Scientists have simulated a moderate- to large-size earthquake in the laboratory. No, there's no shaking going on. Instead, researchers have developed a disc-brake-like device that can simulate motion along a fault line. The industrial-strength apparatus holds two disks of stone (the dotted line marks the right side of the interface between the two disks), each representing one side of a small patch of a fault zone. Sensors in the device (connected to the wires at center left) monitor the temperature of the stone disks as well as their acceleration and deceleration as they grind past each other. The energy needed to drive the faux quakes is stored in a 225-kilogram flywheel; once the flywheel is spinning at the appropriate speed for the test at hand-typically somewhere between 20 revolutions and 300 revolutions per minute-its energy is transferred to one of the stone disks, which then scrubs against the other disk with great pressure and at high speed until frictional forces bring the rotating disk to a halt. The device can simulate quakes measuring between magnitude 4 and 8, the researchers report online today in Science. Such tests may help scientists better identify how the energy released during an earthquake is distributed. At present, it's not well understood what proportion of the energy ends up in seismic waves, what portion is expended fracturing rocks in Earth's crust, and what fraction is spent heating the rocks along the fault zone due to friction.