Ground Motion Sensing Using a Triangular Laser*

Seismologists have known for decades that seismic waves can create rotational ground motion. There are documented cases in Japan where tombstones have been rotated during strong earthquakes. The effect of ground rotation on buildings, bridges, overpasses, hydroelectric dams, pipelines, and levee systems has been hard to determine because of the difficulties in measuring ground rotation. By capitalizing on the extreme sensitivity of large ring lasers to rotation, high resolution ground rotation measurements are now possible. This presentation will include a discussion of the ring laser's operation and the ground rotation results.