Watch U.S. earthquakes unfold, just seconds after they occur. QuakeTracker displays data from the United States Geological Survey on an interactive map, using pulsing yellow circles to indicate a quake's magnitude. Tilt the map using a two-finger swipe to see the quake's depth. Zoom in to see more detail. QuakeTracker has two modes. The first is Latest U.S. Seismic Activity. The app downloads data from the previous seven days, then displays any quake measuring 3.25 or greater in a time-lapse visualization, showing the magnitude and depth as each quake hits. The second mode is Top Ten Quakes, which displays the biggest seismic events in the lower 48 states since 1860. In addition to the graphical display, both modes list the time, date, location, magnitude, and depth of the quake. QuakeTracker originally appeared in an iPad-optimized issue of Popular Mechanics. Check out Popular Mechanics magazine in the App Store, or visit us at popularmechanics.com.