MONITORING AND FORECAST

JAPAN,  Мs≥7.8

Seismic situation in Tokyo area after earthquake from 13 May 2008 on the north of Honshu  /15 June 2008/.

Fig.1a. Japan. Controlled region of the forecast of earthquakes from M≥7.8. After two earthquake-indicators (on May 7, M6.7, and on July 13, M6.9, 2008) seismic situation in Tokyo area somewhat changed. The source of the expected strong earthquake from the zone A moved into the side of ocean to the zone B. From July 25 to August 25, 2008 in the zone C it is expected catastrophic earthquake from М=8.3.

Situation in the system.

At present, on June 15, 2008, after earthquake June 13, 2008 from M=6.9 on the north of Honshu ☼ seismic situation in the system somewhat changed. Strong earthquake from Ms=8.3 by the focal depth to 25 km is expected in Tokyo area in the zone C (see Fig.1a,b) from July 25 to August 25, 2008.  

Before earthquake 13.06.2008 track approached a zone of the instability of the earthquake of 1923 Kanto (zone A) in central Japan. In the previous communications dated May 8 and June 5 we predicted earthquake in the zone A (Fig.1), with relative seismic calm before the forecast earthquake. After earthquake 13.06.2008 track jumped upward and actually it left the zone of the instability of the earthquake of 1923 Kanto, even taking into account her uncertainty (see Tab.1). In Tab.1 is given the interval of the values of cumulative energy of earthquake 1923 Kanto (K=16.726-16.742) taking into account the uncertainty of catalog. Now track has coordinates K=16.756 and W=18.330 (see Tab.1). The coordinates of the nearest point of the instability of the earthquake of 1953 Boso Oki are equal K=16.764 and W=18.351. Scarcity on the energy is equal to energy of earthquake from M=6.4. As we forecast in the communication dated February 21, 2008, in case of the seismic activity the forecast epicenter can migrate to the side of ocean to the zone B.

In Tokyo area into 1703 occurred the catastrophic earthquake Genroku* (see Fig.3) with the magnitude M=8.3. In Table 1, knowing only magnitude and position of this earthquake, we estimated the possible position of the unstable region of this earthquake on the diagrams. It is located between regions 1923 and 1953.

The analysis of the prevailing seismic situation and our experience make it possible to conclude that the preparation of catastrophic earthquake now occurs on the scenario of historical earthquake to 1703 Genroku. The magnitude of the expected earthquake in all forecasts we evaluated 8.3, i.e., more than the magnitude of 8.0 earthquakes of 1923 Kanto. Now the epicenter of the expected catastrophic earthquake moved into the side of ocean on 50 km. In the region of seismic source of the 1703 Genroku will be dangerously from July 25 to August 25, 2008. As it was predicted in the communication dated June 5, now already the probability of tsunami on the southeast of Boso peninsula from the expected earthquake grows.

Now the probability of strong earthquake from M>7.8 in the system it is equal to P=38% (on entropy P_W=59%, and on cumulative energy P_K=64%) (see Fig.2 and Tab.1).   

Fig.1b. Sagami Trough. After earthquake-indicator (on July 13, M6.9, 2008) the situation in Tokyo area somewhat changed. The epicenter of the expected strong earthquake from the zone A (1923, Kanto) moved into the side of ocean on 50 km (zone C). From July 25 to August 25, 2008 here is expected catastrophic earthquake from M8.3. Supposedly, the source of the expected earthquake can coincide with the source of earthquake 1703 Genroku*, which on the magnitude was stronger than the earthquake of 1923 Kanto.

Fig.2. Dynamics of increase the probability of strong earthquake in SS Japan on June 15, 2008. After June 13, 2008 earthquake the probability of strong earthquake grew. Pk=64% (green region), Pw=59% (blue), P=38% (red).

Ross S. Stein, Shinji Toda, Tom Parsons, Elliot Grunewald. A new probabilistic seismic hazard assessment for greater Tokyo. Phil. Trans. R. Soc. Am., 29, 5, 2006, pp. 1–25.

Fig.3. Arrangement of sources and the observed intensity of seismic shakes with the earthquakes to 1703 Genroku and 1923 Kanto.

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