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Information message about destructive earthquake at the Western shore of Honshu Island on October 23, 2004.

On October 23, 2004 the strong destructive earthquake has happened near the Western shore of Honshu Island, Japan, in Niigata prefecture. The earthquake has occurred at 08:55 GMT with magnitude 7.0. Last time this kind of the earthquake in Niigata prefecture has been registered in 1964, it had magnitude 7.5 and the succeeding shocks have killed 26 people. This natural disaster is the most catastrophic after the earthquake of 1995, which destroyed Kobe harbor and killed more than 6400 people.

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

Preliminary processing has been done with data from 24 stations, accurate processing - with data 41 stations.

Fig. 1 presents fragments of records obtained from digital stations South-Sahalinsk (delta 10,1 degrees), Petropavlovsk-Kamchatka (delts 21,0 degrees), Magadan (delta 23,6 degrees), Yakutsk (delta 25,4 degrees), Tiksi (delta 34,9 degrees), Kurchatov (delta 44.2 degrees). Fig. 2 presents fragments of records obtained from digital stations Ala-Archa (delta 48 degrees), Borovoe (delta 49 degrees), Lovozero (delta 61 degrees), Obninsk (delta 67 degrees), Kislovodsk (delta 69 degrees), Garni (delta 70 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	08-55-58.20	37.25	138.85	15	41	7.00/16	6.50/14	9-9.5	112	IPC GS RAS (Accurate)
2	08-55-58.10	37.24	138.9	15	24	7.00/11	6.3/9	9-9.5	112	IPC GS RAS (Preliminary)
3	08-55-59.20	37.38	138.85	10	373	6.8Mw	5.6-6.7		74	CSEM
4	08-56-01.07	37.2	138.81	15.8	232	6.3/109	6.5/122		65	NEIC (Accurate)
5	08-56-01.00	37.2	138.81	16	231	6.2/30	6.5/122		65	NEIC (Preliminary)
6	08-56-07.18	37.38	138.63	30	53		6.3		296	ORFEUS

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

ORFEUS - Observatories and Research Facilities for EUropean Seismology

Epicenter

This earthquake has happened in rather inactive seismic region of Japan (fig.3) at the Western shore of the largest Japanese island - Honshu, the earthquakes with magnitudes 7 and more are unknown here since 1900 (fig.4). Maps of seismic activity, which presented here have been shared from the site of National Earthquakes Information Center of the US Geological Service. http://neic.usgs.gov/neis/bulletin/neic_pyal_h.html.

Figure 3

Figure 4

Aftershock

This earthquake has been accompanied with numerous aftershocks. 290 significant strikes have been registered in the period October 23 - 24, 2004 in accordance with Japanese Meteorological Agency (JMA). Parameters of 15 aftershocks have been determined from data obtained by AS IPC GS RAS.

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
20041816	2004-10-23 09:03:10.0	37.25	138.79	10	22	-	6.2/ 9	8-8.5	Near west coast of Honshu, Japan
20041817	2004-10-23 09:11:54.0	37.2	138.67	15	21	-	5.8/ 9	6.5-7	Near west coast of Honshu, Japan
20041818	2004-10-23 09:34:03.0	37.32	138.82	15	21	6.5/ 9	6.0/ 9	8.5-9	Near west coast of Honshu, Japan
20041819	2004-10-23 09:57:23.0	37.16	138.73	10	17	-	5.0/ 8	5-5.5	Near west coast of Honshu, Japan
20041820	2004-10-23 10:36:44.0	37.22	138.63	15	17	-	5.3/ 7	5.5	Near west coast of Honshu, Japan
20041821	2004-10-23 10:45:54.0	37.23	138.73	15	17	5.3/ 8	5.4/ 6	6.5-7	Near west coast of Honshu, Japan
20041822	2004-10-23 12:44:26.0	37.12	138.85	15	14	4.6/ 6	4.7/ 6	5.5-6	Near west coast of Honshu, Japan
20041823	2004-10-23 14:34:42.0	37.25	138.76	15	15	4.9/ 5	5.1/ 6	6-6.5	Near west coast of Honshu, Japan
20041824	2004-10-24 00:28:01.0	37.14	138.61	15	14	4.3/ 5	4.7/ 6	5-5.5	Near west coast of Honshu, Japan
20041825	2004-10-24 01:05:58.0	37.23	138.38	20	10	3.5/ 5	-	3.5-4	Near west coast of Honshu, Japan
20041826	2004-10-24 05:21:33.0	37.22	138.56	20	15	4.5/ 5	4.9/ 6	5-5.5	Near west coast of Honshu, Japan
20041827	2004-10-24 07:06:29.0	37.24	138.7	15	11	3.7/ 4	4.5/ 5	4-4.5	Near west coast of Honshu, Japan
20041834	2004-10-24 15:28:09.0	37.25	138.63	33	16	4.9/ 6	5.2/ 8	5	Near west coast of Honshu, Japan
20041837	2004-10-24 16:27:52.0	37.12	138.95	33	13	-	4.5/ 6	2-2.5	Near west coast of Honshu, Japan
20041839	2004-10-24 21:04:55.0	37.31	138.79	15	15	5.6/ 8	5.6/ 9	7-7.5	Near west coast of Honshu, Japan

Macroseismic manifestations

Many Russian and International Information Agencies inform about destructive consequences of this earthquake and it’s aftershocks. Here one can find only brief information obtained by October 25 from ITAR TASS and other sources. Initial significant strike residents of Japan have felt in Saturday evening. Since that moment more than 13 strikes with magnitude from 5 to 7 have been registered on the maim Japanese Island Honshu in Niigata prefecture (250 km from Tokyo). Many buildings have been destroyed by these series of the earthquakes. Big ruptures appeared on highways and regular roads. For the first time in history of speed railroad «Sincansen» two trains have been derailed, after that train traffic have been stopped. This earthquake has not influenced the operation of the world’s biggest nuclear power plant located on the shore of Japanese Sea in Kasivadzaki (Niigata prefecture, nearly 30 km from epicenter). Operation there continued in regular mode. Up now 25 people have been killed. 2100 people have been injured. The victims told about falling TV sets, cupboards, refrigerators and destroyed walls and ceilings in houses. Many of them were afraid to return back home and spent the night time under the sky. Nearly 600 houses have been destroyed fully or partially in the zone of natural disaster including 400 administrative buildings. 376 ground slidesо have been registered. Water supply interrupts have been seen everywhere in Niigata. This disaster caused interrupts in electricity supply too. 280 thousands of houses have been left without light. 4 thousand telephone lines have been beaked. Information is available about leaks of natural gas, which caused fires. Total number of registered ebvents of this kind is 12. Here one can see photos obtained from Russian TV channel site http://www.1tv.ru/owa/win/ort6_videopage.img_main?sender=news&p_topic_id=71262&p_img_num=1&counter1_href=287212&counter2_href=id=268366;t=56

Figure 5	Figure 6

Figure 7

Focal mechanism and seismic moment of the earthquake

Focal mechanism solution of the earthquake 23.10.2004 have been calculated by TMC method in NEIC, USA and is presented in table 3 and shown on figure 8. The motion in origin has happened under prevailing compression strengths oriented to the North-West-South-East direction. Both nodal planes Both nodal planes have almost the same spread direction (North-East-South-West) and almost the same falling angles. The type of motion for both planes is - thrust. Average value of seismic moment Мо determined in IPC GS RAS from Р-wave spectra at seismic stations "Obninsk" (delta 67 degrees) and "Kislovodsk" (delta 69 degrees) made 1.3* 10** 19 n*m. The value of moment magnitude from these data is Mw = 6.7. The value of seismic momentМо from NEIC data made 3.8* 10** 18 n*m, the value of moment magnitude - Mw = 6.4.

Table 2

Axes of main strengths

Nodal planes

Center

NP1

NP2

Azm

Stk

Slip

Stk

Slip

216

313

233

105

NEIC

NEIC - National Earthquakes Information Center of US Geological Service

Figure 8