Flash Mob Science: from Landmarks to Love Hz

There is a little seismologist in everyone. One secret to unlocking a student's science potential at the undergraduate level is to offer laboratory exercises that leverage the inspiration, teamspirit, and creativity already present in the current generation of incoming college students. In this lab exercise we do that by using smartphones to cause a bit of scientific mischief. In the Flash Mob Science seismology experiments described here, several groups of 5-15 students download a mobile app that can record time-series data from their phones using the phone's vibrational sensors. This allows each device to record acceleration in the X, Y, and Z directions. We conduct quantitative experiments using student-created linear seismic arrays and deploy these arrays at prominent San Diego, California, landmarks that are known to vibrate in response to relatively small forces. These include the Spruce Street suspension footbridge in Hillcrest and the top floor of a parking garage at Southwestern College's Higher Education Center. Our research team of students tested how these landmarks responded to different energy sources (people jumping, rocks dropping, and rubber mallet impacts). To model strike-slip fault motion, we also used a washing machine drip pan loaded with 150 pounds of sand that we attached to a car bumper using 4 x 48 inch bungee cords. For the experiment, the instructor drove forward at speeds of similar to 5 mph, and the students recorded the "strike-slip" motions. Students studied individual event recordings and the collective suite of data presented as record sections. Concepts such as wavespeeds, wave types, noise, moveout, and reverberations were all discussed. These data exhibit several distinct sets of waves with different frequency characteristics that the students analyze. We found that when students record the data they study, they become more engaged in analyzing the results and postulating what the data impart.