I've spent about 30 minutes so far going through the materials, testing the various features of the site, and thoroughly enjoying the experience. The graphical presentations clearly illustrate the procedures being explored, and the depth and accuracy of the material is impressive. For demonstrating the methods and tools of measurement for seismology, this is by far superior to any text I've reviewed. The hands-on use of the interactive graphics should greatly add to its potential effectiveness as a teaching and learning tool.
While some of the graphics take some time to load, a helper window typically opens up to explain the next component of the module. Correct responses are required at several points in order to continue, but using the demonstration button, an instructor can quickly review the site.