It appears that before the large earthquake that did happen today (11th March 2011) there was a sequence of a pre-earthquakes. The pre-earthquake to the large Mw8.9 earthquake was a Mw7.2 (EMSC data) that took place on the 9th March 2011 at 02:45 UTC. This pre-earthquake was followed by about dozen or so aftershocks, the largest one being Mb6.2 (EMSC data).
The problem with this type of pre-earthquakes is that you cannot know that they are pre-earthquakes until after the large earthquake takes place. Because of that fact, it is only now known that the Mw7.2 was a pre-earthquake to the Mw8.9 earthquake that did hit Japan today (11th March 2011).
Please see BBC News or CNN for more news about this earthquake.
For webicorders that show the earthquake can be found here. USGS webicorders can be found here.
At 05:46 UTC (14:46 local time) there was a Mw8.9 (or up to Mw9.1, it is hard to terminate the exact size of this large earthquakes right away) earthquake in Japan. The depth of this earthquake was registered 24 km depth. But that is the reason why this earthquake did create this big tsunami. According to news there has been great damage following this earthquake. Loss of human lives following this earthquakes is also feared. But already there have been found bodies of 300 people that died following this earthquake. After the earthquake a huge whirlpool was created according to BBC News, a video of it can be seen here.
The rupture zone is estimated to be about 500 km (EMSC). But that number might change on a later date. A lot of aftershocks have followed the main earthquake. The largest aftershock did reach Mw7.0 in size so far. But there have also been a lot of earthquakes that have magnitude Mb6.0 – Mb6.9. Many more aftershocks of size Mb5.0 – Mb5.9 have also happened. I have no information about smaller aftershocks. But I am going assume that the number of earthquakes in smaller range is in the number tens of thousands.
This earthquake was recored on all my geophones. Even the one that I have here in Denmark on the second floor where I live.
Above: The Mw8.9 earthquake in Japan on Heklubyggð (Iceland) geophone. This picture is under CC licence.
Above: The Mw8.9 earthquake in Japan on Hvammstangi (Iceland) geophone. This picture is under CC licence.
Above: The Mw8.9 earthquake in Japan on Sønderborg (Denmark) geophone. This picture is under CC licence.
I am going to post more information about this earthquake when I have them. I am also going to post more information about the aftershocks later on.
Please check all major news networks for news about this earthquake.