Seisimic activity in Japan going down

The seismic activity in the area of the magnitude 9 earthquake seems to be going back to normal. The chart shows the daily number of shocks and maximum magnitude in the period of March 9th - March 29th. Only shocks near the faultzone are counted.





Below is a Google Earth map of the area with all events in the period and a shakemap showing the intensity of the mainshock.

The radiation level in Tokyo is now nearly back to normal background level. Realtime measurements can be followed here.

Increased level of radiation in Tokyo

Geigercounts in Tokyo show increased level of radioactive particles. Although the level is still way below the health risk threshold it is significantly higher than normal background radiation level in Tokyo. The diagram show a mean particle count of 24.18 CPM. Normal background radiation for Tokyo lies around 14 CPM,

Background radiation varies a lot around the globe - some places it is as high as 60 CPM. It's not considered dangerous until it reaches approximatly 130 CPM.

The increase is probably due to the change of the change in wind direction from westerly to north-north easterly with rainshowers.

Realtime measurements can be followed here.

Still high number of aftershocks in Japan earthquake

As of 17:00 GMT today there have been 230 aftershocks of magnitude 5+ after Friday's magnitude 9.0 earthquake.

While everybody seem to be focused on the effects of Friday's quake and tsunami, particularly the Fukushima powerplant, I'm more concerned about another event that happend this afternoon.

The yellow arrow points to a magnitude 6.2 quake. The reason that I'm focusing on this is that it is not part of the same fault as Friday's events. This quake is situated near the famous Mt. Fuji volcano just at the 3 plate intersection of the Okhotsk plate, the Philippino Sea plate and the Eurasian plate. 

This area has for a long time been considered the most dangerous area for a new 8+ magnitude earthquake with a possible eruption of Mt. Fuji. Such a scenario may have devastating effects on the world's most populous metropolitan area.

The image below shows the episenter position in Google Earth overlayed by a colored shakemap showing the intensity of the quake.The lines show the bounderies of the three plates.

Today's event may be a foreshock of the major event (Tokai earthquake) Japan has been fearing and preparing for ever since the 1923 Great Kantō earthquake which put Tokyo in ruins.

High seismic activity after Japan earthquake

The seismic activity after Friday's giant earthquake in Japan is still very high. Hundreds of aftershocks has been recorded after the mainshock which is now upgraded to magnitude 9.0. This means that the earthquake is the 4th largest ever recorded.

The picture shows earthquakes of magnitude 4.5 or larger as of 11:00 GMT today, adding up to a count of 227!

While media is mainly focusing on the problems at the Fukushima nuclear powerplant I'm more concerned about the seismic situation. There is no sign of reduced seismic activity. The possibility of an aftershock of magnitude 7+ is still high. This may trigger yet another tsunami with devastating effect.

A computer generated animation of the tsunami triggered by the mainshock can be viewed here.

Great earthquake followed by tsunami near eastern coast of Japan

A giant earthquake hit the east coast of the island of Honshu, Japan at 05:46 GMT this morning.

The image is a snapshot from my seismic database as of 11:00 GMT. It shows high seismic activity off the eastern coast. Current estimates indicate a magnitude of 8.8 which is one of the biggest earthquakes ever measured. The mainshock triggered a tsunami with waves varying from 2-15m as it hit the coastline some 30 minutes after the main.

More details can be found here.