GS RAS registered 8 aftershocks with М>4.6 for 9 hours 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 |
| 20121162 | 2012-03-20 18:22:33.0 | 16.36 | -98.38 | 20 | 15 | - | 5.2/ 8 | 4.5-5 | Near coast of Guerrero, Mexico | | 20121164 | 2012-03-20 18:35:38.0 | 16.4 | -98.33 | 20 | 25 | - | 5.1/ 11 | 4.5-5 | Near coast of Guerrero, Mexico | | 20121165 | 2012-03-20 19:02:39.0 | 16.19 | -98.33 | 10 | 22 | - | 5.2/ 8 | 5.5-6 | Near coast of Guerrero, Mexico | | 20121166 | 2012-03-20 19:19:49.0 | 16.16 | -98.37 | 10 | 14 | - | 4.7/ 7 | 4.5-5 | Near coast of Guerrero, Mexico | | 20121169 | 2012-03-20 20:14:37.0 | 16.45 | -98.11 | 20 | 24 | - | 5.1/ 11 | 4.5-5 | Near coast of Guerrero, Mexico | | 20121170 | 2012-03-20 22:25:40.0 | 16.48 | -98.61 | 20 | 24 | - | 5.2/ 11 | 4.5-5 | Near coast of Guerrero, Mexico | | 20121171 | 2012-03-21 02:25:30.0 | 16.23 | -98.52 | 20 | 14 | - | 4.9/ 8 | 4-4.5 | Near coast of Guerrero, Mexico | | 20121173 | 2012-03-21 02:54:37.0 | 16.73 | -98.39 | 20 | 27 | - | 5.1/ 15 | 4.5-5 | Near coast of Guerrero, Mexico | |
| Macroseismic manifestations |
| In accordance with RIA-Novosti more than 800 different buildongs and constructions were damaged in Mexican south-western state of Guerrero, where the resort town of Acapulco is located. More then 2,5 million people were left without electricity. Some damage of buildings was observed in Oaxaca, Michoacan and Tabasco states, operation of Nuclear Power Plant Laguna Verde in Verackruz was not interrupted. Some minor damage was observed in Mexico City.
Fig. 4 was obtained from USGS NEIC , it presents the map of intensities composed with calls from 1208 respondents living in 163 places. |
Figure 4 |
|
| Historical records |
| The earthquake has occurred in Guerrero State on December 11, 2011 with magnitude М=6.4. It's epicenter is presented with yellow star and it was located 232 km N-W of the earthquake reported here. |
Figure 5 |
|
| Focal mechanism and seismic moment of the earthquake |
| Focal mechanism of this earthquake which happened on March 20, 2012 at 18:02 (GMT) was calculated with CMT method in NEIC, USGS and Global CMT Catalog, USA. Focal mechanism solutions in stereographic projection on lower hemisphere are presented in figures 6, 7, elements of the solutions are given in table 2. These solutions are similar. The earthquake has occurred under the action of both tension and compression stresses oriented N-E and S-W directions respectively. One nodal plane has low angle dip (DP=12-13º) and N-W strike (STK=295-296º), another plane is steeply dipping (DP=77-78º) and has S-E strike (STK=113-115º). The type of motion in origin is reverse fault along steeply dipping plane and thrust along the flat plane.
Seismic moment of the earthquake according to USGS data makes Мо=1.7*10**20 N*m, the value of moment magnitude makes Mw=7.4. Seismic moment of the earthquake according to Global CMT Catalog is Мо=1.48*10**20 N*m, the value of moment magnitude makes Mw=7.4.
|
| 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 |
| 57 | 22 | 33 | 203 |
1 | 113 | 113 | 78 | 89 | 296 |
12 | 93 | NEIC | | 58 | 24 | 32 | 205 |
0 | 115 | 115 | 77 | 90 | 295 |
13 | 91 | Quick CMT | |
| NEIC - National Earthquakes Information Center of US Geological Service |
| Quick CMT - Quick CMT catalog |
Figure 6 | 
Figure 7 |
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