A simple visualization of the earthquakes in Japan

Because my brother and sister-in-law live in Sendai, Japan (and they're okay!), I've been a bit more focused on this recent disaster than I would be otherwise. Aside from the enormous first quake, there have been an amazing number of aftershocks, many of them quite large. To help myself visualize this, I created a graph (above; click for a larger version) that illustrates the magnitude of these earthquakes as a function of time, starting from the really big quake Friday afternoon until early-morning Sunday (Japan Standard Time). The y-axis is the moment-magnitude scale (M_W), which is apparently the measure of choice among seismologists for measuring the intensity of earthquakes. The x-axis is time, with hourly increments. Each earthquake is a dot at a particular time and magnitude. The red line is at M_W = 6.5, which the USGS uses as its cutoff for "significant" earthquakes. There are 178 earthquakes (!) represented in the graph over about 38 hours. I also added a trend-line (a 6th order polynomial; a sextic function) to help visualize the change in intensity over time.

The data are from the USGS website.

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