SeisMac is a freeware application that uses your MacBook or MacBook Pro’s Sudden Motion Sensor to turn it into a seismograph.

The resizable, real-time scrolling display shows an enormous amount of acceleration information. Place your laptop on a table and see the seismic waves from tapping your toe on the floor. Lay your laptop on your chest and see your heartbeat. And of course, if there is a real earthquake, SeisMac will be displaying full seismic information while you drop, cover and hold-on.

When running on the MacBook or MacBook Pro, SeisMac has a range of plus or minus two gravities of acceleration, displaying 256 values per gravity, sampled two hundred times per second for each axis. SeisMac is also compatible with older Sudden Motion Sensor-equipped iBooks and PowerBooks.

You can download it here.