I finished up Plate Tectonics & Plumes, reviewing plate boundary characteristics in topography (using google Earth) and showing plate reconstructions for the globe and for North America. I then talked about plumes and hot spots, which is another mode of heat transport from the interior.
No in-class exercise today, but I distributed a homework assignment.
I finished up plate tectonics except for showing some historical plate configurations, which I will do next class. Students completed an in-class exercise related to sketching the main earthquake location patterns on global maps. A key pedagogical goal was to remind students of the importance of drafts in the development of anything, not just writing.
We finished our discussion of Earth’s interior and moved on to plate tectonics. Students completed an in-class exercise related to testing the idea of sea-floor spreading.
We discussed patterns associated with earthquake locations (the global map of seismicity and the depth of earthquakes) and the Gutenberg-Richter pattern associated with earthquake size. The development of quantitative, instrumental measures of earthquake size (e.g. magnitude) led to the analysis of size-related patterns in earthquake occurrence. One important pattern is the Gutenberg-Richter Relation, which describes the pattern observed in earthquake size. If we let NC represent the number of earthquakes occurring in a region that have magnitudes larger than M, then
\(log_{10}(N_C) = a \, – \, b\, M\)
Fortunately, large earthquakes are less frequent than small earthquakes. As a rule of thumb, for each magnitude unit increase, there are 10 times fewer earthquakes during a specified time interval. So, for example, there are 10 times as many earthquakes greater than or equal to magnitude 5 than there are greater than or equal to magnitude 6.