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Information message about the earthquake in China (Xinjiang autonomous region) on February 24, 2003

On February 24, 2003 the destructive earthquake has happened in Chinese Xinjiang autonomous region. It occured at 05 hours 03 minutes Moscow time (02 hours 03 minutes GMT) and had magnitude 6.3.

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 1 ч 25 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).

Preliminary processing has been done with data from 25 stations, accurate processing - with data 41 stations.

Figure 1 presents fragments of records for vertical component (BHZ) obtained from digital stations, obtained by IPC in a near to real time mode: Borovoe (delta 14 degrees), Arti (delta 21 degrees), Talaya (delta 22 degres), Kislovodsk (delta 26 degrees), Obninsk (delta 31 degrees), Pulkovo (delta 35 degrees). Figure 2 presents fragments of records for vertical component (BHZ) obtained from digital stations: Lovozero (delta 37 degrees), Yakutsk (delta 39 degrees), Tiksi (delta 41 degrees), South-Sahalinsk (delts 47 degrees), Magadan (delta 49 degrees), Petropavlovsk (delta 55 degrees).

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	02-03-41.60	39	77	15	41	6.30/21	5.70/9	8-8.5	100	IPC GS RAS (accurate)
2	02-03-44.10	39	77	33	25	6.30/10	5.10/3	7-7.5	100	IPC GS RAS (preliminary)
3	02-03-41.30	39	77	10	302	6.3			51	CSEM
4	02-03-44.70	39	77	33	66	6.3/46	5.7/43		51	NEIC (preliminary)
5	02-03-41.00	39	77	11		6.4				NEIC (accurate)

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

In accordance with map the origin place of this earthquake is close to young and active Kashgar fault, which in the South embraces Southern Tian Shan and separates it from Tarinsk cavern "Lithospheric dynamics map of China and adjacent seas" [1], (fig.3).

Figure 3

Aftershock

Geophysical Survey has registered 7 aftershocks with magnitude 4-5 in the period February 24 - 26, 2003 . The list of these aftershocks is given in table 1Р°.

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
20030279	2003-02-26 12:29:54.0	39.92	77.17	33	11	3.6/ 4	3.7/ 4	3	Southern Xinjiang, China
20030278	2003-02-26 10:02:54.0	39.87	77.12	60	6	-	3.8/ 3	-	Southern Xinjiang, China
20030272	2003-02-25 12:16:58.0	39.68	77.05	33	9	4.0/ 5	3.9/ 3	3.5-4	Southern Xinjiang, China
20030271	2003-02-25 10:24:49.0	39.54	77.53	33	8	3.6/ 5	4.2/ 5	3	Southern Xinjiang, China
20030270	2003-02-25 03:52:44.0	39.52	77.21	33	15	5.0/ 8	4.6/ 6	5-5.5	Southern Xinjiang, China
20030268	2003-02-24 21:18:42.0	39.46	77.08	33	13	4.7/ 7	4.5/ 6	4.5-5	Southern Xinjiang, China
20030267	2003-02-24 15:49:02.0	38.95	77.67	33	11	3.6/ 5	4.0/ 4	3	Southern Xinjiang, China

Macroseismic manifestations

Destructive earthquake has happened on February 24, 2003 in NW part of Xinjiang, China. Most destructions have been found in Bachu region located in the border area of China with Kirgizia and Tadjikistan. Epicenter of this earthquake was 100 km from Kashgar (China), and 220 km from Narin (Kirgizia). 261 men have been killed and more than 4 thousand injured, 9 thousand houses have been destroyed (data from ITAR TASS on February 25 at 18-00 Moscow time)

Historical records

The earthquake on February 24, 2003 has happened in seismically active region of Southern Tian Shan. Location of its epicenter is shown on the map with epicenters (fig.4), which was built in the period since 1955 till 2002 from Seismic bulletin data of CEME GS RAS. In the last ten years this area many times has been characteriazed by destructive earthquakes: March 19, 1996 ( Рњ=6.3); January 21, 1997 (Рњ=5.9); April 11, 1997 (Рњ=6.2) and August 28, 1998 (Рњ=6.4). However the earthquake on February 24, 2003 was the most destructive.

Figure 4

Focal mechanism and seismic moment of the earthquake

Focal mechanism of the earthquake 24.02.2003 has been calculated in IPC GS RAS from the first arrivals of Р -waves at 31 stations located in the interval of epicentrical distances 3.7-88 degr. at rather uniform distribution along azimuths from 4 to 359 degrees. Parameters obtained in IPC GS RAS for focal mechanism are presented in table 2. Here one can find parameters determined from CMT method in U.S. National Earthquake Information Center (NEIC) and in Harvard Seismological center ,USA (HRV). Drawings of focal mechanism of the origin in stereographics projection (lower hemisphere) are shown on figures 5-7. As it is seen, focal mechanism solutions obtained in different centers have the same features. The motion in origin place occurred after the action of compression stresses oriented nearly along meredianal direction. One of nodal planes (NP2) in all solutions has along latitudinal spread direction (Stk=92, 84, 70 degr. ) and steep fall (dp=73, 84, 68 degr.), reverse prevails in this motion. Orientation of this plane corresponds with direction of Kashgar fault [1]. Possibly it is this plane which acted in the origin of considered here earthquake. Average value of seismic moment РњРѕ determined in IPC GS RAS from spectra of Р -waves at "Obninsk" station (delta=31.1 degr.), Mo=1.4*10*18 n*m. The value of moment magnitude from these data - Mw=6.1. The value of seismic moment Mo determined in NEIC - Mo=2.8*10*18 n*m, the value of moment magnitude Mw=6.3. The value of seismic moment Mo obtained in HRV - Mo=4.1*10*18 n*m, the value of moment magnitude Mw=6.3. As it is seen, the values of Mo and Mw determined from different sources are close to each other.

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
53	327	23	204	28	101	335	34	148	92	73	61	IPC GS RAS
51	353	39	175	1	84	273	6	99	84	84	89	NEIC
66	324	22	168	9	74	274	24	112	70	68	81	HARVARD

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

NEIC - National Earthquakes Information Center of US Geological Service

HARVARD - Harvard Geophysical Center (USA)

Figure 5	Figure 6

Figure 7

Literature

1. Lithospheric dynamics Atlas of China. 1989. State Seismological Bureau. Cartographic Publishing House. Beijing. China. Chief Editor Ma Xingyuan. Lithospheric dynamics map of China and adjacent seas. 1:4 000 000. 1986. Compiled by the Editorial Board of the Atlas on the Lithospheric Dynamics of China, State Seismological Bureau. Chief Compiler Ma Xingyuan.