Live Seismic Data Tool

PBS Newshour has offered up this fancy tool to keep tabs on all of the seismic activity occurring around Japan.

I grabbed the following screenshot yesterday with the intention of posting about this then, but got distracted by shiny things and wandered off.

You'll likely notice the largest of the orange circles a little right of center on the map.  That was the epicenter of yesterday's 8.9/9.0 earthquake.  You'll also likely notice the relatively concentrated group of yellow circles near the mainshock's epicenter.  Those are the foreshocks -- smaller seismic events preceding a larger earthquake.  Most large scale earthquakes -- those 7.0 magnitude and above -- tend to have foreshocks events associated with them.  However, foreshock activity is not always guaranteed to be associated with a large scale earthquake.  Foreshock activity also can occur within a rather wide time-frame before the mainshock occurs.  Foreshocks can occur mere minutes, days, months or years before a mainshock.  Also, it is difficult to classify a foreshock event from a stand earthquake until after a mainshock event occurs and correlation can be the events established.  As such, determining whether any particular seismic action is a foreshock for a larger earthquake in the future is not the most exact science at present.