Information message about sensitive earthquake in the northern part of Honshu Island, Japan, July 23, 2008 |
| The sensitive earthquake with М=6.8 has happened on July 23, 2008 at 3:26 pm. GMT (19:26 Moscow time) in the northern part of Honshu Island, Japan. |
| 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 24 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). |
| Preliminary processing has been done with data from 33 stations, accurate processing - with data 55 stations. |
| Fig. 1 presents fragments of records obtained from digital stations Erimo (∆ 2.5º), Matsushiro (∆ 4.2º), Yuzhno-Kurilsk (∆ 5.3º), Vladivostok (∆ 7.9º), Petropavlovsk (∆ 17.6º), Hailar (∆ 18.1º). Fig. 2 presents fragments of records obtained from digital stations Borovoe (∆ 48.8º), Ala Archa (∆ 49.2º), Arti (∆ 54.3º), Tennant Creek (∆ 59.9º), Obninsk (∆ 65.9º), Kislovodsk (∆ 69.1º).
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Figure 1
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Figure 2
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|
| 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 |
15-26-18.8 |
39.89 |
141.5 |
110 |
55 |
| 6.8/30 | 6-6.5 | 116 | IPC GS RAS (Accurate) | | 2 |
15-26-15.6 |
39.81 |
141.41 |
80 |
33 |
| 6.8/13 | 6-6.5 | 116 | IPC GS RAS (Preliminary) | | 3 |
15-26-19.2 |
39.83 |
141.52 |
112 |
439 |
6.8Mw | | | 33 | CSEM | | 4 |
15-26-20.2 |
39.81 |
141.47 |
111 |
296 |
6.8Mw | 6.7/236 | | 22 | NEIC (Accurate) | | 5 |
15-26-20.5 |
39.79 |
141.43 |
112 |
264 |
6.8Mw | 6.7/237 | | | NEIC (Preliminary) | |
| 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 borrowed from geological Service USA NEIC depicts epicenter of this earthquake, which was located in the northern part of Honshu Island, Japan, in the mountainous area of Ivate province at the depth of 110 km, in 30 km to the east-north-east from Morioka, in 485 km to the north-north-east from Tokyo. |
Figure 3 |
|
| Macroseismic manifestations |
| At least 130 people were affected with this earthquake, police reported about 15 persons in bad condition. Residents of five Japanese prefectures were influenced. The shock was felt even in Tokyo capital, which is located at 485 km to the south-south-west from epicenter. The motion of speed trains was fully stopped on Honshu Island and motor vehicle highways closed too. More then 10000 families were left without electricity. Heat power plant was shutdown in the alert mode in Aomori Prefecture, however all local nuclear power plants were operated in normal mode. Land slides were notices in numerous places and a few fires were registered. Potential damage of underground gas pipe lines is possible.
This earthquake was felt on Kuril Islands. In Malokurilsk it was felt with intensity 4 MSK, in Yuzhno-Kurilsk located at 585 km to the north-east from epicenter – with intensity 3 MSK (fig. 4).
|
Figure 4 |
|
| Historical records |
| This earthquake has happened at 100 km from epicenter of the strong earthquake on June 13, 2008 with magnitude М=7.2 . GS RAS registered more than 40 earthquakes in this region for the period since June 13 till July 23, 2008. |
| Focal mechanism and seismic moment of the earthquake |
| Focal mechanism solutions of the earthquake 23.07.2008 have been calculated with TMC method in NEIC USA, USGS and Harvard Center USA, HRVD (Global CMT Catalog), they are presented in table 2 and shown on fig. 5, 6. These solutions are very similar.
The earthquake has happened under prevailing action of expansion forces oriented to the west. Nodal plane NP1 has along meridian direction of propagation, nodal plane NP2 – north-north–east direction. The type of motion along both planes – fault with drift components (right side along NP1 and left side along NP2).
The value of seismic moment Мо obtained in GS RAS with Р-wave spectra at three stations: «Arti» – delta 54.3 degrees, "Obninsk" – delta 65.9 degrees, "Kislovodsk" – delta 69.1 degrees, made Мо=3.5* 10** 19 n*m, the value of moment magnitude calculated with Kanamori formula made Mw = 7.0;
The value of seismic moment Мо of the earthquake 23.07.2008 in accordance with USGS made 1.9* 10** 19 n*m, the value of moment magnitude Mw = 6.8; in accordance with HRVD Мо=1.79* 10** 19 n*m, Mw = 6.8.
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| 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 |
| 27 | 271 | 62 | 81 |
4 | 179 | 178 | 73 | -93 | 12 |
18 | -75 | NEIC | | 27 | 274 | 63 | 82 |
5 | 181 | 180 | 72 | -95 | 16 |
19 | -75 | HARVARD | |
| NEIC - National Earthquakes Information Center of US Geological Service |
| HARVARD - Harvard Geophysical Center (USA) |
Figure 5 | 
Figure 6 |
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