Japan Seismicity

Magnitude vs. Time

Location vs. Depth (3D)

This image illustrates earthquakes leading up to the Magnitude 9.1 earthquake that occurred in Japan in April, 2011 causing the tsunami. Most of the quakes were closer to Magnitude 7, but the large downward spike, trending west, shows the mean depth related to magnitnitude and of the subducting plate beneath Japan.
This image shows Earthquakes as a function of depth. The shallow quakes trend sounth and east;deeper quakes trend west and north.

Plots with half degree steps
Plots with one degree steps
Plots with two degree steps

Text files of MATLAB Script and Scaled Image Function

Discussion: Japan is part of an island arc chain above a convergent boundary. As demonstrated in both the Location vs. Depth plots and the Scaled Image plots, the Pacific plate is being subducted because earthquakes trend deeper towards the west and north. The trend of the subduction zone has roughly a NE-SW orientation.
Japan Seismicity Main Script
Scaled Image Function Script