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Information message about earthquake on March 8 1999

On March the 8-th 1999 at 3:25 pm Moscow time (12:25 pm GMT) strong earthquake has happened close to the eastern coast of Kamchatka in Avachinsky gulf, which was felt in Petropavlovsk-Kamchatsky with intensity 4-5 MSK.

Parameters of this earthquake (table 1, item 1) have been determined by the Alert Service (AS) of Information Processing Center (IPC) in Geophysical Survey of GS RAS in Obninsk with the use of stationary data obtained from digital and analog seismic stations of Russia, countries of CIS and from abroad.

Waveforms of this event, which were received by IPC in a close to real time mode from digital seismic stations on a territory of Russia, are shown in figure 1, 2.

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	12-25-44.50	52	159	33	21	7.10/6	6.90/6	8-8.5		IPC GS RAS (AS)
2	12-25-51.80	52	157	33	166		5.7			CSEM
3	12-25-45.50	52	159	33		6.7/18				NEIC
4	12-25-47.90	52	159	33	28		5.1			pIDC
5	12-25-46.10	52	159	3		6.9				KRIPC

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

pIDC - Prototype International Data Center

KRIPC - Regional Informational Processing Center of Kamchatka

Macroseismic manifestations

This earthquake was felt in Petropavlovsk-Kamchatka town with intensity 4-5 MSK. 8 earthquakes with less magnitudes have been registered in this region by Alarm Service since the beginning of 1999 (table 2):

N	Date & Time (GMT) yy-mm-dd hh:mm:sec	Lat. degr.	Long. degr.	Depth km	N of st.	mb/ N	MS/ N	Io calcul.	Region
262	99-03-08 05:57:47	52.17	159.7	33.0	8	5.2/ 3	5.7/ 5	6-6.5	Near the east coast of Kamchatka
261	99-03-08 05:39:57	52.11	159.75	50.0	8	5.4/ 3	6.0/ 5	6	Near the east coast of Kamchatka
258	99-03-07 10:55:18	52.78	159.58	33.0	5		3.9/ 2	3.5	Near the east coast of Kamchatka
221	99-02-27 02:18:13	52.5	158.25	33.0	9		3.4/ 2	2.5-3	To the east of Kamchatka coast
142	99-02-10 02:30:14	51.02	158.56	33.0	4		3.4/ 1	2.5-3	To the east of Kamchatka coast
28	99-01-11 10:48:50	52.45	159.45	33.0	9		5.5/ 4	5.5-6	Near the east coast of Kamchatka
20	99-01-07 08:34:52	51.62	160.06	33.0	3		4.0/ 1	3.5-4	Near the east coast of Kamchatka
19	99-01-07 08:28:59	51.61	159.92	33.0	4		3.9/ 2	3.5	Near the east coast of Kamchatka

Historical records

Historical facts on seismicity of the earthquake's region This earthquake has happened in Avachinsky gulf, where strong earthquakes with magnitudes more than 7 and intensities in epicenter Io up to 10-11 MSK took place in the previous years. The strongest of them were accompanied with occurrence of tsunami waves. They are: May 17 1841 with M=8.4 Io=10-11 MSK; June 25 1904 with M=7.7, Io=10 MSK; February 3 1923 with M=8.5 Io=11 MSK; November 4 1952 with M=8.5 Io=11 MSK. The locations of epicenters of this region earthquakes with M>6.5 as well as the location of the main strike of this event on March 8 1999 is shown in figure 2:

Figure 3

Focal mechanism and seismic moment of the earthquake

Focal mechanism of the earthquake 08.03.1999 has been calculated in CEME GS RAS by the first signs of P-waves arrival at 46 stations, which are located in the interval of epicentral distances 1.2 - 85.2 degrees with enough uniform distribution between azimuths from 21 to 360 degrees. Locations of nodal planes in projection of the lower hemisphere are shown in figure 3. Parameters of the best solution as well as parameters of focal mechanism have been calculated by CMT method in Harvard (USA) and are presented in table 3. As one can see, the solutions obtained by different methods are very close to each other. Focal mechanism represents the thrust. Both nodal planes are spread to the north-east in the direction which coincides with the direction of Kurilo-Kamchatka bow. One plane lays almost horizontally and overthrusting component prevails in motion over it, while the over one has a steep fall and thrust component prevails here in motion over it. Shrink and expanding axes are directed in cross of Kurilo-Kamchatka bow spread direction, that is very specific for the earthquakes of this zone [2]. Seismic moment Мо of the earthquake is determined from spectra of Р-waves, registered by digital equipment IRIS on four seismic stations: Arti (ARU), Obninsk (OBN), Kislovodsk (KIV) and Talaya (TLY), which are located at distances 34-70 degrees. Average value of Mo made 2.8 E 19 n*m. Momentary magnitude Mw has been determined from Kanamori formula [3], Mw=6.9.

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
64	287	5	27	26	119	220	20	104	25	71	85	IPC GS RAS
64	301	1	29	26	119	208	19	88	30	71	91	HARVARD

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

HARVARD - Harvard Geophysical Center (USA)

Figure 4

Literature

1. New Catalogue of strong earthquakes on a territory of USSR from most ancient times till 1975. M. "Science" 1977. 2. Balakina L.M., Zaharova A.I., Moskvina A.G., Chepkunas L.S. Natural relations of earthquake focal mechanisms with a geological structure of area // Physics of the Earth. 1996. N3. pp. 33-52. 3. Hanks Tc and Kanamori J. A moment magnitude scale. //Jornal Geophys. Res. 1979. V 84, p. 2348-2350.