When installed in multi-story buildings, the new sensors directly measure interstory drift, helping to determine whether the structure is safe after an earthquake. Scientists have developed a low-cost, laser-based sensor that can monitor and quickly assess earthquake damage to buildings. Here's how to use a laser sensor to assess earthquake damage:

Spectral confocal sensors are designed to be installed in multi-story buildings in earthquake-prone areas and can determine if floors in buildings are displaced relative to each other. The sensor's inventors say the device can speed up the assessment of the condition of critical buildings after a disaster.

A seismic sensor system developed at a national laboratory shines a laser from the ceiling onto a detector on the floor to measure drift between layers.

During an earthquake, horizontal ground motion can shift the individual floors of a multi-story building sideways relative to each other. This is what engineers call "interlayer drift." Assessing this drift is key to ensuring that buildings are safe to use after an earthquake and identifying needed structural repair work.

But until now, methods of assessing building conditions have been expensive and time-consuming. Traditional methods use accelerometers, installed at key points around a building, to determine the force exerted on the structure during an earthquake and then calculate the extent of the drift. This approach is hampered by sensor frequency limitations and is sometimes unsuccessful in the case of permanent structural damage. Moreover, accelerometers are expensive to implement on a broad basis.

Their device, called a discrete diode position sensor (DDPS), shines a laser light from the ceiling of a room onto a sensor pad on the floor. The autonomous detector contains a series of inexpensive photosensitive diodes that, by measuring the displacement of the laser beam, can determine the extent and direction of the ceiling's drift relative to the floor after an earthquake. From this, engineers can determine the impact of earthquakes on the integrity of buildings.