Seismic velocities and geologic logs from borehole measurements at seven strong-motion stations that recorded the 1989 Loma Prieta earthquake

Abstract

Drill sites in this study were chosen in order to provide detailed geologic, geophysical and geotechnical data at several "deep soil" sites and at two rock-soil site pairs, namely Yerba Buena Island (rock)-Treasure Island ("soft soil") and Gilroy #1 (rock)-Gilroy #2 ("stiff soil"). Gilroy #1 has been previouly investigated At each site a pilot hole approximately 5 inches in diameter was drilled for sampling purposes using rotary wash drilling with bentonite mud. At most sites this pilot hole penetrated about 15 meters into bedrock. At Gilroy #2 (USGS) and at Alameda Naval Air Station drilling was stopped about 1 to 2 meters into rock. At San Francisco International Airport, drilling was stopped 5 meters into rock because the bit twisted off.