ShakeMovie Animation: 1989 M6.9 Loma Prieta Earthquake

The 1989 Loma Prieta earthquake, measuring magnitude 6.9, was the strongest to hit the San Francisco Bay Area since the Great San Francisco earthquake of 1906. Although it provided extensive data on ground shaking, the available observations don’t fully capture all the quake's important features. 

To improve our understanding, the ShakeMovie animation uses advanced computer models to show how seismic waves were generated as the fault broke and how they traveled through the Bay Area’s complex geology. 

As the animation shows, the rupture started at the fault's center and spread both northwest and southeast. This leads to the phenomena of "rupture directivity," where shaking is stronger in the direction the rupture moves, leading to enhanced ground motions off the ends of the fault. The animation also shows how waves are channeled into the sedimentary rocks in the Santa Clara and Livermore Valleys, slowing down and increasing in intensity and shaking duration as they do.