Investigations of Thirty-Three Loma Prieta Earthquake Strong Motion Recording Sites

The advance of earthquake engineering in general, and strong motion seismology in particular, depends on data—observations and measurements of earthquake response. These data will help in formulating, calibrating and verifying existing and future analytical procedures. Over the past 60 years, and particularly in the last two decades, an unheralded group persisted in installing and maintaining strong motion instruments, just waiting for the moment when useful data would be recorded. For instruments in the San Francisco Bay area, that moment came in 1989 with the Loma Prieta earthquake of October 17.

Now we have a wealth of strong motion recordings, but we do not know much about the sites where the instruments were installed and how these site conditions may have effected the recordings. In the desire for data, instruments were installed without determining the details of their supporting foundation materials. This was prudent: the number of instruments installed could thereby be substantially increased whereas site information could be collected after the earthquake. Collection of such subsurface site information was the goal of this project.