This research is to analyze 16 well-recorded aftershocks of the October 17, 1989 Loma Prieta earthquake recorded on a variety of site conditions in the East Bay area using the new NSF/IRIS PASSCAL seismic instruments. Preliminary analysis of these data shows clear amplification on mud with respect to both alluvium and rock sites. Further analysis is necessary to quantify rigorously the details of the site response, including a quantification of uncertainties. We will investigate ground motions on sediment sites over the entire available frequency band, roughly 1 to 40 Hz. Converted S-to-P phases may be useful for constraining the depth of the sediment layers, a quantity that is constrained in some places by geotechnical data but which is known to vary considerably over scales of 100 meters. This research is a component of the National Earthquake Hazard Reduction Program.
