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Information message about sensitive earthquake in the region of Baikal Lake on August 27, 2008

The sensitive earthquake with М=6.1 has occured on August 27, 2008 at 1:35 GMT (5:35 Moscow time) in the region of Baikal Lake.

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 35 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).

Preliminary processing has been done with data from 41 stations, accurate processing - with data 55 stations.

FIg. 1 presents fragments of records obtained from digital stations Kurchatov (∆ 16º), Yakutsk (∆ 17.3º), Borovoe (∆ 20.6º), Ala Archa (∆ 22º), Tiksi (∆ 22.9º), Yuzhno-Sakhalinsk (∆ 25.4º). Fig. 2 presents fragments of records obtained from digital stations Petropavlovsk (∆ 32.7º), Lovozero (∆ 36.2º), Obninsk (∆ 39º), Kingsbay, Spitsbergen, (∆ 40.3º), Kislovodsk (∆ 40.9º), Garni (∆ 41.9º).

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	01-35-29.4	51.64	104.15	10	55	6.1/21	6/22	8.5-9	56	IPC GS RAS (Accurate)
2	01-35-29.3	51.63	104.19	10	41	6.1/14	6/17	8.5-9	56	IPC GS RAS (Preliminary)
3	01-35-29.1	51.75	104.21	10	218	6.3Mw			60	CSEM
4	01-35-31.1	51.73	104.25	10	33	6.3Mw	5.7/27		65	NEIC
5	01-35-31.1	51.6	104.1	10		15К				BRIPC

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

BRIPC - Regional Informational Processing Center of Baikal Experimental-Methodical Seismological Expedition Geophysical Survey Siberian Branch Russian Academy of Sciences

Epicenter

Epicenter of the earthquake is shown on Fig.3 with red arrow, it was located in the southern part of Baikal Lake at the depth of 10 km, at 15 km to the north from Baikalsk, at 30 km to the east from Sludanka, at 35 km to the east-south-east from Kulutuka, at 70 km to the south from Irkutsk, at 240 km to the west from Ulan Ude.

Figure 3

Aftershock

Within two hours after the mail shock Geophysical Survey of RAS registered 3 significant aftershocks with magnitudes from 4.3 to 5.3.

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
20082839	2008-08-27 01:41:31.0	51.63	104.01	15	6	5.3/ 1	-	6.5-7	Lake Baykal region, Russia
20082840	2008-08-27 02:07:56.0	51.63	103.81	15	6	4.5/ 1	-	5.5-6	Lake Baykal region, Russia
20082841	2008-08-27 03:29:13.0	51.63	104.07	15	4	4.3/ 1	-	5-5.5	Lake Baykal region, Russia

Macroseismic manifestations

This earthquake has been felt in Baikalsk with intensity 8, in Sludanka and Kulutuk with intensity 7, in Irkutsk with intensity 6-7. Three aftershocks have been felt in Irkutsk with intensity 5, 3 and 2 respectively. No serious destructions were registered. In accordance with information from EMERCOM of Irkutsk Region there were registered the breaks of electric power supply lines and drifts of railways in the region of Sludanka. Cracks in the walls of some buildings were determined in Irkutsk along with temporary shutdowns of electricity and water supply. In accordance with more accurate date from Baikal Branch of GS RAS this earthquake was felt on the vast territory from Chita to Krasnoyarsk (fig.4): Arshan, Utulik, Listvianka 6 -7 MSK, Bol.Goloustnoe, Kabansk,Selenga, Angarsk, Mondi, Elanci 5- 6 MSK, Zakamensk 5, Sherigino, Gusinoozersk 4-5, Huzhir 4, Kizil 3-4, Bratsk 3, Abakan 2-3, Chita, Krasnoyarsk 2 MSK.

Figure 4

Historical records

This earthquake has happened in seismic active region of Pribaikalie in tectonic zone of south-western end of Primorsk ridge, historically known as the area of the earthquakes with magnitudes 6.5 and more, felt in some settlements with intensities up to 9-10 MSK. These are the earthquakes: August 1, 1779 with М=6.6 Io=9; March 7, 1829 with М=7.2-7.5 Io=9-10; August 17, 1846 with М=6.7 Io=9; April 11, 1902 with М=6.6 Io=8-9. The last strong earthquake of the previous century has happened on February 25, 1999 at 18:58 GMT with М=6.1, it was felt in the number of living places with intensities from 3 to 5-6 MSK.

Focal mechanism and seismic moment of the earthquake

Focal mechanism of the origin for the earthquake 27.08.2008 is presented on fig.5 and in table 2 in accordance with NEIC information. Focal mechanism was determined by tectonic processes in the rift zone of Baikal Lake and is characterized by fault -slide. Both nodal planes have north-eastern direction of propagation, right side slide component prevails in the motion along the flat NP1 plane, left side slide component prevails in the motion along the steep NP2 plane. The motion has happened at the near horizontal expansion and near vertical compression, this is typical for the earthquakes of this zone [Balakina and others., 1996, Melnikova and others., 2008]. The same kind of focal mechanism is obtained from the fist signs of P wave motions at 46 stations (fig.6, table.2) The value of moment magnitude Mw in accordance with NEIC makes Мw=6.1.

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
0	341	79	72	11	251	82	46	-75	241	46	-105	IPC GS RAS
11	338	69	215	16	72	48	36	-118	263	59	-69	NEIC

IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences

NEIC - National Earthquakes Information Center of US Geological Service

Figure 5

Figure 6